Rod-like Ligands Research Articles

Syntheses, crystal structures, and luminescence properties of three cadmium coordination polymers assembled from a semi-rigid tetracarboxylate ligand

Crystal engineering is considerably useful in the preparation of functional coordination polymers. In the present study, a new semi-rigid tetracarboxylate, 4,5-bis(4-carboxyphenoxy)phthalic acid (H4L), was designed and applied for assembling metal coordination polymers. Self-assembling process involving Cd(II) metal ions, H4L and 4,4′-bipyridine (4,4′-bpy), (E)-1,2-bis(pyridin-4-yl)ethane (bpe) or 1,4-bis(1-imidazolyl)benzene (bib) resulted into the formation of coordination polymers, including [Cd2(L)(4,4′-bpy)1.5(H2O)]n·(H2O)n (1), [Cd2(L)(bpe)1.5(H2O)]n·(H2O)3.5n (2), and [Cd2(L)(bib)1.5]n·(H2O)n (3). Through X-ray single crystal diffraction analysis, the three compounds 1–3 were found to exhibit isostructural three-dimensional polymeric structures composed of two-dimensional secondary layers pillared by different rod-like N-donor ligands. Compared with the uncoordinated H4L exhibiting a symmetric crystal structure, the molecular configurations of L4− in 1–3 were tuned due to the complexation of cadmium ion and the introduction of different N-donors. Additionally, the coordination geometries of cadmium ions and luminescence properties in compounds 1–3 were finely tuned due to the introduction of different lengths of rod-like ligands. The thermostability and luminescence properties of compounds 1–3 were determined. The present results provide further understanding of the crystal engineering of semi-rigid ligands to a certain extent.

Anion-dependent construction of a series of fluorescent coordination polymers based on 1D zinc∩4,4′-bis(imidazol-1-yl)-biphenyl substrates

In this work, the rod-like ligand 4,4′-bis(imidazol-1-yl)-biphenyl (bibp) has been utilized as a building block to carry out counterion effects on the structural diversities of coordination polymers. A series of new zinc complexes, [Zn(trans-bibp)Cl2]∞ (1), [Zn(trans-bibp)Br2]∞ (2), {[Zn(cis-bibp)(Ac)2]·(H2O)}∞ (3), [Zn(trans-bibp)SO4]∞ (4), {[Zn2(cis-bibp)2(ipa)2]·(H2O)}∞ (5, H2ipa=isophthalic acid) and {[Zn(trans-bibp)(cis-bibp)]·(ClO4)2(CHCl3)2(CH3OH)}∞ (6) have been successfully synthesized. Complexes 1 and 2 are iso-structural, which show a 1D W-type chain [Zn(trans-bibp)]∞. Complex 3 exhibits a 2D wave-like layer formed by the hydrogen bond among the 1D linear chain [Zn(cis-bibp)]∞. Complex 4 displays a 2D fish-bone lattice, which is generated from connecting the 1D W-type chain [Zn(trans-bibp)]∞ by the μ2-SO42-. Complex 5 presents an interesting 2D–3D 65·8 architecture, including two 1D chains [Zn(ipa)]∞ and [Zn(cis-bibp)]∞. Complex 6 demonstrates a 2D wave-like layer [Zn(trans-bibp)(cis-bibp)]∞. The structural diversities among 1–6 have been carefully discussed, and the role of counterion in the self-assembly of coordination polymer have also been well documented from the coordination affinity and bridging mode. Furthermore, the solid-state fluorescence properties of 1–6 at room temperature have been studied.

Anion effect on the topological frameworks of a series of manganese coordination polymers based on 1,4-bis(imidazol-1-yl)-benzene: Syntheses, crystal structures and magnetic properties

