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DALTON PERSPECTIVE J. Chem. Soc., Dalton Trans., 1999, 1–8 1 Complementary hydrogen bonds and ionic interactions give access to the engineering of organometallic crystals Dario Braga * and Fabrizia Grepioni * Dipartimento di Chimica G. Ciamician, Università di Bologna, Via Selmi 2, 40126 Bologna, Italy. E-Mail: dbraga@ciam.unibo.it; grepioni@ciam.unibo.it; http://catullo.ciam.unibo.it Received 3rd August 1998, Accepted 2nd October 1998 A crystal synthesis strategy based on a sequence of redox/acid– base/self-assembly/crystallisation processes has been devised and successfully applied to prepare a number of mixed organic/ organometallic and organometallic/organometallic crystalline materials. An adequate choice of the building blocks permits design and construction of mono-, two- and three-dimensional superanion framework structures encapsulating organometallic cations.The superanions are generated by partial deprotonation of polyprotic acids from the reaction with the organometallic hydroxides [Cr(Á6-C6H6)2][OH] and [Co(Á5-C5H5)2][OH], produced in situ by direct oxidation of the neutral complexes [Cr(Á6-C6H6)2] and [Co(Á5-C5H5)2].The anionic superstructures are held together by a combination of neutral and interionic O–H ? ? ? O hydrogen bonds, while the interaction with the organometallic cations is based on a profusion of C–H? ? ? O bonds reinforced via charge assistance. 1 Introduction “. . . in order to achieve the maximum stability, the two molecules must have complementary surfaces, like die and coin, and also a complementary distribution of active groups.The case might occur in which the two complementary structures happened to be identical; however, in this case also the stability of the complex of two molecules would be due to their complementariness rather than their identity” (L. Pauling, M. Delbrück, 1940).1 Organometallic crystal engineering is an emerging field of research.2 Much of the excitement arises from the idea of being able to combine the plethora of functional group characteristics of organic molecules 3 with the co-ordination geometry, ionic charges, valence and spin states typical of organometallic complexes in order to obtain novel crystalline materials.4 An intelligent choice of the building blocks may yield materials with magnetic, conducting, superconducting 5 and non-linear optical properties.6 Crystal engineering proceeds via the essential steps of analysis, synthesis and application.Analysis is the examination of available information on intermolecular interactions and molecular recognition,7 but also nucleation and crystallisation processes.8 It relies largely on expert analysis of data depositories, such as the CSD,9 on computer graphics and on the utilisation of computational tools. The theoretical generation of crystal structures starting from molecular structure alone can also be seen as a sophisticated kind of crystal structure analysis.10 2 The energy issue and the target material Synthesis is where the chemist works on his/her more congenial ground. Crystal synthesis strategies depend on the choice of target materials, hence depend on the energetics of the supramolecular bonding interactions one is planning to master.There is a substantial energetic diVerence between crystal syn- Fabrizia Grepioni graduated at the University of Bologna in 1985 and received her Ph.D.in Inorganic Chemistry in 1989. Her scientific interests are in the fields of inorganic and organometallic structural chemistry, organometallic crystal architectures, database analysis, hydrogen bonding, empirical packing energy calculations and the molecular and crystal structure of transition metal clusters and complexes. She has published more than 150 papers Fabrizia Grepioni Dario Braga and several review articles on organometallic solid state chemistry and intermolecular interactions in organometallic crystals.She was awarded the 1997 Raffaello Nasini Medal from the Inorganic Chemistry Division of the Italian Society of Chemistry. She has recently been appointed Associate Professor of General and Inorganic Chemistry. Dario Braga graduated in Chemistry at the University of Bologna in 1977. He was a postdoctoral fellow in Italy and the UK. He joined the Faculty of Science of the University of Bologna in 1982, where he is currently Associate Professor of General and Inorganic Chemistry.He was awarded the Raffaello Nasini Prize from the Inorganic Chemistry Division of the Italian Society of Chemistry in 1988 for his studies on solid state dynamic processes. He received the FEDERCHIMICA Prize for 1995 for his research on the intermolecular interactions in organometallic systems. His major current interests are in extramolecular interactions and hydrogen bonding in organometallic materials, and the engineering of organic–organometallic crystals. He is a Member of the Dalton Council, of the international editorial board of Chem.Commun. and of the Research Observatory of Bologna University.2 J. Chem. Soc., Dalton Trans., 1999, 1–8 theses involving only non-covalent interactions and those in which covalent bonds are broken and formed to build the crystal edifice. This diVerence has important methodological consequences. In the construction of non-covalent crystals use is made prevalently of molecular 11 or ionic 12 building blocks held together by bonds weaker than those between atoms forming the building blocks.In covalent crystal engineering, on the contrary, use is made of covalent bonds between components that do not have a chemical identity on their own.13 Covalent and non-covalent crystal engineering admit an intermediate situation, that is co-ordination crystal engineering 14 where the link between building blocks is provided by polydentate ligands that can join together co-ordination complexes in extended networks (‘co-ordination polymers’).This perspective will deal essentially with non-covalent crystal engineering in which the building blocks are molecules or ions. In recent years we have devoted our eVorts, also in collaboration with others, to expanding crystal engineering from its cradle, which is organic, to the organometallic chemistry area. The objective is that of bringing the electronic, magnetic, and structural properties of transition metal atoms into crystals that behave very much like organic crystals (but see below).The role of metal atoms in crystal engineering has been addressed in other reports and will not be dealt with in any great detail here.15 We have identified five distinct functions of metal atoms. (i) A topological function: the co-ordination geometry around the metal centres can be used to preorganise in space the extramolecular bonding capacity of the ligands.16 (ii) An electronic function: the electronics of metal–ligand bonding interactions, such as donation and back donation, permit tuning of ligand polarity and acid/base behaviour.17 (iii) A (tuneable) electrostatic function: metal atom variable oxidation states and/or the utilisation of non-neutral ligands permit ‘charge assistance’ to weak bonds (see also below).(iv) Direct participation of metal atoms in extramolecular bonds: electron deficient metal atoms may accept electron density intermolecularly from suitable Lewis bases, while electron rich metal atoms may have sterically unhindered lone pairs that accept hydrogen bonds.18 (v) A templating function: organometallic complexes chosen for their size and shape may be used to template self-assembly of organic, inorganic and organometallic molecules or ions into mono- di-, and three-dimensional superstructures.This article describes how the above functions, in particular (iii) and (v), have been used in our laboratory to produce mixed organic, inorganic and organometallic crystals.We have entered the field with the initial objective of building organometallic (OM hereafter) systems that would mimic the packing of organic (OR hereafter) crystals through bringing in the solid transition metal complexes. The first step was the preparation of a bis(benzene) chromium analogue of Etter’s cyclohexane-1,3-dione (CHD) inclusion compound (see Scheme 1 and Fig. 1).19 We succeeded only partially because [Cr(h6-C6H6)2] is easily oxidised to [Cr(h6-C6H6)2]1 which then forms ionic systems.20 Etter’s benzene cyclamer and our bis(benzene) chromium analogue [Cr(h6-C6H6)2]1- [(CHD)2]2?2CHD present many analogies and diVerences: (i) benzene and [Cr(h6-C6H6)2] have similar discoidal shape, (ii) in both systems the diones are linked via O–H ? ? ? O hydrogen bonds and here is where they are similar, (iii) the interaction between [Cr(h6-C6H6)2]1 and the surrounding superanion is chiefly coulombic in nature and here is where the two systems are fundamentally diverse. 3 The crystal synthesis strategy The dione/[Cr(h6-C6H6)2] experiment showed us that the bis- (benzene) chromium hydroxide could provoke self-assembly of the deprotonated dione into superanions via formation of negatively charged O–H ? ? ?O2 hydrogen bond interactions. The step from the dione to polycarboxylic OR acids came quite naturally with the realisation that the reproducibility of the selfassembly strategy was controlled by two factors: (i) the absence of hydrogen bond acceptors on the cation that could compete with the acid itself and (ii) the complementary role of strong and weak hydrogen bonds reinforced by coulombic contributions.Many novel crystalline materials have been prepared based on the combination of redox processes, acid–base and solubility equilibria as summarised below. Scheme 1 Colour scheme adopted for all figures, which have been produced with the computer graphic program SCHAKAL 97 (E.Keller, University of Freiburg, Germany). Fig. 1 Space filling representation of Etter’s crystalline (CHD)6(C6H6) cyclamer (a) and of the organometallic inclusion compound [Cr(h6- C6H6)2]1[(CHD)2]2?2CHD (b).J. Chem. Soc., Dalton Trans., 1999, 1–8 3 This, of course, does not imply a temporal sequence, rather serves the scope of describing the chemical and physical processes that lead from the initial neutral OR and OM molecular building blocks to the desired OR/OM or OM/OM crystalline solids.In the first step of the crystal synthesis sequence the highly basic O2 2 anion is produced by oxidation of the OM cation. Redox potentials for many OM sandwich complexes are available and have recently been reviewed.21 Two distinct processes occur in water and in less polar solvents (e.g. thf) because reactants and products have inverse solubility in the two types of solvent. In water the neutral OM species, namely [Cr(h6-C6H6)2] and [Co(h5-C5H5)2], are insoluble while the acid is usually (from very to fairly) soluble.In thf, on the contrary, the neutral OM species is soluble while the acid is usually only sparingly (if at all) soluble. Hence, in water oxidation of the OM species occurs in the heterogeneous phase (e.g. the solid neutral OM goes into solution as a cation together with the reduced oxygen species), whereas the acid deprotonation and formation of carboxylate anions occurs in the homogeneous phase.On the contrary, in thf OM oxidation occurs in the homogeneous phase, but the subsequent acid–base reaction is heterogeneous (e.g. in the presence of the solid acid) and the product is insoluble and precipitates, as soon as it is formed, as a powder material which then needs to be recrystallised from water or nitromethane. This is an important point because one may wonder if the aggregation in highly organised superstructures (see below) occurs as the product is formed or only upon recrystallisation from polar solvents.We do not have a definitive answer to this question. Although in most cases powder diVraction spectra of the bulk materials obtained from thf could be assigned on the basis of the experimental single crystal structure, we have also observed diVerences which may indicate the occurrence of polymorphic forms or diVerent degrees of solvation for the same crystalline materials. 4 The organometallic hydroxides [Cr(Á6-C6H6)2]- [OH]?3H2O and [Co(Á5-C5H5)2][OH]?4H2O The possibility of using oxygen as oxidant is the beauty and limitation of the process described above.Oxidation with oxygen is clean and does not produce undesired anions that Oxidation of neutral sandwich OM molecules to the corresponding cations Reduction of O2 to strongly basic O2 2 Deprotonation of the acid and generation of OR/OM anions fi The OM cations are stable fi The metal atoms are not available for co-ordination fi Neutral species are insoluble in water or polar solvents and soluble in thf fi In water the solutions are those of hydroxides The anions form O–H ? ? ?O, O–H2 ? ? ?O2 and O–H ? ? ?O2 interactions and self-assemble into supramolecular anions The cations mould the O–H ? ? ? O hydrogen bonded frameworks via charge assisted C–H d1 ? ? ?Od2 bonds fi The strongly basic CO2 2 groups seek strong donors which are only available on the neutral or partially deprotonated acid itself fi The supramolecular salts are insoluble in low polarity solvents while they are soluble in water fi The aggregates precipitate immediately in apolar solvents and can be recrystallised from water or nitromethane may compete with those obtained from the acid molecules by deprotonation.Furthermore, it generates in situ the strongly basic O2 2 anion which deprotonates the acid. Of course, if the acid is the water used as solvent, the reaction simply leads to formation of bright yellow solutions of the hydroxides [Cr(h6-C6H6)2][OH] and [Co(h5-C5H5)2][OH], which we have been able to isolate and characterise in their hydrated crystalline forms.22,23 The crystal of the hydroxide [Cr(h6-C6H6)2][OH]?3H2O is constituted of a stacking sequence of layers containing [Cr(h6-C6H6)2]1 cations intercalated with layers of hydrogen bonded water molecules and OH2 groups. Therefore, the layers carry opposite ionic charge and result in a system with crystal faces of completely diVerent chemical composition (see Fig. 2). The ([OH2]?3H2O)n layer is formed of a slightly puckered hexagonal network containing three water molecules and one OH2 group per formula unit, with the oxygen atoms hydrogen bonded to three neighbours. Contrary to [Cr(h6-C6H6)2][OH]?3H2O, which is solid at room temperature and fairly stable in the air, crystals of the analogue cobaltocenium hydroxide [Co(h5-C5H5)2][OH] have been, thus far, obtained at temperatures below 273 K where it solidifies with a variable number of water molecules.Successful structural characterisation has been possible for the hydrated form [Co(h5-C5H5)2][OH]?4H2O.23 The [OH]2?4H2O system forms a three-dimensional structure (see Fig. 3) based on hydrogen bonded zigzag chains of disordered ‘ice-like’ hexagonal rings interconnected via oxygen atoms.24 Both crystals show that the interaction between the OM cations and the negatively charged hydrogen bonded water/ OH2 superstructures is based on several C–H ? ? ? O bonds Fig. 2 Space filling representation of crystalline [Cr(h6-C6H6)2]- [OH]?3H2O. The crystal is constituted of a stacking sequence of layers containing [Cr(h6-C6H6)2]1 cations intercalated with ([OH]2?3H2O)n layers of hydrogen bonded water molecules and OH2 groups. Fig. 3 Space filling representation of crystalline [Co(h5-C5H5)2]1- [OH]2?4H2O. The [OH]2?4H2O system forms a three-dimensional structure based on hydrogen bonded zigzagged chains of disordered ‘ice-like’ hexagonal rings interconnected via oxygen atoms.4 J. Chem.Soc., Dalton Trans., 1999, 1–8 between oxygen atoms and the C–H systems of the ligands (see also below). 5 Horseshoes and clamps As mentioned in the Introduction, the crystals obtained from cyclohexane-1,3-dione were the first to be prepared. In a similar way, the aggregate [Cr(h6-C6H5Me)2]1[(CHD)2]2 has been obtained starting from [Cr(h6-C6H5Me)2].25 While in crystalline [Cr(h6-C6H6)2]1[(CHD)2]2?2CHD the dione “horseshoes” are related by a centre of inversion resulting in a large nearly planar system formed by two [(CHD)4]2 systems that embrace two bis(benzene)chromium cations [Fig. 1(b)], substitution of one methyl group for a hydrogen atom on the cation changes the overall shape of the fragment. The “arms” of the toluene ligands are not compatible with a tetrameric unit and the superanion [(CHD)2]2 acts as a “clamp” around the OM cation. The relationship between [Cr(h6-C6H6)2]1[(CHD)2]2?2CHD and [Cr(h6-C6H5Me)2]1[(CHD)2]2 is shown in Fig. 4. 6 Ribbons, sheets, honeycombs and boxes The experiments with the dione systems taught us that selfassembly in supraanionic structures can be attained (i) if the metal centres on the OM species are “protected” from coordination and do not carry ligands which can compete in strong hydrogen bonding formation, and (ii) if the anions have a “reserve” of strong proton donors for O–H ? ? ?O bonding.These simple design criteria have been exploited to prepare a number of new crystalline materials based on polyprotic organic and organometallic acids. These will be briefly described in the following. Squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione, H2SQA) has been treated with cobaltocenium hydroxide in 1 : 1 and 2 : 1 stoichiometric ratios obtaining two diVerent crystalline materials. The 1 : 1 system is constituted of ([HSQA]2)n ribbons and of ribbons of cobaltocenium cations, see Fig. 5.26 The good Fig. 4 The analogy between (a) [Cr(h6-C6H6)2]1[(CHD)2]2?2CHD and (b) [Cr(h6-C6H5Me)2]1[(CHD)2]2. Note how the structure of the bis- (toluene)chromium diVers from that of the bis(benzene)chromium by the absence of the two pendant neutral CHD. matching in size and shape between the cyclopentadienyl ligands and the [HSQA]2 ions leads to a superstructure in which the squarate ribbons intercalate between cobaltocenium cations (Fig. 5). The p–p distance is ca. 3.35 Å. The oxygen atoms from the rims of the ([HSQA]2)n ribbons interact with the [Co(h5-C5H5)2]1 cations via charge-assisted C–Hd1 ? ? ?Od2 hydrogen bonds (five H ? ? ? O distances in the range 2.272–2.500 Å). What is more, the packing arrangement is chiral in space group P21. The unusual orange colour suggests formation of a charge transfer complex, whose properties are under investigation. On changing the stoichiometry to 2 : 1 the unusual orange colour is lost, and [Co(h5-C5H5)2]1[(HSQA)(H2SQA)]2 is obtained as yellow crystals.The crystals contain supramolecular monoanions [(HSQA)(H2SQA)]2 resulting from the loss of one proton for every two squaric acid molecules bonded via interanion O–H ? ? ? O hydrogen bonds (O ? ? ? O distances 2.440 and 2.436 Å). The monoanions form ribbons via O–H? ? ? O hydrogen bond interactions, with formation of tenmembered ring systems (O ? ? ? O distances in the range 2.539– 2.574 Å) reminiscent of the carboxylic rings.The ribbons are stacked in such a way that squarate moieties overlap hydrogen bonded rings, resulting in layers with oxygen atoms protruding above and below the layer surface. The cobaltocenium cations lie side-on to the layer and interact via charge-assisted C-Hd1 ? ? ?Od2 hydrogen bonds. Tartaric acids Similarly to the squarate systems, diVerent stoichiometries lead to isolation of diVerent crystalline systems when D,L-tartaric acid (D,L-H2TA) is used. In crystalline [Co(h5-C5H5)2]1- [(D,L-HTA)(D,L-H2TA)]2 the acid forms an anionic organic honeycomb framework [see Fig. 6(a)].27 The superanion [(D,LHTA)( D,L-H2TA)]2 is formally the result of the loss of one proton for every two tartaric acid molecules, with the two units bonded via a short –C(O)O–H ? ? ? O(O)C– hydrogen bond [2.434(1) Å]. The dimers are then linked in the honeycomb framework via O–H ? ? ? O bonds involving the two external carboxyl groups and the hydroxyl groups. The interaction between the supraanionic network and the encapsulated [Co(h5-C5H5)2]1 cations occurs via C–Hd1 ? ? ?Od2 hydrogen bonds between the staggered cyclopentadienyl ligands of the cations and the CO and the OH groups of the anionic framework [Fig. 6(b)]. If the stoichiometric ratio between [Co(h5-C5H5)2][OH] and tartaric acid in the acid–base reaction is changed from 1: 2 to 1: 1, the hydrated crystalline salt [Co(h5-C5H5)2]1[(D,L-HTA)]2?H2O is obtained. Trimesic acid When the acid C6H3(CO2H)3-1,3,5-(H3TMA) is treated with Fig. 5 Ribbons of [HSQA]2 monoanions bonded via negatively charged O–H ? ? ? O hydrogen bonds and ribbons of cobaltocenium cations form the crystal of the 1 : 1 system.J. Chem. Soc., Dalton Trans., 1999, 1–8 5 [Co(h5-C5H5)2]1[OH]2 crystalline [Co(h5-C5H5)2]1[(H3TMA)- (H2TMA)]2?2H2O is obtained 23 in which (formally) one monodeprotonated and one neutral acid molecule form a dimeric superanion held together by an O–H ? ? ? O hydrogen bond interaction.The superanion can be described as formed by a deprotonated dimeric system of two trimesic acid moieties which maintains four CO2H groups to employ in hydrogen bonding systems with the surrounding anions. The distribution of trimesic acid moieties results in a large anionic organic superstructure which folds around the cobaltocenium cation as shown in Fig. 7. Two water molecules also participate in the hydrogen bond network. Fig. 6 The honeycomb arrangement of D,L-tartaric acid in crystalline [Co(h5-C5H5)2]1[(D,L-HTA)(D,L-H2TA)]2 (a) and a view of the honeycomb type structure with the cobaltocenium cations occupying the channels (b).Fig. 7 The anionic organic superstructure which folds around the cobaltocenium cation in crystalline [Co(h5-C5H5)2]1[(H3TMA)- (H2TMA)]2?2H2O. Phthalic acid The acid C6H4(CO2H)2-1,2-(H2PA) has been used to produce {[Co(h5-C5H5)2]1}4[HPA2]2[PA22]?6H2O.28a The interest in this particular building block stems from the possibility for phthalic acid of forming both intra- and inter-molecular hydrogen bonds.The crystal of {[Co(h5-C5H5)2]1}4[HPA2]2[PA2]?6H2O contains ribbons formed by mono-deprotonated anions and ribbons formed by fully deprotonated anions interlinked by water molecules (see Fig. 8). The two types of ribbons form, respectively, the “ceiling and floor” and “walls” of the crystalline edifice. Chiral acids: L-tartaric and dibenzoyl-L-tartaric acid The idea of using commercially available enantiomerically pure OR acids to build up chiral frameworks is a logical progression of the results described above.The possibility of reproducible strategies for the preparation of chiral frameworks in which dipolar electronic systems could be accommodated is of primary importance in the search for eYcient second harmonic generation materials. When enantiomerically pure L-tartaric acid is employed the chiral crystal [Co(h5-C5H5)2]1[L-HTA]2 is obtained.28b The crystal is constituted of a three-dimensional OR superanion.The honeycomb-type structure is no longer based on hexagonal channels as in the previous case but on square ones (see Fig. 9). The monodeprotonated L-HTA2 ions form chains that are cross-linked by other neutral –OH ? ? ?O]] C hydrogen bonds. An analogous preparation can be carried out with enantiomerically pure dibenzoyl-L-tartaric acid (L-H2BTA).28b The crystal structure of [Co(h5-C5H5)2]1[L-HBTA]2 is (obviously) chiral in space group P212121.Since the acid is monodeprotonated, as in the case of [Co(h5-C5H5)2]1[L-HTA]2, one “untouched” CO2H group forms a COO–H–OOC hydrogen bond with the carboxylate system CO2 2 of another anion thus forming ribbons through the crystal. However, since the (L-HBTA2)n anionic chains have no additional donor groups to use in cross-links, the construction of a connected hydrogen bonded three-dimensional network is not possible. The interaction between the anionic chain and OM cations takes advantage of a large number of charge-assisted C–Hd1 ? ? ?Od2 interactions. 7 The organometallic acid [Fe(Á5-C5H4CO2H)2] More recently, the redox/acid–base strategy outlined above has Fig. 8 Space filling representation of {[Co(h5-C5H5)2]1}4[HPA2]2- [PA22]?6H2O which contains ribbons formed by hydrogen bonded mono-deprotonated anions and ribbons formed by fully deprotonated anions interlinked by water molecules forming, respectively, the “ceiling and floor” and “walls” of the crystalline edifice.6 J.Chem. Soc., Dalton Trans., 1999, 1–8 been extended to the use of OM carboxylic acids as building blocks. Although polycarboxylic OM acids are not as common as organic ones, the neutral OM complex [Fe(h5-C5H4CO2H)2] (FeACH2 hereafter) has proved to be extremely versatile.29 The reaction with [Co(h5-C5H5)2] and [Cr(h6-C6H6)2] in thf proceeds similarly to the ones leading to OR/OM systems, with the nontrivial diVerence that the result is an OM/OM mixed system which contains metal atoms in diVerent oxidation and/or spin states.Crystalline [Co(h5-C5H5)2]1[Fe(h5-C5H4CO2H)(h5-C5H4- CO2)]2 and [Cr(h6-C6H6)2]1{[Fe(h5-C5H4CO2H)(h5-C5H4CO2)]- [Fe(h5-C5H4CO2H)2]0.5}2 have been prepared.29 The two species contain diVerent electronic and spin metal centres: 18 electron FeII and CoIII are present in the former whereas 18 electron FeII and paramagnetic 17 electron CrI are present in the latter crystalline material.In the Fe/Co crystal the FeACH2 anions form ribbons via interanion O–H ? ? ?O2 bonds between ligands in transoid conformation (see Fig. 10). In the Fe/Cr system, on Fig. 9 (a) Space-filling representation of the L-tartaric acid framework in crystalline [Co(h5-C5H5)2]1[L-HTA]2 with the cations occupying the channels (b); H atoms bound to C atoms are omitted for clarity. Fig. 10 Ribbons of hydrogen bonded [Fe(h5-C5H4CO2H)(h5-C5H4- CO2)]2 anions interacting with [Co(h5-C5H5)2]1 cations via chargeassisted C–Hd1 ? ? ?Od2 bonds.the other hand, there is one neutral FeACH2 molecule per two FeACH2 anions. The neutral molecule acts as a bridge between hydrogen bonded dimers formed by two FeACH2 anions (see Fig. 11). It is noteworthy that this latter species contains pairs of paramagnetic [Cr(h6-C6H6)2]1 cations, a packing feature observed already with the cyclohexanedione derivative. 8 Heavily hydrated species Rather serendipitously, “heavily hydrated species” are sometimes obtained.Although formation of these compounds is likely to be mainly under kinetic control, we have observed that it is only when a stoichiometric defect of the acid is used that species with a large number of water molecules are obtained. With dibenzoyl-L-tartaric acid the crystalline material {[Co- (h5-C5H5)2]1}2[L-BTA]22?11H2O is obtained. Since the acid is completely deprotonated, no hydrogen bonding donor group is available for the twelve potential hydrogen bonding acceptor sites.The eleven water molecules, therefore, play a twofold function: not only they fill space eYciently, but also, and more importantly, they provide a large number of OH donor groups which are able to stabilise the crystal structure via hydrogen bonding. Crystallisation from water of the Co(C5H5)2–FeACH2 system prepared in 2 : 1 ratio leads to complete deprotonation of the dicarboxylic acid and to crystallisation of {[Co(h5-C5- H5)2]1}2[Fe(h5-C5H4CO2)2]22?7.75H2O.28 9 Co-operative strong and weak hydrogen bonds and charge assistance The hydrogen bond is the principal non-covalent interaction in the synthesis of molecular crystals, because it combines strength with directionality.30 Directionality means predictability and reproducibility, properties which are essential in any synthetic strategy. The classical O–H ? ? ? O hydrogen bonds formed by CO2H and OH groups are among the strongest neutral bonds.When neutral molecules are involved the strength of this three-centre four-electron interaction can be tuned by varying the nature of the acceptors and donors and/or the polarity of the groups involved. In addition to this, the O–H? ? ? O bond can be strengthened if the polarity of the acceptor systems is increased via deprotonation.Negatively charged O–H ? ? ?O2 bonds have been studied extensively and shown to possess dissociation energies in the range 60–120 kJ mol21.31 The hydrogen bond has been subjected to numerous theoretical studies.32 The utilisation of polycarboxylic acids permits the simultaneous use of neutral O–H ? ? ? O and charged O–H ? ? ?O2 bonding interactions, including the participation of water Fig. 11 Ribbons of {[Fe(h5-C5H4CO2H)(h5-C5H4CO2)][Fe(h5-C5H4- CO2H)2]0.5}; note how the neutral molecule acts as a bridge between hydrogen bonded dimers formed by two FeACH2 anions. Chargeassisted C–Hd1 ? ? ?Od2 bonds link the pair of encapsulated [Cr(h6- C6H6)2]1 cations.J.Chem. Soc., Dalton Trans., 1999, 1–8 7 oxygens as donors or acceptors. The “charged” interactions can be grouped in two distinct categories: the O–H ? ? ?O2 interactions when the donor belongs to a neutral molecule and the acceptor is an anion, and (ii) the interanion O–H2 ? ? ?O2 when both donor and acceptor groups belong to an anion. In all cases the O ? ? ? O distances are considerably shorter than the sum of the van der Waals radii and there is a marked preference for linearity.Importantly, O–H? ? ?O2 and O–H2 ? ? ?O2 interactions, although possessing the same geometrical properties as neutral O–H ? ? ? O bonds, are generally associated to O ? ? ?O distances shorter than in the case of neutral systems (roughly 2.45 against 2.65 Å).30b Since we are dealing with O–H ? ? ?O interactions, which are commonly regarded as prototypes of “strong” hydrogen bonds, the decrease in O ? ? ? O distance is usually taken as indicative of a substantial increase in hydrogen bond strength. The relationship between length and strength of the interactions involving ions had recently been begun to be investigated by theoretical methods with intriguing results.33 For instance, it has been demonstrated that the short O– H2 ? ? ?O2 interactions (2.52 Å) present in crystalline KHC2O4 are not associated with stable interanion interactions.In this and similar cases, the O–H2 ? ? ?O2 interaction should be regarded as a supramolecular organiser of anions rather than as a stable bond.A discussion of this aspect, albeit important, is beyond the scope of this article. The interested reader is addressed to recent preliminary communications published by us in collaboration with J. J. Novoa.33,34 It is useful to stress that all interactions of the O–H ? ? ?O type stabilise the supraanionic aggregates. Whether the stabilisation is on a relative energy scale (as in the case of purely interanion O–H2 ? ? ?O2 interactions) or on an absolute scale (as would be the case of “conventional” neutral O–H ? ? ? O and of neutral–anion O–H ? ? ?O2 interactions) it is not of crucial importance for the design strategy.It is clear that the most relevant contribution to crystal cohesion is of electrostatic rather than of covalent nature, e.g. the superstructures are stable because of the anion–cation interplay. The cations are sandwich complexes that do not carry donor/ acceptor groups in competition for hydrogen bond formation with interanion self-assembly.This brings about the question of weak C–H ? ? ? O hydrogen bonds.17,35 The sandwich cations participate in a large number of C–H ? ? ? O interactions with most (but not all) arene or cyclopentadienyl H atoms at a short distance from an oxygen acceptor on the supramolecular anion. In these cases, H ? ? ? O distances are some 0.01–0.03 Å shorter than when the same molecular fragments form C–H ? ? ?O bonds in neutral crystals.One can look at the shortening eVect as another consequence of the strong ionic field generated by the ionic charges, with the far from trivial diVerence that the ionic charge assists the hydrogen bond. The positive charge carried by the cation decreases the shielding of the proton on the donor C–H groups and makes it more acidic; if this occurs simultaneously to the presence of a negative charge on the acceptor, which increases its nucleophilicity, the net result is a strengthening of the weak bonds.Similar behaviour has been observed when the acceptor is a fluorine atom belonging to anions such as PF6 2 and BF4 2,36 or a p system belonging to phenyl groups carried by anions.37 In summary, while the electrostatic field generated by the presence of ions may be said to provide most of the cohesion, the hydrogen bonds (or hydrogen bond like 33) O–H ? ? ? O and C–H? ? ? O interactions provide directionality, selectivity and reproducibility.Since ionic solids are much more stable than most molecular solids, crystalline materials based on charged hydrogen bonded systems involving ions are expected to be much more robust than molecular networks constructed with neutral hydrogen bonds. One may say that charged hydrogen bonds confer directionality to coulombic interactions thus behaving as supramolecular tugboat interactions that organise the ions in space. 10 Conclusions and outlook This article has been devoted to describing a simple, reproducible, and transferable strategy to build crystalline materials.The forces we have exploited are suYciently strong to generate stable and robust edifices with clearly defined two- and threedimensional superstructures. The classification of the crystalline materials described herein in terms of the covalent, ionic, co-ordination solids is not straightforward. It is much easier to state what they are not. The supraanionic hydrogen bonded salts are not extended covalent networks because the basic linker is not a covalent bond but a hydrogen bond and they are not co-ordination networks because the metal centres are unavailable for co-ordination since they are protected by stable p ligands.Although formed of charged particles, they are not, strictly speaking, ionic salts (e.g. alkali metal carboxylates) because of the high dimensionality of the ionic components. The anions are linked in two- or threedimensional networks and are more appropriately described as superanions.On the other hand, they are not molecular crystals because the components do actually carry ionic charges and the anionic frameworks would fall apart if the counter ions were removed. What are they then? They could be considered “organometallic super-salts” which own their cohesion and stability mainly to electrostatic forces, but that possess the shape they have and can be built and rebuilt the way they can thanks to the directionality, predictability and reproducibility of the strong and weak hydrogen bonds.Similar to “conventional” salts, these super-salts are expected to have high melting points and high solubility in polar solvents, such as water or nitromethane, while the presence of extended networks introduces anisotropy in the ion arrangements (e.g. the squarate salts above) and characteristics that are typical of hydrogen bonded molecular crystals. This understanding has implications in crystal engineering studies when ionic building blocks are involved.The utilisation and combination of organometallic acids or bases allow the preparation of crystals that contain metal atoms in diVerent oxidation, charge and spin states. It is also possible to construct non-centrosymmetric crystals, and this is one of the goals of NLO materials chemistry.5 The alignment of dipoles in a polar crystal so that centrosymmetric pairs do not cancel each other is one of the prerequisites of the construction of materials with potential for eYcient secondharmonic generation eVects.The goal is now that of using dipolar OM ions in place of the symmetric sandwich systems to obtain dipole alignment within the chiral frameworks. This project is still at an embryonic stage of development but initial results have been extremely promising. The preparation of hydrogen bonded superstructures hosting metal atoms in diVerent oxidation and/or spin states is also a challenging development of our crystal synthesis strategy. 11 Acknowledgements Financial support by Consiglio Nazionale delle Ricerche, by Ministero dell’ Università e della Ricecca Scientifica e Technologica (project: Supramolecular Devices) and by the University of Bologna (projects: Intelligent molecules and molecular aggregates 1995–1997 and Innovative Materials 1997–1999) is acknowledged. The results described have been possible thanks to the hard work of students from Bologna and from several European laboratories.The ERASMUS program ‘Crystallography’, the Deutscher Akademischer Austauschdienst, Bonn, and the Conferenza Nazionale dei Rettori, Roma, are thanked for scientific exchange grants. The RSC is acknowledged for international author grants. We thank Professors Gautam R. Desiraju, Emilio Tagliavini, Fausto Calderazzo and Juan J. Novoa for many useful discussions. We thank Dr. Claudio Marra for the photograph.8 J.Chem. Soc., Dalton Trans., 1999, 1–8 12 References 1 L. Pauling and M. Delbrück, Science, 1940, 77. 2 D. Braga, F. Grepioni and G. R. Desiraju, Chem. Rev., 1998, 98, 1375. 3 G. R. Desiraju, Crystal Engineering: The Design of Organic Solids, Elsevier, Amsterdam, 1989; Angew. Chem., Int. Ed. Engl., 1995, 34, 2311; C. B. Aakeröy, Acta Crystallogr., Sect. B, 1997, 53, 569. 4 D. Braga and F. Grepioni, Chem. Commun., 1996, 571. 5 J. M. Williams, H. H. Wang, T. J. Emge, U. Geiser, M.A. Beno, P. C. W. Leung, K. Douglas Carson, R. J. Thorn, A. J. Schultz and M. Whangbo, Prog. Inorg. Chem., 1987, 35, 218; J. S. Miller and A. J. Epstein, Angew. Chem., Int. Ed. Engl., 1994, 33, 385; Chem. Eng. News, 1995, 73, 30; O. Khan, Molecular Magnetism, VCH, New York, 1993; D. Gatteschi, Adv. Mater., 1994, 6, 635; A. Müller, F. Peters, M. T. Pope and D. Gatteschi, Chem. Rev., 1998, 98, 239; P. J. Fagan and M. D. Ward, The Crystal as a Supramolecular Entity. Perspectives in Supramolecular Chemistry, ed.G. R. Desiraju, Wiley, Chichester, 1996, vol. 2, p. 107. 6 S. R. Marder, Inorg. Mater., 1992, 115; N. J. Long, Angew. Chem., Int. Ed. Engl., 1995, 34, 21; T. J. Marks and M. A. Ratner, Angew. Chem., Int. Ed. Engl., 1995, 35, 155; D. R. Kanis, M. A. Ratner and T. J. Marks, Chem. Rev., 1994, 94, 195. 7 G. R. Desiraju, Chem. Commun., 1997, 1475; R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384; J. D. Dunitz and R. Taylor, Chem. Eur.J., 1997, 3, 89. 8 A. Gavezzotti and G. Filippini, Chem. Commun., 1998, 287. 9 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 31. 10 A. Gavezzotti, Acc. Chem. Res., 1994, 27, 309; Curr. Opinion Solid State Mater. Sci., 1996, 1, 501; T. Shoda, K. Yamahara, K. Okazaki and D. E. Williams, J. Mol. Struct. (Theochem), 1994, 313, 321; J. Perlstein, K. Steppe, S. Vaday and E. M. N. Ndip, J. Am. Chem. Soc., 1996, 118, 8433; M. U. Schmidt and U. Englert, J. Chem. Soc., Dalton Trans., 1996, 2077; H.R. Karfunkel and R. J. Gdanitz, J. Comput. Chem., 1992, 13, 1171; R. J. Gdanitz, Chem. Phys. Lett., 1992, 190, 391; S. J. Maginn, Acta Crystallogr., Sect. A, 1996, 52, C79. 11 M. W. Hosseini and A. De Cian, Chem. Commun., 1998, 727; G. M. Whitesides, J. P. Mathias and C. T. Seto, Science, 1991, 254, 1312; S. I. Stupp, V. LeBonheur, K. Walker, L. S. Li, K. E. Huggins, M. Kesser and A. Amstutz, Science, 1977, 276, 384. 12 C. B. Aakeröy and M. Nieuwenhuyzen, J.Am. Chem. Soc., 1994, 116, 10983; J. Mol. Struct., 1996, 374, 223; V. A. Russell, C. C. Evans, W. Li and M. D. Ward, Science, 1997, 276, 575; J. A. Swift, V. A. Russell and M. Ward, Adv. Mater., 1997, 9, 1183. 13 C. L. Bowes and G. A. Ozin, Adv. Mater., 1996, 8, 13. 14 See, for example, (a) O. M. Yaghi, C. E. Davis, G. Li and H. Li, J. Am. Chem. Soc., 1997, 119, 2861; (b) R. E. Melendez, C. V. K. Sharma, M. J. Zaworotko, C. Bauer and R. D. Rogers, Angew. Chem., Int.Ed. Engl., 1996, 35, 2231; (c) L. Carlucci, G. Ciani, D. Proserpio and A. Sironi, J. Am. Chem. Soc., 1995, 117, 4562; (d ) G. A. Ozin, Acc. Chem. Res., 1997, 30, 17. 15 D. Braga and F. Grepioni, Coord. Chem. Rev., in the press. 16 B. Olenuyk, A. Fechtenkötter and P. J. Stang, J. Chem. Soc., Dalton Trans., 1998, 1707; A. D. Burrows, C.-W. Chan, M. M. Chowdry, J. E. McGrady and D. M. P. Mingos, Chem. Soc. Rev., 1995, 329; S. Subramanian and M. J. Zaworotko, Coord. Chem. Rev., 1994, 137, 357; M.J. Zaworotko, Nature (London), 1997, 386, 220; D. Braga, F. Grepioni, D. Walther, K. Heubach, A. Schmidt, W. Imhof, H. Görls and T. Klettke, Organometallics, 1997, 16, 4910; P. J. Stang, Chem. Eur. J., 1998, 4, 19. 17 D. Braga and F. Grepioni, Acc. Chem. Res., 1997, 30, 81. 18 L. Brammer, D. Zhao, F. T. Ladipo and J. Braddock-Wilking, Acta Crystallogr., Sect. B, 1995, 51, 632; D. Braga, F. Grepioni, E. Tedesco, K. Biradha and G. R. Desiraju, Organometallics, 1997, 16, 1846 and refs.therein. 19 M. C. Etter, Z. Urbonczyck-Lipkowska, D. A. Jahn and J. S. Frye; J. Am. Chem. Soc., 1986, 108, 5871. 20 D. Braga, F. Grepioni, J. J. Byrne and A. Wolf, J. Chem. Soc., Chem. Commun., 1995, 1023. 21 N. G. Connelly and W. E. Geiger, Chem. Rev., 1996, 96, 877. 22 D. Braga, A. L. Costa, F. Grepioni, L. Scaccianoce and E. Tagliavini, Organometallics, 1996, 15, 1084. 23 D. Braga, A. Angeloni, F. Grepioni and E. Tagliavini, J. Chem. Soc., Dalton Trans., 1998, 1961. 24 Water. A Comprehensive Treatise, ed. F. Franks, Plenum, New York, 1973, vol. 2, p. 55. 25 D. Braga, A. L. Costa, F. Grepioni, L. Scaccianoce and E. Tagliavini, Organometallics, 1997, 16, 2070. 26 D. Braga and F. Grepioni, Chem. Commun., 1998, 911. 27 D. Braga, A. Angeloni, F. Grepioni and E. Tagliavini, Chem. Commun., 1997, 1447. 28 (a) D. Braga, A. Angeloni, A. Goetz, F. Grepioni and L. Maini, New J. Chem., submitted; (b) D. Braga, A. Angeloni, F. Grepioni and E. Tagliavini, Organometallics, 1997, 16, 5478. 29 D. Braga, L. Maini and F. Grepioni, Angew. Chem., Int. Ed. Engl., 1998, in the press. 30 (a) G. A. JeVrey and W. Saenger, Hydrogen Bonding in Biological Structures, Springer, Berlin, 1991; (b) G. A. JeVrey, An Introduction to Hydrogen Bonding, Oxford University Press, New York, 1997; (c) C. B. Aakeröy and K. R. Seddon, Chem. Soc. Rev., 1993, 397; (d ) D. Braga, F. Grepioni and G. R. Desiraju, J. Organomet. Chem., 1997, 548, 33. 31 M. Meot-Ner (Mautner), J. Am. Chem. Soc., 1984, 106, 1257; M. Meot-Ner (Mautner) and L. W. Sieck, J. Am. Chem. Soc., 1986, 108, 7525. 32 See, for example; H. Umeyama and K. Morokuma, J. Am. Chem. Soc., 1977, 99, 1316; M. S. Gordon and J. H. Jensen, Acc. Chem. Res., 1996, 29, 536; P. Gilli, V. Bertolasi, V. Ferretti and G. Gilli, J. Am. Chem. Soc., 1994, 116, 909; O. N. Ventura, J. B. Rama, L. Turi and J. J. Dannenberg, J. Phys. Chem., 1995, 99, 131 and refs. therein; C. Lee, G. Fitzgerald, M. Planas and J. J. Novoa, J. Phys. Chem., 1996, 100, 7398. 33 D. Braga, F. Grepioni and J. J. Novoa, Chem. Commun., 1998, in the press. 34 D. Braga, F. Grepioni, E. Tagliavini, J. J. Novoa and F. Mota, New J. Chem., 1998, in the press. 35 G. R. Desiraju, Acc. Chem. Res., 1996, 29, 441; T. Steiner, Chem. Commun., 1997, 727; D. Braga, F. Grepioni, K. Biradha, V. R. Pedireddi and G. R. Desiraju, J. Am. Chem. Soc., 1995, 117, 3156. 36 F. Grepioni, G. Cojazzi, S. M. Draper, N. Scully and D. Braga, Organometallics, 1998, 17, 296; D. Braga and F. Grepioni, in Current Challenges on Large Supramolecular Assemblies, ed. G. Tsoucaris, Kluwer, Dordrecht, in the press. 37 D. Braga, F. Grepioni and E. Tedesco, Organometallics, 1998, 17, 2669. Paper 8/06069J

