Arene-mercury complexes stabilized by aluminum and gallium chloride: catalysts for H/D exchange of aromatic compounds

Dissolution of Hg(arene)(2)(MCl(4))(2) [arene = C(6)H(5)Me, C(6)H(5)Et, o-C(6)H(4)Me(2), C(6)H(3)-1,2,3-Me(3); M = Al, Ga] in C(6)D(6) results in a rapid H/D exchange and the formation of the appropriate d(n)-arene and C(6)D(5)H. H/D exchange is also observed between C(6)D(6) and the liquid clathrate ionic complexes, [Hg(arene)(2)(MCl(4))][MCl(4)], formed by dissolution of HgCl(2) and MCl(3) in C(6)H(6), m-C(6)H(4)Me(2), or p-C(6)H(4)Me(2). The H/D exchange reaction is found to be catalytic with respect to Hg(arene)(2)(MCl(4))(2) and independent of the initial arene ligand. Reaction of a 1:1 ratio of C(6)H(5)Me and C(6)D(6) with <0.1 mol % Hg(C(6)H(5)Me)(2)(MCl(4))(2) results in an equilibrium mixture of all isotopic isomers: C(6)H(5-x)D(x)Me and C(6)D(6-x)H(x) (x = 0-5). DFT calculations on the model system, Hg(C(6)H(6))(2)(AlCl(4))(2) and [Hg(C(6)H(6))(2)(AlCl(4))](+), show that the charge on the carbon and proton associated with the shortest Hg...C interactions is significantly higher than that on uncomplexed benzene or HgCl(2)(C(6)H(6))(2). The protonation of benzene by either Hg(C(6)H(6))(2)(AlCl(4))(2) or [Hg(C(6)H(6))(2)(AlCl(4))](+) was calculated to be thermodynamically favored in comparison to protonation of benzene by HO(2)CCF(3), a known catalyst for arene H/D exchange. Arene exchange and intramolecular hydrogen transfer reactions are also investigated by DFT calculations.     

Arene-mercury complexes stabilized by gallium chloride: relative rates of H/D and arene exchange

We have previously proposed that the Hg(arene)(2)(GaCl(4))(2) catalyzed H/D exchange reaction of C(6)D(6) with arenes occurs via an electrophilic aromatic substitution reaction in which the coordinated arene protonates the C(6)D(6). To investigate this mechanism, the kinetics of the Hg(C(6)H(5)Me)(2)(GaCl(4))(2) catalyzed H/D exchange reaction of C(6)D(6) with naphthalene has been studied. Separate second-order rate constants were determined for the 1- and 2-positions on naphthalene; that is, the initial rate of H/D exchange = k(1i)[Hg][C-H(1)] + k(2i)[Hg][C-H(2)]. The ratio of k(1i)/k(2i) ranges from 11 to 2.5 over the temperature range studied, commensurate with the proposed electrophilic aromatic substitution reaction. Observation of the reactions over an extended time period shows that the rates change with time, until they again reach a new and constant second-order kinetics regime. The overall form of the rate equation is unchanged: final rate = k(1f)[Hg][C-H(1)] + k(2f)[Hg][C-H(2)]. This change in the H/D exchange is accompanied by ligand exchange between Hg(C(6)D(6))(2)(GaCl(4))(2) and naphthalene to give Hg(C(10)H(8))(2)(GaCl(4))(2,) that has been characterized by (13)C CPMAS NMR and UV-visible spectroscopy. The activation parameters for the ligand exchange may be determined and are indicative of a dissociative reaction and are consistent with our previously calculated bond dissociation for Hg(C(6)H(6))(2)(AlCl(4))(2). The initial Hg(arene)(2)(GaCl(4))(2) catalyzed reaction of naphthalene with C(6)D(6) involves the deuteration of naphthalene by coordinated C(6)D(6); however, as ligand exchange progresses, the pathway for H/D exchange changes to where the protonation of C(6)D(6) by coordinated naphthalene dominates. The site selectivity for the H/D exchange is initially due to the electrophilic aromatic substitution of naphthalene. As ligand exchange occurs, this selectivity is controlled by the activation of the naphthalene C-H bonds by mercury.     