In this work, the rod-like ligand 1,4-bis(imidazol-1-yl)-benzene (bib) has been utilized as a building block to perform counterion researches on the structural diversities of coordination polymers. A series of new manganese compounds, {[Mn(bib)3(ClO4)2](CHCl3)2}n (1), [Mn(bib)2(N3)2]n (2), [Mn(bib)2(HCO2)2]n (3), [Mn(bib)2(Ac)2]n (4), {[Mn(bib)2(CF3SO3)2](CH2Cl2)4}n (5), and [Mn(bib)2(SO4)]n (6) have been successfully synthesized. Compound 1 shows a 3D interpenetrating α-Po network only based on the bib linker. Compounds 2 and 3 exhibit a 2D (4,4) layer with parallel and incline interpenetration, respectively. Compounds 4 and 5 display a parallel-packing 2D (4,4) layer with the porosity of 23.4% and 61.4%, respectively. Compound 6 furnishes a 3D α-Po framework with a 2D (4,4) layer pillared by the μ2-SO42− ion. The structural diversities among 1–6 have been carefully discussed, and the roles of counterions (from coordination affinity and molecular size) in the self-assembly of coordination polymers have also been well documented. Furthermore, magnetic properties of 6 have been carefully studied.

When long bis(pyrazolates) meet late transition metals: structure, stability and adsorption of metal–organic frameworks featuring large parallel channels

A family of bis(pyrazolato)-based metal-organic frameworks (MOFs) was isolated by reacting 1,4-bis(1H-pyrazol-4-ylethynyl)benzene (H2BPEB) with a number of transition metal ions. Special attention was dedicated to their structural features, their thermal and chemical stability, as well as their spectroscopic and adsorption properties. The rod-like ligands, connecting Zn(II), Ni(II) and Fe(III) nodes, fabricate 3-D networks containing 1-D pervious channels. The combination of thermal analysis and variable-temperature XRPD demonstrated the remarkable thermal robustness of the three materials, which are stable in air up to at least 410 °C, and showed their structural response to increasing temperature. Specific experiments permitted us to test the chemical stability of the three species toward water as well as moderately acidic and basic solutions, the Ni(II) derivative being stable and hydrophobic in all the conditions assayed. The electronic transitions of both the ligand and the MOFs were investigated by solid-state UV-Vis absorption as well as by steady-state and time-resolved fluorescence analysis, which showed that the high fluorescence of the linker is perturbed in the three MOFs, suggesting high sensitivity to environmental changes. N2 adsorption measurements at 77 K allowed to estimate promising Langmuir specific surface areas, peaking at 2378 m2 g−1 in the case of the Ni(II) derivative. The best CO2 and CH4 uptake performances were achieved with the Fe(III)-based MOF. Indeed, adsorption experiments with CO2 revealed that a considerable amount, up to 40% wt, is adsorbed by the Fe(III) derivative under the mild conditions of 298 K and 10 bar.

Orientation and Polarized Optical Emission Properties of Platinum(II) Complexes in Smectic Liquid Crystals

AbstractWe have prepared a series of platinum complexes with a rodlike ligand and smectic (Sm) liquid crystals (LCs) to demonstrate polarized phosphorescence. The ligands for the Pt complexes “12F2PPyO8” [2‐(4′‐dodecyl‐5′,6′‐difluorophenyl)‐5‐octyloxypyridinato‐N,C2′] and “12F2PPyO12” [2‐(4′‐dodecyl‐5′,6′‐difluorophenyl)‐5‐dodecyloxypyridinato‐N,C2′] with long alkyl and alkoxy chains exhibited the Smectic A (SmA) phase, however no liquid crystallinity was evident in Pt complexes with LC ligands. The host LCs 1‐(4‐butyl‐2,3‐difluoro‐phenyl)‐4‐(trans‐4‐pentylcyclohexyl)benzene (4F2PPCH5) and 2‐(2,3‐difluoro‐4‐hexylphenyl)‐6‐octyloxynaphthalene (6F2PNaO8) with long flexible chains showed wide SmA phase temperature ranges. Pt complex/Sm LC mixtures were oriented on rubbed polyimide substrates or by applying a magnetic field. The orientation coefficients of the magneto‐oriented samples were recorded to be over 0.6 in the Sm LC temperature range. The oriented samples exhibited polarized optical emissions assigned to the monomer and excimer states, which were perpendicular to the orientation direction. This indicates that the transition dipole moment of the Pt complex is oriented from the ligand to the Pt atom. Pt complexes with rodlike ligands with long alkyl and alkoxy chains and host Sm LC with such chains are much more likely to obtain high order parameters and generate highly polarized optical emissions. In the mixtures, the polarization ratios of the monomer and excimer in the SmA phase were estimated to be approximately 2.5–2.9 and 4.6–5.4, respectively.