ISSN:1477-9226    

DOI:10.1039/a806069j

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Page 3 3 Synthesis and characterisation of tetramethylammonium selenosulfate(VI) tetrahydrate, (NMe4)2SeSO3?4H2O Alexander J. Blake, Victoria Consterdine, Michael F. A. Dove,* Scott Lammas and Linda H. Thompson Department of Chemistry, University of Nottingham, Nottingham, UK NG7 2RD Tetramethylammonium selenosulfate tetrahydrate has been synthesised and characterised; a single-crystal X-ray structure determination shows the presence of the dianion SeSO3 22, in which the central sulfur atom is bonded to three oxygens and one selenium atom [S]Se distance 2.1746(7) Å].The solubility of elemental selenium in aqueous solutions of the sulfites of the more electropositive elements has been known since the middle of the nineteenth century.1 Indeed, the dissolution in and subsequent precipitation of selenium from aqueous sulfite has been described as a means of separating selenium from tellurium.2 In 1995 Ball and Milne 3 reported on their studies of the synthesis and spectroscopy of the selenosulfate anion; their data are fully consistent with the expected structure of this species and, like our earlier work,4 refute the possible existence of both the isomeric thioselenate(VI) and the selenoselenate(VI) dianions.2 Brunner et al.5 had previously shown that a selenium-bridged dirhodium complex, [(C5Me5)- Rh(CO)]2Se could be converted by the action of SO3 into the related m-SeSO3 complex, which they characterised by a singlecrystal X-ray diffraction study.As part of our study of the chemistry of selenosulfates we attempted to isolate single crystals of a salt containing the free anion, searches of the October 1996 release of the Cambridge Structural Database 6 and of the latest Inorganic Crystal Structure Database having revealed the bridged dirhodium complex and the earlier study of a copper complex, Cu(en)2SeSO3 (en = ethane-1,2-diamine),7 as the only relevant structures. Crystallographic studies of M(en)3SeSO3 compounds, MII = Cd,8a Mn, Fe, Co, Ni, Zn or Cd,8b had shown them to have disordered O and Se sites in the selenosulfate anion.We have now succeeded in preparing crystals of the colourless tetrahydrate of tetramethylammonium selenosulfate. The compound was made from excess selenium, aqueous tetramethylammonium hydroxide (2 equivalents) and sulfur dioxide (1 equivalent) and isolated from the concentrated solution.It is stable in air at room temperature for more than a month in the dark; it may be partially dehydrated in vacuo and decomposes at 200 8C to a brown solid, which turns red with further heating. The hydrate was isolated in ca. 50% yield and gave satisfactory elemental analyses, 77Se NMR (in aqueous sulfite), infrared and Raman spectra fully consistent with the formulation.† Its crystal structure has been determined by single-crystal X-ray methods‡ and shows the presence of the tetramethylammonium ions and † Spectroscopic data for the selenosulfate anion.Raman (solid state) 1144(E), 991(A1), 637(A1), 518(E), 303(A1), 279 (sh)(E) cm21; 77Se NMR in aqueous sulfite, a singlet at d 650 relative to Me2Se. ‡ Crystal data for: C8H32N2O7SSe, M = 379.38, monoclinic, a = 8.2902(9), b = 15.551(3), c = 14.198(3) Å, b = 94.924(15)8, U = 1823.7(6) Å3, space group P21/n, Z = 4, Dx = 1.382 g cm23, Mo-Ka radiation, m = 2.198 mm21, T =150 K, w–q scans, 2q < 508, 4499 total data, 3195 unique, Rint = 0.024 after a numerical absorption correction (Tmax = 0.758, Tmin = 0.535), 301 variables refined in full-matrix least squares against 3188 F2 data to R[F > 4s(F )] = 0.0285, wR(F2) = 0.0622, S = 0.99, Drmax = 0.56 e Å23.CCDC reference number 186/793. the free selenosulfate ion interacting via two of its oxygen atoms (O2 and O3) with a network of H-bonded water molecules, Fig. 1. There is also a long selenium–hydrogen interaction, Se1 ? ? ? H3W1 2.58 Å, with a hydrogen bond angle of 1738.The S]Se bond length of 2.1746(7) Å in the anion is shorter than that reported earlier 7 for Cu(en)2SeSO3 in which selenium was said to complete the octahedral co-ordination of copper(II). The length of the S]Se bond in the dirhodium complex is significantly greater, 2.301 Å, consistent with it being a single bond; indeed, it is quite comparable with the related single bond in OnS]Se (n = 2 or 3) fragments listed in the Database,6 for which the average value is 2.26 (±0.03) Å.Acknowledgements Financial support from the EPSRC in the form of a studentship (to L. H. T.) and of funding for the purchase of the X-ray diffractometer is gratefully recorded. References 1 Gmelin’s Handbuch der Anorganische Chemie, Selen, B, Gmelin- Verlag GmbH, Clausthal-Zellerfeld, 1949. 2 K. W. Bagnall, Comprehensive Inorganic Chemistry, eds. J. C. Bailar, H. J. Emeléus, R. Nyholm and A. F. Trotman-Dickenson, Pergamon Press, 1973, vol. 2, p. 938. 3 S. Ball and J. Milne, Can. J. Chem., 1995, 73, 716. 4 L. H. Thompson, Ph.D. Thesis, University of Nottingham, 1993. 5 H. Brunner, N. Janietz, J. Wachter, H.-P. Neumann, B. Nuber and M. L. Ziegler, J. Organomet. Chem., 1990, 388, 203. 6 F. H. Allen and O. Kennard, Chem. Design Automation News, 1993, 8, 1; 31. 7 N. V. Podbereskaya, S. V. Borisov and V. V. Bakakin, Zh. Strukt. Khim., 1971, 12, 840. 8 (a) N. V. Podbereskaya and S. V. Borisov, Zh. Strukt. Khim., 1971, 12, 1114; (b) V. L. Varand, N. V. Podbereskaya, V. M. Shulman, V. V. Bakakin and E. D. Ruchkin, Izv. Akad. Nauk SSSR, Ser. Khim., 1967, 44. Received 10th October 1997; Communication 7/07328C Fig. 1 The asymmetric unit in the structure of tetramethylammonium selenosulfate tetrahydrate. Selected bond distances (Å) and angles (8): Se1]S1 2.1746(7), S1]O1 1.452(2), S1]O2 1.464(2), S1]O3 1.462(2); O1]S1]O3 110.90(13), O1]S1]O2 111.86(12), O3]S1]O2 108.79(12), Se1]S1]O1 108.57(8), Se1]S1]O2 108.35(8), Se1]S1]O3 108.28(9)

