摘要:

J. MATER. CHEM., 1991, 1(4),663-666 Use of Phenylarsine in the Atmospheric Pressure Metal Organic Chemical Vapour Deposition of GaAs on Si(lO0) Neil R. Dennington, Andrew C. Wright and John 0. Williams* Solid State Chemistry Group, Department of Chemistry, UMIST, PO Box 88, Manchester M60 lQD, UK The Ill-V compound semiconductor GaAs has been grown on silicon substrates by atmospheric pressure metal organic chemical vapour deposition (APMOCVD) using trimethylgallium (TMGa) and phenylarsine (PAS). The GaAs exhibited high crystalline quality (X-ray rocking curve FWHM 430 arc seconds) and a specular morphology. Electrical properties were poor with an inversion from p- to n-type within the layers. This is attributed to both dislocations present because of the lattice mismatch at the GaAs/Si interface and doping effects due to impurities introduced from the PAS source.Strong emission due to free-exciton transitions may be seen in the photoluminescence spectra of the samples. Keywords: Gallium arsenide; Metal organic chemical vapour deposition; Photoluminescence spectroscopy; Secondary-ion mass spectrometry; Transmission-electron microscopy The heteroepitaxial growth of GaAs on Si has attracted great interest in recent years owing to the potential use of this system in future electronic devices.' There are, however, several intrinsic difficulties with the GaAs/Si system which reduce the GaAs crystal quality. These include the 4.1% lattice mismatch,2 the formation of antiphase boundaries (APBs),, the large differences in thermal expan~ivities~ and problems of interface charge neutrality.' The severity of these problems has been greatly reduced by the use of two-step growth techniques6 combined with the use of heat cycling7 in situ or ex situ growth annealing,* iso-electronic dopingg and the use of strained-layer superlattices as buffer layers between the GaAs and silicon substrate.lo Conventionally, trimethylgallium (TMGa) and arsine (ASH,) have been used as Group I11 and Group V sources in the MOCVD-growth of GaAs." Arsine is highly toxic at low concentrations [uiz. 0.05 ppm (RL)] l2 and, accordingly, alternative safer As-con- taining precursors for MOCVD have been sought. l3 Several alternative Group V sources have been suggested including tert-butylarsine (TBA)', trimethylarsine (TMA)I4 diethylarsine (DEA)" ethylarsine (EA)16 and phenylar~ine'~ (PhAsH, or PAS).These liquid sources are safer than gaseous arsine since they can be stored and dispensed more easily. They yield GaAs epitaxial layers of varying crystalline quality and electrical properties (see e.g. ref. 18). Prior to the acceptance of any new source material it must be proved to be fully capable of any growth previously performed using ASH,. In this paper we demonstrate the utility of PAS in the growth of GaAs on Si(lO0) and indicate the purity limitations of the presently available precursor material. Experimenta1 Atmospheric pressure MOCVD was used to grow 3 pm thick GaAs layers on Sb-doped Si( 100) & 3"substrates.Trimethyl- gallium and phenylarsine (Epichem), were used as precursor materials. Similar sources have been employed previously in the preparation of homoepitaxial GaAs and the results pub- lished.l7 Details of source impurity concentrations are given in Table 3 of ref. 17. Immediately prior to growth the Si substrate was cleaned using a procedure described else-where,"" and baked out in situ at 1000 "C for 20 min under flowing HZ.In the two-step growth procedure used, a lOOA thick GaAs layer was deposited at 500 "C and a V: I11 ratio of 40: 1, with the remainder of the GaAs layer being grown at 650 "C and a V: I11 ratio of 15 :1. The conditions yielded a growth rate of ca. 3 pm h-' and based on extensive studies of growth parameter variation^'^" were optimum for GaAs growth using the present precursors. The GaAs epilayers were characterised using optical microscopy (Olympus-B4-2), scanning electron microscopy (Philips SEM 525), transmission electron microscopy (Philips, EM430), double-crystal X-ray diffraction (Bede QC-l), capaci- tance-voltage (C-V) profiling and dynamic secondary-ion mass spectrometry (SIMS).Photoluminescence (PL) spectra were recorded in the temperature range 10-300 K following excitation with laser radiation at 514 nm. Experimental details of these techniques may be found else~here.'~~.'~~ Results Fig. 1 compares the surface morphology of GaAs on Si substrate under identical conditions (see Experimental) using trimethylgallium and (a) arsine (b) PAS.To the naked eye the surfaces are mirror smooth but in the optical micrographs compared surface features are observed in the two cases. On close examination these surfaces are inferior to those of homoepitaxial GaAs.lgb A high degree of crystallinity is demonstrated by the narrow double-crystal X-ray rocking curve FWHM values, which are as low as 430 arc seconds. Using similar conditions with trimethylgallium and arsine, corresponding half widths of ca.450 arc seconds have been fo~nd.'~" A typical C-V profile, through a (100) GaAs layer grown using PAS, is shown in Fig. 2. Most striking is the apparent change from p- to n-type behaviour towards the heterointer- face. An increase in p-type carrier concentration is observed from the GaAs surface (depth =zero) towards the heterointer- face (depth=3 pm) until at a distance of 1-2 pm from the layer surface a change to n-type behaviour occurs. Carrier concentration then falls before increasing towards the hetero- interface. Fig.3 shows typical low temperature (10 K) PL spectrum for GaAs layers nucleated at different temperatures. Because of strong absorption at the excitation wavelength (514 nm) spectral information is obtained from the uppermost CQ. 1 pm of the GaAs layer. The spectra are dominated by a narrow, J. MATER. CHEM., 1991, VOL. 1 Fig. 1 Optical micrographs of GaAs surfaces grown on Si surfaces under identical experimental conditions using trimethylgallium and (a) arsine (6)PAS depth/pm Fig.2 A typical C-V profile through a GaAs epitaxial layer. The GaAs surface corresponds to depth zero resolved Si,, (e, A) emission at 1.462 eV. A weak but resolved free-exciton transition (FE) is observed at 1.489 eV, together with a weak shoulder at 1.470eV attributed to a carbon- related (e, A) transition.lgb Increasing levels of Si towards the GaAs layer surface is shown by SIMS which also reveals relatively sharp, discrete GaAs/Si interfaces (Fig. 4). Both C and Zn contamination is found in the layers. Fig. 5 shows cross-sectional transmission electron micrographs (TEM) taken of GaAs/Si interfaces grown from (a)TMGa and ASH, (b) TMGa and PAS under similar conditions. These micrographs show the similarity of the two structures in terms of defect content and also allow clear demarcation of specific imperfections such as dislocations (D) stacking faults (S) and microtwins (M) in the epitaxial GaAs.Discussion The ability to grow epitaxial GaAs of acceptable crystalline quality on Si(100) using PAS and trimethylgallium has been demonstrated by this work. However, only poor electrical behaviour is exhibited by this material. This is thought to I 1 I I I 1 1.54 1.51 1.48 1.45 1.42 1-39 energylev Fig. 3 10 K PL spectra of GaAs epitaxial layer as a function of V :I11 ratio during growth reflect more the insufficient purity of the PAS source and peculiarities of the GaAs/Si system rather than an intrinsic inability to grow GaAs using a combination of trimethylgal- lium and PAS.We have, indeed, shown on a previous occasion that homoepitaxial GaAs of excellent crystalline quality and with background electron concentration of 5 x lo1’ cm-3 and J. MATER. CHEM., 1991, VOL. 1 depth (arb. units) 5:l 0:l 5:1 0: 1 25:l lo3i /t 10 10 depth (arb. units) Fig. 4 Dynamic SIMS profiles for (a) silicon (b) C and (c) Zn of GaAs/Si interfaces as a function of V :I11 ratio during growth. The GaAs surface is at the origin and the profiles show relatively sharp interfaces and an increasing level of Si towards the GaAs surface electron mobility of 20 000 cm2 s-’ V-’ can be grown using this pair of sources.’ The p-type nature of the surface layers is accounted for by the Zn and C incorporation.Both of these species are known to act as acceptors in GaAs, and Zn is known to be present in the present batches of PAS.17 However, the change to n-type behaviour towards the heterointerface cannot be explained in terms of Zn and C contamination alone. It is known that dislocation density and defect concentration increases towards the heterointerface2’.22 and we have con- firmed this by cross-sectional TEM carried out on our layers (see Fig. 5). It is also known that dislocations act as donors in GaAs.22*23 Therefore, it is likely that it is the dislocations that determine the electrical behaviour of the material close to the heterointerface. It is apparent from the electron microg- raps that at ca.1.5-2 pm from the GaAs surface the layer dislocation density increases and this corresponds to the distance where n-type doping (N,) is in excess of p-type doping (NA).Consequently, the background carrier concen- tration (N, -NA)changes to n-type. It is, however, important to remember that this sharp transition from p- to n-type behaviour is highly unlikely to be seen within any actual layer and is in fact an artefact inherent in the C-V profiling technique. This is due to the existence of a depletion region24 Fig. 5 Cross-sectional TEM micrograph of GaAs epilayer grown on Si using (a)TMGa and ASH, (b) TMGa and PAS. Various defects can be identified such as dislocations (D), stacking faults (S) and microtwins (M) in the GaAs. In (b)position of the interface with the Si substrate is marked (I) within the material during profiling which extends from ca.0.2 to 3.0 pm. At each stage of the C-V technique, material is etched away removing the depletion region and allowing the majority carrier concentration to be expressed. In a ‘real’ sample the region over which the alteration takes place will be depleted of carriers. This region may be several micrometres thick. Thus, the real change of electrical behaviour, although representing the variation in doping levels within the layers, is probably not as abrupt as indicated in Fig. 2. The presence of the FE emission in the PL spectrum of the GaAs epilayers is evidence for the high quality of the material. The dominance of the SiGa (e, A) emission is due to the high levels of Si, confirmed by SIMS, in the surface of the layers.This Si is thought to occupy sites along dislocations where it remains electrically ne~tral.~’ The higher surface concen-tration of Si is thought to be due to a vacancy/dislocation- enhanced diffusion mechanism. Following the high-tempera- ture bake out, the surface layer of the substrate will contain many-vacancies.26 During the growth of the GaAs buffer layer, vacancies will be generated at the sample surface allowing Si to diffuse into them. This process will continue throughout growth with Si moving out of the substrate with the growth surface like a ‘wall’. Subsequent diffusion of Si from the substrate will be hindered by the GaAs layers, while the surface diffusion rate of Si may be considerably higher.26 Conclusions Our experiments have demonstrated an ability to grow high- quality GaAs on Si(100) without the complex growth pro- 666 J.MATER. CHEM., 1991, VOL. 1 cedures previously reported. More importantly, the viability of phenylarsine as an alternative As precursor in atmospheric pressure MOVPE has been demonstrated for GaAs/Si. Further purification of this precursor is required if better electrical properties are to be achieved, but characteristics of I1 12 13 G. B. Stringfellow, in Organometallic Vapour Phase Epitaxy: Theory and Practice, Academic Press, New York, 1989. C. Breckerridge, C. Collins, B. Hollomby and G. Lulham G., The Toxicologist, 1983, 3, Abs 93.R. W. Lum, J. K. Klingert and M. G. Lamont, Appl. Phys. Lett., 1987,50, 1151. the GaAs/Si system itself containing appreciable defects may be limiting factors dictating material quality. 14 15 C. Cooper, M. W. Ludowise, V. Aebi and R. L. Moon, Electron Lett., 1980, 16, 20. R. Bhat, M. A. Kozaond and B. J. Skromme, Appl. Phys. Lett., One of us (N.R.D.) would like to acknowledge the financial support of SERC throughout this study. Additionally, we would like to thank M. MacDonald and S. Hibbet for provid- ing PL and SIMS spectra, respectively. 16 17 1987,50, 1194. D. Schimtz, G. Strauch, V. Michno, A. Melas and H. Jurgensen, presented at EW-MO VPE 111, Montpellier, France, 1989. R. D. Hoare, 0.F. Z. Khan, J. 0. Williams, D. M. Frigo, D. C. Bradley, E. Chudzynska, P.Jacobs, A. C. Jones and S. A. Rush- worth, Chemtronics, 1989, 4, 78. 18 N. R. Dennignton and J. 0. Williams, in the press. References 19 (a) N. R. Dennington, PhD Thesis, University of Manchester, 1989; (b) N. Hunt and J. 0.Williams, Chemtronics, 1987, 2, 165; 1 R. P. Gale, J. C. C. Fan, B. Y. Tsaur, G. W. Turner and F. M. (c)N. D. Gerrard, D. J. Nicholas and J. 0.Williams, Chemtronics, Davis, I.E.E.E. Electron Device Lett., 1981, EDL-2, 169. 1988, 3, 17. 2 M. Akiyama, Y. Kawarada and K. Karinishi, J. Cryst. Growth, 20 K. Mohammed, J. L. Merz and D. Kasemset, Appl. Phys. Lett., 1984, 68, 21. 1983, 43, 103. 3 S. K. Ghandi and J. E. Ayers, Appl. Phys. Lett., 1988, 53, 21 H. L. Tsai and J. W. Lee, Appl. Phys. Lett., 1987, 51, 130.1204. 22 N. R. Dennington, A. C. Wright and J. 0.Williams, unpublished 4 5 6 W. A. Harrison, E. A. Grant, J. R. Waldrop and R. W. Grant, Phys. Rev. B., 1978, 18, 4402. H. Kroemer, J. Cryst. Growth, 1987,81, 193. M. Akiyama, Y. Kawarada and K. Kaminishi, J. Cryst. Growth, 1984,68, 21. 23 24 data. A. T. Macronder, S. N. G. Chu, K. E. Strege, A. F. Bloerike and W. D. Johnston, Appl. Phys. Lett., 1984, 44,615. R. W. Lum, J. K. Klingert, R. B. Bylsma, A.M. Glass, A.T. Macronder, T. D. Harris and M. G. Lamont, J. Appl. Phys., 7 M. Yamaguchi, A. Yamamoto, M. Tachikawa, Y.Hoh and 1988, 64, 6727. M. Sugo, Appl. Phys. Lett., 1988, 53, 2293. 25 M. E. Goodye, Semiconductor Device Technology, MacMillon, 8 9 10 R. W. Kaliski, C. R. Ito, D. G. McIntyre, M. Fenn, H. B. Kia, R. Bean, Z. Zanio and K. K. C. Ksieh, J. Appl. Phys., 1988, 64, 1196. W. Walukiewicz, Appl. Phys. Lett., 1989, 54, 2009. D. W. Nam, H. Holonyak, K. C. Hsieh, R. W. Kaliski, J. W. Lee, H. Scichijo, J. E. Elper, R. D. Burnham and T. L. Paoliu, Appl. 26 27 London, 1983, p. 61. A. Freundlick, J. C. Grenet, G. Neg, A. Leycuras and C. Verie, Appl. Phys. Lett., 1988, 52, 1976. J. Huang, M. Meyer and V. Pontikis, Phys. Rev. Lett., 1989, 63, 628. Phys. Lett., 1987, 51, 39. Paper 110I 125A; Received 1 1 th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100663