Unusual six-connected self-catenated network with 5-fold interpenetrated CdSO4subnets: stepwise synthesis, topology analysis and fluorescence properties

In this work, the rod-like ligand 4,4′-bis(imidazol-1-yl)-biphenyl (L) has been utilized as a long building block to perform an intensive study on the entanglement of metal–organic frameworks (MOFs). The room-temperature reaction of Cd(ClO4)2·6H2O with ligand L in a glass-tube affords a new coordination polymer {[Cd(ClO4)2(L)2]·(CH3OH)·(H2O}∞ (1), which exhibits an inter-digitated (4,4) layer pierced by the ClO4− ion. Considering the weak coordination affinity of the ClO4− ion and that it could be easily replaced by other ions, complex 1 was employed as a precursor to react with NH4Cl, resulting in a novel organic–inorganic hybrid material {[CdCl(L)2](ClO4)·(H2O)5.5·(CH3OH)0.5}∞ (2). In complex 2, the heteroleptic octahedral CdII node is connected by the linear spacer L into a five-fold interpenetrated CdSO4 framework. Then, the subnet is further linked together by the Cl− ion to form an unusual self-catenated network with the Schafli symbol of 44·610·8. Great structural diversities in 1 and 2 reveal that the counterion plays an important role in the self-assembly of MOFs. Furthermore, complexes 1 and 2 both exhibit solid-state fluorescence properties at room temperature.

Synthesis, characterization, and polarized luminescence properties of platinum(ii) complexes having a rod-like ligand

We have synthesized a series of platinum (Pt) complexes having a rod-like ligand: 'Pt(F(2)PPy)acac', 'Pt(12F(2)PPy)acac', and 'Pt(12F(2)PPyO4)acac'. The crystal form of Pt(12F(2)PPy)acac was successfully determined to be triclinic by single-crystal X-ray structural analysis. The molecules were parallelly aligned in the unit cell. Monomer and excimer emissions of Pt(12F(2)PPy)acac were observed in hexane solution, poly(methyl methacrylate) film, and various nematic LCs. Homogeneous LC cells with the Pt complex/LC mixtures exhibited polarized optical emission resulting from monomer and excimer states. The PL intensity perpendicular to the orientation direction was higher than the parallel one in the whole wavelength region of the Pt complex and the polarization ratio of the excimer was higher than that of the monomer. The polarization ratios of the excimers were estimated to be 1.4-2.5 in nematic LC at room temperature, and decreased gradually with increasing temperature. The polarization ratios of Pt(12F(2)PPyO4)acac were higher than those of Pt(F(2)PPy)acac and Pt(12F(2)PPy)acac in all the LCs.

Very Long-Distance Magnetic Coupling in a Dicopper(II) Metallacyclophane with Extended π-Conjugated Diphenylethyne Bridges

Self-assembly of the rigid rodlike ligand N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and Cu(2+) ions affords a novel dinuclear copper(II) metallacyclophane (nBu(4)N)(4)[Cu(2)(dpeba)(2)]·4MeOH·2Et(2)O (1) featuring a very long intermetallic distance (r = 15.0 Å). Magnetic susceptibility measurements for 1 reveal a moderately weak but nonnegligible intramolecular antiferromagnetic coupling between the two metal centers across the double para-substituted diphenylethynediamidate bridge (J = -3.9 cm(-1); H = -JS(1)S(2), where S(1) = S(2) = S(Cu) = (1)/(2)). Density functional electronic structure calculations on 1 support the occurrence of a spin polarization mechanism.

Two-Dimensional Coordination Polymer with a Non-interpenetrated (4,4) Net Showing Anion Exchange and Structural Transformation in Single-Crystal-to-Single-Crystal Fashion

A new non-interpenetrated two-dimensional (2D) rectangular-grid coordination polymer, {[Co(L)(2)(H(2)O)(2)] x (BF(4))(2) x 4 DMF}(n) (1), has been synthesized using a new rod-like ligand, 3,5-bis(4-imidazol-1-ylphenyl)-[1,2,4]triazol-4-ylamine (L). Weakly H-bonded BF(4)(-) anions present within the voids can be exchanged by ClO(4)(-) and NO(3)(-) anions to generate {[Co(L)(2)(H(2)O)(2)] x (ClO(4))(2) x 2 DMF x 2 H(2)O}(n) (2) and {[Co(L)(2)(H(2)O)(2)] x (NO(3))(2) x 2 DMF x 2 H(2)O}(n) (3) in single-crystal-to-single-crystal (SC-SC) manner. In the case of exchange by Cl(-) ion, the crystallinity is not maintained, and so it is proven by IR spectroscopy, PXRD, and elemental analysis. In addition, 3 shows an interesting structural transformation (2D --> 1D) with bond rupture/formation leading to the formation of a new coordination polymer, {[Co(L)(2)(H(2)O)(2)] x (NO(3))(2) x 2 DMF x H(2)O}(n), (5), again in SC-SC fashion.