ISSN:1477-9226    

DOI:10.1039/a707328c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, Pages 5–6 5 A novel two-dimensional rectangular network. Synthesis and structure of {[Cu(4,49-bpy)(pyz)(H2O)2][PF6]2}n (4,49-bpy 5 4,49-bipyridine, pyz 5 pyrazine) Ming-Liang Tong,a Xiao-Ming Chen,*,a Xiao-Lan Yu a,b and Thomas C. W. Makb a Department of Chemistry, Zhongshan University, Guangzhou 510275, China b Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong The complex {[Cu(4,49-bpy)(pyz)(H2O)2][PF6]2}n comprising two-dimensional rectangular grids with each cavity enclosed by two 4,49-bipyridine (4,49-bipy) and two pyrazine (pyz) ligands, which superpose in an off-set fashion to give smaller rectangular channels, has been prepared and characterized by single-crystal X-ray structural analysis.Considerable research effort has been focused on the crystal engineering of supramolecular architectures organized by coordinate covalent or hydrogen bonding.1,2 So far a number of one-, two- and three-dimensional infinite frameworks have already been generated with linear N,N9 bidentate spacers.3–9 However, the above-mentioned frameworks are virtually all formed by only one type of bridging ligand; only three infinite frameworks containing two different types of ligand as edges have been reported,9,10 and two of them are triply interpenetrating frameworks.We have initiated a synthetic strategy for the preparation of non-interpenetrating open-frameworks with variable cavities or channels, in which the rod-like rigid spacers such as 4,49-bipyridine (4,49-bpy), pyrazine (pyz) and related species are chosen as building blocks.11 In the present work, we report the preparation and crystal structure of a novel twodimensional rectangular grid constructed simultaneously by 4,49-bpy and pyz ligands, namely {[Cu(4,49-bpy)(pyz)(H2O)2]- [PF6]2}n 1.Complex 1 was synthesized by self-assembly of CuII ions with 4,49-bpy and pyz ligands, as shown in Scheme 1.An alcoholic solution (10 cm3) of pyz (0.080 g, 1.0 mmol) was added dropwise to a stirring aqueous solution (5 cm3) of Cu(NO3)2?6H2O (0.296 g, 1.0 mmol) at 50 8C for 15 min. An alcoholic solution (10 cm3) of 4,49-bpy (0.156 g, 1.0 mmol) was then added and followed by NaPF6 (0.336 g, 2.0 mmol). The resulting blue solution was allowed to stand in air at room temperature for 5 d, yielding deep blue block crystals (65% yield). The elemental Scheme 1 N N Cu Cu N N N N Cu Cu N N N N CuII + + N N EtOH–H2O (the aqua ligands are omitted) * E-Mail: cedc03@zsu.edu.cn analysis and IR spectrum confirmed the formula of 1.† It is noteworthy that no product of square grids based on Cu(4,49- bpy)2 or Cu(pyz)2 has been observed, which could in principle be produced in the reaction.X-ray crystallography ‡ has established that complex 1 is made up of a two-dimensional rectangular network and PF6 2 anions. As illustrated in Fig. 1, each layer consists of perfectly ideal planar rectangles with a CuII ion, a 4,49-bpy and a pyz at each corner and side, respectively, two pyridyl rings of each 4,49-bpy ligand are twisted by 66.5(1)8. The inner rectangular cavity is hydrophobic and has dimensions of 6.83 × 11.15 Å, which are comparable to those of related compounds.4b,10 The CuII ion has an elongated octahedral geometry with two pyridyl [Cu]N 2.045(3) Å] and two pyz groups [Cu]N 2.036(3) Å] at the equatorial positions and two water molecules [Cu]O 2.445(3) Å] at the axial positions (Fig. 1). The off-set superposition of each pair of adjacent layers by half of the longer edges divides the voids into smaller rectangular channels (ca. 5.6 × 6.8 Å) as Fig. 1 An ORTEP14 drawing (at 35% probability level) of the rectangular units in complex 1 † (Found: C, 27.10; H, 2.45; N, 9.15. Calc. for C14H16CuF12N4O2P2 1: C, 26.88; H, 2.58; N, 8.96%). IR data (n& /cm21): 3620s, 3557m, 3423m (br), 3135w, 3071w, 1644s, 1609vs, 1539w, 1496w, 1426s, 1222s, 1173w, 1124m, 1075s, 1018w, 835vs (br), 646m, 561vs, 477m. ‡ Crystal data for complex 1: C14H16CuF12N4O2P2, M = 625.79, orthorhombic, space group Ibam (no. 72), a = 14.756(3), b = 11.149(2), c = 13.656(3) Å, U = 2246.6(8) Å3, Z = 4, Dc = 1.850 g cm23, m = 1.234 cm21. Data collection (2.88 < q<26.78) was performed at 293 K on a Siemens P4 diffractometer (Mo-Ka, l = 0.710 73 Å). The structure was solved with direct methods (SHELXTL-PC)12 and refined with fullmatrix least-squares technique (SHELXL 93)13 to final R1 value of 0.0469 for 87 parameters and 1164 unique reflections with I > 2s(I) and wR2 of 0.1495 for all 1184 reflections.CCDC reference number 186/800.6 J. Chem. Soc., Dalton Trans., 1998, Pages 5–6 shown in Fig. 2, which are similar to those found in A-zeolites and Pentasil zeolites.15 The PF6 2 anions are located in these channels, and each PF6 2 anion forms two accepter hydrogen bonds with two adjacent aqua ligands [O? ? ? F 2.848(4) Å].It is noteworthy that complex 1 is to our knowledge the first example of a two-dimensional framework that is sustained by the self-assembly of two different types of linear bidentate N,N9-donor ligands. Although the porous structures with designable pore sizes are in principle achievable via crystal engineering, interpenetration or self-inclusion commonly occur in these frameworks with voids of large volume, thereby reducing the pore size.4a,5,8a,9 The self-assembly of these frameworks is also highly influenced by factors such as the solvent system,1a template 8c,11,16 and steric requirement of the counter ion;17 the failure to prepare molecular rectangles containing 4,49-bpy and pyz edges is thus not surprising.3 In this sense, the exploration of the synthetic strategies and routes is therefore a long-term challenge.Much work is required to extend the knowledge of the relevant structural types and establish proper synthetic strategies leading to the desired species.The isolation of complex 1 suggests the possibility of constructing similar rectangular frameworks with divalent metal salts and two types of ligand under the appropriate conditions. Acknowledgements This work was supported by the National Natural Science Fig. 2 Top view showing the rectangular channels in complex 1. Carbon and hydrogen atoms are omitted for clarity, the 4,49-bpy and pyz molecular rods are shown as single bold lines Foundation of China (No. 29625102) and a Hong Kong Research Grants Council Earmarked Grant No. CUHK 89/ 93E. References 1 (a) R. Robin, B. F. Abrahams, S. R. Batten, R, W. Gable, B. F. Huskiness and J. Lieu, Supramolecular Architecture, ACS publications, Washington, DC, 1992, p. 256; (b) J. M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995, ch. 9. 2 C. B. Aakeroy and K. R. Seddon, Chem. Soc. Rev., 1993, 397. 3 R. V. Slone, J. T. Hupp, C.L. Stern and T. E. Albrecht-Schmitt, Inorg. Chem., 1996, 35, 4096. 4 (a) L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, J. Chem. Soc., Chem. Commun., 1994, 2755; (b) O. M. Yaghi and H. Li, J. Am. Chem. Soc., 1995, 117, 10 401. 5 G. B. Gardner, D. Venkataraman, J. S. Moore and S. Lee, Nature (London), 1995, 374, 792. 6 R. W. Gable, B. F. Hoskins and R. Robson, J. Chem. Soc., Chem. Commun., 1990, 1677; M. Fujita, Y. J. Kwon, S. W. Ashizu and K. Ogura, J. Am. Chem. Soc., 1994, 116, 1151; X.-M.Chen, M.-L. Tong, Y.-J. Luo and Z.-N. Chen, Aust. J. Chem., 1996, 49, 835; A. J. Blake, S. J. Hill, P. Hubberstey and W. S. Li, J. Chem. Soc., Dalton Trans., 1997, 913. 7 O. M. Yaghi and H. Li, J. Am. Chem. Soc., 1996, 118, 295. 8 (a) M. Fujita, Y. J. Kwon, Y. O. Sasaki, K. Yamaguchi and K. Ogura, J. Am. Chem. Soc., 1995, 117, 7287; (b) P. Losier and M. J. Zaworotko, Angew. Chem., Int. Ed. Engl., 1996, 35, 2779; (c) T. L. Hennigar, D. C. MacQuarrie, P. Losier, R. D. Rogers and M. J. Zaworotko, ibid., 1997, 36, 972. 9 T. Soma, H. Yuge and T. Iwamoto, Angew. Chem., Int. Ed. Engl., 1994, 33, 1665. 10 S. Kawata, S. Kitagawa, M. Konda, I. Furuchi and M. Munakata, Angew. Chem., Int. Ed. Engl., 1994, 33, 1759. 11 M.-L. Tong, B.-H. Ye and X.-M. Chen, unpublished work. 12 G. M. Sheldrick, SHELXTL-PC User’s Manual, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1990. 13 G. M. Sheldrick, SHELXL 93, Program for X-Ray Crystal Structure Refinement, University of Göttingen, 1993. 14 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 15 W. Hölderich, M. Hesse and F. Näumann, Angew. Chem., Int. Ed. Engl., 1988, 27, 226. 16 J.-M. Li, H.-Q. Zeng, J.-H. Chen, Q.-M. Wang and X.-T. Wu, Chem. Commun., 1997, 1213. 17 L. Carlucci, G. Ciani, D. M. Proserpio and A. Sironi, Angew. Chem., Int. Ed. Engl., 1995, 34, 1895. Received 1st September 1997; Communication 7/06363F