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 667-672 Crystal Structures of Chiral Smectogenic 4'-Octylbiphenyl-4-yI p[(S)-I-Methylheptyloxy]benzoate and poctylphenyl 4'-[(S)-I -Methylheptyloxy]biphenyl-4-carboxylate Kayako Hori" and Yuji Ohash?' a Department of Chemistry, Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo 1 12, Japan Department of Chemistry, Tokyo Institute of Technology, Gokayama, Meguro-ku, Tokyo 152, Japan Single-crystal X-ray analyses have been carried out for 4'-octylbiphenyl-4-yI p[(S)-1-methylheptyloxy]benzoate (l),which has a phase sequence of cryst.-sb-chol.-iso., and poctylphenyl 4'-[(S)-l-methylheptyloxy]biphenyl-4-carboxylate (2), which has a phase sequence of cryst.-s&+-chol.-iso. Each crystal has a smectic-like layer structure, in which the molecular tilt angle is large (65') in 1, whereas it is small (10') in 2.These features, which are interpreted to result from the molecular geometry, i.e. the length of the moiety sandwiched by polar groups, are closely related to the structures of the liquid-crystalline phases. Keywords: Crystal structure; Smectic C phase; Liquid crystal; Intermolecular interaction; X-ray diffraction Good correlations have been found between the crystal struc- tures and liquid-crystalline behaviours for three series of chiral smectogenic biphenyl esters with a 2-methylbutyl group.'-4 In order to confirm the relationship between crystal struc- ture and liquid-crystalline phase sequence we extended the crystal-structure determination to biphenyl esters with a 1 -methylheptyloxy group, which show various liquid-crys- talline phase sequences according to the isomeric change of the molecular structure^.^ This paper describes the crystal structures of two isomers, 4'-octylbiphenyl-4-y1 p-[(S)-l- methylheptyloxy] benzoate, 1 and p-octylphenyl 4'-[(S)-1-methylheptyloxy]biphenyl-4-car-boxylate. C6H13cH(cH3)0~2~c8H17 2 The former has a phase sequence of cryst.50.0 "C sE 62.5 "C chol. 87.2 "C isotropic liquid, whereas the latter has the phase sequence of cryst. 55.0 "C sz 71.5 "C sA 83.6 "C chol. 92.3 "C isotropic liquid with a metastable sB (39.5 "C sz). Experimental The compounds were supplied by Drs. T. Inukai and K. Furukawa. Single crystals appropriate to the structure deter- mination were grown from an ether-ethanol solution for 1 and were found in the specimen as supplied for 2.Powder diffraction patterns for smectics were measured on a Rigaku Geigerflex RAD-RA diffractometer. No procedures for sample alignments were applied. Temperature control was within fO.l K. Crystal Data. 4-Octylbiphenyl-4-yl p-[(S)-1-methylheptyloxy] benzoate (l),C3&&, M, =514.72, monoclinic, a =44.09( 1) A, b =5.494(3) A, c =39.52(2) A, /?=139.02( l)', U=6278(4)A3 (by least-squares fit for 15 reflections within the range 32 <28/' <59, i=1.54184 A), space group C2, Z =8, pc= 1.090 g crnp3. Transparent long plate-like crystal. Crystal dimensions 0.4 mm x 0.3 mm x 0.05 mm, p(Cu-Ka) = 4.44 cm-'. p-Octylphenyl 4'-[(S)-l-methylheptyloxy]bi-phenyl-4-carboxylate (2), C35H4603,M, =5 14.72, monoclinic, a=33.818(3) A, b=8.2140(9) A, c=5.7128(5) A, /?=98.733(9)', U= 1568.5(3)A3 (by least-squares fit for 16 reflections within the range 33 <28/' <56, A = 1.54184A), space group P2', Z= 2, pc=1.090 g crnp3.Transparent plate-like crystal. Crystal dimensions 0.45 mm x 0.35 mm x 0.05 mm, p(Cu-Ka) = 4.54 cm-'. Data Collection and Processing. Rigaku AFC-4 diffractometer, 01-28 scan mode with 01 scan width =(1.O +0.1 Stan@', scan speed 4'(28) for 1 and 8'(28) for 2, graphite-monochromated Cu-Ka radiation; 5377 (for 1) and 2708 (for 2) independent reflections measured (3 <28/' <125, & h, +k, +I), giving 2252 with lFol >40( IFo[)(for 1) and 1956 with IFo[>34 IFo[)(for 2).A higher criterion was applied to 1, because intensities of 1 were relatively small owing to the low melting point. There was no significant intensity variation. Lorentz polarization but no absorption correction. Structure Analysis and Refinement. A direct method using the programs SHELX8@ for 1 and MULTAN787 for 2 was employed. Full-matrix least-squares (in two blocks) using SHELX76.* For 1, geometries were loosely constrained to avoid divergence due to the pseudosymmetry. In the course of the refinement of 1, a terminal atom of an alkyl chain, C(38B), was disordered because of its considerably large temperature factors. All the non-hydrogen atoms except for the disordered atom were refined anisotropically. Hydrogen atoms found in the difference maps and derived geometrically (C-H, 1.0 A) were refined isotropically for 2, while only eight hydrogen atoms found in the difference map (D-map) were included in the refinement for 1 owing to the limited number of reflections. The quantity minimized was Xw(IFol-IFc1)2, where w =[C(F~)~+0.004(Fo12]-'. Atomic scattering factors were taken from the International Tables for X-ray Crystallography.' Max.A/a and max. Ap in the final D-map were 0.48 and 0.26 e A-3 for 1 and 0.47 and 0.22 e A-3 for 2. Final R (and R,) is 0.109 (0.1 17) for 1 and 0.089 (0.103) for 2. The large R value of 1 was probably due to the low crystallinity. Computations were carried out on a HITAC M-680H computer at the Computer Center of the University of Tokyo and an IBM 4381-R24 computer at the J.MATER. CHEM., 1991, VOL. 1 Information Processing Center of Ochanomizu University. Normal alkyl chains and long chains of the chiral groups Final atomic coordinates are shown in Tables 1 and 2.t have relatively close contacts between layers, as shown in Fig. 3. Results and Discussion Crystal Structure of 1 Crystal Structure of 2 There are two crystallographically independent molecules, A The ORTEP drawing of 2 is shown in Fig. 1. All the geometri- and B, in an asymmetric unit. ORTEP drawings" of the two cal parameters are compatible with those of other mesogens. molecules with the numbering scheme are shown in Fig. 1. The biphenyl moiety is twisted (21.4'). The normal alkyl chain All the bond lengths and angles are compatible with those has an all-trans conformation, whereas the chain of the chiral found in other me~ogens.'-~ All the phenyl rings are planar group is twisted in the middle, as shown in Table 3.within experimental error. Both molecules have nearly planar Fig.4 shows the crystal structure viewed along the b and biphenyl moieties: dihedral angles are 4.2 and 2.1' for the c axes. Molecules are related by a two-fold screw axis in a molecules A and B, respectively. Alkyl chains have approxi- smectic-like layer structure. The twisted chain of the chiral mately extended conformations, as shown in Table 3. group participates in the lateral overlap of the molecules, Fig. 2 shows the crystal structure. Molecular long axes are leading to a large overlap and hence a small tilt of the largely tilted (65 ') in a smectic-like layer structure.The molecular long axis. The tilt angle is estimated to be ca. lo', although it is difficult to designate a molecular long axis independent molecules, A and B' or A' and B, where A and B' are symmetry-related molecules of A and B, are related by rigorously owing to the bent shape of the molecule. The ester an approximate two-fold screw axis. The ester and ether and ether groups in neighbouring molecules lie in close groups are closely arranged at two positions between the proximity. The arrangement provides a large lateral overlap of molecules, since the moiety sandwiched by the polar groups neighbouring molecules, A and B' or A' and B.is long. t Supplementary data available from the Cambridge Crystallo- On the other hand, the normal chains are found between graphic Data Centre: see Information for Authors, J. Muter. Chem., layers with an all-trans conformation. However, the two zigzag 1991, Issue 1. chains facing each other are out of phase, resulting in a rather Table 1 Final atomic coordinates with their estimated standard deviations (x lo4) for 4-octylbiphenyl-4-yl p-[(S)-1-methylheptyloxy]benzoate (1) atom X Y 2 atom X Y 7 Beq/A20 0 (14 0 PA) 0 (3'4) c (14 c (24 c (34 c (44 c (54 c (64 c (74 c (84 c (9A)C( 1 OA) C(11A) C( 12A) C( 13A) C( 14A) C( 15A) C( 16A) C( 17A) C( 18A) C( 19A) C(21A) C(22A) C(23A) C(24A) C(25A) C(26A) C(27A) C(28A) C(3IA) C(32A) C(33A) C(34A) C( 3 5A) C(36A) C(37A)C(38A) 0 (1B) 2968 (4) 2561 (4) 3529 (3) 1656 (5) 1940 (5) 2113 (5) 1964 (5) 1681 (5) 1515 (6) 2115 (5) 2411 (5) 2560 (5) 2403 (5) 2066 (5) 1936 (5) 2861 (5) 3059 (5) 2906 (4) 3081 (5) 3366 (4) 3319 (4) 3877 (3) 3852 (5) 4171 (5) 4196 (4) 4478 (6) 4445 (9)4687( 12) 4340 (5) 1445 (6) 1317 (6) 1075 (5) 996 (6) 787 (6) 656 (7) 511 (7) 383 (7) 2967 (4) 3493 (4) -2093 (21) 1316 (19) 1213 (20) 1459 (29) 3289 (26) 3112 (26) 1314 (27) -500 (29) -412 (29) 1226 3043 (26) 2970 (24) 1077 (31) -545 (32) -584 (26) -405 (25) 28 (26) 2037 (22) 2473 (25) 690 (24) -1424 (25) -1781 (31) -166 (28) -803 (36) -1024 (58) -105 (69) 575 (38) 499 (38) 2249 (70) 268 (42) 1354 (28) 3909 (33) 3683 (32) 6186 (32) 6005 (35) 8480 (33) 8211 (35) 10647 (36) -1636 (22) 7069 (4) 6787 (4) 9013 (3) 3974 (4) 4346 (5) 4818 (4) 4915 (5) 4545 (5) 4074 (5) 5417 (4) 5777 (5) 6241 (4) 6314 (5) 5922 (5) 5476 (5) 7157 (6) 7666 (5) 7722 (4) 8193 (4) 8569 (4) 8511 (5) 8039 (4) 9482 (4) 9832 (5) 10333 (5) 10702 (4) 11179 (6) 11516(10) 11792(13) 9692 (6) 3443 (5) 3208 (5) 2654 (5) 2429 (5) 1896 (5) 1629 (6) 1128 (6) 877 (6) 2012 (4) 8.4 8.0 6.9 7.8 8.I 9.1 7.1 8.3 9.2 6.2 7.9 8.3 7.8 8.4 8.3 6.3 6.4 5.2 6.3 6.2 6.5 7.8 5.8 9.7 9.3 9.0 18.4 16.9 23.3 10.0 7.7 9.7 8.5 8.3 9.8 10.0 10.5 10.7 8.6 0 (2B)0 (3B) c (1B) c (2B) c (3B) c (4B) c (5B) c (6B) c (7B) c (8B) c (9B)C(1OB) C(l1B) C( I2B) C( 13B) C( 14B) C( 15B) C( 16B) C( 17B) C( 18B) C( 19B) C(21B) C(22B) C(23B) C(24B) C(25B) C(26B) C(27B) C(28B) C(31B) C(32B) C(33B) C(34B) C(35B) C(36B) C(37B) C(38B) C(38B) 2584 (3) 3526 (4) 1638 (6) 1931 (6) 1949 (4) 1687 (6) 1512 (6) 2107 (4) 2433 (4) 2555 (5) 2454 (5) 2144 (6) 1981 (5) 2880 (5) 3027 (4) 2917 (5) 3077 (4) 3370 (4) 3317 (5) 3871 (6) 3876 (5) 4219 (6) 4204 (7) 4530 (7) 4513 (7) 4768 (6) 4346 (5) 1446 (7) 1228 (6) 1085 (8) 908(I 1) 758( 12) 728(10) 533(13) 459(22) 222(23) 2100 (4) 3479 (5) 1702 (22) 895 (22) 2603 (33) 4402 (33) 4263 (26) 2401 (25) 504 (26) 662 (32) 2139 (19) 3758 (26) 3799 (26) 1746 (23) 29 (33) 284 (25) 130 (25) 2212 (24) 2290 (26) 594 (21) -30 (23) -1388 (22) -1658 (24) -723 (36) -52 (32) -1587 (33) -857 (48) -2556 (51) -1615 (49) -3402 (52) -260 (56) 2586 (42) 5022 (44) 4736 (50) 7196 (60) 6669 (61) 8652 (66) 8198 (79) 10190 (93) 101OO( 130) 1786 (4) 4009 (4) -200 (5) -1043 (5) -669 (6) -115 (3) -467 (5) -941 (5) 388 (4) 788 (4) 1233 (5) 1334 (4) 964 (5) 499 (5) 2135 (7) 2608 (5) 2696 (5) 3162 (5) 3556 (5) 3446 (5) 2982 (5) 4436 (6) 4818 (5) 5315 (5) 5680 (8) 6174 (7) 6518 (7) 6952 (7) 4675 (5) -1579 (6) -1842 (5) -2329 (6) -258q10) -3066( 12) -3345411) -3868( 12) -4193(23) -4201(26) 7.6 9.1 9.6 9.7 9.1 7.4 10.1 10.7 4.5 6.4 7.2 5.8 9.3 7.0 7.2 5.5 6.5 7.0 6.0 7.6 6.7 12.1 8.1 9.2 12.7 12.0 12.5 13.1 12.3 11.9 12.4 12.3 19.7 19.1 17.1 22.1 15.5(18)b 19.0(2qb a Be,=(4/3) CBij(ai*uj).'Isotropic temperature factor; occupation factors were fixed to be 0.5 for C(38B) and C(38B').ij J. MATER. CHEM., 1991, VOL. 1 669 Table 2 Final atomic coordinates with their estimated standard devi- ations (x lo4) for p-octylphenyl 4-[(S)-l-methylheptyloxy]biphenyl-4-carboxylate (2) Table 3 Torsion angles(/") of alkyl chains 1 mol.A mol. B 2 6873(2) 6902(2)3781(2) 4 186( 2) 4422(2) 4825(2) 50 12(2) 4762(2)4358(2) 5451(2) 5705(2) 6 1 05(2) 6284(2) 6035(2)5629(3) 67 12(2) 7308(2)7474(3)7858(3) 81 1q3) 795 1( 3) 7554(2) 3 564(2) 3131(3) 2872(3) 2428(3)2284( 3) 1826(3) 1684(5)3646(3) 8555( 3) 8778(3) 92 1 O( 3) 9455(3)9873(3)101 15(4) 10533(5) 10782( 4) a As for Table 1. 621 l(10) 7648 (7) 6158 (7) 6300( 10) 7465(10) 7494 (9) 6393 (9) 5257 (9) 5232(10) 6437( 10) 7 174( 10) 7241( 10) 6628 (9) 5860( 10) 5766(10) 6749 799q 10) 8816(14) 924q 1 5) 8835( 13) 8043( 13) 7587( 13) 7168(10) 7024( 15) 8193( 19) 7980( 19) 8486(15) 8496(18)9 1 3 7( 34) 6724( 12) 9388(20) 8834(16) 9445( 18) 9028(21)9565(27) 8999( 24) 9562(32)8933(36) 38 d 36 38' 3 27 75 12( 1 1) 4220 (8)333 (8)987( 1 1) 85(1 1) 850(11)2547( 10) 3443(10)2687( 1 1) 3287(10) 1910(10) 2621(11) 4803(1 1) 62 16( 10)5463(1 1) 5707( 13) 4764( 12) 6761(14) 7 124( 16) 5567( 16) 3498( 15) 3169(13) -13 14( 12) -1002(15) -2425( 18) -2279(22)-11(18) -266(23)1 9 52( 27) -3863( 13) 6OOO( 16) 8322(15)8597(20) 10943(20)I1255(20) 13511(20) 13955(27)16 177(29) 9.6 7.0 6.6 5.2 6.2 5.8 5.0 5.6 5.7 5.1 5.5 6.2 5.4 6.I 6.3 6.5 6.0 8.2 8.8 8.2 8.3 7.6 6.4 8.8 10.8 12.9 10.7 12.7 19.3 7.9 11.6 9.8 11.5 12.3 14.7 14.2 18.1 21.6 o(3)- C(2 1)-C(22)- C( 23) -176 -179 -172 C(21)-C(22)-c(23)-C( 24) -167 179 -175 C(22)-c(23)- C( 24)- C( 25) -175 -176 -73 C( 23) -C( 24)- C( 25)- C( 26) 169 -177 170 C(24)-C(25)-C(26)-C( 27) 71 -173 175 c* -C(3 1)-C( 32)-C( 33) 176 -178 180 C( 3 1)-C( 32) -C( 3 3) -C( 34) 173 175 -177 C( 32)- C( 33) -C( 34) -C(35) 176 178 -179 C( 3 3)-C( 34) -C( 3 5)-C( 36) -174 I56 175 C(34)-C( 3 5)-C( 36) -C( 37) -172 174 178 C( 35)- C( 36) -C( 37)- C( 38) 180 -175, -134 177 C* denotes C( 1) for 1 and C( 17) for 2.long interchain distance (~4.4 A), as shown in Fig. 5. There-fore, it is concluded that the intermolecular interaction within a layer is more dominant in 2 than in 1.Relationship between Crystal Structure and Liquid-crystalline Phase Sequence It has been generally observed that the tilt angle is almost constant (ca.45 ") in sc followed by nematic, whereas it decreases with increasing temperature from ca. 25' at the lower transition temperature to zero or near zero at T, (sc-sA transition) in sc followed by sA.l1-I3 It was observed by means of an optical method5 that the tilt angle of 1 is 42" at T- T,= -30 "C (in the supercooled range of s;), whereas that of 2 changes from 30' at T -T,= -30 "C (in the superco- oled range of s/) to 19' at T-T,= 5 "C, and tends to zero at T =T, (s?-sA transition). These values are consistent with the general aspect of the tilt angle in sc mentioned above.In order to obtain further structural information in the 7 0 28 19 18 Fig. 1 ORTEP drawing with 50% probability thermal ellipsoids of the molecules A (upper), B (middle) of 1 and the molecules of 2 (lower). Disordered atoms are denoted by spheres with an arbitrary diameter. The molecule B is numbered in the same way as A J. MATER. CHEM., 1991, VOL. 1 Fig. 2 The crystal structure of 1 viewed along the b axis. Layer plane, parallel to (100) plane, is denoted by a broken line. Closed circles denote oxygen atoms. Disordered atoms are denoted by shadowed circles. Short 0-0 distances (/A) are as follows: O(2A) (x, y, 2)-O(1A) (x, y+l, Z) 3.82; O(2B) (x, y, z)-O(lB) (x, y+l, Z) 3.84; O(2A) (x, y, z)-O(3B) (1/2-~,1/2+y,l-z) 4.05,O(2A) (x,y,z)--0(3B) (1/2-~, -1/2+y, 1-2) 4.36; O(3A) (x, y, ~)-0(2B) (1/2-~,1/2+y,l-z) 4.44; O(3A) (x, y, ~)-0(2B) (1/2-~,-1/2+~,1 -z) 4.10 A A II I II I 4.23; (4.25 ,'4.30 I I / I I I I1-26 B 22 24 I' I B B Fig.3 Interchain distances (~4.4A) in 1. The values in parentheses denote those between adjacent cells and the values with a prime denote those of C(38B'). a=3.98, (3.62), (4.36) A;b=4.17', (4.15), (3.91') 8, smectics, interlayer distances (d)were measured in the whole temperature range of the smectics by means of powder X-ray diffraction. Fig. 6 shows the temperature dependence of d values in sz of 1 and in sA, sz, and metastable sB of 2. The d value of sz is constant throughout the temperature range of the stable and metastable regions for 1, whereas it increases with increase in temperature for 2.A similar temperature dependence of the latter was observed for 4'-octyloxybiphenyl- 4-carboxylic acid.I4 These facts confirm a constant tilt angle in 1 and a temperature-dependent tilt angle in 2. Thus, the tilt angles observed in the crystals (65' for 1 and 10' for 2) correspond to those (42' for 1 and 29-0' for 2) in sz. The tilt, angles in the crystals are determined by the overlap of molecules within a layer. In both crystals, the ester and ether groups are closely arranged in neighouring molecules. Similar modes, however, lead to a small overlap in 1 and a large one in 2, depending on the length of the moiety sandwiched by two polar groups.The small overlap of molecules in 1indicates a less stable smectic-like layer structure, leading to the tran- sition from the s: phase to the cholesteric, whereas the larger overlap within a layer in 2 would cause the transition from sz to sA. Interlayer interaction due to the close contact of J. MATER. CHEM., 1991, VOL. 1 a sinp 0 Fig.4 The crystal structure of 2 viewed along the b (upper) and c (lower) axes. In the lower, the c axis is taken downward from the sheet of paper. The layer plane is parallel to the (100) plane. Dotted lines denote close arrangements of 0 atoms (denoted by closed circles) with distances in 8, Fig. 5 Interchain distances (4.6 A) in 2 36 SB pU-8 32 =a 28 I I I I I 40 60 80 T/"C Fig.6 Temperature dependence of interlayer distances in smectics. Closed and open circles denote the values for 1 and 2, respectively. x denotes an effective molecular length of 2 67 1 alkyl chains is more significant in 1 than in 2. It is interpreted that the interlayer interaction, which would remain in s& is responsible for the constant tilt angle in sE of 1. Similar correlations between tilt angle in sz and crystal structure were found for two series of biphenyl esters with a 2-methylbutyl group.'9' However, the following differences are also found in the arrangement of the polar groups. The crystal structure 1 shows close contact between the ester and ether groups at two positions, whereas (n=$7) with the same phase sequence as 17 has an antiparallel arrangement of the ester groups.In the case of the crystals that transform to sz adjacent to sA, the ester and ether groups of the molecule are a short distance apart, with two neighbour- ing molecules on opposite sides in 2, as shown in Fig. 4, whereas they make pairwise association with the same mol- ecule in (n=7,8). In spite of these differences, the length of the moiety sandwiched by two polar groups essentially determines the degree of molecular overlap and hence the tilt angle of molecules, which is closely related to the structure of sz. Nearest phenyl rings between adjacent molecules make angles of 60°, on average, for 1 and 79' for 2. These values are similar to those found in the preceding except for the triclinic form of 4'-hexyloxy-4-biphenylyl p-[(S)-2-methylbutyl] benzoate, in which some of the mutual arrange- ments of the phenyl rings are nearly parallel (ca.20°), being related to the highly ordered sJ*.~Therefore, it is interpreted that rotation around the molecular long axis would be readily induced at the crystal-mesophase transition, i.e. the present crystals transform to a smectic phase with higher disorder, s; . For 2, the d value in sA, an orthogonal smectic, is shorter than that (34.2A) of sB, another orthogonal one. This value coincides with the molecular length in the crystal (34.6&, a sum of the distance between the terminal atoms, C(27) and C(38), and twice the van der Waals radius of a methyl group (2.0 A).A reduction of the d-value in sA was observed also for 4'-octyloxybiphenyl-4-carboxylicacid.I4 The value of d/ cod gives the effective molecular length. Those values for 2 show a slight decrease continuously with an increase in temperature throughout sz and sA, as shown in Fig. 6. This indicates a continuous change in the degree of disorder in the two phases. On the other hand, the value for 1, 35.0 8, (at T-T,= -30 "C), is larger than that for 2. This fact probably suggests more extended conformations of 1 than those of 2, not only in the crystal (estimated to be 35.7 and 36.8 A for the molecules A and B of 1, respectively) but also in sz. It is concluded that the liquid-crystalline phase sequences are well interpreted by intermolecular interactions revealed in the crystal structures, which are controlled by the lengths of the moieties sandwiched by polar groups for the compounds with a 1-methylheptyloxy group as was observed for those with a 2-methylbutyl group.I5 We thank Drs.T. Inukai and K. Furukawa of Chisso Coopor- ation for supplying the samples. This work was supported by ~~~~~~~ ~ For n =5 s: appears only monotropically. 672 J. MATER. CHEM., 1991, VOL. 1 a Grant-in-Aid for Scientific Research No. 02640333 from the Ministry of Education, Science and Culture, Japan. 8 Programs for the Automatic Solution of X-ray Diffraction Data, Universities of York, England and Louvain, Belgium, 1978. G. M. Sheldrick, SHELX76, A Program for Crystal Structure 9 Determination, Univ.of Cambridge, 1976. International Tables for X-ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV. References 1 K. Hori and Y. Ohashi, Bull. Chem. SOC. Jpn., 1988, 61, 3859. 2 K. Hori, M. Takamatsu and Y. Ohashi, Bull. Chem. SOC. Jpn., 1989, 62, 1751. 3 K. Hori and Y. Ohashi, Bull. Chem. SOC. Jpn., 1989, 62, 3216. 4 K. Hori and Y. Ohashi, Liq. Cryst., 1991, 9, 383. 5 T. Inukai, S. Saitoh, H. Inoue, K. Miyazawa, K. Terashima and K. Furukawa, Mol. Cryst. Liq. Cryst., 1986, 141, 251. 6 G. M. Sheldrick, SHELX86, A Program for Crystal Structure Determination, University of Gottingen, 1986. 7 P. Main, S. E. Hull, L. Lessinger, G. Germain, J-P. Declercq, and M. M. Woolfson, MULTAN78, A System of Computer 10 11 12 13 14 15 C. Johnson, ORTEP, Report ORNL-3794, Oak Ridge National Laboratory, Tennessee, 1965. T. R. Taylor, J. L. Fergason and S. L. Arora, Phys. Rev. Lett., 1970, 24, 359. T. R. Taylor, S. L. Arora and J. L. Fergason, Phys. Reu. Lett., 1970, 25, 722. G. W. Gray and J. W. Goodby, Smectic Liquid Crystals, Leonard Hill, Glasgow, 1984, p. 54. G. W. Gray and J. W. Goodby, Mol. Cryst. Liq. Cryst., 1976, 37, 157. K. Hori and Y. Ohashi, Mol. Cryst. Liq. Cryst., in the press. Paper 1/01308D; Received 19th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100667