Synthesis, pH-dependent structural characterization, and solution behavior of aqueous aluminum and gallium citrate complexes

Reactions of Al(III) and Ga(III) with citric acid in aqueous solutions, yielded the complexes (NH(4))(5)[M(C(6)H(4)O(7))(2)].2H(2)O (M(III) = Al (1), Ga (2)) at alkaline pH, and the complexes (Cat)(4)[M(C(6)H(5)O(7))(C(6)H(4)O(7))].nH(2)O (M(III) = Al (3), Ga (4), Cat. = NH(4)(+), n = 3; M(III) = Al (5), Ga (6), Cat. = K(+), n = 4) at acidic pH. All compounds were characterized by spectroscopic (FT-IR, (1)H, (13)C, and (27)Al NMR, (13)C-MAS NMR) and X-ray techniques. Complex 1 crystallizes in space group P1, with a = 9.638(5) A, b = 9.715(5) A, c = 7.237(4) A, alpha = 90.96(1) degrees, beta = 105.72(1) degrees, gamma = 119.74(1) degrees, V = 557.1(3) A(3), and Z = 1. Complex 2 crystallizes in space group P1, with a = 9.659(6) A, b = 9.762(7) A, c = 7.258(5) A, alpha = 90.95(2) degrees, beta = 105.86(2) degrees, gamma = 119.28(1) degrees, V = 564.9(7) A(3), and Z = 1. Complex 3 crystallizes in space group I2/a, with a = 19.347(3) A, b = 9.857(1) A, c = 23.412(4) A, beta = 100.549(5) degrees, V = 4389(1) A(3), and Z = 8. Complex 4 crystallizes in space group I2/a, with a = 19.275(1) A, b = 9.9697(6) A, c = 23.476(1) A, beta = 100.694(2) degrees, V = 4432.8(5) A(3), and Z = 8. Complex 5 crystallizes in space group P1, with a = 7.316(1) A, b = 9.454(2) A, c = 9.569(2) A, alpha = 64.218(4) degrees, beta = 69.872(3) degrees, gamma = 69.985(4) degrees, V = 544.9(2) A(3), and Z = 1. Complex 6 crystallizes in space group P1, with a = 7.3242(2) A, b = 9.4363(5) A, c = 9.6435(5) A, alpha = 63.751(2) degrees, beta = 70.091(2) degrees, gamma = 69.941(2) degrees, V = 547.22(4) A(3), and Z = 1. The crystal structures of 1-6 reveal mononuclear octahedral complexes of Al(III) (or Ga(III)) bound to two citrates. Solution NMR, on both 4- and 5- species, reveals rapid intramolecular exchange of the bound and unbound terminal carboxylates. Upon dissolution in water, the complexes, through a complicated reaction cascade, transform to oligonuclear 1:1 species that, in agreement with previous studies, represent the thermodynamically stable state in solution. The data provide, for the first time, structural details of low MW, mononuclear complexes of Al(III) (or Ga(III)) with citrate that are dictated, among other factors, by pH. The properties of 1-6 may provide clues relevant to their biological association with humans.     

The synthesis and characterization of aluminum,gallium and zinc formamidinates

Reactions of the formamidinate ligand, RN(H)C(H)NR, L^H, (R = 2,6-diisopropylphenyl), with AlMe₃, AlMe₂Cl, GaMe₃ and ZnEt₂ were investigated to examine potential coordination modes of the ligand and the effect of hydrolysis on the products. Nine new complexes have been fully characterized by X-ray crystallography and other spectroscopic techniques and highlight the diverse coordination modes of the formamidinate ligand.     