New 3D Coordination Polymers Constructed from Pillared Metal−Formate Kagomé Layers Exhibiting Spin Canting Only in the Nickel(II) Complex

Sparked by the strategy of pillared-layer MOFs, three formate coordination polymers, {[Ni(2)(HCO(2))(3)(L)(2)](NO(3)).2H(2)O}(infinity) (1), {[Co(2)(HCO(2))(3)(L)(2)](HCO(2)).2H(2)O}(infinity) (2), and {[Cu(2)(HCO(2))(3)(L)(2)](HCO(2)).2H(2)O}(infinity) (3), have been synthesized by employing the rodlike ligand 4,4'-bis(imidazol-1-yl)biphenyl (L) as the pillar. Structural analysis indicates that the title complexes 1-3 are isostructural compounds, which possess metal-formate 2D layers perpendicularly pillared by the ligand L to afford a 3D open framework. This is an interesting example of a Kagome lattice based on the formate mediator. Moreover, the formate anion of this 2D Kagome layer exhibits various bridging modes: anti-anti, syn-anti, and 3.21 modes. Their magnetic measurements reveals that only complex 1 presents the spin canting phenomenon, while its isostructural Co(II) and Cu(II) complexes are simply paramagnets with antiferromagnetic coupling.

Tuning the Polarization Along Linear Polyaromatic Strands for Rationally Inducing Mesomorphism in Lanthanide Nitrate Complexes

The opposite orientation of the ester spacers in the rodlike ligands L 4C12 (benzimidazole-OOC-phenyl) and L 5C12 (benzimidazole-COO-phenyl) drastically changes the electronic structure of the aromatic systems, without affecting their meridional tricoordination to trivalent lanthanides, Ln(III), and their thermotropic liquid crystalline (i.e., mesomorphic) behaviors. However, the rich mesomorphism exhibited by the complexes [Ln(L 4C12)(NO3)3] (Ln=La-Lu) vanishes in [Ln(L 5C12)(NO3)3], despite superimposable molecular structures and comparable photophysical properties. Density functional theory (DFT) and time-dependant DFT calculations performed in the gas phase show that the inversion of the ester spacers has considerable effects on the electronic structure and polarization of the aromatic groups along the strands, which control residual intermolecular interactions responsible for the formation of thermotropic liquid-crystalline phases. As a rule of thumb, an alternation of electron-poor and electron-rich aromatic rings favors intermolecular interactions between the rigid cores and consequently mesomorphism, a situation encountered for L 4C12, L 5C12, [Ln(L 4C12)(NO3)3], but not for [Ln(L 5C12)(NO3)3]. The intercalation of an additional electron-rich diphenol ring on going from [Ln(L 5C12)(NO3)3] to [Ln(L 6C12)(NO3)3] restores mesomorphism despite an unfavorable orientation of the ester spacers, in agreement with our simple predictive model.

2D Hydrogen-Bonded Square-Grid Coordination Networks with a Substitution-Active Metal Site

Reported here is the preparation and property of 2D coordination networks composed of rodlike ligands with ethylene glycol side chains (1). Two 2D coordination networks, [[Co(1)2(H2O)2](NO3)2.1.5H2O]n and [[Ni(1)2(H(2)O)2](NO3)2.1.5H2O]n, have been synthesized and characterized by single-crystal X-ray diffraction, TG, DSC, UV-vis spectroscopy, and magnetic measurements. The structural analyses clarified that infinite 1D hydrogen-bond arrays composed of ethylene glycol chains contribute to the stabilization of 2D coordination frameworks, keeping the environment of substitution-active metal sites unchanged. They are more stable than a similar square-grid coordination network that does not possess an ethylene glycol chain on the ligand. We also succeeded in the direct observation of a reversible apical-ligand-exchange reaction at the cobalt(II) and nickel(II) ions in a single-crystal-to-single-crystal fashion because of the considerable stability as well as moderate flexibility of the framework. The cobalt-containing coordination network crystal showed chromic behavior depending on temperatures. Crystallographic and spectroscopic studies revealed that the color change of the crystal was attributed to the ligand-exchange process between H2O and a NO3 anion on the cobalt metal. Magnetic measurements indicated weak antiferromagnetic nearest-neighbor spin coupling between cobalt(II) ions.