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 673-675 Variation with Composition of the Intrinsic Sensitivity of Halogen-substituted Styrene Copolymers to Electron-beam Radiation Philip C. Miller Tate* and Richard G. Jones Centre for Materials Research, Chemical Laboratory, University of Kent at Canterbury, Canterbury, Kent CT2 7NH, UK In the polymer literature (Handbook of Polymer Science and Technology, ed. N. P. Cheremisinoff, Marcel Dekker, New York, 1989, vol. 1, p. 307) a simple equation has been derived to estimate the lithographic sensitivity of a copolymer of known composition and molecular weight from the constituent homopolymer values. Sensitivity has often been equated with the reactivity parameter DgMwwhere 0, is the gel dose and Mwthe weight-average molecular weight of the polymer.This report demonstrates that the use of the reciprocal reactivity (DgMw)-' leads to a clearer interpretation of the lithographic results and that furthermore, the conclusions drawn from earlier analyses neglect the consequences of co-operative action between differing monomer units within copolymers . Keywords: Lithography; Electron-beam resist; Halogenated polystyrene; Copolymer In an article entitled Radiation-Induced Reactions of Poly-styrene Derioatiues within the Handbook of Polymer Science and Technology,' the authors apply a formula derived on the basis of Charlesby's theory2 to define a theoretical relationship between copolymer composition and sensitivity to electron- beam radiation for polystyrene sensitized with halogen-con- taining functional groups.The form of the equation is as follows: where xMand xNare the mole fractions of monomer units M and N in the copolymer, DgMN, DgMand DgN are the doses corresponding to the onset of gelation of the copolymer and the homopolymers of M and N, respectively, and MwMN, MwM and MwNare the weight-average molecular weights of the copolymer and homopolymers, respectively. It is suggested that the sensitivity of a copolymer may be estimated at any composition by employing this equation with foreknowledge of the sensitivities and molecular weights of the homopoly- mers, and a graphical presentation of experimental data is provided to support the analysis. Although an apparently reasonable fit of data to the theory is shown, their choice of ordinate confuses the issue.DgMNMwMN is plotted on a decreas- ing logarithmic scale, presumably in order to place points for high sensitivity materials at the top of the plot. This leaves the theoretical fit depicted as a curve whose relationship to eqn. (1) is by no means clear to the reader. It would appear far more appropriate to plot the sensitivity parameter as (DgMNMwMN)-', since from eqn. (I), this would present the theoretical fit as a straight line joining the homopolymer points, and any deviation from this line would be immediately apparent. In previous publication^,^ we have dubbed this parameter the intrinsic sensitivity of a negative-working elec- tron-beam resist, since it increases in value with increasing resist sensitivity.This avoids the confusion of citing decreasing gel dose as a measure of increasing sensitivity, and also corrects for the effect of molecular weight variation; hence its value for a particular polymer depends only on the polymer microstructure and is intrinsic to that structure. As a param- eter characteristic of sensitivity, it can be further improved upon by converting the incident lithographic dose to an absorbed radiation dose, or better still by expressing it in terms of the radiation chemical yields for cross-linking and chain scission, G, and G,. It should also be noted that large errors are possible when evaluating the intrinsic sensitivity, since the estimation of both the gel point and the molecular weight of a resist are potentially subject to significant error, particularly when comparing data obtained from different sources.Results and Discussion The data from the above-mentioned article are re-plotted in Fig. 1 as a linear correlation. Despite the scatter in the data, it is now clear that the experimental results do not fit the theoretical prediction of behaviour very well, since the majority of the data points of all three systems, namely poly(styrene-co-chloromethylstyrene),poly(styrene-co-chloro-styrene) and poly(styrene-co-iodostyrene) fall above their pre- dicted lines. In fact, this is to be expected, since the contributions to resist sensitivity in terms of cross-linking mechanisms can be divided into three groups: those arising from processes inherent to one or other homopolymer, which will become more or less prevalent according to the mole fraction of the appropriate monomer unit in the copolymer, plus an additional contribution from cross-linking mechanisms which arise from chemical interactions between both co-monomer units in the copolymer.It is clear that eqn. (1) takes into account only the 'homopolymer' processes, and yet we -0 , 0 I5l =---0+= 0.0 0.25 0.50 0.75 1.0 substituted styrene in copolymer (mole fraction) Fig. 1 Intrinsic sensitivity uersus copolymer composition (data from ref. 1). 0, Poly(styrene-co-chloromethylstyrene);A, poly(styrene-co-iodostyrene); 0,poly(styrene-co-chlorostyrene) have observed that the ‘copolymer’ processes can significantly enhance the sensitivity of the resist.Indeed, the published mechanisms of cross-linking in resists sensitized with chloro- methylstyrene4 centre on the cleavage of the carbon-chlorine bond on irradiation to produce a benzylic radical and a chlorine atom, followed by a-hydrogen or pendant methyl hydrogen atom abstraction from an adjacent styrene or methylstyrene unit by the chlorine atom to yield, overall, two potential cross-linking sites on the chain; this emphasizes the co-operation of the co-monomer units. Only in the absence of such co-operation would the behaviour predicted by eqn. (1) be observed in practice; in fact, the equation treats a statistical copolymer as though it were an ideal blend of the equivalent mole fractions of its constituent homopolymers, and in most cases this assumption is invalid. In the particular case of poly(methy1styrene-co-chloromethylstyrene), there is observed a significant increase in sensitivity for only 5% chloromethylstyrene content and thereafter the improvement is much less pronounced as the composition approaches that of the chloromethylstyrene homopolymer.Such co-operative effects involving the two monomer units are pronounced in copolymer systems containing chlorostyr- ene and our investigations into the performance of resists based on poly(styrene-stat-p-chlorostyrene)yield very different results from those reported in ref. 1. For the purposes of comparison, the variation of intrinsic sensitivity with compo- sition that we have observed, and that of Tanigaki and Tateishi,’ are presented in Fig.2. Our observation is that the synergy arising from the combination of the co-monomers is so great that the intrinsic sensitivities of all of the copolymers are greater than either of the two homopolymers. This phenomenon has also been reported for the same system by Whipps’ who observed a peak in sensitivity for copolymers of similar molecular weight, at a copolymer composition of between 20 and 30% chlorostyrene. We have also reported the same phenomenon in both poly(o-methy1styrene-stat-p-chlorostyrene) and poly(p-methylstyrene-stat-p-chlorostyr-ene)6 and have offered an explanation in terms of a cross- linking mechanism that correlates with the distribution of the two types of monomer unit in the copolymer.The discrepancy between our value of the intrinsic sensitivity of p-chlorostyrene homopolymer and the value given by Tateishi and Tanigaki is large (almost a factor of 2) but this is not unusual when comparing lithographic values in the literature, particularly when dealing with gel dose, which is notoriously difficult to estimate accurately. Our estimates of gel dose are determined by extrapolation from data plotted in the manner described by Charlesby and Pinner,7 a technique which is superior to estimation from lithographic contrast curves. In the case of poly(styrene-co-iodostyrene), Tateishi and Tanigaki refer to a discrepancy in the fit of experimental data 0 0 0 0 0q I 0.0 0.25 0.50 0.75 1-0 chlorostyrene in copolymer (mole fraction) Fig.2 Intrinsic sensitivity uersus copolymer composition for poly(styrene-co-chlorostyrene):0 Data from ref. 1; 0 authors’ data J. MATER. CHEM., 1991, VOL. 1 12 - k3 r ‘do - r I 0 -8-E 6 N 6- % 0 0 A A 0 7 4- z g h i QA 07 I Fig. 3 Intrinsic sensitivity versus copolymer composition for poly- (chlorostyrene-stat-chloromethylstyrene). 0,poly(o-chlorostyrene-stat-chlorometh ylst yrene); A thylstyrene); 0,poly(p-chlorostyrene-stat-chloromethylstyrene) to their theoretical curve at high iodostyrene contents, and furthermore assert that this discrepancy is greater for the iodostyrene system than for the chlorostyrene system ‘due to the difference in hydrogen abstraction strength between a chlorine radical and an iodine radical’.They also point out that eqn. (1) does not take such considerations into account. When the data are plotted as in Fig. 1, it becomes clear that the major deviation from the theory is in fact at low iodostyr- ene content, but it is not clear as to whether this can be attributed to the susceptibility of hydrogen atoms to abstrac- tion by halogen atoms, since there is no obvious reason why this should vary with composition in the manner shown. In our explanation of the lithographic behaviour of the poly(me- thylstyrene-co-chlorostyrene)systems, the cross-linking mech- anism in the copolymer does not involve the generation of a halogen atom, but rather depends on the formation of an intramolecular exciplex between differing adjacent units on the chain.Again, Whipps has reported a peak in sensitivity of copolymers of styrene and iodostyrene corresponding to ca. 35% iodostyrene content,’ which is not very different from that suggested by the data presented in Fig. 1. We are aware of only one family of copolymers for which eqn. (1) does apparently hold true, namely copolymers of chlorostyrene and chloromethylstyrene where the chloro sub- stituent can be in the ortho, meta or para position and the chloromethylstyrene monomer is vinyl benzyl chloride (VBC), a 2: 1 mixture of the meta and para isomers. In all three systems there is a linear increase in intrinsic sensitivity with increasing VBC content (see Fig.3) and, furthermore, esti- mation of the radiation chemical yields demonstrates a con- comitant linear increase in both G, and G,. The reason for the apparent absence of ‘copolymer’ cross-linking processes in these materials is not yet fully explained. In conclusion, analysis of experimentally determined intrin- sic sensitivities of copolymer resists is useful in designing resists, but particularly so in systems where a maximum in the sensitivity plot may determine an optimal composition for a resist of given M,. However, it is our experience that simple analyses based on homopolymer contributions should be treated with considerable scepticism since generally they do not provide results which accord with current knowledge or understanding.Funding for the work described here has been provided by Plessey Research Caswell (now part of GEC Marconi) and SERC. The authors wish to express their gratitude to Dr. David Brambley and the UK Advanced Lithography Research Initiative for help and encouragement. J. MATER. CHEM., 1991, VOL. 1 675 References 5 P. W. Whipps, Proc. Microcircuit Eng. '79 Conf. (Microstructure Fabrication), Elsevier Science Publishers B.V., London, 1980, 1 K. Tanigaki and K. Tateishi, Handbook of Polymer Science and p. 118. Technology, ed. N. P. Cheremisinoff, Marcel Dekker, New York, 6 R. G. Jones, P. C. Miller Tate and D. R. Brambley, J. Mater. 1989, vol. 1, p. 307. Chew., 1991, 401. 2 K. Tanigaki, Y. Ohnishi and S. Fujiwara, ACS Symp. Ser. 242, 7 A. Charlesby and S. H. Pinner, Proc. R. SOC. London, A, 1959, ACS, Washington DC, 1984, p. 177. 249, 367. 3 D. R. Brambley, R. G. Jones, Y. Matsubayashi and P. Miller 8 P. W. Whipps, Society of Plastics Engineers Con5 Photopolymers: Tate, J. Vuc. Sci. Technol. B, 1990, 8(6), 1412. Principles, Processes and Materials, Ellenville N.Y., 1985. 4 See, for example, Y. Tabata, S. Tagawa and M. Washio, ACS Symp. Ser. 266, ACS, Washington DC, 1984, p. 151. Paper 1 lOl7201; Received 21st March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100673

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 677-679 Synthesis, Structure and Electrical Properties of Sr,CuO,(CO,), an Oxide Carbonate related to Perovskite T. G. Narendra Babu, Deborah J. Fish and Colin Greaves* Superconductivity Research Group, School of Chemistry, University of Birmingham, Birmingham B152TT, UK The phase Sr,CuO,(CO,) occurs as an intermediate in the reaction between SrCO, and CuO to form Sr,CuO,. The conditions of formation have been examined, and the structure determined from time-of-flight neutron powder diffraction [tetragonal, P4/mmm; a= 3.9033(2)A, c= 7.492544) A]. The structure consists of alternating layers of composition [Cu0,l2- and [CO,]'- perpendicular to [OOl], separated by layers of Sr2+ cations. The carbonate groups are all oriented to have one C-0 bond along [IOO] or [OlO], and two bonds at ca.30" to [OOl]. No clear evidence for long-range ordering of the CO, groups was found.Keywords: Strontium copper oxide carbonate; Perovskite; Neutron diffraction; Powder diffraction The observation of superconductivity at relatively high tem- program TFlSLS, which is based on the Rietveld method peratures in mixed metal copper oxides appears to be associ- and the Cambridge Crystallography Subroutine ated with the presence of low-dimensional structural Scattering lengths of 0.702, 0.7718, 0.5805 and 0.6648 (all characteristics, especially planes of corner-linked square Cu04 x 10-l2 cm) were assigned to Sr, Cu, 0 and C, respectively. units with short (ca. 1.95A) Cu-0 bonds. The chemistry of For electrical resistivity measurements, sintered pellets were materials with such features is consequently of considerable prepared by pressing the SrC03/Cu0 reactants at interest.The compound Sr2Cu02(C03) has been reported' ca. 2300 kg cmP2 followed by heating in oxygen or nitrogen to contain layers of this type, and hence appears very closely as above. The successful synthesis of Sr2Cu02(C03) within related to the superconducting phases Ndl~85Ceo.lsC~04-,2 the pellets was confirmed by X-ray diffraction. Rods were cut Structural details of Sr2Cu02(C03) from the pellets and resistivity values determined for 20< and Nd2C~03,6Fo,4.3 have not been reported, but on the basis of X-ray diffraction T/K <260 using a low-frequency (30 Hz) a.c. 4-probe evidence,'g4 it was assumed that the carbonate groups have technique.one C-0 bond perpendicular to the plane containing the C atoms, but otherwise are orientationally disordered. Owing to the limitations of X-ray powder diffraction for determining Results and Discussion accurate anion parameters in such a material, Sr2Cu02(C03) The X-ray powder diffraction profile was indexed on a tetra- has been re-examined in this paper using neutron powder techniques. The conditions required for the successful synthesis gonal, perovskite-related unit cell with a =3.907 A, c = of this phase, and its electrical properties have also been 7.499 A. Although two weak peaks could be attributed to an enlarged cell with a =3.907J2 A, as previously ~uggested,~ examined.the possible presence of impurities and the fact that these peaks were not apparent in all samples suggested that such Experiment a1 an interpretation was unjustified on this evidence alone. The neutron diffraction profile revealed the presence of Sr2Cu02(C03) forms as an intermediate during the formation SrC03 as a minor phase, and structure refinement was initially of Sr2Cu03 from SrC03 and CuO. The conditions required attempted using the basic doubled perovskite cell with the 0 to prepare Sr2Cu02(C03) were examined using intimate atoms of the carbonate groups excluded. At this stage, the mixtures of high-purity SrC03 and CuO. It was found reason- lowest symmetry space group, P4, was adopted. A difference ably pure products could be obtained by heating at 940 "C Fourier map was obtained using calculated phases and ampli- for 14 h using a conventional horizontal-tube furnace provided tudes corresponding to IFo[-IF,[ values.Deconvolution of very slow gas flows of air, nitrogen or oxygen were used (ca. overlapping reflections was accomplished by partitioning in 150 cm3 h- ' in a tube of internal diameter 45 mm). However, accordance with the ratio of IF,[ values. Although such the required product could not be prepared in static air in syntheses are therefore biased towards the model employed, an open furnace, presumably owing to the influence of convec- in this case, where no relevant 0 atoms were included, the tion currents. X-Ray diffraction traces generally revealed some method clearly revealed the orientation of the C03 groups.contamination with SrC03, and rapid decomposition to Fig. 1 demonstrates that one C-0 bond is directed towards Sr2Cu03 appeared to occur as soon as all the SrC03 had an adjacent C03 group in the plane containing the C atoms, disappeared from the reaction mixture. which is perpendicular to Cool]. This is contrary to the A 5 g sample of Sr2Cu02(C03) was prepared for examin- previously suggested alignment in which each C03 group was ation using time-of-flight neutron diffraction. A representative thought to have one C-0 bond pointing along [OOl] or portion of this sample was reduced to SrO and Cu in [OOT]. Since subsequent refinements of the structure were 1O%H2-90%N2 (Stanton Redcroft STA 780 analyser, heating consistent with the higher symmetry space group P4/mmm, rate 10 "C min-' to 930 "C).The weight loss, 18.5%, is in this was employed in the final refinements. Very high isotropic excellent agreement with that expected, 18.1 YO. Ambient- temperature factors were obtained for the 0 atoms of the temperature neutron diffraction data were collected on the C03 groups, and these were therefore allowed to vibrate diffractometer POLARIS at the Rutherford Appleton Labora- anisotropically. Fig. 2 shows the observed and calculated tory. Structure refinement (for 0.486 <d/A<1.620) used the neutron profiles, and the refined structural parameters are 678 ? P n E;0 Y t / -1A-+ [loo] Fig. 1 Difference Fourier section, (OIO), through the C atom at (0, 0, &), with the implied C03 orientation marked.The appearance of six 0 atoms round the C is a consequence of the disordered nature of the C03 groups r--0.5 0:7 0:9 d-spacinglii Fig. 2 Observed (dots), calculated (continuous line) and difference neutron diffraction profiles given in Table 1. Selected bonding information is given in Table 2. Although the detailed local ordering of the C03 groups cannot be determined, it is clear that the C-0(2) bonds of nearest-neighbour C03 groups will be at 90" to each other in order to avoid short 0-0 distances. A represen-tation of the structure is shown in Fig. 3. The additional peaks, which are clearly evident in the neutron diffraction profile, are primarily due to SrC03, and are responsible for the slightly large profile R-factors, Table 1.No strong evidence for superstructure peaks consistent with long-range ordering of the carbonate groups could be found. The anisotropic thermal factors for O(2) and O(3) are consist- ent with oscillations of the C03groups about an axis through C and perpendicular to the plane of the group. Allowing for the difference in orientation of the O(2) and O(3) thermal J. MATER. CHEM., 1991, VOL. 1 Table 1 Refined structural parameters for Sr2Cu02(C03)" atom position x y z '/A2 site occupancy Sr 2h 4 3 0.2283(4) 0.65(5) I Cu la 00 0 0.52(5) I C lb 0 0 4 0.66(8) 1 O(1) If 0 4 0 0.78(5) 1 O(2) 4m 0.334(2) 0 3 t 0.25 O(3) 8s 0.862(3) 0 0.646(2) t 0.25 t Anisotropic thermal parameters/A2: Bl1 '22 '33 '12 '13 B23 O(2) -0.6(2) 2.7(6) 9(1) 0 0 0 O(3) 6.2(6) 2.0(4) 3.5(4) 0 -4.8(4) 0 " Tetragonal, P4/mmm,a =3.9033(2)A, c =7.4925(4) A.R-factors: R,= 3.8%, R,,=4.5%, RE=2.3%, R,= 11.0%. Table 2 Selected bond distances (/Hi) and angles (/O) c-O(2) 1.304(8) Cu-O(l) 1.9517(2) [~4] C-0(3) 1.22(2) [x 21 Sr-O(1) 2.595(3) [x 41 O(3)-C-O(3) 128(2) Sr-0(2) 2.894(4) [x 27 0(2)-C-0(3) 116(1) Sr-0(3) 2.588(8) [x 2"] " Average number of bonds. .O@C 0 Sr Cu Fig. 3 Structural representation showing three subcells with appropri- ate alignment of the carbonate groups ellipsoids, the vibrations at both atoms are virtually identical, with the major axis (calculated from the thermal parameter matrices to be B=9 and 10 A', respectively) being in the plane of the C03 group and perpendicular to the C-0 bond.Even though the standard deviations for the oxygen thermal parameters are high, the slightly negative value of BI1 for O(2) clearly indicates that they still underestimate the true standard deviations, which is a common problem encountered in refinements based on powder diffraction data. The carbon- ate groups are slightly distorted, with the two C-0(3) bonds, which are directed out of the z=O.5 plane, being slightly shorter than C-0(2), Table 2. In accordance with electro- static considerations, the 0(3)-C-0(3) angle is greater [128(2)"] than the two 0(2)-C-0(3) angles [116(1)"]. The O(3) atoms are displaced 0.54A from positions directly above and below the Cu atoms, and since the Cu-0(3) distances are very long (2.71 A), the Cu stereochemistry is more closely related to that in Nd2C~047 than L~,CUO,.~ The Cu-0 distances in the CuOz layers (1.952A) are, however, smaller by ca.0.02 A. The Sr-0 distances are similar to those observed in other systems; for example, Sr2Cu03 has distances of 2.51, 2.62 [x 41, and 2.56 A [x 21.' In view of the structural similarity to Nd2Cu04, which J. MATER. CHEM., 1991, VOL. 1 h 51 .-31 .-> 0' I I 1 I I 0 10 20 30 40 50 lo3K/ T Fig. 4 The resistivity of Sr,Cu02(C0,) pellets sintered in oxygen and nitrogen atmospheres: *, oxygen; 0,nitrogen In view of the structural similarity to Nd2Cu04, which becomes superconducting when appropriately doped, the elec- trical resistivity of Sr,Cu02(C03) was determined on two pellets, one synthesised in oxygen the other in nitrogen. As shown in Fig.4, both samples were semiconducting over the temperature range examined, and the preparative conditions had little influence on the resistivity. The apparent decrease in resistivity at low temperature for the oxygen-sintered sample is the subject of further investigations. Attempts at modifying the electronic properties uia chemical doping have so far proved unsuccessful since the thermal instability of Sr2Cu02(C03) imposes severe restrictions on the preparative conditions that can be employed. We are grateful to SERC for providing financial support and neutron diffraction facilities; we also thank ICI for additional funding. We are grateful for the assistance of S. Hull during the collection of neutron diffraction data. References 1 Hk. Miiller-Buschbaum, Angew. Chem. Int. Ed. Engl., 1989, 28, 1472. 2 Y. Tokura, H. Tagaki and S. Uchida, Nature (London), 1989, 337, 345. 3 A. C. W. P. James, S. M. Zahurak and D. W. Murphy, Nature (London), 1989,338,240. 4 Hk. Miiller-Buschbaum, personal communication, 1990. 5 J. C. Matthewman, P. Thompson and P. J. Brown, J. Appl. Crystallogr., 1982, 15, 167. 6 P. J. Brown and J. C. Matthewman, Rutherford Appleton Laboratory Report RAL-87-010, 1987. 7 Hk.Muller-Buschbaum and W. Wollschlager, 2. Anorg. A&. Chem., 1975,414, 76. 8 B. Grande, Hk. Miiller-Buschbaum and M. Schweitzer, 2.Anorg. AIIg. Chem., 1977, 428, 120. 9 Von Chr. L. Teske and Hk. Miiller-Buschbaum, 2.Anorg. Allg. Chem., 1969, 371, 325. Paper 1/O 1501J; Received 28th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100677