Sigma-borane complexes of iridium: synthesis and structural characterization

Reaction of NaBH4 with (tBuPOCOP)IrHCl affords the previously reported complex (tBuPOCOP)IrH2(BH3) (1) (tBuPOCOP = kappa(3)-C6H3-1,3-[OP(tBu)2]2). The structure of 1 determined from neutron diffraction data contains a B-H sigma-bond to iridium with an elongated B-H bond distance of 1.45(5) A. Compound 1 crystallizes in the space group P1 (Z = 2) with a = 8.262 (5) A, b = 12.264 (5) A, c = 13.394 (4) A, and V = 1256.2 (1) A(3) (30 K). Complex 1 can also be prepared by reaction of BH3 x THF with (tBuPOCOP)IrH2. Reaction of (tBuPOCOP)IrH2 with pinacol borane gave initially complex 2, which is assigned a structure analogous to that of 1 based on spectroscopic measurements. Complex 2 evolves H2 at room temperature leading to the borane complex 3, which is formed cleanly when 2 is subjected to dynamic vacuum. The structure of 3 has been determined by X-ray diffraction and consists of the (tBuPOCOP)Ir core with a sigma-bound pinacol borane ligand in an approximately square planar complex. Compound 3 crystallizes in the space group C2/c (Z = 4) with a = 41.2238 (2) A, b = 11.1233 (2) A, c = 14.6122 (3) A, and V = 6700.21 (19) A(3) (130 K). Reaction of (tBuPOCOP)IrH2 with 9-borobicyclononane (9-BBN) affords complex 4. Complex 4 displays (1)H NMR resonances analogous to 1 and exists in equilibrium with (tBuPOCOP)IrH2 in THF solutions.     

Convenient synthesis of aluminum and gallium phosphonate cages

The reactions of AlCl 3.6H 2O and GaCl 3 with 2-pyridylphosphonic acid (2PypoH 2) and 4-pyridylphosphonic acid (4PypoH 2) afford cyclic aluminum and gallium phosphonate structures of [(2PypoH) 4Al 4(OH 2) 12]Cl 8.6H 2O ( 1), [(4PypoH) 4Al 4(OH 2) 12]Cl 8.11H 2O ( 2), [(2PypoH) 4Al 4(OH 2) 12](NO 3) 8.7H 2O ( 3), [(2PypoH) 2(2Pypo) 4Ga 8Cl 12(OH 2) 4(thf) 2](GaCl 4) 2..8thf ( 4), and [(2PypoH) 2(2Pypo) 4Ga 8Cl 12(OH 2) 4(thf) 2](NO 3) 2.9thf ( 5). Structures 1- 3 feature four aluminum atoms bridged by oxygen atoms from the phosphonate moiety and show structural resemblance to the secondary building units found in zeolites and aluminum phosphates. The gallium complexes, 4 and 5, have eight gallium atoms bridged by phosphonate moieties with two GaCl 4 (-) counterions present in 4 and nitrate ions in 5. The cage structures 1- 3 are interlinked by strong hydrogen bonds, forming polymeric chains that, for aluminum, are thermally robust. Exchange of the phosphonic acid for the more flexible 4PyCH 2PO 3H 2 afforded a coordination polymer with a 1:1 Ga:P ratio, {[(4PyCH 2PO 3H)Ga(OH 2) 3](NO 3) 2.0.5H 2O} x ( 6). Complexes 1- 6 were characterized by single-crystal X-ray diffraction, NMR, and mass spectrometry and studied by TGA.     