The size-selective synthesis of folded oligomers by dynamic templation.

A dynamic pool of m-phenylene ethynylene oligomers generated by sequence ligation using the imine metathesis reaction was equilibrated under a variety of conditions, and the mixture of products was analyzed by HPLC. The equilibration was performed in the presence and absence of rodlike ligand 2b, which exhibits an affinity for the helical oligomers that is very length specific. Among the eight oligomers generated during metathesis equilibrium, the formation of 22-mer 6b was enhanced in acetonitrile in the presence of 2b. This particular oligomer has the highest binding affinity for 2b. Quantitative analysis by HPLC of the products indicated that 6b was produced in 66% yield in the presence of 2 equiv 2b while a 37% yield was produced in the absence of 2b. Judging from the binding affinities of oligomers 6 with 2b, the equilibrium shifting was driven by the selective binding of 6b with 2b.

Foldamers as Dynamic Receptors: Probing the Mechanism of Molecular Association between Helical Oligomers and Rodlike Ligands

Ein dynamischer Bindungsmechanismus ermöglicht die Assoziatbildung des hantelförmigen Liganden 2 mit helicalen gefalteten Oligo(m-phenylenethinylenen) 1 (siehe Schema). Die Assoziationskonstanten hängen von der Länge des Oligomers ab, wobei man die höchsten Werte für das Icosamer und das Docosamer findet. Die Oligomere nehmen helicale Konformationen ein, die formkomplementär zu 1 sind; kürzere und längere Oligomere weisen um etwa eine Größenordnung kleinere Assoziationskonstanten auf.

Foldamers as dynamic receptors: probing the mechanism of molecular association between helical oligomers and rodlike ligands.

A dynamic binding mechanism allows the association of dumbbell-shaped ligand 2 with helical folded oligo(m-phenyleneethynylene)s 1 (see schematic representation). Association constants are oligomer length specific, with a maximum value for the icosamer and docosamer. These oligomers have helical conformations that are highly shape-complementary to 1; shorter and longer oligomers exhibit association constants roughly an order of magnitude smaller.

SYNTHESIS OF ONE-AND TWO-DIMENSIONAL ZINC AND CADMIUM COMPLEXES WITH 4, 4′-BIPY

The zinc(II) and cadmium(II) complexes [Zn(4, 4′-bipy)(SCN)2]∞ 1 and [Cd(4, 4′-bipy)-(SCN)2]n 2 have been synthesized and their crystal structures determined by X-ray crystallography. Complex 1 is monoclinic, space group C2/c, with a = 18.076(5), b = 5.190(1), c = 17.315(4)Å; β = 115.54(2), V = 1465.8(8)Å3, calculated density 1.530gcm−3, Z = 4. In this compound, the rod-like ligand 4, 4′-bipy bridges Zn(II) centres, and the NCS groups are terminally coordinated. (N-Zn-N) is 108.5°, resulting in the formation of a zigzag Zn-bipy-Zn chain. These chains are arranged in parallel fashion. The 4, 4′-bipy ligands of adjacent layers are separated by 3.95 (Å). Complex 2 is monoclinic, space group C2/c, a = 11.902(2), b = 11.745(2), c = 10.500(2)Å; β = 109.71(3), V = 1381.8(4)Å3 calculated density 1.849gcm−3, Z = 4. In this structure, the cadmium(II) ion is slightly distorted octahedral and the SCN groups act as doubly bridging ligands connecting cadmium atoms to form zigzag chains, separated by 4, 4′-bipy to create two-dimensional planes.