ISSN:1477-9226    

DOI:10.1039/a706363f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 7–13 7 Organophosphoryl derivatives of trivacant tungstophosphates of general formula ·-A-[PW9O34(RPO)2]52: synthesis and structure determination by multinuclear magnetic resonance spectroscopy (31P, 183W)‡ Cédric R. Mayer and René Thouvenot *,† Laboratoire de chimie des métaux de transition, URA CNRS 419, case 42, Université Pierre et Marie Curie, 4 place Jussieu, F75252 Paris cedex 05, France In the presence of NBun 4Br acting as phase-transfer reagent, organophosphonic acids RPO(OH)2 reacted in acetonitrile with the trivacant tungstophosphate sodium salt b-A-Na8[HPW9O34]?24H2O to give hybrid organophosphoryl polyoxotungstate derivatives a-A-[NBun 4]3Na2[PW9O34(RPO)2] (R = Et 1, Bun 2, But 3, allyl 4 or Ph 5) in satisfactory yield (>65%).The structure of the hybrid anions has been inferred from spectroscopic data, especially from multinuclear (31P, 183W) NMR studies. In particular, the five-line (1:2:2:2:2) 183W spectrum indicates a lowering of the symmetry of the tungstophosphate framework from C3v to Cs.According to spectroscopic observations and chemical analyses, the hybrid anion consists of an a-A-[PW9O34] framework on which are grafted two RPO groups through P]O]W bridges. This structure displays two nucleophilic oxygen atoms at the polyoxotungstate surface and thus remains unsaturated. Derivatized polyoxometalates (POMs) have received increasing attention for the last twenty years owing to their potential in bifunctional catalysis.2 It has been recognized for a long time that the versatility of the polyoxometalates and their catalytic applications can be significantly increased by grafting organic and organometallic groups onto the polyoxometalate surface.Our group is currently engaged in the systematic investigation of the reactivity of organohalogenosilanes SiRX3 towards plurivacant polyoxotungstates.1,3 For example the trivacant Keggin tungstate anions [XW9O34]n2 (X = SiIV or GeIV, n = 10; X = PV or AsV, n = 9) yield organosilyl derivatives such as [XW9O34(ButSiOH)3](n 2 6)2 and [XW9O34(RSiO)3- (RSi)](n 2 6)2.Similarly, [AsW9O33(ButSiOH)3]32 is obtained from the trivacant species B-[HAsIIIW9O33]82. All these hybrid anions are built up on the polyoxometalate surface which becomes saturated by formation of six Si]O]W bridges connecting three organosilyl groups RSi (Fig. 1). By an appropriate choice of the organic part, e.g.with the help of polymerizable groups or by setting up coupling reactions, one can conceive the easy synthesis of polyoxometalate-based interconnected networks which could give rise to polymeric hybrid organic– inorganic materials. The reactivity of polyvacant polytungstates with organochlorostannanes was systematically investigated by Pope and co-workers:4 because of the preference of tin for six-coordination, the structures of organotin derivatives are different from those of organosilyl hybrids, for example in [{b- A-(PW9O34)}2(PhSnOH)3]1224a and [{a-A-(SiW9O34)}2- (BuSnOH)3]1424b three organostannyl groups are embedded in between two 9-tungsto anions.To the best of our knowledge, the reaction of polyvacant polytungstates with organophosphonic acids has not yet been investigated. Except for a unique study of Kim and Hill5 on PhPO derivatives of monovacant tungsto-phosphate and -silicate, the other reported RPO derivatives of POMs were obtained by self-assembly processes and present some new structural arrangements.6 The present paper reports the synthesis and spectroscopic study of RPO derivatives of the trivacant tungstophosphate [PW9O34]92.The structural charac- † E-Mail: rth@ccr.jussieu.fr ‡ Organic–inorganic hybrids based on polyoxometalates. Part 3.1 terization of these new species is achieved through a detailed multinuclear NMR investigation (31P, 183W) in solution. Results A suspension of powdered b-A-Na8H[PW9O34]?24H2O7 in an acetonitrile solution of organophosphonic acid RPO(OH)2 (R = Et, Bun, But, allyl or Ph) and tetra-n-butylammonium bromide NBun 4Br was acidified with hydrochloric acid.After filtration and subsequent evaporation to dryness a white solid was obtained which was recrystallized from dimethylformamide (dmf). The compounds were characterized in the solid state by infrared spectroscopy and in solution by multinuclear magnetic resonance.Elemental analyses are consistent with the formula [NBun 4]3Na2[PW9O34(RPO)2]?xdmf (R = Et 1, Bun 2, But 3, allyl 4 or Ph 5; x = 0, 0.5 or 1). Infrared characterization The infrared spectra of all the compounds are very similar. A representative spectrum of 5 is shown in Fig. 2 and all data are given in Table 1. The low-wavenumber part (n& < 1000 cm21) is characteristic of the polyoxometalate framework.8 The stretching vibrational bands [nasym(W]Ob]W) and nasym(W]] Oter)] are shifted to higher frequency, compared to those of the starting trivacant [PW9O34]92 anion (Table 1).This effect, previously observed for organosilyl derivatives of trivacant polyoxotungstates,1,3 is attributed to a partial saturation of the polyoxometallic moiety through the fixation of RPO units. Moreover, the pattern of the 400–300 cm21 region is Fig. 1 Polyhedral representations of [PW9O34]92 and [PW9O34- (ButSiOH)3]328 J. Chem. Soc., Dalton Trans., 1998, Pages 7–13 Table 1 Infrared data (cm21) for [NBun 4]3Na2[PW9O34(RPO)2] and b-A-Na8H[PW9O34]?24H2O R Assignmenta n(P]C) nasym(P]O)b nasym(P]O)c nasym(W]] Oter) nasym(W]Ob]W) dasym(O]P]O) dasym(W]Ob]W) Et 1153w 1091s 1026m 1005m 958vs 877vs 859vs 750vs 600vw 523m 377m 367m 330w Bun 1153w 1091s 1023m 1002m 959vs 877vs 858vs 751vs 596vw 527m 378m 369m 326w But 1175w 1090s 1034m 1012m 955vs 878vs 858vs 747vs 601vw 527m 379m 367m 333w Allyl 1155w 1090s 1024m 1002m 959vs 877vs 857vs 601vw 522w 376m 367m 333w Ph 1134w 1089s 1029w 1004w 957vs 877vs 850vs 750vs 601w 527w 377m 369m 334w b-PW9 1056s 1014w 931vs 821vs 737vs 511w 363w 330m a Ref. 8. b PO4. c RPO. characteristic of the a isomer of the PW9O34 unit.9 The stretching vibration bands of the PO4 and RPO3 groups are observed between 1000 and 1100 cm21. As for the W]O modes, the high-frequency shift of the nasym(PO4) modes is indicative of the partial saturation of the polyoxometalate. 31P NMR characterization Each 31P NMR spectrum presents two lines with a relative intensity of 2 : 1 (Fig. 3). Integration was carried out on protoncoupled spectra, with interpulse delays allowing full relaxation of the nuclei. The high-frequency resonance, with the expected multiplicity according to R (see Fig. 3), is attributed to the RPO group. This line displays satellites due to heteronuclear coupling [2J(WP) ª 8 Hz, Table 2], which are most visible under protondecoupling conditions. Integration of these satellites with respect to the central line 10 shows that the P atom is connected to two tungsten atoms of the polyoxotungstate framework.The low-frequency singlet (d 211.46 ± 0.2 for all R) of relative intensity 1 is assigned to the central PO4 unit of the polyoxotungstate. 7 This chemical shift, which is intermediate between Fig. 2 Part of the IR spectrum (n& < 1750 cm21) of [NBun 4]3Na2- [PW9O34(PhPO)2] Table 2 The 31P NMR data a for [PW9O34(RPO)2]52 anions R Relative PW9O34 RPO Et 211.36 34.23 (7.9) Bun 211.26 33.37 (7.9) But 211.23 36 (7.6) Allyl 211.51 27.33 (7.9) Ph 211.66 17.82 (8.5) intensity b 1 2 a Chemical shifts in ppm relative to 85% H3PO4, 2J(WP) in Hz in parentheses.b Measured on fully relaxed undecoupled spectra. that of the starting anion [PW9O34]92 (d 25, in the solid state) 11 and that of [PW9O34(ButSiOH)3]32 (d 215.9),1 is in accordance with a partially saturated tungstophosphate structure. 183W NMR characterization The 183W NMR spectra of all species exhibit the same 1:2:2:2:2 pattern, consistent with Cs symmetry of the PW9O34 framework (Fig. 4). All the signals present several satellites due to homonuclear tungsten–tungsten couplings. However, because of overlapping of these satellites, the determination of the 2J(WW) coupling constants required broad-band 31P decoupling in order to suppress the multiplicity (see below). The three high-frequency lines appear as doublets due to the small coupling [2J(WP) < 2 Hz] with the central phosphorus atom of the PW9O34 unit (Table 3).The two remaining (lowfrequency) signals appear as doublets of doublets (Fig. 5); the smaller coupling [2J(WP) ª 1.5 Hz] is similar to the previous one and the stronger coupling (6–9 Hz) corresponds to the m-oxo junction W]O]P with the phosphorus atom of the RPO groups. For all species, the most shielded signal presents a significantly larger coupling (8–9 Hz) than the other one (6–8.5 Hz) (Table 3).These values are consistent with those observed by 31P NMR spectroscopy (see above). Assignment of heteronuclear couplings was confirmed by selective 31P decoupling experiments: by irradiating at the resonance frequency of the phosphonate group both low-frequency signals become doublets [keeping the small coupling 2J(WP) ª 1.5 Hz] while the other signals are unchanged. Discussion Syntheses The trivacant polyoxotungstate b-A-[PW9O34]92 reacts readily Fig. 3 Proton-coupled 31P NMR spectrum of a mother solution of [NBun 4]3Na2[PW9O34(EtPO)2] (pulse angle 258, acquisition time 0.8 s, relaxation delay 5 s) with expansion of the high-frequency line showing the tungsten satellitesJ.Chem. Soc., Dalton Trans., 1998, Pages 7–13 9 Table 3 The 183W NMR data a for [PW9O34(RPO)2]52 anions R Assignmentb W(1) W(6),W(7) W(2),W(3) W(4),W(9) W(5),W(8) Et 242.8 294.6 2140.0 2189.0 (6.1) 2193.8 (7.9) Bun 241.5 294.1 2138.5 2190.8 (6.6) 2193.3 (8.0) But 244.2 296.8 2141.6 2180.0 (6.4) 2190.4 (7.9) Allyl 239.9 293.9 2137.6 2191.3 (7.1) 2192.3 (7.9) Ph 240.4 292.5 2138.6 2191.1 (8.5) 2192.9 (9.0) Relative intensity 1 2 2 2 2 a Chemical shifts in ppm, 2J(WP) in Hz in parentheses (only coupling with RPO).b Numbering of the atoms, corresponding to structure I of Scheme 1. with electrophilic organophosphonic acids to yield hybrid organic–inorganic species [PW9O34(RPO)2]52. As for organochlorosilanes, 1,3 the reaction with organophosphonates proceeds under phase-transfer conditions with NBun 4 1 acting as phase-transfer agent, equation (1).After filtration of a white b-A-[PW9O34]92 1 2RPO(OH)2 1 4H1 MeCN NBun 4Br [PW9O34(RPO)2]52 1 4H2O (1) 1–5 solid consisting of NaCl, NaBr and a small amount of unchanged sodium polyoxotungstate, the acetonitrile solution contains a single hybrid anionic species, as shown by 31P NMR spectroscopy (see above), which has been isolated in high yield (ca. 70%) as its tetrabutylammonium salt.It can be recrystallized from a saturated dimethylformamide solution giving small well shaped plaquettes. Unfortunately all crystals (whatever R) appeared to be twinned and all our attempts to obtain suitable crystals for X-ray analyses (from other solvents and with other cations) were unsuccessful. The molecular structure of the hybrid anion is therefore derived from the spectroscopic results. Infrared spectroscopy The IR spectra of compounds 1–5 are nearly superimposable in the low-wavenumber (n& < 1000 cm21) region which is characteristic of the W]O stretching and bending vibrations.8 By comparison with b-A-Na8H[PW9O34]?24H2O, the vibrational bands of [NBun 4]3Na2[PW9O34(RPO)2] appear relatively narrow, as is Fig. 4 A 12.5 MHz 183W-{31P} NMR spectrum of [NBun 4]3Na2- [PW9O34(ButPO)2] in dmf–(CD3)2CO (0.3 M, pulse angle 908; acquisition time 1.64 s; number of scans 24 000; total acquisition time 11 h). The abscissa expansion of the d 244.2 and 296.8 lines shows the tungsten satellites (digital resolution 0.15 Hz per point after 24 K points zero filling).The asterisk indicates [PW12O40]32 impurity usually observed for tetrabutylammonium salts of polyoxometalates (Fig. 2).12 Moreover the bands are shifted to higher wavenumbers which is indicative of saturation of the polyoxotungstate framework. In addition, it appears that the fixation of the phosphonate groups induces a b æÆ a isomerization of the PW9O34 structure; this effect, deduced from the characteristic pattern in the 400–300 cm21 region,9 was also observed for organosilyl derivatives.1,3 31P NMR spectroscopy The attachment of phosphonate groups onto the polyoxotungstate surface is demonstrated by the presence of tungsten Fig. 5 Expansion of the d 2189 line of the 12.5 MHz 183W NMR spectrum of [NBun 4]3Na2[PW9O34(EtPO)2] in dmf–(CD3)2CO: (a) undecoupled, (b) selectively 31P decoupled (irradiation at the PW9O34 resonance) and (c) selectively 31P decoupled (irradiation at the EtPO resonance)10 J.Chem. Soc., Dalton Trans., 1998, Pages 7–13 Scheme 1 Representation of the four possible structures for the [PW9O34(RPO)2]52 anion, based on a-A-PW9O34 (I,II) and b-A-PW9O34 (III, IV) units. For the polyoxotungstate framework in the plane representation, heavy and thin lines represent edge and corner junctions between adjacent octahedra respectively. The dashed lines correspond to peculiar corner junctions with expected low 2J(WW) coupling constants (trans influence) satellites [2J(WP) ª 8 Hz] around the high-frequency [d 118 (5)–36 (3)] organophosphonate resonance.The relative intensity of these satellites with respect to the central line indicates that each RPO group is linked to two W atoms through two W]O]P bridges (Itheor = 24.6, Iexp ª 25%).10 Moreover the 31P NMR spectra of compounds 1–5 are consistent with the grafting of only two phosphonate groups. Indeed, for all R, the integration of the phosphonate resonance with respect to the phosphate resonance indicates a ratio of two RPO groups per polyoxometalate, which is consistent with the chemical analysis.This result is rather surprising, as in the case of the organosilyl derivatives of PW9O34 three RSi groups are simultaneously linked to the tungstophosphate framework. Partial ‘saturation’ of the polyoxotungstate surface in RPO derivatives is also revealed by the chemical shift of the PO4 unit (d 211.5) which is less shielded than in the ‘saturated’ organosilyl species [PW9O34(ButSiOH)3]32 (d 215.9).1 183W NMR spectroscopy The 183W NMR spectra of compounds 1–5 are also consistent with the loss of the ternary symmetry of the PW9O34 framework.Actually, five lines (1:2:2:2:2) are observed for all organophosphonate derivatives which is in agreement with Cs symmetry for the PW9O34 unit. Four different Cs structures can be considered (Scheme 1); two are based on a b-A-PW9O34 moiety (III, IV) and two on a a-A-PW9O34 moiety (I, II) with each RPO fragment linked either to a ditungsten group (I, III) or to two W atoms belonging to adjacent diads (II, IV).All resonances have been assigned for the But derivative 3, with the following guideline: homonuclear tungsten–tungsten couplings 2J(WW) are less than 10 Hz for nuclei belonging to the same di- or tri-metallic group, and of the order of 20 Hz in Scheme 2 The trans influence and its consequences on homonuclear 2J(WW) coupling constants (Oter = terminal oxygen, Ob = m-bridging oxygen) Oter Ob Oter Ob 150° 190pm 190pm Oter W O Ob Oter W Oter 150° 210pm 190pm Saturated anion 2 J(W-W) » 20Hz Lacunary anion 2 J(W-W) <10Hz the other cases,13 except for W]O]W bridges trans to a W]] Oter group [2J(WW) < 10 Hz]. The trans influence in polyoxotungstates.The first unambiguous assignment of 183W NMR spectra of polyoxotungstates relied on the differences in homonuclear tungsten–tungsten coupling constants: indeed Brévard and co-workers 13a observed rather small 2J(WW) coupling constants (10 Hz or less) for edge junctions, with W]O]W angle of about 1208, with respect to corner junctions, with W]O]W about 145–1508 [2J(WW) ª 20 Hz].It was shown later that more open m-oxo bridges such as those in Dawson-type polyoxotungstates (W]O]W about 1608) display even larger coupling constants (ª30 Hz).14 This correlation between 2J(WW) and the W]O]W angle holds only for saturated polyoxotungstates, with nearly symmetrical W]O]W bridges (both W]O bonds ª190 pm).In lacunary derivatives the W]O]W bridge trans to a W]] Oter group is dissymmetrical, displaying a long W]O bond, in the range of 210–220 ppm (trans influence). Consequently, the coupling constant through the corresponding bridge is significantly reduced (Scheme 2).10,15 For example a corner-junction coupling as small as 4.9 Hz has been observed in the 183W NMR spectrum of the divacant lacunary anion g-[SiW10O36]82.15 The normal coupling constant is recovered by filling the lacuna.15b,16 Assignments. The less-shielded resonance, with relative intensity one (d 241.3 ± 1.3), is unambiguously assigned to the tungsten atom W(1) lying in the plane of symmetry.Under 31P decoupling (Fig. 4), two pairs of satellites, with two different homonuclear coupling constant values [2J(WW) ª 7.3 and 24.4 Hz], are observed around this line.When considering the four different proposed structures (Scheme 1), in two of them (II, III) the W(1) atom is connected to W(4) [º W(9)] which carries two terminal oxygen atoms. According to the trans influence, the corresponding coupling constant would be relatively low and W(1) should contract two small couplings. Thus, the exceptionally large value (24.4 Hz) is inconsistent with structures II and III. Only the two remaining structures I and IV may account for the large 2J(WW) constant, owing to the presence of a heteronuclear P]O]W bridge between the phosphonate group and the W(4) atom.Consistently the small coupling constant (7.3 Hz) corresponds to the W(1)]O]W(2) [º W(1)]O]W(3)] bridge (a ª 1208) in the trimetallic group.13aJ. Chem. Soc., Dalton Trans., 1998, Pages 7–13 11 Table 4 The 183W chemical shifts/coupling constants connectivity matrix for [PW9O34(ButPO)2]52 * W(1) W(6),W(7) W(2),W(3) W(4),W(9) W(5),W(8) W(1) 244.2 7.3 24.4 W(6),W(7) 296.8 11.3 27.6 W(2),W(3) 7.5 11.3 2141.6 24.4 W(4),W(9) 24.4 2180.0 6.7 W(5),W(8) 27 24.1 6.3 2190.4 *Diagonal terms: chemical shifts, d.Off-diagonal terms: 2J(WW) in Hz. Numbering of the atoms as in structure I of Scheme 1. Unfortunately the other 183W resonance lines appear relatively broad even under 31P decoupling (Dn2� 1 ª 3–5 Hz). This prevents an accurate determination of the small tungsten– tungsten couplings, as the corresponding satellites appear generally as shoulders at the foot of the central resonance.The large couplings are more easily observed: indeed, all four remaining lines present satellites with 2J(WW) > 20 Hz. However, a coupling constant of nearly the same value (24–25 Hz) is observed for three resonances. Thus, the assignment of W(4) [º W(9)] is not possible on the basis of 2J(W1W4) [º 2J- (W1W9)] = 24.4 Hz. To proceed further with the assignment, we should consider the two most shielded resonances; they appear as doublets of doublets due to heteronuclear 2J(WP) couplings with the phosphorus atom of the PW9O34 moiety (J ª 2 Hz) and that of one RPO group (J ª 6–9 Hz, depending on R).These lines should be assigned to the two pairs W(4) [º W(9)] and W(5) [º W(8)] of the structures I and IV. Under broad-band 31P decoupling, the outermost line presents two pairs of tungsten satellites with large couplings [2J(WW) ª 24 (1W) and 27 Hz (1W)], whereas the second line exhibits only one pair of such satellites [2J(WW) ª 24 Hz (1W)] (Table 4, Fig. 4). Considering structure IV one would expect two strong couplings for both W(4) [º W(9)] and W(5) [º W(8)] pairs; therefore this structure can be ruled out and I remains as the only one consistent with the observed spectra. Consequently, the outermost line corresponds to W(5) and the second to W(4) with an observed homonuclear coupling constant [2J(W1W4) º 2J(W1W9) ª 25 Hz] consistent with the value (24.4 Hz) observed for the W(1) atom (see above).Among the two remaining lines, the one at about d 2140 clearly presents three pairs of satellites [2J(WW) ª 7.5, ª 11 and 24.5 Hz] while that around d 295 exhibits only two pairs (even with resolution enhancement) (Fig. 4). The latter therefore corresponds to W(6) [º W(7)], which is connected to W(5) through a strong coupling (ª27 Hz) and to W(2) [º W(3)] through a medium coupling (ª11 Hz). For two tungsten nuclei belonging to corner-sharing octahedra (W]O]W ª 1508), this relatively small coupling constant is consistent with the already mentioned trans influence (see above).Finally, assignment of the last line (d 2140) to W(2) is consistent with the observed coupling constants 2J(W1W2) [º 2J(W1W3)] = 7.3, 2J(W2W6) [º 2J(W3W7)] = 11.3 and 2J(W2W5) [º 2J(W3W8)] = 24.4 Hz respectively. Heteronuclear 2J(WP) couplings. The heteronuclear 2J(WP) coupling constants follow a pattern similar to that of the homonuclear 2J(WW): the coupling constant through the m-oxo bridge depends on the bridge angle and on both P]O and W]O distances. Mainly as a result of the long W]O bonds (ª230–240 pm) involving oxygen atoms of the central PO4 tetrahedron, the corresponding coupling constants are generally small (less than 2 Hz).One should notice that the two resonances of the tungsten atoms belonging to the trimetallic group W(1)–W(3) display a particularly small coupling constant with the central phosphorus nucleus (<1 Hz) whereas this constant is signifi- cantly larger (ª2 Hz) for the three other resonances. Such a decrease of 2J(WP) through mn]O bonds with increasing n is generally observed for phosphorus-centered Keggin and Dawson polyoxometalates.14,17 The phosphonate groups are connected to the polyoxotungstate framework through m-O oxygen atoms.Therefore the 2J(WP) coupling constants along these bridges are relatively large, of the order of 6–9 Hz. However they remain signifi- cantly smaller than those observed by Kim and Hill 5 for the phenylphosphonate derivatives of monovacant lacunary anions [PW11O39]72 and [SiW11O39]82 [2J(WP) ranging from 15 to 30 Hz].In the absence of any metrical parameter for our species, one can only speculate about the origin of these differences: although the anionic charge of the trivacant anion [PW9O34]92 is higher than that of the monovacant anion [PW11O39]72, the charge density is expected to be lower at each of the six oxygen atoms of the former species compared to the four oxygen atoms of the latter.Consequently the less nucleophilic O atoms of the trivacant anion should form weaker bonds with the phosphonate group. It should be noticed that a similar trend in heteronuclear coupling constants has been observed for organosilyl derivatives of lacunary polyoxotungstates: 2J(W]Si) is 6–7 Hz for the compounds derived from the trivacant anions a-A-[PW9O34]92 and a-A-[SiW9O34]102,1,3 whereas a coupling constant of 16.7 Hz has been reported for the vinylsilyl derivative of the monovacant tungstosilicate [SiW11O39]82.18 For [Xn1W11O39(PhPO)2](8 2 n)2 (Xn1 = P51 or Si41) two coupling constants 2J(WP) of 14–15 and 26–27 Hz were reported, corresponding to two different P]O]W bridges, with tungsten atoms belonging either to a diad or to a triad.5 Two different coupling constants 2J(WP) are also observed for [PW9O34- (RPO)2]52 (Table 3).However the differences are relatively small [2J(W4P) = 6–8.5, 2J(W5P) = 8–9 Hz] and arise only in the 183W NMR spectra.Indeed, according to the proposed structure, the bridge between the phosphonate group and the tungsten nuclei W(4) is not symmetrically related to that between the phosphonate group and the tungsten nuclei W(5). The different coupling constants 2J(WP) might reflect a slightly larger P]O]W angle or a shorter P]O bond in the (R)P]O]W(5) bridge than in the (R)P]O]W(4) bridge. Homonuclear 2J(WW) couplings.As a result of the low symmetry of the [PW9O34(RPO)2]52 anions, different tungsten– tungsten coupling constants are observed in the 183W NMR spectra. Compared to those of the organosilyl derivatives, the coupling constants involving the W atoms of the triad W(1)– W(3) and the tungsten atoms connected to the phosphonate are relatively large (25 compared to 22 Hz). The large coupling constants 2J(W5W6) [º 2J(W7W8)] should be considered together with the smalr one 2J(W2W6) [º 2J(W3W7)].Actually a redistribution of the homonuclear tungsten–tungsten coupling constants in the vicinity of a cis-WO2 unit has been observed in any case of a small corner coupling induced by trans influence. For example, in the monovacant polyoxotungstate [SiW11O39]82 and polyoxomolybdotungstate [SiMo2W9O39]82, the cis-WO2 units display two peculiar corner-coupling constants: a small one (ª10 Hz) which involves the oxygen atom trans to Oter and a large one (>25 Hz) (Scheme 3).15b,19 The same effect has also been observed in monovacant lacunary anions of the Dawson structure.2012 J.Chem. Soc., Dalton Trans., 1998, Pages 7–13 Scheme 3 Comparison of 2J(WW) corner-coupling constants for saturated and monovacant lacunary Keggin polyoxotungstates 15b,19 In the present case, as for monovacant species, the redistribution of the homonuclear coupling constants might be interpreted by a geometrical rearrangement in the vicinity of the cis-WO2 groups.As a consequence of the trans influence, the tungsten atom is markedly displaced from the centre of the WO6 octahedron. Molecular models show that this might result in a relatively large W]O]W angle (>1508) for the second corner junction. Conclusion Despite all our efforts to grow suitable crystals of the RPO derivatives of [PW9O34]92, no X-ray diffraction study was possible. Nevertheless the molecular structure of the hybrid anion can be confidently deduced from the spectroscopic data (Fig. 6). This anion consists of an a-A-PW9O34 unit on which are grafted two RPO groups through two P]O]W bridges. As for the analogous organosilyl derivatives, each RPO group is connected to two W atoms belonging to the same dimetallic unit (diad). However, contrary to organosilyl derivatives where the six nucleophilic oxygen atoms of the trivacant anion are saturated, the grafting of organophosphonates retains intact two oxygen atoms. Together with the two free oxygen atoms of the phosphonate groups, they define a new lacuna, for the binding of the two sodium cations revealed by chemical analysis.However the electrostatic interaction between Na1 and these oxygen atoms should be relatively weak so that the polyoxotungstate surface remains available to further electrophilic attack. Indeed the hybrid [PW9O34(RPO)2]52 anions react with trichloroorgano-silanes, -germanes and -stannanes to afford saturated derivatives. Work on this subject is in progress.Experimental General The compound b-A-Na8H[PW9O34]?24H2O was prepared according to the literature.7 Other reagents, [RPO(OH)2 and NBun 4Br] and solvents were from Aldrich and used as received. Elemental analyses were performed by the Service central de microanalyses du CNRS, Vernaison, France. The IR spectra (4000–250 cm21) were recorded on a Bio-Rad FTS 165 IR FT spectrometer with compounds sampled in KBr pellets, 13C (75.46) and 31P (121.5 MHz) NMR spectra at room temperature in 5 mm outside diameter tubes on a Bruker AC 300 spectrometer equipped with a QNP probehead.The chemical shifts are given according to the IUPAC convention, with respect to SiMe4 and 85% H3PO4 respectively. The 12.5 MHz 183W NMR spectra were recorded at 300 K on nearly saturated dmf–(CD3)2CO (90: 10, v/v) solutions in 10 mm outside diameter tubes on the same spectrometer equipped with a lowfrequency special VSP probehead. The chemical shifts are given with respect to 2 M Na2WO4 aqueous solution and were determined by the substitution method using a saturated D2O solution of tungstosilicic acid H4SiW12O40 as secondary standard Fig. 6 Polyhedral representation of the proposed structure for [PW9- O34(RPO)2]52 (R = Et)J. Chem. Soc., Dalton Trans., 1998, Pages 7–13 13 (d 2103.8). The 31P decoupling experiments were performed with a B-SV3 unit operating at 121.5 MHz and equipped with a B-BM1 broad-band modulator. Selective or broad-band decoupling was determined by appropriate choice of the synthesizer frequency and of the output power (4–40 W) before entering the decoupling coil of the low-frequency probehead.Preparations ·-A-[NBun 4]3Na2[PW9O34(EtPO)2] 1. The compounds b-ANa8H[ PW9O34]?24H2O (11.5 g, 4 mmol) and NBun 4Br (4.62 g, 14 mmol) were suspended in MeCN (50 cm3); EtPO(OH)2 (0.88 g, 8 mmol) was added under vigorous stirring, then HCl (1.36 cm3, 16 mmol) was added dropwise and the mixture stirred overnight at reflux.After separation of a white solid (NaCl, NaBr 1 traces of Na8H[PW9O34]), the white compound [NBun 4]3Na2[PW9O34(EtPO)2] was formed by evaporation of the resulting solution in a rotary evaporator. The crude compound was recrystallized from dmf. Yield: 8.5 g (67.5%) (Found: C, 20.22; H, 3.87; N, 1.30; Na, 1.34; P, 2.88, W, 51.10. Calc. for C52H118N3Na2O36P3W9: C, 19.80; H, 3.77; N, 1.33; Na, 1.46; P, 2.95; W, 52.44%). dC(75.46 MHz, solvent acetone, standard SiMe4) 22.73 [1C, d, J(PC) 147] and 7.25 [1C, d, J(PC) 6.49 Hz].·-A-[NBun 4]3Na2[PW9O34(BunPO)2]?dmf 2. This compound was similarly synthesized from b-A-Na8H[PW9O34]?24H2O (11.5 g, 4 mmol). NBun 4Br (4.62 g, 14 mmol), BunPO(OH)2 (1.1 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 8.9 g (67.4%) (Found: C, 21.12; H, 4.09; N, 1.74; Na, 1.36; P, 2.78; W, 49.75. Calc. for C59H133N4Na2O37P3W9: C, 21.58; H, 4.08; N, 1.71; Na, 1.40; P, 2.83; W, 50.38%). dC(75.46 MHz, solvent acetone, standard SiMe4) 27.90 [1C, d, J(PC) 146.5], 24.75 [1C, d, J(PC) 4], 23.0 [1C, d, J(PC) 7.1 Hz] and 12.65 (1C, s).·-A-[NBun 4]3Na2[PW9O34(ButPO)2]?0.5dmf 3. This compound was similarly synthesized from b-A-Na8H[PW9O34]? 24H2O (11.5 g, 4 mmol), NBun 4Br (4.62 g, 14 mmol), But- PO(OH)2 (1.1 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 9.0 g (68.1%) (Found: C, 21.14; H, 3.97; N, 1.43; Na, 1.41; P, 2.87; W, 51.16. Calc. for C57.5H129.5N3.5Na2O36.5P3W9: C, 21.27; H, 4.02; N, 1.51; Na, 1.42, P, 2.86; W, 50.95%).dC(75.46 MHz, solvent acetone, standard SiMe4) 33.04 [1C, d, J(PC) 148.3 Hz] and 26.29 (3C, s). ·-A-[NBun 4]3Na2[PW9O34(C3H5PO)2]?0.5dmf 4. This compound was similarly synthesized from b-A-Na8H[PW9O34]? 24H2O (11.5 g, 4 mmol), NBun 4Br (4.62 g, 14 mmol). C3H5PO(OH)2 (0.98 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 8.3 g (65.4%) (Found: C, 20.81; H, 3.81; N, 1.49; Na, 1.41; P, 2.82; W, 50.16. Calc. for C55.5H121.5N3.5Na2O36.5P3W9: C, 20.73; H, 3.81; N, 1.52; Na, 1.43; P, 2.89; W, 51.46%). dC(75.46 MHz, solvent acetone, standard SiMe4) 131.1 [1C, d, J(PC) 10.6], 115.8 [1C, d, J(PC) 15] and 34.42 [1C, d, J(PC) 146.0 Hz].·-A-[NBun 4]3Na2[PW9O34(PhPO)2] 5. This compound was similarly synthesized from b-A-Na8H[PW9O34]?24H2O (11.5 g, 4 mmol), NBun 4Br (4.62 g, 14 mmol), PhPO(OH)2 (1.26 g, 8 mmol) and HCl (1.36 cm3, 16 mmol). Yield: 9.2 g (71%) (Found: C, 21.79; H, 3.76; N, 1.27; Na, 1.39; P, 2.82; W, 49.96.Calc. for C60H118N3Na2O36P3W9: C, 22.17; H, 3.66; N, 1.29; Na, 1.41; P, 2.86; W, 50.89%). dC(75.46 MHz, solvent acetone, standard SiMe4) 136.5 [1C, d, J(PC) 147.5], 130.8 [2C, d, J(PC) 6], 129 (1C, s) and 127.72 [2C, d, J(PC) 9 Hz]. References 1 Part 2, A. Mazeaud, N. Ammari, F. Robert and R. Thouvenot, Angew. Chem., Int. Ed. Engl., 1996, 35, 1961; Angew Chem., 1996, 108, 2089. 2 See, for example, M. T. Pope and A. Müller, Angew. Chem., Int. Ed. Engl., 1991, 30, 34; Angew.Chem., 1991, 103, 56; Polyoxometalates: From Platonic Solids to Anti-Retroviral Activity, eds. M. T. Pope and A. Müller, Kluwer, Dordrecht, 1994. 3 N. Ammari, G. Hervé and R. Thouvenot, New. J. Chem., 1991, 15, 607; N. Ammari, Ph.D. Thesis, Université Pierre et Marie Curie, Paris, 1993. 4 (a) F. Xin and M. T. Pope, Organometallics, 1994, 13, 4881; (b) F. Xin, M. T. Pope, G. J. Long and U. Russo, Inorg. Chem., 1996, 35, 1207. 5 G. S. Kim and C. L. Hill, Inorg. Chem., 1992, 31, 5316. 6 P. R. Sethuraman, M. A. Leparulo, M. T. Pope, F. Zonnevijlle, C. Brévard and J. Lemerle, J. Am. Chem. Soc., 1981, 103, 7665; U. Kotz, B. Jameson and M. T. Pope, J. Am. Chem. Soc., 1994, 116, 2659. 7 R. Massart, R. Contant, J.-M. Fruchart, J.-P. Ciabrini and M. Fournier, Inorg. Chem., 1977, 16, 2916. 8 C. Rocchiccioli-Deltcheff, R. Thouvenot and R. Franck, Spectrochim. Acta, Part A, 1975, 32, 587. 9 R. Thouvenot, M. Fournier, R. Franck and C. Rocchiccioli- Deltcheff, Inorg. Chem., 1984, 23, 598. 10 R. Thouvenot, A. Tézé, R. Contant and G. Hervé, Inorg. Chem., 1988, 27, 524. 11 W. H. Knoth, P. J. Domaille and R. D. Farlee, Organometallics, 1985, 4, 62. 12 C. Rocchiccioli-Deltcheff, M. Fournier, R. Franck and R. Thouvenot, Inorg. Chem., 1983, 22, 207. 13 (a) J. Lefebvre, F. Chauveau, P. Doppelt and C. Brévard, J. Am. Chem. Soc., 1981, 103, 4589; (b) P. J. Domaille, J. Am. Chem. Soc., 1984, 106, 7677. 14 R. Contant and R. Thouvenot, Inorg. Chim. Acta, 1993, 212, 41. 15 (a) J. Canny, A. Tézé, R. Thouvenot and G. Hervé, Inorg. Chem., 1986, 25, 2114; (b) E. Cadot, R. Thouvenot, A. Tézé and G. Hervé, Inorg. Chem., 1992, 31, 4128. 16 A. Tézé, J. Canny, L. Gurban, R. Thouvenot and G. Hervé, Inorg. Chem., 1996, 35, 1001. 17 R. Acerete, C. F. Hammer and L. C. W. Baker, J. Am. Chem. Soc., 1979, 101, 267; R. Acerete, S. Harmalker, C. F. Hammer, M. T. Pope and L. C. W. Baker, J. Chem. Soc., Chem. Commun., 1979, 777; R. Acerete, C. F. Hammer and L. C. W. Baker, J. Am. Chem. Soc., 1982, 104, 5384; Inorg. Chem., 1984, 23, 1478; M. Abbessi, R. Contant, R. Thouvenot and G. Hervé, Inorg. Chem., 1991, 30, 1695. 18 P. Judeinstein, C. Deprun and L. Nadjo, J. Chem. Soc., Dalton Trans., 1991, 1991. 19 R. Contant, G. Hervé and R. Thouvenot, presented at the CNRSNSF polyoxometalate workshop, St-Lambert des Bois, 1983. 20 R. Thouvenot and R. Contant, unpublished work. Received 21st July 1997; Paper 7/05216B