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 681-684 68 1 Sol-Gel Synthesis of Zr(HP0,),*H20 Hafida Benhamzab, Philippe Barboux,*a Ahmed Bouhaouss,b Francois-Andre Josiena and Jacques Livage" a Chimie de la Matiere Condensee, Universite P. et M. Curie, Paris, France Laboratoire de Chimie Physique, Universite Mohammed V, Rabat, Maroc Inorganic ion exchangers such as a-Zr(HPO,),*H,O are usually synthesized from aqueous solution. Amorphous precipitates are then obtained, which crystallize very slowly upon ageing at ca. 90°C in their mother liquor. Crystallization could be much faster if alkoxide precursors are used. The sol-gel synthesis of a-Zr(HPO,),-H20 from both inorganic and metallo-organic precursors has been followed by solid-state 31PMAS NMR and X-ray diffraction. Condensation mechanisms leading to the formation of a solid phase are discussed. Compared to ZrOCI, in aqueous solution, zirconium mpropoxide allows shorter reaction times and lower crystallization temperatures.This results in a material with smaller grains which should exhibit enhanced exchange properties. Keywords: Alkoxide; Sol-gel processing; Ion exchange; Phosphate; Nuclear magnetic resonance spectroscopy Acid phosphates of tetravalent metals have been extensively Experimental studied since the discovery of their ion-exchange proper tie^.'-^ The aim was to make inorganic exchange membranes whose Acid zirconium phosphates were prepared by adding H3P04 chemical resistance toward strongly acidic and basic solutions (85%) to an equal volume of the precursor solution (1 mol was expected to be higher than that of the equivalent organic dmP3).In both cases a white gelatinous precipitate is obtained materials. as soon as the solutions are mixed together. Precipitates are These phosphates correspond to the general formula kept in their mother liquor for different times at different M(HP04)2* H20 where M is a tetravalent cation (Zr, Ti, Hf, temperatures as indicated below in order to follow the crys- Ge, Sn, Pb). The a-crystalline form exhibits a layered structure tallization process. The resulting precipitate is then filtered, of planar macroanions [M(PO,),]~"-. The negatively charged washed with distilled water and dried in air at ca.60 "C. oxygen atoms are compensated by an equivalent number of 31PMAS NMR spectra were recorded at room temperature protons forming weak PO-H bonds3 These acid protons with a MSL400 Bruker spectrometer at a frequency of can be easily replaced by other cations without any structural 161.98 MHz.Samples were spun at a rate of ca. 5 kHz. change of the layered host lattice. IR absorption experiments were performed with a Perkin- Zirconium phosphates are usually synthesized by reacting Elmer 610 continuous wave spectrometer. Solid samples were concentrated phosphoric acid (H3P04, 4 mol dm-3) with an pressed into KBr pellets. TG of powders dried at 60 "C was performed in air at a aqueous solution of a zirconium salt such as ZrOC1,. A heating rate of 10 "Cmin-'.gelatinous amorphous precipitate is readily obtained.Slow crystallization then occurs when the precipitate is heated under reflux in its mother liquor. After 2 weeks of reflux, crystallites of ca. 1 pm in diameter are obtained.' Results One of the main drawbacks of aqueous solutions is that X-Ray Diffraction water is both a solvent of the inorganic salt and a chemical reagent for the hydrolysis of metal cations. It is therefore The X-ray diffraction pattern of powders obtained from rather difficult to control the hydrolysis and condensation of propoxide precursors after 1 h at 60 "C exhibits only broad aqueous molecular precursors. It would therefore be interest- peaks corresponding to the a-Zr(HPO,), * H20 phase. Crys- ing to look for more versatile precursors. tallization occurs within 1 day at 60 "C [Fig.l(a)J. It can also In the framework of the so-called sol-gel process, metal be obtained at room temperature after a few weeks when the alkoxides are known to offer many advantages despite their precipitate is left in its mother liquor. Crystallization occurs higher cost.4 (i) Metal alkoxides can be dissolved in their progressively. It is therefore not possible to define an exact parent alcohol so that hydrolysis may be carefully controlled crystallization time since it depends on the criterion of crystal- by adding small amounts of water diluted in the alcohol. (ii) line quality. The molecular structure and the functionality of these precur- Precipitates obtained from ZrOC1, in water remain sors can be designed by adding nucleophilic modifiers.It amorphous even after 1 week at 60 "C. Their X-ray diffraction therefore becomes possible to control the hydrolysis and patterns then exhibit broad peaks similar to those observed condensation reactions in order to tailor the morphology and with the alkoxide precursor after 1 h [Fig. I@)]. Crystalliz-structure of the resulting material. ation has never been observed at room temperature even after Although the classical synthesis of cr-Zr(HP04)2 *H20 from several months. aqueous solutions is very simple, alkoxide precursors also offer an opportunity to study the chemical substitution of alkoxy groups by inorganic nucleophilic reagents such as "P MAS NMR Spectroscopy PO2-. This paper reports on the reaction of phosphoric acid (85Y0 More accurate information on the local environment of in water and anhydrous) with the following zirconium precur- phosphate groups has been obtained by solid-state 31Pmagic-sors: ZrOC1, in aqueous solution; zirconium propoxide, angle-spinning NMR.The spectra are reported in Fig. 2. Zr(OPr"),, in propan-1-01. Chemical shifts are referenced to H3P04 (85%). Surprisingly, J. MATER. CHEM., 1991, VOL. 1 A B & > 10 20 30 40 10 20 30 40 61" 01" Fig. 1 X-Ray diffraction pattern of Zr(HPO,),-H,O precipitated from: A, Zr(OPr"),; B, ZrOC1, and heated for different times, (a) 1 h, (6) 1 day, (c) 8 days, at 60 "C in its mother liquor _h - I I I I I 1 1 I I 20 10 0 -10 -20 -30 -40 -50 -60 8 (PPW B -22.3 b. ---.-< 1 I I I I I I I I 20 10 0 -10 -20 -30 -40 -50 -60 6 (PPW Fig.2 31P MAS NMR spectra (shifts relative to H3PO4) for Zr(HP04)2. H20 precipitated from: A, Zr(OPr"),; B, ZrOC1, and heated for different times (a) 1 h, (6) 1 day, (c) 8 days, at 60 "C in its mother liquor. Peaks marked with * are rotation bands. Minor peaks are found around 0.0, -7.0, -14.0 and -27 ppm as discussed in the text even amorphous samples give sharp peaks, showing that phosphate groups have a rather well defined co-ordination. The NMR spectra of amorphous powders precipitated from aqueous solutions exhibit a main peak at -22.3 ppm [Fig. 2(b), t= 1 h]. Some smaller peaks are also observed on each side (6=0, -7, -14 and -27 ppm). The positions of all these peaks remain unchanged to within kO.2 ppm, which is the experimental error, when precipitates are heated at 60 "C in their mother solution.Small peaks decrease slightly in intensity while the main one does not change. The behaviour of powders precipitated from alkoxide pre- cursors is somewhat different. A main peak is again observed at -22.3 pprn with a shoulder at -19.3 ppm [Fig. 2(a), t= 1 h]. As in the case of aqueous precursors, smaller peaks can be seen on both low- and high-field sides (around 6=0.0, -7.0, -14.0 and, as traces, -27.0 ppm). These small peaks rapidly disappear upon ageing. The peak at -19.3 ppm progressively increases in intensity while the one at -22.3 ppm decreases. A single sharp peak at 19.1 ppm is observed after 1 week at 60 "C.This peak is characteristic of the crystalline C~-Z~(HPO,)~H20 phase.It obviously corresponds to a phos- phate group HPOi- triply bound to three different zirconium atoms. The small variation of the chemical shift from -22.3 ppm to 19.3 ppm after 8 h and -19.1 ppm after 1 week could be due to some modification in the second co-ordination shell of the phosphorus atom or some variation in the P-0-Zr angle. Smaller peaks which are visible in the 31P NMR spectra of amorphous samples could be assigned to phosphate groups bonded to one (6% -7ppm), two (6z -14 ppm) or even four (6%-27 ppm) zirconium atoms. Such behaviour would agree with a previous study performed on phosphatoantimonate compounds showing that the chemi- cal shift is displaced toward high fields when the connectivity of phosphate groups increase^.^ However, chemical shifts close to 0 and +1 ppm have been observed for other compounds such as KTiOPO,, in which phosphate groups are bonded to four titanium atoms.Connectivity should therefore not be the only parameter to be taken into account. The large distortion of the [PO,] tetrahedron in the KTiOPO, structure may also be responsible for the observed chemical shifts- Actually, the 31Pchemical shifts mainly depend on the amount of 0 and R bonding. They are therefore very sensitive to 0-P-0 angles.6 Infrared Absorption Infrared spectra of precipitates obtained from alkoxide precur- sors do not exhibit any vibration band corresponding to organic groups (Fig.3). This indicates that all alkoxy ligands have been completely removed by hydrolysis or phosphatis- ation and points out the high reactivity of alkoxide precursors. J. MATER. CHEM., 1991, VOL. 1 I I 4000 3000 2000 1600 1200 800 400 wavenurnber/crn -' Fig. 3 IR absorption spectra of zirconium phosphates precipitated from zirconium alkoxide after (a) 1 h (amorphous) and (b) 8 days (crystallized) Vibrations corresponding to phosphate groups are located between 1200 and 900 cm-'. They become sharper when crystallization improves. Two broad peaks at 2400 and 1250 cm- are also seen with amorphous samples. They can be assigned to P-0-H stretching and bending vibrations, re~pectively.~The peak at 2400 cm -almost disappears in the well crystallized samples although all other vibrations tend to sharpen.This could be due to the fact that P-OH groups form stronger hydrogen bonds resulting in a broaden- ing of the vibration band. Such a modification of the infrared absorption spectrum may be related to the slight change Observed in the main peak Of the 31pNMR spectrum that shifts from -22.3 to -19.1 ppm. Such a shift could also arise from some modification of the hydrogen-bond network. The infrared 'Pectra Of Powders Precipitated from aqueous ZrOC12 do not change 'POn ageing*They remain similar to that of Fig. 3(a)even after 1 week at 60 "C. Thermal Analysis TG curves are shown in Fig. 4. All samples precipitated from ZrOC1, aqueous solutions exhibit a single progressive weight loss up to 600 "C.According to literature such behaviour is typical of amorphous phosphates. Different behaviour is -5 = -10OI 0 200 400 600 800 1000 T/"C Fig. 4 Thermogravimetric analysis under ambient oxygen of zir- conium phosphate powders precipitated from: A, Zr(OPr"),; B, ZrOC1, after thermal treatment for different times (a)0, (b) 1 day, (c) 8 days, (d) 4h, at 60 "C observed with powders precipitated from alkoxides. Two weight losses are clearly visible even after a reflux of 4 h only. This is typical of the thermal decomposition of crystalline a-Zr(HP04),*H20. The first step at ca. 150 "C corresponds to the departure of intercalated water molecules, whereas the second one at ca. 550 "C corresponds to the condensation of phosphate groups into pyrophosphates as follows: Zr(HP04), *H20 -+ Zr(HP04), +H20 + ZrP207+H20 The total weight loss gives the amount of water in the precipitate.It appears to be larger for amorphous samples. This must be related to the larger surface area of these samples which are known to exhibit better exchange capacities.2 Electron Microscopy Electron micrographs of crystalline a-Zr(HPO& H20 pow-ders (Fig. 5) illustrate the effect of the thermal treatment required to obtain crystalline phases. Well crystallized samples are obtained from zirconium propoxide precursors after heat- ing the precipitate for 8 days at 60 "C. A longer thermal treatment is required to obtain the same result from aqueous solutions of ZrOC1, (t=1 week, T= 95 "C).Fig. 5 shows that crystallites are significantly smaller in the first case. Faster exchange reactions and larger capacities are therefore expected with phosphates precipitated from alkoxide precursors. Discussion Molecular Structure of the Precursors Zirconium alkoxides usually exhibit oligomeric structures via bridging alkoxide groups. Solvation by alcohol molecules is also observed in order to expand the co-ordination state of zirconium. The molecular structure of the precursor then depends on parameters such as the steric hindrance of the Fig. 5 Transmission electron micrographs of zirconium phosphate particles precipitated from: (a) Zr(OPr), and heated at 60 "C for 8 days in propanol; (b) ZrOC1, and heated at 95 "C for 8 days in water alkoxy ligand, the nature of the solvent and, of course, the concentration.According to the literature, dimers or trimers should be formed mainly when zirconium n-propoxide is dissolved in propan- l-ol. Zirconium atoms are hexaco-ordi- anted in these oligomers.8 ZrIV ions are known to form tetrameric species in aqueous solutions at low pH, [Zr4(OH)8(H20)16]8+. Zirconium atoms are co-ordinated by eight ligands, four bridging OH groups and four solvating water molecule^.^ Aqueous molecular precursors are thus more condensed and zirconium exhibits a higher co-ordination. They should therefore be less reactive than metal alkoxides. Hydrolysis and Complexation Zirconium precursors are very prone to nucleophilic reactions, and therefore may react with the nucleophilic species present in the solution, namely water molecules and phosphate groups.Hydrolysis and phosphatisation mainly depend on the positive charge of the zirconium atom, the nucleophilic power of the entering species and the ability of a protonated group to be released. (HPO,)' -groups are obviously better nucleophiles than water molecules so that in both cases, zirconium precur- sors should react with phosphoric acid rather than with water. The possibility of phosphatisation occurring prior to hydroly- sis was investigated in the case of titanium phosphates by dissolving anhydrous H3P04 (solid) in propan- l-ol. No esteri- fication was observed even after 1 week as evidenced by liquid 31PNMR. This anhydrous phosphoric acid solution reacts readily with titanium propoxide giving a precipitate.The 31P NMR spectrum of this precipitate is just the same as that of the precipitate obtained by adding an aqueous solution of H3P04 (85%).lo Chemical analysis on this precipitate dried under vacuum indicated the presence of only 0.2 of a carbon atom per titanium atom and a ratio P:Ti of 2.0, showing that alkoxy groups are removed by phosphate groups without hydrolysis. The complexing power of H3P04 towards alkoxides is greater than for aqueous precursors. This mainly arises from the ability of alkoxy groups to be protonated and released in the solution as follows: -Zr-OPr +H-OPOa- +[-Zr-0PO3l2- +ROH which is easier than -Zr-OH+H-OPO~-+[-Zr-OP03]2- +H,O The complexing phosphate group still exhibits other P-OH acidities.It can react with other zirconium precursors leading to the formation of Zr-0-P-0-Zr bridges until J. MATER. CHEM., 1991, VOL. I three P-OH have reacted. A solid network is then built in which phosphate groups are bonded to three different zir- conium atoms. Such a reaction is not so easy with aqueous solutions in which zirconium precursors are already hydrolysed giving rise to tetrameric hydroxylated species. Protonation of bridging OH groups by phosphoric acid is more difficult. Therefore, heating is required to favour this reaction in order to build a zirconium phosphate network. Alkoxide precursors react faster with phosphoric acid, and precipitates of smaller grain size are obtained at lower tem- peratures.Moreover, zirconium alkoxides would react with a wide range of nucleophilic species such as carboxylic acids or fi-diketones." It should therefore be possible to design these molecular precursors in order to tailor their functionality and chemical reactivity. Such molecular engineering is already currently performed in the sol-gel synthesis of glasses and ceramics uia chemical modification of metal alkoxides. Conclusions Alkoxide precursors appear to give better results than aqueous solutions of ZrOC1,. Crystallization of m-Zr(HP04), H,O is obtained faster and at lower temperatures. IR absorption and 31 P NMR experiments suggest that the phosphate groups are similar in all amorphous precipitates.This seems reasonable as phosphoric acid is used as a precursor in both cases. The main differences should then arise from the reactivity of zirconium precursors towards water (hydrolysis) and phos- phoric acid (complexation). References 1 A. Clearfield, in Inorganic Exchange Materials, CRC Press, Boca Raton, 1981, and references therein. 2 A. Clearfield, A. Oskarsson and C. Oskarsson, Zon Exch. Membr., 1972, 1, 9. 3 A. Ahrland and J. Albertson, Acta Chem. Scand., 1969, 23, 1446. 4 J. Livage, M. Henry and C. Sanchez, N. J. Chem., 1990, 14, 513. 5 F. Taulelle, C. Sanchez, J. Livage, A. Lachgard and Y. Piffard, J. Phys. Chem. Solids, 1988, 49, 299. 6 J. H. Letcher and J. R. Van Wazer, J. Chem. Phys., 1966,44,815. 7 S. E. Horsley, D. V. Nowell and D. T. Stewart, Spectrochim. Acta, Part A, 1974,30, 535. 8 D. C. Bradley, Coord. Chem. Rev., 1967, 2, 299. 9 G. M. Muha and P. A. Vaughan, J. Chem. Phys., 1960, 33, 194. 10 C. Schmutz, E. Basset, P. Barboux and J. Livage, unpublished results. 11 C. Sanchez, J. Livage, M. Henry and F. Babonneau, J. Non-Cryst. Solids, 1988, 100, 65. Paper 1/01503F; Received 28th March, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100681

