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J O U R N A L O F C H E M I S T R Y Materials Feature Article New directions in tin sulfide materials chemistry Tong Jiang and GeoVrey A. Ozin* Materials Chemistry Research Group, Lash Miller Chemical Laboratories, University of Toronto, Toronto, Ontario, Canada, M5S 3H6 Tin sulfide-based materials can exist in many forms, ranging from discrete molecular species, to 1D chains, 2D dense and porous sheets and 3D open frameworks.The local coordination geometry around a tin center may vary from trigonal pyramidal, to tetrahedral, trigonal bipyramidal and octahedral, and around sulfur from terminal, v-shaped to trigonal pyramidal. The oxidation state may take +2 and+4 for tin and -2, -1, 0 for sulfur. The tin sulfide chemistry is further enriched by the catenation ability of sulfur.In addition, other elements (metal and non-metal) can be incorporated into the tin sulfide structures to yield ternary and quaternary materials. More importantly, using the recent developed ‘soft chemistry’ synthetic approach, various novel porous tin (poly)sulfide materials have emerged that display interesting optical, electrical and adsorption properties. Representative tin sulfide materials will be presented and discussed in this review to demonstrate the development of tin sulfide chemistry in the last three decades.monomeric8 (SnS4)4-, dimeric9,10 (Sn2S6)4- and (Sn2S7)6- 1.0 Introduction species. In (SnS4)4-, regular Td symmetry exists around the Attributed to the versatile coordinating characteristic of tin tin(IV) site, while in (Sn2S6)4- and (Sn2S7)6-, a distorted and sulfur, tin sulfide-based solid state materials exhibit a rich tetrahedral geometry is present.The versatile bonding characstructural chemistry.1 As a main group 14 element on the fifth teristic of tin sulfide-based structures is evident in the two row of the Periodic Table, a tin atom can take a coordination dimeric tin(IV) thiostannate anions (Sn2S6)4- and (Sn2S7)6-. number of 2 to 9, and as a result, the environment around tin Both anions are constructed from two SnS4 tetrahedra, through embraces many geometrical arrangements. The most common corner-sharing in (Sn2S7)6- and edge-sharing in (Sn2S6)4-. ones are trigonal pyramidal for divalent tin, and tetrahedral, The preparation and structure of tetrameric (Sn4S10)4- have trigonal bipyramidal and octahedral for tetravalent tin.2 Sulfur, been reported by Krebs.1b The tetrameric anion consists of a main group 16 element on the third row of the Periodic four corner-sharing SnS4 tetrahedral units with an adamantane Table, displays an equally diverse coordination chemistry as geometry cluster.The stability of these tin(IV) thiostannates in tin.In addition sulfur chemistry is adorned by the catenation aqueous solution is believed to be pH dependent and generally ability of sulfur. The catenation length can be as short as in a lower pH favors higher oligomers or polymers.1b For example, S2 and as long as in a polymeric sulfur chain which may both Na4SnS4 and Na4Sn2S6 can be prepared by dissolving contain more than 200 000 sulfur atoms.3 One may think of freshly precipitated SnS2 in an aqueous solution of Na2S; numerous ways to link tin and sulfur and/or polysulfur together however, the pH for the crystallization of Na4SnS4 is around with diVerent coordination geometries around the tin and 11, while that for Na4Sn2S6 is around 9.sulfur sites. In the past three decades, various synthetic One can imagine that if a terminal sulfur on each tin site in approaches, including solid state reactions,4 hydrothermal or the dimeric (Sn2S7)6- anion coordinates to another (Sn2S7)6- organothermal5 synthesis, and molten salt (flux) methods,6 and this process continues indefinitely, a polymeric tin(IV) have been employed and developed in the search for new tin thiostannate chain would be created.Indeed, this type of tin(IV) sulfide and/or polysulfide-based solid state materials, especially thiostannate, (SnS3)2- polymer chain has been crystallized those with open-framework structures. As a result, many new from a reaction mixture of KOH, H2S and SnS2 in aqueous discrete molecular and 1D chain, 2D sheet and 3D frameworks solution, the single crystal structure of which is shown in have emerged and some of them present interesting optical Fig. 2.11 In (SnS3)2- a monomeric SnS4 building unit shares and electrical properties for device applications.7 It has proven two corners with two neighbouring units. The charge-balancing possible to incorporate other elements into the tin sulfide- and K+ cations and occluded water molecules reside between the polysulfide-based structures, to form ternary or quaternary polymeric (SnS3)2- chains.An extended hydrogen-bonding structures. As tin has stable positive oxidation states of two network is produced through the involvement of terminal and four, mixed-valence tin(II,IV ) structures are also known. In sulfur and occluded water. what follows, a brief summary of each structure type will be Tin sesquisulfide, Sn2S3, is one of the tin sulfide minerals, presented to exemplify the achievements of tin sulfide and and named ottemannite after its discovery by the German polysulfide materials chemistry over the last thirty years, and mineralogist J.Ottemann.12 In the laboratory, acicular crystals to demonstrate the structural diversity of these materials. The of this material can be prepared by heating a stoichiometric large family of organotin sulfide compounds, although importmixture of elemental Sn and S powders at 720 °C in a sealed ant and fascinating in their own right, tend to be molecular, quartz tube.13 Sn2S3 is the best known mixed-valence tin sulfide low melting, volatile and soluble in organic solvents and on compound and has an aesthetic ribbon structure as shown in this basis they are considered distinct from the solid state tin Fig. 3. The tin(IV) sites in the ribbon are octahedrally coordi- sulfides and are therefore excluded from this survey. nated with SnMS distances of 2.459–2.604 A ° . The tin(II) sites on the edge of the ribbon have a typical trigonal pyramidal geometry with two SnMS distances of 2.645 and 2.765 A ° . At 2.0 Tin sulfide molecules and chains least three ‘polytypes’ of Sn2S3, i.e. a-Sn2±xS3, b-Sn2±xS3 and c-Sn2S3, have been identified.Moh has examined the In discrete molecular tin(IV) thiostannate anions, tin centers often display a tetrahedral geometry as shown in Fig. 1 for phase diagram of tin sulfide systems and related minerals, and J. Mater. Chem., 1998, 8(5), 1099–1108 1099Fig. 2 An illustration of the zig-zag chain structure of K 2 SnS 3 ·2H 2 O11 with the K+ and water molecules omitted for clarity Fig. 3 A representation of the ribbon structure of Sn 2 S 3 ,13 the trigonal-pyramidal tin(ii) locating at the edge and the octahedral tin(iv) at the center of the ribbon reported that the non-stoichiometric a-Sn 2±xS 3 and b-Sn 2±xS 3 phases exist above 700 °C, while the c-Sn 2 S 3 phase is stable below 675 °C.12 However, there are incidents for which the Sn 2 S 3 phases do not fall into the right region of Moh’s phase diagram.13 Isostructural PbIISnIVS 3 and SnIIGeIVS 3 have also been synthesized under similar conditions. 3.0 Tin sulfide layers In general, tin sulfides favor a two-dimensional structure. Quite a few layered structure types have been reported, with various combinations of tin and sulfur local coordination geometries.The topology of tin sulfide sheets may feature a close-packing or an open structure which is decorated by regular arrays of Fig. 4 A representation of the layered structure of SnS with one pores with a variety of geometric shapes and sizes circumdistorted SnS6 octahedron highlighted (note that the sixth sulfur apex scribed by the tin and sulfur components.The sheet itself may on the neighboring tin sulfide layer is not shown)15 be flat or undulated. A summary of representative 2D tin sulfide structures is given in Table 1. octahedral geometry. As the octahedra are so distorted the tin 3.1 Tin monosulfide atom is actually displaced toward one of the faces of the octahedra as shown in Fig. 4. This leads to three short SnMS Tin monosulfide, also called herzenbergite, was first reported by the German mineralogist R. Herzenberg.14 Single crystals bonds of ca. 2.7 A° and three long SnMS bonds of almost 3.4 A° . There are two SnS layers in one unit cell and one of the long of this material can be prepared by reacting stoichiometric Sn and S elements over a temperature range of 600–750 °C.14 At distance sulfurs actually resides on the neighboring SnS layer.This weak SnMS interaction binds the two tin sulfide layers room temperature, tin monosulfide adopts the GeS structure. The corrugated tin sulfide double layers are displayed in Fig. 4. together to form a double-layer structure. Tin monosulfide undergoes a complicated thermal expansion from room tem- Each tin atom is coordinated by six sulfurs in a highly distorted Table 1 A summary of representative 2D tin sulfide structure types coordination number chemical character of tin synthetic formula Sn S sulfide layer technique SnS 6 3 dense, undulated high temperature SnS2 6 3 dense, flat CVT Rb2Sn3S7·2H2O 4, 6 2, 3 porous, flat hydrothermal Cs4Sn5S12·2H2O 5, 6 2, 3 porous, flat hydrothermal SnS-1 (Cat2Sn3S7) 5 2, 3 porous, flat hydrothermal SnS-3 (Cat2Sn4S9) 4, 5 2, 3 porous, undulated hydrothermal 1100 J.Mater. Chem., 1998, 8(5), 1099–1108perature to ca. 605 °C at which temperature it transforms to 3.3 Rb2Sn3S7·2H2O the TlI structure type. This solid state phase transition is Single crystals of Rb2Sn3S7·2H2O have been prepared by accompanied by a continuous movement of Sn and S along hydrothermal treatment of SnS2 and Rb2CO3 in a H2S satuthe entire [1 0 0] direction in the unit cell.An intralayer optical rated aqueous solution at 190 °C.22 As displayed in Fig. 6, it Ag phonon softening mechanism has been proposed to explain contains layered thiostannate (Sn3S7)2- anions with octahedral this polymorphic phase transition.Non-stoichiometric Sn1±xS SnS6 and tetrahedral SnS4 units. The (Sn3S7)2- anions are phases have also been reported with a wide variety of unit cell partially constituted by chains of the SnS6-based dense strucdimensions. 12 ture as found in bulk tin(IV) disulfide, (Fig. 5), plus Sn2S6-based open structures. One way to view these (Sn3S7)2- sheets is 3.2 Tin disulfide and polytypism that the original close-packed SnS2 layer is dissected after every two rows of octahedral SnS6 units and then sewed Tin disulfide is probably the first known tin sulfide material, the laboratory synthesis of which can be traced back some together by Sn2S6 chains, Fig. 6, to create an open 2D structure. The tetrahedral tin and double bridge (m-S)2 sulfur linkages (in two hundred years.15 Crystals of SnS2 are typically prepared through the chemical vapor transport technique (CVT) over a green), i.e.the Sn(m-S)2Sn units of the Sn2S6 chains are found to be disordered with an overall occupancy of 0.5 in the single temperature range of 600–800 °C, with I2 as a transport agent.16 Tin disulfide adopts the PbI2 layered structure with a hexag- crystal structure.The disorder of the Sn2S6 chains illustrates the versatile bonding character of tin sulfide-based structures. onal unit cell, in which tin atoms are located in the octahedral sites between two hexagonally close-packed sulfur slabs to One can imagine that the three-coordinated sulfur from the Sn2S6 chains in Fig. 6 are sometimes two-coordinated, due to form a sandwich structure, as shown in Fig. 5. The SnS2 layer can be viewed as composed of all-edge-sharing octahedral the 0.5 partial occupancy of the Sn(m-S)2Sn unit. However, these diVerent coordination environments are happily sharing SnS6 building units with the sulfurs exhibiting three-coordination and local trigonal-pyramidal symmetry. The SnS2 layers one unit cell position. The 8-atom-membered rings shown in Fig. 6 can also randomly assume many diVerent sizes. The are then stacked on top of one other along the crystallographic c-axis and held together by weak van der Waals forces. There rigid structure of SnS2 is now attached to flexible and open Sn2S6 structure units. The physical properties, especially small are many ways to stack these layers together to create various polytypes.More than 70 polytype structures of SnS2 have been molecule adsorption character, of this material, should be very interesting. established through a complicated single crystal structure analysis procedure. All of the polytypes have the same hexagonal close-packed structure within the layer, and therefore an 3.4 Cs4Sn5S12·2H2O identical unit cell parameter a of 3.647 A° ; however, they exhibit When Rb2CO3 was substituted by Cs2CO3 in the above a diVerent parameter c orthogonal to the layer which is an reaction mixture for Rb2Sn3S7·2H2O, a new tin(IV) sulfide integral number of the interlamellar spacing 5.899 A ° .17 Some material, Cs4Sn5S12·2H2O, was crystallized at 130 °C.23 It has polytypes may have a giant unit cell with a very large c a 2D porous layer structure, consisting of octahedral and parameter, as they contain many tin sulfide layers in one unit trigonal bipyramidal tin sites, Fig. 7. The basic building unit cell. For example, the polytype 258 R1 contains as many as in bulk SnS2 can also be found in this structure. In SnS2, three 258 tin sulfide sheets in one unit cell, with a c parameter of all-edge-sharing octahedral SnS6 units create a Sn3S4 broken- 761 A ° !18 It should be mentioned that one crystallite of SnS2 cube building block.Therefore, the layered structure of SnS2 often contains domains of diVerent polytypes, and the struccan be envisioned as being built from these edge-sharing Sn3S4 tural details of one polytype have to be extracted from a broken cubes. In (Sn5S12)4-, two of the primary Sn3S4 broken crystal of mixed phases.Therefore, the determination of an cubes are linked together by sharing one octahedral tin to SnS2 polytype structure has never been a trivial task.19,20 yield double Sn3S4 secondary broken-cube building blocks. Recently, Palosz proposed that the polytypes of SnS2 orig- They are further connected through double bridge Sn(m-S)2Sn inate from the partial occupancy of the tin and sulfur sites in sulfur bonds to create the 20-atom-membered rings found in the SnS2 crystal.21 Through measuring the density of SnS2 the 2D porous layers of (Sn5S12)4-.It is interesting to note polytype crystals, he found that the overall occupancy of tin that a larger pore has been created when the size of the chargeand sulfur in some polytypes can be as low as 80%.He balancing cation is increased from Rb+ to Cs+. The other attributed the diVerent stacking sequences of tin sulfide layers point worth mentioning is that by reducing the reaction to the occupancy deficiency level of the tin sulfide layers. In temperature below 200 °C, the open-layered structures of view of the many stoichiometries of tin and sulfur in stable tin sulfide materials, like SnS, Sn2S3, Sn4 S5 and SnS2, Polasz suggested that it is the versatile bonding nature of tin and sulfur that is responsible for the many stoichiometric, nonstoichiometric and lattice site-deficient structures of tin sulfides, and the occurrence of polytypes.Fig. 6 A representation of the 2D structure of Rb2Sn3S7·2H2O, the Rb+ and water molecules are omitted for clarity.The tetrahedral tin and attached double bridge Sn(m-S)2Sn sulfurs (in green) are disordered Fig. 5 A representation of the dense-packed layered structure of SnS2 16 with a partial occupancy of 0.5.22 J. Mater. Chem., 1998, 8(5), 1099–1108 1101Fig. 9 A representation of the 2D open structure of (Pr4nN)2Sn4S9, the Prn4N+ cations are omitted for clarity.The 32-membered elliptical rings are parallel to the (1 0 1) plane.28 Fig. 7 A representation of the 2D open structure of Cs4Sn5S12·2H2O, while those in SnS-3 display both distorted trigonal-bipyrami- the caesium cations and water are omitted for clarity. The 20- dal and tetrahedral symmetries. The diversity of tin sulfide membered elliptical rings are parallel to the (0 0 1) plane.23 bonding patterns is evident in these materials.Note that the tin thiostannate layer, (Sn3S7)2-, in SnS-1 has an identical Rb2Sn3S7·2H2O and Cs4Sn5S12·2H2O are created, in contrast composition to that of Rb2Sn3S7·2H2O, Fig. 6, although the to the dense layered structure of SnS2, which is crystallized at macroscopic structures of these two materials are completely temperatures above 600 °C.This exemplifies the ‘soft chemistry diVerent. approach’ to new, open framework solid state materials. Various SnS-1 and SnS-3 materials, with diVerent space groups, layer spacings and stacking sequences, have been 3.5 SnS-1 and SnS-3 obtained in the presence of a range of template cations. For example, tert-butylammonium,24 Me3HN+,25 Me4N+,26 The above two open-framework tin(IV) thiostannate materials NH4+/Et4N+,27 Et4N+,27 DABCOH+27 and quinuclidin- are built entirely of inorganic components with alkali metal ium24 have all resulted in the SnS-1 structure; while Prn4N+ cations, Rb+ and Cs+, as counter ions.It has proven feasible and Bun4N+ resulted in SnS-3.28 A comparison of some of the to employ organic cations as charge balancing moieties for the SnS-n materials is given in Tables 2 and 3.It is evident that assembly of new open-framework structures.5a For example, in the assembly of the SnS-n materials, the organic cations 2D porous materials, R-SnS-1 [(Cat+)2Sn3S7] and R-SnS-3 appear to have a particular kind of templating function. The [(Cat+)2Sn4S9], have been prepared in the presence of a large 24-atom rings present in the SnS-1 structure are templated by variety of tetraalkylammonium and amine molecules under smaller cations, while the 32-atom rings present in the SnS-3 hydrothermal reaction conditions, where R represents the structure by larger cations.The interlamellar spacing is about occluded organic cations. The basic building blocks of these 8.5–9 A ° in the SnS-1 structure, and about 14 A ° in the SnS-3 two materials are the same Sn3S4 broken cube as found in structure.The pore size and interlamellar spacing among the Cs4Sn5S12·2H2O, but, with diVerent connectivity. In SnS-1, the various SnS-n families of materials also display certain corre- Sn3S4 broken cubes are joined together by double bridge Sn(mspondence with the size of the template cations as summarized S)2Sn sulfur bonds to form hexagonally shaped 24-atom rings, in Tables 2 and 3.Interestingly, as described above, the Cs+ Fig. 8, and in SnS-3 by double bridge Sn(m-S)2Sn sulfur bonds cation with a radius of 1.81 A ° has templated the open layered as well as tetrahedral SnS4 spacer units to form elliptically structure of Cs4Sn5S12, in which 20-atom rings are present in shaped 32-atom rings, Fig. 9. The tin atoms in SnS-1 materials the tin(IV) sulfide layer with an interlamellar spacing of 7.166 A ° . feature a single kind of distorted trigonal-bipyramidal site, However, in the presence of cyclooctasulfur molecules, Cs- SnS-1 (Cs2Sn3S7·1/2S8) has been synthesized.29 Cs-SnS-1 is isostructural with (DABCOH)2Sn3S7·H2O. The Cs+ cations are located between the tin sulfide gaps to give an interlamellar distance of 8.151 A ° .The 24-atom rings are occupied by cyclooctasulfur rings which cannot be removed without harming the integrity of the tin sulfide framework. It appears that the cyclooctasulfur molecule functions as a co-templating agent with the Cs+ cation, and the Cs+ alone is not large enough to direct the formation of the SnS-1 structure.The cations in the open-framework tin chalcogenides appear to have a chargebalancing, space-filling and structure-directing role, possibly analogous to the templating properties of cations in the synthesis of zeolites and molecular sieves. It is interesting to mention that the remarkable structural diVerences among the R-SnS-1 and R-SnS-3 families of materials indicate that the bonding between tin and sulfur, and thus the constituent [Sn3S7]2- and [Sn4S9]2- tin(IV) sulfide layers, is extremely flexible.As summarized in Tables 2 and 3, Fig. 8 A representation of the 2D open structure of the shape and size of the 24-atom rings in the SnS-1 and the (Me4N)2Sn3S7·H2O, the Me4N+ cations and H2O molecules are omit- 32-atom rings in the SnS-3 structures, as well as the layer ted for clarity.The 24-membered hexagonal rings are parallel to the stacking sequence and interlamellar spacings, can be modified (1 0 1) plane.26 1102 J. Mater. Chem., 1998, 8(5), 1099–1108Table 2 A summary of the dimensions of the 24-atom rings and the interlayer spacing and layer stacking sequences of various SnS-1 materials space pore dimensionsa interlamellar stacking R-SnS-1 material group /A ° ×A ° ×A ° spacing/A ° sequence Cs2Sn3S7·0.5S8 C2/c 10.79×10.79×10.47 8.151 AB (Me4N)2Sn3S7·H2O P21/n 11.69×11.03×9.69 8.511 AA (DABCOH)2Sn3S7·H2O C2/c 10.98×10.98×9.95 8.594 AB (NH4)0.5(Et4N)1.5Sn3S7 P3121 10.94×10.94×10.88 9.011 ABC (Et4N)2Sn3S7 P21/n 11.58×10.84×10.42 8.915 AA aDimensions are defined from sulfur center to sulfur center as illustrated in Fig. 8. Table 3 A comparison of TPA-SnS-3 and TBA-SnS-3 structures brought additional flexibility to the tin sulfide-based layered structures. TPA-SnS-3 TBA-SnS-3 3.6 Tin sulfide–organic composite mesophases formula (Prn4N)2Sn4S9 (Bun4N)2Sn4S9 space group P21/n Pbcn Thermotropic tin(IV) sulfide–organic composite semiconductor pore dimensionsa/A° 20.65×9.32 19.8×11.3 materials have been synthesized recently in the presence of interlamellar dimension/A ° 14.05 14.2 long-chain amine molecules.27,32a The as-synthesized crystalline layer stacking sequence AA AB form of Meso-SnS-1 is established to have a structure that is aDimensions defined as sulfur center to sulfur center as illustrated based upon well registered yet poorly ordered porous tin(IV) in Fig. 9. sulfide layers with a layer spacing of 50 A ° , between which are sandwiched well organized hexadecylamine bilayers, Fig. 10. considerably in response to the change of size and shape of This material displays interesting thermal transitions upon the organic templates. This phenomenon may explain the heating. On warming this material to around 45 °C the hexaderelatively smaller structural variety so far observed for micro- cylamine bilayer first becomes disordered while the porous porous tin(IV) sulfide-based materials in comparison with the tin(IV) sulfide sheets remain registered.This is followed, around myriad of structure types for the microporous oxide-based 85 °C, by a transition where both the alkylamine bilayer and relatives like zeolites and aluminophosphates.In order to the porous tin(IV) sulfide lamellae become liquid crystalline at accommodate the size/shape changes of templates, the micro- which point the intralayer but not the interlayer registry is porous layers of the tin(IV) sulfide materials undergo elastic lost. The liquid crystal organic–inorganic composite phase has deformation to alter the void spaces within and between the either a nematic or a smectic C structure.Electrically, the layers, rather than forming a completely new microporous room temperature ordered phase of Meso-SnS-1 has a conducstructure type. This is to be contrasted with 3D microporous tivity of 5.3×10-8 V-1 cm-1 which increases by more than structures, in which there exists a greater restriction on the 1000 times on transforming to the LC phase where it behaves size and shape of the void space, either a cavity or channel, as a semiconducting metallogen. The conductivity of Mesowhich can barely be deformed without an accompanying SnS-1 cycles reversibly with temperature and displays disconticomplete reorganization of the 3D framework.However, it nuities that are coincident with the crystal–semiliquid crystal should be mentioned that the 3D open frameworks of RHO and semiliquid crystal–liquid crystal thermal transitions.Mesoand ZSM-5 zeolite materials have been found to display SnS-1 can readily form electrically conducting thin films which interesting framework flexibility similar to that described for are able to reversibly adsorb molecules like H2O and CO2.the 2D SnS-n materials.30 It has also been shown that a similar These properties bode well for the use of this new class of structural flexibility of the R-SnS-n structures can be induced by pressure27 and adsorbed guest molecules with a concomitant, drastic electrical property change.27,31 In addition, attributed to the 2D open structure nature of the SnS-n materials, they are found to display unique adsorption behaviour towards guest molecules.For example, they may behave like a microporous material and/or an intercalation host. In other words, the adsorption of guest molecules in the SnS-n materials is controlled by both the size/shape and the properties of guest molecules. The unique structural flexibilty and adsorption properties of these materials make them of considerable interest as potential chemoselective sensory element for molecular recognition devices.7,31 It is interesting to note that the framework flexibility of the SnS-n materials is related to the well known polytype phenomenon occurring in bulk SnS2.They all originate from the flexible bonding nature of tin(IV) and sulfur(-II) centers. However, the constituent tin sulfide layers in diVerent SnS2 polytypes are identical and all of the polytypes have the same 2D unit cell parameters and structure within the tin sulfide sheet.The only diVerence among them is the stacking sequence Fig. 10 Illustration of the structures of the as-synthesized crystalline of the constituent layers and the cell parameter along the porous layer form of mesomorphic tin(IV) sulfide (top) and its semi- stacking direction.In this regard, diVerent SnS-1 or SnS-3 liquid and liquid crystalline phases. On warming the material the structures have diVerent 3D cell parameters and space groups. alkylamine bilayer first becomes disordered around 45 °C while the Furthermore, the tin sulfide constituent layer in each particular porous tin(IV) sulfide sheets remain more-or-less registered (middle), structure has unique SnMS bond angles and distances, and and then around 85 °C, both the alkylamine bilayer and the porous therefore a distinct pore size and shape.It appears that the tin(IV) sulfide lamellae become liquid crystalline at which point the intralayer but not the interlayer registry is lost (bottom).32 regular microscopic perforations of the tin sulfide layer have J.Mater. Chem., 1998, 8(5), 1099–1108 1103inorganic–organic semiconducting LCs for electro-optical displays and chemical sensing applications. The advantages of thermotropic Meso-SnS-1 over the R-SnS-1 and R-SnS-3 materials are that it is a better electrical conductor, and most importantly, thin films can be readily fabricated for device applications by simply warming the sample to its liquid crystalline state.Thin films of the material are expected to provide more sensitive and faster response to small and large molecule analytes. 4 3D Tin sulfide frameworks In contrast to the 2D tin sulfide-based structures, 3D tin(IV) thiostannates are relatively rare, so far only two structure types have been reported.A summary of their structural characteristics is given in Table 4. K2Sn2S5 was prepared by heating a mixture of Sn, K2S, and S in an evacuated, sealed Pyrex tube Fig. 12 An illustration of the channel structure of Na4Sn3S8, viewed down the b axis34 at 320 °C.33 The 3D framework of (Sn2S5)2- is presented in Fig. 11. It is built entirely from trigonal-bipyramidal SnS5. The SnS5 building units form through edge-sharing, zig-zag chains running along the a axis as highlighted in Fig. 11. They are bridged by sulfide ligands to yield 12-membered channels running down the b axis, with charge-compensating K+ cations snugly fitting inside. As shown in Fig. 12, the structure of Na4Sn3S8 34 is closely related to that of K2Sn2S5. The only diVerence is that in Na4Sn3S8, the zig-zag chains are linked together by tetrahedral SnS4 spacer units, leaving two terminal sulfurs located in the channels (Fig. 12). The charge-balancing Na+ cations reside inside the channels. Although both materials appear to have an open channel structure, the chargebalancing cations fit tightly inside the channels, and they are thus actually quite dense. Tl2Sn2S5, isostructural with K2Sn2S5, has been crystallized by heating a stoichiometric mixture of Fig. 13 Structures of [Sn(S4)3]2- and [Sn(S4)2S6]2- 38 Tl, Sn and S powders at 350 °C.35 In view of the similar diameters of K+ (1.52 A ° ) and Tl+ (1.54 A ° ), but the smaller size 5 Tin(IV) polythiostannates of Na+ (1.16 A ° ),36 the formation of the Na4Sn3S8 structure, with two large terminal sulfurs located inside of the channel, Discrete and polymeric tin(IV) polythiostannates have been suggests that the tin sulfide-based all-inorganic frameworks characterized with varied polysulfide ligand chain lengths and favors a dense-packed, rather than an open structure.geometric tin sites, see Table 5. The best known discrete tin(IV) polythiostannate anions are [Sn(S4)3]2- and [Sn(S4)2S6]2-, both having an octahedral tin(IV) site.The former contains three bidentate tetrasulfide ligands, while the latter has two Table 4 A summary of 3D tin(IV) thiostannates bidentate tetrasulfide and one bidentate hexasulfide ligand, Fig. 13. Interestingly, these two anions often co-crystallize in coordination a single unit cell to form a disordered structure. For example, number chemical synthetic in (Et4N)2[Sn(S4)3]0.4[Sn(S4)2S6]0.6, the [Sn(S4)3]2- and formula Sn S character of structure technique [Sn(S4)2S6]2- moieties are found to be located at the same crystallographic site with a partial occupancy of 0.4 and 0.6, K2Sn2S5 5 2 12-membered channel solid state respectively;37 while in [DABCOH]2[Sn(S4)3]0.5[Sn(S4)2 Na4Sn3S8 4, 5 1, 2 14-membered channel solid state S6]0.5, they each have a partial occupancy of 0.5.27,38, In contrast to the discrete [Sn(S4)3]2- and [Sn(S4)2S6]2- anions, b-Rb2Sn2S8 features an extended 2D framework as displayed in Fig. 14.33 It contains octahedral and tetrahedral tin(IV) sites. The basic building units can be viewed as facesharing double semi-broken cubes that are linked via. double bridge Sn(m-S)2Sn sulfur bonds to create parallel chains along the a axis direction.These chains are cross-linked by tetrasul- fide S4 ligands to yield the elaborate 2D structure of b- K2Sn2S8. The charge-compensating cation, Rb+ resides between the tin(IV) polysulfide sheets. The linkage between the Table 5 A summary of representative tin(IV) polysulfide structures chemical structure tin sulfide polysulfide formula dimensionality polyhedra ligands [Sn(S4)3]2- monomer SnS6 S4 [Sn(S4)2S6]2- monomer SnS6 S6 Rb2Sn2S8 2D framework SnS6, SnS4 S4 Fig. 11 An illustration of the channel structure of K2Sn2S5, viewed Cs2Sn2S6 2D framework SnS5 S2 down the b axis33 1104 J. Mater. Chem., 1998, 8(5), 1099–1108Fig. 14 A representation of the 2D open structure of K2Sn2S8, the K+ Fig. 16 An illustration of the layered structure of the rhombohedral cations are omitted for clarity (note the tetrapolysulfide ligand)33 Sn2P2S6.Note that it is similar to the berndtite SnS2 structure shown in Fig. 5, but with one half of the octahedral tin sites replaced by P2.42 which the element A is covalently bonded to Sn and/or S. Most ternary tin sulfides are metal tin sulfides, and were prepared through a conventional direct reaction of stoichiometric SnSx (x=1, 2) with MySz, or elements Sn, M, and S in an evacuated ampoule at elevated temperatures.A large collection of metals has been studied, including Na, K, Ba, In, Tl, Ge, Pb, Sb, Mn, Cu, and Eu.39 As the applied reaction temperature is normally high, up to 1000 °C, most of the produced materials feature a dense packed 2- or 3D structure. For example, CuSn3.75S8 has been synthesized by reacting elements Cu, Sn, and S at 1100 °C.It has a defect spinel structure, with SnIV occupying 15/16 of the octahedral and CuI residing in 1/2 of the tetrahedral sites.40 Na2SnS3 was prepared by melting a stoichiometric mixture of SnS2 and Na2S at 750 °C, followed by slow cooling to room temperature at 16 °C h-1.41 It has a NaCl type structure with tin and sodium distributed over the cation positions.Recently, non-metal elements have also been sucessfully introduced into tin sulfide-based frameworks. For example, crystals of Sn2P2S6 have been prepared from stoichiometric Fig. 15 A representation of the 2D open structure of Cs2Sn2S6, the Sn, P, and S elements sealed in a quartz tube and heated at Cs+ cations are omitted for clarity (note the disulfide ligand)33 high temperatures.42 Three polymorphic Sn2P2S6 phases have been reported, two of which, monoclinic(I) and rhombohedral, display a 2D structure similar to bulk berndtite SnS2, where chains through the S4 ligands is rather flexible.In this context, it has been found that a polytype of b-Rb2Sn2S8, namely a- 50% of the octahedral metal sites are, however, replaced by P2 (Fig. 16). By contrast, the monoclinic(II) phase consists of Rb2Sn2S8, can be crystallized from an identical reaction mixture to that used to prepare b-Rb2Sn2S8 but at a slightly lower discrete P2S64- anions that are linked together via weak SMSn interactions.43 In all of these phases, the oxidation state of tin temperature.33 In comparison with monoclinic a-Rb2Sn2S8, the high-temperature product has its layers slightly shifted atoms is tin(II ).Recently, SnP2S6 was synthesized under similar reaction condition as Sn2P2S6, but with a reduced tin content along the [1 0 2] crystallographic axis to form a more symmetric, i.e. orthorhombic, lattice. of Sn5P5S of 15256 in the reaction mixture.44 SnP2S6 has an ordered defect structure of the Fe2P2S6 structure type.The tin Cs2Sn2S6 also features a 2D framework as shown in Fig. 15.33 However, in this case, it contains one unique trigonal bipyrami- centers are in the +4 oxidation state, half of the metal sites are thus vacant and this results in a 2D open structure (Fig. 17). dal tin(IV) site which shares two common edges to form polymeric chains along the c axis.These chains are cross- Both SnP2S6 and Sn2P2S6 are found to display interesting non-linear optical properties.45 linked by disulfide S2 ligands to form arrays of 14-membered distorted rectangular pores parallel to the [1 0 0] plane. It is Solid solutions of SnS2-xSex (0x2) and (Me4N)2Sn3S7-xSex (0x7) families have been synthe- clear that tin polysulfides have a diverse bonding character and many more new structures are expected to emerge with sized.16,46,47 All members of the SnS2-xSex series crystallize in the Cd(OH)2 type structure, as shown in Fig. 5, to yield an diVerent polysulfide ligands and coordination geometries around the tin centers.isostructural family of solid solutions, i.e. sulfur and selenium are randomly distributed over the chalcogenide sites in the lattice.16,46 The intercalation chemistry of the SnS2-xSex series 6 Ternary tin sulfides has been investigated by O’Hare and co-workers.They have successfully included cobaltocene [Co(g-Cp)2] into the van der All the aforementioned structures contain only tin–sulfide covalent bonds, and the metal and organic cations in the Waals’ gaps between the tin chalcogenide layers, to form a series of SnS2-xSex{Co(g-Cp)2}0.33±0.02 materials.Through X- structure are ionically bonded to the tin(IV) thio- and polythiostannate anions to compensate the charge. However, a large ray and neutron diVraction and 2H solid state NMR studies, it was found that the cobaltocene is ordered in the tin number of ternary tin sulfide SnxSyAz systems (A represents any elements other than tin or sulfur) have been studied in chalcogenide gap, with the C5 axis of the g-Cp ring parallel to J.Mater. Chem., 1998, 8(5), 1099–1108 1105Fig. 17 An illustration of the 2D open structure of SnP2S6. Note that this structure is related to the Sn2P2S6 structure shown in Fig. 15, but half of the octahedral tin sites are vacant.44 Fig. 19 A representation of the open-framework structure of [Sn5S9O2][HN(CH3)3]2, for clarity showing only one of the interpenetrated diamond-type tin sulfide networks50 [Sn20S37O8]10-, each (Sn10O4S20)8- is connected to three neighboring (Sn10O4S20)8- clusters through corner-sharing of the sulfur apex to form a 2D open-framework structure,49 while in [Sn5O2S9][HN(CH3)3]2, each (Sn10O4S20)8- being linked to four neighboring (Sn10O4S20)8- clusters to form two interwoven diamond-type structures Fig. 19.50 It is interesting to mention that the (Sn4Se10O)6- tetrameric-unit has recently been synthesized in this laboratory, a reduced size version of Fig. 18 Structure of the supercluster (Sn10O4S20)8- 48 the supertetrahedral (Sn10O4S20)8- cluster.51 In (Sn4Se10O)6-, the tin selenide cluster has an adamantane structure and the oxygen is located in the central tetrahedral void and coordi- the layers.In the intercalated materials, SnIV in the host layers nated to the four tin apexes to make them five-coordinated. is partially reduced to SnII as seen by Mo�ssbauer spectroscopy. The (Sn4Se10O)6- clusters are linked together through the four The conductivities of both the host and the host–guest intercaterminal seleniums to distorted tetrahedral SnIV centres to lated series were studied through variable temperature single form (Sn5Se10O)2-, a 3D open-framework diamond-type struc- crystal measurements.The intercalated materials display ture where the charge balance is maintained by two (CH3)4N+ reduced resistivity in comparison with the hosts. Remarkably, cations occupying the void spaces (Fig. 20). the high selenium content members, i.e. SnS2-xSex{Co(g- Cp)2}0.33±0.02 (1.85x2), exhibit superconductivity at temperatures below 6 K. In comparison, the (Me4N)2Sn3S7-xSex (0x7) family has a 2D open structure.47a It displays a similar framework architecture to that of the SnS-1 material displayed in Fig. 8. The (Me4N)2Sn3S7-xSex series is found to crystallize in an orthorhombic space group, P212121. The optical absorption edge of the (Me4N)2Sn3S7-xSex series is found to display a monotonic red shift with increasing Se content as found in the isostructural SnS2-xSex family. The results of a detailed recent study47b show that the distribution of the chalcogenides in (Me4N)2Sn3S7-xSex is random (solidsolution, Vegard law) at the length scale of the unit cell but site-selective at the level of the trigonal bipyrimidal buildingblocks.In addition to the mixed sulfur–selenium based materials, tin oxy-sulfides have also been reported. For example, the ‘supertetrahedron’ (Sn10O4S20)8- has been crystallized as a discrete anion in Na8Sn10O4S20·32H2O and Cs8Sn10O4- S20·13H2O compounds.48 The (Sn10O4S20)8- cluster is built of ten corner-sharing SnS4 tetrahedrons, Fig. 18. Four oxygen atoms are located in the supertetrahedral voids and are coordinated to six of the ten tin atoms to form SnS4O2 distorted octahedra. Recently, these supertetrahedral clusters have been linked together through sulfur bridging bonds to Fig. 20 An illustration of the 3D open framework structure of (Me4N)2(Sn5Se10O). The Me4N+ cations are omitted for clarity.51 give rise to 2D and 3D open-framework structures.In 1106 J. Mater. Chem., 1998, 8(5), 1099–1108sandwiched by two Sn metal layers in which one-half of the Sn sites are missing to form parallel grooves. The Rb+ cations are located inside the grooves. K2Au2SnS4 and K2Au2Sn2S6 were obtained by heating Sn and Au powder at 350 °C in a K2S5 and K2S9 flux, respectively.52 As shown in Fig. 23(A), the 1D structure of the former is constituted by tetrahedral SnS4 and linear AuS2 building blocks in a ratio of 152. The paralell zig-zag [Au2SnS4]2- chains are separated by K+ cations. K2Au2Sn2S6 is constructed from dimeric Sn2S6 units that are linked together by linear Au atoms to form fully extended infinite chains, Fig. 23(B). Note that although these two materials have similar chemical formulae to those of the Cu analogs discussed above, they present completely diVerent structures due to the diVerent preferred coordination geometries of CuI and AuI. The former favors a tetrahedral coordination environment while the latter favours a linear geometry. Fig21 A representaion of the 2D open structure of Rb2Cu2SnS4. Rb+ cations residing between the (Cu2SnS4)2- sheets are omitted.52 7 Quatenary tin sulfides Quaternary Rb2Cu2SnS4 and Rb2Cu2Sn2S6 have been synthesized by heating Sn and Cu powder in a Rb2S5 flux at 400 °C.52 In both materials, tetrahedral SnS4 and CuS4 units are the basic building blocks.The edge sharing of SnS4 and CuS4 creates a 2D open structure of Rb2Cu2SnS4 with 8-atom rings (Fig. 21). The rubidium cations are located between the anionic layers of [Cu2SnS4]2- to balance the charge. The corner sharing of SnS4 and CuS4 results in the 2D open struuture of A2Cu2Sn2S6 (Fig. 22). It can be viewed as a derivative of a 3D zinc blende adamantane-type structure material of formula Cu2SnS3. However, the replacement of half of the Cu atoms in Cu2SnS3 by alkali-metal atoms reduces the dimensionality of the framework structure from three to two due to the interruption of covalent bonding through the structure.Each [Cu2Sn2S6]2- slab contains three metal layers, i.e. a Cu layer Fig. 23 An illustration of the chain structures of (A) K2Au2SnS4 and Fig. 22 A representaion of the 2D open structure of Rb2Cu2Sn2S6 (B) K2Au2Sn2S6.The K+ cations residing between the chains are omitted for clarity.52 viewed parallel to the layers52 J. Mater. Chem., 1998, 8(5), 1099–1108 110717 B. Palosz, W. Steurer and H. Schulz, Acta Crystallogr., Sect. B, 8 Conclusion 1990, 46, 449. 18 B. Palosz, W. Palosz and S. Gierlotka, Acta Crystallogr., Sect. B, Representative tin sulfide-based materials that have appeared 1986, 42, 653.in the recent materials chemistry literature, ranging from 19 A. R. Verma and P. Krishna, Polymorphism and Polytypism in molecular species to 1D chain, 2D dense and porous sheets Crystals, John Wiley & Sons, New York, 1969. and 3D open frameworks, have been reviewed. In particular, 20 H. Jagodzinski, Neues Jahrb. Mineral. Abh., 1954, 3, 49. ‘soft chemistry approaches’ such as hydro- and solvothermal 21 B.Palosz, W. Steurer and H. Schulz, Acta Crystallogr., Sect. B., 1990, 46, 449. synthesis, and the molten-salt flux technique, have generated 22 W. S. Sheldrick and B. Schaaf, Z. Anorg. Allg. Chem., 1994, 620, a large collection of novel microporous tin (poly)sulfide mate- 1041. rials and the first example of a mesoporous tin sulfide, which 23 W.S. Sheldrick, Z. Anorg. Allg. Chem., 1988, 562, 23. present interesting optical, electrical, adsorption and liquid 24 C. Bowes, PhD Thesis University of Toronto, 1996. crystal properties. In the 1D, 2D and 3D extended tin (poly)sul- 25 T. Tan, Y. Ko and J. B. Parise, Acta Crystallogr., Sect. C, 1995, fides, molecular tin sulfide species, [SnS4]4-, [Sn2S6]4- and 51, 398. 26 J. B. Parise, Y. Ko, J. Rijssenbeek, D. M. Nellis K. Tan and [Sn4S10]4- are found to serve as structure building blocks. S. Koch, J. Chem. Soc., Chem. Commun., 1994, 527. This suggests that by employing modular-assembly synthetic 27 (a) T. Jiang, PhD Thesis University of Toronto, 1997; (b) T. Jiang, approaches, in combination with templating agents, many A. J. Lough, G.A. Ozin, R. L. Bedard and R. W. Broach, J. Mater. more novel binary, ternary, quaternary tin sulfide structures Chem., 1998, 8, 721; T. Jiang, A. Lough and G. A. Ozin, Adv. are expected to emerge with desired properties and functions, Mater., 1998, 10, 42. for the development of a range of new sensing, separation and 28 (a) T. Jiang, A. J. Lough, G. A. Ozin, D. Young and R. L. Bedard, Chem.Mater., 1995, 7, 245; (b) Y. Ko, K. Tan, D. M. Nellis, S. Koch catalysis applications. and J. B. Parise, J. Solid State Chem., 1995, 114, 506. 29 G. A. Marking and M. G. Kanatzidis, Chem. Mater. 1995, 7, 1915. The financial assistance of the Natural Sciences and 30 (a) D. R. Corbin, L. Abrams, G. A. Johns, M. M. Eddy, Engineering Research Council of Canada (NSERC) is deeply W.T. A. Harrison, G. D. Stucky and D. E. Cox, J. Am. Chem. Soc., appreciated. T.J. expresses her gratitude to University of 1990, 112, 4821; (b) C. A. Fyfe, H. Strobl, G. Kokotailo, Toronto for an Open Fellowship held through the course of G. J. Kennedy and G. E. Barlow, J. Am. Chem. Soc., 1988, 110, her PhD study. 3373. 31 (a) H. Ahari, C. L. Bowes, T. Jiang, A. Lough, G.A. Ozin, R. L. Bedard, S. Petrov and D. Young, Adv. Mater., 1995, 7, 375; References (b) G. A. Ozin, Supramol. Chem., 1995, 6, 125. 32 T. Jiang and G. A. Ozin, J. Mater. Chem., 1997, 7, 2213. 1 (a) N. N. Greenwood and A. Earnshaw, The Chemistry of the 33 J. Liao, C. Varotsis and M. G. Kanatzidis, Inorg. Chem., 1993, Elements, Pergamon Press, New York, 1984, ch. 10 and 15; (b) 32, 2453.B. Krebs, Z. Anorg. Allg. Chem., 1983, 22, 113; (c) D. J. Vaughan 34 J.-C. Jumas, E. Philippot and M. Maurd, J. Solid State Chem., and J. R. Craig, Mineral Chemistry of Metal Sulfides, Cambridge 1975, 14, 152. University Press, Cambridge, 1978. 35 G. Eulenberger, Z. Naturforsch., Terl B, 1981, 36, 687. 2 P. G. Harrison, Chemistry of Tin, Blackie, Glasgow, 1989. 36 (a) F. A.Cotton, G. Wilkinson and P. L. Gaus, Basic Inorganic 3 N. N. Greenwood and A. Earnshaw, A. The Chemistry of the Chemistry, John Wiley & Sons, New York, 1987; (b) J. E. Huheey, Elements, Pergamon Press, New York, 1984, p. 780. Inorganic Chemistry: Principles of Structure and Reactivity, Harper 4 B. Krebs and W. Schiwy, Z. Anorg. Allg. Chem. 1973, 398, 63. & Row, New York, 1983, p. 258. 5 (a) R. L. Bedard, L. D. Vail, S. T. Wilson and E. M. Flanigen, US 37 A. Mu� ller, J. Schimanski, M. Ro� mer, H. Bo� gge, W. Baumann, Patent, 4 880 761, 1989; R. L. Bedard, L. D. Vail, S. T. Wilson and W. Eltzner, E. Krickemeyer and U. 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Blutau, D. Ga�thje and B. Krebs, Z. Anorg. Allg. 46 D. O’Hare, Chem. Rev., 1992, 121 and references therein. Chem., 1975, 412, 1. 47 (a) H. Ahari, G. A. Ozin, R. L. Bedard, S. Petrov and D. Young, 12 G. H. Moh, Neus Jahrb. Mineral. Abh., 1969, 111, 227. Adv. Chem., 1995, 7, 370; (b)H. Ahari,O� . Dag, A. G. Ozin, S. Petrov 13 R. Kniep, D. Mootz, U. Severin and H. Wunderlich, Acta and R. L. Bedard, J. Phys. Chem., in press. Crystallogr., Sect. B, 1982, 38, 2022; D. Mootz and H. Puhl, Acta 48 W. Schiwy and B. Krebs, Z. Angew. Chem., 1975, 8ystallogr., Sect. B, 1967, 23, 471. 49 J. B. Parise, Y. Ko, K. Tan, D. M. Nellis and S. Koch, J. Solid State 14 R. Herzenberg, Rev. Mineral., 1932, 4, 33. Chem., 1995, 117, 219. 15 (a) H. Wiedemeier and F. J. Csillag, Z. Kristallogr., 1979, 149, 17; 50 J. B. Parise and Y. Ko, Chem. Mater., 1994, 6, 718. (b) H. G. von Schnering and H. Wiedemeier, Z. Kristallogr., 1981, 51 H. Ahari, A. Lough and G. Ozin, unpublished work. 156, 143. 52 J. H. Liao and M. G. Kanatzidis, Chem. Mater., 1993, 5, 1561. 15 P. Woulfe, Philos. Trans. R. Soc. London, 1771, 61, 114. 16 H. P. B. Rimmington and A. A. Balchin, J. Cryst. Growth., 1972, 15, 51. Paper 7/09054D; Received 17th December, 1997 1108 J. Mater. Chem., 1998, 8(5), 1099–1108