ISSN:1477-9226    

DOI:10.1039/a705216b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 9–10 9 Construction of a unique three-dimensional array with cadmium(II)† Arunendu Mondal,a Golam Mostafa,b Ashutosh Ghosh,c Inamur Rahaman Laskar a and Nirmalendu Ray Chaudhuri *a a Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-700 032, India b X-Ray Crystallography Laboratory, Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-700 032, India c Department of Chemistry, University College of Science and Technology, Calcutta-700 009, India Received 8th September 1998, Accepted 11th November 1998 The complex [Cd3(dien)2(NCS)6]n?nH2O (dien 5 diethylenetriamine) is prepared and characterised by X-ray diffraction studies, which show a new type of threedimensional polymeric structure having cadmium centres which are linked to each other via NCS bridges in such a way that two types of Cd environment (one involving only N-donor atoms and the other only S-donor atoms) are produced.In search of molecular based materials with interesting properties such as catalysis, clathration etc. much attention has been given to the synthesis of one-, two- and three-dimensional extended solids involving cadmium.1–4 Rigid bridged ligands are frequently employed to construct these materials. The ambidentate thiocyanate ion which is usually S-bonded to a soft and N-bonded to a hard metal centre can also act as a bridging bidentate ligand to satisfy the coordination number of the metal ion, although the thiocyanate anion has not been widely used in the construction of inorganic polymeric networks. 5,6 In order to synthesise uncharged three-dimensional polymers7 where channels remain unblocked by anions and free for solvent inclusion, we have chosen cadmium(II) thiocyanate as an eVective building block. Cadmium is well suited for this as its d10 configuration permits a wide variety of geometries and coordination numbers.By utilising fully the bridging potential of the thiocyanate anion we have synthesised an inorganic coordination polymer with a Cd(NCS)2 : dien ratio of 3 : 2 (dien = diethylenetriamine). Single crystal X-ray structure analysis reveals that it is a new type of 3-D network which contains solvent filled channels. Channels containing solids have been and continue to be intensively investigated because of their actual and potential applications, for example as heterogeneous catalysts and molecular sieves. Another striking feature of the molecule is that the cadmium(II) ions which are linked to each other (via thiocyanate bridge) are alternatively hard (having only N-donor atoms) and soft (having only S-donor atoms) centres.The ligand (diethylenetriamine) (2 mmol) in methanol (5 cm3) was added dropwise with stirring to Cd(NCS)2 (3 mmol) dissolved in methanol (10 cm3). A sticky oily layer separated at the bottom of the container.The supernatant solution was filtered and the filtrate was kept in a CaCl2 desiccator for a few days at ª30 8C giving the polymer as shining transparent crystals in ª34% isolated yield. Elemental analysis supports the unusual stoichiometry of the compound. The structure determination ‡ reveals that the polymer has stoichiometry Cd3(dien)2(NCS)6?H2O having a three-dimensional infinite chain forming a large spherical molecule in which water molecules (Ow) are accommodated in interstitial positions which have a nearly rectangular shape of van der Waals dimensions 14.26 × 3.30 Å.The nearest atom to Ow is N1 [Ow? ? ? N1 4.090(6) Å]. A ZORTEP view with atom numbering scheme is shown in Fig. 1. Every cadmium atom Cd2, surrounded by six sulfur atoms, is linked to six other cadmium atoms Cd1 by thiocyanato bridges. Since the site symmetry of Cd1 is 3, its three sites of coordinating N1 atoms, are accordingly, related by symmetry.The primary nitrogen atoms N2 and the secondary nitrogen atom N3 of the tridentate dien ligand are also related by the same symmetry 3. As both N2 and N3 are in general positions, there are three symmetry related sites for each of them. These six sites (3 1 3) were envisaged to be occupied by three groups of two N2 atoms and one N3 atom with occupancy 2/3 for N2 atoms and 1/3 for N3 leading to a three-fold disorder about the [111] direction. Thus three N1 atoms, two symmetry related N2 atoms and one N3 atom complete the CdN6 chromophore.The geometry around the cadmium atom Cd2 is trigonally distorted octahedral and around Cd1 is distorted octahedral. The extended structure is represented in Fig. 2. It is noted that each cadmium atom Cd1, Fig. 1 ZORTEP14 plot of the complex showing the extended structure of Cd1 and Cd2 octahedra. Selected bond distances (Å) and angles (8): Cd1–N1 2.287(6), Cd1–N3 2.31(2), Cd1–N2 2.453(8), N1–C1 1.140(8), C1–S(i) 1.646(8), Cd2–S 2.711(2), N1–Cd1–N1(ii) 92.4(2), N1–Cd1–N3 103.7(5), N1–Cd1–N2 82.7(3), N3–Cd1–N2 70.6(5), C1–N1–Cd1 176.6(6), N1–C1–S(i) 179.8(5), S(iii)–Cd2–S(iv) 92.62(6), S(iii)–Cd2–S 87.38(6), S(v)–Cd2–S 180.0.Symmetry transformations to generate equivalent atoms: (i) y 2 1/2, 2z 1 1/2, x; (ii) y, z, x; (iii) 2y 1 1, 2z 1 1, 2x 1 1; (iv) 2z 1 1, 2x 1 1, 2y 1 1; (v) 2x 1 1, 2y 1 1, 2z 1 1.10 J. Chem. Soc., Dalton Trans., 1999, 9–10 which is coordinated by the N atoms of the dien ligand, is invariably linked with the hard atom N of the thiocyanate ion.In other words the N-atoms of the dien ligand “harden” Cd1, and so the thiocyanate bonds to it preferentially through the Natom. Conversely the soft end of each thiocyanate ion (S-atom) is coordinated to Cd2 making it “soft”. Thus all the S-atoms of the thiocyanate ion are clubbed together around Cd2. The NCS bridging between the Cd centres is quite common in Cd–amine complexes.8–11 The usual feature of these structures is that each Cd ion is coordinated by both N and S atoms.In the present compound, generation of two types of Cd environment, one involving only N-donor atoms and the other only S-donor atoms, is rather unique. There are six branches emanating from the centre Cd2. In each branch Cd2 is connected to Cd1 via NCS bridges. Every such Cd1 produces two other branches which are connected via NCS bridges to two other Cd2, each of which in turn produces five other branchings.The sequence in one branch can be written as Cd2–S–C1–N1–Cd1–N1*– C1* –S*–Cd2*. The Cd–N (2.287 Å for Cd–N1, 2.453 Å for Cd–N2 and 2.31 Å for Cd–N3) and Cd–S (2.711 Å) distances are comparable to corresponding values of other analogous octahedrally coordinated Cd complexes.12,13 The thiocyanate ligands are almost linear (179.88). Other bond distances and angles in the ligand are close to expected values. Acknowledgements The authors are grateful to the National Single Crystal Diffractometer Facility at the I.A.C.S.for providing single crystal Fig. 2 View of the polymeric array formed by [Cd3(dien)2(NCS)6]n? nH2O illustrating the water molecule (red) filled channel (Cd—blue; S— yellow; C—black; N—green; for clarity dien is not shown). data. Funding for the work described here was provided by the Council of Scientific and Industrial Research (New Delhi) Grants Scheme and is gratefully acknowledged. Notes and references † Supplementary data available: two views of the polymeric array formed by [Cd3(dien)2(NCS)6]n?nH2O including the disordered ligand.For direct electronic access see http://www.rsc.org/suppdata/dt/1999/ 9/, otherwise available from BLDSC (No. SUP 57459, 4 pp.) or the RSC Library. See Instructions for Authors, 1999, Issue 1 (http:// www.rsc.org/dalton). ‡ Crystal data for [Cd3(dien)2(NCS)6]n?nH2O: cubic, space group Pa3� , a = b = c = 14.871(4) Å, V = 3288.7(3) Å3, Z = 4, rcalc = 1.838 Mg m23, rm = 1.842 Mg m23, m(Mo-Ka) = 2.333 mm21, T = 295(2) K, no.of measured and independenteflections 2260 and 725, no. of reflections included in the refinement 725, s limits I � 2s(I), no. of parameters 71, R1 = 0.0360, wR2 = 0.0874, refined against F2. CCDC reference number 186/1252. See http://www.rsc.org/suppdata/dt/1999/9/ for crystallographic files in .cif format. 1 B. F. Abrahams, M. J. Hardie, B. F. Hoskins, R. Robson and E. E. Sutherland, J. Chem.Soc., Chem. Commun., 1994, 1049. 2 T. Soma, H. Yuge and T. Iwamoto, Angew. Chem., Int. Ed. Engl., 1994, 33, 1665. 3 M. Fujita, Y. J. Kwon, M. Miyazawa and K. Ogura, J. Chem. Soc., Chem. Commun., 1994, 1977. 4 H. Yuge and T. Iwamoto, Acta Crystallogr., Sect. C, 1995, 51, 374. 5 E. Bouwman, W. L. Driessen and J. Reedijk, J. Chem. Soc., Dalton Trans., 1988, 1337. 6 S. R. Petrusenko, V. N. Kokozay, O. Y. Vassilyeva and B. W. Skelton, J. Chem. Soc., Dalton Trans., 1997, 1793; J. Lu, T. Paliwala, S. C. Lim, C. Yu, T. Niu and A. J. Jacobson, Inorg. Chem., 1997, 36, 923; O.-S. Jung, S. H. Park, D. C. Kim and K. M. Kim, Inorg. Chem., 1998, 37, 610. 7 A. J. Blake, N. R. Champness, M. Crew, L. R. Hanton, S. Parsons and M. Schroder, J. Chem. Soc., Dalton Trans., 1998, 1533. 8 R. G. Goel, W. P. Henry, M. J. Olivier and A. L. Beauchamp, Inorg. Chem., 1981, 20, 3924. 9 M. B. Cingi, A. M. M. Lanfredi, A. Tiripicchio, J. G. Haasnoot and J. Reedijk, Acta Crystallogr., Sect. C, 1986, 42, 1509. 10 W. G. Haanstra, W. L. Driessen, J. Reedijk, U. Turpeinen and R. Hämäläinen, J. Chem. Soc., Dalton Trans., 1989, 2309. 11 A. Mondal, G. Mostafa, A. Ghosh and N. Ray Chaudhuri, J. Chem. Res., 1998, (S), 570. 12 F. A. Mautner, M. A. M. Abu-Youssef and M. A. S. Goher, Polyhedron, 1997, 16, 235. 13 M. Cannas, G. Carta, A. Cristini and G. Marongiu, Inorg. Chem., 1977, 16, 228. 14 L. Zsolnai, ZORTEP, A program for the presentation of thermal ellipsoids, University of Heidelberg, 1994. Communication 8/0699

ISSN:1477-9226    

DOI:10.1039/a806999i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 11–12 11 Chirality probing of amino alcohols with lanthanide complexes via induced circular dichroism spectroscopy Hiroshi Tsukube,*a Miwa Hosokubo,a Masatoshi Wada,a Satoshi Shinoda a and Hitoshi Tamiaki b a Department of Chemistry, Graduate School of Science, Osaka City University, Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan. E-mail: tsukube@sci.osaka-cu.ac.jp b Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan Received 21st August 1998, Accepted 13th November 1998 Achiral lanthanide tris(‚-diketonates) selectively formed 1:1 highly coordinated complexes with amino alcohols and the resulting complexes exhibited characteristic circular dichroism signals depending on the absolute configuration of the bound guests.Induced circular dichroism (CD) spectroscopy has proved useful for the assignment of the stereochemistry of chiral guest molecules.When a probe is achiral but chromophoric and a guest is chiral but nonchromophoric, only the probe–guest complex oVers induced CD which reflects the chirality of the guest. In this method, several micrograms of the guest are required without any chemical derivatization and these can be readily recovered. Although calixarenes, resorcinarenes, porphyrins and other achiral receptors have been successfully used,1 the number of eVective CD probes for sensing the chirality of specific guests remains limited.We present achiral lanthanide tris(b-diketonates) 1–3 as a new type of CD probe capable of specific binding and chirality sensing of amino alcohols (Fig. 1). Although the employed complexes are electronically neutral (as they contain three diketonate ligands), they often have neutral guests in addition to the diketonate ligands and form highly coordinated complexes.2 We demonstrate below that lanthanide complexes 1–3 selectively form 1: 1 complexes with amino alcohols and the resulting highly coordinated complexes exhibit characteristic CD signals depending on the absolute configuration of the bound amino alcohols.Several lanthanide complexes are employed as shift Fig. 1 Lanthanide tris(b-diketonates) 1–3 and reference probes 4 and 5. C(CH3)3 C O C CF2 O CF2 CF3 C(CH3)3 C O C CF2 O CF2 CF3 OH HO OH OH R R HO OH HO HO R R H H H H 3 Cu 2 1: M=Pr, 2: M=Gd, 3: M=Yb M 4 5: R = (CH2)10CH3 reagents in NMR spectroscopy, catalysts in organic synthesis, probes in fluorescence/MRI analysis and hydrolytic catalysts in protein and gene technology,3 but their receptor functions, particularly CD probe abilities, have rarely been characterized. Radzki and Giannotti reported UV spectroscopic studies demonstrating that some gadolinium porphyrins bound achiral amines, phenols and nucleic bases,4 and we also developed extraction systems of anionic and zwitterionic amino acids via lanthanide coordination chemistry.5 Here, we apply a series of lanthanide tris(b-diketonates) as specific CD probes to the chirality sensing of neutral amino alcohols of biological and chemical interest.6 Three lanthanide tris(b-diketonates) 1–3 were examined which have trivalent praseodymium, gadolinium and ytterbium ions as metal centers.Their receptor and CD probing functions were compared with those of the corresponding copper bis(bdiketonate) 4. The employed lanthanide ions have larger ionic radii (0.87–0.99 Å) 7 and higher coordination numbers (8–12) than those of transition metal cations.Chiral amine 6, alcohol 7, diol 8 and amino alcohols 9–14 were chosen as neutral guests which are nonchromophoric and CD silent under the conditions employed (>250 nm). Fig. 2 illustrates the CD spectra of the CH2Cl2 solutions containing several combinations of chiral guests 6–9 and achiral probes 3 and 4. Ytterbium tris(bdiketonate) 3 exhibited a split Cotton eVect in its CD spectrum as well as significant UV changes upon addition of the chiral amino alcohol 9.Since chiral monoamine 6, monoalcohol 7 and diol 8 did not induce any change in the UV or CD spectra of 3, it is concluded that the ytterbium tris(b-diketonate) 3 chemo-selectively formed a complex with chiral amino alcohol 9. The copper bis(b-diketonate) 4 did not give any perceptible CD or UV changes for guests 6–9. When the enantiomers (S)- and (R)-9 were compared, they aVorded symmetrical CD spectra in the presence of ytterbium complex 3, while they gave exactly the same UV changes.The achiral praseodymium and Fig. 2 CD Spectra of 3 and 4 in the presence of chiral guests (6, 7, 8 and 9). [3 or 4] = 3.5 × 1025 mol l21; [guest] = 3.5 × 1024 mol l21 in CH2Cl2.12 J. Chem. Soc., Dalton Trans., 1999, 11–12 gadolinium complexes 1 and 2 similarly acted as CD probes specific for chiral amino alcohol 9. The three lanthanide complexes employed produced induced CD signals with the same sign for amino alcohol 9 of the same configuration, and their amplitudes (Amp = [q at 1st l] 2 [q at 2nd l] × 1025 deg cm2 dmol21) were shown to be dependent on the size of the central metal cations: Pr31 (10.24) < Gd31 (10.83) < Yb31 (11.25) for (S)-9.This order indicates that the largest CD signal was observed in the complex with the smallest ion system. The UV and CD titration experiments confirmed 1: 1 complexation between amino alcohol and lanthanide tris(b-diketonates), and the stability constant (log K) was typically determined as 5.6 for the highly coordinated complex between 2 and 9 in CH2Cl2.Resorcinarene 5 was reported to form hydrogen-bonded complexes with chiral polyols and to oVer induced CD signals specific for their stereochemistry.1a This macrocycle operated for chiral amino alcohols, but the amplitude of the CD signals for (S)-9 (Amp < 0.1) was much smaller than that with lanthanide tris(b-diketonate) 1, 2 or 3 under the employed conditions. Thus, the present type of lanthanide complexes can be considered as being sensitive and selective CD probes for chiral amino alcohols.This CD probing method does not require any chemical modification of the guest and can be extended to various amino alcohols 10–14. Table 1 indicates that the absolute configurations of the six amino alcohols were well determined with ytterbium tris(b-diketonate) 3. The amino alcohols of the same Table 1 CD Data of amino alcohols with 3 in CH2Cl2 a Amino alcohol OH H H2N OH H H2N H H2N OH OH H H2N OH H H2N OH H NH 9 d 10 d 11 12 d 13 14 Configuration S S R S S S 1st l/nm (q) b 2nd l/nm (q) b 284 (10.57) 312 (20.68) 285 (10.67) 313 (20.87) 283 (20.60) 312 (10.71) 284 (11.12) 311 (21.22) 284 (10.83) 312 (20.97) 298 (10.25) 325 (20.24) Ampc 11.25 11.54 21.31 12.34 11.80 10.49 a Conditions: [3] = 3.5 × 1025 mol l21; [amino alcohol] = 3.5 × 1024 mol l21.b They are indicated as [q] × 1025/deg cm2 dmol21. c Amp = [q at 1st l] 2 [q at 2nd l]. d Their enantiomers showed mirror image CD spectra. configuration exhibited the same Cotton eVect sign, and the magnitude of the CD greatly depended on the nature of the attached substituent to the asymmetric carbon of the guest: 12 (Me2CH) > 13 (Me2CHCH2) > 10 (CH3) > 11 (MeCH2). Although the type of amino function (primary amine 9–13 vs. secondary amine 14) influenced the locations of the CD signals, their signs can be used as eVective probes for chirality and stereochemical assignments of the amino alcohols.As reported earlier,3b the lanthanide tris(b-diketonates) 1–3 caused serious broadening of the 1H NMR signals of all the guests examined. Thus, these achiral lanthanide complexes are not chemoselective probes and oVer no enantiomer-selective change in the NMR spectroscopy. When we applied them as CD probes, the situation dramatically changed.They preferred amino alcohols to amine, alcohol and diol guests and sensitively responded to their chirality.† Thus, further combinations of central lanthanide ions and achiral ligands can provide wide variations in the design of a new chirality sensory system for other important guests. Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research (No. 10440198) from the Ministry of Education, Science, Culture and Sports, Japan. Financial support from the Ritsumeikan University Foundation Memorial Trust Research Fund is also acknowledged. Notes and references † Chiral diamine, (S)-2-pyrrolidinemethylamine, also gave induced CD signals in the presence of lanthanide complexes, but their amplitudes were smaller than those with the corresponding amino alcohol 14. 1 (a) Y. Kikuchi, K. Kobayashi and Y. Aoyama, J. Am. Chem. Soc., 1992, 114, 1351; (b) T. Morozumi and S. Shinkai, J. Chem. Soc., Chem. Commun., 1994, 1219; (c) M. Crossley, L.G. Mackay and A. C. Try, J. Chem. Soc., Chem. Commun., 1995, 1925; (d ) H. Tamiaki, N. Matsumoto and H. Tsukube, Tetrahedron Lett., 1997, 38, 4239; (e) T. Mizutani, T. Kurahashi, T. Murakami, N. Matsumi and H. Ogoshi, J. Am. Chem. Soc., 1997, 119, 8991; ( f ) X. Huang, B. H. Rickman, B. Borhan, N. Berova and K. Nakanishi, J. Am. Chem. Soc., 1998, 120, 6185; ( g) E. Yashima, T. Natsushima and Y. Okamoto, J. Am. Chem. Soc., 1997, 119, 6345. 2 L. A. Laplanche and G. Vanderkooi, J. Chem. Soc., Perkin Trans. 2, 1983, 1585. 3 (a) M. Bednarski and S. Danishefsky, J. Am. Chem. Soc., 1983, 105, 3716; (b) M. Calmes, J. Daunis, R. Jacquier and J. Verducci. Tetrahedron, 1987, 43, 2285; (c) F. E. Ziegler and S. B. Sobolov, J. Am. Chem. Soc., 1990, 112, 2749; (d ) S. Aime, M. Botta, M. Fasano and E. Terreno, Chem. Soc. Rev., 1998, 27, 19. 4 S. Radzki and C. Giannotti, Inorg. Chim. Acta, 1993, 205, 213. 5 H. Tsukube, S. Shinoda, J. Uenishi, T. Kanatani, H. Itoh, M. Shiode, T. Iwachido and O. Yonemitsu, Inorg. Chem., 1998, 37, 1585. 6 S. W. Graves, J. A. Fox and B. M. Babior, Biochemistry, 1980, 19, 3630; T. Shibata, T. Takahashi, T. Konishi and K. Soai, Angew. Chem., Int. Ed. Engl., 1997, 36, 2458; T. Schrader, J. Org. Chem., 1998, 63, 264. 7 The ionic radii reported for coordination number 6 are shown: R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751. Communication 8/06582I