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4),685-689 Reorientational Motions of Hydrogenic Species in 12- Tungstophosphoric Acid 14-Hydrate: A Neutron Scattering Studyt Robert C. T. Slade,* Gillian P. Hall, Helen A, Pressman and Ian M. Thompson Department of Chemistry, University of Exeter, Exeter EX4 4QD, UK Variable-temperature incoherent quasielectric neutron scattering (QENS) measurements have been used to investigate motions of hydrogenic species in 12-tungstophosphoric acid 14-hydrate (H3PW120,,* 14H20). Reorien- tational motions are classifiable as those of H20 (free and coordinated to hydrated protons) and H,O+ [free and in non-centrosymmetric H+(H20), units]. Scattering spectra are satisfactorily modelled assuming quasielastic broadening to arise from a three-fold reorientation of H,O+ about an ionic C, axis with a (model independent) €,= 19+ 1 kJ mol-'.Slower reorientation of H20 and H self-diffusion would not give discernible broadenings on the instrument used. Keywords: 12-Tungstophosphoric acid 16hydrate; Quasielastic neutron scattering; H30+ Reorientation Hydrates of the heteropolyacid 12-tungstophosphoric acid (TPA, H3PW12040) provide a range of related structures and Hf/H20/H30f environments. Heteropolyacids have the highest protonic conductivities reported for inorganic mater- ials at ambient temperat~re'~~ and are potentially important in a range of devices including H2/02 fuel cells4 and electro- chromic displays. The stable TPA hydrate is a function of temperature and relative h~midity;~ TPA 6H20, TPA.14H20, TPA.21H20 and TPA*29H20 are all known single phases. The dominant structural feature in these hydrates is the a-Keggin type [PW,20,0]3- anion of overall tetrahedral symmetry,6 the acid protons being associated with a permeating Hf(H20), network. TPA. 14H20 has a triclinic unit cell.7 Structural studies have been made of the related triclinic (Pi) structure of H3PMo12040~(13-14)H20.8In that case the anion is of the p-Keggin type with reduced pseudosymmetry (C3J. A range of 'water oxygen' environments was observed (H atoms not being detectable by X-ray techniques) and the presence of H20, H30+, H50z (and possiblyH,O,+) inferred. At Exeter a systematic study of ion-molecule dynamics of hydrogenic species in TPA hydrates is in progress, probing both bulk (protonic conductivity) and atomic-level (reorien- tational, diffusive) phenomena.In the case of TPA*6H20 (correctly formulated as [H50~]3[PW120~;]) at the atomic level, we have reported (i) inelastic neutron scattering (IINS) vibrational spectra and normal coordinate analyses for H502f ion9*'O and (ii) a quasielastic neutron scattering (QENS) study of internal reorientation in the H,OZ ion." For TPA 14H20 we have reported the separation of contributions to the temperature dependences of 'H NMR relaxation times into those arising from diffusive and reorientational processes, the latter having been detected in preliminary variable tem- perature QENS st~dies.~ We now report investigation by neutron scattering techniques of reorientational processes in TPA.14H20. Experimental Sample Preparation 12-Tungstophosphoric acid 14-hydrate (TPA 14H20) was prepared via hot filtration of TPA -xH20 (Ventron) dissolved t Neutron scattering experiments carried out at the Institut Laue- Langevin (Grenoble, France) and at the Rutherford Appleton Labora- tory (Oxfordshire, UK). in a minimum of deionised water. The solution was then heated until the first signs of crystallisation were apparent and then allowed to cool with continuous stirring to form a damp paste. This was then equilibrated over 47% (by mass) aqueous sulphuric acid (relative humidity 45%) for 48 h. The powder X-ray diffraction pattern (Cu-Kcr radiation, Philips diffractometer) was fully indexed (0<28/"<25) in terms of a triclinic unit cell [a= 14.38(4)A, b = 14.46(8)A, c= 13.97(4)A, a = 112.07",p= 110.85",y =61.93"].Thermogravimetric analy- sis (Stanton-Redcroft STA-780, flowing air) confirmed the formula TPA*(14+0.5)H20. IINS Spectrum This spectrum (Fig. 1) was recorded using the spectrometer TFXA at the ISIS pulsed neutron source (Rutherford Appleton Laboratory). The sample was contained in a rectangular cross- section aluminium slab can (window thickness 0.1 mm) and maintained at T <20 K using a closed-cycle refrigerator. The energy-transfer resolution of TFXA is 2-3%. QENS Spectra Samples for QENS studies were mounted in circular cross- section aluminium slab cans (window thickness 0.1 mm, sealed with indium gaskets) to give <lo% scattering of the incident beam.Spectra were recorded on the focussing time-of-flight spectrometer IN6 at the Institut Laue-Langevin (ILL). 1 I I 11 1 0 10 20 30 10 50 60 70 80 90 100 energy transfer/ rneV Fig. 1 The incoherent inelastic neutron scattering (IINS) spectrum of 12-tungstophosphoric acid 14-hydrate at Tc20 K Measurements were made in the range 230 < T/K <300 (con- trolled using a standard ILL cryostat, the upper limit chosen to avoid sample dehydration) using an incident neutron wavelength A. of 5.9 A, elastic energy resolution (FWHM) AEo of 70peV and an elastic scattering vector magnitude range 0.25 <Qe,/k <1.75 (at scattering angle 8, Qel= 4.n sin 8/lo).The sample was inclined at 135" to the incident beam.Data acquisition times were typically 2 h. The exper- imental Qel-dependent resolution function was determined using a similarly mounted vanadium sheet sample and empty- can scattering was also determined (both at 300 K). Qel values corresponding to diffraction peaks were known from X-ray diffraction and confirmed using the local program CSUM (following elastic peak heights as a function of Qel). Spectra at these values were removed from further data analysis. Sample spectra were corrected (after subtraction of back- ground and empty-can scattering) for absorption and slab geometry, normalised by comparison to vanadium spectra and then converted to the symmetrised scattering law S(Q, w) form (all steps using standard ILL procedures).Results Vibrational Spectra These spectra were recorded to yield any further information concerning H +(H20), (hydrated protons) present. The infra- red spectrum is dominated by modes for H20 and heteropoly- anions present, these obscuring any information on hydrated protonic species. In the IINS spectrum (Fig. 1) only three bands were discerned (the experimental range was 50-5000 cm-I), these being at ca. 100, 160 and 330 cm-'. These features may arise from H20 molecules in an ice-like state, IINS and IR spectra of ice and sorbed water having features in this Information on hydrated protonic species such as has been obtained for TPA*6H209-12 and HUP (HU02P04*4H20)15is not available in this case, where there is a disordered hydrogen-bonded network and nearly all H atoms will be present in discernible H20 molecules (coordinat- ing H+ and otherwise).Quasielastic Scattering (IN6) Spectra were initially fitted individually to a simple analytical form, consisting of a simple scattering law S(Q, a)=Bo(QP(w)+F(Qy0) (1) convoluted with the instrumental resolution function. The quasielastic component F(Q, w) was taken to be adequately represented by a single Lorentzian (L). The empirical elastic incoherent structure factor [EISF(Q)] is the ratio of the elastic to the total (elastic +quasielastic) intensity in the incoherent scattering spectrum EISF(Q) =Bo(QNBo(Q)+JF(Q, w)dwl- =Bo(Q)for normalised S(Q, w) (2) and is a measure of the time-averaged spatial distribution of the proton (incoherent scattering being dominated by the 'H present), while the time-dependent proton position is in the quasielastic term F(Q, w).Spectra at T<270 K were indistinguishable from the instru- mental resolution function (no discernible quasielastic broad- ening). At higher temperatures the half-width for the Lorentzian (quasielastic) component was found to be Qel-independent at each temperature, indicating that rotation/ reorientation of hydrogenic species is being detected. Empiri- cal EISFs are shown in Fig. 2 as a function of temperature, along with the predicted variations for various dynamical J. MATER. CHEM., 1991, VOL. 1 models (see below). It is expected that EISF+l as Qel+O.The observed small deviations from this behaviour arise from unavoidable incomplete removal of multiple scattering effects in data reduction. A temperature dependence of the EISF is apparent at the highest temperatures and could arise in two ways: (1) the broadenings at the lowest T values are narrow and difficult to determine accurately, (2) a change in the motion@) detected may occur (see below). Discussion Protonic Species and Reorientational Motions Protonic species in TPA. 14H20 include H20 and hydrated protons H+(H20), (one or more of H30+,H50;, H703f; see above). In the case of TPA*6H20 (all H in centrosymmetric H5O;), reorientations of 'terminal waters' were characterised by QENS studies [residence time, r,,,(300 K)=2 x 10-'os].In the case of the related protonic conductor HUP (HU02 Po4*4H2O), QENS data were interpreted in terms of an H30+ reorientation occurring more rapidly [z,,,(303 K) = 4 x 10-l2 s] than H20 reorientations [zreS(303K)= lo-'' s, comparable to that in TPA*6H20].'6 That observation was explained in terms of H30+ reorientation being possible without changes in H-bond distribution, while H20 re-orientations are likely to be coupled. consideration of those results and formulation of TPA*14H20 as [H30+]3[PW12040]3-1 1H20 suggests that: (i) motions described as H20 reorientations may be monitored for recog- nisable H20 molecules [both 'free' and coordinated to acid protons i.e. for H20 and 'terminal waters' in H+(H20),, where n >I], (ii) motions described as H30+ reorientations may be monitored for recognisable H30+ ions ('free', in non- centrosymmetric H50; and in more hydrated groupings).The H-bonded network itself will prevent concerted reorien- tation of larger groupings. The geometries of protonic species present are not known. In order to generate predicted EISFs for various possible motions, it is therefore necessary to choose appropriate bond lengths and angles (EISFs are insensitive to small variations in these parameters). For H20 a bond length of 0.951 A and a bond angle of 118.7' (as found in TPA*6H20 and typical of crystal hydrate^'^) were taken. For H30+ examination of the literature18-20 and assumption of C3" symmetry led to the choice of 1.01 8, and 118'.While possible motions are likely to be classifiable as characteristic of H20 or H30+ (see above), it is possible that within each class crystallographically inequivalent species will have differing residence times zres (and reorientational activation energies and prefactors). Reorientational Models A simple approach to modelling reorientational dynamics in the H-bonded region (following from previous work on HUP16) is to consider separate H20 and H30+ populations and all H atoms within a given population to be dynamically equivalent (or very nearly so). Theoretical EISFs can then be calculated for motions of each population, assuming the other to be reorientating more slowly (contributing only an 'elastic' component to the spectra, no corresponding quasielastic broadening being discernible) and hence describable as a 'static fraction' of the H present.Reorientations of H20 and H30+ can be discussed in terms of jumping of H atoms between equivalent sites on a circle (following Barnes21) or on the surface of a sphere (isotropic rotational diffusion, following Sears22). For a population reorientating about a single axis (Barnes model) the scattering law is then in the form of eqn. (1) (convoluted with the instrumental resolution J. MATER. CHEM., 1991, VOL. 1 0.6-LL v,W 0.4-0.21 ~~ I,,,, QeIlA-' Oa2I to.21 I I I 1 0.00 0.50 1.00 1.50 2.00 2.50 0.00 0.50 1.00 1.50 2.00 2.50 Qe,/A-' QdlA-' Fig. 2 Comparison of empirical Q,,-dependent elastic incoherent structure factors (EISFs) for 12-tungstophosphoric acid 14-hydrate with the predictions of various reorientational models involving hydrogenic species present (see text): at (a)270, (b) 280, (c)290 K, (d) 300 K.Error bars for empirical points are < the diameter of the symbols (0)used function) with where n Bn(Qa)=N-' j0[2Qa sin (np/N)] cos (2nnplN) (4) p= 1 and jo(x)=(sin x)/x for a powder sample, a is the radius (of gyration) of the circle, N is the number of sites and zn= z1 sin2(n/N)/sin2(nn/N).z1is the half-width at half maximum (HWHM) in angular frequency for the first Lorentzian and is related to the mean residence time on a site z,,, by zre,=z'[l -cos(2n/N)] (5) In the case of observation of distinct reorientating and 'static' populations, the predicted EISF(Q) for QENS spectra is simply related to EISFrof(Q) appropriate to the dynamic population [calculated via eqn. (1) and (3)] by EISF(Q)=[Patic +Pro']+Pr0'EISFro'(Q)]/[PStatiC (6) where Paticand Pro'are the (relative) magnitudes of the static and rotating H populations.In calculating theoretical EISFs the following motions were considered. (i) Reorientation of H30+ (H20 Molecules taken as Static) Model A: Three-fold reorientation of H30+ ions about the ionic C3axis (N=6, a= 1.00 A). Model B: Six-fold reorien- tation of H30+ ions about the ionic C3 axis (N=6, a= 1.00 A). This allows for a possible higher order axis at the H30+ site. Model C: Rotational diffusion of H30+ ions about the ionic C3axis (N =co,a = 1.OO A).Model D:Isotropic rotational diffusion of H on a sphere (radius 1.00 A) centred on the 0 atom. Such descriptions correspond to nine of the H atoms in the chemical formula participating in reorien- tation, with 22 H atoms (71% of those present) being 'static'. (ii) Reorientation ofH20 (H30+Ions taken as Static) Model E: Two-fold reorientation of H20 molecules about the molecular C2 axis (N =2, a =0.818 A). Model F: Four-fold reorientation of H20 molecules about the molecular C2 axis (N =4, a=0.818 A). This allows for a possible higher order axis at the H20 site. Model G: Rotational diffusion of H20 molecules about the molecular C2 axis (N =00, a =0.818 A. Model H: Isotropic rotational diffusion of H on a sphere (radius 0.951 A) centred on the 0 atom.Such descriptions correspond to 22 of the H atoms in the chemical formula participating in reorientation, with nine H atoms (29% of those present) being 'static'. EISFs calculated for these models are shown in Fig. 2. Over the experimental Qel range, the predictions of H30+ models 688 A-C are indistinguishable and differ little from model D (H30+ isotropic rotational diffusion). The predictions of H20 models F and G are likewise indistinguishable. Agreement between empirical and theoretical EISFs is best for the naive reorientational models involving a population of dynamically equivalent H30+ ions (models A-D). The possible temperature dependence of the empirical data could then be assigned to dynamic inequivalences within that popu- lation.The separation of populations is simplistic. The pos- sibility that some of the H20 molecules can rotate more freely than others (with H30f as a static species) and hence that a higher static fraction should be included in models E-H (leading to closer agreement with experimental EISFs) cannot be ruled out. Interpretation of the data in terms of observation of the effects of H30+ reorientation is, however, in agreement with earlier studies of TPA*6H2O1' and HUP16 in which H20 reorientations [zre,(3O0K) z10-lo s] were too slow to produce quasielastic broadenings of the magnitude observed in this study. Modelling the Scattering Law The '(Q,O) data were fitted to the form corresponding to model A (three-fold reorientation of H30 + ion).The hydrogen-bonded network discourages further con- sideration of models involving rotational diffusion (uniaxial or isotropic) and there are no grounds for preferring model B (six-fold reorientation), the predictions of which are very similar in the experimental Qel range. Spectra were initially fitted individually as a function of Qel to yield the temperature dependent HWHMs of the first Lorentzian in the Barnes model [eqn. (3)-(5) with N= 31 and the z,,, values given in / I I 10 i 0a 7 0 0-7 E/meV # 1 1 1 I 1 J. MATER. CHEM., 1991, VOL. 1 Table 1. Fig. 3 presents final fits of S(Q,o)as a function of Qe, and temperature (HWHM now fixed to the mean value at each temperature), which appear satisfactory at all tempera- tures and Qel values.Naively assuming an Arrhenius temperature dependence for qes,it follows that the pre-exponential factor z,OS= (3.0& 0.2) x 10-l2 s and the (model-independent) activation energy E,= 19+1 kJ mol-'. Relationship to Previous (IN5) Data In the spectra reported previously (obtained using instrument IN5 at ILL), quasielastic broadenings were discerned only at 280 and 290 K.7 The Qel-dependent EISFs were compatible with those we now report (from IN6 data), but the poorer counting statistics of IN5 lead to considerably large errors and more scatter in the data. Refitting of individual IN5 spectra to the theoretical form used for the IN6 data (above) led to large uncertainties in HWHM values at each tempera- ture.IN5 spectra (summed in groups of four for each detector angle to improve counting statistics) were therefore remodelled Table 1 Reorientational parameters for H,Of reorientation in 12- tungstophosphoric acid 14-hydrate T/K HWHM/peV" Tres/lo-lls 270 16+4 6.17 f0.28 280 26k4 3.75 k0.45 290 47+4 2.10 k0.45 300 83k2 1.19f0.03 aFor the first Lorentzian in the Barnes modelz1 (see text). 1 f II\. I 1 0 I 0-7 I 0 0.7 ElmeV I \ 0 0-7 0 J. MATER. CHEM., 1991, VOL. 1 (as a function of temperature and Qel)assuming model A and fixing the HWHM to the values predicted from IN6 data analysis (above). The consequent fits were similar in quality to those reported previ~usly.~ The poor statistics characteristic of the IN5 spectra combined with the small broadenings observed prevented reliable modelling with IN5 data alone.Other Motions While conductivity studies support conduction via crystallite surfaces as the most rapid H+ conduction pathway in a pelletised ample,^ it is evident from NMR studies that self- diffusion of H occurs within the crystallites3 and the H20 present will also be capable of reorientational motions. Direct measurement by pulsed field gradient (PFG) NMR of the H self-diffusion coefficient gave D (300 K)zl x1OP6 cm2 s-'.~ At low Qel values the quasielastic broadening (HWHM) due to self-diffusion r(Q)= DQz1.23It follows that the correspond- ing maximum quasielastic broadening (at Qel= 1.75A-') is < 1 peV (calculated value 3 x Hz =7 x lop8eV) and is too small to discern with the instrumental resolutions used.As discussed above, broadenings due to slow H20 reorien-tations are also too small to detect at the resolutions used. The above considerations could suggest further measure- ments on instruments of higher resolution such as the back- scattering spectrometers IN10 and IN13 at the ILL. The shorter wavelengths then used and the low (triclinic) symmetry of the unit cell preclude such studies, contamination of spectra by coherent scattering (diffraction) occurring in all detectors. It has been possible to correct data for such prevalent Bragg ~cattering,~~but only with prior assumption of a particular reorientational model.NMR studies3v7 detect both H self-diffusion (by 'H PFG NMR and high-temperature variations in 'H relaxation times TI and T2)and a reorientational contribution (deconvoluted as a lower temperature minimum in Tl). The 'reorientational Tl minimum' is likely to be the sum of separate minima, one arising from H20 reorientations and another (at lower tem- perature) arising from H30+ reorientation. The deduced E, (15fl kJ mol-') and 7: (1 x s) are therefore not directly comparable to values obtained in this study. Conclusions The proton-conducting solid electrolyte 12-tungstophosphoric acid 14-hydrate (TPA. 14H20) contains a range of protonic species [H,O and H+(H20),]. Vibrational spectra do not allow further characterisation of hydrated protons present.Reorientational motions can be classified as those of H20 (free and coordinated to hydrated protons) and H30+ [free and in non-centrosymmetric Hf(H20), units]. Incoherent QENS spectra of H30+ ions can be satisfac- torily (if naively) modelled assuming three-fold reorientation H30+ ions about the ionic C3 axis with a (model-independent) activation barrier E, = 19f1 kJ mol -'. Quasielastic broaden- ings that would arise from a slower reorientation of H20 and from H self-diffusion (both evident in NMR relaxation stud- ie~~.~)are too small to be discerned with the instrumentation used. This interpretation is in line with previous studies of hydrated proton-conducting solid electrolytes,"~'s but the possibility that a fraction of the H20 present rotates more freely than other hydrogenic species present (with the quasi- elastic broadenings observed then arising from that motion) cannot be ruled out.We thank the Institut Laue-Langevin for access to the spec- trometers IN5 and IN6 and the ISIS source (Rutherford Appleton Laboratory) for access to the spectrometer TFXA. We thank SERC for grants in support of the Exeter neutron scattering programme and studentships for G.P.H., H.A.P. and I.M.T. We thank Drs. G.J. Kearley, C. Poinsignon, J.Tomkinson and R.C. Ward for practical assistance and helpful discussions. References 0. Nakamura, T. Kodama, I. Ogino and Y. Mikaya, Chem. Lett., 1980, 1, 231. A. Hardwick, P.G. Dickens and R. C. T. Slade, Solid State Zonics, 1984, 13, 345. R. C. T. Slade, J. Barker, H. A. Pressman and J. H. Strange, Solid State Ionics, 1988, 28-30, 594. 0. Nakamura, I. Ogino and M. Adachi, US Pat., US 4554224 A, 1985. 0.Nakamura, I. Ogino and T. Kodama, Solid State Zonics, 1981, 3-4, 341. M. T. Pope, Heteropoly and Zsopoly Oxometalates, Inorganic Chemistry Concepts 8, Springer-Verlag, Berlin, 1985, p. 26. R. C. T. Slade, I. M. Thompson, R. C. Ward and C. Poinsignon, J. Chem. Soc., Chem. Commun, 1987, 726. H. DAmour and R. Allmann, 2. Kristallogr., Kristallgeom., Kristallphys., Kristallchem., 1976, 143S, 1. G. J. Kearley, H. A. Pressman and R. C. T. Slade, J. Chem. Soc., Chem. Commun., 1988, 1801. G. J. Kearley, R. P. White, C. Forano and R. C. T. Slade, Spectro-chim. Acta, Part A, 1990,46, 419. H. A. Pressman and R. C. T. Slade, Chem. Phys. Lett., 1988, 151, 354. P. G. Hall, A. Pidduck and C. J. Wright, J. Colloid Interface Sci., 1981, 79, 339. M. Marchi, J. S. Tse and M. L. Klein, J. Chem. Phys., 1986, 85, 5. J.C. Li, D.K. Ross, L. Howe, P.G. Hall and J.Tomkinson, Physica B, 1989, 156-157, 376. G. J. Kearley, A. N. Fitch and B. E. F. Fender, J. Mol. Struct., 1984, 25, 229. C. Poinsignon, A. N. Fitch and B. E. F. Fender, Solid State Zonics, 1983,8/9, 1049. Z. M. El Saffar, J. Chem. Phys., 1966,45,4643. 18 M. R. Spirlet and W. R. Busing, Acta Crystallogr., Sect. B, 1978, 34, 907. 19 D. E. O'Reilly, E. M. Peterson and J. M. Williams, J. Chem. Phys., 1973, 58, 1593. 20 R. Savoie and P. A. Giguere, J. Chem. Phys., 1964,41, 2698. 21 J. 0. Barnes, J. Chem. Phys., 1973,58, 5193. 22 V. F. Sears, Can. J. Phys., 1967, 45, 2037. 23 M. Bee, Quasielastic Neutron Scattering. Principles and Appli- cations in Solid State Chemistry, Biology and Materials Science, Adam Hilger, Bristol, 1988, ch. 5. 24 R. M. Richardson and J. Howard, Chem. Phys., 1984,86, 235. Paper 1/016221; Received 8th April, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100685