ISSN:0959-9428    

DOI:10.1039/a709054d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Communication Synthesis and polymerization of 3,3-di[(S)-(+)-2-methylbutyl]- 2,2¾:5¾,2-terthiophene: a new monomer precursor to chiral regioregular poly(thiophene) Franco Andreani, *† Luigi Angiolini, Daniele Caretta and Elisabetta Salatelli Dipartimento di Chimica Industriale e dei Materiali, Universita` di Bologna, V iale Risorgimento 4, 40136 Bologna, Italy oxidative methods, such as FeCl3 oxidation, which is easy to use and suitable to large scale production. 3,3-Di[(S)-(+)-2-methylbutyl]-2,2¾:5¾,2-terthiophene, having two equivalent reactive positions, allows the synthesis of the Monomer (+)-3,3-DMBTT was prepared from 3-[(S)-(+)- 2-methylbutyl]thiophene (+)-1, itself derived from optically corresponding optically active poly(thiophene) with regioregular enchainment by using an aspecific oxidative pure (S)-(-)-2-methylbutan-1-ol, according to the reported procedure3 which involves a bromination step to (S)-(+)-1- polymerization method.bromo-2-methylbutane followed by Grignard reaction and coupling with 3-bromothiophene in the presence of 1,3- diphenylphosphinopropanenickel dichloride [Ni(dppp)Cl2]. The 3-alkylthiophene (+)-1 was then submitted to iodination Much eVort has been devoted in the recent years to the using the method of Suzuki,19 thus obtaining a mixture of the investigation of optically active polythiophenes characterized 2-iodo and 2,5-diiodo derivatives.Iodination, instead of broby the presence of a chiral moiety linked to the 3-position of mination, of (+)-1 was adopted due to the expected higher the aromatic ring.In addition to their potential technological reactivity of the iodinated derivative in the subsequent prepapplications as materials for enantioselective electrodes and aration of the Grignard reagent. The pure mono-iodinated membranes,1–4 chiral poly(thiophene)s oVer the possibility of product, 2-iodo-3-[(S)-(+)-2-methylbutyl]thiophene (+)-2, studying the structural changes accompanying the transition [a]D25+3.95 (c 2.1, CHCl3), was obtained in good yield by from the disordered state in solution to the ordered micro- fractional distillation in vacuo, then allowed to react with aggregate or solid state by following the variation of their magnesium in THF, and finally coupled with 2,5-dibromothiochiroptical properties by circular dichroism (CD).5–8 A crucial phene in the presence of Ni(dppp)Cl2 and anisole to give (+)- role in obtaining remarkable chiroptical properties is however 3,3-DMBTT, according to Kobayashi’s procedure.20 played by a highly predominant or exclusive presence in the Monomer (+)-3,3-DMBTT purified by column chromatogmacromolecular backbone of regioregular head-to-tail raphy (SiO2, hexane), [a]D25+16.0 (c 1.7, CHCl3), was fully sequences of the 3-substituted thiophene repeating units, as characterized by IR and 1H NMR spectroscopy, mass specthe lack of this structural requirement strongly reduces the trometry (m/z 388; M+, 100%) and elemental analysis (Found: possibility of the existence of extended co-planar structures C, 67.8; H, 7.4; S, 24.8.Calc. for C22H28S3: C, 67.99; H, 7.26; characterized by a large extent of aromatic conjugation. S, 24.75%). In particular, it is worth noting the presence in Synthetic methods to produce highly regioregular poly(thio- the IR spectrum of two bands at 3102 and 3063 cm-1, related phene)s have been developed9–11 and McCullough’s procedure, to Ca–H and Cb–H stretching, respectively, typical of 3-alkylin particular, has been applied to the preparation of highly substituted thiophene rings,21 as well as the presence of an regioregular optically active 3-alkyl substituted poly(thio- out-of-plane bending signal at 797 cm-1, attributed to the 2,5- phene)s,5–8 exhibiting much enhanced optical activity as com- disubstituted central ring.22,23 pared to the corresponding regiorandom derivatives when the The 1H NMR spectrum in CDCl3 [Fig. 1(a)] exhibits the macromolecules are in the micro-aggregate or solid (film) state. expected pattern in the aromatic region, consisting of two A possible way to avoid the need for using regiospecific doublets at 7.17 and 6.91 ppm, related to the a and b protons, synthetic methods is given by the preparation of symmetrical respectively, and of one singlet at 7.05 ppm (c protons).monomers inherently unable to aVord regiorandom polymeric The oxidative polymerization of (+)-3,3-DMBTT has been derivatives even in the presence of an aspecific polymerization carried out following the general method of Sugimoto et al.,24 mechanism. Whereas symmetrically 3,3¾- or 4,4¾-disubstituted 2,2¾-bithiophenes give polymers containing regularly spaced head-to-head (50%) and tail-to-tail (50%) coupled repeating units, symmetrically 3,3- and 3¾,4¾-disubstituted 2,2¾:5¾,2- terthiophenes have been reported12–18 to produce the corresponding polythiophenes characterized by a regioregular enchainment free from head-to-head connections, provided that two identical ring substituents are present.However, no optically active terthiophene monomer precursor to a regioregular optically active polymer is mentioned in the literature. We report here the possibility of synthesizing poly(thiophene)s, characterized by relevant chiroptical properties, from the optically active 3,3-di[(S)-(+)-2-methylbutyl ]-2,2¾:5¾2-terthiophene monomer [(+)-3,3-DMBTT] (Scheme 1) having two identical reactive sites and hence polymerizable using chemical S CH3 CH3 S R* I S S S R* R* i ii, iii 73% 52% (+) - 1 (+) - 2 (+) - 3,3¢¢-DMBTT S S S R* R* n poly(3,3¢¢-DMBTT) iv 25% poly(3,3��-DMBTT) 3,3��-DMBTT Scheme 1 Reagents and conditions: i, I2, H5IO6; ii, Mg, THF; iii, 2,5- dibromothiophene, anisole, Ni(dppp)Cl2 (cat.); iv, FeCl3, CCl4 † E-mail: andreani@ms.fci.unibo.it J.Mater. Chem., 8(5), 1109–1111 1109Fig. 2 (a) UV and (b) CD spectra of poly(3,3-DMBTT) in (i) CHCl3 and (ii) CHCl3–CH3OH (71529) 5000 g mol-1, corresponding roughly to a polymerization degree x: n of 13, expressed as terthiophene co-units. This value appears to be in good agreement with the M9 n value of 4300 g mol-1 (x: n=11), determined by gel permeation chromatography using monodisperse polystyrene samples as standard references.Optimization of the polymerization reaction aimed at obtaining both better yields and higher values of M9 n in the soluble fraction of poly(3,3-DMBTT) is currently under study. Fig. 1 1H NMR spectra in CDCl3 of the aromatic region of (a) (+)- The UV spectrum of poly(3,3-DMBTT) in CHCl3 (Fig. 2) 3,3-DMBTT and (b) poly(3,3-DMBTT) displays an absorption maximum at 454 nm, related to the p–p* electronic transition of the conjugated aromatic system, similar or even higher than the maximum wavelength values using CCl4 in place of CHCl3 and lower monomer and FeCl3 molar concentrations (0.025 and 0.1 M, respectively), in order reported in the literature4,5,7,8 for optically active regioregular head-to-tail poly(3-alkylthiophene)s, thus suggesting an to reduce, according to recently reported18 results, the relative amount of insoluble material.Although the reaction conditions enhanced extent of conjugation, probably attributable to improved coplanarity of the thiophene rings along the main have not been yet optimized, we have observed that, indeed, no insoluble polymer fraction is produced at all, even though chain.A solvatochromic eVect is also evidenced in the UV spectrum upon addition of increasing amounts of methanol poly(3,3-DMBTT) is reasonably expected to be not very soluble, due to the lower average density of 2-methylbutyl side (poor solvent), which promotes the aggregation of the macromolecules. A progressive appreciable red-shift of the maximum chains as compared to the corresponding poly[3-(2-methylbutyl) thiophene].3 Poly(3,3-DMBTT), purified by exhaustive absorbance, accompanied by the appearance of vibronic bands and shoulders, up to a lmax of 467 nm is observed, correspond- extraction with CH3OH of any unreacted monomer and low molecular weighons, exhibits the disappearance of the ing to a CHCl3–CH3OH ratio of about 70530 (v/v).Upon further addition of CH3OH, precipitation of the solute takes band at 3102 cm-1, while the 3063 and 797 cm-1 signals remain unchanged, with respect to the IR spectrum of the place. This behaviour indicates an increase of conjugation length attributable to an increase of the conformational order monomeric precursor. Moreover, two bands at 818 and 833 cm-1, typical of the out of plane bending of the Cb–H in the micro-aggregate state.In this state, also, the polymer main chain becomes optically active, as revealed by its CD bond in 2,3,5-trisubstituted thiophene rings,23 appear in the spectrum, thus confirming that the polymerization has taken spectrum (Fig. 2), as a consequence of chirality transmitted by the alkyl side-chain to the conjugated backbone.place only at the Ca atom of the monomer, with no mislinkages through the b-positions occurring during the process. The The CD spectrum of the micro-aggregated macromolecules displays strong dichroic signals which correspond closely to 1H NMR spectrum [Fig. 1(b)] is in accordance with the proposed structure, as it displays two main resonances at 7.10 the UV absorbances, originated by the presence of chiral conformations assumed by the macromolecules when the crys- and 6.99 ppm, related to the c and d protons, respectively, located along the main chain.Less intense signals are also tallization begins to take place, with a remarkable value of the chiral anisotropy factor g (De/e) of -3×10-2 at 578 nm, close observable in the spectrum, due to the hydrogen atoms of terthiophenic end groups.Calculations based on the integrated to the values reported for regioregular poly(3-alkylthiophene) s.8 By contrast, the CD spectrum of poly(3,3-DMBTT) areas of these last resonances allow the assessment that the mean molecular weight of the macromolecular chains is around in pure CHCl3, which favours the presence of disordered 1110 J.Mater. Chem., 8(5), 1109–11118 B. M. W. Langeveld-Voss, M. M. Bouman, M. P. T. Christiaans, random coil conformations of the macromolecules, does not R. A. J. Janssen and E. W. Meijer, Polym. Prepr., 1996, 37, 499. display any optical activity (Fig. 2), due to the absence of 9 R. D. McCullough and R. D. Lowe, J. Chem. Soc., Chem. Commun., chirally ordered structures in the polymer in solution. 1992, 70. It can therefore be concluded that although poly(3,3- 10 R. D. McCullough, R. D. Lowe, M. Jayaraman and D. L. DMBTT) has a lower content of chiral alkyl substituents per Anderson, J. Org. Chem., 1993, 58, 904. 11 T. A. Chen and R. D. Rieke, J. Am. Chem. Soc., 1992, 114, 10 087. thiophene ring with respect to regioregular poly(3-alkylthio- 12 M.C. Gallazzi, L. Castellani, G. Zerbi and P. Sozzani, Synth.Met., phene)s, it behaves similarly, or better, as regards extent of 1991, 41–43, 495. conjugation and chiroptical properties. Interestingly, it could 13 M. C. Gallazzi, L. Castellani, R. A. Marin and G. Zerbi, J. Polym. be synthesized also by electrochemical oxidative coupling of Sci., Part A: Polym.Chem., 1993, 31, 3339. (+)-3,3-DMBTT, thus directly yielding a thin chiral polymeric 14 K. Faý� d and M. Leclerc, J. Chem. Soc., Chem. Commun., 1993, 962. film on the electrode surface, which would be particularly 15 C. Wang, M. E. Benz, E. LeGoV, J. L. Schindler, J. Allbritton- Thomas, C. R. Kannewurf and M. G. Kanatzidis, Chem. Mater., useful for electrochemical characterizations and applications. 1994, 6, 401. 16 P. T. Henderson and D. M. Collard, Chem. Mater., 1995, 7, 1879. Financial support by University of Bologna (Fondi 60%) is 17 G. Zotti, M. C. Gallazzi, G. Zerbi and S. V. Meille, Synth. Met., gratefully acknowledged. 1995, 73, 217. 18 F. Andreani, E. Salatelli and M. Lanzi, Polymer, 1996, 37, 661. 19 H. Suzuki, K. Nakamura and R. Goto, Bull. Chem. Soc.Jpn., 1966, References 39, 128. 20 M. Kobayashi, J. Chen, T. C. Chung, F. Moraes, A. J. Heeger and 1 J. Roncali, Chem. Rev., 1992, 92, 711. F.Wudl, Synth.Met., 1984, 9, 77. 2 M. Lemaire, D. Delabouglise, R. Garreau, A. Guy and J. Roncali, 21 M. Sato, S. Tanaka and K. Kaeriyama, Makromol. Chem., 1987, J. Chem. Soc., Chem. Commun., 1988, 658. 188, 1763. 3 D. Kotkar, V. Joshi and P. K. Ghosh, J. Chem. Soc., Chem. 22 Y. Furakawa, M. Akimoto and I. Harada, Synth. Met., 1987, 18, Commun., 1988, 917. 151. 4 D. Kotkar, P. K. Ghosh and A. Ray, in Frontiers of Polymer 23 S. Hotta, M. Soga and N. Sonoda, Synth.Met., 1988, 26, 267. Research, ed. P. N. Prasad and J. K. Nigam, Plenum, New York, 24 R. Sugimoto, S. Takeda, H. B. Gu and K. Yoshino, Chem. Express, 1991, p. 407. 1986, 1, 635. 5 M. M. Bouman and E. W. Meijer, Polym. Prepr., 1994, 35, 309. 6 M. M. Bouman and E. W. Meijer, Adv. Mater., 1995, 7, 385. 7 G. Bidan, S. Guillerez and V. Sorokin, Adv.Mater., 1996, 8, 157. Communication 8/01593G; Received 25th February, 1998 J. Mater. Chem., 8(5), 1109–1111 11