ISSN:1477-9226    

DOI:10.1039/a806582i

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年代:1999

数据来源: RSC

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DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 13–14 13 Coupling and disproportionation reactions of ethyne on ruthenium carbonyl clusters: molecular structures of Ru5(Ï4-CHCHCCH2)- (CO)15 and Ru6(Ï-H)(Ï4-C)(Ï4-CCMe)(Ï-CO)(CO)16† Michael I. Bruce,a Brian W. Skelton,b Allan H. White b and Natasha N. Zaitseva a a Department of Chemistry, University of Adelaide, Adelaide, South Australia 5005. E-mail: mbruce@chemistry.adelaide.edu.au b Department of Chemistry, University of Western Australia, Nedlands, Western Australia 6907 Received 6th October 1998, Accepted 13th November 1998 Thermolysis of Ru3(Ï3-C2H2)(Ï-CO)(CO)9 1 (50 8C, 6 h) has given Ru5(Ï4-CHCHCCH2)(CO)15 3 and Ru6(Ï-H)(Ï4-C)- (Ï4-CCMe)(Ï-CO)(CO)16 4, both characterised by X-ray crystallography; in 3, coupling of two ethyne molecules occurred, likely with prior isomerisation of one to vinylidene, whereas in 4, two molecules of ethyne disproportionate to carbide and methylethynyl.Reactions of alkynes with ruthenium cluster carbonyls are rich sources of complexes with unusual structures.1,2 Reactions of the simplest alkyne, ethyne, with Ru3(CO)12 have been known since the 1960s, when the carbonyl was used to catalyse the synthesis of hydroquinone from C2H2, CO and H2.3 The complex Ru3(CO)11(h-C2H2), prepared from Ru3H(m-H)(CO)11 and ethyne at low temperatures,4 is converted to Ru3(m3-C2H2)- (m-CO)(CO)9 1 at room temperature. In turn, heating 1 in pentane (bp 36 8C) for 1 h gave Ru3(m-H)(m3-C2H)(CO)9 2 in 91% yield.5 We have been interested to find reactions in which further coupling of the cluster-bonded alkyne or alkynyl ligands might occur.With this objective in mind, we examined the thermolysis of 1 in more detail. When 1 (160 mg, 0.26 mmol) is heated in hexane (50 ml) at 50 8C for 6 h, only 78 mg (50%) of 2 is isolated. Other products, isolated in between 1 and 12% yield, include Ru4(m4-C2H2)- (CO)12, Ru5(m4-CCH2)(CO)15 and Ru6(m4-CCH2)2(CO)16, containing either ethyne or its tautomer, vinylidene.6 The structures of two other complexes have special interest and form the subjects of this work.The complexes can be separated readily by preparative TLC (silica gel, hexane–C6H6 4:1). The complexes Ru5(m4-CHCHCCH2)(CO)15 3‡ and Ru6(m-H)(m4-C)- (m3-CCMe)(m-CO)(CO)16 4‡ were isolated in 6–8% yields from the fractions with Rf 0.19 and 0.25, respectively. Both complexes were characterised by single-crystal X-ray structure determinations.§ Fig. 1 is a plot of a molecule of 3, selected bond parameters being given in the caption. The cluster core is a C3Ru4 pentagonal bipyramid, one carbon of which is linked via a CH2 C C (OC)3Ru Ru(CO)3 Ru (CO)3 H H C O (OC)3Ru Ru C H H (CO)3 Ru (CO)3 C Ru1 Ru4 (CO)2 C1 C3 C4 Ru5(CO)4 (OC)3 Ru3 (CO)3 Ru6(CO)3 (OC)3Ru5 Ru2(CO)3 C1 Ru3(CO)3 C2 Me H C12 C(0) (OC)3Ru4 Ru1 1 2 3 O 4 (OC)3Ru2 C2 H H CO H2 group to the fifth Ru atom, which is also bonded to Ru(4).Atoms Ru(1,2,3) each have three terminal CO ligands; the Ru(5)(CO)4 group takes the place of the third CO group on Ru(4) [angles Ru(3)–Ru(4)–Ru(5) 94.42(8), Ru(1)–Ru(4)–C(41) 112.6(6)8]. Atoms Ru(1,3) are s-bonded to C(1) and C(3), respectively; the strain inherent in the four-membered C(3)– C(4)–Ru(5)–Ru(4) ring is evidenced by the internal angle at C(4) being only 98(1)8. Three carbons C(1,2,3) of the organic ligand are coplanar with Ru(1) and Ru(3) and interact equally with Ru(2) and Ru(4) in a p-type bond.This cluster is best described as an Ru-spiked Ru4C3 system with 76 cluster valence electrons (c.v.e.). A plot of 4 is given in Fig. 2, the caption containing selected bond parameters. In this hexanuclear cluster, the Ru6 core can be described as a butterfly, to a hinge atom of which an Ru2 unit is attached. The cleft of the butterfly carries a carbon atom and the hinge vector is bridged by a CO ligand. This structural feature has been described previously in Ru4C(m-CO)(CO)12 7 and comparable structural parameters are similar.Apart from Ru(1), which has only one CO, all Ru atoms carry three terminal CO ligands. The Ru(2)–Ru(3) vector is bridged by a hydrogen atom, but as found in other hydrido–alkynyl Ru3 complexes, is not particularly lengthened as a result. The m4-CCMe is bonded to Ru(1) and Ru(4) via C(1) and to Ru(2,3) via both carbons. As judged by the C(1)–C(2) separation of Fig. 1 Plot of a molecule of Ru5(m4-CHCHCCH2)(CO)15 3 showing atom numbering scheme.Bond lengths: Ru(1)–Ru(2) 2.834(3), Ru(1)– Ru(3) 2.807(3), Ru(1)–Ru(4) 2.849(2), Ru(2)–Ru(3) 2.782(3), Ru(3)– Ru(4) 2.874(2), Ru(4)–Ru(5) 2.815(2), Ru(1)–C(1) 2.09(1), Ru(2)– C(1,2,3), 2.24(2), 2.20(2), 2.45(2), Ru(3)–C(3) 2.13(1), Ru(4)–C(1,2,3) 2.25(2), 2.23(2), 2.24(2), Ru(5)–C(4) 2.17(2), C(1)–C(2) 1.43(2), C(2)– C(3) 1.43(2), C(3)–C(4) 1.47(2) Å. Bond angles: C(1)–C(2)–C(3) 121(1), C(2)–C(3)–C(4) 117(1), Ru(5)–C(4)–C(3) 98(1), Ru(4)–Ru(5)–C(4) 78.7(4)8.14 J.Chem. Soc., Dalton Trans., 1999, 13–14 1.308(6) Å and the angle C(1)–C(2)–C(3) of 136.6(5)8, this ligand is a m4-alkynyl group, similar to that found in Ru3Pt- (m-H)(m4-C2But)(CO)9(dppe), for example.8 The c.v.e. count is 90. The spectroscopic properties of 3 and 4 are consistent with their solid-state structures. Their IR n(CO) spectra contain respectively ten and eleven terminal CO absorptions, while a band at 1887 cm21 in the spectrum of 4 is assigned to the bridging CO ligand.In the 1H NMR spectrum of 3, no high-field signals were detected; signals at d 5.84, 9.64 and at 3.01 and 4.12 were assigned to protons in C(1) and C(2) and to the CH2 group, respectively. For 4, the Me resonance is at d 1.65, while a singlet at d 219.3 confirms the presence of the cluster-bound hydride. The organic ligands in 3 and 4 are formed by coupling of two C2H2 ligands of the original complex 1, with concomitant cluster expansion and hydrogen migration from C(3) to C(4).In 3, the latter process is reminiscent of the common alkyne to vinylidene isomerisation that is widespread in mononuclear and cluster chemistry. For example, conversion of ethyne to vinylidene on an Os3 cluster has been described by Deeming.9 Subsequent cluster-mediated coupling of the vinylidene with ethyne would give the C4 ligand. The course of this reaction is not obvious, dimerisation of the Ru3 cluster being accompanied by considerable rearrangement and loss of one ruthenium atom.The formation of 4 requires a more fundamental change, three of the four hydrogens of two ethyne molecules ending up on the same carbon atom [C(3)], while the fourth is attached to the cluster. Further, disproportionation of the two alkynes, an uncommon process on Group 8 carbonyl clusters, results in formation of the novel carbido cluster. This reaction may be related to the cleavage of alkynes by Co3(m3-CO)2Cp3, for example.10 In conclusion, we have demonstrated the occurrence of two novel reactions of ethyne on an Ru3 cluster leading to com- Fig. 2 Plot of a molecule of Ru6(m-H)(m4-C)(m3-CCMe)(m-CO)(CO)16 4 showing atom numbering scheme. Bond lengths: Ru(1)–Ru(2) 2.8303(8), Ru(1)–Ru(3) 2.8076(8), Ru(1)–Ru(4) 2.8341(7), Ru(1)–Ru(5) 2.7543(7), Ru(1)–Ru(6) 2.8272(7), Ru(2)–Ru(3) 2.7819(9), Ru(4)–Ru(5) 2.8373(8), Ru(5)–Ru(6) 2.8258(8), Ru(1)–C(0) 2.123(4), Ru(4)–C(0) 1.955(4), Ru(5)–C(0) 2.144(5), Ru(6)–C(0) 1.911(4), Ru(1)–C(1) 2.027(4), Ru(2)–C(1) 2.304(5), Ru(2)–C(2) 2.143(5), Ru(3)–C(1) 2.251(5), Ru(3)–C(2) 2.247(5), Ru(4)–C(1) 2.297(4), C(1)–C(2) 1.308(6) Å.Bond angles: Ru(1)–C(0)–Ru(5) 80.4(2), Ru(4)–C(0)–Ru(6) 174.9(3), Ru(4)–C(1)–C(2) 135.5(4), C(1)–C(2)–C(3) 136.6(5)8. plexes containing acyclic C4 (in 3) or carbide and methylethynyl ligands (in 4) which do not have counterparts in the chemistry of mono- or di-substituted alkynes on Group 8 metal carbonyl clusters.Acknowledgements We thank the Australian Research Council for support of this work and Johnson Matthey plc, Reading, for a generous loan of RuCl3?nH2O. Notes and references † Dedicated to Warren Roper on the occasion of his 60th birthday, in recognition of his outstanding contributions to organometallic chemistry. ‡ Selected spectroscopic data. For 3. IR (cyclohexane); n(CO) 2116w, 2079m, 2057m, 2049s, 2041s, 2033s, 2017m, 2010m, 1986w (br), 1953w cm21. 1H NMR (CDCl3): d 3.01 [d, 1H, J(HH) 7, CH2], 4.12 [d, 1H, J(HH) 7, CH2], 5.84 [d, 1H, J(HH) 5.4 Hz, CH], 9.64 (d, 1H, CH).For 4. IR (cyclohexane): n(CO) 2081s, 2077s, 2072m, 2062vs, 2047m, 2036m, 2027m, 2019m, 1992w, 1985w, 1945w (br), 1887w (br) cm21. 1H NMR (CDCl3): d 219.3 (s, 1H, RuH), 1.65 (s, 3H, Me). § Crystal data for 3: red crystal, Ru5(m4-CHCHCCH2)(CO)15 3 º C19H4O15P2Ru5, M = 977.6, monoclinic, space group P21/c, a = 11.517(8), b = 14.792(11), c = 16.503(18) Å, b = 113.41(7)8, V = 2580 Å3, Z = 4, rc = 2.516 g cm23, F(000) = 1832. Crystal dimensions: 0.05 × 0.24 × 0.32 mm, m(Mo-Ka) = 29.3 cm21, A* (min, max) = 1.15, 1.96.N = 4511, No [I > 3s(I)] = 3179; R = 0.061, Rw = 0.067. For 4: dark red crystal, Ru6(m-H)(m4-C)(m4-CCMe)(m-CO)(CO)16 (4) º C21H4O17Ru6, M = 1134.7, monoclinic, space group C2/c, a = 34.595(9), b = 9.534(2), c = 19.461(4) Å, b = 108.97(2)8, V = 6070 Å3, Z = 8, rc = 2.483 g cm23, F(000) = 4240. Crystal dimensions: 0.08 × 0.58 × 0.23 mm, m(Mo-Ka) = 29.8 cm21, A* (min, max) = 1.26, 1.81.N = 5329, No [I > 3s(I)] = 4521; R = 0.027, Rw = 0.031. Unique diVractometer data sets were measured at ca. 295 K to 2qmax = 508 (CAD4 diVractometer, 2q–q scan mode; monochromatic Mo-Ka radiation, l = 0.71073 Å); N independent reflections were obtained No being considered ‘observed’ and used in the full-matrix least squares refinements after Gaussian absorption correction. Anisotropic thermal parameters were refined for the non-hydrogen atoms; (x, y, z, Uiso)H were included constrained at estimated values for 3 and refined in 4.The precision of the determination for 3 was adversely aVected by the use of a split crystal. CCDC reference number 186/1245. See http://www.rsc.org/suppdata/dt/1999/13/ for crystallographic files in .cif format. 1 M. I. Bruce, in Comprehensive Organometallic Chemistry, eds. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon, Oxford, 1982, vol. 4, p. 858. 2 A. K. Smith, in Comprehensive Organometallic Chemistry II, eds. E. W. Abel, F. G. A. Stone and G. Wilkinson, Elsevier, Oxford, 1995, vol. 7, p. 772. 3 P. Pino, G. Braca, G. Sbrana and A. Cuccuru, Chem. Ind. (London), 1968, 1732. 4 S. Aime, W. Dastru, R. Gobetto, L. Milone and A. Viale, Chem. Commun., 1997, 267. 5 S. Aime, R. Gobetto, L. Milone, D. Osella, L. Violano, A. J. Arce and Y. De Sanctis, Organometallics, 1991, 10, 2854. 6 M. I. Bruce, N. N. Zaitseva, B. W. Skelton and A. H. White, in preparation. 7 A. G. Cowie, B. F. G. Johnson, J. Lewis and P. R. Raithby, J. Organomet. Chem., 1986, 306, C63. 8 P. Ewing and L. J. Farrugia, Organometallics, 1989, 8, 1246. 9 A. J. Deeming and M. Underhill, J. Chem. Soc., Dalton Trans., 1974, 1415. 10 J. R. Fritsch and K. P. C. Vollhardt, Angew. Chem., Int. Ed. Engl., 1980, 19, 559. Communication 8/07781I

ISSN:1477-9226    

DOI:10.1039/a807781i

出版商:RSC    

年代:1999

数据来源: RSC

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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 15–18 15 N,N9,N0-Triphenylguanidinate(12) complexes of ruthenium and palladium: syntheses and crystal structures † K. Travis Holman, Stephen D. Robinson,* Arvind Sahajpal and Jonathan W. Steed Department of Chemistry, King’s College London, Strand, London, UK WC2R 2LS Received 17th August 1998, Accepted 27th October 1998 N,N9,N0 -Triphenylguanidine (HTpg) reacted with [Ru(O2CCF3)2(CO)(PPh3)2] in boiling toluene to yield [Ru(Tpg)2(CO)(PPh3)], the first example of a mononuclear complex containing two chelate guanidinate(12) ligands.Palladium(II) acetate reacted with HTpg in warm benzene to form an adduct [Pd(O2CMe)2(HTpg)2] which, under more forcing conditions, converts into the novel binuclear guanidinate(12) bridged complex [{Pd(m-Tpg)(Tpg)}2]. Crystal structures have been determined for both guanidinate(12) complexes. Guanidines RHNC(]] NR)NHR (R = H, alkyl or aryl) are compounds of considerable biological and chemical importance.2 They are also very strong organic bases which readily undergo protonation to generate resonance-stabilised guanidinium cations (guanidinium, pKa 13.65).3 Guanidines are encountered in co-ordination chemistry as guanidinium counter cations and somewhat less frequently as neutral monodentate ligands coordinated through the imine nitrogen.4 However, complexes containing co-ordinated guanidinate(12) anions are of recent origin and to date are restricted to a relatively small number of examples,5,6 several of which were first synthesized in our laboratory.1 We now report the synthesis and crystal structures of two N,N9,N0-triphenylguanidinate (Tpg) complexes, the first bis(chelate) guanidinate(12) derivative [Ru(Tpg)2(CO)(PPh3)] and the novel binuclear palladium(II) species [{Pd(m-Tpg)- (Tpg)}2].Results and discussion Treatment of [Ru(O2CCF3)2(CO)(PPh3)2] with N,N9,N0- triphenylguanidine (HTpg) in boiling toluene aVorded lemon yellow crystals of the bis(guanidinato) complex [Ru(Tpg) 2(CO)(PPh3)] 1.In order to establish the stereochemistry of 1 and gain information concerning the co-ordination and structure of the chelate guanidinate(12) ligands an X-ray crystal structure determination was undertaken using a crystal grown from CH2Cl2–MeOH solution. The molecular structure of 1 is shown in Fig. 1; selected bond length and angle data are collated in Table 1. The carbonyl and triphenylphosphine ligands are located at adjacent sites in the distorted octahedral coordination sphere. The remaining four sites are occupied by the nitrogen donor atoms of the two chelate guanidinate ligands.The co-ordination sphere is highly distorted due to the presence of the two small ‘bite’ guanidinate ligands [N–Ru–N 61.47(8) and 62.00(8)8]. The angles around the central carbon atom total 360 ± 18 for each of the guanidinate ligands and thus establish the planarity of the N2CN skeletons.The values of the dihedral angles between these N2CN planes and the corresponding N–Ru–N planes [1.20(15) and 3.96(16)8] are even smaller than the value of 4.2(2)8 reported by Bailey et al.5 for the ruthenium complex [RuCl(Tpg)(h-MeC6H4Pri-p)]. The stereochemistry about the non-co-ordinated nitrogens is less unambiguous; in each case the N-bound hydrogen atom has been located but errors associated with their positions are such that, of the angles subtended at these nitrogens, the only ones that can be determined with precision are those involving the attached † Complexes of the platinum metals.Part 50.1 carbon atoms [C–N–C 126.5(2) and 123.9(2)8]. However, when combined with the somewhat less accurate values available for angles involving the N–H bonds (see Table 1), they give totals of 345.6 and 337.98 for the angles subtended at N(3) and N(6) respectively. These totals, almost equidistant between the theoretical summations for sp2 (3608) and sp3 (3278) hybridisation, would appear to imply a stereochemistry midway between the two ideal arrangements.The observation that the corresponding values for the palladium complex 2 (see below) are all very close to the ideal value of 3608 (sp2) suggests that complexes 1 and 2 display real diVerences in stereochemistry at the non-co-ordinated nitrogen atoms. The phenyl groups attached to the co-ordinated nitrogen atoms and the planar NHPh moiety are all rotated out of the plane of the guanidinate skeleton (torsion angles ca. 30 to 608). The N–C bond lengths within the chelate rings [average 1.330(3) Å] are very similar to those reported for related amidinate [PhN–C(R)–NPh] ligands, and are consistent with the presence of a delocalised N–C–N ligand backbone.7 The small degree of asymmetry found within the chelate rings can be attributed to the diVering trans influences of the opposing ligands. In each guanidinate ligand the length of the bonds between the central carbon and the non-co-ordinated nitrogen [C–N average 1.391(3) Å] and in particular the lengths of the Fig. 1 Molecular structure of [Ru(Tpg)2(CO)(PPh3)] 1.16 J. Chem. Soc., Dalton Trans., 1999, 15–18 bonds between the three nitrogen atoms and their attached phenyl groups [C–N average 1.411(3) Å] show little evidence of carbon–nitrogen double bond character. Taken together the bond length and bond angle data suggest that there is a little delocalisation of the lone pair on the non-co-ordinated nitrogen over the guanidine skeleton, and that there appears to be no significant delocalisation of the lone pair electron density from any of the nitrogen atoms out on to the attached phenyl groups. Treatment of palladium acetate with N,N9,N0-triphenylguanidine in benzene at 60 8C leads to formation of a stable insoluble yellow powder which deposits from solution in Fig. 2 Molecular structure of [{Pd(m-Tpg)(Tpg)}2] 2. Phenyl rings are represented by the ipso-C atoms for clarity.Table 1 Selected bond lengths (Å) and angles and torsion angles (8) for [Ru(Tpg)2(CO)(PPh3)] 1 Ru–C(1) Ru–N(5) Ru–N(1) Ru–N(2) Ru–N(4) Ru–P O(1)–C(1) N(1)–C(2) N(1)–C(3) N(2)–C(2) N(2)–C(9) C(1)–Ru–N(5) C(1)–Ru–N(1) N(5)–Ru–N(1) C(1)–Ru–N(2) N(5)–Ru–N(2) N(1)–Ru–N(2) C(1)–Ru–N(4) N(5)–Ru–N(4) N(1)–Ru–N(4) N(2)–Ru–N(4) C(1)–Ru–P N(5)–Ru–P N(1)–Ru–P N(2)–Ru–P N(4)–Ru–P C(2)–N(1)–C(3) C(2)–N(1)–Ru C(3)–N(1)–Ru C(2)–N(2)–C(9) C(2)–N(2)–Ru C(9)–N(2)–Ru C(2)–N(3)–C(15) N(1)–Ru–N(2)–C(2) N(4)–Ru–N(5)–C(21) 1.827(3) 2.114(2) 2.128(2) 2.138(2) 2.150(2) 2.3152(7) 1.161(3) 1.332(3) 1.406(3) 1.325(3) 1.399(3) 103.04(11) 98.30(11) 151.24(9) 94.43(11) 97.55(8) 61.47(8) 164.80(11) 62.00(8) 95.00(8) 85.47(9) 89.57(9) 91.55(6) 107.79(6) 168.96(6) 93.36(6) 126.3(2) 94.24(15) 138.62(17) 127.7(2) 93.97(16) 137.89(17) 126.5(2) 1.20(15) 3.96(16) N(3)–C(2) N(3)–C(15) N(3)–H(N3) N(4)–C(21) N(4)–C(22) N(5)–C(21) N(5)–C(28) N(6)–C(21) N(6)–C(34) N(6)–H(N6) C(2)–N(3)–H(N3) C(15)–N(3)–H(N3) C(21)–N(4)–C(22) C(21)–N(4)–Ru C(22)–N(4)–Ru C(21)–N(5)–C(28) C(21)–N(5)–Ru C(28)–N(5)–Ru C(21)–N(6)–C(34) C(21)–N(6)–H(N6) C(34)–N(6)–H(N6) O(1)–C(1)–Ru N(2)–C(2)–N(1) N(2)–C(2)–N(3) N(1)–C(2)–N(3) N(2)–C(2)–Ru N(1)–C(2)–Ru N(3)–C(2)–Ru N(5)–C(21)–N(4) N(5)–C(21)–N(6) N(4)–C(21)–N(6) 1.384(3) 1.416(3) 0.93 1.332(3) 1.409(3) 1.331(3) 1.409(3) 1.399(3) 1.425(4) 1.16 108.4 110.7 123.5(2) 92.40(16) 137.59(17) 127.5(2) 94.01(16) 138.37(19) 123.9(2) 104.2 109.8 176.2(3) 110.3(2) 123.8(2) 125.8(2) 55.37(13) 54.94(13) 178.64(19) 111.2(2) 126.1(2) 122.5(2) essentially quantitative yield.On the basis of infrared spectra and elemental analysis data this product is formulated as the adduct [Pd(O2CMe)2(HTpg)2]. On heating with an excess of N,N9,N0-triphenylguanidine in boiling toluene the adduct eliminates acetic acid to form the bis(guanidinato)palladium(II) complex 2 which deposited from solution as dark red crystals. The binuclear nature of 2 was confirmed by X-ray diVraction methods which revealed the novel bridged structure [{Pd- (m-Tpg)(Tpg)}2] and thereby established the first example of a complex containing chelate and bridging guanidinate(12) ligands.The molecular structure of 2 is shown in Fig. 2; selected bond length and angle data are collated in Table 2. The geometry and dimensions of the N,N9,N0-triphenylguanidinato complex 2 are very similar to those previously reported for the corresponding N,N9-diphenylbenzamidinato complex.8 In both complexes the angles subtended at the palladium by the NTable 2 Selected bond lengths (Å) and angles and torsion angles (8) for [{Pd(m-Tpg)(Tpg)}2] 2 Pd(1)–N(10) Pd(1)–N(2) Pd(1)–N(7) Pd(1)–N(1) Pd(1)–C(1) Pd(1) ? ? ? Pd(2) Pd(2)–N(8) Pd(2)–N(5) Pd(2)–N(11) Pd(2)–N(4) Pd(2)–C(20) N(1)–C(1) N(1)–C(2) N(2)–C(1) N(2)–C(8) N(3)–C(1) N(3)–H(N3) N(3)–C(14) N(4)–C(20) N(4)–C(21) N(10)–Pd(1)–N(2) N(10)–Pd(1)–N(7) N(2)–Pd(1)–N(7) N(10)–Pd(1)–N(1) N(2)–Pd(1)–N(1) N(7)–Pd(1)–N(1) N(10)–Pd(1)–Pd(2) N(2)–Pd(1)–Pd(2) N(7)–Pd(1)–Pd(2) N(1)–Pd(1)–Pd(2) N(8)–Pd(2)–N(5) N(8)–Pd(2)–N(11) N(5)–Pd(2)–N(11) N(8)–Pd(2)–N(4) N(5)–Pd(2)–N(4) N(11)–Pd(2)–N(4) N(8)–Pd(2)–Pd(1) N(5)–Pd(2)–Pd(1) N(11)–Pd(2)–Pd(1) N(4)–Pd(2)–Pd(1) C(1)–N(1)–C(2) C(1)–N(1)–Pd(1) C(2)–N(1)–Pd(1) C(1)–N(2)–C(8) C(1)–N(2)–Pd(1) C(8)–N(2)–Pd(1) C(1)–N(3)–C(14) C(1)–N(3)–H(N3) C(14)–N(3)–H(N3) C(20)–N(4)–C(21) C(20)–N(4)–Pd(2) C(21)–N(4)–Pd(2) C(20)–N(5)–C(27) C(20)–N(5)–Pd(2) N(1)–Pd(1)–N(2)–C(1) N(4)–Pd(2)–N(5)–C(20) 2.037(3) 2.045(3) 2.055(3) 2.057(3) 2.505(4) 2.9678(4) 2.029(3) 2.050(3) 2.051(3) 2.071(3) 2.503(4) 1.348(5) 1.404(5) 1.329(5) 1.416(5) 1.367(5) 1.005 1.413(5) 1.332(5) 1.405(5) 165.41(22) 90.49(11) 102.35(12) 101.82(12) 64.47(12) 164.92(12) 77.84(8) 111.92(9) 75.13(8) 115.71(9) 164.73(12) 90.67(11) 104.45(12) 100.30(12) 64.47(12) 168.39(12) 80.32(8) 104.63(9) 77.81(8) 107.60(9) 126.2(3) 92.3(2) 132.9(2) 125.7(3) 93.5(2) 140.8(3) 128.9(4) 123 108 128.5(3) 92.1(2) 137.7(3) 125.7(3) 92.8(2) 0.3(2) 0.8(2) N(5)–C(20) N(5)–C(27) N(6)–C(20) N(6)–C(33) N(6)–H(N6) N(7)–C(39) N(7)–C(40) N(8)–C(39) N(8)–C(46) N(9)–C(39) N(9)–C(52) N(9)–H(N9) N(10)–C(58) N(10)–C(59) N(11)–C(58) N(11)–C(65) N(12)–C(58) N(12)–C(71) N(12)–H(N12) C(27)–N(5)–Pd(2) C(20)–N(6)–C(33) C(20)–N(6)–H(N6) C(33)–N(6)–H(N6) C(39)–N(7)–C(40) C(39)–N(7)–Pd(1) C(40)–N(7)–Pd(1) C(39)–N(8)–C(46) C(39)–N(8)–Pd(2) C(46)–N(8)–Pd(2) C(39)–N(9)–C(52) C(39)–N(9)–H(N9) C(52)–N(9)–H(N9) C(58)–N(10)–C(59) C(58)–N(10)–Pd(1) C(59)–N(10)–Pd(1) C(58)–N(11)–C(65) C(58)–N(11)–Pd(2) C(65)–N(11)–Pd(2) C(58)–N(12)–C(71) C(58)–N(12)–H(N12) C(71)–N(12)–H(N12) N(2)–C(1)–N(1) N(2)–C(1)–N(3) N(1)–C(1)–N(3) N(4)–C(20)–N(5) N(4)–C(20)–N(6) N(5)–C(20)–N(6) N(7)–C(39)–N(8) N(7)–C(39)–N(9) N(8)–C(39)–N(9) N(11)–C(58)–N(10) N(11)–C(58)–N(12) N(10)–C(58)–N(12) 1.341(5) 1.413(5) 1.388(5) 1.405(5) 0.827 1.331(4) 1.438(4) 1.344(4) 1.413(4) 1.382(5) 1.410(5) 0.722 1.335(4) 1.425(4) 1.335(4) 1.433(4) 1.384(5) 1.404(5) 0.645 138.2(3) 125.0(4) 113 118 120.6(3) 125.4(2) 113.9(2) 122.0(3) 119.7(2) 118.3(2) 127.6(3) 116 115 121.0(3) 123.5(2) 115.5(2) 120.2(3) 122.8(2) 117.1(2) 129.1(4) 115 115 109.7(3) 123.1(4) 127.2(4) 110.6(3) 125.5(4) 123.8(4) 121.1(3) 120.0(3) 118.8(3) 120.8(3) 121.6(3) 117.5(3)J. Chem.Soc., Dalton Trans., 1999, 15–18 17 donor atoms of the chelate ligands are ca. 648 and in each case the Pd–N bond lengths for the chelate and bridging ligands are very similar. Evidence for a significant degree of steric interaction between the two halves of the guanidinato complex is provided by values for the non-bridging Pd ? ? ? Pd distance [2.9678(4) Å], the dihedral angle between the two PdN4 planes (39.48) and the N–Pd ? ? ? Pd–N torsion angle (298) all of which are significantly larger than those reported for the corresponding N,N9-diphenylbenzamidinato complex [2.900(1) Å, 35 and 198 respectively]. The angles subtended at palladium by the N-donor atoms of the chelating guanidinate(12) ligands [both 64.47(12)8] reflect the small ‘bite’ of this ligand.In contrast the corresponding angles for the nitrogen atoms of the bridging guanidinate ligands are almost exactly 908 as required for rigorous square planar co-ordination. The Pd–N bond lengths averaging 2.055(3) and 2.043(3) Å for chelate and bridging guanidinato ligands respectively, are very similar to those previously reported for the corresponding N,N9-diphenylbenzamidinate complex.8 For each of these chelate and bridging guanidinato ligands the sum of the angles subtended at the central carbon equals 3608 thereby establishing the planarity of the N2CN skeletons.For each of the chelate guanidinate ligands the dihedral angle between the N2CN plane and the corresponding N–Pd–N plane is less than 18. Therefore in contrast to the ruthenium complex 1 discussed above, and the ruthenium and rhodium complexes reported by Bailey et al.,5 the palladium complex has essentially planar chelate rings.For the two bridging guanidinate ligands the sum of the angles subtended at each of the co-ordinated nitrogen atoms is exactly 3608. However in the case of the chelate guanidinate ligands there are small deviations from planarity at two of the coordinated nitrogens, N(4) and N(5) (sum of angles = 358.3 and 356.78), and a somewhat larger deviation at a third, N(1) (sum of angles = 351.48), which we attribute to steric interactions between adjacent phenyl rings.As in the case of the ruthenium complex, the hydrogen atoms attached to the non-co-ordinated nitrogens have been located (average N–H 0.8 Å) but once again errors associated with their positions are such that bond angles incorporating the N–H bonds cannot be determined with a high degree of accuracy. However, the totals obtained for the angles subtended at the non-co-ordinated nitrogen atoms, N(3) 359.9, N(6) 356.0, N(9) 358.6 and N(12) 359.18, are very close to 3608 in three cases and not far removed in the fourth, N(6).Even allowing for the errors associated with the involvement of the N–H groups referred to above, these data suggest the adoption of trigonal planar (sp2) stereochemistry in each instance, and are in marked contrast to those found for the ruthenium complex 1 (see above). Finally the phenyl groups attached to the co-ordinated nitrogen atoms and the non-co-ordinated NHPh moieties are rotated out of the plane of the guanidinate skeleton.The C–N bond lengths observed for the chelate and bridging guanidinate ligands in complex 2 are very similar, and agree well with those found for the chelate guanidinate ligands in [Ru(Tpg)2(CO)(PPh3)] 1. Taken together the bond length and bond angle data for 2 suggest that, as in the case of complex 1, the lone pair on the non-co-ordinated nitrogen is not extensively delocalised over the guanidinate skeleton, and that delocalisation of the nitrogen lone pairs out into the attached phenyl groups is minimal.Experimental Palladium acetate and N,N9,N0-triphenylguanidine were obtained from Avocado Research Chemicals; [Ru(O2CCF3) 2(CO)(PPh3)2] was prepared by a literature method.9 Preparations [Ru{PhNC(NHPh)NPh}2(CO)(PPh3)] 1. Carbonylbis(tri- fluoroacetato)bis(triphenylphosphine)ruthenium (0.5 g, 0.57 mmol) and N,N9,N0-triphenylguanidine (0.8 g, 2.79 mmol) were heated together under reflux in toluene (40 cm3) for ca. 5.5 h to give a greenish yellow solution. Concentration under reduced pressure left an oil which on crystallisation from CH2Cl2–MeOH aVorded lemon yellow crystals (0.31 g, 56%), mp 212–214 8C (Found: C, 70.25; H, 4.75; N, 8.6. Calc. for C57H47N6OPRu: C, 71.0; H, 4.9; N, 8.7%). IR: n(CO) 1930 cm21, n(NH) 3389, 3400 cm21. 31P NMR (CDCl3), (145.785 MHz): d 52.59 (s). [Pd(O2CMe)2{PhNC(NHPh)NHPh}2].Palladium acetate (0.3 g, 1.34 mmol) was dissolved in benzene (50 cm3) to give an orange solution. N,N9,N0-Triphenylguanidine (0.8 g, 2.78 mmol) was then added and the mixture maintained at 60 8C for ca. 2.5 h. The product which deposited was filtered oV, washed repeatedly with methanol and dried in vacuo as yellow microcrystals (0.86 g, 80%), mp 176–178 8C (decomp.) (Found: C, 63.15; H, 5.0; N, 10.4. Calc. for C42H40N6O4Pd: C, 63.1; H, 5.05; N, 10.5%). IR n(N–H) 3177, n(O2C)asym 1613, 1631 cm21.[Pd2{Ï-PhNC(NHPh)NPh}2{PhNC(NHPh)NPh}2]?CH2Cl2. Bis(acetato)bis(N,N9,N0-triphenylguanidine)palladium (0.4 g, 0.5 mmol) and N,N9,N0-triphenylguanidine (0.35 g, 1.2 mmol) were stirred and heated together under reflux in toluene (50 cm3) for ca. 2 h. The dark red solution was filtered to remove a small amount of greenish yellow solid residue and then concentrated under reduced pressure to form an oil which was redissolved in the minimum volume of CH2Cl2.Careful addition of MeOH led to slow crystallisation of the product which was filtered oV, washed with methanol and dried in vacuo as dark maroon crystals (0.18 g, 53%), mp 194–196 8C (decomp.) (Found: C, 62.15; H, 4.3; N, 10.85. Calc. for C38H32N6Pd?0.5CH2Cl2: C, 61.3; H, 4.35; N, 11.0%). IR: n(N–H) 3396 cm21. X-Ray crystallography Crystals were mounted on thin glass fibres using fast setting epoxy resin and cooled on the diVractometer to the temperature stated using an Oxford Cryostream low temperature attachment.A total of either 90 or 180 oscillation frames each of width either 2 or 18 in f respectively and of 10–160 s exposure time (depending upon crystal quality) were recorded on a Nonius Kappa CCD diVractometer, using Mo-Ka radiation (l = 0.71070 Å), with a detector to crystal distance of 25–30 mm. Crystals were indexed from the first ten frames using the DENZO package 10 and positional data were refined along with diVractometer constants to give the final cell parameters. Integration and scaling (DENZO, Scalepack 10) resulted in unique data sets corrected for Lorentz-polarisation eVects and for the eVects of crystal decay and absorption by a combination of averaging of equivalent reflections and an overall volume and scaling correction.Crystallographic data are recorded in Table 3. The structures were solved using SHELXS 9711 and developed via alternating least squares cycles and Fourier diVerence synthesis (SHELXL 97 11) with the aid of the program RES2INS.12 In general all non-hydrogen atoms were modelled anisotropically, while hydrogen atoms were assigned an isotropic thermal parameter 1.2 times that of the parent atom (1.5 for terminal atoms) and allowed to ride.Hydrogens bound to nitrogen were located by Fourier diVerence syntheses and allowed to ride on the atoms to which they are attached. All calculations were carried out with either a Silicon Graphics Indy R5000 work station or an IBM compatible PC.CCDC reference number 186/1220. Acknowledgements We thank the Royal Society for the provision of funds to purchase platinum metals, EPSRC and KCL for funding for the18 J. Chem. Soc., Dalton Trans., 1999, 15–18 Table 3 Crystallographic data for complexes 1 and 2 Molecular formula MT /K Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 m/mm21 F(000) Crystal size/mm q Range for data collection/8 Index ranges Reflections collected/unique Rint Absorption correction Refinement method Data/restraints/parameters Goodness of fit on F2 Final R1, wR2 [I > 2s(I)] (all data) Largest diVerence peak and hole/e Å23 1 C57H47N6OPRu 964.05 173(2) Monoclinic P21/n 10.0246(3) 22.7693(7) 20.7373(4) 94.553(1) 4718.4(2) 4 1.357 0.414 1992 0.25 × 0.20 × 0.20 3.37 to 26.00 0 to 12, 0 to 28, 225 to 25 36696/8994 0.0520 Scalepack Full matrix least squares on F 2 8994/0/595 1.074 0.0387, 0.0898 0.0507, 0.0983 0.464 and 20.622 2 C76H64N12Pd2 1358.19 123(2) Monoclinic P21/n 11.5530(3) 25.9674(8) 21.8712(8) 103.190(2) 6388.2(3) 4 1.412 0.618 2784 0.10 × 0.10 × 0.10 3.24 to 25.00 213 to 13, 230 to 30, 225 to 26 51426/11206 0.0472 Scalepack Full matrix least squares on F 2 11206/0/827 1.064 0.0433, 0.0863 0.0631, 0.0927 0.855 and 20.925 diVractometer and the NuYeld Foundation for provision of computing equipment.References 1 Part 49, S. D. Robinson and A. Sahajpal, J. Chem. Soc., Dalton Trans., 1997, 3349. 2 C. Grambow, in Ullmann’s Encyclopaedia of Industrial Chemistry, VCH, Weinheim, 1989, vol. A12, p. 545. 3 P. A. S. Smith, Open Chain Nitrogen Compounds, W. A. Benjamin Inc., New York, 1965, vol. 1, p. 277. 4 R. C. Mehrotra, in Comprehensive Coordination Chemistry, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon, Oxford, 1987, vol. 2, p. 281; P. J. Bailey, K. J. Grant, S. Pace, S. Parsons and L. J. Stewart, J. Chem. Soc., Dalton Trans., 1997, 4263. 5 P. J. Bailey, L. A. Mitchell and S. Parsons, J. Chem. Soc., Dalton Trans., 1996, 2839. 6 E. M. A. Ratilla, B. K. Scott, M. S. Moxness and N. M. Kostic, Inorg. Chem., 1990, 29, 918; P. J. Bailey, S. F. Bone, L. A. Mitchell, S. Parsons, K. J. Taylor and L. J. Yellowlees, Inorg. Chem., 1997, 36, 867; H.-K. Yip, C.-M. Che, Z.-Y. Zhou and T. C. W. Mak, J. Chem. Soc., Chem. Commun., 1992, 1369; J. R. da S. Maia, P. A. Gazard, M. Kilner, A. S. Batsanov and J. A. K. Howard, J. Chem. Soc., Dalton Trans., 1997, 4625. 7 L. D. Brown, S. D. Robinson, A. Sahajpal and J. A. Ibers, Inorg. Chem., 1977, 16, 2728. 8 C.-L. Yao, L.-P. He, J. D. Korp and J. L. Bear, Inorg. Chem., 1988, 27, 4389. 9 A. Dobson, S. D. Robinson and M. F. Uttley, J. Chem. Soc., Dalton Trans., 1975, 370. 10 Z. Otwinowski and W. Minor, Methods Enzymol., 1996, 276, 307. 11 G. M. Sheldrick, SHELX 97, University of Göttingen. 12 L. J. Barbour, RES2INS, University of Missouri-Columbia, 1995. Paper 8/06454G