Rare earth metal complexes bearing thiophene-amido ligand: synthesis and structural characterization

2,6-diisopropyl-N-(2-thienylmethyl)aniline (H2L) has been prepared, which reacted with equimolar rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2, afforded rare earth metal mono(alkyl) complexes, LLn(CH2SiMe3)(THF)3 (:Ln=Lu; :Ln=Y). In this process, H2L was deprotonated by one metal alkyl species followed by intramolecular C-H activation of the thiophene ring to generate dianionic species L2- with the release of two tetramethylsilane. The resulting L2- combined with three THF molecules and an alkyl unit coordinates to Y3+ and Lu3+ ions, respectively, in a rare N,C-bidentate mode, to generate distorted octahedron geometry ligand core. Whereas, with treatment of H2L with equimolar Sc(CH2SiMe3)3(THF)2, a heteroleptic complex (HL)(L)Sc(THF) () was isolated as the main product, where the dianionic L2- species bonds to Sc3+ via chelating N,C atoms whilst the monoanionic HL connects to Sc3+ in an S,N-bidentate mode. All complexes have been characterized by NMR spectroscopy and X-ray diffraction analysis.     

Four- and five-coordinate aluminum ketiminate complexes: synthesis,characterization, and ring-opening polymerization

A series of aluminum complexes featuring with the ketiminate ligand, OCMeCHCMeNHAr (Ar = 2,6-(i)Pr(2)C(6)H(3), 1), have been prepared and characterized spectroscopically and structurally. Reactions of 1 with trialkylaluminum in 1:1 or 1:2 molar ratio generate four- and five-coordinated aluminum complexes (OCMeCHCMeNAr)AlR(2) (R = Me (2); R = Et (3)) and (OCMeCHCMeNAr)(2)AlR (R = Me (4); R = Et (5)) in high yields. Similarly, reaction of AlCl(3) with 1 or 2 equiv of the lithiated 1 in toluene afforded bis(ketiminate) aluminum chloride complex, (OCMeCHCMeNAr)(2)AlCl (6) or (OCMeCHCMeNAr)AlCl(2) (7). Surprisingly, reacting 6 with 1 equiv of AgBF(4) in methylene/acetonitrile mix-solvents generates (OCMeCHCMeNAr)(2)AlF (8) in moderate yield. The structures of complexes 2-6 and 8 have been determined by X-ray crystallography. Complexes 2 and 3 both exhibit tetrahedron structures with the aluminum atom surrounded by oxygen and nitrogen atoms of chelating ketiminate and two alkyl groups. The mono- and bis-ketiminate aluminum complexes 2-5 have shown moderate activity toward the ring-opening polymerization of epsilon-caprolactone.     

Synthesis, structural characterization, and theoretical studies of complexes of magnesium and calcium with gallium heterocycles

The magnesium- and calcium-gallium heterocycle complexes [Mg{Ga[(ArNCH)2]}2(THF)3] and [Ca{Ga[(ArNCR)2]}2(THF)4], R = H or Me, Ar = C6H3Pr(i)2-2,6, have been prepared via the reduction of [I2Ga{(ArNCR)2}] with the group 2 metal in tetrahydrofuran. The mechanisms of the reactions have been elucidated, and the crystal structures of the complexes exhibit the first structurally authenticated Ga-Mg and Ga-Ca bonds in molecular species. Theoretical studies suggest that the heterocycle-group 2 metal interactions have significant ionic character.     

Synthesis and structural characterization of gallium and indium complexes obtained from redistribution reactions of mixed chalcogen-imidodiphosphinate ligands

The ionic complex [Ga{N(SPⁱPr₂)(SePⁱPr₂)-S, Se}₂]⁺[GaCl₄]⁻ (5) was prepared by a ligand redistribution process from the mono-chelate [Cl₂Ga{N(SPⁱPr₂)(SePⁱPr₂)-S, Se}] (3) complex in benzene. A similar phenomenon was observed for the heavier indium homologues, where the neutral complexes [ClIn{N(SPⁱPr₂)(SePⁱPr₂)-S, Se}₂] (7) and [ClIn{N(OPⁱPr₂)(SPⁱPr₂)-O, S}₂] (8) were isolated along with InCl₃ as the main reaction by-product. Complexes 5, 7 and 8 were characterized by single-crystal X-ray structural analysis.     