ISSN:0959-9428    

DOI:10.1039/a801593g

出版商:RSC    

年代:1998

数据来源: RSC

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J O U R N A L O F C H E M I S T R Y Materials Communication Synthesis of IPN polymer hybrids of polystyrene gel and silica gel by an in-situ radical polymerization method Ryo Tamaki and Yoshiki Chujo* Department of Polymer Chemistry Graduate School of Engineering Kyoto University Yoshida Sakyo-ku Kyoto 606-01 Japan Homogeneous IPN polymer hybrids of polystyrene gel and silica gel were prepared by applying an in-situ polymerization method to styrene monomer and divinylbenzene. The monomers were mixed in the sol–gel reaction mixture of tetramethoxysilane and subjected to radical polymerization resulting in transparent glassy materials. The homogeneity was confirmed by nitrogen porosimetry methods. The organic part was found to be dispersed at the nanometer scale. The obtained IPN polymer hybrids are highly solvent resistant.In recent years a large variety of organic and inorganic polymer hybrids have been synthesized by utilizing the sol–gel technique Scheme 1 with alkoxysilanes.1,2 The sol–gel reaction comprises the hydrolysis and subsequent condensation reaction of alkoxysilanes. 3–7 When alkoxysilanes are used as precursors Si–OH sol–gel reaction of TMOS. The mixture was stirred at room temperature for 5 h and subsequently heated at 60 °C under groups are formed by hydrolysis of alkoxy groups and Si–O–Si linkages are obtained by condensation of the hydroxyl groups. nitrogen for 1 week with an aluminium foil cover having a few pinholes. Sol–gel reaction of TMOS and radical polymerization One of the interesting properties of the obtained silica gel is that it contains unreacted residual silanol groups even after of styrene and DVB were expected to proceed simultaneously entrapping the organic network in the silica gel.After removal gelation which allow us to utilize hydrogen bonding interactions between the silanol groups and amide groups of organic of the solvent glassy materials were obtained. The conversion of the monomer to polymer was confirmed polymers to obtain homogeneous organic–inorganic polymer hybrids. Poly(2-methyl-2-oxazoline) poly(N-vinyl-2-pyrroli- by thermogravimetric analysis (TGA) which shows the onset of polymer decomposition around 350 °C (Fig. 1).19 The weight done) and poly(N,N-dimethylacrylamide) have been incorporated homogeneously by adding them into a sol–gel reaction loss at around 100 °C corresponds to residual solvent.The polymer hybrids obtained were ground and subjected to CHCl3 mixture at an initial stage.8–18 On the other hand we have successfully prepared homo- extraction using a Soxhlet apparatus. The contents of organic polymer in the hybrids after CHCl3 extraction were confirmed geneous polymer hybrids of polystyrene which has no polar functional groups utilizing the in-situ radical polymerization by TGA as the weight loss at 900 °C. As shown in Fig. 1 the polymer contents decreased dramatically after the extraction of styrene monomer in the sol–gel reaction mixture.19 In contrast to the prepolymer incorporation method used for in the polymer hybrid prepared without DVB. The polymer contents before and after the extraction were 48% and 17% poly(2-methyl-2-oxazoline) and the other polymers described above hydrogen bonding interactions between silica gel and respectively (Table 1).The results indicate 64% of polystyrene was extracted from the polymer hybrid prepared without DVB. organic polymers are not so critical in this in-situ polymerization technique. It is rather confinement of the growing On the other hand the polymer contents hardly changed before and after extraction when 0.1 equiv. of DVB was used organic polymer by silica gel that aVects the homogeneity.20 Here we have applied this in-situ polymerization method for (Fig. 2). In this case the polymer contents before and after extraction were 53% and 50% respectively. The loss of organic the synthesis of polymer hybrids of polystyrene gel and silica gel with a so-called interpenetrating polymer network (IPN) polymer was only 6%.For clarity the polymer loss was plotted against DVB contents as illustrated in Fig. 3. The plot structure. The polymer hybrids were expected to be highly solvent resistant because of the presence of cross-linking points shows the considerable improvement of the resistivity to solvent extraction with increasing DVB content and the extrac- in the organic network. Polystyrene gel and silica gel polymer hybrids were prepared tion was almost prevented above 10 wt.% of DVB. The results indicate polystyrene formed a percolation network in silica gel by the in-situ polymerization method as shown in Scheme 1. Divinylbenzene (DVB) was used to introduce cross-linking with 10 wt.% of DVB resulting in strong resistance to dissolution in chloroform. points in the organic network.Styrene and DVB were mixed with 0.01 equiv. of 2,2¾-azobisisobutyronitrile (AIBN) and 1.0 g The homogeneity of IPN polymer hybrids could be estimated by optical observation. Since the refractive indices of organic of tetramethoxysilane (TMOS) in 10 ml of acetone. The weight ratio of DVB and styrene was varied from 0 to 0.2 to control and inorganic parts have diVerent values i.e. 1.46 and 1.60 at 20 °C for polystyrene and silica gel respectively the composites the density of cross-linking points while the total weight of the organic monomers was fixed at 1.0 g (Table 1). 0.24 ml of would become opaque when the domain of each component is larger than wavelength of visible radiation.2 As shown in 0.1 M HCl was added to the solution as a catalyst for the J. Mater. Chem.1998 8(5) 1113–1115 1113 Table 1 Synthesis of polystyrene IPN polymer hybridsa polym. cont.c run DVB/St homogeneityb before(%) after(%) weight lossc (%) 1 0 transparent 48.0 17.4 63.8 2 0.05 transparent 49.5 40.3 18.9 3 0.1 transparent 53.0 49.7 6.2 4 0.2 transparent 55.8 51.9 7.0 aEach hybrid was prepared with 0.01 equiv. of AIBN 1.0 g of TMOS 0.24 ml of 0.1 M HCl in 10 ml of acetone. The total amount of DVB and St was 1.0 g. The mixture was heated at 60 °C under nitrogen. bHomogeneity was evaluated optically. cThe polymer contents in the hybrids were calculated by TGA. dWeight loss of the organic part was calculated as follows weight loss={polym.cont.(before)-polym.cont. (after)}/polym.cont.(before)×100. Scheme 2 Table 1 the obtained polymer hybrids were all transparent indicating the homogeneous dispersion of the organic domain in the silica matrix.The homogeneity of the polymer hybrids was also evaluated quantitatively by nitrogen porosimetry of Fig. 1 TGA traces of polystyrene–silica gel IPN polymer hybrid porous silica obtained from the polymer hybrids. The organic (DVB/styrene=0) before (a) and after (b) CHCl3 extraction polymer was removed from the polymer hybrids by charring at 600 °C for 24 h resulting in porous silica with pores of comparable size to the organic domains in the polymer hybrids (Scheme 2).18 Therefore the dispersity of organic polymers in the hybrids could be evaluated by measuring the pores.18 The BET method was applied to the isotherm curves to calculate surface areas and pore volumes of porous silicas.21 As shown in Table 2 it was found that the porous silica obtained from these polymer hybrids had surface areas of more than 200 m2 g-1.If an aggregation of the organic segment occurred the porous silica would have much smaller values for surface area and pore volume.20 The pore size was calculated by the BJH method from the desorption isotherm curve from which the pore radius (Rp) was obtained assuming cylindrical pores.22 The results are illustrated in Fig. 4 and Table 2. Although the pore size is larger than that of porous silica obtained from a polymer hybrid of linear polystyrene and silica gel the pore size distribution plot for the porous silica obtained from the Fig. 2 TGA traces of polystyrene–silica gel IPN polymer hybrid polymer hybrids prepared with 10 and 20 wt.% DVB exhibited (DVB/styrene=0.1) before (a) and after (b) CHCl3 extraction peaks at 1.9 and 2.7 nm respectively.As the pore of the silica obtained from polymer hybrids corresponds to the domain size of the organic segment it seems reasonable to say that the polystyrene gel was dispersed at a nanometer level in these polymer hybrids. This is very interesting for the organic segment which does not possess hydrogen bond accepting groups and has poor solubility in the solvent. The homogeneity could be attributed to confinement of the polystyrene network Table 2 Pore volume and surface area of porous silicaa DVB/ pore volumeb/ surface areab/ pore radiusc/ run St ml g-1 m2 g-1 nm 1 0 63.6 277 1.8 2 0.1 64.7 282 1.9 3 0.2 67.9 295 2.7 aThe porous silicas were obtained by charring the polymer hybrids at 600 °C for 24 h.bCalculated by BET method. cCalculated by BJH Fig. 3 Weight loss by CHCl3 extraction for 1 week method from desorption curve. 1114 J. Mater. Chem. 1998 8(5) 1113–1115 3 H. Schmidt H. Scholze and A. Kaiser J. Non-Cryst. Solids 1984 63 1. 4 C. J. Brinker K. D. Keefer D. W. Schaefer R. A. Assink B. D. Kay and C. S. Ashley J. Non-Cryst. Solids 1984 63 45. 5 F. Orgaz and H. Rawson J. Non-Cryst. Solids 1986 82 57. 6 C. J. Brinker and G. W. Scherer J. Non-Cryst. Solids 1985 70 301. 7 C. J. Brinker and G. W. Scherer Sol–Gel Science Harcourt Brace & Co. Boston 1990. 8 Y. Chujo E. Ihara S. Kure and T. Saegusa Macromolecules 1993 26 5681. 9 M. Toki T. Y. Chow T. Ohnaka H. Samura and T. Saegusa Polym. Bull. 1992 29 653. 10 T. Saegusa and Y. Chujo J.Macromol. Sci. Chem. 1990 A27 1603.11 Y. Chujo and T. Saegusa Adv. Polym. Sci. 1992 100 11. 12 Y. Chujo J. T hermosetting Plast. Jpn. 1995 16 99. 13 Y. Chujo E. Ihara S. Kure N. Suzuki and T. Saegusa Makromol. Chem. Macromol. Symp. 1991 42/43 303. 14 Y. Chujo Organic/Inorganic Polymer Hybrids CRC Press Boca Raton New York London Tokyo 1996; vol. 6 p. 4793. Fig. 4 Pore size distribution plots of porous silica gels 15 Y. Chujo Polym. Mater. Sci. Eng. 1996 74 65. 16 T. Saegusa and Y. Chujo Makromol. Chem. Macromol. Symp. within the silica gel matrix. The formation of polystyrene gel 1991 51 1. and silica gel proceeded simultaneously resulting in an IPN 17 T. Saegusa and Y. Chujo Makromol. Chem. Macromol. Symp. 1992 64 1. structure in this in-situ polymerization method. It was thus 18 Y. Chujo H. Matsuki S. Kure T. Saegusa and T. Yazawa J. Chem. expected that the rigid structure of silica gel suppressed the Soc. Chem. Commun. 1994 635. mobility of polystyrene and then prevented aggregation of the 19 R. Tamaki K. Naka and Y. Chujo Polym. Bull. 1997 39 303. organic segment. 20 R. Tamaki K. Naka and Y. Chujo Polym. J. 1998 30 60. 21 S. Brunauer P. H. Emmett and E. Teller J. Am. Chem. Soc. 1938 60 309. References 22 E. P. Barrett L. G. Joyner and P. P. Halenda J. Am. Chem. Soc. 1951 73 373. 1 J.Wen and G. L. Wilkes Chem. Mater. 1996 8 1667. 2 B. M. Novak Adv. Mater. 1993 5 422. Communication 7/08915E; Received 11th December 1997 J. Mater. Chem. 1998 8(5) 1113–1115 1115

ISSN:0959-9428    

DOI:10.1039/a708915e

出版商:RSC    

年代:1998

数据来源: RSC

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J O U R N A L O F C H E M I S T R Y Materials Communication New electron acceptors containing thieno[3,4-b]pyrazine units Kazuharu Suzuki, Masaaki Tomura and Yoshiro Yamashita* Department of Structural Molecular Science, T he Graduate University for Advanced Studies and Institute forMolecular Science,Myodaiji, Okazaki 444-8585, Japan Reaction of 6a with tetracyanoethylene oxide (TCNEO) in refluxing 1,2-dibromoethane aVorded 4a and 5a in 6 and 5% Tetracyano-p-quinodimethane (TCNQ) analogues containing the title heterocyclic units were synthesized, and the interesting yields, respectively.The reaction in the presence of Cu powder gave 4a in 15% yield along with a trace amount of 5a. Reaction crystal structures of the neutral compounds and the chargetransfer complexes with TTF were revealed by X-ray analysis.of 6b with TCNEO without Cu gave 5b in 30% yield along with a trace amount of 4b. The reaction in the presence of Cu gave 4b and 5b in 24 and 6% yields, respectively. Such a reaction of TCNEO with dibromo compounds was used in the synthesis of 1–3. In these cases, the yields were higher than those of 4a,b, but no dimerization products such as 5 were Electron acceptors containing sulfur atoms are of interest as obtained.The low yields of 4 may be attributed to the lability components for organic conductors since the intermolecular of the pyrazine ring to TCNEO.6 The mechanism of formation interactions leading to multi-dimensionality can be expected of 5 is still unclear. to result from interheteroatom contacts.1 With this in mind, The absorption maxima of 5 are red-shifted compared to the TCNQ analogue 1 containing a thiophene unit was prethose of 4 as shown in Table 1.The PM3 calculations7 show pared.2 Furthermore, p-extended compounds 23 and 34 were the smaller HOMO–LUMO gap of 5a compared to those of prepared to decrease on-site Coulombic repulsion. 4a and TCNQ, where the LUMO energies of TCNQ, 4a and Benzothiophene–TCNQ 2 is a weak acceptor due to the fused 5a are -3.06, -2.85 and -2.84 respectively, and the HOMO benzene ring.3 In order to overcome this disadvantage, we energies of TCNQ, 4a and 5a are -9.58, -9.72 and -9.01 eV, have now replaced the benzene ring by electron-withdrawing respectively.It is noteworthy here that the LUMO level pyrazine rings to give 4.We have also prepared new acceptors becomes a little higher with increasing p-extension. Actually 5 which are pyrazine fused derivatives of p-extended acceptor the first reduction potentials of 5 are lower than those of 4 as 3. The new acceptors 4 and 5 are expected to be planar shown in Table 1, indicating that compounds 5 are weaker molecules due to the absence of peri-hydrogen atoms, and the electron acceptors than 4.The same trend is observed in the nitrogen atoms of the pyrazines may be involved in the system of 1 and 3.3 The diVerences between the first and second interheteroatom contacts. reduction potentials (DE) decrease in 5 compared to 4, indicat- The acceptors 4 and 5 were prepared from 5,7-dibromoing the decrease in on-site Coulombic repulsion in 5 due to thieno[3,4-b]pyrazines 6 which were obtained by bromination the extended p-conjugation.with NBS of the corresponding thieno[3,4-b]pyrazines.5 N N S R R NC NC S N N R R CN CN S CN NC NC CN 1 S CN NC NC CN 2 S NC NC 3 S CN CN N N S R R CN NC NC CN N N S R R Br Br 4a R = H 4b R = C6H5 5a R = H 5b R = C6H5 6a R = H 6b R = C6H5 Fig. 1 Crystal structure of 4a (orthorhombic crystal) *E-mail: yoshiro@ims.ac.jp J.Mater. Chem., 1998, 8(5), 1117–1119 1117Table 1 The absorption maxima and reduction potentials of acceptors heteroatom contact was observed. On the other hand, in the monoclinic crystal there exist three crystallographically indeacceptor lmax/nma Ered/Vb DE/V pendent molecules and three kinds of short S,N contacts (3.15, 3.26 and 3.28 A ° ) between the S atoms of the thiophene 4a 403 -0.04, -0.56 0.52 rings and the N atoms of the pyrazine ones, which are shorter 4b 402 -0.10, -0.59 0.49 5a 512 -0.22, -0.47 0.25 than the sum of the van der Waals distance (3.35 A ° ).The net 5b 531 -0.28, -0.52 0.24 atomic charges of 4a calculated by the PM3 method show TCNQ 401 +0.22, -0.35 0.57 that the sulfur and nitrogen atoms are positively and negatively charged, respectively, suggesting an electrostatic interaction aIn CH2Cl2 .b0.1 mol dm-3 Bu4NClO4 in CH2Cl2 , Pt electrode, scan rate 100 mV S-1, V vs. saturated calomel electrode (SCE). leading to the S,N contacts. These interactions result in an interesting molecular network as shown in Fig. 2, where a helical structure is constructed. Reaction of the acceptor 4a with an equal amount of TTF in acetonitrile aVorded two kinds of charge-transfer complexes with TTF [a 152 complex (green plates) and a 352 complex (green needles)] in the same batch, which could be separated on the basis of the diVerence in the crystal form.The bond lengths of the TTF and acceptor molecules in the complexes are comparable to those of neutral ones.8 The nitrile stretching frequencies for the 152 and 352 complexes were observed at 2225.4 and 2224.0 cm-1, respectively, which are almost the same as that for the neutral 4a (2224.2 cm-1).These facts Fig. 3 Crystal structure of (TTF) (4a)2 Fig. 2 Crystal structure of 4a (monoclinic crystal ) The single crystals of 4a were obtained as two crystal forms, i.e. orthorhombic (yellow cubes) and monoclinic forms (yellow needles).† In the orthorhombic crystal (Fig. 1) no short inter- †Crystal data for 4a: C12H2N6S, M=262.25, orthorhombic, space group P212121 , Z=4, a=10.517(5), b=14.683(5), c=7.628(5) A ° , V= 1177(1) A ° 3, Dc=1.479 g cm-3. The final R value was 0.037 for 405 reflections with I>3s(I). 4a: C12H2N6S, M=262.25, monoclinic, space group P21/c, Z=12, a=12.636(2), b=15.086(3), c=18.350(5) A° , b= 93.57(1)°, V=3491(1) A ° 3, Dc=1.497 g cm-3.The final R value was 0.048 for 2508 reflections with I>3s(I). (TTF) (4a)2: C30H8N12S6 , M=728.83, triclinic, space group P19, Z=1, a=7.3720(6), b= 7.5992(5), c=14.3903(7) A ° , a=96.607(5), b=98.741(5), c=99.304(6)°, V=778.22(10 A ° 3, Dc=1.555 g cm-3. The final R value was 0.053 for 2313 reflections with I>3s(I).(TTF) (4a)2: C42H16N12S14 , M= 1137.51, triclinic, space group P19, Z=1, a=7.4174(3), b=11.6811(5), c=13.9003(8) A ° , a=95.824(4), b=93.879(4), c=98.471(4)°, V= 1180.90(10) A ° 3, Dc=1.599 g cm-3. The final R value was 0.056 for 4246 reflections with I>3s(I). Full crystallographic details, excluding structure factors, have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Information for Author, J. Mater. Chem., 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference Fig. 4 Crystal structure of (TTF) (4a)2 number 1145/90. 1118 J. Mater. Chem., 1998, 8(5), 1117–1119suggest that the component molecules are almost non-ionic. References Therefore, the conductivities are low [152 complex; 5×10-9 1 F.Ogura and T. Otsubo, Handbook of Organic Conductive S cm-1 as a compressed pellet, 352 complex; 5×10-4 S cm-1 Molecules and Polymers, ed. H. S. Nalwa, John Wiley & Sons Ltd, as a single crystal (Ea=0.11 eV)]. However, the crystal struc- 1997, vol. 1, ch. 4, pp. 229–248; N. Martý�n, J. L. Segura and tures are interesting as shown in Fig. 3 and 4.† In the 152 C. Seoane, J.Mater. Chem., 1997, 7, 1661. 2 S. Gronowitz and B. Uppstro�m, Acta Chem. Scand., 1974, B28, 981; complex the TTF molecule bridges two acceptor molecules. N. F. Haley, J. Chem. Soc., Chem. Commun., 1979, 1030. To the best of our knowledge, this type of molecular overlap- 3 K. Yui, Y. Aso, T. Otsubo and F. Ogura, J. Chem.Soc., Chem. ping has not been observed in the charge-transfer complexes. Commun., 1987, 1816. In the crystal there are short S,N contacts (3.15 and 3.35 A ° ) 4 D. Lorcy, K. D. Robinson, Y. Okuda, J. L. Atwood and M. P. Cava, between the S atoms of the TTF and the N atoms of the CN J. Chem. Soc., Chem. Commun., 1993, 345. group, which may result in the unique crystal structure. In the 5 F.Outurquin a. Paulmier, Bull. Soc. Chim. Fr. II, 1983, 159. 6 G. Matsubayashi, Y. Sakamoto and T. Tanaka, J. Chem. Soc., 352 complex a mixed stacking is formed and the S,N contacts Perkin T rans. 2, 1985, 947. (3.03 and 3.26 A ° ) are observed between the columns as shown 7 J. J. P. Stewart, J. Comput. Chem., 1989, 10, 209, 221. in Fig. 4. Another TTF molecule is located at the position 8 D. A. Clemente and A. Marzotto, J.Mater. Chem., 1996, 6, 941. orthogonal to the column. These results suggest that TCNQ analogues containing polarizable heterocycles are promising Communication 8/01558I; Received 24th February, 1998 electron acceptors to give organic conductors with multidimensional structures by the interheteroatom contacts. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture, Japan. J. Mater. Chem., 1998, 8(5), 1117–1119 1119