ISSN:1477-9226    

DOI:10.1039/a806454g

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1996, Pages 17–19 17 Discotic bimetallomesogens: highly disordered mesophases of columnar hexagonal arrangements in bis(tetraketonate) vanadyl and copper complexes † Chung K. Lai * and Fun-Jane Lin Department of Chemistry, National Central University, Chung-Li, Taiwan, Republic of China A series of bis(tetraketonate) complexes of dicopper and divanadyl has been prepared and their mesomorphic properties investigated by polarized optical microscopy and powder X-ray diffraction.Molecular design and synthesis of new metal complexes with novel mesophases and/or physical properties represent an active research area in metallomesogenic materials.1 The incorporation of a metal or metal centres can not only lead to new structures and geometries capable of generating new mesogenic materials,1,2 but also results in interesting electrical, optical and magnetic properties. In bimetallic liquid crystals the interaction between metal centres in molecular structures, whether in close proximity or remote from each other, may influence the formation of liquid-crystalline mesophases, and consequently determines the physical properties of these complexes.However, this approach to an understanding of bimetallic liquid crystals still remain limited, and only a few bimetallic complexes have been prepared 3 and studied. We report herein our results on the development of the first discotic 4 divanadyl and dicopper liquid-crystalline complexes. We have prepared and characterized a number of bimetallic complexes.The typical synthetic procedures are summarized in Scheme 1. The tetraketones 1,3-bis[3-(3,4,5-trialkoxyphenyl)- 3-oxopropanoyl]benzene‡ and 1,3-bis[3-(3,4-dialkoxyphenyl)-3- oxopropanoyl]benzene, were synthesized by condensation of the isophthalic acid dimethyl esters, the appropriate acetophenone derivatives and sodium hydride in refluxing thf or 1,2- dimethoxyethane. Reactions of the tetraketones with copper acetate and vanadyl sulfate in refluxing CHCl3–MeOH gave the bimetallic tetraketonate complexes 5 in high yields.Satisfactory elemental analysis for these metal complexes were obtained after several recrystallizations (SUP 57200). The mesomorphic properties of these bimetallic complexes are summarized in Table 1. Copper complexes 1a (n = 12 or 18) showed only crystal phases with isotropic temperatures at ca. 250–300 8C. However, when the number of carbon atoms in the sidechains is greater than ten for complexes 2a and six for complexes 3a, the copper complexes exhibited columnar discotic † Supplementary data available, (No.SUP 57200, 6 pp.): tables of enthalpies of phase changes and elemental analyses for all compounds reported. See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. ‡ 1,3-bis[3-(3,4,5-tridocenoxyphenyl)-3-oxopropanoyl]benzene: yield, 86%, light yellow solids. 1H NMR (CDCl3): d 0.87 (t, CH3, 18 H), 1.29– 1.51 (m, CH2, 108 H), 1.76–1.90 (m, CH2, 12 H), 4.06 (t, OCH2, 12 H), 6.83 (s, CH]] C, 2 H), 7.19 (s, C6H2, 4 H), 7.63 (t, C6H4, 1 H), 8.12 (d, C6H4, 2 H), 8.58 (s, C6H4, 1 H), 17.02 (s, COH, 2 H). 13C NMR (CDCl3): d 12.02, 14.71, 19.35, 23.31, 26.74, 30.03, 30.31, 30.99, 32.21, 32.56, 35.29, 36.70, 70.14, 74.26, 93.81, 106.9, 110.7, 126.3, 129.6, 130.9, 131.1, 136.8, 143.5, 153 .8, 183.9, 187.5.liquid phases (SUP 57200). Differential scanning colorimetry (DSC) analysis of complexes 2a and 3a showed typical discotic phase transitions of crystal-to-discotic-to-isotropic (K æÆ D æÆ I).These copper complexes showed a large enthalpy (88.0–305.0 kJ mol–1) for the crystal-to-liquid crystal transitions at lower temperatures (124–132 and 91–120 8C for Scheme 1 (a) RBr (3.0 equivalents), K2CO3 (7.0 equivalents), KI (catalyst) refluxing in MeCOMe, 72 h, 73–94%. (b) KOH (2.0 equivalent), refluxing in tetrahydrofuran (thf)–water (5 : 1), 12 h, 92–98%.(c) LiMe (2.0 equivalents) stirred in dried thf at room temperature, 12 h, 82–87%. (d) Isophthalic acid dimethyl ester (0.5 equivalents), NaH (3.0 equivalents), refluxing in thf, 4 d, 72–85%. (e) Cu(O2CMe)2 or VOSO4 (1.1 equivalents) refluxing in CHCl3–MeOH, 12 h, 73–83% OR RO RO O O O O OR OR OR RO RO OR O O O O OR OR OR M M OR RO RO OH O OH O OR OR OR OH OH OH EtO O OR OR OR EtO O OR OR OR HO O OR OR OR O (a ) (b ) (c ) (d ) (e ) DC6/06770K/A118 J.Chem. Soc., Dalton Trans., 1997, Pages 17–19 complexes 2a and 3a) and a low enthalpy (1.13–5.77 kJ mol–1) for the liquid crystal-to-isotropic transition at higher temperatures (220–258 and 169–236 8C for complexes 2a and 3a), indicating that the mesophases are in highly disordered states. The temperature range of the mesophases is fairly wide and slightly side-chain dependent at about 79–126 8C. Under a polarized microscope these complexes gave pseudo-focal-conic or fan textures with linear birefringent defects and large areas of uniform homeotropic domains.The vanadyl complexes 3b showed similar discotic behaviour. Transitions of crystal-to-isotropic phases were only observed for vanadyl complexes 1b (n = 12) and 2b (n = 10, 12 or 16). The results revealed that the stronger intermolecular co-ordination between the vanadyl centres inhibited the formation of the liquid-crystal phases. However, increasing the total number of side-chains to 12 (when n > 6) in complexes 3b facilitated the Table 1 Phase behaviour of bimetallic complexes * Complex M n 2a Cu 12 14 16 K K K 132.3 (104) 115.6 (29.5) 126.7 (87.4) 114.1 (24.2) 123.5 (115) 116.0 (34.1) Dhd Dhd Dhd 254.4 (1.46) 249.6 (0.75) 232.7 (1.13) 229.5 (4.97) 219.2 (1.76) 215.0 (0.42) I I I 3a Cu 6 10 12 14 K1 K K K 119.2 (2.73) 99.5 (5.10) 107.8 (268) 54.6 (279) 99.7 (307) 48.2 (321) 90.8 (280) 40.8 (245) K2 Dhd Dhd Dhd 248.5 (3.72) 243.7 (4.01) 235.7 (5.14) 232.3 (5.60) 193.2 (5.56) 189.5 (5.77) 169.0 (4.39) 165.5 (3.59) I I I I 2b VO 10 K 183.8 (6.14) 175.1 (6.06) I 3b VO 6 10 12 14 K K K K 289.9 (38.7) 267.3 (38.0) 78.5 (51.4) 48.7 (55.2) 60.5 (36.4) 34.2 (38.2) 48.7 (31.8) 18.2 (29.9) I Dhd Dhd Dhd 223.6 (5.14) 220.6 (4.26) 187.6 (3.51) 185.5 (4.85) 159.5 (0.38) 156.1 (1.05) I I I * K1, K2 = crystal phase; Dhd = discotic hexagonal disordered; I = isotropic; the transition temperature (8C) and enthalpies (in parentheses, kJ mol–1) were determined by DSC at a scan rate of 10 8C min–1.formation of columnar discotic hexagonal phases as for the copper complexes. The identification of columnar hexagonal discotic phases was confirmed by variable-temperature X-ray powder diffraction (XRD), as shown in Table 2. Complex 3b (n = 12) displays a diffraction pattern of a two-dimensional hexagonal lattice with a strong peak and two weak peaks at 33.15, 19.13 and 16.57 Å. However, complexes 2a (n = 16) exhibited similar diffraction patterns at 34.88, 20.14 and 17.07 Å.These are typically characteristic of a Dhd phase with a dspacing ratio2a,3a,c of 1, ÷��� and ��� , respectively. However, liquid-like correlations between the rigid cores occur at wide angle regions of 5.30–4.64 Å. Temperature dependence of the lattice parameters is also observed in these metal complexes. We find that the lowangle reflections of complexes 3a (n = 16) generally shift to a larger d spacing with decreasing temperatures, thereby indicating a lattice expansion.Absence of distinct peaks at wide angles is consistent with DSC analysis of low enthalpies of discotic-toisotropic transitions, indicative of a highly disordered mesophase. The geometry of the divanadyl centres in complexes 1b–3b either syn or anti, is uncertain based on IR data. The growth of single crystals for X-ray structural determination is in progress. In summary, we have discussed our results on the dicopper and divanadyl complexes of tetraketones. Future research will be focused on the study of related physical properties of these bimetallic complexes, particularly in understanding the effects of two remote metal centres on liquid crystallinity.X RO Y O O O O X OR Y Y RO X O O O 1 X = Y = H 2 X = OR, Y = H 3 X = Y = OR M = Cu (a) or VO (b) R = (CH2)n –1CH3 DC6/06770K/A2 Table 2 Variable-temperature XRD diffraction data for the discotic hexagonal disordered bimetallic complexes 2 and 3 * Complex M n T/8C Lattice constant (a)/Å d Spacing obs.(calc.)/Å Miller indices 2a Cu 16 170 40.28 34.88 (34.88) 20.14 (20.14) 17.07 (17.44) 5.30 (br) (100) (110) (200) halo 110 46.60 40.35 (40.35) 23.29 (23.30) 20.16 (20.17) 13.31 5.30 (br) (100) (110) (200) halo 3a Cu 12 100 29.66 29.67 (29.67) 14.86 (14.83) 5.04 (br) (100) (200) halo 3b VO 12 100 38.28 33.15 (33.15) 19.13 (19.14) 16.57 (16.58) 4.64 (br) (100) (110) (200) halo * The measurements were conducted on an INEL MPD-diffractometer with a 2.0 kW Cu-Ka X-ray source equipped with an INEL CPS-120 position sensitive detector and a variable-temperature capillary furnace with an accuracy of ±0.10 8C in the vicinity of the capillary tube.J. Chem.Soc., Dalton Trans., 1997, Pages 17–19 19 Acknowledgements We thank the National Science Council of Taiwan, ROC for funds (NSC-85-2113-M008-001) in generous support of this work. References 1 S. A. Hudson and P. M. Maitlis, Chem. Rev., 1993, 93, 861; P.Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and E. Sola, Coord. Chem. Rev., 1992, 117, 215; P. Maitlis and A. M. Giroud-Godquin, Angew. Chem., Int. Ed. Engl., 1991, 30, 375. 2 (a) H. Zheng, C. K. Lai and T. M. Swager, Chem. Mater, 1995, 7, 2067; (b) A. G. Serrette and T. M. Swager, J. Am. Chem. Soc., 1993, 115, 8879; (c) E. Constable, M. J. Hannon and D. A. Tocher, Angew. Chem., Int. Ed. Engl., 1992, 31, 230. 3 (a) A. G. Serrette, C. K. Lai and T. M. Swager, Chem. Mater., 1994, 6, 2252; (b) D. Lelievre, L. Bosio, J. Simon, J. J. Andre and F. J. Benselbaa, J. Am. Chem. Soc., 1992, 114, 4475; (c) C. K. Lai, A. G. Serrette and T. M. Swager, J. Am. Chem. Soc., 1992, 114, 7948; (d) L. Barbera, M. A. Esteruelas, A. M. Levelut, L. A. Oro, J. L. Serrano and E. Sola, Inorg. Chem., 1992, 31, 732; (e) R. H. Cayton, M. H. Chisholm and F. O. Darrington, Angew. Chem., Int. Ed. Engl., 1990, 29, 1481. 4 S. Chandrasekhar, Liq. Cryst., 1993, 14, 3; S. Chandrasekhar and G. S. Ranganath, Rep. Prog. Phys., 1990, 53, 57. 5 G. R. Newkome and T. Kawato, Inorg. Chim. Acta, 1979, 37, L481; D. E. Fenton, C. M. Regan, U. Casellato, P. A. Vigato and M. Vidali, Inorg. Chim. Acta, 1982, 58, 83. Received 3rd October 1996; Communication 6/06770K