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 691-697 69 I Synthesis and Characterisation of Crystal Structure of the One-dimensional Salt [(q-C,Me,)Ru(p,q-C,Me,)Ru(q-C,Me,)l +[TCNE]-Dermot O'Hare,*a Jillian Brookesa and David J. Watkinb a Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, UK Chemical Crystallography Laboratory, 9 Parks Road, Oxford OX1 3PQ UK Charge-transfer salts [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)]+ [anion]-[Cp*=C,Me,; anion =tetracyanoethylene (TCNE, 2), 7,7,8,8-Tetracyano-pquinodimethane (TCNQ, 3), or C3[C(CN)J3(4)] prepared from [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)+ OTf-(1) (OTf-=trifluoromethanesulphonate) and M+[anion]- (M+ = Li+, NBuZ) salts are described. Single- crystal X-ray studies show that 2 crystallises in the trigonal system, in the non-centrosymmetric space group R3m with a=b= 14.432(3)A, c=14.432(3) A, a=B=90", y=120° with hexagonal indexing, V=2603.3 A3, pc= 1.41 g ~m-~, Z=3, R=0.0634 and Rw=0.0715.The unit cell in 2 comprises alternating cations and anions aligned parallel to the crystallographic c axis. The cation has a multidecker structure with parallel Cp* rings and Ru-Cp~,,,,,,,,, distances of 1.826(7), 1.89(8), 1.826(7), and 1.828(9)A. The diamagnetic [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)]+ cation and the S=1/2 [TCNEI-radical anion lie on the crystallographic three-fold symmetry axis and consequently are highly disordered. The disordered anions possess local D2,,symmetry with C-CN, CEN distances of 1.39(3)and 1.10(3)A, respectively. For 2 and 3 the magnetic susceptibility obeys the Curie-Weiss expression x= C/(T-0),with pefland O values of 1.73 pe and 0.07"for 2 and 1.45 pBand -3.7" for 3.Keywords: Charge-transfer salts; Metallocene; Crystal structure; Magnetism; Organometallic complex One-dimensional ( 1-D) charge-transfer complexes have been shown frequently to exhibit unusual optical and electrical properties. In particular, several organometallic charge- 9' transfer complexes containing alternating donor/acceptor lin- ear chains have been reported to exhibit co-operative magnetic properties3 For example, metarnagnetic behaviour (i.e. field-dependent switching from an antiferromagnetic ground state to a high moment state) has been observed for the 1-D phase +[Fe(Cp*),] [TCNQ] -.4 However, the tetracyanoethylenide and hexacyanobutadienide salts of Fe(Cp*), have been shown to exhibit ferromagnetic behaviour.' The former charge-trans- fer complex possesses a spontaneous magnetic moment at zero applied magnetic field.In the future, the design and synthesis of low-dimensional molecular organic, inorganic and organometallic solids with desirable electronic and/or magnetic properties will require an understanding of the factors that affect the formation of structural phases, coupled with elucidation of the structure- function relationships in these materials. Approaches to controlling solid-state architecture have been illustrated by the covalently linked metallophthalocyanine rings in polymeric-Si(Pc)O,-, (Pc=phthalocyanine), which upon doping exhibits metallic conductivity due to n-overlap of the Pc rings.6 Recently, Fagan et elegantly demon- ~1.~7~ strated the use of polycations based on [Ru( q-Cp*)( q-arene)] + complexes to control molecular architecture.Here, we report results of our investigations of the synthesis, structure and physical characterisation of charge-transfer salts derived from the multidecker 'cylinder-like' monocation +[( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] with the planar organic acceptors [TCNE] -, [TCNQl- and C3[C(CN)2];: Experimental General The reactions were carried out in an inert atmosphere of nitrogen by the use of vacuum line or inert atmosphere dry box. Solvents were rigorously dried under a continuous stream of nitrogen. THF and diethyl ether were refluxed over sodium/ potassium alloy, and DME was refluxed over potassium metal.Dichloromethane was dried by refluxing over P205, and nitromethane and acetonitrile by refluxing over CaH,. Solvents were distilled prior to use and were stored over molecular sieves in flame-dried ampoules under nitrogen. Equipment Infrared spectra were recorded on a Mattison Instruments Polaris Fourier Transform spectrometer as mulls in Nujol between KBr plates. UV-VIS spectra were recorded on a Perkin-Elmer Model 330 spectrophotometer. The samples were made up under nitrogen in CH2C12 or THF using an air-tight cell. Electron paramagnetic resonance spectra were obtained using the X-band of a Bruker ESP-300 spectrometer. The samples were made up under nitrogen and run in 4mm high-purity Spectosil quartz tubes fitted with a Young's Teflon stopcock.The solutions were made up in CH2C12 or THF. The magnetic susceptibility data were collected over the range 2-325 K by using a high-sensitivity computer-interfaced Faraday balance, which is described in detail elsewhere.8 The susceptibilities were corrected for the intrinsic diamagnetism of the sample container and the diamagnetism of the electronic cores of the constituent atoms (zdia=410 x lop6 emu mol-' for 2 and 448 xIO-~emu mol-' for 3). Elemental microanalyses were performed by the Analytical Services of the Inorganic Chemistry Laboratory. Synthesis of [Cp*RuCI2lx The compound [Cp*RuC121x was prepared by scaling-up the following literature procedure of Tilley et a1.' RuC1, *3H20 (20.00g) was dissolved in 400cm3 of CH30H and filtered into a flask containing 30 cm Cp*H; the mixture was refluxed for 3 h under N2.The volume was reduced to 350 cm3 under reduced pressure, the crystalline dark precipitate was isolated by filtration, washed with methanol and hexane, and dried under high vacuum, yield 21.1 g (91%). Typically 5-10% of Ru(Cp*), was also isolated as a side-product of the reaction from the hexane washings. Synthesis of [Cp*Ru(p,-Cl)], A 300cm3 round-bottomed flask was charged with log (66.0 mmol) of [Cp*RuC12], and 100 cm3 THF. Lithium triethylborohydride (33 cm3; 1 mol dm-3) in THF (33.0 mmol) was added with stirring. The reaction mixture turned a dark blue-green initially during the addition, and gas evolution was observed (CARE).After 45 min the crystalline orange precipitate which formed was isolated by filtration and rinsed twice with small amounts (ca.5 cm3) of THF. The orange precipitate was then dried in uacuo to yield 7.1 g of [Cp* Ru(~ 3-C1)]4 (79 YO). Synthesis of [Cp*Ru(MeCN),] OTf-+ A 300 cm3 round-bottomed flask was charged with [Cp*Ru(p3-C1)I4 (1 5 g, 13.8 mmol) and acetonitrile (100 cm3). The mixture was refluxed for 1 h and then allowed to cool to room temperature. To the stirred mixture was added 14.25 g (55.2 mmol) of silver trifluoromethanesulphonate (Ag+ OTf-) whereupon a white precipitate of AgCl formed. After 1 h of stirring, the solution was filtered, and the solvent was removed under reduced pressure. Diethyl ether (100 cm3) was added to the residue, and the orange-yellow crystalline solid was collected by filtration, washed twice with 20cm3 portions of diethyl ether and dried in uacuo to yield 26.7 g of [cp*R~(MecN)~]+ OTf- (95%).Synthesis of [(Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] +OTf -(1) A small Schlenk tube (ca. 100cm3) was charged with [Ru( q-C,Me,)(MeCN),]OTf (1.42 g, 2.8 mmol), R~(q-c,Me,)~ (1.06 g, 2.85 mmol) and nitromethane (ca. 30 cm3), and the mixture was held at reflux for 11 h. The solvent was evaporated under reduced pressure and the dark-brown resi- due was washed with diethyl ether to remove any unreacted decamethylruthenocene. The residue was dissolved in acetone, and chromatographed on an alumina column made up with light petroleum (b.p.40-60 "C) and eluted with acetone. A yellow-orange band was collected and the solvent was removed in uacuo to give an orange powder. Recrystallisation from ethanol at -20 "C formed 0.53 g of orange-yellow +cry st als of [( q-C, Me ,)Ru(p,q-C ,Me,)Ru( q-C ,Me,)I OTf-(25%). The reaction was sensitive to the length of reflux and 11 h gave the optimum yield. Refluxing for 9 h gave a yield of 21% and 21 h gave a low yield of 12%. After it had been refluxed for several days the product decomposed to give decamethylruthenocene (confirmed by NMR spectroscopy) and a brown-black tarry residue. (Found: C, 49.3; H, 6.2. Calc. for C, 49.2; H, 6.0%); A,,, (CH2C12) 232,284,368 and 408 nm; JH(solvent CD2C12, standard TMS, 300 MHz) 1.55 (s, q-C,Me,) and 2.16 (s, p,q-CSMe5).Preparation of [(q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)] + [TCNEI-(2) A solution of [( q-CSMe,)Ru(p,q-CSMe,)Ru(q-C,Me,)]OTf (0.050 g, 0.066 mmol) in MeCN (ca. 1 cm3) was added drop- J. MATER. CHEM., 1991, VOL. 1 wise to a solution of Li+[TCNE]- (0.009 g, 0.67 mmol) in MeCN (ca. 3 cm3). After slow cooling to -20 "C overnight orange needle-shaped crystals were obtained in a quantitative yield. Orange crystals suitable for X-ray crystal-structure studies were obtained after 2 weeks from a three-compartment H-diffusion cell set-up using [( q-CSMe,)Ru(p,q-CSMe,)Ru(q-C,Me,)]OTf (0.030 g, 0.040 mmol) and Li+[TCNE]-(0.006 g, 0.044 mmol) in THF.(Found: N, 7.6; C, 59.0; H, 6.3. Calc. for Ru~C~~H~~N~: vmax (NujolN, 7.6; C, 59.0; H, 6.1YO); mull) 2181 (C=N), 2142 (C-N)cm-'; A,,, (CH2C12) 231, 282 and 418 nm; EPR, solid-state single isotropic resonance, g= 2.0068 with AHpp=5.0 G at 298 K, solution (THF) nine line multiplet, g= 2.0063, aN=1.61 G. Synthesis of [(q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)] + CTCNQl-(3) To a concentrated solution of [( q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)]OTf (0.030 g, 0.040 mmol) in DME (ca. 6 cm3) was added a solution of "But] [TCNQ] -(0.018 g,+ 0.040 mmol) in DME (ca. 4 cm3). A green precipitate formed immediately which was washed with diethyl ether (2 x 10 cm3) and dried in uacuo. Recrystallisation from THF-diethyl ether (1 : 1) at -20 "C gave large green needles.(Found: N, 6.9; C, 62.2; H, 6.4. Calc. for Ru~C~~H~~N~: N, 6.9; C, 62.1; H, 6.1 %); v,,, (Nujol mull) 2177 (C-N), 2152 (C-N) cm-'. A,,, (THF) 230, 284, 425, 686, 750 and 849 nm; EPR, solid-state single isotropic resonance, g =2.0066, solution (THF) 45 line mul- tiplet observed, g =2.0064, aN= 1.0 G, aH= l .4 G. Preparation of [(q-C,Me,)Ru(p,q-C,Me,)Ru( q-C,Me,)] + cc6(cN)61-(4) Addition of a concentrated solution of [( q-C5Me5)Ru(p,q-C,Me,)Ru( q-C,Me,)]OTf (0.030 g, 0.040 mmol) in DME (ca. 6 cm3) to a concentrated solution of "But] +C,(CN); (0.019 g, 0.040 mmol) in DME (ca. 2 cm3) immediately pro- duced a deep-blue precipitate. The precipitate was washed with diethyl ether and recrystallised from a mixture of CH2C12 and diethyl ether at -80 "C to form blue microcrystals.(Found: N, 9.9; C, 60.3; H, 5.4. Calc. for Ru2C42H45N6: N, 10.05; C, 60.34; H, 5.34%); v,,, (Nujol mull) 2207 (CEN), 2193 (C=N) cm-'; Amax (THF) 232,283,323,410,600,674 nm; EPR solid-state single isotropic resonance, g =2.0059, solution (THF) 13 line multiplet, g=2.0057, ~'~~=0.88G. Crystal-structure Determination Crystals of [( q-C,Me,)Ru(p,q-CSMe,)Ru( q-C,Me,)]+ [TCNEl-were sealed under nitrogen in Lindemann glass capillaries. All calculations were performed on a VAX 11/750 computer in the Chemical Crystallography Laboratory using the Oxford CRYSTALS system" and plotted using the CHEMX package.' Crystal Data. C3,H4,N4Ru2, M =735.92, trigonal, a =b = 14.432(3)A, c= 14.432(3)A, V=2603.3 Pi3 (by least-squares refinement on diffractometer angles of 25 accurately centred reflections), A =0.7 1069 A, space group R3m, 2=3, pc= 1.41 g cm- '.Orange, air-sensitive tablets. Crystal dimensions 0.88 mm x 0.64 mm x 0.32 mm, p(Mo-Kor)= 8.81 cm-', F(000)= 1131. Data Collection and Processing. CAD4 diffractometer, 0-28 mode, scan width = 1.OO +0.35 tan 8, scan speed 1 .O-6.6" min-',graphite-monochromated Mo-Kor radiation; a total of J. MATER. CHEM., 1991, VOL. 1 41 78 reflections were measured in the range (1 .OOo 68<2Y), including those absent due to the R centring in the index ranges -1 <h<17, -17<k<17, -1 <l<17 (more than the minimum requirement due to the initial space-group uncer- tainties).After merging in R3m this yields 585 unique reflec- tions (Sheldrick merging R =0.018 after absorption correction), giving 489 with I >341). This corresponds to a very complete set of data, with 120 out of the 120 possible reflections being measured in Sheldricks 'critical resolution' range of 1.1-1.2 A, with 100 at I>3o(I). Linear and approx. isotropic crystal decays, ca. 2%, corrected during processing; correction for Lorentz and polarisation effects.12 The authors were very surprised by the curious coincidences in the cell parameters. The hexagonal cell as reported with a =b -C-was subjected to intensive investigation. 41 78 reflections were measured when only ca. 600 reflections were in the final asymmetric region of reciprocal space; in addition, selected reflections were remeasured from all their potentially equival- ent positions. Structure Analysis and Refznement.Direct methods (Ru atoms) were followed by normal heavy-atom procedures. The crystal- lographic disorder of the structure resulted in an extremely low ratio of observations to refined parameters. To achieve an acceptable refinement of the structure, 145 non-crystallo- graphic chemical restraint^'^ were included in the least-squares refinement. These restraints took the form of equival- encing the internal bond lengths and angles of each of the Cp* ligands to their arithmetic mean. In addition, some slack chemical restraints were also applied to the [TCNE] -anion. Full-matrix least-squares refinement of 108 independent par- ameters with anisotropic thermal parameters for Ru( l), Ru(2) and the atoms comprising the [TCNEI- anion plus the 145 observations of restraint gave a final agreement R and R, of 0.0634 and 0,0715 and an observation to parameter ratio of 5.9 : I.We also note that, although the crystallographic mirror symmetry reduces the number of unique atoms defining the structure, the carbon atoms of the Cp* rings which lie on the mirror plane [C(l), C(4), C(7), C(lO), C(13), and C(16)] exhibit very large isotropic thermal parameters. However, refinement of the structure in the lower symmetry space group R3 gave a significantly less satisfactory refinement. Hydrogens were placed in calculated positions (C-H =0.95 A) and allowed to ride on their attached C atoms with one, overall refined Uiso[=0.2l(6) A2].Corrections for anomalous dispersion, and isotropic e~tinction'~ were made in the final cycles of refine- ment; a four-term Chebysev weighting scheme15 was applied with coefficients 3.23, 17.04, -1.27, and 4.25. Final residual electron density <0.91 e A-3. Atomic scattering factors and anomalous dispersion coefficients were taken from ref. 16. Results and Discussion The ability of Cp'M+ (Cp'=q-C5HS or q-C5Me,; M=Fe, Ru) moieties to form adducts with aromatic ligands has been known for some time.17 Recently, it has also been reported that these fragments may complex to the cyclopentadienyl ligands of simple metallocenes,18 and so we speculated that this may be a useful reaction to prepare 'cylinder-like' cations.Synthesis of [( q-Cp*)Ru(p,qCp*)Ru( q-Cp*)] [TCNE] (2) The multidecker 'cylinder-like' cation [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] +OTf- (1) can be conveniently prepared in 25% yield by refluxing [Ru( q-Cp*)(MeCN)3]+OTf- (OTf- = trifluoromethanesulphonate) with an equimolar amount of Ru(Cp*), in CH3N02. Addition of a solution of 1 to an equimolar solution of Li+TCNE- in MeCN gave a green solution, which on slow cooling to -20 "Covernight gave orange needle crystals of [( q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)] [TCNE] (2). The orange crystals have been characterised by elemental microanalysis, infrared, UV-VIS, and EPR spectroscopy, magnetic susceptibility measurements, and a single-crystal X-ray structure determination.Crystal-structure determination Crystals suitable for X-ray structure determination were obtained by slow diffusion of solutions of 1and Li+[TCNE]- in THF for 2 weeks. Compound 2 crystallises in the trigonal non-centrosymmetric crystal system with space group R3m. The hexagonal cell as reported has a curious coincidence of the three cell parameters (see Experimental); we can see no way to make use of this extra symmetry they may imply in addition to the evident symmetry. The molecular structure is shown in Fig. 1, and selected bond distances and angles are given in Tables 1 and 2.7 The positional parameters are given in Table 3. The elemental analysis, infrared, and EPR spec- troscopy, and magnetic susceptibility measurements are in agreement with the X-ray analysis. The asymmetric unit consists of one cation and one anion, in which the metal atoms of the [(q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)]+ cation lie on the special positions (0, 0, z) and (0, 0, z').Consequently, both the crystallographic three-fold rotation axis and mirror plane pass through the ruthenium atoms, the ring centroids of the cyclopentadienyl rings, and the plane containing the [TCNE-J- anion. Thus, the three q-C,Me, rings and the [TCNE] -ion exhibit three-fold disorder. The least-squares plane containing the [TCNE] -anion was very poorly resolved; however, we were able to model the observed electron density by using a model consisting of three overlap- ping TCNE moieties as shown in Fig.2. Centrosymmetric t Supplementary data available from the Cambridge Crystallo- graphic Data Centre: see Information for Authors, J. Mater. Chem., 1991, Issue 1. Fig. 1 Molecular structure of 2, showing the atomic labelling scheme. Atoms suffixed by B were generated by the crystallographic symmetry operator (-x+y, y, 2). Atoms suffixed by C were generated by the crystallographic symmetry operator (x, y -x, 2). Atoms suffixed by D were generated by the crystallographic symmetry operator (-Y, X-Y, 4 J. MATER. CHEM., 1991, VOL. I Table 1 Selected intramolecular distances for 2 (R3 and R3m) and space groups containing two-fold axes ~~ (R32) were rejected because they introduced unnecessaryatoms distance/8i atoms distance/A disorder in the TCNE group.The large Uequivof atoms C(7), Ru( 1)-C( 1) 2.2 17(6) C(2)-C(5) 1.56(2) C(1), and C(13), which lie in the mirror plane already reflect Ru(1)-C(2) 2.223(4) C(3)-C(36) 1.450(6) the extensive disorder. Ru( 1)-C(3) 2.233(5) C(3)-C(6) 1.59( 1) In view of the extensive disorder in the structure determi- Ru( 1)- C(7) 2.19q4) C(7)-C(8) 1.432(4) nation and the relatively small number of unique observations Ru( 1)- C( 8) 2.19 l(3) C( 7)- C( 10) 1.58(3) a number of non-crystallographic restraints13 were imposed Ru(1)- C( 9) 2.193(3) C(8)-C(9) 1.433(6) on the internal geometry of the Cp* and TCNE moieties in Ru(2)-C( 1) 2.198(6) C(9)-C(9C) 1.427(7) order to achieve a satisfactory refinement. Consequentially it Ru(2)-C(2) 2.202(4) C(8)-C(11) 1.58(2) Ru(2)-C( 3) 2.208(5) C(9)-C( 12) 1.59(2) would not be appropriate to discuss in detail any of these Ru(2)- C( 13) 2.206(4) C( 13)- C( 14) 1.353(4) dimensions; however, we can conclude that the observed mean Ru(2)-C( 14) 2.208( 3) C( 13)- C(16) 1.57(3) distances and angles are in close agreement with other crystal- Ru(2)- C( 1 5) 2.2 1 O( 3) C( 14)- C( 1 5) 1.353(6) lographically determined structures containing either q-Cp* N( 1)-C(2 1) 1.IO(3) C( 15)-C( 1 5B) 1.349(7) ligands" or [TCNE] -anions.20N(2)-C(20) 1.1 3(4) C( 14)-C( 17) 1.58(2) The X-ray structure confirms the triple-decker structure for N(2)-C(2 1) 1.28(2) C( 15)- C( 18) 1.60(2) C( I)-C(2) 1.45 l(4) C(19)- C(20) 1.37(3) the cation.Other crystallographically characterised multi- C(1)-C(4) 1.56( 3) C(20)- C(2 1) 1.39(3) decker sandwich complexes containing q-C5H, or q-C,Me, C(2)-C(3) 1.453(5) rings include [( q-Cp)Ni(p,q-Cp)Ni( q-Cp)] 'BF, 21 and [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp)] PF6+.18The Ru-C distances+ E.s.d.s are given in parentheses.in 2 range from 2.192(3) to 2.221(4)A and agree well with those found for [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp)] +PF, (2.11-Table 2 Selected intramolecular angles for 2 atoms angle (") atoms angle (") C(4)-C( 1) -C(2) 125.999(7) C( 1 7)- C( 14)-C(13) 125.999(6) c(3)-c(2) -C( 1) 108.000(9) C( 17)-C( 14)-C( 15) 125.999(7) C(5)-C(2)-C(1) 126.00( 1) C( 1 8)-C( 15)-C( 14) 125.998(6) C(5)-C(2)-C(3) 126.00( 1) C( 1 9)-C(20) -N( 2) 179.6(5) C( 6)- C( 3)- C(2) 126.00( 1) C( 2 1)-C( 20) -N(2) 60.00( 4) C(10)-C( 7)- C(8) 125.998(8) C(21)-C(20)-C( 19) 120.00(4) C( 9) -C(8)-C(7) 108.00(1) C( 2 1)-C( 20) -C( 20E) 120.00(7) C(l l)-C(8)-C(7) 126.0q2) N(2)-C(21)-N( 1) 130.0(22) C(1I)-C(8)-C(9) 126.0q2) C(20)-C(2 1)- N( 1) 1794 10) C( 12) -C(9)- C( 8) 126.Oq2) C(20)-C( 2 1)-N(2) 49.6(20) C( 16)- C( 1 3)- C( 14) 125.998(5) C(21)-N(2)-C(20) 70.4(20) C( 1 5)-C( 14)- C( 1 3) 108.002(7) ~ ~~ E.s.d.s are given in parentheses.Table 3 Fractional atomic coordinates, isotropic thermal parameters or equivalent isotropic parametef, and crystallographic site occupancies for 2 atom X Y Z U(equiv.)/U(iso) crystallographic site occupancy 0.0000 0.0000 0.068 l(2) 0.0459 0.1667 0.0000 0.0000 0.3229(2) 0.0504 0.1667 -0.044(2) 0.2 lO(3) 0.6924(4) 0.1456 0.3334 0.1OO(2) 0.200(4) 0.6925(5) 0.4143 0.3334 -0.0978(6) -0.0489(3) 0.1963(4) 0.2( 1) 0.1667 -0.0295(6) 0.0666( 3) 0.1964(3) 0.037(7) 0.3334 0.08 lO(6) 0.0908(3) 0.1966(3) 0.024(4) 0.3334 -0.223(2) -0.1 11( 1) 0.1957(6) 0.1 q3) 0.1667 -0.068 l(7) 0.150( 1) 0.1964(4) 0.08(1) 0.3334 0.184( 1) 0.207( 1) 0.1972(4) 0.032(6) 0.3334 -0.0846(8) -0.0423(4) -0.0648(4) 0.5(3) 0.1667 -0.0176(7) 0.0715(4) -0.0598(3) 0.03(2) 0.3337 0.091 l(7) 0.095 l(4) -0.0519(4) 0.016(5) 0.3337 -0.21 l(2) -0.105(1) -0.0731(6) 0.20(6) 0.I667 -0.0565(8) 0.156( 1) -0.0625(4) 0.09(2) 0.3334 0.194(1) 0.21 l(1) -0.0456(4) 0.044(7) 0.3334 0.045 l(4) 0.0901(8) 0.4544(4) 0.17(6) 0.1667 -0.0626(4) 0.0265( 7) 0.4538(3) 0.033(7) 0.3337 -0.085 l(4) -0.0764(7) 0.4528(3) 0.08(2) 0.3337 0.108( 1) 0.2 1 6( 2) 0.4544(6) 0.09(2) 0.1667 -0.147( 1) 0.0656(8) 0.4539(4) 0.08(2) 0.3337 -0.202(1) -0.180( 1) 0.453 l(4) 0.047(7) 0.3337 0.0000 0.0000 0.6956( 6) 0.1789 0.1667 0.055( 1) 0.1 lO(3) 0.6942(4) 0.23 16 0.5000 -0.00 l(2) 0.166( 3) 0.6929(4) 0.1340 0.3337 U(equiv.)= 1/3[U(ll)+ U(22)+ U(33)].J. MATER. CHEM., 1991, VOL. 1 .. NA N Fig. 2 (a) Observed molecular structure of the TCNE anion, showing the full crystallogaphic disorder. Atoms suffixed by B were generated by one of the crystallographic mirror symmetry operators. Atoms suffixed by C, D, E, or F were generated by one of the crystallographic three-fold symmetry operators. (Note some atoms possess more than one label since they can be generated by several symmetry operators.) (b)The observed electron density can be modelled by three overlap- ping TCNE groups 2.26 A).The pentamethylcyclopentadienylrings (A, B, C) are almost parallel with angles between the normals to the least- squares planes A/B, A/C, and B/C equal to 4.73, 4.61 and 0.4", respectively. The Ru-Ru separation is 3.677(1) A. The distances of Ru(1) and Ru(2) to the ring centroids of the terminal q-C5Me5 rings are 1.826(7) and 1.89(8) A, respect-ively, which are within experimental error equal to the dis- tances of the Ru(1) and Ru(2) to the bridging q-C5Me5 ring of 1.826(7) and 1.828(9) A, respectively. This compares to a mean value of 1.917 A quoted by Orpen et al. for the Ru- Cpgentroid)distance for all crystallographically characterised ruthenium complexes containing Cp* ligands.However, we were particularly interested in determining the three-dimensional arrangement of the cations and anions in the solid state. Selected packing diagrams are shown in Figs. 3, and 4. The solid-state structure consists of 1-D stacks of alternating [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] cations (D') + and [TCNEI- anions (A-) i.e. ... A-*D'*A-*D+*A-.... The 1-D stacks are orientated parallel to the principle three- fold symmetry axis of the trigonal crystal system. Adjacent stacks are out of registry and have an interchain separation of 8.33(2)A (Fig. 3). 3.514Ai kG-A Fig. 3 Packing diagram for 2 viewed perpendicular to the c axis Fig. 4 Packing diagram for 2 viewed along the c axis The 3-D arrangement of the cations and anions is similar to the stacking motif observed for the molecular ferromagnet [Fe( q-Cp*),][TCNE] *MeCN22 which has a 1-D structure with alternating [Fe( q-Cp*),] radical cations and [TCNE] -+ radical anion in a ...D'A-D'A-D'A-... motif. The unit cell of [Fe( q-Cpf)2][TCNE] MeCN contains two pairs of chains; an out-of-registry pair separated by 8.23 A, and a pair of in-registry chains separated by 8.73 A. Infrared Spectroscopy Infrared spectroscopy has proven a useful tool to elucidate the degree of charge transfer for complexes containing polycy- ano electron acceptors.20 The v(C-N) stretching frequencies for a series of charge-transfer salts containing [TCNE]"- anions are given in Table 4.The infrared spectrum of 2 as a Nujol mull exhibits, inter ah, peaks at 2181 and 2142 cm-' assignable to v(C=N) stretches, which strongly indicates that solid 2 contains the [TCNE] -radical monoanion. U V-VIS Spectroscopy The UV-VIS spectrum of a solution of 2 in CH2C1, exhibits the absorbances characteristic of 1 at 282 and 231 nm. In addition, the spectrum contains an absorbance at 418nm with additional fine structure. This absorbance can be assigned to an internal (n)2(n*)' +( n)'( n*)' transition in the [TCNE] -radical anion.,' The spacing of the fine structure (ca. 520 cm-') is consistent with a vibrational transition. The vibration spectrum of the [TCNEI- anion contains an aB transition at 532 cm-' which can be assigned to this mode.EPR Spectroscopy The EPR spectrum of a single crystal of 2 exhibits a single isotropic resonance with a g-value equal to 2.0068. The line Table 4 Infrared vibrational transitions observed for v(C=N) in [TCNE]"- salts compound v(C =N)/cm- ref. TCNE TCNE- 2221, 2259 2144,2183 23 20 TCNE2- 2069,2104 20 (TCNE); - 2159, 2170, 2189 24 CRU2(CP*)31 CTCNEI(2) 2142,2181 this work width at half height (AH,,)=5.0 G at 298 K. The isotropic nature of the signal together with a g-value close to the 'free electron' value is consistent with a signal derived from the [TCNE] -radical anion. The temperature dependence of the integrated signal intensity obeys the Curie law IccC/T expected for magnetically isolated radicals.Solutions of 2 in THF exhibit nine lines EPR spectrum with g-value of 2.0063. The hyperfine splitting (aN)= 1.61 G arises from coupling of the unpaired electron with the four equivalent I4N [I(I4N)= 13 nuclei. Magnetic Susceptibility Measurements Faraday balance magnetic susceptibility measurements in the temperature range 2-300 K indicate that 2 obeys the Curie- Weiss law, 2-'=C/(T-0), with 8 =0.07 "C and an effective moment of 1.71 pB (Fig. 5). The magnitude of the observed paramagnetism indicates that the [TCNE] -S = 1/2 radical anion is the sole contributor to the observed moment. We can therefore conclude that the diamagnetic cations are acting as magnetic insulators preventing co-operative magnetic inter- actions between the unpaired spins on neighbouring anions.Synthesis of [(q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] [TCNQ] (3) Addition of a solution of 1 in dimethoxyethane (DME) to an equimolar solution of [NBuz] +[TCNQ] -in DME instantly gave a green precipitate. The green precipitate was recrystal- lised from THF as green needle-shaped crystals of [(q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] [TCNQ] -(3).It was not poss- +-ible to grow crystals suitable for an X-ray structure determi- nation, although a wide range of common solvents and crystal growing techniques were used. The green needles have been characterised by elemental microanalysis, infrared, UV-VIS, and EPR spectroscopy, and magnetic susceptibility measurements. Infrared Spectroscopy The v(C=N) stretch frequencies for a series of charge-transfer salts containing [TCNQ]"- anions are given in Table 5.The infrared spectrum of 3 as a Nujol mull exhibits, inter alia, peaks at 2178 and 2152 cm-' assignable to v(C=N) stretches, which strongly indicates that the solid 3 contains the [TCNQ] -radical monoanion. 5 1200 E 1000 600 400 200 0 0 50 100 J. MATER. CHEM., 1991, VOL. I Table 5 Infrared vibrational transitions observed for v(C-N) in [TCNQ3" -salts compound v( C=N)/cm -ref. TCNQ 2222, 2226 25 TCNQ-2153, 2179 26 TCNQ2-2105, 2150 26 CCPWzl CTCNQI(3) 2178, 2152 this work EPR Spectroscopy The EPR spectrum of a crystal of 3 exhibits a single isotropic resonance with a g-value equal to 2.0066 and AH,, =20 G at 298 K.The isotropic nature of the signal together with a g-value close to the 'free electron' value is consistent with a signal derived from the [TCNQ] -radical anion. Solutions of 3 in THF exhibit a 45 line EPR spectrum with a g-value of 2.0064. The hyperfine splitting (a") =1.O G and aH = 1.4 G arises from coupling of the unpaired electron with the four equivalent I4N nuclei and four equivalent 'H nuclei. A full simulation of the spectrum has been performed previo~sly.~~ Magnetic Susceptibility Measurements Faraday balance magnetic susceptibility measurements in the temperature range 2-300 K indicate that 3 obeys the Curie- Weiss law, x-'=C/(T-0),with 8= -3.7 "C and an effective moment of 1.46 pB (Fig. 5). The observed paramagnetism indicates that the [TCNQl- S= 1/2 radical anion is the sole contributor to the observed moment.The observed effective magnetic moment is significantly less than expected for one unpaired electron using the spin-only formalism. The origin of this disagreement is unknown in view of the lack of structural characterisation. Synthesis of [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] [C3{ C(CN),),] (4) Addition of a solution of 1 in DME to an equimolar solution of [NBu~]+[C,{C,(CN),),]- 28 also in DME gave an in-stantaneous blue precipitate. The blue precipitate was recrystallised from a mixture of CHzC12 and diethyl ether giving blue microcrystals of [( q-Cp*)Ru(p,q-Cp*)Ru(q-Cp*)][C,{C(CN),),] (4). It was not possible to grow crystals 150 200 250 300 TIK Fig. 5 Plot of inverse molar susceptibility (x-') us.T for 2 (A) and for 3 (B) J. MATER. CHEM., 1991, VOL. 1 suitable for X-ray structure determination despite using a wide range of common solvents and crystal-growth techniques. The blue needles were characterised by elemental microanal- ysis, infrared, UV-VIS and EPR spectroscopy. Infrared Spectroscopy The infrared spectrum of 4 as a Nujol mull exhibits, inter ah, peaks at 2207 and 2194 cm-' assignable to v(C=N) stretches, which agree closely with the v(C=N) stretches +observed for [NBu;] [C,(C,(CN),},] -at 22 10 and 2196 ~m-'.~' EPR Spectroscopy The EPR spectrum of a crystal of 4 exhibits a single isotropic resonance with a g-value equal to 2.0059 and AH,,=20 G at 298 K.The calculated g-value is in close agreement with the value previously reported for the [C,(C,(CN),>,] -radical anion.28 Solutions of 4 in THF exhibit a 13 lines EPR spectrum with g-value of 2.0057. The hyperfine splitting (a") = 0.88 G arises from coupling of the unpaired electron with the six equivalent 14N nuclei. Conclusions Charge-transfer salts containing the 'cylinder-like' cation [( q-Cp*)Ru(p,q-Cp*)Ru( q-Cp*)] have been prepared containing + the planar organic radicals TCNE, TCNQ, and C,{C,(CN),},. The X-ray structure determination of the [TCNE] -salt indicates that using cations of this type we can achieve 1-D stacking in an analogous fashion to the molecular ferromagnet [Fe(Cp*),] + [TCNE] -.Unfortunately, these materials do not exhibit co-operative magnetic interactions. However, further research is in progress to synthesise paramagnetic multidecker cations. We would like to thank SERC and The Nuffield Foundation for financial support. We also thank S. McLean, CR&D, E.I. duPont, U.S.A. for conducting the Faraday magnetic suscepti- bility experiments. References Synthesis and Properties of Low Dimensional Materials, Ann. N.Y. Acad. Sci., ed. J. S. Miller and A. J. Epstein, 1978, 313, and refeences therein. Extended Linear Chain Compounds, ed. J. S. Miller, Plenum Press, 1982, vol. 2. (a) J. S. Miller and A. J. Epstein, Prog. Znorg. Chem., 1986, 20, 1; (b)J. S. Miller, A. J. Epstein and W. M. Reiff, Acc. Chem. Res., 1988, 21, 114.G. A. Candela, L. J. Schwartzendruber, J. S. Miller and M. J. Rice, J. Am. Chem. SOC., 1979, 101, 2755. 5 J. S. Miller, J. H. Zhang and W. M. Reiff, J. Am. Chem. SOC., 1987, 109,4584. 6 (a) J. G. Gaudiello, M. Almeida, T. J. Marks, W. J. McCarthy, J. C. Butler and C. R. Kannwaurf, J. Phys. Chem., 1986,90,4917; (b)T. Inabe, J. G. Gaudiello, M. K. Moguel, J. W. Lyding, R. L. Burton and W. J, McCarthy, C. R. Kannewurf and T. J. Marks, J. Am. Chem. SOC., 1986, 108, 7595. 7 P. J. Fagan, M. D. Ward and J. C. Calabrese, J. Am. Chem. SOC., 1989, 111, 1698. 8 M. D. Ward, P. J. Fagan, J. C. Calabrese and D. C. Johnson, J. Am. Chem. SOC., 1989, 111, 1719. 9 T. D. Tilley, R. H. Grubbs and J. E. Bercaw, Organometallics, 1984,3,274.U.Koelle and J. Kossakowski, J. Organomet. Chem., 1989, 362, 383. 10 J. R. Carruthers and D. J. Watkin, CRYSTALS User ManuaI; Oxford University Computing Centre, Oxford, 1975. 11 E. K. Davies, ChemX User Manual, Chemical Crystallography Laboratory, Oxford, 1975. 12 A. C. T. North, D.C. Philips and F. S. Mathews, Acta Crys- tallogr., 1968, A24, 351. 13 D. Watkin, Crystallographic Computing 4, Techniques and New Techniques, eds. N. W. Isaacs and M. R. Taylor, Oxford Univer- sity Press, Oxford, 1988. 14 A. C. Larson, Acta Crystallogr., 1967, 23, 664. 15 J. R. Carruthers and D. J. Watkin, Acta Crystallogr., 1979, A35, 698. 16 International Tables for X-ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, p. 99. 17 (a)M.Lacoste, F. Varret, L. Toupet and D. Astruc, J. Am. Chem. SOC., 1987, 109, 6504; (b) J. L. Schrenk, A.M. McNair, F. B. McCormick and K. R. Mann, Znorg. Chem., 1986, 25, 3501; (c) T. P. Gill and K. R. Mann, Organometallics, 1982, 1, 485. 18 A. R. Kudinov, M. I. Rybinskaya, Y. T. Struchkov, A. I. Yanov-skii and P. V. Petrovskii, J. Organomet. Chem., 1987, 336, 187. 19 A. G. Orpen, L. Brammer, F. H. Allen, 0.Kennard, D. G. Watson and R. Taylor, J. Chem. SOC., Dalton Trans., 1989, SI. 20 D. A. Dixon and J. S. Miller, J. Am. Chem. SOC., 1987, 109, 3656. 21 E. Dubler, M. Textor, H. R. Oswald and A. Salzer, Angew. Chem., Int. Ed. Engl., 1974, 13, 135; E. Dubler, M. Textor, H. R. Oswald and G.B. Jameson, Acta Crystallogr. B, 1983, 39, 607. 22 J. S. Miller, J. C. Calabrese, A. J. Epstein, R. W. Bigelow, J. H. Zhang and W. M. Reiff, J. Chem. SOC., Chem. Commun., 1986, 1026. 23 F. A. Miller, 0.Sala, P. Devlin, J. Overend, E. Lippert, W. Lunder, J. Moser and J. Varchim, Spectrochem. Acta, 1964, 20, 1233. 24 J. S. Miller, D. O'Hare, A. Chakraborty and A. J. Epstein, J. Am. Chem. SOC., 1989, 111, 7853. 25 0.W. Webster, W. Mahler and R. E. Benson, J. Am. Chem. SOC., 1962,84, 3679. 26 J. S. Miller, J. H. Zhang, W. M. Reiff, D. A. Dixon, L. D. Preston, A. H. Reis, E. Gebert, M. Extine, J. Troup, A. J. Epstein and M. D. Ward, J. Phys. Chem., 1987,91,4344. 27 P. H. H. Fisher and C. A. McDowell, J. Am. Chem. SOC., 1963, 85, 2694. 28 (a) T. J. Fukanaga, J. Am. Chem. SOC., 1976, 98, 610; (b) T. Fukunaga, M. D. Gordon and P. J. Krusic, J. Am. Chem. SOC., 1976, 98, 61 1. Paper 0/04643D; Received 16th October, 1990