两种含氮芳香羧酸配合物的水热合成及结构表征

用水热法合成了两种结构新颖的配合物[Cu(PDA)(H2O)2](Ⅰ)和[Ni(PZCA)2(H2O)2](Ⅱ)(H2PDA=2,6-吡啶-二甲酸,HPZCA=2-吡嗪羧酸);利用元素分析、红外光谱和X射线单晶衍射等分析了产物的组成和结构.结果表明,两种配合物均属单斜晶系,空间群均为P21/c,中心离子Cu(Ⅱ)和Ni(Ⅱ)均采取畸变的六配位八面体配位方式;配合物I通过π-π堆积作用和氢键构筑成三维结构,配合物Ⅱ以氢键联接形成二维层状结构.此外,配合物Ⅱ中的PZCA-来自于Ni(Ⅱ)对2,3-吡嗪-二羧酸(H2PZDA)配体的催化脱羧过程.     

Copper oxalate complexes: synthesis and structural characterisation

Six copper(II) oxalate complexes, namely {K₂[Cu(ox)₂]} _n (1), {(Hiz)₂[Cu(ox)₂]} _n (2), {[Cu(ox) (N-Bzliz)₂]} _n (3), (HMeiz)₂[Cu(ox)₂] (4), {[Cu(ox)(Meiz)₂]} _n (5), and [Cu(Hox)₂(H₂O)₂](N-Bzliz) (6) where ox = oxalate ion, iz = imidazole, N-Bzliz = N-benzylimidazole, Meiz = 2-methylimidazole, were synthesised and characterised by single crystal X-ray diffraction (complexes 1–5) or powder X-ray diffraction (compound 6). The three-dimensional crystal packing structures of 2, 4, and 5 are consolidated by intermolecular hydrogen bonds linking the oxygen atom of the oxalate group and the amine or imine group of the imidazole-based part into chains. The molecules of complex 6 are held together by intermolecular hydrogen bonds between the oxygen atoms of the oxalate group and coordinated water molecules.     

Uranyl sequestration: synthesis and structural characterization of uranyl complexes with a tetradentate methylterephthalamide ligand

Uranyl complexes of a bis(methylterephthalamide) ligand (LH(4)) have been synthesized and characterized by X-ray crystallography. The structure is an unexpected [Me(4)N](8)[L(UO(2))](4) tetramer, formed via coordination of the two MeTAM units of L to two uranyl moieties. Addition of KOH to the tetramer gave the corresponding monomeric uranyl methoxide species [Me(4)N]K(2)[LUO(2)(OMe)].     

Reactions of 2-chlorobutane with polynuclear bimetallic aluminum and cobalt chloride complexes: low-temperature synthesis and structure of adducts

Co-condensation of aluminum and cobalt chlorides and 2-chlorobutane leads to the formation of triple complexes. Density functional method PBE was used for the quantum chemical calculations of structures and harmonic vibration frequencies. The structures of associates were established by the comparison of experimental and theoretical IR spectra. Introduction of cobalt chloride into the system 2-chlorobutane-aluminum chloride leads to the formation of a triple molecular associate, in which coordination of the organic substrate with the bimetallic complex is accomplished through the transition metal atom. The triple complex is stable in the temperature range 80–240 K and in contrast to the binary complex of butyl chloride with aluminum halide is not capable of self-ionization to form sec-butyl cation.     

Preparation, characterization, and structural systematics of diphosphane and diarsane complexes of gallium(III) halides