ISSN:0959-9428    

DOI:10.1039/a801558i

出版商:RSC    

年代:1998

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J O U R N A L O F C H E M I S T R Y Materials The synthesis and characterisation of hyperbranched poly(diethyl 3-hydroxyglutarate) W. James Feast,*a Lesley M. Hamilton,a Lois J. Hobsona and Steve P. Rannardb aIRC in Polymer Science and T echnology, University of Durham, South Road, Durham, UK DH1 3L E bCourtaulds Corporate T echnology, PO Box 111, L ockhurst L ane, Coventry, UK CV 6 5RS Hyperbranched aliphatic polyesters derived from the AB2 monomer diethyl 3-hydroxyglutarate in the presence of titanium(IV) butoxide are reported.The oligomeric products were characterised by GPC, NMR spectroscopy and MALDI-TOF mass spectrometry. The degree of branching, molecular weights and the possibility of intramolecular cyclisation reactions have been evaluated. MALDI-TOF mass spectrometry was used to quantify the extent of possible side reactions, particularly those resulting from alkoxide exchange with the catalyst.The field of hyperbranched and dendritic polymers is of interest IR spectra were recorded on a Perkin-Elmer 1600 series FTIR. 1H and 13C NMR spectra were recorded using a Varian chiefly because of the unusual properties associated with these macromolecular architectures.1–3 These materials, whether per- 400 MHz spectrometer. DSC measurements were recorded using a Perkin-Elmer DSC7, at a scanning rate of 10 °C min-1.fectly regular monodisperse dendrimers,4,5 or the less well defined hyperbranched structures,6 possess a large number of GPC was performed using a Waters system with a diVerential refractometer detector and three PL-gel columns (exclusion branches and hence numerous end groups.Consequently, physical properties which contrast with those of conventional limits 100, 103 and 105 A ° ) with CHCl3 as the eluent. Columns were calibrated using polystyrene standards (Polymer Labs). linear polymers are to be expected. Indeed, the recent literature includes a number of articles contrasting the physical properties Solution viscosity measurements were carried out in chloroform, at 25 °C over a range of dilutions, using a Laude/Schott of linear, dendritic and hyperbranched polymers constructed from analogous units.7,8 From these and related studies9 it can automated system.MALDI-TOF mass spectra were recorded using the Kratos Kompact MALDI IV instrument (nitrogen be concluded that thermal properties are largely independent of architecture but extremely sensitive to both the number and laser 337 nm) operated in both linear and reflection mode to generate positive ion spectra.The MALDI-TOF spectra nature of the end groups; whilst solubility, viscosity and reactivity are heavily influenced by topology. reported were calibrated against a range of external standards.Samples were prepared for analysis by MALDI-TOF MS by Since Kim and Webster reported the first synthetic hyperbranched polymer,10 work in this field has shown that materials first laying down the matrix solution, 0.5 ml of a 10-1 mol dm-3 solution of 2,5-dihydroxybenzoic acid in water–acetonit- which retain many of the structural features and physical properties of monodisperse dendrimers can be prepared at a rile (40560), followed by 0.5 ml of a 10-3 mol dm-3 polymer solution in acetone.lower cost via the single step polymerisation of an ABx (x>1) monomer. For example, the intrinsic viscosity–molecular weight relationship, which has been shown to pass through a Polymerisation procedures maximum for dendrimers11 and described as one of their The general procedures adopted are illustrated by specific characteristic features, has also been established for a core examples.terminated hyperbranched polymer with a high degree of branching.12 Although a number of diVerent routes to hyperbranched Method (a). Titanium(IV) butoxide (0.1 g, 0.29 mmol) was polymers have been reported, including the use of self-condens- added to a glass reaction vessel fitted with a mechanical stirrer ing vinyl polymerisation13 (SCVP) and atom transfer radical and containing diethyl 3-hydroxyglutarate (2.0 g, 9.80 mmol).polymerisation14 (ATRP) techniques, simple poly-condensation The reactor was immersed in a preheated oil bath, held at reactions are the most common. Following Kricheldorf ’s syn- 80 °C, and the temperature raised to 100–125 °C at a rate of thesis of hyperbranched polyesters, from mixtures of 3-(tri- ca. 3 °C min-1. The reaction vessel was maintained at this methylsiloxy)benzoyl chloride and 3,5-bis(trimethyl- temperature for 3.5–6.5 h with stirring, a vacuum (10 mmHg) siloxy)benzoyl chloride,15 a series of publications have being applied during the final 30 min. The product, a viscous addressed key analytical problems; namely, calculation of yellow liquid, was dissolved in chloroform (300 ml) and washed degree of branching,16,17 the possibility of intramolecular cyclis- with water (3×200 ml) to remove the catalyst.The organic ation18–20 and the inherent problems associated with molecular fraction was separated and concentrated under reduced pressweight determination for non-linear structures.ure to yield the hyperbranched polymeric product as a paleyellow oil. Experimental section Method (b). Titanium(IV) butoxide (50 mg, 0.147 mmol, Materials and methods 1.0 wt%) was added to a glass reaction vessel fitted with a All organic reagents were purchased from the Aldrich Chemical mechanical stirrer and containing diethyl 3-hydroxyglutarate Company and used as received without further purification.(5.0 g, 24.48 mmol). The reactor was heated to 170 °C at a rate of 10 °C min-1 and maintained at this temperature for 2.0–4.0 h with stirring. After cooling under nitrogen, the hyperbranched * E-mail: w.j.feast@durham.ac.uk J. Mater. Chem., 1998, 8(5), 1121–1125 1121polymer was isolated from the reaction flask and characterised without further purification.Results and Discussion As part of an ongoing research programme into the preparation of hyperbranched polyesters, we report here the synthesis of a series of aliphatic hyperbranched polyesters from the commercially available AB2 monomer, diethyl 3-hydroxyglutarate, via a titanium(IV) butoxide catalysed step-growth condensation process.The synthesis, polymerisation and characterisation of a series of dimethyl 5-(hydroxyalkoxy)isophthalates has previously been described20 but this new system represents one of the few examples of completely aliphatic hyperbranched polyesters, the only prior examples being described by the group of Hult.21 Diethyl 3-hydroxyglutarate was polymerised in the bulk at elevated temperatures and a systematic variation of catalyst concentration, reaction time and temperature was undertaken in an attempt to optimise the polymerisation.Initial reactions were carried out using method (a) (see Experimental section) and it was observed that although polyesterifications are usually performed in the presence of 0.05–0.5 wt% titanium alkoxide catalysts,22 for this system studies showed that when the reaction time and temperature were kept constant at 270 min and 100 °C respectively, 5.0 wt% of catalyst relative to the monomer appeared to be optimum.23 However, even at such high catalyst concentrations, polymerisations failed to give high molecular weight products as have been observed for other AB2 hyperbranched polyesters studied.20 Other catalysts, including the manganese acetate–antimony trioxide system used in the synthesis of PET, were investigated but no substantial molecular weight improvements were observed.It is also noteworthy that after prolonged heating (210 °C, 4 h) in the absence of a catalyst, less than 2% polymerisation and Fig. 1 1H NMR spectroscopy data: i ) diethyl 3-hydroxyglutarate no degradation products were observed.While in the presence monomer, ii) poly(diethyl 3-hydroxyglutarate) prepared by method (b) of 2–5 wt% of titanium butoxide catalyst variation of reaction using 0.5 wt% titanium butoxide catalyst at 170 °C, 4.0 h, Mn~1400 temperature across the range 100–170 °C also produced no (1H NMR data), iii) poly(diethyl 3-hydroxyglutarate) prepared by significant molecular weight improvement.This was an method (a) using 5.0 wt% titanium butoxide catalyst at 100 °C, 3.5 h, unexpected result which merited investigation and Mn~800 (1H NMR data) explanation. the focal point and the terminal groups, as this would result Structural characterisation in an overestimation of Mn by such end group counting techniques. For these polyesters such calculations were carried The materials prepared were characterised by a combination of analytical techniques, including NMR and IR spectroscopy, out on the basis of the integrated intensities of the signal at 4.44 ppm ( f ), assigned to the CHMOH of the focal point and DSC, GPC and MALDI-TOF mass spectrometry.Using 1H (Fig. 1) and 13C (Fig. 2) NMR spectroscopy it that of the CHMO signal at 5.51 ppm (g) assigned to the combined linear, terminal and branched sub-units.An ana- could be shown that polymerisation occurred through reaction of the alcohol (A group) and ethyl ester (B group) logous pair of signals are those due to the CH2 at 2.54 (d), the focus, and 2.69 (e) ppm, the combined linear, terminal and functionalities of the AB2 monomer. The 1H NMR spectrum of the polymer shows a major triplet at 1.26 ppm (a) due to branched sub-units.In the 13C NMR spectrum the signal observed at 14.14 ppm the CH3 hydrogens of the terminal ester units, whilst the multiplet at 4.15 ppm (b) is due to the OCH2 hydrogens of (a) is assigned to the CH3 of the terminal esters, whilst the signal at 60.82 ppm (b) arises from the OCH2 of the ethyl the ethyl groups.The minor multiplet at 2.54 ppm (d) coincides in chemical shift with the CH2 doublet of the groups. The minor peak at 40.61 ppm (d) is due to the CH2 of the focal units whilst the signal at 38.23 ppm (e) is due to the monomer, and can therefore be assigned to the CH2 hydrogens adjacent to the polymer foci whereas the major signal at CH2 of the remaining linear, terminal and branched sub-units; in theory, this latter signal could be deconvoluted to determine 2.69 ppm (e) is assigned to the analogous CH2 hydrogens in the branched, linear or terminal sub-units of the polymer.the degree of branching, however, the peak at 67.19 ppm ( f ), due to the combined CHMOM signals for linear, branched The minor multiplet at 4.44 ppm ( f ) is due to the CHMOH hydrogen of the focus, whilst the signal at 5.51 ppm (g) is due and terminal units was better resolved making the assignment and relative intensity measurement of the constituent signals to CHMOMCO of a methine hydrogen in the branched, linear or terminal sub-units of the polymer.simple and straightforward. The CHMOH of the focus is distinct and readily observable at 64.73 ppm ( f ).The carbonyl As, in the ideal case considered by Flory,24 every polymer wedge has a single A group at its focus, 1H NMR spectroscopy region of the spectrum (c) shows a number of peaks, consistent with several carbonyl environments, as expected. also allows calculation of an idealised number average degree of polymerisation, extent of reaction and number average As described, quantitative 13C NMR spectroscopy provides a method to calculate the degree of branching (DB), a param- molecular weight.These calculations rely upon the premise that there are no intramolecular cyclisation reactions between eter that has received much attention of late; Frey’s re- 1122 J. Mater. Chem., 1998, 8(5), 1121–1125Thus, it is expected that the polymerisation process will give rise to a series of peaks in the mass spectrum which may be represented as: Y=nM-(n-1)EtOH+x Y=n(M-EtOH)+46+23 therefore n= Y-69 158 Where Y is the observed peak mass from the spectrum, n is the number of monomer units incorporated,Mis the monomer molecular mass (204), 46 is the molecular mass of the eliminated ethanol and x is the molecular mass of the associated cation, sodium in the example above.Analysis of the MALDI-TOF spectrum obtained from a sample of poly(diethyl 3-hydroxyglutarate) prepared by method (b), using 0.5 wt% titanium butoxide catalyst, revealed a main series of peaks corresponding to the predicted oligomers detected as the sodium cation attached species, Fig. 3. Peaks corresponding to DP 2–18 were well resolved and therefore easily assigned.The minor series, located at major series peak masses plus 16 amu, can be assigned as the corresponding potassium cation attached species. When larger quantities of the titanium butoxide catalyst were used, namely 2.5, 5, 10 and 25 wt% [method (a)], additional signals were present in both the 1H and 13C NMR spectra. The minor multiplets arising in the 1H NMR spectrum (Fig. 1 iii) at 0.93 (h), 1.36 (i ), and 1.60 ppm ( j) and represented in the 13C NMR spectrum, (Fig. 2 iii ) at 13.68 (h), 19.06 (i ) and 30.51 ppm ( j), can be assigned to the methyl and two methylene units of a butoxide residue arising from exchange with the catalyst. Analysis of these samples by MALDI-TOF MS confirms the suspected ethoxide–butoxide exchange. The Fig. 2 13C NMR spectroscopy data: i ) diethyl 3-hydroxyglutarate spectra reveal additional discrete series of peaks associated monomer, ii) poly(diethyl 3-hydroxyglutarate) prepared by method (b) with each oligomer, corresponding to exchange of one or using 0.5 wt% titanium butoxide catalyst at 170 °C, 4.0 h, Mn~1400 multiple ester ethoxides by butoxide groups from the catalyst; (1H NMR), iii) poly(diethyl 3-hydroxyglutarate) prepared by method Fig. 4 shows a typical example. (a) using 5.0 wt% titanium butoxide catalyst at 100 °C, 3.5 h, Mn=800 This is shown more clearly in the expansion of the spectrum (1H NMR data). (The signal observed at 45 ppm has been confirmed as a machine artefact related to that at ~150 ppm.) between m/z 1480 and 1750, Fig. 5, where ethoxide–butoxide exchange at DP 9 and 10 is illustrated.These subsequent series can be described by the following equation, where a represents the number of butoxide groups evaluation of the definition of DB17 receiving broad acceptance exchanged per molecule. in the field. Calculation of DB for the polyesters prepared in Y=nM-(n-1)EtOH+x+(C2H4)a this study gives values between 0.52 and 0.57 (±0.05), consistent with a statistically branched structure as proposed by From the MALDI-TOF spectrum reproduced as Fig. 4, we Flory for an AB2 system in the absence of cyclisation. observe that the relative proportion and number of species During a typical step growth condensation polymerisation detected showing butoxide exchange increases as we go to one molecule is eliminated at each step; the first step in the higher molecular weight.This is expected because butoxide polymerisation of diethyl 3-hydroxyglutarate is shown in exchange can only occur at the ester end groups and, by the Scheme 1. very nature of an AB2 polymerisation, at higher DP there are more end groups per molecule and therefore it is statistically more likely that butoxide exchange will occur. The MALDIFig. 3 MALDI-TOF spectrum of poly(diethyl 3-hydroxyglutarate) prepared by method (b), 170 °C, 4 h, using 0.5 wt% titanium butox- Scheme 1 First step in the step growth polymerisation of diethyl 3- hydroxyglutarate ide catalyst J. Mater. Chem., 1998, 8(5), 1121–1125 1123niques provide any evidence to suggest the occurrence of side reactions, namely dehydration and intramolecular cyclisation between the focal OH group and the terminal ethyl ester groups. These would be the most likely reactions to compete with the polyesterification of diethyl 3-hydroxyglutarate, both of which would severely hinder polymerisation by removing the reactive hydroxy A group from the reaction.However, neither of these processes, distinguishable by MALDI-TOF MS through the observation of peaks at 18 and 46 amu less than the main oligomer peaks, were found to occur in these systems under any conditions.The failure to detect evidence for cyclic structures in the polymerisation product of diethyl 3-hydroxyglutarate is consistent with the results of Hawker and Chu for the polymerisation of 4,4-bis(4¾-hydroxyphenyl) pentanoate ester19 but in contrast to the work of Percec18 and Fig. 4 MALDI-TOF spectrum of poly(diethyl 3-hydroxyglutarate) Feast20 where cyclisation is shown to dominate in the polyesters prepared using 5 wt% catalyst, method (a), 100 °C, 3.5 h studied. It can therefore be concluded that cyclisation is extremely system specific, even within the single class of hyperbranched polymers considered. It is possible that the probability of intramolecular cyclisation is related to the conformational mobility of the particular system.Molecular weight determination In recent years, problems associated with molecular weight determination for non-linear polymers with a broad distribution of mass and structure have been highlighted. It is now widely accepted that there is no universally applicable ideal technique for such characterisations. Although MALDI-TOF MS allows some valuable assignment of the structural subunits of the polymer, which can provide useful insights into the mechanistic details of the polymerisation process and side reaction (vide supra), it is well documented that the technique fails to provide a realistic interpretation of either molecular Fig. 5 Expansion of MALDI-TOF spectrum of poly(diethyl glutarate), weight or molecular weight distribution for materials with a reproduced as Fig. 4, to illustrate ethoxide–butoxide exchange wide polydispersity,25,26 a classification which includes the hyperbranched polymers.27 The spectrum, reproduced as Fig. 3, TOF spectra reproduced as Fig. 3–5 were generated using the is of a low molecular weight sample of the polymer detected Kratos Kompact MALDI IV spectrometer operated in linear detection mode, to generate positive ion spectra.The same Table 2 Characteristics of oligomers produced from 4.5 h reactions at 100 °C with varying amounts of catalyst, using method (a) information was obtained using the instrument in reflection mode. initial amount DBc From the NMR studies undertaken it is possible to calculate catalyst (wt%) Mn a BuOb (%) (±0.05) percentage butoxide exchange as a function of both temperature and the initial wt% of titanium butoxide catalyst added 2.5 820 5.1 0.44 to the polymerisation mixture. 5 2700 6.8 0.54 10 1800 15.1 0.52 The results, Table 1, show a general trend towards increasing 25 1100 51.9 0.53 extent of butoxide exchange with temperature across the limited range studied. On inspection of the 1H NMR spectra aAs determined using GPC with CHCl3 as eluent and linear of the polymers produced in the presence of 2.5, 5, 10 and polystyrene standards.bmol% of butyl ester groups. cAs determined 25 wt% catalyst, it was clear that the concentration of butoxide via 13C NMR spectroscopy. groups present in the polymer increased as the amount of catalyst used increased, Table 2.It was possible to determine Table 3 Molecular weights of oligomers measured by GPC (Mn, Mw the amount of butoxide exchange present in the polymer from and PDI) and 1H NMR spectroscopy (Mn) the relative integrated intensities of the ethyl triplet at 1.26 ppm GPC data (CDCl3) 1H NMR data (CDCl3) (a) and the butoxide CH3 triplet at 0.93 ppm (h) since these signals are reasonably well resolved (Fig. 1 iii ). Mn Mw PDI Mn a Mn b Neither NMR spectroscopy nor MALDI-TOF MS tech- 3200 5000 1.58 2000 2100 2700 3800 1.38 2400 2600 Table 1 Characteristics of oligomers produced at 5 wt% catalyst concentration in 4.5 h reactions at diVerent temperatures, using method (a) 2200 3200 1.45 1500 1800 2000 2700 1.35 1200 1600 2000 3100 1.52 1700 2100 DBc T /°C Mn a BuOb (%) (±0.05) 1800 2400 1.33 870 990 1500 1900 1.24 760 850 1500 1900 1.28 970 1200 100 2700 6.8 0.54 115 2200 7.3 0.57 1100 1200 1.13 470 470 1100 1400 1.31 630 680 125 2000 7.9 0.57 820 926 1.13 420 440 aAs determined using GPC with CHCl3 as eluent and linear polystyrene standards.bmol% of butyl ester groups. cAs determined aCalculated from the aliphatic CH2 region of the 1H NMR spectrum. bCalculated from the CHOM region of the 1H NMR spectrum.via 13C NMR spectroscopy. 1124 J. Mater. Chem., 1998, 8(5), 1121–1125as its sodium adduct. It has been proposed that by selective may account for the limited molecular weights attainable as compared with the superficially similar system studied by Hult. cationisation polymer spectra can be biased towards detecting the higher molecular weight species in the distribution, specifi- We acknowledge the support of the EPSRC for the provision cally, use of caesium and rubidium has been reported.28 of facilities through the IRC Grant and a Maintenance Grant However in-depth analysis of these polyesters by MALDIto L.M.H.; we thank Courtaulds Plc for financial support TOF MS, using the series of counter ions Li, Na, K, Rb and (CASE award to L.M.H.) and EPSRC for a ROPA grant Cs, revealed no really significant change in the intensity (L.J.H.).The authors are also indebted to Dr A.M. Kenwright distribution across the molecular weight range observed. and Mrs J. Say for their assistance with the NMR studies. Significantly, use of sodium as the counter ion gave the simplest spectrum over the widest range, as in the case of larger ions incomplete cationisation was observed over a range of solution References concentrations.In the light of these observations and rec- 1 D. A. Tomalia, D. M. Hedstrand and L. R. Wilson, Encyclopaedia ent literature observations on the uncertainty of molecular of Polymer Science and Engineering, Wiley, Chichester, 1990, 2nd weight measurement by this technique, we limited our use of edn., Index vol., p.46.MALDI-TOF MS to structural analysis in this study. 2 J. M. J. Fre� chet and C. J. Hawker, Comprehensive Polymer Science, Although the problems associated with determining molecu- 2nd suppl., ed. S. L. Agarawal and S. Russo, Pergamon, Oxford, 1996, ch. 3. lar weights of non-linear polymers by GPC are recognised, 3 L.J. Hobson and R. M. Harrison, Curr. Opin. Solid State Mater. Mn, Mw and polydispersity indices are quoted for this system Chem., 1997, 2(6), 683. in terms of polystyrene equivalents, Table 3. These results are 4 C. J. Hawker and J. M. J. Fre� chet, J. Am. Chem. Soc., 1990, 112, supported by comparison with the Mn values calculated from 7638.the corresponding 1H NMR spectra by end group counting. 5 E. M. M. de Brabander-van den berg, A. Nijenhuis, M. Mure, Some reliability can be associated with these latter figures as J. Keulen, R. Reintjens, F. Vandenbooren, B. Bosman, R. Denaat, T. Frijins, S. V. D. Wal, M. Castelijns, J. Put and E. W. Meijer, MALDI-TOF MS has unequivocally shown that intramolecu- Macromol.Symp., 1994, 77, 51. lar cyclisation reactions do not occur for this system; in general 6 A. Hult and E. Malmstro�m, J. M. S. -Rev. Macromol. Chem. Phys. it appears that the GPC analysis errs on the side of optimism. C, 1997, 37, 555. 7 C. J. Hawker and J. M. J. Fre� chet, Am. Chem. Soc. Symp., 1996, 624, 132. Physical properties 8 C. J. Hawker, E. Malmstro�m, C. W. Frank, J.P. Kampf, C. Mio and J. Prausnitz, Proc. Am. Chem. Soc., Div. Polym. Mater.: Sci. The products of these polymerisations were oils; DSC experi- Eng., L as Vegas, 1997, 77, 61. ments revealed Tg values in the range-35 to-65 °C. Although 9 E. Malmstro�m, A. Hult, U. W. Gedde, F. Liu and R. H. Boyd, Polymer, 1997, 38(19), 4873. it is common practise to analyse these data in terms of observed 10 Y.H. Kim and O. W.Webster, J. Am. Chem. Soc., 1980, 112, 4592. Tg as a function of molecular weight, in this case the extent of 11 H. Mourey, S. R. Turner, M. Rubinstein, J. M. J. Fre�chet, reaction is too low and the molecular weight range too narrow C. J. Hawker and K. L.Wooley, Macromolecules, 1992, 25, 2401. to extract a meaningful relationship. Similarly, useful con- 12 L.J. Hobson and W. J. Feast, Chem. Commun., 1997, 2067. clusions could not be drawn from intrinsic viscosity (g) 13 J. M. J. Fre� chet, M. Hemni, I. Gitsov, S. Aoshima, M. Leduc and R. B. Grubbs, Science, 1995, 269, 1080. measurements; g values for the polymers produced were in the 14 S. G. Gaynor, S. Edelman and K. Matyjaszewski, Macromolecules, range 1.00–5.00 cm3 g-1. 1996, 29, 1079. 15 H. R. Kricheldorf, Q-Z. Zhang and G. Schwarz, Polymer, 1982, 23, 1821. Conclusions 16 C. J. Hawker, R. Lee and J. M. J. Fre� chet, J. Am. C13, 4583. In summary, although AB2 hyperbranched polyesters have 17 D. Holter and H. Frey, Acta Polymerica, 1997, 48, 30. been synthesised from diethyl 3-hydroxyglutarate in the pres- 18 V. Percec, P. Chu and M. Kawasumi, Macromolecules, 1994, 27, ence of a titanium(IV) butoxide catalyst, the system fails to 4441. 19 F. Chu, C. J. Hawker, P. J. Pomery and D. J. T. Hill, J. Poly. Sci. attain the high molecular weights reported for other hyper- Part A, Polym. Chem., 1997, 35, 1627. branched polyesters. The observation that the monomer fails 20 W. J. Feast, A. J. Keeney, A. M. Kenwright and D. Parker, Chem.to react at elevated temperatures leads us to believe that, Commun., 1997, 1749. despite the similarity of the polymeric backbone to that of the 21 E. Malmstro�m and A. Hult,Macromolecules, 1995, 28, 1698. systems described by Hult et al., polymerisation will remain 22 Comprehensive Polymer Science, vol. 5: Step Polymerization, ed. unfavourable whatever reaction conditions are employed. G. C. Eastmond, A. Ledwith, A. Russo and P. Sigwalt, Pergamon Oxford, 1989, ch. 17. However, the oligomeric materials produced were amenable 23 L. M. Hamilton, PhD Thesis, University of Durham, 1996. to fairly detailed analysis, which provided insights into this 24 P. J. Flory, J. Am. Chem. Soc., 1952, 74, 2718. polyesterification reaction. In particular MALDI-TOF MS has 25 K. Martin, J. Spickermann, H. J. Rader and K. Mullen, Rapid been shown to provide useful structural analysis of these Commun.Mass Spectrom., 1996, 10, 1471. relatively low molecular weight polyesters, revealing the 26 C. Jackson, B. Larson and C. McEwan, Anal. Chem., 1996, 68, 1303. absence of cyclic and dehydration by-products and allowing 27 L. J. Hobson, A. M. Kenwright and W. J. Feast, Chem. Commun., the identification of alkoxide exchange reactions during polym- 1997, 1877. erisation. This exchange reaction between alkoxide ligands on 28 A. T. Jackson, H. T. Yates, W. A. MacDonald, J. H. Scrivens, the titanium catalyst and the alkoxide fragment of the terminal G. Critchley, J. Brown, M. J. Deery, K. R. Jennings and ester units in the hyperbranched polyester is, in this particular C. Brookes, J. Am. Soc. Mass Spectrom., 1997, 8, 132. system, competitive with polymerisation. This feature, along with the steric shielding of the secondary alcohol focal unit, Paper 8/00538I; Received 20th January, 1998 J. Mater. Chem., 1998, 8(5), 1121–1125 11