Bent Tridentate Receptors in Calamitic Mesophases with Predetermined Photophysical Properties: New Luminescent Lanthanide-Containing Materials

A new synthetic strategy has been developed to introduce bent and rigid tridentate 2,6-bis(benzimidazol-2‘-yl)pyridine cores into rodlike ligands L11-17. The crystal structure of the nonmesogenic ligand L13 (C39H37N5O4, triclinic, P, Z = 2) shows the expected trans−trans conformation of the tridentate binding unit, which provides a linear arrangement of the semirigid aromatic sidearms. The crystal structure of the related mesogenic ligand L16 (C61H81N5O4, triclinic, P, Z = 2) demonstrates the fully extended conformation adopted by the lipophilic side chains, leading to a slightly helically twisted I-shaped molecule. A rich and varied mesomorphism results which can be combined with the simultaneous tuning of electronic and photophysical properties via a judicious choice of the spacers between the rigid central core and the semirigid lipophilic sidearms. Ligands L13,14 react with Ln(NO3)3·xH2O to give quantitatively and selectively the neutral 1:1 complexes [Ln(Li)(NO3)3] (Ln = La to Lu), which are stable in the solid state at room temperature but partially dissociate in acetonitrile to give the cationic species [Ln(Li)(NO3)2]+. The crystal structure of [Lu(L13)(NO3)3]·3CH3CN (30, LuC45H46N11O13, monoclinic, C2/c, Z = 8) reveals a U-shaped arrangement of the ligand strand arising from the cis−cis conformation of the coordinated tridentate binding unit. This drastic geometric change strongly affects the thermal behavior and the photophysical and electronic properties of the lipophilic complexes [Ln(L14)(NO3)3]. Particular attention has been focused on structure−properties relationships, which can be modulated by the size of the lanthanide metal ions.

Grand canonical Monte Carlo molecular and thermodynamic predictions of ion effects on binding of an oligocation (L8+) to the center of DNA oligomers

Grand canonical Monte Carlo (GCMC) simulations are reported for aqueous solutions containing excess univalent salt (activities a +/- = 1.76-12.3 mM) and one of the following species: an octacationic rod-like ligand, L8+; a B-DNA oligomer with N phosphate charges (8 < or = N < or = 100); or a complex resulting from the binding of L8+ at the center of an N-mer (24 < or = N < or = 250). Simplified models of these multiply charged species are used in the GCMC simulations to predict the fundamental coulombic contributions to the following experimentally relevant properties: 1) the axial distance over which ligand binding affects local counterion concentrations at the surface of the N-mer; 2) the dependence on N of GCMC preferential interaction coefficients, gamma 32MC identical to delta C3/delta C2l a +/-, T, where C3 and C2 are, respectively, the molar concentrations of salt and the multiply charged species (ligand, N-mer or complex); and 3) the dependence on N of SaKobs identical to d in Kobs/d in a +/- = delta (magnitude of ZJ + 2 gamma 32J), where Kobs is the equilibrium concentration quotient for the binding of L8+ to the center of an N-mer and delta denotes the stoichiometric combination of terms, each of which pertains to a reactant or product J having magnitude of ZJ charges. The participation of electrolyte ions in the ligand binding interaction is quantified by the magnitude of SaKobs, which reflects the net (stoichiometrically weighted) difference in the extent of thermodynamic binding of salt ions to the products and reactants. Results obtained here from GCMC simulations yield a picture of the salient molecular consequences of binding a cationic ligand, as well as thermodynamic predictions whose applicability can be tested experimentally. Formation of the central complex is predicted to cause a dramatic reduction in the surface counterion (e.g., Na+) concentration over a region including but extending well beyond the location of the ligand binding site. For binding a cationic ligand, SaKobs is predicted to be negative, indicating net electrolyte ion release in the binding process. At small enough N, -SaKobs is predicted to decrease strongly toward zero with decreasing N. At intermediate N, -SaKobs appears to exceed its limiting value as N-->infinity.