The diphosphane o-C6H4(PMe2)2 reacts with GaX3 (X = Cl, Br, or I) in a 1:1 molar ratio in dry toluene to give trans-[GaX2{o-C6H4(PMe2)2}2][GaX4], the cations of which contain the first examples of six-coordinate gallium in a phosphane complex. The use of a 1:2 ligand/GaCl3 ratio produced [GaCl2{o-C6H4(PMe2)2}][GaCl4], containing a pseudotetrahedral cation, and similar pseudotetrahedral [GaX2{o-C6H4(PPh2)2}][GaX4] complexes are the only products isolated with the bulkier o-C6H4(PPh2)2. On the other hand, Et2P(CH2)2PEt2, which has a flexible aliphatic backbone, formed [(X3Ga)2{mu-Et2P(CH2)2PEt2}], in which the ligand bridges two pseudotetrahedral gallium centers. The diarsane, o-C6H4(AsMe2)2, formed [GaX2{o-C6H4(AsMe2)2}][GaX4], also containing pseudotetrahedral cations, and in marked contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two much studied ligands behave differently towards a common metal acceptor. The complexes [(I3Ga)2{mu-Ph2As(CH2)2AsPh2}] and [GaX3(AsMe3)] are also described. The X-ray structures of trans-[GaX2{o-C6H4(PMe2)2}2][GaX4] (X = Cl, Br or I), [GaCl2{o-C6H4(PPh2)2}][GaCl4], [GaX2{o-C6H4(AsMe2)2}][GaX4] (X = Cl or I), [(I3Ga)2{mu-Ph2As(CH2)2AsPh2}], and [GaX3(AsMe3)] (X = Cl, Br or I) are reported, and the structural trends are discussed. The solution behavior of the complexes has been explored using a combination of 31P{1H} and 71Ga NMR spectroscopy.     

Preparation and characterization of mixed alkyl amido complexes of gallium

A series of primary amido gallium alkyl complexes that includes a base free dimer, [^tBu₂Ga(μ-N(H)^tBu)]₂ (1), Lewis base stabilized monomeric complexes, ⁿBu₂Ga(N(H)^tBu)(THF) (2) and ⁿBu₂Ga[NH(2,6-Me₂C₆H₃)]py (3) and an anionic complex, ⁿBu₂Ga[NH(2,6-Me₂C₆H₃)]₂[Li(Et₂O)] (4) is reported. Complex 1 crystallizes in the triclinic space group P-1 (a = 10.265(5) Å, B = 15.752(6) Å, C = 8.932(4) Å, = 90.32(3)°, β = 105.61(3)°, γ = 88.24(4)°) with two molecules, each residing on an inversion center, in the asymmetric unit. Structural analysis revealed a planar Ga₂N₂ core with both the bridging N and the Ga centers in distorted tetrahedral environments (Ga---C distances 2.052(3)-2.065(3) Å and Ga---N distances 2.060(3)-2.069(3) Å). The use of excess amido ligand allowed the isolation and crystallization of 4. Complex 4 crystallized in the monoclinic space group P21/n (a = 8.666(2) Å, B = 22.305(3) Å, C = 15.570(3) Å, β = 103.47(2)) with Z = 4. The pseudotetrahedral gallium center has a coordination sphere composed of two amido ligands (Ga---N1 = 2.011(8) Å, Ga---N2 = 2.006(7) Å), and two ⁿBu ligands (Ga---C17 = 2.002(9) Å Ga---C21 = 1.985(12) Å). A bridging interaction of the lithium cation with the lone pair of electrons on each of amido nitrogen atoms generates a molecular core which is made up of a planar Ga---N1---Li---N2 distorted square (N1---Gal---N2 94.4°, Gal---N2---Lil 86.2°, N1---Li1---N2 92.2°, Gal---N1---Li1 87.1°).     

The synthesis and structural characterization of transition metal coordination complexes of coumarilic acid

The coumarilate (coum^?) complexes of Co^II(1), Ni^II(2) Cu^II(3) and Zn^II(4) were synthesized and characterized by elemental analysis, magnetic susceptibility, solid-state UV–Vis, FTIR spectra, thermoanalytical TG–DTG/DTA and single-crystal X-ray diffraction methods. It was found that all of the complex structures have 2 mol (coum^?) ligand bonded as monoanionic monodentate in the structures of 1 and 2 while they were coordinated to metal cations as monoanionic bidentate in the complexes 3 and 4. There was not any hydrate water in the metal complexes. The complexes of 1 and 2 have four moles of aqua ligand, and the other complexes have two moles. Thermal decomposition of each complex starts with dehydration, and then the decomposition of organic parts goes. The thermal dehydration of the complexes takes place in one (for the compounds of 2, 3, 4) or two (for the compound 1) steps. The decomposition mechanism and the thermal stability of the complexes under investigation were determined on the basis of their structures. Metal oxides were obtained as the final decomposition product.     