ISSN:0959-9428    

DOI:10.1039/a800538i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Thermal stability of styrene grafted and sulfonated proton conducting membranes based on poly(vinylidene fluoride) Sami Hietala,a Mihkel Koel,b Eivind Skou,c Matti Elomaa,a and Franciska Sundholm*a aL aboratory of Polymer Chemistry, University of Helsinki, PB 55, FIN-00014 Helsinki, Finland bInstitute of Chemistry, Estonian Academy of Science, Akadeemia tee 15, EE-0026 T allinn, Estonia cDepartment of Chemistry, University of Odense, DK-2530 Odense M, Denmark The thermal stability of styrene grafted and sulfonated poly(vinylidene fluoride), PVDF-g-PSSA, proton conducting membranes has been studied using thermal gravimetric analysis in combination with mass spectrometry and thermochromatography.The matrix polymer, PVDF, and the non-sulfonated counterpart, PVDF-g-PS, were studied as reference materials. It was found that the degradation of the PVDF-g-PS membrane proceeds in two steps starting at ca. 340 °C with the evolution of degradation products typical of polystyrene. The PVDF-g-PSSA membranes are stable to around 270 °C even in a strongly oxidising atmosphere. The degradation starts with the simultaneous evolution of water and sulfur dioxide.The polystyrene grafts start decomposing at 340 oC in the PVDF-g-PSSA membranes. Thus the membranes are suitable for tests in electrochemical applications at elevated temperatures. Polymeric separator materials for use in electrochemical cells in the temperature range 20–650 °C in an inert gas atmosphere, and fuel cells have to meet a combination of conditions: high and in oxygen atmosphere of the thermal degradation of ion conductivity, excellent electrochemical and chemical long PVDF based membranes. In addition the influence of crosslinkterm compatibility with the reducing and oxidative reagents ing the styrene grafts with two diVerent crosslinkers, diviat the electrocatalysts, reasonable mechanical stability includ- nylbenzene, DVB, and bis(vinylphenyl)ethane, BVPE, on the ing a defined swelling behaviour in the presence of water are thermal properties of the membranes was studied. The evolved among the most important requirements.1 Thermal stability is gaseous products were analysed by mass spectrometry and of crucial importance for membrane materials.Polyanskii and with thermochromatography to correlate mass losses at diVer- Tulupov2 have published a detailed review on the thermal ent temperatures with the formation of low molar mass degraproperties of polymer electrolytes.dation products related to the structure of the membranes. In the development of new polymer electrolyte materials Nafion 117 membranes were used as reference materials in the proton exchange membranes have been made by radiation- thermal degradation experiments.induced graft polymerisation.3–9 The process involves the polymerisation of a monomer in the presence of a preformed polymer film. The preparation of cation exchange membranes Experimental by the simultaneous radiation grafting of styrene monomer onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) Materials films has been reported by Rouilly et al.10 The grafted films The matrix material was PVDF film supplied by Goodfellow were sulfonated to introduce the ion exchange groups.A three (Cambridge) as melt processed 80 mm sheets. Pre-irradiated step pattern in the thermal degradation of these membranes films (electron beam under nitrogen gas, 100 kGy) were grafted was attributed to dehydration, desulfonation and degradation in styrene (Fluka) solution and subsequently sulfonated with of the FEP backbone.11 A detailed study of the thermal chlorosulfonic acid (Merck) in a three step procedure which properties of FEP based membranes has been done with has been described in detail previously.13,14 Membranes with thermal gravimetric analysis11 and with a combination of degrees of grafting, d.o.g., of 18, 32, 48, 60, 73 and 100%, thermogravimetry, FT IR and mass spectrometry.12 respectively, (PVDF-g-PS membranes), were fully sulfonated The preparation of proton exchange membranes by pre- (PVDF-g-PSSA membranes).Part of the membranes were irradiation induced styrene grafting onto poly(vinylidene flucrosslinked in the grafting step with either DVB (Fluka, oride) (PVDF) films followed by sulfonation has been reported isomeric mixture in ethylvinylbenzene) or BVPE (isomeric previously.13,14 It was found that the grafting occurs mainly in mixture) as has been previously described.16 the amorphous regions of the PVDF in which polystyrene The original PVDF film and the irradiated film were meas- domains are formed.14 In the sulfonation sulfonic acid groups ured without further treatment.The PVDF-g-PS samples were are introduced in the polystyrene chains thus forming hydromeasured as received, after drying in vacuo at 80 °C for 20 h, philic domains in the hydrophobic matrix polymer. The crystaland after a second drying period in vacuo at 120 °C for 20 h. linity of the matrix polymer changes only slightly during the The PVDF-g-PSSA membranes were treated for 1 h in boiling grafting and sulfonation.14 Good ion conductivities were found water and dried in vacuo at 80 °C for 20 h before measurement.for membranes based on PVDF.15 High conductivity, although The Nafion 117 membrane was boiled for 0.5 h in 3% aqueous an important factor, is not suYcient to make the polymer H2O2, 0.5 h in water, 0.5 h in 1 M aqueous H2SO4, 0.5 h in electrolyte suitable for demanding applications, such as fuel water and finally dried in vacuo at 80 °C for 20 h before cells.The clear identification of the degradation products measurement. The samples were stored in plastic bags in formed at various temperatures oVers the possibility of underambient conditions. 5–10 mg pieces of membrane were cut for standing the mechanisms of the thermal degradation of the membranes. This paper contains the results of an investigation the measurements. J. Mater. Chem., 1998, 8(5), 1127–1132 1127Measurements The thermal analyses were done with a Setaram 92-12 thermobalance connected to a Varian CH 7A mass spectrometer through a flow meter and a heated tube, approximately 40 cm in length.The samples were typically 4–6 mg. The inlet to the mass spectrometer was through a membrane inlet using a silicone rubber membrane, SR 606 by Radiometer Copenhagen, thickness 25 mm. Excess gases were directed out through holes in the inlet. HO3S F F F F F F F SO3H m n y x Tentative structure of the styrene grafted and sulfonated poly(vinylid- The samples were weighed on the thermobalance without ene fluoride), PVDF-g-PSSA any gas flow.Before the measurement the furnace was purged with a nitrogen flow of 150 ml min-1 (high flow) for 10 min. The gas flow was then changed to 25 ml min-1 (low flow) for The supermolecular structure of the system forms a very 1 min to stabilise the balance, after which the balance was complex system of crystalline and amorphous domains of tared.For measurements in an O2–N2 atmosphere this stabilis- PVDF, in which the sulfonated polystyrene grafts form hydroation was made accordingly with a 50550 mixture flowing at philic domains within the amorphous parts of the hydrophobic 50 ml min-1. The samples were heated from 20–650 °C with a PVDF.14 It was found that the ion conductivity at 20 °C in heating rate of 10 K min-1 under a nitrogen flow of the PVDF-g-PSSA membranes is of the same order of magni- 25 ml min-1, and the thermograms were recorded.The samples tude as measured for Nafion 117. The ion conductivities were were kept at 650 °C for 10 min, then the residue was burned measured with impedance spectroscopy. The values varied by flowing the O2–N2 mixture through for 2 min.During with d.o.g. and were typically around 100 mS cm-1.15 The measurements in an O2–N2 atmosphere the heating procedure hydrogen and helium gas permeabilities through the mem- was the same, but the gas atmosphere was kept constant. The branes were measured with a mass spectrometric leak detector, results were corrected by subtracting a baseline measurement and gas permeabilities equal to or lower than those for Nafion with an empty crucible. 117 were found.20 The detailed structural analysis of the Mass spectra were recorded every 60 s. The scanning was PVDF-g-PSSA membranes is still in progress in our started 5 min before the gas purging and the actual measurelaboratory. ment to check the mass spectrometer stability and record the The thermal degradation of the matrix polymer PVDF, the intensity of atmospheric air for comparison.The mass specgrafted PVDF-g-PS membranes, and the sulfonated PVDF-g- trometer responded quickly to weight losses and changes in PSSA membranes were studied in a nitrogen atmosphere, and the gas composition. However, due to the large volume of the in a nitrogen–oxygen (15:1) atmosphere.oven and condensation of high molar mass products in the It was found that the PVDF is very stable to around 420 °C tubing the decay of some peaks was slow and occasionally in a nitrogen atmosphere, and to around 410 °C in the presence produced a constant background for several mass peaks. The of oxygen which is to be expected for a fluorinated polymer accuracy of the mass data is one mass unit for masses below backbone.The thermal stability is slightly lower than for fully m/z 100, and two units for masses over m/z 100. The accuracy fluorinated vinyl polymers like FEP in which the degradation is adequate for this kind of mass trace analysis. starts at around 450 °C in a helium atmosphere, according to The thermochromatographic (ThGC)17,18 analysis was done a report by Gupta et al.12 In another report by the same group with a gas chromatograph (Carlo Erba 4200) equipped with a the ungrafted FEP was shown to be stable up to 490 °C in a pyrolysis oven, a sampling valve, a capillary column [NSWnitrogen atmosphere.21 The degradation products of FEP were Plot (HNU Nordion), inner diameter 0.53 mm and length determined using mass spectrometry.The main products in 25 m] and a thermal conductivity detector (Model 430). The the decomposition correspond to the splitting of fragments of pyrolysis oven was a quartz tube with an inner diameter of the main monomer, C2F4, and the comonomer, C3F6.12 In 4 mm and length of 250 mm having a centrally located 25 mm PVDF, the degradation caused formation of fragments corre- long quartz sample vessel.The sample size was around 5 mg. sponding to dimers, monomers and oligomers of vinylidene The samples were conditioned to constant mass in a constant fluoride (m/z=129, 130, 63, 64, 65 and larger fragments). Some relative humidity of 75% over a saturated aqueous solution of typical mass traces from degradation products of PVDF are sodium nitrate at room temperature before the analysis.The shown in Fig. 1. The irradiated PVDF film (radiation dose heater for the pyrolysis consisted of a copper block with 100 kGy) showed the same fragmentation pattern as the resistor heating elements surrounding the quartz tube. untreated film, but the onset of the degradation was about Temperature calibration was achieved by placing a thermo- 5 °C lower. When heated in an inert atmosphere only a charred couple in the sample vessel in place of a sample.The heating residue of almost 30% was left of the PVDF at 650 oC. In the ramp could be repeated with a measured precision of ±1 °C. presence of oxygen the whole sample was burned to gaseous The sampling valve consisted of a Deans’ type valve19 inside products at around 530 °C, see Fig. 2. the column oven run by a three way solenoid valve outside Thermograms measured in an inert atmosphere of an the oven. A microcomputer was used to control both the ungrafted and several grafted PVDF-g-PS films are shown in heating of the pyrolysis oven and the timed sampling of Fig. 3. The grafted films show mainly a two step degradation. the evolved gases in the pyrolyser tube head space. The sample The first degradation occurs at 390 °C in the non-crosslinked was heated from 70–400 °C with a heating rate of 5 K min-1.grafted films. In the crosslinked films the first degradation step Helium gas (99.99%) was used to purge the pyrolyser at a rate occurs at 10–15 °C lower temperatures than in the non- of 10 ml min-1 and through the column at a rate of 4 ml min-1.crosslinked films. Thermograms of samples crosslinked with An injection period of 1 s was repeated at 110 s intervals. The 5% BVPE and 5% DVB, respectively, are shown in Fig. 4. design of the device permitted eYcient, rapid separation of low The degradation in the PVDF-g-PS film crosslinked with DVB boiling point components of the pyrolysate at a constant starts at the lowest temperature.The second degradation step column-oven temperaure of 70 °C. occurs in all these samples at around 420 °C and corresponds to the degradation of PVDF. This is clearly illustrated in Fig. 5 Results and Discussion which shows the mass trace for typical degradation products from polystyrene (m/z 103, 104) and from PVDF (m/z 130) as The tentative chemical structure of the PVDF-g-PSSA membranes is shown: a function of temperature, recorded during the thermal analysis. 1128 J. Mater. Chem., 1998, 8(5), 1127–1132Fig. 4 The thermal degradation of non-crosslinked PVDF-g-PS (—), Fig. 1 The thermal degradation of poly(vinylidene fluoride), PVDF. Mass trace of the evolution of fragments with m/z 63–65 (%), 80 (o), and of PVDF-g-PS crosslinked with 5% BVPE (- - -) and with 5% DVB (....) in a nitrogen atmosphere.The d.o.g. is 32%, 30% and 31%, 115 (+) and 130 (×). respectively. Fig. 2 The thermal degradation of PVDF in a nitrogen atmosphere Fig. 5 The thermal degradation of PVDF-g-PS crosslinked with 5% (—) and in an O2–N2 atmosphere (- - -), and of styrene grafted PVDF, DVB. Mass trace of the evolution of fragments with m/z 104–105 (%) PVDF-g-PS in a nitrogen atmosphere (....) and in an O2–N2 atmosphere from polystyrene grafts and 130 (o) from the PVDF matrix.(-.-.-). Degree of grafting, d.o.g., 48%. Thus the conclusion is drawn that the matrix polymer remains unchanged in the grafted samples and the polystyrene grafts do not alter the inherent decomposition of the PVDF. The two components, PVDF and PS, undergo fragmentation separately.Once the decomposition of the polystyrene grafts is completed, it leaves behind the more stable PVDF backbone which decomposes above 430 °C. This is in accordance with the view that the polystyrene grafts are incompatible with the PVDF matrix and form phase separated microdomains in the grafted polymer,13 and behave as a distinct two phase system on thermal degradation.Similar observations have been made by Momose et al.22 for the decomposition of a,b,b-trifluoroethylenesulfonyl fluoride grafted onto polyethylene film. Furthermore, Gupta et al.12,21 conclude that the introduction of polystyrene onto FEP films introduces a two step degradation behaviour in the thermograms of copolymer films where both the polystyrene and FEP components undergo degradation in separate steps.The decreased thermal stability of the crosslinked PVDF-g- Fig. 3 The thermal degradation of PVDF (—) and PVDF-g-PS mem- PS membranes with respect to the non-crosslinked is somewhat branes with d.o.g. 18% (- - -), 32% (....), 48% (-.-.), 68% (-..-) and surprising, since it has been shown that crosslinks stabilise the 73% (-.-.) in a nitrogen atmosphere polymer structure.23,24 These studies were concerned with styrene grafted and sulfonated FEP membranes crosslinked with DVB or triallyl cyanurate.It was shown that the grafting of FEP was considerably reduced by the presence of the J. Mater. Chem., 1998, 8(5), 1127–1132 1129crosslinker, and that the rate and the final d.o.g. were decreased. 20% in PVDF in films with d.o.g.=75%, which further points to some synchronous degradation mechanism of PVDF and In the present case it was found that both crosslinkers, DVB and BVPE, increase the final d.o.g. dramatically.16 Thus the short residual polystyrene grafts in the films. If all the polystyrene were to decompose, the residue would be about 17% grafting reactions in PVDF and in FEP diVer in mechanism.Higher d.o.g. can be achieved in PVDF than in FEP under for the sample with d.o.g.=75% at 650 °C. The thermal degradation of the PVDF-g-PS films in the similar reaction conditions. One possible explanation is the diVerence in glass transition temperatures, Tg, which for FEP presence of oxygen is illustrated in Fig. 2. The mass loss curve shows the onset of the degradation of the PVDF part at is 55 °C21 and for PVDF is -40 °C.25 Thus the FEP is close to its glassy state during the grafting, whereas the grafting of slightly lower temperatures than in the ungrafted film.The degradation of the styrene grafts starts at around 270 °C, the the PVDF takes place in the rubbery state. The diVusion of the styrene and the crosslinkers into the irradiated matrix is mass loss in the interval 270–420 °C is of the same order of magnitude as for the PVDF-g-PS sample in a nitrogen atmos- influenced by the diVerence in mobility of the polymer matrices.The diVerence between the two crosslinkers, DVB and BVPE, phere in the interval 390–410 °C. The degradation of the sample in the presence of oxygen is complete at around 530 °C.on the other hand is explained by the very large diVerence in their reactivities compared with the reactivity of styrene.16,26 The sulfonation of the polystyrene grafts in PVDF-g-PS produces a strongly acidic polyelectrolyte membrane, PVDF- DVB has a much higher reactivity than styrene which results in the formation of highly crosslinked stiV areas close to the g-PSSA. The thermograms of the degradation of the PVDFg- PSSA membranes in an inert atmosphere are shown in grafting points. The product of the reactivity ratios r1/r2 of BVPE and styrene is close to 1, hence the reaction results in Fig. 7. The decomposition reaction diVers from the one in the PVDF-g-PS membranes since the residue at 650 °C increases a more homogeneously and randomly crosslinked membrane.16 The degradation pattern of the PVDF-g-PS films is slightly with increasing d.o.g.This is probably due to an increase in char formation of the polystyrene grafts in the presence of dependent on the preceding drying procedure. In samples dried at 120 oC the thermograms show only the two degradation sulfur dioxide (and other acidic fragmentation products originating from the sulfonic acid groups) and water during the steps of the polystyrene grafts and the matrix polymer, see Fig. 2 and 3. Samples which were measured as received, or thermal degradation. Similar eVects have been reported in the thermal degradation of polystyrene in the presence of sulfuric had been dried in vacuo at 80 °C, showed a small mass loss around 120 °C. The mass loss is about 1% at d.o.g.= 18%, acid or Lewis acids.27,28 The first stage in the thermal degradation of the PVDF-g- and it increases to about 4% at d.o.g.=73%. Mass spectra recorded of the evolving gases at 120 °C do not, however, PSSA membranes is a mass decrease of 1–10% depending on d.o.g. between 100 and 180 °C. This mass decrease is due to indicate evaporation of residual solvents or reagents from the membranes.The fragmentation trace points to chain end loss of bound water in the membranes. The introduction of the hydrophilic sulfonic acid group in the membrane makes it fragmentation in the PVDF matrix; the peaks in the mass spectrum can be attributed to fragments of type CHxCFy. hygroscopic. Part of the water becomes hydrogen bonded to the sulfonic acid groups, and remains in the membrane even There is no indication of fragmentation of the polystyrene grafts at this temperature.Since it was found that the PVDF after drying in vacuo at 80 °C. Similar behaviour has been observed in the FEP based proton exchange membranes12 and and the irradiated PVDF are stable at 120 °C the conclusion is drawn that the styrene grafting reaction has caused some in commercial membranes.29 Massive degradation of the membranes starts at 220 °C.decomposition of the PVDF matrix. The mass losses from PVDF-g-PS films with various d.o.g. Fig. 8 shows the mass trace of the thermal degradation of a PVDF-g-PSSA membrane with d.o.g. 48%. The mass trace at 420 °C are seen in Fig. 6. The polystyrene content of the PVDF-g-PS films was calculated from the d.o.g.{d.o.g. %= shows that there is a simultaneous increase in water formation and onset of formation of sulfur dioxide at 220 °C. The [(W-W0)/W0]×100, polystyrene content=[d.o.g./(d.o.g. +100)]×100% where W is the mass of the grafted membrane evolution of sulfur dioxide is clearly seen from the mass spectra. Evidence of the formation of sulfur oxide and sulfur trioxide and W0 is the mass of the ungrafted membrane, respectively}.It is seen that the mass loss at the temperature of the onset of decomposition of PVDF, 420 °C, increases with increasing d.o.g. However, in the grafted films there is a polystyrene residue of 4–10% left at this temperature. This implies that the mechanism of degradation of the polystyrene changes as the decomposition of the chains approaches the graft points.The polystyrene decomposition becomes linked to the decomposition of the PVDF when small amounts of the grafts are left. The residue at 650 °C decreases with increasing d.o.g. on heating in a nitrogen atmosphere, from around 30 to only Fig. 7 The thermal degradation of PVDF-g-PSSA membranes with d.o.g. 18% (- -), 32% (....), 48% (.-.-) and 73% (-.-.-.) in a nitrogen atmosphere.The thermogram of pure PVDF (—) is included as a Fig. 6 Mass loss at 420 °C from PVDF-g-PS membranes as a function reference, as is the degradation of a PVDF-g-PSSA membrane with d.o.g. 70% and crosslinked with 5% DVB (6) and the degradation of the mass% styrene in the membrane, non-crosslinked (&), crosslinked with 5% BVPE ($) and crosslinked with 5% DVB (+), of a PVDF-g-PSSA membrane, d.o.g. 60%, in an O2–N2 atmosphere (+++). respectively 1130 J. Mater. Chem., 1998, 8(5), 1127–1132Fig. 9 The mass loss from PVDF-g-PSSA membranes between 220 °C and 320 °C ($) and the ion exchange capacity Q (&) as a function Fig. 8 The thermal degradation of PVDF-g-PSSA membrane with of d.o.g. d.o.g. 48%. Mass traces of evolving fragments m/z 18 (water %), 64 (SO2 o), 104 (styrene +) and 117 (×) are shown.was also seen in the mass trace. Desulfonation is at its maximum around 320 °C. Depolymerisation of the polystyrene grafts occurs after this in the interval 390–410 °C, and degradation of the PVDF matrix sets in at 430 °C as in the PVDFg- PS membranes. The desulfonation temperature, the decomposition temperatures of the polystyrene grafts and of the PVDF backbone are unaVected by the degree of grafting. The crosslinkers DVB and BVPE shift the degradation to lower temperatures, DVB more than BVPE.The degradation trace for a PVDF-g-PSSA membrane crosslinked with 5% DVB is included in Fig. 7. The onset of the formation of sulfur dioxide is as low as 200 °C. The degradation pattern of the PVDF-g-PSSA membranes resembles the degradation trace obtained under similar conditions from styrene grafted and sulfonated FEP membranes.11,12 The main diVerence is that the degradation of the PVDF-g-PSSA membranes starts at Fig. 10 Thermochromatogram showing the evolution of water (reten- lower temperatures. Since the chemical composition of the tion time 60–70 s) and sulfur dioxide (retention time 130–140 s) from FEP based and the PVDF based membranes is very similar a PVDF-g-PSSA membrane as a function of temperature.D.o.g. 48%. this marked diVerence could be due to diVerent mechanisms of formation due to the very diVerent Tg values of the matrix materials leading to diVerences in morphologies in the prod- PVDF-g-PSSA membranes; an example with d.o.g. 48% is seen in Fig. 10, with a maximum around 135 s at 300 °C. The ucts. Further studies are in progress. The mass loss due to evolution of sulfur dioxide from the evaporation of the strongly bound water in the range 70–180 °C as a function of d.o.g. is illustrated in Fig. 11. Formation of PVDF-g-PSSA membranes correlates with measured values of the ion exchange capacity, Q, giving further evidence for the water and sulfur dioxide in the range 180–400 °C as a function of d.o.g.is included in the same figure. The conclusion is drawn loss of sulfonic acid groups from the membrane at elevated temperatures. The measurements of Q have been reported that water evaporates in two distinct fractions, and the water formation in the higher temperature range is accompanied by previously.30 The mass loss in the PVDF-g-PSSA membranes in the temperature interval 220–320 °C as a function of d.o.g. the simultaneous formation of sulfur dioxide.Thus the results from the thermal analysis with gas leak detection and from is shown in Fig. 9. The formation of water in the degradation of the PVDF-g- the thermochromatography are in excellent agreement. The degradation of the PVDF-g-PSSA membranes in the PSSA films is not very clearly seen from the mass trace because of the high water background. This is because some atmos- presence of oxygen is very similar to the degradation in nitrogen atmosphere.In the oxidising environment the degra- pheric water is present in the ionisation chamber, and because of the hydrophobic nature of the silicone membrane in the dation of the PVDF component starts at a lower temperature than in the nitrogen atmosphere, see Fig. 7. The membrane is spectrometer inlet; water does not pass the membrane at rates corresponding to the evolution of water in the degradation. completely combusted at 480 °C in the oxidising environment. Therefore the thermal degradation of the PVDF-g-PSSA membranes was analysed with thermochromatography.The two Conclusion dimensional picture of gas evolution as a function of temperature is shown in Fig. 10. The thermogram shows a secondary The matrix polymer, PVDF, is thermally stable to 420 °C in an inert atmosphere, and to 400 °C in the presence of oxygen. background peak seen as a front at retention time 43 s. This peak is due to secondary degradation products formed from In the PVDF-g-PS films the degradation of the polystyrene grafts at lower temperatures than the PVDF is evident. degradation products in previous heating cycles.The evaporation of strongly bound non-freezing water is clearly seen after Crosslinking of the grafts decreases the thermal stability of the grafted polymers. The PVDF-g-PSSA membranes are stable 63 s at around 100 °C, as is water formed as a degradation product from the sulfonate groups at around 63 s above 200 °C.to 370 °C in an inert atmosphere, and to 270 °C in a highly oxidising atmosphere. The degradation starts with the splitting The formation of sulfur dioxide is seen in thermograms of a J. Mater. Chem., 1998, 8(5), 1127–1132 11313 A. Bozzi and A. Chapiro, Eur.Polym. J., 1987, 23, 255. 4 A. Chapiro, Radiat. Phys. Chem., 1979, 9, 55. 5 A. Bozzi and A. Chapiro, Radiat. Phys. Chem., 1988, 32, 193. 6 B. D. Gupta and A. Chapiro, Eur. Polym. J., 1989, 11, 1137. 7 B. D. Gupta and A. Chapiro, Eur. Polym. J., 1989, 11, 1145. 8 E. A. Hegazy, I. Ishigaki, A. M. Dessouki, A. Rabie and J. Okamoto, J. Appl. Polym. Sci., 1982, 27, 535. 9 A.Chapiro and A. M. Jedrychowska-Bonamour, Eur. Polym. J., 1984, 20, 1079. 10 M. V. Rouilly, R. Ko� tz, O. Haas, G. G. Scherer and A. Chapiro, J.Membr. Sci., 1993, 81, 89. 11 B. Gupta and G. G. Scherer, J. Appl. Polym. Sci., 1993, 50, 2129. 12 B. Gupta, J. G. Highfield and G. G. Scherer, J Appl. Polym. Sci., 1994, 51, 1659. 13 S. Holmberg, T. Lehtinen, J. Na�sman, D. Ostrovskii, M.Paronen, R. Serimaa, F. Sundholm, G. Sundholm, L. Torell and M. Torkkeli, J.Mater. Chem., 1996, 6, 1309. 14 S. Hietala, S. Holmberg, M. Karjalainen, J. Na�sman, M. Paronen, R. Serimaa, F. Sundholm and S. Vahvaselka�, J.Mater. Chem., 1997, 7, 721. 15 T. Lehtinen, F. Sundholm, G. Sundholm, P. Bjo�rnbom and Fig. 11 The evolution of water and sulfur dioxide as a function of M. Bursell, Electrochim.Acta, accepted. d.o.g. Water evolved in the range 100–180 °C from a PVDF-g-PSSA 16 S. Holmberg, J. H. Na�sman and F. Sundholm, Polym. Adv. membrane (o), and from a BVPE crosslinked (5 mol%) PVDF-g- T echnol., accepted. PSSA membrane (×). Water evolved in the range 180–400 °C from a 17 M. Kaljurand and M. Koel, Computerized Multiple Input PVDF-g-PSSA membrane (%), and from a BVPE crosslinked Chromatography, Ellis Horwood, Chichester 1989, p. 139. (5 mol%) PVDF-g-PSSA membrane (6). Sulfur dioxide evolved in 18 M. Elomaa, PhD Thesis, University of Helsinki, Helsinki 1991. the range 180–400 °C from a PVDF-g-PSSA membrane ($), and from 19 D. R. Deans, J. Chromatogr. 1984, 289, 43. a BVPE crosslinked (5 mol%) PVDF-g-PSSA membrane (s) . 20 S. Hietala, E.Skou and F. Sundholm, submitted to Polymer. 21 B. Gupta and G. G. Scherer, Angew. Makromol. Chem., 1993, 210, 151. of the sulfonic acid groups as water and mainly sulfur dioxide. 22 T. Momose, I. Ishigaki and J. Okamoto, J. Appl. Polym. Sci., 1988, The degradation of the polystyrene grafts start at 390 °C. 36, 669. Crosslinking of the grafts decreases the thermal stability of the 23 F. N. Bu� chi, B. Gupta, O. Haas and G. G. Scherer, J. Electrochem. membranes. Thus the PVDF-g-PSSA membranes can be Soc., 1995, 142, 3044. 24 F. N. Bu� chi, B. Gupta, O. Haas and G. G. Scherer, Electrochim. regarded as suitable for tests as polyelectrolyte membranes in Acta, 1995, 40, 345. applications at elevated temperatures up to 200 °C. 25 J. Brandrup and E. H. Immergut, Polymer Handbook, Wiley, New York, 3rd edn., 1989, p. VI-226 and VI-258. S.H. and M.E. are indebted to the Nordic Energy Research 26 R. Wiley and G. Mayberry, J. Polym. Sci. A, 1963, 1, 217. Programme (NEFP) for grants. F.S. acknowledges research 27 C. F. Cullis and M. M. Hirschler, T he Combustion of Organic funding from The Academy of Finland. The authors are well Polymers, Clarendon, Oxford, 1981, pp. 229–230. 28 X. Zhu, M. Elomaa, F. Sundholm and C. H. Lochmu� ller, aware that without the assistance with the syntheses by Svante Macromol. Chem. Phys. 1997, 198, 3137. Holmberg and Jan Na�sman, A ° bo Akademi University, this 29 T. A. Zawodzinski, Jr., M. Neeman, L. O. Sillerud and study would not have been possible. S. Gottesfeld, J. Phys. Chem., 1991, 95, 6040. 30 S. Hietala, S. Holmberg, J. Na�sman, D. Ostrovskii, M. Paronen, R. Serimaa, F. Sundholm, L. Torell and M Torkkeli, Appl. References Macromol. Chem. Phys., 1997, 253 151. 1 Fuel Cell Handbook, ed. A. J. Appleby and R. L. Foulkes, Van Nostrand, New York, 1989, G. G. Scherer, Ber. Bunsenges. Phys. Paper 7/08288F; Received 18th November, 1997 Chem., 1990, 94, 1008. 2 N. G. Polyanskii and P. E. Tulupov, Russ. Chem. Rev., 1971, 40, 1030. 1132 J. Mater. Chem., 1998,

ISSN:0959-9428    

DOI:10.1039/a708288f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Stability of antiferroelectricity and molecular reorientation in the hexatic smectic IA* phase as studied by X-ray diVraction and NMR spectroscopy Yoichi Takanishi,a* Kouichi Miyachi,a Shohei Yoshida, a Bo Jin, a Huiyong Yin, a Ken Ishikawa,a Hideo Takezoe, a and Atsuo Fukudab aDepartment of Organic and Polymeric Materials, T okyo Institute of T echnology, O-okayama, Meguro-ku, T okyo 152-8552, Japan bDepartment of Kansei Engineering, Shinshu University, Ueda-shi, Nagano-ken 386-8567, Japan We have investigated molecular orientation in the hexatic antiferroelectric SIA* phase by X-ray diVraction and nuclear magnetic resonance (NMR) spectroscopy.In the phase transition from SCA* to SIA*, the layer thickness increases and becomes larger than that in SA.The third-order diVraction peak intensity becomes stronger than the second-order one at this transition and increases with decreasing temperature in SIA*. According to the magic angle spinning NMR measurements, on the other hand, the isotropic chemical shift scarcely moves at this transition. These results suggest that the layer structure is reconstructed by the molecular reorientation but not by a molecular conformation change.We have also discussed the stability of antiferroelectricity and the origin of its appearance in hexatic ordering. Smectic liquid crystals have a variety of phase sequences. In ray measurements, we found that the layer thickness increases at the phase transition from SCA* to SIA* and that the third- particular, the discovery of the antiferroelectric liquid crystal (AFLC) phase makes the system more complex, attracting order peak intensity becomes larger than the second-order one.We also found that the isotropic chemical shift assigned much research interest. One of the most interesting phenomena is the appearance of many subphases such as a ferrielectric to the chiral alkyl chain scarcely moves with temperature on the NMR timescale.These results do not suggest a molecular SCc*1 and a reentrant antiferroelectric AF phase2 between the ferroelectric SC* and antiferroelectric SCA* phases. This is conformational change, but molecular reorientation within a layer at this transition. We also discuss the origin of the called the ‘devil’s staircase’,3 which appears to be due to the competition between ferroelectricity and antiferroelectricity.antiferroelectricity in hexatic smectics based on these experimental results. Yamashita4 adopted the axial next-nearest neighbor Ising spin (ANNNI) model as an explanation for this successive phase transition. Experimental Also of interest is the occurrence of the hexatically ordered The compounds used were (R)-TFMHPNCBC and [2H19]- antiferroelectric phase.5 Fig. 1 shows the X-ray Laue pattern (R)-TFMHPNCBC,8 whose chemical structure and the phase in a 100 mm thick freely suspended film, the optical transmitsequence (temperatures in °C) are as follows. tance spectrum of oblique incidence, and the electrooptic response showing the double hysteresis loop in the smectic phase just below SCA* in 4-(1-trifluoromethylheptyloxycarbonyl) phenyl 4¾-nonylcarbonyloxybiphenyl-4-carboxylate (TFMHPNCBC). These results indicate that this phase has both SI-like hexatic ordering and antiferroelectricity.Therefore, COO n-C9H19COO COO CH(CF3)C6H13 ( R )-TFMHPNCBC * we call this phase SIA*. Although the normal ferroelectric hexatic SI* phase has been studied,6 the origin of its appearance Iso 121–120.3 SA 107.0–106.8 SCA* 56–55 SIA* ~28 Cryst.has not been clarified; less is known about the hexatic antiferroelectric phase. Neundorf et al.7 studied the binary systems of two AFLCs, and proposed a diVerent intermolecular interaction from that stabilizing SCA* as a possible origin of the stabilization of SIA*. However, the suggestion has not yet been COO n-C9D19COO COO CH(CF3)C6H13 [2H19]-( R )-TFMHPNCBC * verified.Hence, it is important to consider the origin of Iso 120 SA 106 SCA* 55 SIA* ~28 Cryst. antiferroelectricity in the hexatic smectics from the viewpoint not only of the relation between the intermolecular interactions The deuteration scarcely changed its phase sequence at each producing hexatic ordering and antiferroelectric properties but transition temperature.also in the discussion of the origin of the antiferroelectric In the X-ray measurements, we used a Rigaku RU-200 (Cu- SCA* phase. Ka, 12 kW) instrument with a temperature controller with an In this paper, we investigated molecular orientation in the accuracy of ±0.1 °C. A sample was stretched thin with a SIA* phase in detail by X-ray diVraction and NMR specspatula just above the Iso-SA phase transition, so that it was troscopy.We measured the temperature dependence of the uniformly and homeotropically aligned. The film thickness was layer thickness, the higher-order diVraction intensity by X-ray ca. 25 mm. The temperature dependences of the layer thickness diVraction and the isotropic chemical shift by NMR.In the Xand the corresponding higher-order peaks were measured by the conventional 2h–h method.9 The apparent optical tilt angle, hopt, was determined by measuring the extinction direction in * E-mail: ytakanis@o.cc.titech.ac.jp J. Mater. Chem., 1998, 8(5), 1133–1138 1133Fig. 2 (a) Temperature dependence of the layer thickness of (R)- TFMHPNCBC and (b) temperature dependence of (#) the apparent optical tilt angle, hopt, and (&) the tilt angle determined by X-ray, hX-ray Fig. 1 Evidence for the hexatic antiferroelectricity in SIA* of TFMHPNCBC, (a) an X-ray Laue pattern in a 100 mm thick freely suspended film (b) an optical transmittance spectrum of oblique incidence in a 50 mm thick homeotropic cell, and (c) an optical transmittance change by applying a triangular wave electric field in a 2 mm thick homogeneous cell a 2mm thick homogeneously aligned cell between crossed polarizers when we applied a suYciently high electric field to make the field induced phase transition to the ferroelectric state.NMR spectroscopic measurements were performed with a Chemagnetics high resolution solid NMR spectrometer CMX- 300WB (300 MHz for 1H).Isotropic chemical shifts at each carbon were measured by magic angle spinning (MAS) with and without cross-polarization (CP). The 90° pulse width was 2.4 ms, and the contact time was 5 ms in the CP method. The sample rotation frequency was 4 kHz. The samples were packed into a zirconia tube of diameter 7 mm. We started the NMR measurements after 10 min to obtain thermal equilibration at each temperature.Although each temperature was stabilized by using VT (variable temperature) air to within ±1 °C accuracy, the absolute value of the sample temperature was Fig. 3 Temperature dependences of (a) the first- and (b) higher-order diVerent from the set value. The temperature was calibrated peak intensities of the X-ray diVraction peak due to the layer spacing (#) 2nd-order ($) 3rd-order (%) 4th-order and (6) 5th-order by finding the temperature at which a free induction decay 1134 J.Mater. Chem., 1998, 8(5), 1133–1138(FID) signal drastically changes; note that a FID signal shows a long decay in the isotropic liquid state. Results and Discussion X-Ray studies Fig. 2(a) shows the temperature dependence of the layer thickness of (R)-TFMHPNCBC.At the phase transition from SA to SCA*, the layer thickness decreases because of molecular tilting from the layer normal. With a decrease in temperature Fig. 6 Temperature dependence of the in-plane molecular distance determined by a wide angle X-ray diVraction peak Fig. 4 Temperature dependences of the normalized amplitudes of the higher-order diVraction, |an/a1|: (#) a2/a1 ($) a3/a1 (%) a4/a1, and (6) a5/a1 Fig. 7 (a) Typical CP-MAS spectrum in SA of TFMHPNCBC, and (b) the temperature dependence of the isotropic chemical shift. The assigned number in Fig. 7(b) corresponds to the number in the chemical structure shown above in SCA*, the layer shrinkage saturates at about 90 °C, and the layer thickness begins to increase at the far lower temperature region in SCA*.The layer thickness steeply increases at the transition from SCA* to SIA*, and to our surprise, it becomes longer than that in the SA phase. On the other hand, the apparent optical tilt angle, hopt, continuously increases in the temperature region of the SCA* phase, and it only decreases slightly at the SCA*–SIA* phase transition, as shown in Fig. 2(b). In Fig. 2(b), the tilt angle, hx-ray, given by eqn. (1),10 hx-ray (T )=cos-1[d(T )/dA] (1) is also shown as a function of temperature. Here, d(T ) is the Fig. 5 Density projection profiles along the layer normal, z, in the SA, SCA* and SIA* phases determined by the results of Fig. 4 layer thickness in the SCA* and SIA*, and dA is that in the SA J. Mater. Chem., 1998, 8(5), 1133–1138 1135not show any decrease, and becomes larger than the secondorder one.These results qualitatively indicate that the smectic layer order is very high compared with that of other fluid smectic phases of low molecular weight compounds. We consider the projection of the electron density along the layer normal, r(z). The smectic layer is symmetric with respect to the layer normal because of the head-and-tail equivalence of the molecule, r(z)=r(-z).Since r(z) is a periodic function of the layer thickness, d, it may be expanded as a Fourier series as given by eqn. (2). r(z)=r0(z)+S an cos (2pnzd)11 (2) The absolute values of the coeYcients |an| can be obtained by the higher-order peak intensities corresponding to the layer thickness after making a correction for Lorentz factors.The normalized amplitudes of the higher-order diVractions, |an/a1| Fig. 8 13C NMR spectra of the alkyl chain region of [2H19]- (n=2–5), are shown as a function of temperature in Fig. 4. TFMHPNCBC in the MAS measurement (a) without and (b) with CP Based on this figure, we depicted the density projection profile along the layer normal at each phase in Fig. 5. For the calculation we chose the signs of a1, a2, a3, a4, a5 as +, +, phase at 110 °C, determined by the X-ray measurements.The temperature dependence of hx-ray is clearly diVerent from that -, +, - on the basis of the bent molecular structure and the molecular reorientation at the SCA*–SIA* phase transition, of hopt. By taking into account the fact that hopt and hx-ray are governed by the tilting of the core part of the molecules and which is discussed below. In the SA phase and the higher temperature region of SCA*, the density profiles are similar to that of the average long molecular axis, respectively, the diVerent h could be attributed to molecular conformational the sinusoidal wave-form, although |a2/a1| and |a3/a1| are much larger than that in the normal smectic liquid crystals such as change and/or the change of the molecular interdigitation in a smectic layer. 8CB.12 In contrast, the profile is separate from the sinusoidal wave in the lower temperature region of SCA*, and a substruc- In order to study the layer structure in detail, we measured the higher-order Bragg peaks corresponding to the layer ture arises at the layer boundaries in SIA*.Fig. 6 shows the temperature dependence of the in-plane thickness.9 Fig. 3 shows the temperature dependence of the higher-order peak intensities. The first- and second-order peaks molecular distance obtained by wide angle X-ray diVraction. In the temperature region of SCA*, the distance gradually decrease at the SA–SCA* and SCA*–SIA* phase transitions, indicating the occurrence of molecular reorientation.In the decreases with a decrease in temperature. It indicates that the fluctuation of the molecule is gradually hindered and molecular SIA* phase, even a fifth-order peak was detected. In the vicinity of the SCA*–SIA* phase transition, the third-order peak does order in the layer increases. At the transition from SCA* to Fig. 9 Temperature dependences of the chemical shift corresponding to the alkyl carbons 1136 J.Mater. Chem., 1998, 8(5), 1133–1138Fig. 10 Schematic illustration of the model structure at the phase transition from SCA* to SIA*. The result in the MOPAC calculation was adopted as the molecular shape. Bend type molecular length: L 0=33.829 A ° ; layer thickness in SA (112 °C): dA=35.429 A ° ; layer thickness in SIA* (40 °C): dIA=37.015 A ° ; apparent tilt angle in SIA* (40°C): hopt=28.15°.Supposing that L=d/costhopt, L A(112 °C)=dA=35.429 A ° , L IA (40 °C)= 41.9806 A ° (L=the average length along the molecular long axis). Then SA: L A-L 0=1.6 A ° and SIA*: L IA-L 0=8.1516 A ° . The diVerence of interdigitation is estimated to be about 6.55 A ° . SIA*, the molecular distance starts increasing.If the molecular C19 and C24 appear to coalesce. Yoshizawa et al.13 reported that line broadening occurs when v1t1, where v1 corre- conformation change to an elongated form at the transition sponds to the proton decoupling power and t is the correlation causes the thickness of the layer to increase, the molecular time of the molecular motion. If this is the case, the present distance within each layer should also exhibit a significant result indicates the reorientation of molecules in a layer.The change. Therefore, the increasing layer thickness at this transtemperature at which this line broadening occurs is almost the ition is thought to be caused by a change in molecular same as the temperature at which hx-ray saturates (around interdigitation but not by a large change in conformation. 90 °C).In addition, the chemical shifts of the phenyl carbons connected to the carbons of the ester groups, C18 and C23, NMR studies and ester carbons, C19 and C24, hardly move in the tempera- In order to investigate the molecular conformation in detail, ture range, suggesting that the angle between the dipole of the NMR measurements were performed.Fig. 7(a) and 7(b) show ester and the phenyl plane connected to them remains a typical CP-MAS spectrum in SA of (R)-TFMHPNCBC and unchanged. In contrast, the chemical shift assigned to some the temperature dependence of the isotropic chemical shift, alkyl carbons moves to lower field in the vicinity of the respectively. The assigned number of each carbon is indicated transition from SCA* to SIA*.on the figure. With decreasing temperature in the SCA* phase, In order to distinguish between the peaks corresponding to the peak intensities corresponding to the chemical shifts the alkyl carbons of the achiral and chiral sides, [2H19]-(R)- assigned to the phenyl carbons (C11, C14, C15 and C20) TFMHPNCBC was used. Fig. 8 shows a part of the MAS decrease and move up field.The decrease in intensity indicates spectrum of [2H19]-(R)-TFMHPNCBC with and without CP. the slow movement of the molecules, and the low-field shift Some peaks exhibit up field shifts in the MAS measurement suggests a change in the dihedral angle at the corresponding (no CP) while these peaks disappear with CP. The upfield shift position. The peaks assigned to the ester carbons (C10, C19, is caused by the dipolar coupling with deuteriums, and thus we could distinguish between chiral and achiral alkyl chains.C24) become broad and in particular the peaks assigned to J. Mater. Chem., 1998, 8(5), 1133–1138 1137The temperature dependence of the chemical shifts correspond- diYcult to propose that the excluded volume eVect is the origin of the appearance of the hexatic phase in which molecules tilt ing to some of the alkyl carbons is shown in Fig. 9. The peaks in the same direction in neighboring layers such as SI(*). assigned to the achiral carbons, with the exception of C9, shift Therefore, dispersion forces may be the cause. At the phase slightly to lower field with decreasing temperature, while the transition from SCA* to the hexatic phase at lower temperature, chiral carbon peaks do not move.Ishikawa and Ando14 the competition between dipole–dipole interactions stabilizing reported that the 13C chemical shift moves to lower field if a antiferroelectric ordering and the interaction stabilizing hexatic carbon atom three-bonds distant is trans rather than gauche. ordering such as dispersion forces is important.If the former Therefore, this low-field shift may indicate a conformational interaction is stronger than the latter then the antiferroelectric change of the achiral alkyl chain. Benattar et al.15 explained SIA* phase appears. In contrast, if the latter overcomes the that the increase in layer thickness at the transition from SC* former, the phase transition to SI* occurs.to the hexatic SI* phase is caused by an increase in the orientational order of an alkyl chain. In the present case, the layer thickness in SIA* in which the long molecular axis tilts Conclusions with respect to the layer normal by 30° is larger than that in The conformation and reorientation of TFMHPNCBC mol- the SA phase. Hence the layer thickness change is too large to ecules were studied in the SCA* and the SIA* phases by X-ray be explained by only an increase in the alkyl chain orientational diVraction and NMR spectroscopy. The layer thickness gradu- ordering.Therefore, the main cause of the layer thickness ally increases in the lower temperature region of SCA*, and change, we suggest, is the change in molecular interdigitation becomes larger in SIA* than in SA.Higher-order X-ray diVrac- due to intralayer molecular reorientation, though the confortion results and NMR spectroscopy strongly indicate that this mational change of the achiral chain may influence the pretranlayer thickness increase is caused by translational molecular sitional phenomenon of the appearance of hexatic ordering. reorientation within a layer and not by a conformational These results are also consistent with the polarized FT-IR change. From these results, we claim that this translational results of Yin et al.;8 even in the SIA* phase, the chiral chain reorientation is due to the strong dipole interaction between is bent and the angle between the long molecular axis and the molecules in adjacent layers, suggesting that the origin of the average chiral chain axis is much larger, as observed in antiferroelectric ordering in hexatic smectics is the same as MHPOBC and reported by Nakai et al.,16 Jin et al.17 and that in SCA*.Ouchi et al.18 Let us consider the origin of the antiferroelectricity in the We are very grateful to Showa Shell Sekiyu K. K. for supplying hexatically ordered smectic phase.Neundorf et al.7 assumed (R)-TFMHPNCBC. This work was supported by a Grant-in- that the layer increase is due to a conformational change and Aid for Scientific Research (Specially Promoted Research proposed that it is probable that the Coulomb interaction No. 06102005) from Monbusho. through polarization changes due to positional fluctuations inherent in the hexatic order causes the SIA* antiferroelectricity.However, the assumption, i.e. a significant molecular confor- References mation change is the cause, is not correct as we have shown 1 J. Lee, A. D. L. Chandani, K. Itoh, Y. Ouchi, H. Takezoe and byNMRin this paper. Since the hexatic phases are a commonly A. Fukuda, Jpn. J. Appl. Phys., 1990, 29, 1122. observed phase in non-tilted and tilted smectic phases, the 2 N.Okabe, Y. Suzuki, I. Kawamura, T. Isozaki, H. Takezoe and stabilization of SIA* can naturally be considered to have the A. Fukuda, Jpn. J. Appl. Phys., 1992, 32, L793. 3 T. Isozaki, T. Fujikawa, H. Takezoe, A. Fukuda, T. Hagiwara, same origin as that of SCA*, i.e. the so-called Px model19 or Y. Suzuki and I. Kawamura, Phys. Rev. B, 1993, 48, 13439. the pairing model.20 In both models, intermolecular inter- 4 M.Yamashita, Ferroelectrics, 1996, 181, 201. actions at the layer boundary are important. If we consider 5 Y. Takanishi, H. Takezoe and A. Fukuda, Ferroelectrics, 1993, the unchanged chemical shift, the increase of the layer thickness 149, 135. and electron density change at the SCA*–SIA* phase transition, 6 S. K. Prasad, G. G.Nair and S. Chandrasekhar, J. Mater. Chem., the origin of the antiferroelectricity in hexatic SIA* should be 1995, 5, 2253. 7 M. Neundorf, Y. Takanishi, A. Fukuda, S. Saito, K. Murashiro, the same as in SCA*; the electric interaction in the vicinity of T. Inukai and D. Demus, J.Mater. Chem., 1995, 5, 2221. layer boundaries. Therefore, we can conclude that the increase 8 H. Yin, B.Jin, Y. Takanishi, K. Ishikawa, H. Takezoe, A. Fukuda of layer thickness at this transition is caused by a molecular and M. Kakimoto, Mol. Cryst. L iq. Cryst., 1997, 303, 285. interdigitation change, which keeps the interlayer dipole inter- 9 Y. Takanishi, A. Ikeda, H. Takezoe and A. Fukuda, Phys. Rev. E, action, so stabilizing the antiferroelectricity, which may be 1995, 51, 400. accompanied by an increase in the orientational order of the 10 T.P. Rieker, N. A. Clark, G. S. Smith, D. S. Parmar, E. B. Sirota and C. R. Safinya, Phys. Rev. L ett., 1987, 59, 2658. alkyl chains. We propose a model of molecular reorientation 11 P. Davidson and A. M. Levelut, L iq. Cryst., 1992, 11, 469. at the phase transition from SCA* to SIA* in Fig. 10. 12 J. W. StamatoV, P.E. Cladis, D. Guillon, M. C. Cross, T. Bilash Now, we have to give a reasonable explanation for the and P. Finn, Phys. Rev. L ett., 1980, 44, 1509. appearance of SI* below SCA* or SIA * as discovered by 13 A. Yoshizawa and H. Kikuzaki, Ferroelectrics, 1993, 147, 447. Neundorf et al.7 The key to the explanation is the temperature 14 S. Ishikawa and I. Ando, J.Mol. Struct., 1992, 271, 57.dependence of the layer spacing. The layer spacing shows a 15 J. J. Benattar, F. Moussa and M. Lambert, J. Chim. Phys. Phys. - Chim. Biol., 1983, 80, 99. typical increase after the SCA*–SIA* phase transition as shown 16 T. Nakai, S. Miyajima, S. Yoshida, Y. Takanishi and A. Fukuda, in Fig. 2(a) and in ref. 5 and 7. This may be due to the reduction submitted to Phys. Rev. E. of the interdigitation of molecules caused by the highly ordered 17 B. Jin, Z. Ling, K. Miyachi, Y. Takanishi, K. Ishikawa, H. Takezoe, smectic layer compared with that of the fluid smectic phases. A. Fukuda, M. Kakimoto and T. Kitazume, Phys. Rev. E, 1996, As the layer becomes well ordered and the spacing gets thicker, 53, R4295. 18 Y. Ouchi, Y. Yoshioka, H. Ishii, K. Seki, M. Kitamura, R. Noyori, the dipole–dipole interaction becomes weak. Then SI* emerges. Y. Takanishi and I. Nishiyama, J.Mater. Chem., 1995, 5, 2221. This happens within the SIA* phase (SIA*–SI*) or at the phase 19 K. Miyachi, J. Matsushima, Y. Takanishi, K. Ishikawa, H. Takezoe transition from SCA* to a hexatic phase (SCA*–SI*) depending and A. Fukuda, Phys. Rev. E, 1995, 52, R2153. on the strength of the dipole–dipole interaction. Both transition 20 Y. Takanishi, K. Hiraoka, V. K. Agrawal, H. Takezoe, A. Fukuda sequences were observed in a mixture system.7 and M. Matsushita, Jpn. J. Appl. Phys., 1991, 30, 2023. Considering that the ferroelectric SI* phase appears at a lower temperature than the antiferroelectric SIA* phase, it is Paper 7/07920F; received 4th November, 1997 1138 J. Mater. Chem., 1998, 8(5), 1133–1138