ISSN:0959-9428    

DOI:10.1039/JM9910100691

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 699-700 MATERIALS CHEMISTRY COMMUNICATIONS Electrochemical Probing of the Sol-Gel-Xerogel Evolution Pierre Audebert,*" Pascal Griesmarb and Clement Sanchez*b a Laboratoire d 'Electrochimie moleculaire, URA CNRS 438, Universite de Paris Vll, Paris, France Laboratoire de Chimie de la Matiere Condensee, URA CNRS 1466, Universite Pierre et Marie Curie, 4, place Jussieu, 75252 Paris, France Chronoamperometry has been performed on ferrocene embedded in silica and zirconia gels. The diffusion coefficient of ferrocene was measured along the sol-gel-xerogel transformations. Such electrochemical measurements are a sensitive probe of the structural and textural changes occurring in the sol-gel process. Keywords: Sol-gel processing; Ferrocene; Chronoamperometric probe The sol-gel synthesis of glasses and ceramics has received a great amount of scientific and technological interest during the last decade.' Sol-gel chemistry is mainly based on inor- ganic polymerization reactions.Starting from molecular pre- cursors such as metal alkoxides M(OR), (M=Si, Ti, Zr), a macromolecular oxide network is obtained uia hydroxylation-polycondensation reactiom2 A variety of physical and chemi- cal factors (e.g. temperature, pH, concentration of reactants, catalyst, chemical additives) influence the polymerisation pro- c~ss~'~and thus the properties of the final glass or the final ceramic. A detailed understanding of the underlying polymer growth process and of the evolution of the gel texture upon gelation, ageing and drying is essential because the subsequent stages of the glass- or ceramic-making procedure depend strongly on the initial structure and texture of the gel and xerogel.,3 Therefore, research is currently being carried out to study the physical and chemical transformations that occur during the sol-gel-xerogel transformations. Fluorescence p~larisation,~2H NMR4 or rigidochromic fluorescent probes' have been used to characterize silicon oxide based gels. Recently, cyclic voltammetry studies have demonstrated the feasibility of electrochemical experiments in gelling systems.6 This communication describes a convenient method to study the microviscosity of sol-gel systems based on chronoamperometric measurements performed on ferrocene molecules embedded in gels.Such measurements do not necessarily require transparent matrices or deuteriated sol- vents. The diffusion coefficient of ferrocene in different inor- ganic gels has been measured along the sol-gel-xerogel transformation. The microviscosity, q, experienced by the ferrocene probe all along the sol-gel transformation has been deduced from the diffusion coefficient, D, by using the Stokes- Einstein relationship, D = kBT/6nrq (a mean size r= 2.50 A has been taken for ferrocene). Such measurements provide a sensitive means of probing the structural and textural changes that occur during gelation, ageing, and drying of silica and transition-metal oxide based gels. Ferrocene-doped silica gels (gel 1) with a convenient mechanical resistance, and short gelation time have been synthesized by hydrolysing tetra-methoxysilane Si(OMe), in the presence of a nucleophilic activator catalyst SNaSi' (DMAP=4-dimethylaminopyrid-ine) as follows.Tetramethoxysilane (TMOS) (0.01 mol) was dissolved in methanol (0.06 mol) containing ferrocene, LiC104 and DMAP as a catalyst. Pure water (0.07 mol) was then added and the mixture was stirred for 1 min. The concen- trations of the reagents were adjusted to yield a final molar ratio of TMOS : H20:CH30= 1 :6 :7. LiC104 and ferrocene concentrations were, respectively, 0.1 and 0.01 mol dmP3. The sol gelled at tgel= 10 min at T= 21 "C. Ferrocene-doped zirconium oxide based gels (gel 2) have been prepared from Zr(OPr"), precursors chemically modified with acetylacetone2 as follows.Zr(OPr"), was dissolved in n-propanol containing ferrocene and LiC104, and acetylacetone was added. The solution was hydrolysed by adding water dissolved in n-propanol (10% water by volume in n-propanol). The concentrations of the reagent were adjusted to yield a final molar ratio of Zr :water :propanol :acetylacetone = 1 :10 :3 :0.5. LiC104 and ferrocene concentrations were, respectively, 1 and 0.01 mol dmP3. A gel was obtained within ca. 40 min at T =21 "C. Voltamperometric experiments were performed on ferrocene ([Fe] = loP2mol dm-3, [LiC104] = lo-' mol dm-3, Pt or Ag working electrodes, Ag wire quasi- reference). Ferrocene exhibits classical behaviour in sols, gels and xerogels (Fig.1) featuring classical le- reversible voltam- mograms, with peak currents decreasing in relation to the evolution of the diffusion coefficient of the species. As expected, the Cottrell law is followed with better accuracy in the gels than in classical solutions, since no deviations due to convec- tion can be seen, even after long times. This allows an accurate calculation of the diffusion coefficient, D, for the ferrocene inside different sol-gel systems as a function of time. A typical plot (gel 1) of the reduced diffusion coefficient (DR=D/Do) of these gels versus time (t/tgel) is shown in Fig. 2. Typical D values for silica and zirconia sols and the ensuing gels immediately after the gelation are reported in Table 1.They are close to those reported for ferrocene in acetonitrile (D= 2.4 x lo-' cm-2 s-').~No special variation of D is observed i Fig. 1 Cyclic voltammograms at 100 V s-' of the ferrocene embedded in the gels at three different characteristic times: sol (t=O); gel point (t = tg);partially dried gel (t =580tg) 0.1 -a" 6.b b 0.01 -0.1 0 4 8 12 16 20 ti tgel t 0 200 400 600 800 Wg.1 Fig. 2 Dependence of reduced diffusion coefficient of ferrocene .-.the gel on reduced gelation time for silica gel Table 1 Diffusion coefficient of ferrocene in metal oxide based sols and gels system Do (s01)/105cm2 sC1 Do (gel)/105 cm2 s-l SiO, (gel 1) 2.9 2.9 ZrO, (gel 2) 1.2 1.2 at the gelation point although the initial solution has turned to a solid amorphous material which does not exhibit macro- scopic flow.Thus, in the case of a solidification process caused by gelation, the electrochemical results show that the macro- scopic rigidification of the sol is not accompanied by rigidity at the microscopic level. The solid phase causing the rigidity at the macroscopic level and characterized by the divergence of the viscosity represents only a small percentage of the total volume of the gel. The solvent phase at the gel point (alcohol and water) constitutes the largest volume fraction of the gel. At this stage, the mobility of the ferrocene molecules is not constrained by the open structure of the gel. Subsequently, the diffusion coefficient of ferrocene is about the same in the gel and in the liquid sol (Table 1).The second step of the process is the ageing period. These experiments were performed on a slightly open cell (open diameter 0.5 cm) so that slow drying was allowed continu- ously. A decrease of the diffusion coefficient is observed. Such a phenomenon starts at ca. t = 3t, and reaches a first plateau at a time of ca. 10-20tg. Molecular transport of reactants and products is possible through the interstial liquid phase allowing hydrolysis and condensation reactions to continue. The electrochemical probe is not simply surrounded by the interstitial solvent as during the gelation stage, but now interacts with small percolating 0x0-polymers. Such results are in agreement with a polymerization process that produces a collection of branched polymers with a wide size distribution.The smaller ones, which are more numerous, control the local densities of chain segment, whereas the few larger ones are responsible for the macroscopic phenomenon of gelati~n.~ With increased ageing period (t/tg=20-100) in a closed vessel, the gel exhibits a slight increase of DR.Such an increase is probably related either to depolymerisation reactions," which J. MATER. CHEM., 1991, VOL. 1 lead to a partial depercolation of polymeric species, or to the fact that small polymers located inside the porous structure can condense (stick to larger polymers) at the pore surface. This latter phenomenon must decrease the number of poly- meric species present in the liquid phase of the gel and thus decrease the viscosity experienced by the ferrocene probe.Then DRreaches a plateau in which the diffusion coefficient of ferrocene is still quite high (D/Do=0.8). This indicates that the fluidity around many ferrocene molecules is still quite high in the wet gel even a long time after the sol-gel transition (t >loot,). This behaviour has already been observed from 3H NMR4 and fluorescence meas~rements.~ Such phenomena might be better characterized by microviscosity, which indi- cates only the local friction between dye molecules, medium- sized polymeric species and solvent moving inside the remain- ing porous texture of the gel. Thus, changes in D can be related to modifications of the microviscosity experienced by the ferrocene probe via the Stocke-Einstein relationship.After it has been air-dried, the gel structure collapses and the gel shrinks continuously. A strong and continuous decrease of the D, (increase of the microviscosity) starts when ca.40% of the liquid phase has been removed (Fig. 2). This step is accompanied by a progressive and eventually complete rigid- ification of the matrix. D can be measured even when ~70% of the liquid phase has been removed. Subsequent drying results in a porous solid called a xerogel. At this stage of drying, electrochemical measurements could not be performed. The exploitable timescale on which our experiments were made is ca. 10-500 ms, which corresponds roughly to a mean free path, L [L=(Dt)O.'], between 5 and 50 pm for the ferrocene molecule in the sol and gel.This shows that the ferrocene effectively has an extended motion over several pore diameters, and thus that these electrochemical measurements are probing changes in the distance travelled by the molecule as influenced by polymer growth. In the most aged measurable gel, this mean free path value falls by a factor of ca. 10, clearly showing the restriction of the molecular motion. Work is in progress to expand such measurements to a wide path range as well as to other silica- and titania-based gels. Moreover, the understanding of the structural and textural evolution of sol-gel systems can be improved greatly by using electro- chemical probes of different size or probes chemically bonded to the alkoxide precursors.References 1 Sol-Gel Technology For Thin Films, Fibers, Preforms, Electronics and Specialty Shapes, ed. L. C. Klein, Noyes, Park Ridge, 1988. 2 J. Livage, M. Henry and C. Sanchez, Prog. Solid State Chem., 1988, 18, 259. 3 C. J. Brinker and G. Scherrer, Sol-Gel Science, the Physics and Chemistry of Sol-Gel Processing, Academic Press, San Diego, 1989. 4 R. Winter, D. W. Hua, X. Song, W. Mantulin and J. Jonas, J. Phys. Chem., 1990, 94, 2706. 5 J. M. McKierman, J. C. Pouxviel, B. Dunn and J. I. Zink, J. Phys. Chem., 1989, 93, 2129. 6 Y. Zhang and R. W.P.H. Murray, Conf. Abs., March 4-8, Pittsburg, 1991. 7 R. J. P. Corriu, D. LeClercq, A. Vioux, M. Pauthe and J. Phalippou, in Ultrastructure Processing of Advanced Ceramics, ed. J. D. Mackenzie and D. R. Ulrich, Wiley, New York, 1988, p. 113. 8 T. Kowhnat and D. E. Boblitz, J. Am. Chem. Soc., 1960, 82, 584. 9 B. Cabane, M. Dubois and R. Duplessix, J. Phys., 1987, 48, 2131. 10 V. R. Kaufman and D. Avnir, Muter. Res. SOC. Symp., 1986, 13, 145. Communication 1/O 18 17E; Received 18th April, 199 1