Open-Framework Solids with Diamond-Like Structures Prepared from Clusters and Metal-Organic Building Blocks

AbstractThe tetrahedral cluster Ge4S104- and the rodlike ligand 4,4′-bipyridine are utilized in addition copolymerization reactions with the metal (II) ions of Mn, Fe, Co, Cu, and Zn in the preparation of 3-D open-framework solids, MxCol-xGe4S10-2(CH3)4N (x = 0.86, M = Mn; x = 1, M = Mn, Fe, Co, and Zn), 1, and Cu(4,4′-bpy)2. PF6, 2, having diamond-like structures. These structures are viewed in terms of the cubic diamond structure, where the carbon atoms have been replaced by either a cluster or a metal ion and the C-C bond by a sulfide or the 4,4′-bpy. These compounds have been fully characterized by single crystal x-ray crystallography and their composition was confirmed by elemental analysis; they contain 3-D channel systems where cations or anions reside to balance the charge on the framework.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 84. Carbaborane tungsten–platinum complexes having a µ-CC6H3Me2-2,6 ligand; crystal structures of [WPt(µ-CC6H3Me2-2,6)(CO)n(PEt3)(µ-σ:η5-C2B9H8Me2)](n= 2 or 3)

The reaction between the salts [PtH(Me2CO)(PEt3)2][BF4] and [NEt4][W(CC6H3Me2-2,6)(CO)2(η5-C2B9H9Me2)] in acetone at low temperature (ca. –30 °C) affords the dimetal compound [WPtH(µ-CC6H3Me2-2,6)(CO)2(PEt3)(η5-C2B9H9Me2)], in which the carbaborane ligand forms a B–H⇀Pt three-centre bond by employing a BH group in the pentagonal face of the cage. This product readily affords, via loss of hydrogen, the complex [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(µ-σ:η5-C2B9H8Me2)] as a mixture of two isomers. The structure of the major isomer (ca. 80%) has been established by X-ray diffraction. The W–Pt bond [2.728(1)A] is asymmetrically bridged by the CC6H3Me2-2,6 group [µ-C–W 1.88(2), µ-C–Pt2.15(2)A]. Indeed with a W–µ-C–C1(C6H3) angle of 175(1)° these three atoms are nearly linear. The carbaborane ligand has undergone ‘slippage’ along the W–Pt vector to accommodate formation of a direct exopolyhedral B–Pt σ bond [2.01(2)A]. This linkage involves the central boron in the [graphic omitted] face of the icosahedral fragment η5 bonded to tungsten. The PEt3 ligand attached to the platinum atom [Pt–P, 2.251(7)A] is transoid to the µ-C and W atoms [µ-C–Pt–P, 160.6(4)°, W–Pt–P 155.9(1)°]. The n.m.r. data (1H, 13C-{1H}, 11B-{1H}, and 31P-{1H}) are in accord with the structure established by the X-ray diffraction study. Similar data for the minor isomer reveal that this species had a structure in which the B–Pt σ bond involves a boron atom [graphic omitted] in the face of the cage, adjacent to a CMe group. The two isomers may be separated by column chromatography, but solutions equilibrate on standing. Formation of the major isomer from [WPtH (µ-CC6H3Me2-2,6)(CO)2(PEt3)(η5-C2B9H9Me2)] can be partially reversed by treating solutions of the former with hydrogen. Mechanisms are proposed for these various transformations based in part on deuteriation studies employing [PtD(Me2CO)(PEt3)2][BF4] as a precursor to the W–Pt species. The compound [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(µ-σ:η5-C2B9H8Me2)](major isomer) is relatively inert to the addition of ligands at the formally 14-electron platinum centre, presumably due to the presence of the bulky xylyl group. However, reactions very readily occur with rod-like ligands (L = CO or CNBut) to give the compounds [WPt(µ-CC6H3Me2-2,6)(CO)2(PEt3)(L)(µ-σ:η5-C2B9H8Me2)]. Indeed the tricarbonyl complex is a major constituent of the mixture of products obtained by treating the complex [NEt4][W(CC6H3Me2-2,6)(CO)2(η5-C2B9H9Me2)] with [PtH(Me2CO)(PEt3)2][BF4]. An X-ray study of the carbon monoxide adduct revealed a structure similar to the precursor with parameters W–Pt, 2.728(1),µ-C–W 1.89(1), µ-C–Pt 2.29(1), B–Pt 2.16(1)A, W–µ-C–C1(C6H3) 160.0(8), and P–Pt–W 138.5(1)°. The significantly lower W–µ-C–C1(C6H3) angle (ca. 160°) compared with that in the precursor is presumably a consequence of the presence of the additional CO ligand terminally bound to the platinum and cisoid to the alkylidyne group [µ-C–Pt–CO 83.5(4)°].