ISSN:0959-9428    

DOI:10.1039/a707920f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials 5-Amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine: characterization of the solvent-free solid phase and interaction with ammonia and water Vincenzo Fares,*a Alberto Flamini,*†a Donatella Capitanib and Roberto Rellac aIstituto di Chimica deiMateriali del CNR, Area della Ricerca di Roma, PO Box 10, 00016 Monterotondo Stazione, Roma, Italy bIstituto di Strutturistica Chimica del CNR, Area della Ricerca di Roma, PO Box 10, 00016 Monterotondo Stazione, Roma, Italy cIstituto per lo Studio di NuoviMateriali per l’Elettronica del CNR, V ia Arnesano, 73100 L ecce, Italy The 5-amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine (LH, C11H3N7), previously characterized as the 251 1-chloronaphthalene adduct, has been further investigated as a solvent-free solid phase.Strong intermolecular interactions take place in this phase, as revealed by the optical spectra of evaporated LH thin films (lmax=615 and 570 nm) compared to the optical spectrum of LH in solution (lmax=580 nm). 13C NMR spectra also support the occurrence of intermolecular attractive CN group interactions in the solid state. X-Ray diVraction patterns indicate that the controlled sublimation process of LH (Tsubl=200 °C, 10-6 mmHg) leads to films composed of highly oriented crystallites, with two main sets of diVracting planes parallel to the film surface.The refractive index of LH as an evaporated thin film has also been determined in the 400–800 nm spectral range (n=1–2). LH interacts with ammonia and/or water in the gas phase.In the first case the acid–base reaction (LH+NH3PL¾·NH4+) occurs. The resulting L¾ anion (L¾OC11H2N7-) is the 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (A, lmax=525 nm) or the isomer 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinide (B, lmax=680 nm), depending on the relative amount of water to ammonia in the gas phase. This reaction is driven by the hydrogen bonding of NH4+ to B and/or to water.In the second case a fast proton scrambling occurs. We have recently synthesized and structurally characterized the title pyrrolizine (LH, Scheme 1) as the 251 1-chloronaphthalene adduct: 2LH·NAPH.1 Our interest in LH is mainly due to its chemico-physical properties: (i ) it is a planar, intensely coloured molecule [in tetraydrofuran (THF): lmax= 580 nm, e580=20 000 dm3 mol-1 cm-1], (ii ) it can develop attractive potentials in the solid state through several mechanisms such as p-orbital overlap, hydrogen bonding, dipolar CN group interactions, (iii ) it forms mono- and/or bis-pyrrolizinato metal complexes, (iv) it can be deposited under vacuum as thin Scheme 1 Non-systematic numbering is used for the NMR assignments films and (v) in this state it is a semiconductor of low conductivity.In research aimed at addressing its possible use in technological applications, by analogy with molecular materials based on evaporated dyes and/or semiconductors,2 LH It was recrystallized from acetone–water (151) and then dried has been further characterized both in solution and in the in an oven at 60 °C in air for 4 h.From thermal gravimetric solid state. Moreover, we investigated whether LH has any and diVerential analyses, performed with a Du Pont 950 recognition properties for selective detection of species of apparatus, it did not show any weight loss nor heat exchange environmental interest in air. Herein the results of these studies up to 250 °C. Its density (d) was measured (1.45 g cm-3) by are reported.suspending the powder in a suitable mixture of solvents. Evaporated films were deposited on glass plates in an Edwards Auto 306 vacuum coater as described previously.1 LH can be Experimental fully deuterated on exposure to D2O vapor in a dry-box, as Materials proved by the infrared spectra (Fig. 11; see later). Spin coated films were deposited from a THF solution with a Convac LH was prepared from NaL¾ according to the previously spinner model 1001.Film thicknesses were measured using an reported procedure.1 Alpha-Step stylus profilometer. Scanning electron microscopy (SEM) images were recorded on a JEOL SM6100 instrument. Powder X-ray diVraction (XRPD) X-Ray diVraction data, both for powder samples and for polycrystalline thin films, were collected on a Seifert XRD3000 two-circle automated diVractometer at room temperature using Cu-Ka radiation with a graphite monochromator.The step scanning technique, with steps of 2h=0.025° and a stepping time of 10 s, was used over the range 5°2h50 °. † E-mail: flamini@nserv.icmat.mlib.cnr.it J. Mater. Chem., 1998, 8(5), 1139–1144 1139Optical and infrared spectroscopic measurements Optical spectra were recorded on a Cary 5 spectrometer.Dried and freshly distilled solvents were used for the solution spectra. The spectra of the films were measured by inserting the glass slide supporting the film vertically across the light beam into a 10 mm square quartz cuvette. An uncoated glass slide was placed in the reference compartment. In addition, reflectivity measurements in the 400–800 nm spectral range were carried out using the integrating sphere accessory of the spectrophotometer. IR spectra were recorded on a Perkin Elmer 16F PC FTIR spectrometer as Nujol mulls. 13C NMR measurements Solid state 13C CP-MAS NMR spectra at 50.13 MHz were recorded on a Bruker AC-200 spectrometer, equipped with an HP amplifier, 1 H 200 MHz, 120 W cw, and with a pulse amplifier, M3205.The spin rate of the sample was 8 kHz. The p/2 pulse width was 3.1 ms, the contact time for the crosspolarization experiment was 4 ms and the relaxation delay was 10 s. 13C spectra were obtained with 512 words in the time domain, zero filled and Fourier transformed with a size of 1 K. Fig. 1 XRD patterns of diVerent samples of LH: (a) evaporated film, All the solution experiments were performed on a Bruker (b) solvent-free microcrystalline powder and (c) microcrystalline 2LH·NAPH AMX-600 spectrometer.High resolution 13C NMR spectra at 50.9 MHz were obtained with broad band proton decoupling performed with a GARP sequence.3 Acquisition and relaxation 3.17(100), 2.76(32). (ii ) Microcrystalline 2LH·NAPH, of known delay were chosen according to the Ernst relationship4 in order structure.1 From the corresponding XRPD [Fig. 1(c)] it shows to maximize the signal to noise ratio for the long relaxation a much higher degree of crystallinity in this case, the FWHM of quaternary C atoms. Spectra were obtained with 16 K words ranging from 0.12 to 0.90 °. (iii ) Microcrystalline powder, in the time domain and Fourier transformed on a size of 8 K.obtained by accurate grinding of LH evaporated films. Its diVraction pattern is identical with that of powder (i ), so Electrical resistivity measurements and sensor property studies proving that the films deposited by sublimation have the same crystal structure as the source powder. (iv) LH deposited under Electrical measurements were performed on our samples in vacuum as thin films.Several samples of diVerent thickness order to test the electrical sensing properties of the active layer. (50–800 nm) have been examined. Their XRD patterns are all To this end, alumina substrates were first prepared by thermal identical: the one relating to a 400 nm thin film is reported in evaporation and deposition of a patterned microelectrode [Fig. 1(a)]. As only two peaks are present, at 5.21 and 3.17 A ° , array consisting of interdigitated pairs of gold fingers about replacing the set of peaks from the same films once ground 40 nm thick. The dc resistance of the various samples was (see point iii ), we must infer that the controlled sublimation measured by an electrometer, Keithley model 617.The average process leads to thin films constituted of highly oriented resistivity of the samples of typical dimension crystallites, with two main sets of diVracting planes parallel to 1×1×1.5×10-5 cm3 measured in a flux of dry air was about the film surface, with interplanar distances typical for face-to- 1.7×106 V cm. The eVect of diVerent toxic gases on electrical face p-interacting conjugated systems, so suggesting a depos- conductivity was measured in a dynamic pressure system ition process leading to face-to-face LH units.implemented in our laboratory where dry air at ambient pressure was used as the carrier and reference gas. The gas Optical spectra concentration was varied by using a MKS Instrument mass flow controller, model 647. Evaporated thin films deposited on glass showed well resolved optical spectra.From these spectra, after normalization to the Results and Discussion concentration of LH in the solvent-free solid phase (C=6.2 M) and to the film thickness, the molar extinction coeYcient (e) For our objectives, one of the most relevant properties of LH of LH in the film vs. wavelength can be calculated. On is that it sublimes without decomposition aVording thicknesscomparison with the corresponding values of LH in solution controlled thin films.Thus, the following discussion deals (Fig. 2) a remarkable feature appears. The single band of LH mainly with diVerent sets of experimental data for LH in the in solution (lmax=580 nm) is replaced in the solid state by a solvent-free solid phase, either as a powder or thin films.When double band (lmax=615 and 570 nm) of approximately the appropriate, a comparison with the corresponding data for same total area and with two associated components of the 2LH·NAPH and of LH in solution is made. same intensity. Clearly, such spectral variations originate in solid-state intermolecular interactions. In this regard, either of X-Ray diVraction patterns the following mechanisms could be in operation, depending on the crystal structure: the well-known Davydov-type XRD measurements were made on several samples.(i ) Solventfree microcrystalline powder was obtained as described in the coupling5 or a charge-transfer between adjacent molecules, which occurs widely in polycyano-substituted molecules.6 Experimental. The corresponding XRPD pattern [Fig. 1(b)] shows a series of broad peaks characterized by FWHM values Occasionally, some evaporated thin films, as well as the spincoated films, showed optical spectra quite diVerent from that in the range 0.30–1.20°; this indicates a poorly crystalline structure. Consequently, any attempt to indicize the spectrum just discussed. In Fig. 3 the spectra in question, derived from evaporated LH films of the same thickness, are reported: failed.The main peaks (interplanar distances, in A ° ) and their relative intensities (in parentheses), are as follows: 9.04(9), spectrum 1 exhibits more than the two bands expected for exciton splitting within the crystal as usually observed (spec- 8.26(39), 5.57(61), 5.21(28), 4.54(21), 4.02(21), 3.50(8), 1140 J.Mater. Chem., 1998, 8(5), 1139–1144Fig. 2 Normalized optical spectra of LH: (~) as evaporated film and (-- -- -) in THF solution Fig. 4 SEM micrographs of the LH evaporated films, whose optical spectra are reported in Fig. 3 Fig. 3 Optical spectra of two diVerent LH evaporated films of the same thickness (150 nm) trum 2). In conjunction with the SEM images of the source films (1¾ and 2¾ of Fig. 4), this could be explained by the diVerent film morphology, which may imply a larger amorphous content in 1¾, than in 2¾. In turn, 2¾ clearly shows a layered Fig. 5 Refractive index (n) vs. wavelength for a typical evaporated LH crust probably of crystalline structure. thin film The refractive index n of the as-deposited LH thin films vs. wavelength was also calculated from a computer fit of both transmission T ( l ) and reflection R( l ) measurements based on 13C NMR spectra a model that considers a parallel sided isotropic and absorbing film between transparent media of indexes n0 (air) and n2 Before examining these data, let us consider the tautomerism between the two energetically equivalent LH configurations (a (glass substrate), the latter being assumed to be very thick with respect to the wavelength.7 Fig. 5 shows the refractive and b in Scheme 1), which would directly influence the NMR spectra. Previously we ascertained that such tautomerism exists index n of a typical evaporated LH thin film in the 400–800 nm spectral range. As can be seen, the refractive index n of the only in solution. Accordingly, it was found that the NMH proton exchange at room temperature is fast in THF solution film changes slowly between 1 and 2.J. Mater. Chem., 1998, 8(5), 1139–1144 1141as revealed by the 13C NMR spectrum of LH in this solvent, to zero in solution. The resonances of these carbons are shifted to high field either due to intermolecular attractive CN group while it does not occur in the solid state for the 1-chloronaphthalene adduct, as proved by the successful refinement of the interactions9 or by the magnetic anisotropy of a neighboring CN group.10 molecular structure of LH from the single crystal X-ray analysis of 2LH·NAPH. These findings indicate that the tautomerism in question requires an intermolecular exchange mechanism.Sensing properties of LH The current 13C NMR data, as it will be seen, substantiate the In view of the utilization of LH for detecting species of supposed mechanism and in addition indicate that the NMH environmental interest in the air, we probed LH films, deposited proton exchange even in solution can be slowed down by a on interdigitated electrodes, as conductimetric sensors.No suitable solvent such as dimethoxyethane (DME).Thus, LH significant variations in their electrical conductivity were in DME exhibits eleven 13C NMR resonances (Fig. 6). The observed on exposure to NH3, NO, CO or H2 gas up to assignments, presented in Table 1, are based on the correlation 100 ppm in dinitrogen. However, see the following section. between the observed intensity of the resonance with the relaxation time of the carbon atom originating from the Interaction with ammonia resonance itself.8 That is, the nearer the carbon atom is to an eYcient relaxation center, i.e.a proton, the higher the intensity The interaction of LH with NH3 occurs only in the presence of the associated resonance. The NMR spectrum of the solid of water and it depends markedly on the experimental conshows a clear correspondence with the solution spectrum, for ditions.We selected and present here three typical examples. the most intense peaks. Two extra broad resonances appear (1) When NH3 (500 ppm in N2) is slightly humidified, by in the solid spectrum, absent in the solution spectrum, at passing over liquid water before interacting with LH, the limiting high field (110 ppm). We tentatively assigned these spectral changes occurring (Fig. 7) are not fully reversible and, resonances to the nitrile carbon atoms, whose resonance is on comparison with the results of the subsequent experiments broadened by the 14N quadrupole, which in turn is averaged (2 and 3), they indicate the formation of two species in the film, A and B (lmax=525 and 680 nm, respectively). (2) Only B is formed when experiment (1) is carried out immediately after exposing the film to a water-free ammonia stream.In this case, the film will sense a smaller amount of water relative to the ammonia content in the gas phase. The consequent modifi- cation occurring is rapid and irreversible (Fig. 8). In (3), only A is formed when LH comes into contact, in air, with the saturated vapor of a concentrated aqueous ammonia solution (35 wt%).In this case the interaction is fully reversible, so that LH is reformed from A in the absence of ammonia in air with an associated negligible hysteresis (Fig. 9). On the basis of our previous studies on LH and of the wellknown solvatation eVects on the basicity of NH3,11 the results of the above experiments can be reasonably interpreted as follows.A and B are simply L¾ isomers, resulting from the same reaction LH+NH3�NH4+·L¾. LH is a weak acid and it reacts with NH3 provided that the resulting NH4+ is Fig. 6 13C NMR spectra of LH as solid sample (top) and in DME solution (bottom) Table 1 13C solution and CP-MAS NMR spectral data of LHa d Assignmentb Solution Solid Assignmentb C1, C7 110.8, 112.35 0 C1, C7, C3 C2, C6 126.6, 152.15 107, 92 C8, C9, C10, C11 C8, C9, C10, C11 114.8, 114.5, 113.1, 112.7 C3, C5 111.8, 123.2 125 C2, C5 Fig. 7 Spectral changes with time (every 2 min) undergone by a thin C4 154.9 150 C4, C6 film of LH (thickness 150 nm) on exposure to NH3 (500 ppm in N2) humidified by passing over liquid water. The arrows indicate the aSee Experimental for details of data collection.bSee Scheme 1 for the numbering. direction of the spectral changes. 1142 J. Mater. Chem., 1998, 8(5), 1139–1144metal [e.g. ZnII], is stabilized by hydrogen bonding to NH4+. At the end of experiment (1), NH4+ will be solvated partly as NH4+·4H2O lying close to A as the counteranion and partly as B·NH4+·2H2O. For further support of this explanation, we report (Fig. 10) the normalized solution optical spectra of AsPh4·L¾ and (acac)ZnL¾ (acac=acetylacetonato), both structurally characterized,12,13 as representative examples of the isomers A and B, respectively. Note that LH, due to the absence of mesomeric resonance, exhibits a less intense spectrum relative to A and B both in solution and in the solid state. Finally, as implicated by these findings, we infer that LH could be used as a specific optical sensor for ammonia in air under rigorously humidity controlled conditions.Such a sensor would be highly desirable for practical use, given that the existing ones lack selectivity as they are based on pH indicator dyes.14 In our laboratory, several trials are in progress to this end. Fig. 8 Spectral changes with time (every 1 min) undergone by a thin film of LH (thickness 150 nm) on exposure to NH3 as described in Fig. 7. In this case, the film was previously exposed to a water-free ammonia stream immediately before the interaction with humidified ammonia (see text). The arrows indicate the direction of the spectral changes. Fig. 10 Normalized solution optical spectra of (- -- --) AsPh4·L¾ in THF, (~) LH in THF and (A) (acac)ZnL¾ in toluene Fig. 9 Spectral changes with time (every 20 min) undergone by a thin film of LH (thickness 170 nm) after exposure to the saturated vapor of a concentrated aqueous ammonia solution (35 wt%). The arrows indicate the direction of the spectral changes. (--) Spectrum of the sample prior to exposition to NH3–H2O vapor. eYciently solvated. This may likely occur with the intervening four hydrogen bonds.So, NH4+ forms four hydrogen bonds with four H2O molecules if there is enough water available in the system then L¾ adopts the most stable configuration A as in experiment (3). Alternatively, NH4+ forms two hydrogen bonds with two H2O molecules and two others with the imino groups of isomer B as in the experiment (2) if there is little water available. We note that in the latter case, B itself, which so far Fig. 11 Infrared transmission spectra of (~) LH and (- -- --) LD both as Nujol mulls was known to exist only when coordinated to a late transition J. Mater. Chem., 1998, 8(5), 1139–1144 11433 A. J. Shaka, P. B. Baker and R. Freeman, J. Magn. Reson. 1985, Interaction with water 64, 547. 4 R. R. Ernst, G. Bodenhauesen and A.Wokaun, Principles of LH in the solid state interacts with water vapor, causing fast Nuclear Magnetic Resonance in One and Two Dimensions, and quantitative scrambling protons, despite its lack of aYnity Clarendon Press, Oxford, 1987, ch. 4, p. 125. for water. This property is remarkable and in the appropriate 5 M. Pope and C. E. Swenberg, Electronic processes in organic crysconditions can be exploited for detecting water in air by means tals, Oxford University Press, New York, 1982, p. 59. of infrared spectroscopy. For istance, LH can be easily fully 6 (a) M. Bonamico, V. Fares, A. Flamini, A. M. Giuliani and P. Imperatori, J. Chem. Soc., Perkin T rans. 2, 1988, 1447; (b) deuterated (see Experimental). In the 3500–3000 cm-1 IR M. Bonamico, V. Fares, A.Flamini and P. Imperatori, J. Chem. spectrum of the deuterated species, say LD, this region lacks Soc., Perkin T rans. 2, 1990, 121; (c) M. Bonamico, V. Fares, any absorptions (Fig. 11). On exposure to air, the strong NMH A. Flamini, P. Imperatori and N. Poli, J. Chem. Soc., Perkin T rans. stretching vibration infrared-active absorptions appear in this 2, 1990, 1359; (d) V. Fares, A.Flamini and N. Poli, J Chem. Res., spectral region as a consequence of the transformation 1995, (S) 494; (M) 3054. 7 O. S. Heavens in Physics of thin Films, ed. G. Hass and R. E. Thun, LD�LH by water vapor. In no case is water (H2O or D2 O) Academic Press, New York, 1964, p. 193. trapped in the sample, thus avoiding the additional compli- 8 E. Breitmaier and W. Voelter, 13C NMR Spectroscopy, 2nd edn., cation of discriminating between OMH(D) and NMH(D) Verlag Chemie, New York, 1978, p. 111. absorptions in evaluating IR sensor applications. It is also 9 J. B. Stothers, Carbon-13 NMR Spectroscopy, Academic Press, found, as expected, that this transformation is chemically fully New York, 1972, p. 226 10 J. A. Polple, J. Chem. Phys., 1956, 24, 1111. reversible. 11 F. E. Condon, J. Am. Chem. Soc., 1965, 87, 4481. We thank the Progetto Strategico ‘Materiali Innovativi’ of 12 V. Fares, A. Flamini and N. Poli, J Chem. Res., 1995, (S) 228; CNR for partial financial support, Mr Claudio Veroli for (M) 1501. technical assistance during the X-ray work and Dr A. 13 V. Fares and A. Flamini, to be published. 14 (a) C. Preininger, G. J. Mohr, I. Klimant and O. S. Wolfbeis, Anal. Capobianchi for help in the experiments with ammonia. Chim. Acta, 1996, 334, 113; (b) A. Mills, L. Wild and Q. Chang, Mikrochim. Acta, 1995, 121, 225; (c) R. Klein and E. Voges, Fresenius J. Anal. Chem., 1994, 349, 394; (d) A. Sansubrino and M. Mascini, Biosens. Bioelectron., 1994, 9, 207; (e) Y. Sadaoka, Y. Sakai and M. Yamada, J. Mater. Chem., 1993, 3, 877; ( f ) References Y. Sadaoka, Y. Sakai and Y. Murata, Talanta, 1992, 39, 1675; (g) 1 V. Fares, A. Flamini and N. Poli, J. Am. Chem. Soc., 1995, 117, P. C� ag¡lar and R. Narayanaswamy, Analyst, 1987, 112, 1285; (h) J. F. Giuliani, H.Wohltjen and N. L. Jarvis, Opt. L ett., 1983, 8, 54. 11 580. 2 H. Bo� ttcher, T. Fritz and J. D. Wright, J. Mater. Chem., 1993, 3, 1187. Paper 7/06942A; Received 25th September, 1997 1144 J. Mater. Chem., 1998, 8(5), 1139&ndas