ISSN:0959-9428    

DOI:10.1039/JM9910100699

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 701-702 701 Low-temperature Vapour Deposition of High-purity Copper Coatings from Bis[~(Fluoroalkyl)salicylaldiminato]copper Chelates Jeffrey B. Hoke* and Eric W. Stern Engelhard Corporation, Menlo Park, CN 40, Edison, NJ 08818, USA High-purity copper coatings have been prepared by chemical vapour deposition at low temperature from two novel bis[N-(fluoroalkyl)salicylaldiminato]chelates of copper(I1). When hydrogen is used as the carrier gas at ambient pressure, copper coatings containing < -1 atom.% carbon, oxygen, nitrogen, and fluorine are generated at 290 and 330 "C using Cu(NCH,CF2CF3-SAL), and Cu(NCH,CF,CF2CF3-SAL),, respectively (SAL=salicylaldiminato). When the deposition is carried out in vacuo, ca. 6% carbon, 2% oxygen, and 3% fluorine are incorporated into the films using Cu(NCH,CF,CF,-SAL), as the copper source.Keywords: Metal-organic chemical vapour deposition; copper(I1) complex; coating In recent years there has been growing interest in the develop- ment of volatile organometallic precursors to low-temperature vapour deposited metal and metal oxide coatings.'-6 Of the metals used in the microelectronics industry, copper is of interest, owing to its extensive application in packaging metal- lization.2b Additionally, with the discovery of copper-based high-temperature superconducting oxides, interest in the util- ization of potential copper-containing CVD precursors has grown markedly. Owing to their volatility, air stability, and ready availability, precursors for the chemical vapour deposition of metallic copper traditionally have been confined to the copper(I1) p-diketonates, in particular the fluorinated copper(I1) acetylace- tonato complexes, Cu(hfa), (hfa = hexafluoroacetylacetonato) and Cu(tfa), (tfa = trifluoroacetyla~etonato).~~~Other copper complexes which have been used as precursors for CVD include the related chelates, bis(acetylacetoneimide)copper(II) and (acetylacetoneethylenediimide)copper(II): tert-butoxy-copper(I ), c yclopen t adien yl( t rimet h ylp hosp hine)copper(I ),, a cyclopen tadien y1 (trimet h ylp hosphine)copper(I ),, and tert-butoxy(trimethylphosphine)copper(I).2b These precursors are sufficiently volatile for CVD, but many give rise to coatings that contain carbon, oxygen, or fluorine contamination.Since fluorine-containing copper p-diketonate complexes are known to be more volatile than their non-fluorinated analogues [e-g. Cu(hfacac), us. Cu(acac),], we have attempted to prepare other volatile copper chelates that contain fluorinated substituents and which can be decomposed cleanly to metallic copper. In this communication we describe preliminary findings on the chemical vapour deposition of metallic copper at low temperature (< 330 "C) from two novel, air-stable N-(fluoroalky1)salicylaldi-minatocopper(I1) precursors: Cu(NCH2CF2CF,-SAL), and CU(NCH,CF,CF~CF~-SAL)~. The new chelates were prepared by the Schiff's base conden- sation of bis(salicylaldehydato)copper(Ii) with a three-fold excess of the respective primary fluoroalkylamine in refluxing ethan01.~ Yields > 90% were obtained.Both complexes are volatile and sublime readily at ca. 150 "C and ca. 7 mT0rr.t Characterization data are given below.$ Depositions onto readily available, polished, fused quartz substrates were accomplished using a 2.54 cm (outer diameter) externally thermostatted hot-walled quartz reactor. The cop- per precursor was sublimed into the hot zone of the reactor either in a stream of hydrogen (ca. 1.6 cfhR or under vacuum in the absence of a carrier gas. A typical run lasted ca. 5 h. Hydrogen reduction of CU(NCH,CF,CF~-SAL)~ and Cu(NCH2CF2CF,CF3-SAL), vapours (sublimation tempera- ture ca. 190 "C) at ca. 290 and 330 "C, respectively, resulted in the deposition of reflective, crystalline coatings of copper (Table 1).ESCA depth-profile analyses detected c1 atom% carbon, oxygen, nitrogen, and fluorine within the bulk of the coatings which were obtained up to 2050 A thick. Thin-film (grazing-angle) X-ray analysis (Cu-Ka radiation) confirmed the crystallinity of the coating obtained from Cu(NCH2CF2CF2CF3-SAL),. For coatings derived from either precursor, representative scanning electron microscopy (SEM) photographs (Fig. 1) showed two distinct surface mor- phologies. In Fig. 1 (a), a polycrystalline granular morphology is shown with a roughly uniform crystallite size of 0.5 pm. However, in Fig. l(b) individual crystallites appear to have sintered into a smooth coating retaining wavy microcracks. Although the origin of this variability is not known, it does not appear to result from differences in deposition tempera- ture, film thickness, or CVD precursor.Owing to the gradual decomposition of the source materials under hydrogen during sublimation at 190 "C, the observed deposition rates were slow. (Attempts at using the NCH2CF3- SAL derivative were unsuccessful in producing a continuous copper coating since this precursor decomposed quite readily during sublimation.) In principle this problem can be allevi- ated by a modification to the quartz reactor that allows the organometallic vapours to be directed onto the substrate prior to hydrogen exposure. Id Consequently, the precursor will not see hydrogen until the point of deposition, and a significant improvement in rate should be observed.Nuclear magnetic resonance (NMR) spectroscopy and gas chromatography (GC) were utilized to deduce a possible mechanism for the reduction of Cu(NCH2CF2CF3-SAL), at t 1 Torr z 133.322 Pa. $ (a) Cu(NCH,CF,CF,-SAL),: m.p. 197.5-199.0 "C; Tub 145 "C (ca. 0.007 Torr). (Found: C, 42.46; H, 2.60. Calc. for C,,H14CuFl,N,0,: C, 42.30; H, 2.48%). FAB(-) in NBA: M+ at 567 with the correct isotope pattern for 63Cu and 65Cu. (b) Cu(NCH,CF,CF2CF3-SAL),: m.p. 184-185 "C; Tub 150 "C (ca. 0.007 Torr). (Found: C, 39.72; H, 2.12. Calc. for C22H14C~F14N202: C, 39.56; H, 2.11%). FAB(-) in NBA: M+ at 667 with the correct isotope pattern for 63Cu and 65Cu. (c) Cu(NCH,CF,-SAL),: m.p.225- 226 "c; Tub155 "c(CU. 0.007 Torr). (Found: c,46.58; H, 3.22. Calc. for C1,H,4CuF6N202: C, 46.21; H, 3.02%). FAB(-) in NBA: M+ at 467 with the correct isotope pattern for ',Cu and 65Cu. 9 1 cfhz2.83 XIO-' m3 h-'. J. MATER. CHEM., 1991, VOL. 1 precursor CU(NCH,CF,CF~CF~-SAL), CU(NCH~CF,CF~-SAL)~Cu(NCH,CF,CF,-SAL), Table 1 Data summary for CVD copper coatings ~~ co-reactant Tdecl "C depth/8, composition deposition rate/A h-' H2 330 1190 <1% C, 0, N, F 250 H2 290 2050 <1% C, 0,N, F 400 vacuum 485 2900 6% C, 2% 0,3% F 600 Fig. 1 Representative SEM photographs of deposited copper coatings showing varied coating morphologies (bars = 1 pm) 290 "C. GC analysis of the volatile organic products collected during vapour deposition showed two major species in an approximate 2 :1 ratio.'H, 13C, and I9F NMR spectroscopy identified the major product as free NCH2CF2CF3-salicylaldi- mine ligand and the minor product as o-cresol. These results would indicate that the primary reduction mechanism pro- ceeds via homolysis of the salicylaldimine-copper bonds and subsequent reaction of the transient organic radical with hydrogen to form free NCH,CF,CF3-salicylaldimine. Met-allic copper is thus generated. Apparently, further reduction of the free salicylaldimine ligand with hydrogen at high temperature yields o-cresol as a secondary product. When the decomposition of CU(NCH~CF~CF~-SAL)~was accomplished under vacuum in the absence of hydrogen carrier gas, a coating 2900 A thick incorporating ca.6 atom% carbon, 2 atom% oxygen, and 3 atom% fluorine, as deter- mined by ESCA, was obtained at 485 "C (sublimation tem- perature ca. 180 "C). Presumably, hydrogen is required to react with transient salicylaldiminyl radicals and thus prevent the formation of carbonaceous and fluorine-containing resi- dues. Despite the presence of these impurities, however, the morphology of the coating surface (Fig. 2) displays unusual columnar copper 'whiskers' extending away from rounded crystallites of roughly uniform 1 pm diameter. Further experi- ments aimed at exploring this unusual crystallite growth are in progress. References (a)J. E. Gozum, D. M. Pollina, J. A.Jensen and G. S. Girolami, J. Am. Chem. SOC., 1988, 110, 2688; (b) Z. Xue, M. J. Strouse, D. K. Shuh, C. B. Knobler, H. D. Kaesz, R. F. Hicks and R. S. Williams, J. Am. Chem. SOC., 1989, 111, 8779; (c) H. D. Kaesz, R. S. Williams, R. F. Hicks, Y. A. Chen, Z. Xue, D. Xu, D. Shuh and H. Thridandam, Muter. Res. SOC. Symp. Proc., 1989, 131, 395; (d) E. Feuer, S. Kraus and H. Suhr, J. Vuc. Sci. Technol. A, 1989, 7, 2799; (e) C. Larson, T H. Baum and R. L. Jackson, J. Electrochem. SOC.,1987,134,266; (f) T. H. Baum, J. Electrochem. Fig.2 SEM photograph of a copper coating obtained from the decomposition of Cu(NCH,CF,CF3-SAL), in uucuo (bar =5 pm) SOC.,1987, 134, 2616; (g) D. C. Smith, C. J. Burns, A. P. Sattel- berger, S. G. Pattillo, D. W. Carroll and J. R. Laia, Muter. Res. SOC.Symp. Proc., 1990, 168, 369. (a) C. G. Dupuy, D. B. Beach, J. E. Hurst and J. M. Jasinski, Chem. Muter., 1989,1, 16; (b)M. J. Hampden-Smith, T. T. Kodas, M. Paffet, J. D. Farr and H.-K. Shin, Chem. Muter., 1990, 2, 636. (a) R. W. Moshier, R. E. Sievers and L. B. Spendlove, US. Put. 3 356 527, 1967; (b)R. L. Van Hemert, L. B. Spendlove and R. E. Sievers, J. Electrochem. SOC., 1965, 112, 1123. R. G. Charles and J. G. Cleary, US. Put. 3 594 216, 1971. P. M. Jeffries and G. S. Girolami, Chem. Muter., 1989, 1, 8. (a)C. R. Jones, F. A. Houle, C. A. Kovac and T. H. Baum, Appl. Phys. Lett., 1985,46,97; (b)F. A. Houle, C. R. Jones, T. H. Baum, C. Pic0 and C.A. Kovac, Appl. Phys. Lett., 1985, 46, 204. (a)L. Sacconi and M. Ciampolini, J. Chem. SOC., 1964, 276; (b) R. G. Charles, J. Org. Chem., 1957, 22, 677. Communication 1/01941D; Received 24th April, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100701

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 703-704 Liquid-crystalline Zinc and Nickel 1,4,8,11,15,18,22,25-Octaalkylphthalocyaninates: Beneficial Effect of the Zinc Ion on Mesophase Stabilities Michael J. Cook,"' Steven J. Cracknell" and Kenneth J. Harrisonb a School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK Defence Research Agency, Electronics Division, RSRE, St Andre ws Rd., Great Malvern, Worcs. WR143PS, UK Zinc 1,4,8,11,15,18,22,25-octaalkylphthalocyaninates exhibit discotic mesophase behaviour over a much wider temperature range than their nickel analogues. In the former series a mesophase is exhibited by compounds bearing substituents as short as pentyl groups. Keywords: Liquid crystal; Phthalocyanine; Alkylphthalocyanine A common structural feature among compounds that exhibit discotic columnar mesophase behaviour is that the molecules contain a planar or near-planar core which bears six or eight long-chain substituents.' Available experimental evidence sug- gests that the presence of these side chains is crucial, though as yet it is unclear what the limiting chain length is before a liquid-crystalline phase arises.Recently, we reported columnar mesophase behaviour within two series of octa-substituted phthalocyanines, la and 1 b.2 1 R = C,H9 through C,,H,, a M=H,H b M=Cu c M=Zn d M=Ni The compounds are distinguished from previous examples of liquid-crystalline phthalo~yanines~3~ in that their substitution pattern is 1,4,8,11,15,18,22,25 and in exhibiting a total of three distinct mesophases.Also significant is the observation of mesophase behaviour when the alkyl substituent groups were as short as hexyl. The incorporation of copper into the phthalocyanine ring system, series 1 b, raised the temperature of the mesophase to isotropic liquid transition (D-I) and the melting transitions, either from crystal to mesophase (K-D) or crystal to isotropic liquid (K-I). The effect on the former, an increase of some 65-70 "C, was by far the more significant. These observations raise the interesting possibility that another central metal ion might stabilise the mesophase assemblies still further, offering the possibility of a discotic liquid crystal with substituent chain lengths shorter than c6.Recognizing that zinc(I1) shows a propensity for five-co- ordination, which in principle could help stabilise a columnar structure, we have now investigated the novel series of phthalocyaninato zinc analogues (lc). For comparative pur- poses we also examined the series Id containing nickel@), a da ion in its favoured spin-paired, square-planar four-co- ordinate state. Thermal behaviour of the zinc and nickel derivatives was investigated optically using a polarising microscope fitted with a heating unit and by differential scanning calorimetry (DSC). A total of three mobile birefringent mesophases were observed on cooling members of the series from the isotropic liquid state, each mesophase having a distinct texture when viewed under the polarising microscope. By comparing their textures with those observed for series la and lb we tentatively identify them as the D1, D2 and D3 mesophases described earlier and assigned as Dhd, Dhd and Drd, respectively.2 X-Ray diffraction studies are in hand to confirm these characterisations.Transition temperatures and enthalpy data obtained by DSC during heating within the second cycle are plotted in Fig. 1. Among the Cs-Clo compounds, the nickel derivatives with one exception (C,) have lower K-D transition tempera- tures than the metal-free analogues2 The zinc derivatives have significantly higher K-D transition temperatures and are raised above those of the corresponding copper com-pounds by between 2 and 25 "C. The D-I transition tempera- tures for the c6-Clo compounds in both the nickel and zinc series decrease linearly as the chain is lengthened, a feature which was observed earlier for series la and lb.2 In the nickel series they are within 1-3 "C of those for the metal-free series.Those for the zinc phthalocyanines are 90-1 15 "C higher. The latter are also some 27-43 "C higher than the corresponding transition temperatures in the copper series. This demonstrates that the central zinc ion significantly stabilises the mesophase assemblies. Indeed the octapentyl derivative in the zinc series shows the characteristic fan texture of the D1 mesophase when cooled from the isotropic liquid: the compound is thus one of the most lightly substituted phthalocyanine derivatives known to exhibit liquid-crystalline behavio~r.~ However, it is interesting that its D-I transition temperature falls several degrees below the extrapolation of the straight line correlating the data for the c6-cIo compounds, Fig.l(a). This departure suggests that the C5 chain is approaching the limiting length which can support mesophase behaviour. Experiments on the octabutyl analogue confirm that this is indeed the case, at least for the present series. The DSC thermogram taken up to 320 "C shows just one exotherm which is at 296 "C. This is ca. 15 "C below the appropriate point on the extrapolated D-I plot. However, there is no evidence from microscopy of mesophase formation and we deduce that the exotherm corre- sponds to a K-I transition rather than a K-D transition. We thank SERC for a studentship to S.J.C., Dr.J. McMurdo and Miss Isabelle Chambrier for donating some of the mater- 704 J. MATER. CHEM., 1991,VOL. 1 ( b)\ \ !96.1 (7.85)- 300 300 . *291.9, ,285.0 (3.50) ?.27b7 279.8 (V) 271.6 (4.07) 258.0 (2.89) 250 250 245 (4.80) 242.0 (3.57) 225.1 (2.88) '-.. 219.8 (8.24) 223.7 (V) ? 209.3 (2.57)<*. 200 200 169.1 (247) U. 150 T 158.4 (248) *. 152.0 (2.46) 150 n~ L. 145.3 (3.63) *'... l m . 9 (2.10) 113.9 (13.47) '... 118.2 (276) 9 .."' ..a.-.. ';,*.0 -..!06.6 (r)104.8 (1.02," 100 f P.923 (11.0) In 89.6 (16.94) .. .. .... bke 9 19 11)~ ,-..., -u64.2 (25.5)54.8 (90 ,I j5050 :+,4I 4 5 6 7 8 9 10 4 5 6 7 8 9 10 number of carbon atoms in the alkyl chains number of carbon atoms in the alkyl chains Fig.1 Transition temperatures and AH values (kcal mol-' measured on the heating cycle, in parentheses) of the phase changes for (a) zinc 1,4,8,11,15,18,22,25-octaalkylphthalocyaninates m,K(crysta1)-I(isotropic liquid); and (b)nickel 1,4,8,11,15,18,22,25-octaalkylphthalocyaninates. 17, K-mesophase (D, or DJ; +, D,-D,; 0, D3-D,; A,D,-I. Mesophases have been assigned by comparing the optical textures observed under the polarising microscope with those observed previously (ref. 2).D,, fan, Dhd; D,, needle, Dhd; D,, mosaic, Drd. Y Indicates a very low value for AH. AH data for the C5 zinc derivative could not be measured because the peaks were not resolved on the heating cycle ials, and Dr.K. Welford (Malvern) and Professor A. J. Thom-son (UEA) for helpful discussions. References 1 2 S. Chandrasekhar and G.S. Ranganath, Rep. Prog. Phys., 1990, 53, 57. M.J. Cook, M. F. Daniel, K. J. Harrison, N. B. McKeown and A. J. Thomson, J. Chem. Soc., Chem. Commun., 1987, 1086; A. S. C. Piechocki, J. Simon and P. Weber, Mol. Cryst. Liq. Cryst., 1983,100,275; D. Guillon, P. Weber, A. Skoulios, C. Piechocki and J. Simon, Mol Cryst. Liq. Cryst., 1985,130, 223; P. Weber, D.Guillon and A. Skoulios, J. Phys. Chem., 1987, 91,2242; M. Hanack, A. Beck and H. Lehmann, Synthesis, 1987, 703; D. I. Cho and Y.Lim, Chem. Lett., 1987, 2107; I. Cho and Y. Lim, Mol. Cryst. Liq. Cryst., 1988, 154, 9; J. F. van der Pol, E. Neeleman, J. W. Zwikker, R. J. M. Nolte and W. Drenth, Red. Trav. Chim. Pays-Bas, 1988, 107, 615; J. F. van der Pol, E. Neeleman, J. W. Zwikker, R. J. M. Nolte, W. Drenth, J. Aerts, 3 Cherodian, A. N. Davies, R. M. Richardson, M. J. Cook, N. B. McKeown, A. J. Thomson, J. Feijoo, G. Ungar and K. J. Harri-son, Mol. Cryst. Liq. Cryst., 1991,196,103. e.g.C. Piechocki, J. Simon, A. Skoulios, D. Guillon and P. Weber, J. Am. Chem. SOC., 1982, 104, 5245; D. Guillon, A. Skoulios, 4 R. Visser and S. J. Picken, Liq. Cryst., 1989,6, 577. T. Sauer and G. Wegner, Mol. Cryst. Liq. Cryst., 1988, 162B, 97. Communication 1/01990B;Received 29th April, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100703

出版商:RSC    

年代:1991

数据来源: RSC