ISSN:1477-9226    

DOI:10.1039/a606770k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 19–23 19 Interaction of polypyridyl ruthenium(II) complexes containing non-planar ligands with DNA Ya Xiong,*a Xiao-Feng He,a Xiao-Hua Zou,a Jian-Zhong Wu,a Xiao-Ming Chen,a Liang-Nian Ji,*a Run-Hua Li,b Jian-Ying Zhou b and Kai-Bei Yu c a Department of Chemistry, Zhongshan University, Guangzhou 510275, P. R. China b State Key Laboratory of Ultrafast Laser Spectroscopy, Zhongshan University, Guangzhou 510275, P. R. China c Chengdu Institute of Organic Chemistry, Academia Sinica, Chengdu 610093, P.R. China Received 5th August 1998, Accepted 9th October 1998 2-(2-Chlorophenyl)imidazo[4,5-f ]1,10-phenanthroline (CIP) or 2-(2-nitrophenyl)imidazo[4,5-f ]1,10-phenanthroline (NIP) and their complexes [Ru(bpy)2(CIP)]21 and [Ru(bpy)2(NIP)]21 (bpy = 2,29-bipyridine) have been synthesized and characterized. The binding of the two complexes to calf thymus DNA has been investigated with spectrophotometric methods and viscosity measurements.The experimental results indicate that the two complexes bind to DNA through a partial intercalative mode that is diVerent from the bonding mode for their parent compound, [Ru(bpy)2(PIP)]21 (PIP = 2-phenylimidazo[4,5-f ]1,10-phenanthroline). The crystal structure of [Ru(bpy)2(CIP)]- [ClO4]2?2H2O was determined by X-ray diVraction analysis; the imidazo[4,5-f ]1,10-phenanthroline moiety is not coplanar with the 2-chlorophenyl ring, having a dihedral angle of 44.58 in the CIP.There has been substantial interest in understanding the DNA binding properties of polypyridyl ruthenium(II) complexes in the hope of developing novel probes of nucleic acid structure and sites.1–6 The strong visible absorbance and the luminescent characteristics of the ruthenium(II) complexes and their perturbations on binding to DNA provide a convenient handle for monitoring the DNA binding process. Since pioneering studies by Barton and co-workers1a–c showed that optically active isomers of [Ru(phen)3]21 (phen = 1,10-phenanthroline) bind to DNA with distinctive characteristics, the binding of the complex to DNA has been actively studied and many new structural analogues based on the prototype [Ru(phen)3]21 have been also synthesized and investigated.However, most of these reported complexes contain only planar aromatic ligands and investigations of polypyridyl ruthenium(II) complexes with non-planar ligands as DNAbinding reagents have been relatively few.In fact, some of these complexes also exhibit interesting properties upon binding to DNA. For example, although the DIP (DIP = 4,7- diphenyl-1,10-phenanthroline) ligand in [Ru(DIP)3]21 is not flat, with phenyl groups twisted out of the phenanthroline plane,7 experimental data are consistent with intercalation binding by this ligand 1f and show it can distinguish between leftand right-handed DNA helices.1a,b Morgan et al.8 have also addressed two ruthenium(II) complexes with out-of-plane ligands, [Ru(bpy)2(qpy)]21 (qpy = quaterpyridyl) and [Ru(bpy)2- (dpp)]21 (dpp = 2,3-di-2-pyridylpyrazine). The former can intercalate DNA, whereas the latter cannot.In this paper we report the DNA binding behaviour of two bpy ruthenium(II) complexes with a non-flat ligand, 2-(2-chlorophenyl) imidazo[4,5-f ]1,10-phenanthroline (CIP) or 2-(2-nitrophenyl) imidazo[4,5-f ]1,10-phenanthroline (NIP). In each complex two bpy are used as co-complexation ligands with CIP or NIP, because bpy has been previously demonstrated to be at best only minimally eYcient at inducing intercalative binding with DNA,1b, f allowing us to focus on the influence of the conformation of CIP or NIP on the interaction.Experimental Syntheses The complex cis-[Ru(bpy)2Cl2]?2H2O, 1,10-phenanthroline-5,6- dione and [Ru(bpy)2(PIP)][ClO4]2?3H2O (PIP = 2-phenylimidazo[ 4,5-f ]1,10-phenanthroline) were prepared according to the literature procedures.9–11 Other materials were commercially available.CIP. The compound was synthesized according to the method for the preparation of imidazole rings established by Steck and Day.12 A mixture of 2-chlorobenzaldehyde (3.5 mmol, 0.4 cm3 of 98% solution), 1,10-phenanthroline-5,6-dione (2.5 mmol, 0.525 g), ammonium acetate (50 mmol, 3.88 g) and glacial acetic acid (7 cm3) was refluxed for about 2 h, then cooled to room temperature and diluted with water (ca. 25 cm3).Dropwise addition of concentrated aqueous ammonia gave yellow precipitates, which were collected and washed with water. The crude products were purified by silica gel filtration (60–100 mesh, ethanol). The principal yellow band was collected. Crystalline solids were obtained by slow evaporation of the solution, then were dried at 50 8C in vacuo. Yield 0.678 g, 82% (Found: C, 68.85; H, 3.3; N, 17.0. Calc. for C19H11ClN4: C, 69.1; H, 3.4; N, 17.0%). n& max/cm21 3423 (N–H) 3057 (C–H) and 1609 (C]] N). 1H NMR [(CD3)2SO]: d 13.83 (s, 1 H), 9.05 (d, 1 H), 9.01 (d, 1 H), 8.95 (d, 1 H), 8.86 (d, 1 H), 7.94 (d, 1 H), 7.89– 7.80 (m, 2 H), 7.70 (d, 1 H) and 7.60–7.53 (m, 2 H). NIP?0.5H2O. This compound was obtained with a procedure analogous to that for CIP, using 2-nitrobenzaldehyde in place of 2-chlorobenzaldehyde. Yield 0.656 g, 75% (Found: C, 64.85; H, 3.4; N, 19.8. Calc. for C19H12N5O2.5: C, 65.2; H, 3.45; N, 20.0%). n& max/cm21 3402 (N–H), 3057 (C–H), 1609 (C]] N) and 1532 (NO2). 1H NMR [(CD3)2SO]: d 14.11 (s, 1 H), 9.05 (d, 1 H), 9.00 (d, 1 H), 8.86 (d, 1 H), 8.71 (d, 1 H), 8.08 (d, 1 H), 7.96 (d, 1 H), 7.90–7.84 (m, 2 H) and 7.80–7.75 (m, 2 H). [Ru(bpy)2(CIP)][ClO4]2?2H2O. A mixture of cis-[Ru(bpy)2- Cl2]?2H2O (0.5 mmol, 0.261 g), CIP (0.5 mmol, 0.165 g), methanol (20 cm3) and water (10 cm3) was refluxed under argon for 2 h to give a clear red solution. After most of the methanol solvent was removed under reduced pressure, a red precipitate was obtained by dropwise addition of a saturated aqueous NaClO4 solution.The product was purified by column chromatography on alumina using acetonitrile–toluene (2 : 1 v/v) as eluent and then dried in vacuo. Yield 0.313 g, 64% (Found: C,20 J. Chem. Soc., Dalton Trans., 1999, 19–23 48.0; H, 3.0; N, 11.7. Calc. for C39H31Cl3N10O10Ru: C, 47.6; H, 3.2; N, 11.45%). n& max/cm21 3428 (N–H), 3074 (C–H), 1606 (C]] N) and 1092 (ClO4 2). lmax/nm (e/dm3 mol21 cm21) (water) 457 (14100), 283 (80000), 255 (36900) and 211 (41300). 1H NMR [(CD3)2SO]: d 14.55 (s, 1 H), 9.08 (dd, 2 H), 8.89 (d, 2 H), 8.85 (d, 2 H), 8.23 (t, 2 H), 8.12–8.09 (m, 4 H), 7.92–7.91 (m, 3 H), 7.88 (d, 2 H), 7.77 (d, 2 H), 7.64–7.60 (m, 6 H) and 7.35 (s, 1 H). [Ru(bpy)2(NIP)][ClO4]2?H2O. This complex (deep red) was synthesized in an identical manner to that described for [Ru- (bpy)2(CIP)][ClO4]2?2H2O, with 0.5 mmol, 0.175 g NIP?0.5H2O in place of CIP. Yield 0.28 g, 59% (Found: C, 48.15; H, 2.8; N, 13.0. Calc.for C39H31Cl3N10O10Ru: C, 48.0; H, 3.0; N, 13.0%). n& max/cm21 3430 (N–H), 3070 (C–H), 1601 (C]] N), 1534 (NO2) and 1091 (ClO4 2). lmax/nm (e/dm3 mol21 cm21) (water) 457 (17400), 283 (88900), 255 (53900) and 205 (51500). 1H NMR [(CD3)2SO]: d 8.89–8.83 (m, 4 H), 8.28 (d, 1 H), 8.2 (t, 2 H), 8.08 (t, 2 H), 7.88 (d, 2 H), 7.82 (d, 2 H), 7.76–7.70 (m, 6 H), 7.59– 7.57 (m, 4 H), 7.54 (t, 1 H) and 7.37 (t, 2 H). CAUTION: Perchlorate salts of metal complexes with organic ligands are potentially explosive, and only small amounts of the material should be prepared and handled with great care.Measurements The analyses (C, H and N) were performed using a Perkin- Elmer 240Q elemental analyser. Infrared spectra were obtained with a Nicolet 170SX-FTIR spectrophotometer and KBr discs, UV/VIS spectra on a Shimadzu MPS-2000 spectrophotometer and 1H NMR spectra on a Bruker ARX-300 spectrometer with (CD3)2SO as solvent and Me4Si as an internal standard.Steadystate emission experiments were performed with a Shimadzu RF-5000 fluorescence spectrometer. Time-resolved emission measurements were conducted with the same detection system and procedure as described previously.11 All the experiments involving the interaction of the complexes with DNA were carried out in aerated buVer (5 mmol dm23 Tris–HCl, pH 6.8, 50 mmol dm23 NaCl). Solutions of calf thymus DNA in the buVer gave a ratio of UV absorbance at 260 and 280 nm of ca. 1.9 : 1, indicating that the DNA was suYciently free of protein.13 The DNA concentration per nucleotide was determined by absorption spectroscopy using the molar absorption coeYcient (6600 dm3 mol21 cm21) at 260 nm.14 Viscosity experiments used a Ubbelodhe viscometer, immersed in a thermostatted water-bath maintained at 28 (±0.1) 8C. The DNA samples, approximately 200 base pairs in average length, were prepared by sonication in order to minimize complexities arising from DNA flexibility.15 Data were presented as (h/h0)1/3 versus the concentration of ruthenium(II) complex, where h is the viscosity of DNA in the presence of complex and h0 that of DNA alone.Viscosity values were calculated from the observed flow time of DNA-containing solutions (t) corrected for that of buVer alone (t0), h = t 2 t0.3b Crystallography The red prismatic crystals of [Ru(bpy)2(CIP)][ClO4]2?2H2O were grown from the diVusion of diethyl ether vapour into a concentrated acetonitrile solution of the complex.A single crystal of dimensions 0.60 × 0.44 × 0.34 mm was used for data collection. Crystal data and data collection parameters. C39H27Cl3N8- O8Ru?2H2O, M = 979.14, monoclinic, space group P21/n, a = 14.283(2), b = 16.671(2), c = 17.596(2) Å, b = 91.02(1)8, U = 4189.2(9) Å3, Z = 4, Dc = 1.552 g cm23, m(Mo-Ka) = 0.632 mm21, F(000) = 1984, T = 295 K. 7159 Reflections were measured (6582 unique, Rint = 0.0204) on a Siemens P4 diVractometer in the range 1.68 < q < 25.988, 0 < h < 16, 0 < k < 20, 220 < l < 20, operating in w scan mode and using graphite-monochromated Mo-Ka radiation (l = 0.71073 Å).A semiempirical absorption correction via y scans was applied. Structure solution and refinement. The structure was solved by the direct method and refined anisotropically on F 2 by fullmatrix least-squares techniques using the SHELXTL 97 program. 16 All hydrogen atoms were generated geometrically (C–H 0.96 Å).The final refinement gave R = 0.0506, R9 = 0.1286. The final diVerence map had peaks between 20.536 and 1.179 e Å23. CCDC reference number 186/1195. See http://www.rsc.org/suppdata/dt/1999/19/ for crystallographic files in .cif format. Results and discussion Crystal structure The molecular structure of [Ru(bpy)2(CIP)][ClO4]2?2H2O has been confirmed by single crystal X-ray diVraction analysis. It consists of a [Ru(bpy)2(CIP)]21 cation, two disordered ClO4 2 and two water molecules, one of which occupies two positions (O10W and O11W) with an occupancy of 0.5, respectively; the other has full occupancy and forms a hydrogen bond with the imidazole hydrogen, H(2N), O9W ? ? ? H(2N) 2.84 Å.An ORTEP17 drawing of the cation with atomic numbering scheme is depicted in Fig. 1. Selected bond lengths and angles are summarized in Table 1. As shown in Fig. 1, the central ruthenium atom is chelated by two bpy ligands oriented in a cis geometry and a CIP ligand.The co-ordination geometry about the ruthenium atom is that of a distorted octahedron, with a bite angle of 79.28 averaged over the three bidentate ligands. This distortion from an ideal Fig. 1 An ORTEP drawing of [Ru(bpy)2(CIP)]21 and the atom numbering. Table 1 Selected bond lengths (Å) and angles (8) for [Ru(bpy)2(CIP)]- [ClO4]2?2H2O Ru–N(3) Ru–N(4) Ru–N(5) N(6)–Ru–N(7) N(6)–Ru–N(5) N(7)–Ru–N(5) N(6)–Ru–N(8) N(7)–Ru–N(8) N(5)–Ru–N(8) N(6)–Ru–N(3) N(7)–Ru–N(3) N(5)–Ru–N(3) N(8)–Ru–N(3) N(6)–Ru–N(4) N(7)–Ru–N(4) N(5)–Ru–N(4) N(8)–Ru–N(4) 2.064(2) 2.075(2) 2.063(3) 86.73(10) 78.83(10) 95.21(10) 97.80(10) 79.09(10) 173.60(10) 95.26(10) 177.23(10) 87.09(10) 98.70(10) 173.97(10) 98.49(10) 97.61(10) 86.20(10) Ru–N(6) Ru–N(7) Ru–N(8) N(3)–Ru–N(4) C(12)–N(3)–Ru C(13)–N(3)–Ru C(15)–N(4)–Ru C(14)–N(4)–Ru C(24)–N(5)–Ru C(20)–N(5)–Ru C(25)–N(6)–Ru C(29)–N(6)–Ru C(30)–N(7)–Ru C(34)–N(7)–Ru C(39)–N(8)–Ru C(35)–N(8)–Ru 2.052(3) 2.061(3) 2.063(3) 79.63(9) 128.2(2) 114.08(18) 128.1(2) 114.25(19) 115.1(2) 126.4(2) 116.0(2) 125.4(2) 124.9(2) 115.0(2) 126.4(2) 115.2(2)J.Chem. Soc., Dalton Trans., 1999, 19–23 21 octahedral geometry is due to the customary narrow bite angles of the bipyridine moieties, as seen in other ruthenium– bipyridine complexes.18 The torsion angles between the pyridine pairs of two bpy ligands of the complex are non-equivalent, one being 2 and the other 88; however, they are all located in the range expected for this type of compound such as [Ru- (bpy)2(gly)]1 (gly = glycinate) (1.4 and 7.48),19 [Ru(bpy)2(ip)]21 [ip = imidazo[4,5-f ]1,10-phenanthroline] (5.7 and 8.68),12 [Ru(bpy)2(phen)]21 (6.4 and 10.38) and [Ru(bpy)2(mphen)]21 (mphen = 5-methyl-1,10-phenanthroline) (1.9 and 12.38).20 In the CIP ligand the ip moiety is planar with an average deviation of 0.0385 Å from the least-squares plane, but the 2-chlorophenyl group is remarkably twisted with respect to the ip plane forming a dihedral angle of 44.58 to minimize possible steric interaction between the substituent Cl and the imidazole ring.Although the crystal structure of [Ru(bpy)2(NIP)]21 is not known, it is guessed that the NIP also might possess a non-planar conformation because the NO2 group in NIP has a larger steric volume than the substituent Cl. The arrangement of CIP or NIP is diVerent from the geometry of their parent compound, PIP, all atoms of which basically lie on a plane.21 The mean Ru–N bond length (2.063 Å) is comparable with those published for [Ru(bpy)3]21 (2.056 Å),22 [Ru(bpy)2(phen)]21 (2.069 Å) 20 and [Ru(phen)3]21 (2.063 Å),23 although there are larger diVerences in size and shape for bpy, phen and CIP.There are two ways of explaining why these Ru–N bond lengths are similar to each other. One may be that the changes of s bonding are almost balanced by those of p bonding in Ru–N with the changes of these ligand structures such that the interatomic Ru–N are basically constant.22 Another possible interpretation is that these bonds are not particularly sensitive to the total electronic density, as seen in the structures of [Ru(bpy)3], [Ru(bpy)3]21 and [Ru(bpy)3]31.24 An interesting feature of the crystal structure is the packing of the complex cation with respect to its chirality.A pair of [Ru(bpy)2(CIP)]21 enantiomers (D and L) are arranged asymmetrically together by the mutual penetration of the two CIP ligands.The closest distance between the two imidazo[4,5-f ]- 1,10-phenanthroline planes is 3.7 Å. Such a close packing arrangement implies that there are some ‘p–p’ stacking interactions between the aromatic systems of the two intruding CIP ligands. Absorption spectroscopic studies The electronic absorption spectra of the two complexes mainly consist of four well resolved bands, similar in shape to those of [Ru(bpy)3]21.25 The lowest energy absorption bands at 457 nm and the middle intensity peaks at 255 nm are assigned to metalto- ligand charge transfer (MLCT) transitions;25 the two bands with maxima of 283 and 211 nm for [Ru(bpy)2(CIP)]21 and 283 and 205 nm for [Ru(bpy)2(NIP)] are attributed to intraligand p–p* transitions by comparison with the spectrum of [Ru(bpy)3]21.25 The interaction of the two complexes with DNA was investigated using absorption spectra.The electronic spectral trace of the two complexes titrated with DNA is given in Fig. 2, using [Ru(bpy)2(CIP)]21 as an example. In both cases, although no red shift was found, notable hypochromicities were observed. The MLCT transitions at 457 nm show a decrease in intensity with a maximum value of 12% as the amount of DNA was increased. The spectroscopic changes suggest that there are some interactions between the complexes and DNA. However, it is noteworthy that the hypochromicity of the MLCT peaks is much smaller than that of their parent complex, [Ru(bpy)2- (PIP)]21 (21.9%), in which PIP can insert deeply into DNA base pairs.11 Thus it is believed that the binding mode of the two complexes to DNA is likely diVerent from that of [Ru(bpy)2(PIP)]21.Luminescence studies In water or CH3CN, [Ru(bpy)2(CIP)]21 can emit luminescence with similar emission maxima, 611 and 613 nm, but diVerent lifetimes, 624 and 1579 ns, respectively. Its quantum yields relative to [Ru(bpy)3]21 are 0.78 in water and 0.96 in CH3CN, comparable to those of [Ru(bpy)2(PIP)]21 (0.81 and 0.94).For [Ru(bpy)2(NIP)]21 no emission is observed in the two media. This could be explained in the terms of the photoexcited electron being captured by the strong electron-accepting group, NO2, in the NIP ligand and being unable to give emission to return to the ground state. A similar case was observed for ruthenium(II) complexes containing 5-nitro-1,10-phenanthroline. 26 The results of the emission titrations for [Ru(bpy)2(CIP)]21 with DNA are illustrated with the titration curves in Fig. 3. Upon addition of DNA the emission intensity grows steadily to around 1.9, and the lifetime increases from 624 to 1310 ns. The magnitudes of emission enhancement are much larger than that for [Ru(bpy)3]21,1f but obviously smaller than that of the structurally related DNA intercalator [Ru(bpy)2(PIP)]21.11 Although the emission enhancement and lifetime increase could not be regarded as a criterion for binding mode, they are related to the extent to which the complex gets into a hydrophobic environment inside the DNA and avoids the quenching eVect of solvent water molecules.Therefore we infer that [Ru(bpy)2(CIP)]21 inserts less deeply into the hydrophobic environment of DNA than does [Ru(bpy)2(PIP)]21. Steady-state emission quenching experiments using [Fe(CN)6]42 as quencher support the above proposal. As shown in Fig. 4, in the absence of DNA, [Ru(bpy)2(CIP)]21 was eY- Fig. 2 Electronic spectral traces of [Ru(bpy)2(CIP)]21 in Tris–HCl buVer upon addition of calf thymus DNA.[Ru] = 10 mmol dm23, [DNA] = (0–5) × 1024 mol dm23.22 J. Chem. Soc., Dalton Trans., 1999, 19–23 ciently quenched by the quencher, resulting in a linear Stern– Volmer plot (slope 2.2, correlation coeYcient 0.999). In the presence of DNA the slope of the plot is remarkably decreased (slope 0.86, correlation coeYcient 0.995), but not nearly equal to zero just like that of [Ru(bpy)2(PIP)]21.11 The ion [Fe(CN)6]42 has been shown to be able to distinguish diVerently bound ruthenium(II) species.27 Positively charged ‘free’ complex ions should be readily quenched by [Fe(CN)6]42 when the complex bound to DNA can be protected from the quencher because highly negatively charged [Fe(CN)6]42 would be repelled by the negative DNA phosphate backbone, hindering quenching of the emission of the bound complex. Therefore a larger slope for the Stern–Volmer curve parallels poorer protection. So [Ru(bpy)2(CIP)]21 binds less tightly than does [Ru- (bpy)2(PIP)]21. This is just the expected result on the basis that PIP possesses a flatter conformation than CIP, which would lead PIP to intercalate more easily into DNA than does CIP.In previous studies on DNA-complex binding biexponential emission decay curves were observed. They were usually ascribed to two diVerent binding forms.1b,c, j,k,8 For [Ru(bpy)2- (CIP)]21 the emission decay curves fit well with monoexponential functions.So we speculate that it interacts with DNA through a binding mode11 and that the bound component exchanges rapidly with coexisting free component.1c For [Ru(bpy)2(NIP)]21 no luminescence was detected, either alone in aqueous solution or in the presence of DNA. The quenching is caused by the strong electron-accepting group, NO2, in the complex structure itself. So it is not sensitive to the environment. The observed non-emissive behaviour of [Ru(bpy)2(NIP)]21 does not imply it cannot interact with DNA.Viscosity measurements Optical photophysical probes generally provide necessary, but Fig. 3 Plots of relative emission intensity (d) and excited state lifetime (m) versus DNA:Ru ratio for [Ru(bpy)2(CIP)]21 ([Ru] = 2 mmol dm23). Fig. 4 Emission quenching curves of [Ru(bpy)2(CIP)]21 with increasing concentration of quencher [Fe(CN)6]42 in the absence (d) and presence (m) of DNA. [Ru] = 2 mmol dm23, DNA:Ru = 40:1. not suYcient, clues to support a binding model.Hydrodynamic measurements that are sensitive to length change (i.e. viscosity and sedimentation) are regarded as the least ambiguous and most critical tests of a binding model in solution in the absence of crystallographic structural data.2a,b A classical intercalation model demands that the DNA helix lengthens as base pairs are separated to accommodate the bound ligand, leading to the increase of DNA viscosity. In contrast, a partial, non-classical intercalation of ligand could bend (or kink) the DNA helix, reduce its eVective length and, concomitantly, its viscosity.2a,b The eVect of rac-[Ru(bpy)2(PIP)]21, [Ru(bpy)2(CIP)]21 and [Ru(bpy)2(NIP)]21 on the viscosity of rod-like DNA is shown in Fig. 5. The complex [Ru(bpy)2(PIP)]21 can increase the viscosity of DNA, consistent with the classical intercalation mode; the last two complexes decreased DNA viscosity as the molar ratio of ruthenium(II) complex to DNA was increased, similar to experiments on interactions of DNA with D-[Ru(phen)3]21.2a The experimental results suggest the two complexes could bind to DNA not by the classical intercalation binding mode but by the partial, non-classical intercalation model.This may be related to the molecular structures of the complexes. Since the steric constraint to coplanarity of the phenyl containing the larger substituent group and ip moiety in the CIP or NIP is obviously more severe than that for DIP in [Ru(DIP)3]21 or qpy in [Ru(bpy)2(qpy)]21, in which the torsion between the aromatic rings is involved in the interaction of the smaller hydrogen atoms,8 the CIP or NIP ligand could not completely intercalate {like [Ru(DIP)3]21 or [Ru(bpy)2(qpy)]21 does}, at most they could penetrate their substituted phenyl moieties into the DNA base pairs, leaving the other part of the ligand in the groove.The partial intercalation may act as a “wedge” to pry apart one side of a basepair stack, as observed for the D-[Ru(phen)3]21,2a,b but not fully separate the stack as required by the classical intercalation mode.This would cause a static bend or kink in the helix and decrease the viscosity of DNA. In conclusion, based on the variations of photophysical properties and viscosity measurement on binding to DNA, as well as the crystal structure, it is concluded that the torsion between the aromatic rings of CIP or NIP, due to the introduction of the bulky substituent, results in [Ru(bpy)2(CIP)]21 or [Ru(bpy)2(NIP)]21 only partially intercalating into DNA, differing from the binding behaviour of their parent complex, [Ru(bpy)2(PIP)]21.11 Acknowledgements We acknowledge the financial support from the National Natural Science Foundation of China, the State Laboratory of Coordination Chemistry in Nanjing university and Postdoctoral Foundation of Guangdong Province.Fig. 5 EVect of increasing amounts of [Ru(bpy)2(PIP)]21 (m), [Ru(bpy)2(CIP)]21 (j) and [Ru(bpy)2(NIP)]21 (d) on the relative viscosity of calf thymus DNA.J.Chem. Soc., Dalton Trans., 1999, 19–23 23 References 1 (a) J. K. Barton and A. L. Raphael, J. Am. Chem. Soc., 1984, 106, 2466; (b) C. V. Kumar, N. J. Turro and J. K. 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ISSN:1477-9226    

DOI:10.1039/a806170j

出版商:RSC    

年代:1999

数据来源: RSC