ISSN:0959-9428    

DOI:10.1039/a706942a

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials New semiconductors obtained by reaction of 4-imidazoline-2-selone† derivatives with TCNQ. Characterization and X-ray structure of (C9H12N4Se)2+(TCNQ)2- 3 Francesco Bigoli,a,b Paola Deplano,c Francesco A. Devillanova,c Alberto Girlando,*a Vito Lippolis,c M.-Laura Mercuri,c M.-Angela Pellinghellia,b and Emanuele F.Troguc aDip. Chimica Generale ed Inorganica, Chimica Analitica e Chimica Fisica, Parma University, 43100 Parma, Italy bCentro di Studio Strutturistica DiVrattometrica del CNR viale delle Scienze 78, 43100 Parma, Italy cDip.Chimica e T ecnologie Inorganiche e Metallo-organiche, Cagliari University, 09124 Cagliari, Italy The charge transfer complexes I, II and III of three new electron donors, 1,1¾-ethylenebis(3-methyl-4-imidazoline-2-selone) 1, 1,1¾-methylenebis(3-methyl-4-imidazoline-2-selone) 2 and 1,3-dimethyl-4-imidazoline-2-selone 3, with TCNQ have been synthesized.We report the X-ray crystal structure of II, (C9H12N4Se)(TCNQ)3, which crystallizes in the triclinic system, space group P1, with one molecule per unit cell and a=7.563(7), b=10.371(6), c=13.575(5) A ° , a=95.00(2), b=95.54(2), c=109.74(2)°. The comparison with the already described crystal structure of I and a detailed spectroscopic characterization of all three complexes, allows us to show that the change of the donor yields compounds characterized by quite diVerent charge distributions and stack types.The semiconducting properties, ranging from~10-2 to 6×10-4 S cm-1, are most likely due to the TCNQ stacks, where two negative charges are distributed among three TCNQ units.At room temperature, the charge is fully delocalized along the TCNQ stack of I, the semiconductor with the highest conductivity, whereas in II and III the charge is unevenly distributed among the TCNQ units. The donors show a strong tendency to form stable dications: in I and III they give rise to mixed-valence cations and a new dication with elimination of an Se atom is formed in II.Among the various classes of electron donor molecules cur- molecules are faced plane to plane in groups of three, closely resembling the trimerized stack structure of other TCNQ salts, rently synthesized in the field of molecular metals, the derivalike Cs2(TCNQ)3.4 The similarity between the bond distances of the TCNQs in the triads suggested that the dinegative charge is not localized on the TCNQ units, but because of the lack of single crystal vibrational spectra no definite conclusion on the charge distribution could be reached.1 N NMe Se R = 1 R-(CH2)2-R 2 R-CH2-R 3 R-CH3 tives of imidazoline-2-selone occupy a rather peculiar place. These molecules are good donors, having a first oxidation potential intermediate between those of TTF‡ and of BEDT–TTF,1 but also exhibit a quite varied and interesting chemistry.Reaction with diiodine or interhalogens, for instance, yields several diVerent types of compounds, such as insertion compounds, neutral adducts and dications.2,3 We recently started investigating the charge transfer (CT) complexes of imidazoline-2-selone derivatives with p-electron acceptor molecules.The reaction of 1 with TCNQ produces a mixed-valence N MeN N NMe Se Se N Me N N Me N Se MeN N Se NMe N Se Se 4+ 4 salt I formed by a tetracation (4) consisting of one centrosymmetrical molecule of the neutral ligand and two dications, In the present paper we report the structural and spectromutually related by a symmetry center and bearing an SeMSe scopic characterization of the complex II obtained from bridge.1 The neutral ligand and the two dications are held RM(CH2)MR (2) and TCNQ.Furthermore, we complete the together by an SeUSe donor–acceptor interaction between characterization of I through its single crystal polarized infraeach Se atom of 1 and the adjacent Se of each dication. Two red (IR) spectra from room temperature to 77 K.The comparidinegative triads of TCNQ act as counterions. The TCNQ son of the spectral data of I and II with those of the complex III obtained by reacting 3 with TCNQ also gives useful hints †4-Imidazoline=2,3-dihydroimidazole. about the structure of the latter semiconductor. A preliminary ‡List of abbreviations: BEDT–TTF=bis(ethylenedithio)tetrathiafulvacomparison between the structure and spectroscopic properties lene; CT=charge transfer; IR=infrared; MEM=methylethylmorpholof the three CT complexes obtained by reacting 1–3 with inium; TCNQ=7,7,8,8-tetracyano-p-quinodimethane; TTF=tetrathiafulvalene.TCNQ is given in ref. 5. J. Mater. Chem., 1998, 8(5), 1145–1150 1145Table 1 Crystallographic data for compound II, (C9H12N4Se) (TCNQ)3 Experimental formula C45H24N16Se Materials Mw 867.75 crystal system triclinic The electron donors 1, 2 and 3 were prepared as previously space group P1 described.2 TCNQ, the solvents and the reagents were commera/ A ° 7.563(7) cial products (Aldrich), used without further purification. b/A ° 10.371(6) Compounds I, II and III are the reaction products of TCNQ c/A° 13.575(5) with 1, 2 and 3, respectively.The synthesis of I has already a(°) 95.00(2) been described.1 II and III were obtained by mixing CH2Cl2 b(°) 95.54(2) c(°) 109.74(2) solutions of 2 and 3 with a CH3CN solution of TCNQ in 152 U/A° 3 989(1) and 151 ratio, respectively. The mixed solutions were left to Z 1 stand at room temperature, and after several days well-shaped Dc/Mg m-3 1.457 crystals of II and lustrous dark-blue microcrystals of III were radiation Ni-filtered obtained in about 70% yield.Elemental analysis: II, Calc. for wavelength Cu-Ka(l=1.541838 A° ) C45H24N16Se: C 62.29, H 2.79, N 25.83; Found: C 62.38, H 2.62, T/K 295 m/cm-1 17.52 N 25.42%. III, Calc. for C17H12N6Se: C 53.79, H 3.16, N 22.15; h-range for intensity collection(°) 3–70 Found: C 54.09, H 3.31, N 22.64%.data collected ±h,±k,l no. of measured reflections 3760 Spectroscopic measurements no. of reflections with I>2s(I) 2226 no. of refined parameters 317 Single crystal polarized infrared spectra were obtained with a min/max height in final Dr map/eA° -3 -0.35/0.71 Bruker IFS66 FT-IR spectrometer, equipped with a Bruker largest shift/e.s.d. 0.20 A590 microscope, and a KRS5 grid polarizer (Specac).Low R=S|DF|/S|F| 0.0596 temperature measurements under the IR microscope were wR=ÓS w(DF )2/S wF2 0.0607 performed by using a Linkam FTIR-600 liquid nitrogen cold stage. The FT-Raman spectra were recorded on a Bruker RFS100 FTR spectrometer, operating with an excitation fre- temperature conductivities ranging from ~10-2 to quency of 1064 nm (Nd:YAG laser). The power level of the 6×10-4 S cm-1.An almost complete characterization of I, laser source was 20–40 mW, and the powdered samples were including the crystal structure, has already been described,1 as dispersed in KBr and packed into a glass capillary for 180° summarized in the introduction. scattering geometry. No sample decomposition was observed during the experiments.Crystal structure of II Compound II crystallizes in the triclinic system, space group Conductivity measurements P1, Z=1, and can be formulated as (C9H12N4Se)(TCNQ)3. A Conductivity measurements were made at room temperature summary of the crystallographic data is reported in Table 1. on pellets (thickness 0.5 mm, diameter 12 mm) using the two- The structure (Fig. 1) consists of homologous layers of alternatpoint probe method. s(I)=1.0×10-2; s(II)=5.9×10-4; ing (C9H12N4Se)2+ dications and (TCNQ)2- 3 anions, roughly s(III)=6.5×10-3 S cm-1. parallel to the ab plane, the cations and anions lying roughly parallel to the bc and ac planes, respectively. X-Ray diVraction measurements Compound II diVers from I in both the cation and the anion structure.In I, a mixed-valence cation is present, with dications The diVraction measurements on the complex II were made characterized by an SeMSe bridge and the formation of an on a Siemens AED diVractometer. The crystals to choose from were not of good quality; the one selected had dimensions of 0.05×0.21×0.36 mm. Accurate unit cell parameters and the orientation matrix for data collection were obtained from leastsquares refinements, using the setting angles of 29 reflections (18°<h<31°).The check on the standard reflection showed no significant crystal decay under irradiation. Intensities were corrected for Lorentz and polarization eVects. No correction for absorption was applied. The structure was solved and refined using the SHELX-766 and SHELX-867 computer programs.Only the non-hydrogen atoms of the dication were refined anisotropically. All hydrogen atoms were placed at their geometrical position (CMH: 0.96 A ° ) and refined by ‘riding‘ on the corresponding atoms with unique isotropic thermal parameters [U=0.0969(86) A° 2]. In the last stages of refinement the best result was obtained using unit weights. Scattering factors and correction for anomalous dispersion eVects were taken from ref. 8. Full crystallographic details, excluding structure factors, have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Information for Authors, J. Mater. Chem., 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 1145/84.Results Compounds I, II and III, obtained by reacting TCNQ with 1, Fig. 1 Projection of the structure of II along [001] 2 and 3, respectively, are molecular semiconductors with room 1146 J. Mater. Chem., 1998, 8(5), 1145–1150Table 3 Raman spectra of the compounds I, II and IIIa I II III n� /cm-1 n� /cm-1 n� /cm-1 tentative assignmentb 227 w 229 w 226 m 308 w 332 m 331 m 328 m T, agn9 433 w 490 w 567 w 609 w 605 m 600 m T, agn8 705 w 708 w 706 w 967 m 970 w,br 962 m T, agn6 1156 m D 1196 s 1195 s 1195 s T, agn5 1374 m,br 1388 m 1384 w T, agn4 Fig. 2 Perspective view of (C9H12N4Se)2+ cation in II, showing the 1413 s 1417 s 1417 s T, agn4 atomic numbering scheme. The thermal ellipsoids are drawn at the 1451 m 1443 m D? 30% probability level. 1603 s 1601 s 1601 s T, agn3 2202 m 2205 m,br 2205 m,br T, agn2 eight-membered central ring (see structural formula 4 in the aQualitative relative intensities indicated by: s, strong; m, medium; introduction).In II, the donor 2 gives rise to a dication with w, weak; br, broad; sh, shoulder. bD: donor; T: TCNQ. For the elimination of one Se atom, and the formation of a six- numbering of the normal modes see ref. 13. membered ring. The molecular structure and atomic labelling scheme of the dication are shown in Fig. 2; the bond lengths and angles are given in Table 2. The central ring of when it is used in the analysis of an homologous series of (C9H12N4Se)2+ has a boat conformation, with h and w9 equal compounds, as in the present case. We have recorded the to 86.6(9)° and -6.1(9)°, respectively, whereas the dihedral powder Raman spectra and the single crystal polarized IR angle between the two planar imidazoline rings is of 50.2(5)°. spectra of I, II and III, and the interpretation of the data will The dication structural data are in agreement with those be reported in that order.Tables 3 and 4 report the frequencies observed in the diiodine neutral adducts of 2,2 and of its sulfur observed in the Raman and IR spectra (polarization perpenanologue, 10 and in the insertion derivatives of 2 with chlorine.11 dicular to the stack) for the three compounds.The TCNQ stacks of the complex I are formed by triads in a Partial vibrational data for I have already been published, zig-zag arrangement. In II, on the other hand, the TCNQ but no definite conclusion could be reached about the charge stack is better described as being made up of TCNQ dimers distribution on the TCNQ sites.1 The single crystal IR spectra (A and C¾ in Fig. 1), separated by a third TCNQ (B), shifted up to 2500 cm-1 are reported in Fig. 3. The spectrum polarized in the a direction. The dihedral angles between the meanparallel to the stack is similar to that of the powders,1 being weighted planes of the non-exactly planar TCNQ molecules dominated by the electronic CT transition (maximum around are in the range 1.5(2)–3.9(2)°. 5000 cm-1, not shown in Fig. 3) along the TCNQ stack. We have not been able to obtain single crystals of III Superimposed on it the vibronic bands typical of the TCNQ suitable for X-ray analysis, so that all the information on the molecule13 are clearly identified.These bands correspond to complex III formed by reacting 3 with TCNQ relies on the the totally symmetric (ag) modes of TCNQ, the intramolecular spectroscopic measurements reported in the following section. modes which, modulating the on-site energies, are coupled to the CT electron and borrow IR intensity from the CT trans- Spectroscopic studies ition.12 As for the powder spectra, these bands are normal absorptions below ca. 1000 cm-1, but above this frequency Vibrational spectroscopy is an invaluable tool for a detailed characterization of organic semiconductors,12 particularly they appear as indentations in the continuum single-electron transition. This well known phenomenon14 allowed us to when it is associated with X-ray structure determination or Table 2 Selected bond distances (A ° ) and angles (°) for the dication in complex II (e.s.d.in parentheses) bond length/A° Angle(°) SeMC(11) 1.908(13) C(21)MN(21)MC(51) 127.1(12) SeMC(12) 1.865(13) C(11)MN(21)MC(51) 124.6(11) N(11)MC(11) 1.319(17) C(11)MN(21)MC(21) 108.2(11) N(11)MC(31) 1.402(16) C(12)MN(12)MC(32) 109.7(11) N(11)MC(41) 1.440(14) C(41)MN(12)MC(32) 127.3(12) N(21)MC(11) 1.348(14) C(41)MN(12)MC(12) 122.6(12) N(21)MC(21) 1.353(21) C(22)MN(22)MC(52) 126.3(15) N(21)MC(51) 1.468(18) C(12)MN(22)MC(52) 125.3(13) N(12)MC(41) 1.468(21) C(12)MN(22)MC(22) 108.2(12) N(12)MC(12) 1.345(20) N(11)MC(11)MN(21) 107.5(11) N(12)MC(32) 1.366(20) SeMC(11)MN(21) 128.0(9) N(22)MC(12) 1.351(20) SeMC(11)MN(11) 124.1(9) N(22)MC(22) 1.387(23) N(21)MC(21)MC(31) 110.1(13) N(22)MC(52) 1.446(27) N(11)MC(31)MC(21) 103.5(12) C(21)MC(31) 1.358(21) N(11)MC(41)MN(12) 108.7(11) C(22)MC(32) 1.353(31) N(12)MC(12)MN(22) 107.4(13) C(11)MSeMC(12) 88.4(5) SeMC(12)MN(22) 128.7(10) C(31)MN(11)MC(41) 126.6(11) SeMC(12)MN(12) 123.8(9) C(11)MN(11)MC(41) 122.5(11) N(22)MC(22)MC(32) 107.5(16) C(11)MN(11)MC(31) 110.7(10) N(12)MC(32)MC(22) 107.1(15) J.Mater. Chem., 1998, 8(5), 1145–1150 1147Table 4 Infrared spectra, polarized perpendicularly to the stack, of the TCNQ units. However, in trimerized stacks the ag frequencies compounds I, II and IIIa may be perturbed by electron–phonon coupling.15 A safe and accurate estimate of r must then rely on the frequencies of the I II III normally IR active ungerade modes.The IR spectra of I n� /cm-1 n� /cm-1 n� /cm-1 tentative assignmentb polarized perpendicularly to the stack (Fig. 3 and Table 4) 626 w yield a straightforward assignment of the main in-plane (b1u 646 s and b2u) vibrations of TCNQ. The CON stretching frequencies 675 m 2D2+ around 2200 cm-1 have often been used to determine the 707 w D average charge on the TCNQ units.16 The spectra of I show 734 m 2D2+ two CON stretching bands, one of b1u and the other of b2u 751 m 747 m 744 m D symmetry, again indicating uniform charge distribution. 759 w 800 w 805 m However, since several authors have reported deviations from 830 m the expected linear dependence of the CON frequencies from 1033 w 1023 w 2D2+ r,17–19 we prefer to use the CC stretching mode b1un20.17 Its 1079 w frequency occurs at 1517 cm-1 (Table 4), indicating an average 1097 w 1092 m D charge of 0.68.We can now safely conclude that in I the 2e- 1122 m 1115 w charge is uniformly distributed among the three TCNQ units 1147 w 1134 w 1132 m D 1176 m 1170 m in the trimerized stack. This finding explains well the remark- 1209 s 1203 s T, b2un36 able conductivity of I: about two orders of magnitude higher 1230 m 1222 s D than that of Cs2(TCNQ)3.20 1251 w We have also obtained single crystal polarized IR spectra at 1333 m 1334 s D, 2D2+ low temperature, to detect the presence of phase transitions in 1375 s 1349 m 1372 w D? the complex I.Fig. 4 compares the CON stretching region 1405 w 1442 w 1453(perpendicular polarization) at 300 and 77 K. It is seen immedi- 1480 w 1492 s 2D2+ ately that the room temperature doublet becomes a complex 1503 w 1505 sh T, b1un20 structure at liquid nitrogen temperature, with at least five 1517 s 1524 s 1519 sh T, b1un20 maxima clearly identified.Indeed, at temperatures below 250 K 1566 s 1569 ms 1560 m D, 2D2+ the charge is no longer uniformly distributed on the TCNQ 1633 m 1629 w sites, as revealed by the structure of the CON stretching 2162 s 2158 s T, b2un33 2175 s 2176 s T, b1un19 region.The change appears to occur rather smoothly with 2191 s 2189 s T, b2un33 temperature variation, so it is hardly possible to speak of a 2194 s T, b2un33 phase transition, nor can we determine precisely the diVerence 2198 s 2198 s 2198 s T, b1un19 in charge among the TCNQ sites, which remains rather small. 2203 s 2207 sh T, b1un19 The intensity of the vibronic bands in the parallelel IR spectrum does not change significantly, indicating that the stack structure aQualitative relative intensities indicated by: s, strong; m, medium; w, weak; br, broad; sh, shoulder. bD: donor; T: TCNQ. For the is aVected very little by the localization of the charge. numbering of the normal modes see ref. 13. The crystal structure and conductivity show that II is a Fig. 3 Polarized IR spectra of I: (a) electric vector parallel to the stack axis; (b) electric vector perpendicular to the stack axis estimate the room temperature optical gap of I at ca. 1000 cm-1 (~0.12 eV).1 In the previous work,1 the frequency of the Raman active Fig. 4 Polarized IR spectra of I in the CON stretching region, at (i) TCNQ agn4 mode, observed for I at 1413 cm-1 (Table 3), room (300 K) and (ii) liquid nitrogen (77 K) temperature.Only the polarization perpendicular to the stack axis is shown. suggested a uniform charge distribution (r) among the trimeric 1148 J. Mater. Chem., 1998, 8(5), 1145–1150In the light of the above data, and of the X-ray analysis, we suggest that the TCNQ oVset of the stack (B in Fig. 2) bears a unit negative charge, whereas the other electron is slightly unevenly distributed among the A and C TCNQ units, as in the dimerized stack structure of MEM(TCNQ)2.22 As far as we know, the present stack structure and charge distribution have not been encountered so far in TCNQ stacks. The charge localization of II as opposed to the charge delocalization of I may well explain the large diVerence in room temperature conductivities (5.9×10-4 vs. 1.0×10-2 S cm-1) between the two compounds. We have not been able to obtain single crystals of III suitable for X-ray analysis, so that all the information on the complex formed by reacting 3 with TCNQ relies on the spectroscopic measurements. Fig. 6 shows the IR spectra polarized parallel and perpendicular to the stack axis, whereas Tables 3 and 4 report the Raman and IR frequencies.The IR spectrum polarized parallel to the stack shows an electronic transition centered around 4000 cm-1, lower than for I or II, but without trace of vibronic absorptions. Therefore the stack along which the CT transition occurs, most probably the TCNQ stack, is a regular one, i.e. a stack with constant distance between the molecular units.12 In such a case one would expect a uniform charge distribution, but the Raman spectrum in the TCNQ agn4 mode spectral region is rather Fig. 5 Polarized IR spectra of II: (a) electric vector parallel to the similar to that of II (Table 3), where the charge is localized. stack axis; (b) electric vector perpendicular to the stack axis Analogous information comes from the IR spectrum polarized perpendicular to the stack.The spectrum (Fig. 6 and Table 4) shows four bands in the CON stretching region, indicating quite diVerent complex from I. The spectroscopic measurements oVer further clues about the origin of the diVerence. two diVerently charged TCNQ units, one with charge ~1 and the other between 0.4 and 0.5. Careful analysis of the b1un20 Fig. 5 reports the IR absorption spectra polarized parallel and perpendicular to the stack axis. The spectra polarized parallel spectral region, partially obscured by the presence of a strong absorption due to the donor at 1492 cm-1 (see below) confirms to the stack show the CT electronic absorption with a maximum beyond 5000 cm-1, over which the vibronic transitions the presence of both TCNQ- and TCNQ-0.5 units.The comparison of the IR spectrum of III (Table 4) with due to the TCNQ ag modes are superimposed. The optical gap can again be estimated from the frequency above which those of the neutral donor 3 and of the dication formed by the latter by reaction with Br211 indicates the presence of a mixed- the vibronic bands appear as indentations (~1000 cm-1 or ~0.12 eV).However, it should be noted that, at variance with valence counterion. Since analytical results indicate that III contains TCNQ and 3 in a 151 molar ratio, we suggest that what is observed in I, the structure of the indentations is rather complex. Apart from other diYcult to analyze features, a the complex is composed of a mixed-valence dication formed by the dimerized donor with an Se–Se bridge and a neutral doublet structure is clearly resolved, with a narrow component immediately below the main transition. This fact suggests that molecule of 3, and by a triad of TCNQs bearing two negative in II the 2e- charge is not uniformly distributed on the TCNQ sites,21 as the following analysis will confirm.As shown by the X-ray data, the donors give rise to a new type of dication, whose vibrational frequencies are of course unknown. Therefore, it is diYcult in some cases to disentangle the frequencies due to TCNQ from those of the dication. In the Raman spectrum (Table 3) we observe three bands (1451, 1417 and 1388 cm-1) in the spectral region of the TCNQ agn4 mode (see above).13 The first one would indicate the presence of neutral TCNQ, but since other Raman or IR bands attributable to this species are not seen, we prefer to attribute this band to the donor.If the other two bands are assigned to TCNQ, they indicate the presence of at least two diVerently charged TCNQs, one with intermediate charge and one fully charged. The IR spectra polarized perpendicularly to the stack (Fig. 5 and Table 4) confirm that in II the charge is unevenly distributed on the TCNQ sites. The CON spectral region shows six bands, instead of the two expected for uniform charge distribution, suggesting the presence of three diVerently charged TCNQs, one with r~1 and the other two both with a charge close to 0.5. The assessment of the precise estimate of r cannot rely on the CON stretching frequencies, however, 17–19 and we can reasonably assign only two bands in the C–C stretching region, at 1503 and 1524 cm-1.If they are both assigned to the TCNQ b1un20 mode, they would indicate a charge of r~1 and of r~0.5, respectively, consistent with what can be qualitatively deduced from the analysis of the Fig. 6 Polarized IR spectra of III: (a) electric vector parallel to the stack axis; (b) electric vector perpendicular to the stack axis CON stretching region.J. Mater. Chem., 1998, 8(5), 1145–1150 1149charges. At this point we can advance two hypotheses about by the National Research Council (CNR) under the Coordinate Project No. 96/215. the structure of the TCNQ stack. The first is that the stack somehow resembles that of II, with two TCNQ-0.5 and one TCNQ-1 units forming a repetitive trimeric pattern.In the References second hypothesis the TCNQ bearing unit negative charge 1 F. Bigoli, P. Deplano, F. A. Devillanova, A. Girlando, V. Lippolis, instead does not belong to the stack, which is made up solely M.-L. Mercuri, M.-A. Pellinghelli and E. F. Trogu, Inorg. Chem., from TCNQ0.5- units.We have performed single crystal low 1996, 35, 5403. temperature IR measurements to verify whether complex III 2 F. Bigoli, M.-A. Pellinghelli, P. Deplano, F. A. Devillanova, undergoes a Peierls transition. In such a case, the frequency V. Lippolis, M.-L. Mercuri and E. F. Trogu, Gazz. Chim. Ital., and shape of the vibronic bands would help us to decide 1994, 124, 445. between the two hypotheses.However, we have not detected 3 F. Bigoli, F. Demartin, P. Deplano, F. A. Devillanova, F. Isaia, V. Lippolis, M.-L. Mercuri, M.-A. Pellinghelli and E. F. Trogu, phase transitions down to liquid nitrogen temperature. With Inorg. Chem., 1996, 35, 3194; F. Bigoli, P. Deplano, the lack of further data, and considering that the conductivity F. A. Devillanova, V.Lippolis, M.-L. Mercuri, M.-A. Pellinghelli and the electronic spectrum of III diVer from those of II, we and E. F. Trogu, Chem. Ber., in press. prefer the second of the two above-mentioned hypotheses, i.e. 4 C. J. Fritchie and P. Arthur, Acta Crystallogr., 1966, 21, 139. a TCNQ stack formed solely by TCNQ0.5- units. The fact 5 F. Bigoli, P. Deplano, F. A. Devillanova, A. Girlando, V.Lippolis, that we have not observed the Peierls transition, together with M.-L. Mercuri, A. Pelagatti, M.-A. Pellinghelli and E. F. Trogu, Synth.Met., 1997, 86, 1853. the problems encountered in obtaining the X-ray structure of 6 G. M. Sheldrick, SHEL X-76: Programs for Crystal Structure III, suggest the presence of structural disorder in the Determination, University of Cambridge, UK, 1976.compound. 7 G. M. Sheldrick, SHEL X-86: Program for the Solution of Crystal Structures, Universita�t Go� ttingen, Germany, 1986. 8 International Tables for X-ray Crystallography, The Kynoch Press, Conclusions Birmingham, 1974, vol. IV. 9 D. Cremer and J. A. Pople, J. Am. Chem. Soc., 1975, 97, 1354. The donors 1, 2 and 3, based on the same imidazoline-2-selone 10 F.Bigoli, P. Deplano, F. A. Devillanova, M.-L. Mercuri, group, react with TCNQ to produce new molecular semi- M.-A. Pellinghelli, A. Sabatini, E. F. Trogu and A. Vacca, J. Chem. conductors (I, II and III) showing conductivities ranging from Soc., Dalton T rans., 1996, 3583. ~10-2 to 6×10-4 S cm-1 at room temperature. Structural 11 F. Bigoli and P. Deplano, et al., in preparation.and spectroscopic results show that I, II and III complexes 12 C. Pecile, A. Painelli and A. Girlando,Mol. Cryst. L iq. Cryst., 1989, 171, 69. are quite diVerent. In I and III the donor gives rise to mixed- 13 R. Bozio, I. Zanon, A. Girlando and C. Pecile, J. Chem. Soc., valence cations, whereas a new dication with elimination of an Faraday T rans. 2, 1978, 74, 235. Se atom is formed in II.In any case the donors confirm the 14 M. J. Rice, L. Pietronero and P. Bruesch, Solid State Commun., tendency to form closed-shell dications. The imidazoline ring 1977, 21, 757. loses one electron in agreement with the 4n+2 rule, but then 15 A. Painelli, C. Pecile and A. Girlando,Mol. Cryst. L iq. Cryst., 1986, two rings associate through Se bridges. The charge transfer 134, 1. 16 J. S. Chappell, A. N. Bloch, W. A. Bryden, M. Maxfield, and conductivity are essentially associated with the TCNQ T. O. Poehler and D. O. Cowan, J. Am. Chem. Soc., 1981, 103, 2442. stacks. In all three complexes, two negative charges are distrib- 17 A. Girlando, A. Painelli and C. Pecile,Mol. Cryst. L iq. Cryst., 1984, uted among three TCNQ units. Yet, the TCNQ stack structure 112, 325. and charge distribution is diVerent, the most interesting case 18 M. Meneghetti and C. Pecile, J. Chem. Phys., 1986, 84, 4149. being that of I, the complex with highest conductivity. At 19 K. A. Hutchison, G. Srdanov, R. Menon, J.-C. P. Gabriel, 300 K the charge is fully delocalized along the trimerized B. Knight and F.Wudl, J. Am. Chem. Soc., 1996, 118, 13081. 20 K. D. Cummings, D. Tanner and J. Miller, Phys. Rev., 1981, B24, TCNQ stack, and becomes localized below 250 K. 4142. 21 R. Swietlik, Synth.Met., 1995, 74, 115. We wish to thank Dr C. Bellitto (Istituto di Chimica dei 22 M. J. Rice, V. M. Yartsev and C. S. Jacobsen, Phys. Rev., 1980, Materiali, CNR, Rome) for the conductivity measurements. B21, 3437. This work has been supported by the Ministry of University and of Scientific and Technological Research (MURST) and Paper 7/07223F; Received 6th October, 1997 1150 J. Mater. Chem., 1998, 8(5), 1145–

ISSN:0959-9428    

DOI:10.1039/a707223f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Low temperature crystal and electronic band structure of the (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O stable organic metal Rimma P. Shibaeva,*a† Salavat S. Khasanov,a Bakhyt Z. Narymbetov,a Leokadiya V. Zorina,a Larisa P. Rozenberg,a Anatolii V. Bazhenov,a Nataliya D. Kushch,b Eduard B. Yagubskii,b Carme Rovirac and Enric Canadell*d‡ aInstitute of Solid State Physics, Russian Academy of Sciences, 142432 Chernogolovka,MD, Russia bInstitute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, 142432 Chernogolovka,MD, Russia cDepartament de Quý�mica-Fý�sica, Facultat de Quý�mica, Universitat de Barcelona, 08028 Barcelona, Spain dInstitut de Ciencia de Materials de Barcelona (CSIC), Campus de la U.A. B., 08193 Bellaterra, Spain A bis(ethylenedioxy)tetrathiafulvalene (BEDO–TTF) chloride was synthesized by a combined diVusion-electrocrystallization method using the [(C2H5)4N]2CuCl4 salt as supporting electrolyte.An X-ray analysis has been carried out at both room and low (160 K) temperatures: a=5.097(1), b=8.592(2), c=16.236(2) A ° , a=98.13(1)o, V=703.8 A ° 3 (293 K) and a=5.069(2), b=8.435(6), c=16.137(4) A ° , a=97.82(4)o, V=683.6 A ° 3 (160 K); space group P21/b.This salt seems to be the same BEDO–TTF chloride previously reported by several groups although its composition was never firmly established. The crystal structure is characterized by the presence of H-type radical cation layers alternating along the c-direction with honeycomb-like polymeric networks including Cl- anions, H2O molecules and H3O+, hydroxonium ions.The band structure and Fermi surface for diVerent electron transfers at both 160 and 293 K have been calculated. The combination of these results with IR spectral data and analysis of the physical properties led to the conclusion that the real composition of this salt is (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O. Using a crown ether route Schweitzer et al.1 prepared for the molecules and Cl- anions is still not clear.The problem lies in the statistical occupation of four symmetrically equivalent first time a (BEDO–TTF) chloride which is a stable organic metal. On the basis of X-ray and IR studies they proposed the crystallographic positions in the unit cell by the Cl- anions and H2O molecules. However, determination of the real com- composition (BEDO–TTF)Cl H2O for this salt.This was a surprising result because it was the first stable metallic radical position of this salt is an essential step in understanding its physical properties. As shown below, neither the cation salt with a half-filled band. Later, the formation of the same (BEDO–TTF) chloride with Bu4NCl as a supporting (BEDO–TTF)Cl H2O nor the (BEDO–TTF)2Cl 3H2O formulae seem to be entirely appropriate for this molecular metal.electrolyte was described by Mori et al.2 However, they proposed the composition (BEDO–TTF)2Cl 3H2O. Very recently, This is why we considered it worth restudying this salt in order to elucidate its true composition. we tried to synthesize a radical cation salt of BEDO–TTF with the magnetic anion CuCl42-.Salts of the bis(ethylenedi- Here, we report our work concerning the synthesis as well as the room and low temperature (160 K) crystal structures of thio)tetrathiafulvalene (BEDT–TTF) donor and its selenium analog—bis(ethylenedithio)tetraselenafulvalene (BETS)—with this BEDO–TTF chloride. We assumed that when lowering the temperature the thermal motion of the atoms will become this anion have already been reported.4–8 However, an X-ray study of the single crystals obtained showed that no Cu atoms slower and thus, the refinement of the occupation factors for the Cl and O atoms would be more precise.We also report were present and that the radical cation salt prepared was really a BEDO–TTF chloride with unit cell parameters very IR spectral measurements as well as local X-ray microprobe analysis (LRMA) in order to check the chlorine content.close to those reported by Schweitzer et al.1 Almost simultaneously, the same BEDO–TTF chloride was accidentally Finally, we also analyze the band structure and Fermi surface at both room temperature and 160 K in an attempt to correlate prepared by another group,9 while trying to synthesize BEDO–TTF salts with HgX42- anions in the presence of the results of these studies with magnetoresistance measurements. As a result of this combined eVort we believe that the supporting electrolytes with the composition Bu4NHgX3+ Bu4NX (X=I, Br, Cl).true composition of this BEDO–TTF chloride can now be given as (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O. Experimental Synthesis S S S S O O O O BEDO-TTF Crystals of the BEDO–TTF chloride were obtained by a The exact composition of this BEDO–TTF chloride has not combined diVusion–electrocrystallization method from a yet been firmly established, i.e.the exact content of H2O BEDO–TTF solution in benzonitrile with addition of ethanol (10% vol) at 20 °C. A constant current of 0.2 mA was applied. † E-mail: shibaeva@issp.ac.ru ‡ E-mail: canadell@icmab.es The [(C2H5)4N]2CuCl4 salt was used as supporting electrolyte.J. Mater. Chem., 1998, 8(5), 1151–1156 1151Table 2 Atomic coordinates and equivalent isotropic parameters for Addition of BEDO–TTF to the electrolyte solution led to the (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O. Ueq is defined as one third almost instantaneons precipitation of the products of the of the trace of the orthogonalized Uij tensor chemical oxidation of the donor by the Cu2+ ions.In order to avoid this, BEDO–TTF (1.5×10-3 mol l-1) and the electrolyte atom x/a y/b z/c Ueq (5×10-3 mol l-1) were placed in diVerent compartments of S(1) 0.2250(1) 0.8499(1) 0.0741(0) 0.0137(2) an H-like electrochemical cell. After approximately 30 min the S(2) -0.1965(1) 1.0923(1) 0.1172(0) 0.0142(2) cell was connected to the current source. O(1) 0.2623(3) 0.8162(2) 0.2350(1) 0.0192(4) The use of this method leads to the oxidation of BEDO–TTF O(2) -0.1566(3) 1.0476(2) 0.2759(1) 0.0180(4) both electrochemically and chemically (because of the diVusion C(1) 0.0054(4) 0.9876(3) 0.0408(1) 0.0124(5) of CuCl42- or CuCl3- anions through the glass frit separating C(2) 0.1312(5) 0.8928(3) 0.1789(1) 0.0149(5) the cell compartments). The appearance of the Cl- anions in C(3) -0.0606(5) 1.0015(3) 0.1982(1) 0.0144(5) C(4) -0.0663(5) 0.9394(3) 0.3331(1) 0.0215(5) the solution was probably caused by the dissociation of the C(5) 0.2223(5) 0.9007(3) 0.3188(1) 0.0212(5) electrolyte (CuCl42-=CuCl3-+Cl-) and/or BEDO–TTF Cla 0.9722(3) 0.3295(2) 0.5171(1) 0.031(1) oxidation by Cu2+ ions.Note that BEDO–TTF is a stronger Ow a 0.9722(3) 0.3295(2) 0.5171(1) 0.081(3) reducing agent than BEDT–TTF and BETS donors. Within H(41) -0.168(6) 0.845(3) 0.324(2) 0.0215(5) 18–20 days BEDO–TTF chloride crystals grow on the anode H(42) -0.095(6) 0.992(3) 0.387(2) 0.0215(5) as rhombic- or hexagonal-like plates.H(51) 0.330(6) 0.998(3) 0.323(2) 0.0212(5) H(52) 0.283(6) 0.833(3) 0.357(2) 0.0212(5) Hw(1)a 0.96(1) 0.442(3) 0.510(5) 0.081(3) X-Ray structure determination Hw(2)a 1.07(1) 0.337(8) 0.569(2) 0.081(3) X-Ray experimental data were collected at room temperature aOccupancy factors are 0.32 for Cl and 0.68 for Ow, Hw(1) and Hw(2). and at 160 K on an Enraf-Nonius CAD-4F diVractometer [l(Mo-Ka)=0.71073 A ° , graphite monochromator, v-scan].At room temperature the intensities of 956 non-zero reflections were measured up to (sinh/l)max=0.549; 572 were unique cation are given in Table 3. Full crystallographic details, exclud- (Rint=0.029) with I2s(I). The structure was solved by direct ing structure factors, have been deposited at the Cambridge methods and refined by a least-squares technique in the full- Crystallographic Data Centre (CCDC).See Information for matrix anisotropic approximation to R=0.044 using the Authors, J. Mater. Chem., 1998, Issue 1. Any request to the AREN programs.10 The unit cell pers (T=293 K) are CCDC for this material should quote the full literature citation as follows: a=5.097(1), b=8.592(2), c=16.236(2) A ° , a= and the reference number 1145/86. 98.13(1)o, V=703.8 A° 3, space group P21/b. Crystal data and experimental details of the BEDO–TTF chloride single crystals IR spectra at T=160 K are listed in Table 1. The atomic coordinates and the room temperature crystal structure were used as a starting The smallest single crystals under investigation had dimensions point and the low temperature structure was refined by a full- of 1×0.5×0.06 mm.As a result, the measurements of the matrix least-squares method in the anisotropic approximation infrared transmittance and reflectance spectra were carried out for all non-hydrogen atoms by using the SHELXL-93 package using the IR microscope of a Fourier-transform spectrometer. of programs.11 The hydrogen atoms were located from a Spectra were measured at 300 K in the spectral range diVerence synthesis and only their position parameters were 600–6000 cm-1.The electrical vector of the light beam was refined. Their thermal parameters were kept equal to those of parallel to the highly conductive ab-plane of the BEDO–TTF the atoms to which they are bonded. The final coordinates of chloride single crystals.The absorption spectra were calculated the atoms and their thermal parameters are listed in Table 2. from the transmittance ones. The bond distances and angles of the BEDO–TTF radical Electrical resistivity measurements Table 1 Crystal and experimental data Resistivity was measured by the standard four-probe dc technique (in the ab plane). Contacts to the crystals were glued formula C20H21.72S8O10.72Cl1.28 with a graphite paste using 10–30 mm diameter platinum wires.M 735.47 The room temperature conductivity was found to be about 60 T /K 160 ohm-1 cm-1. crystal system monoclinic space group P21/b a/A ° 5.069(2) b/A ° 8.435(6) c/A ° 16.137(4) Table 3 Bond lengths and angles for BEDO–TTF in a/° 97.82(4) (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O V /A ° 3 683.55 Z 1 bond distances/A ° bond angles (°) F(000) 378.5 Dc/g cm-3 1.787 S(1)MC(1) 1.746(2) C(1)MS(1)MC(2) 93.8(1) m(Mo-Ka)/cm-1 7.1 S(1)MC(2) 1.745(2) C(1)MS(2)MC(3) 93.8(1) 2Hmax (°) 50 S(2)MC(1) 1.746(2) C(2)MO(1)MC(5) 109.6(2) h, k, l limits ±h, -k,±l S(2)MC(3) 1.744(2) C(3)MO(2)MC(4) 110.4(2) 5, 10, 19 O(1)MC(2) 1.355(3) S(1)MC(1)MS(2) 116.8(1) data collected 2028 O(1)MC(5) 1.455(3) S(1)MC(1)MC(1)¾ 121.3(2) independent data 1026 O(2)MC(3) 1.352(3) S(2)MC(1)MC(1)¾ 122.0(2) Rint(F2) 0.031 O(2)MC(4) 1.458(3) S(1)MC(2)MO(1) 117.3(2) observed data, F>4s(F) 1023 C(1)MC(1)¾ 1.362(4) S(1)MC(2)MC(3) 117.8(2) parameters refined 116 C(2)MC(3) 1.344(3) O(1)MC(2)MC(3) 124.9(2) Ra 0.026 C(4)MC(5) 1.510(4) S(2)MC(3)MO(2) 116.9(2) goodness of fit 0.656 S(2)MC(3)MC(2) 117.8(2) Drmax/e A° -3 0.37 O(2)MC(3)MC(2) 125.2(2) Drmin/e A° -3 -0.24 O(2)MC(4)MC(5) 110.4(2) O(1)MC(5)MC(4) 110.2(2) aR=S||Fo|-|Fc||/S|Fo|. 1152 J. Mater. Chem., 1998, 8(5), 1151–1156Band structure calculations The tight-binding band structure calculations are based upon the eVective one-electron Hamiltonian of the extended Hu� ckel method.12 The oV-diagonal matrix elements of the Hamiltonian were calculated according to the modifiedWolfsberg–Helmholz formula.13 All valence electrons were explicitly taken into account in the calculations and the basis set consisted of double-f Slater-type orbitals for C, S and O and single-f Slater type orbitals for H.The exponents, contraction coeYcients and atomic parameters were taken from previous work.14 Results and Discussion The temperature dependence of the resistivity of our crystals is analogous to that of the BEDO–TTF chloride crystals previously prepared by electrochemical oxidation of BEDO–TTF using the crown ether route.1 The crystals exhibit a metallic behavior down to 1.3 K (Fig. 1) and the ratio R1.3 K/R293 K is 7×10-3. Fig. 2 shows a projection of the 160 K BEDO–TTF chloride structure along the a-direction.The structure is characterized by layers of the BEDO–TTF radical cation alternating along the c-direction with honeycomb-like polymeric anion networks. The BEDO–TTF radical cations (see Fig. 3 for atom labelling) are located on an inversion center and have an eclipsed conformation of the terminal ethylene groups: the C(4) and C(5) atoms deviate from the average plane of the molecule by +0.27 and -0.49 A ° , respectively.The ethylene groups are ordered. The nature of the bond lengths and angle distribution (Table 3) probably corresponds to (BEDO–TTF)0.5+. It is noteworthy that the CNC double bonds C(1)NC(1¾) [1.362(4) A ° ] and C(2)NC(3) [1.344(3) A ° ] are longer than the corresponding bonds in the neutral (BEDO–TTF)0 molecule. Fig. 2 (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O viewed along the aaxis Their values are close to those found in the 251 salts (BEDO–TTF)2AuBr2,15 (BEDO–TTF)2ReO4 H2O16 and (BEDO–TTF)2CF3SO3.17 The projection of the radical cation layer along the cdirection is shown in Fig. 4(a). It is a layer of the H-type first discovered in the organic superconductor H-(BEDT-TTF)2I318 and later in a number of organic metals.This type of conducting layer is built from regular BEDO–TTF stacks parallel to the short a-axis. The overlap mode of adjacent radical cations in Fig. 3 Atomic labelling for the BEDO–TTF radical cation the stack is shown in Fig. 4(b) and it is the same at room and low temperatures. The mean BEDO–TTF interplanar distances in the stack are 3.532 (293 K) and 3.475 A ° (160 K). The planes of the radical cations from neighboring stacks are approximately perpendicular to each other.There are several short S,S and S,O intermolecular contacts (see Table 4) which allow the electron delocalization within the slabs. As mentioned above, the main goal of our study is the establishment of the true composition of this ubiquitous BEDO–TTF chloride. A projection of the arrangement of the anion layer is shown in Fig. 5. By analogy with the works of Schweitzer et al.1 and Mori et al.2 we have assumed that the BEDO–TTF chloride single crystals contain water molecules. Table 4 Short S,S (r<4.0 A ° ) and S,O (r<3.5 A ° ) distances and absolute values of the bHOMO–HOMO interaction energies (eV) for the two diVerent donor,donor interactions in the 160 and 293 K crystal structures of (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O interaction S,S/A ° S,O/A ° bHOMO–HOMO interstacks (160 K) 3.365, 3.576, 3.726 3.324 0.2975 (293 K) 3.428, 3.621, 3.767 3.375 0.2747 intrastack (160 K) 3.588 (×2) 0.2238 Fig. 1 Temperature dependence of the relative resistivity of (293 K) 3.630 (×2) 0.2173 (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O J. Mater. Chem., 1998, 8(5), 1151–1156 1153band structure near the Fermi level is shown in Fig. 6(a) (the band structure and Fermi surfaces for the room temperature structure are almost identical—except for a slightly smaller band dispersion—and are not reported here). Since there are two donor molecules per unit cell there are two HOMO bands (i.e. two bands mainly built from the highest occupied molecular orbital of the BEDO–TTF donor).The sticking together of the two bands is due to the non-symmorphic symmetry elements along the a- and b-directions. There are only two diVerent types of BEDO–TTF,BEDO–TTF intermolecular interactions in the slab: those along the stacks and those between stacks. The absolute values of the bHOMO–HOMO interaction energies19 for these intermolecular interactions as well as the associated short S,S and S,O distances are reported in Table 4.The interaction energies are a measure of the strength of the interaction between a pair of donor HOMOs in adjacent sites of the crystal and give important insight concerning the correlation between the crystal and electronic structureof molecular solids.19 As shown in Fig. 4(b) the intrastack donor,donor interaction is such that the p orbitals of the S atoms in the HOMOs are engaged in a very favorable s-type overlap.On the basis of this and the fact that there are two relatively short S,S contacts, it is easy to understand the quite high value of the corresponding bHOMO–HOMO interaction energy. In contrast, because of the almost orthogonal arrangement of the two donors in the interstack interaction, the overlap between the S p orbitals in the HOMOs is much less favorable.A considerably smaller bHOMO–HOMO could be expected. However there is a very short S,S contact (3.365 A ° at 160 K) associated with the interstack interaction. This very short contact overrides the eVect of the less favorable geometric arrangement and leads, in fact, to a slightly larger interaction energy (at this Fig. 4 (a) Projection of the radical cation layer along the c-axis; (b) overlap mode of the BEDO–TTF radical cations along the stack point it should be noted that the relatively short S,O contact has only a minor contribution to the bHOMO–HOMO because the HOMO of BEDO–TTF has a very small contribution from the O p orbitals). Thus, the interaction between a BEDO–TTF and the six nearest neighbors in the slab is expected to be very isotropic at both room temperature and 160 K.Consequently, for any reasonable filling of the HOMO bands the Fermi surface should have an almost circular shape. We have carried out a complete study of the Fermi surface of these slabs as a function of the electrons transferred per BEDO–TTF donor (r). As shown in Fig. 6(b)–(d) for r=0.25, 0.50 and 0.75, respectively, the Fermi surface is just a circle of increasing area, as expected. (Note: because of the degeneracy of the HOMO bands along the Brillouin zone boundary it is more convenient to represent the Fermi surface in an extended zone scheme.) With such a simple Fermi surface, the Shubnikov–de Haas frequency observed in the magnetoresistance measurements gives directly the number of holes in the HOMO bands and consequently, the average charge of the BEDO–TTF radical cations.The Shubnikov–de Haas oscillations observed for our single Fig. 5 The polymeric [Cl1.28(H3O)0.28 2.44H2O]- anion layer viewed crystals (data by S. I. Pesotski and R. B. Lyubovsky, practically down the c-axis identical to those reported by the same authors for single crystals prepared by a diVerent method9) consist of a single fundamental frequency corresponding to a closed orbit associ- The unit cell of the crystal has four symmetrically equivalent positions for the (Cl, O) atoms.Consequently, we can represent ated with an area of 51% of the first Brillouin zone. Thus, within the limits of experimental accuracy, the upper HOMO its composition as (BEDO–TTF)2Clx (4-x)H2O.The refinement of the occupancy factors for the Cl and O atoms band should be half-empty (or equivalently, the whole HOMO band should be a quarter-empty). Consequently, this result as well as their corresponding positions gave the same value for x at both temperatures (x=1.28). This value is close to strongly suggests that the BEDO–TTF chloride should be a 251 radical cation salt as first suggested by Mori et al.2 It is that found by LRMA (x=1.25).Note that the hydrogen atoms of the water molecules have been unambiguously localized in thus quite puzzling that our X-ray study seems to provide evidence against such a conclusion (i.e. according to the diVerence Fourier maps. Thus, for the time being we can conclude that the composition of the BEDO–TTF chloride (BEDO–TTF)2Cl1.28 2.72H2O formula there should be a 64% empty upper HOMO band).However, the magnetoresistance can be written as (BEDO–TTF)2Cl1.28 2.72H2O. At this point we must examine the electronic structure of and X-ray results can be easily reconciled if it is assumed that the extra negative charge (0.28) is compensated by the presence the BEDO–TTF chloride.The calculated low temperature 1154 J. Mater. Chem., 1998, 8(5), 1151–1156Fig. 6 Electronic structure of (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O calculated on the basis of its low temperature crystal structure. Dispersion relations (a) and Fermi surface for diVerent values of the charge per BEDO–TTF donor (r): (b) +0.25, (c) +0.50 and (d) +0.75.The dashed line in (a) indicates the Fermi level for r=0.5. C, X, Y and M are refer to the (0, 0), (a*/2, 0), (0, b*/2) and (a*/2, b*/2) wave vectors, respectively. of H3O+ hydroxonium ions in the lattice. Such hydroxonium tures are superimposed upon the electronic backgrounds. Some cations have been previously found in other radical cation of them are modified molecular vibrations of the BEDO–TTF salts like (BT)2Cl2(H5O2) [BT=bis(butylenedithio)tetrathia- single crystal.Strong vibrational features around 3500 cm-1 fulvalene]20 and (BEDT–TTF)3Cl2.5(H5O2).21 The BEDO– are observed in the spectra of (BEDO–TTF)2Cl1.28(H3O)0.28 TTF chloride would then have the composition (BEDO– 2.44H2O and (BEDO–TTF)2ReO4 H2O single crystals. We TTF)2Cl1.28(H3O)0.28 2.44H2O.have subtracted the electronic backgrounds and presented In order to test our suggestion we studied the IR spectra of these features in Fig. 7 for the spectral range 3000–4000 cm-1. the BEDO–TTF chloride single crystals and compared the The features around 3500 cm-1 in the spectra of results with those for the organic metal (BEDO– (BEDO–TTF)2ReO4 H2O and (BEDO–TTF)2Cl1.28 TTF)2ReO4 H2O and BEDO–TTF itself.Fine structure of the (H3O)0.28 2.44H2O correspond to the stretching vibrations of IR spectra is observed in both absorption and reflection the OH groups in the H2O molecules. The ratio of integrals although it is more clearly seen in the absorption spectra in these spectra is approximately 3, which is in fair agreement (Fig. 7). The insert in Fig. 7 shows that the spectra of with the H2O content found in the X-ray structural determithe (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O and (BEDO– nations. The narrow lines at 3570 and 3690 cm-1 in the TTF)2ReO4 H2O salts diVer from that of the BEDO–TTF spectrum of (BEDO–TTF)2ReO4.H2O are due to the single crystal in that they exhibit broad backgrounds. vibrations of the two nonequivalent OH groups of the water Intraband transitions of free carriers and, maybe, interband molecules in the room temperature crystal structure of this transitions, contribute to these backgrounds.Vibrational fea- salt.16 The strong and broad line in the spectral range 3320–3900 cm-1—with a maximum at 3380 cm-1—in the spectrum of (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O can also be ascribed to the stretching vibration of the H2O molecules.It is important to point out the remarkable diVerence between the shape of this line and those observed in ordinary water and ice. The sharp low energy side of the line in the spectrum of (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O is indicative of the strong interaction of the H2O molecules with the neighboring atoms in the crystal. In the context of the present work, the more important feature of the IR spectra of (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O is the line at 3250 cm-1 which should be ascribed to the hydroxonium ion H3O+.22 This result reconciles the magnetoresistance and X-ray studies and suggests that the (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O composition is a reasonable one.The very good coincidence in the transport properties of our single crystals with those of the diVerent BEDO–TTF chlorides reported by Schweitzer et al.,1 Mori et al.2 and Lyubovskaya et al.,9 suggests that despite the Fig. 7 Vibrational features of the OMH bonds in the absorption diVerent synthetic routes all of the BEDO–TTF chlorides are spectra of (a) (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O and (b) the same (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O salt.(BEDO–TTF)2ReO4 H2O single crystals in the spectral range of the Thus, the anionic part of the BEDO–TTF chloride (see OMH vibrations. The insert shows the full spectra of the same crystals Fig. 5) is a complex anion including the Cl- anions, H2O as well as of (c) BEDO–TTF single crystals in a wider spectral range (T=300 K). water molecules and the H3O+ cations.It is a polymeric J. Mater. Chem., 1998, 8(5), 1151–1156 1155of Organic Superconductors, ed. G. Saito and S. Kagoshima, corrugated network in which all positions are statistically Springer-Verlag, Berlin, Heidelberg, 1990, p. 364. occupied either by Cl or O atoms, Each position in this 5 M. Kurmoo, T. Mallah, P. Day, I. Marsden, M. Allan, R. H. network is surrounded by three neighbors in a pyramidal Friend, F.L. Pratt, W. Hayes, D. Chasseau, J. Gaultier and arrangement with bond angles 108.2, 118.5 and 122.9° at 160 K G. Bravic, in T he Physics and Chemistry of Organic and 111.2, 121.2 and 121.5° at room temperature. The height Superconductors, ed. G. Saito and S. Kagoshima, Springer-Verlag, Berlin, Heidelberg, 1990, p. 290. of the pyramid is 0.547 at 160 K and 0.421 A ° at room tempera- 6 A.Kobayashi, T. Udagawa, H. Tomita, T. Naito and ture. The distances between two successive positions of this H. Kobayashi, Chem. L ett., 1993, 2179. network along the zig-zag chains parallel to the a-axis (see 7 I. R. Marsden, M. I. Allan, R. H. Friend, M. Kurmoo, D. Fig. 5) are 2.886(2) (160 K) and 2.920(7) A ° (293 K) whereas Kanazawa, P.Day, G. Bravic, D. Chasseau, L. Ducasse and W. those between zig-zag chains are 3.015(2) (160 K) and Hayes, Phys. Rev. B, 1994, 50, 2118. 2.976(7) A° (293 K). Such a corrugated hexagonal network 8 N. D. Khushch, Ch. Faulmann, P. Cassoux, L. Valade, I. Malfant, J.-P. Legros, Ch. Bowlas, A. Errami and A. Kobayashi, Inorg. seems to be quite able to accommodate H3O+ hydroxonium Chem., in press.ions. The tendency of water molecules towards formation of 9 E. I. Zhilyaeva, S. A. Torunova, R. N. Lyubovskaya, S. polymeric networks in the solid state probably plays a major V. Konovalikhin, O. A. Dyachenko, R. B. Lyubovskii and S. I. role in leading to the structure of this anionic network.23 It is Pesotskii, Synth.Met., 1996, 83, 7. worth pointing out that polymeric networks containing infinite 10 V.I. Andrianov, AREN-88, The System of Programs for Solving and Refinement of Crystal Structures, Institute of Crystallography chains of Cl- ions and H2O molecules (or hydroxonium ions) AN SSSR, Moscow, 1988. have also been found in the crystal structure of the radical 11 G. M. Sheldrick, SHELX-93, Program for Refinement of Crystal cation salts (BEDT–TTF)4Cl2 4H2O,24,25 (BEDT–TTF)4Cl2 Structures, University of Go� ttingen, Germany, 1993. 6H2O26–28 and (BEDT–TTF)3Cl2.5(H5O2).21 In the well known 12 M.-H. Whangbo and R. HoVmann, J. Am. Chem. Soc., 1978, 100, organic metal (BEDT–TTF)3Cl2 2H2O24,29,30 the Cl- ions 6093. and H2O molecules lead to a discrete complex anion. No 13 J. Ammeter, H.-B. Bu� rgi, J. Thibeault and R. HoVmann, J.Am. Chem. Soc., 1978, 100, 3686. structurally characterized BEDT–TTF or BEDO–TTF salts 14 S. S. Khasanov, B. Zh. Narymbetov, L. V. Zorina, L. P. Rozenberg, containing chloride ions alone are known. R. P. Shibaeva, N. D. Kushch, E. B. Yagubskii, R. Rousseau and E. Canadell, Eur. Phys. J. B., in press. 15 M. A. Beno, H. H. Wang, K. D. Carlson, A. M. Kini, G. Conclusion M.Frankenbach, J. R. Ferraro, N. Larson, G. D. McCabe, J. Thompson, C. Purnama, M. Vashon, J. M. Williams, D. Jung A hydrated BEDO–TTF chloride was previously reported by and M.-H. Whangbo,Mol. Cryst. L iq. Cryst., 1990, 181, 145. several groups although the composition was never firmly 16 R. P. Shibaeva and V. E. Zadovnik, Kristallografiya, 1993, 38, 114. established. The same BEDO–TTF chloride has been obtained 17 M.Fettouhi, L. Ouahab, D. Serhani, J.-M. Fabre, L. Ducasse, J. Amiell, R. Canet and P. Delhaes, J.Mater. Chem., 1993, 3, 1101. through an alternative (unexpected) route. As a result of a 18 H. Kobayashi, R. Kato, A. Kobayashi, I. Nishio, K. Kajita and combined study of the IR spectra, magnetoresistance and low W. Sasaki, Chem. L ett., 1986, 789. temperature (160 K) crystal and electronic structures, we con- 19 (a) M.-H.Whangbo, J. M. Williams, P. C. W. Leung, M. A. Beno, clude that this salt can be adequately described as T. J. Emge and H. H. Wang, Inorg. Chem., 1985, 24, 3500; (b) J.M. (BEDO–TTF)2Cl1.28(H3O)0.28 2.44H2O. This salt is a two- Williams, H. H.Wang, T. J. Emge, U. Geiser, M. A. Beno, P. C. W. dimensional organic metal stable down to 1.3 K, containing Leung, K.D. Carlson, R. Thorn and A. J. Schulz, Prog. Inorg. Chem., 1987, 35, 51; (c) Since overlap is explicitly included in radical cation layers of the so-called H-type and a corrugated extended Hu� ckel calculations, these interaction energies (b) should hexagonal network of Cl- anions, water molecules and H3O+ not be confused with the conventional transfer integrals (t).hydroxonium cations. It is the second radical cation salt of Although the two quantities are obviously related and have the BEDO–TTF with halogen ions, the first one, (BEDO– same physical meaning, the absolute values of b are somewhat TTF)2(I3)0.83,31,32 exhibiting a radically diVerent crystal struc- larger than those of t. 20 V. E. Korotkov and R.P. Shibaeva, Sov. Phys. Crystallogr., 1991, ture. It is also worth noting that after completion of this work 36, 509. we have obtained BEDO–TTF chloride single crystals as long 21 H. Mori, I. Hirabayashi, S. Tanaka and Y. Maruyama, Bull. Chem. thin plates, with unit cell parameters a=4.015(2), b=5.344(1), Soc. Jpn., 1993, 66, 2156. c=33.245(8) A ° , c=98.38(1)o, V=705.7(5) A ° 3 (space group 22 C. C.Ferriso and D. F. Hornig, J. Chem. Phys., 1955, 23, 1464. P21/b). The structural study of this phase will be carried out 23 A. F. Wells, Structural Inorganic Chemistry, Clarendon, Oxford, 5th edn., 1984. as soon as appropriate single crystals can be found. 24 R. P. Shibaeva, R. M. Lobkovskaya, L. P. Rozenberg, L. I. Buravov, A. A. Ignatiev, N. D. Kushch, E.E. Laukhina, M. The authors wish to thank S. I. Pesotskii and R. B. Lyubovskii K. Makova, E. B. Yagubskii and A. V. Zvarikina, Synth. Met., for the information on the SdH oscillations observed in the 1988, A27, 189. 25 R. P. Shibaeva, L. P. Rozenberg, A. F. Shestakov and T. single crystal investigated. The present study was supported A. Khannanova, Zh. Strukt. Khimii, 1991, 32, 98. by an NWO Grant, RFBR Grants 96–03–32029 and 26 M. B. Inoue, M. A. Bruck. M. Carducci and Q. Fernando, Synth. 97–03–33581, the Russian National Program ‘Physics of quan- Met., 1990, 38, 353. tum wave processes’ and DGES (Spain) Project PB96–0859. 27 G. Bravic, D. Chasseau, M. Kurmoo, J. Gaultier, M. J. Rosseinsky, A. Filhol and P. Day, Synth.Met., 1991, 42, 2035. 28 M. J. Rosseinsky, M. Kurmoo, P. Day, I. R. Marsden, R. H. Friend, D. Chasseau, J. Gaultier, G. Bravic and L. Ducasse, J. Mater. References Chem., 1993, 3, 801. 1 D. Schweitzer, S. Kahlich, I. Heinen, S. E. Lan, B. Nuber, 29 T. Mori and H. Inokuchi, Chem. L ett., 1987, 1657. H. J. Keller, K. Winzer and H. W. Helberg, Synth. Met., 1993, 30 M. J. Rosseinsky, M. Kurmoo, D. R. Talham, P. Day. D. Chasseau 56, 2827. and D. Watkin, J. Chem. Soc., Chem. Commun., 1988, 88. 2 T. Mori, K. Oshima, H. Okuno, K. Kato, H. Mori and S. Tanaka, 31 F. Wudl, H. Yamochi, T. Suzuki, H. Isotalo, C. Fite, H. Kasmai, K. Liou, G. Srdanov, P. Coppens, K. Maly and A. Frost-Jensen, Phys. Rev. B, 1995, 51, 11110. J. Am. Chem. Soc., 1990, 112, 2461. 3 T. Mori, S. Ono, H. Mori and S. Tanaka, J. Phys. I Fr., 1996, 32 V. Petricek, K. Maly, P. Coppens, X. Bu, I. Cisarova and A. Frost- 6, 1849. Jensen, Acta Crystallogr., Sect A., 1991, 47, 210. 4 A. V. Gudenko, V. B. Ginodman, V. E. Korotkov, A. V. Koshelap, N. D. Kushch, V. N. Laukhin, L. P. Rozenberg, A. G. Khomenko, R. P. Shibaeva and E. B. Yagubskii, in T he Physics and Chemistry Paper 7/07959A; Received 5th November, 1997 1156 J. Mater. Chem., 1998, 8(5), 1151&ndas

ISSN:0959-9428    

DOI:10.1039/a707959a

出版商:RSC    

年代:1998

数据来源: RSC