Cd(II) complexes based on a tricarboxylate: synthesis,structural characterization and properties

Reactions of cadmium(II) with 5-(4-carboxybenzylamino)isophthalic acid (H₃L) in the presence of 2-(pyridin-2-yl)-1H-benzo[d]imidazole (pybim) and 2,2′-bipyridine (bpy) by hydrothermal method lead to two complexes, [Cd(HL)(pybim)]·H₂O (1) and [Cd₂(L)(HCOO)(bpy)₂(H₂O)]·H₂O (2). Complexes 1 and 2 have been characterized by single-crystal and powder X-ray diffraction, Infrared spectra, and elemental and thermogravimetric analyses. 1 has a double-chain structure while 2 consists of uninodal 3-connected 2-D hcb networks with (6³) topology. Luminescence and sorption properties of 1 and 2 were also investigated.     

Crystallographic and structural characterization of heterometallic platinum complexes Part VI. Heterohexanuclear complexes

This review classifies and analyzes heterohexanuclear platinum clusters into seven types of metal combinations:Pt₅M, Pt₄M₂, Pt₃M₃, Pt₂M₄, PtM₅, Pt₂M₃M′, and Pt₂M₂M₂′. The crystals of these clusters generally belong to six crystal classes: monoclinic, triclinic, orthorhombic, tetragonal, trigonal and cubic. Among the wide range of stereochemistry adopted by these clusters, octahedral and capped square-pyramidal are the most common. Although platinum is classified as a soft metal atom, it bonds to a variety of soft, borderline and hard metals. Nineteen different heterometal ions are involved in hexanuclear platinum clusters. The shortest Pt-M bond distance in the case of M being a non-transition element is 2.395(4) Å for germanium and for M being a transition metal ion it is 2.402(2) Å for Cobalt. The shortest Pt-Pt bond distance observed in these clusters is 2.532 Å. Several relationships between the structural parameters are identified and discussed. Some clusters exist in two isomeric forms and some show crystallographically independent molecules within the same crystal. Such isomers and independent molecules are examples of distortion isomerism.      

Mixed guanidinato/alkylimido/azido tungsten(VI) complexes: synthesis and structural characterization

A series of structurally characterized new examples of pentacoordinated heteroleptic tungsten(VI)-guanidinates complexes are described. Starting out from [WCl(2)(Nt-Bu)(2)py(2)] (1) (py = pyridine) and the guanidinato transfer reagents (TMEDA)Li[(Ni-Pr)(2)CNi-Pr(2)] (2a) (TMEDA = N,N,N',N'-tetramethylethylendiamine) and [Li(NC(NMe(2))(2))](x) (2b), the title compounds [WCl(Nt-Bu)(2)[(Ni-Pr)(2)CNi-Pr(2)]] (3) and [W(Nt-Bu)(2)Cl{NC(NMe(2))(2)]](2) (6) were selectively formed by the elimination of one mole equivalent of lithium chloride. The isopropyl-substituted guanidinato ligand [(Ni-Pr)(2)CNi-Pr(2)} of monomeric 3 is N(1),N(3)-bonded to the tungsten center. The introduction of the sterically less-demanding tetramethyl guanidinato ligand [NC(NMe(2))(2)] expectedly leads to dimeric 6 exhibiting a planar W(2)N(2) ring with the guanidinato group bridging the two tungsten centers via the deprotonated imino N-atom. The remaining chloro ligand of 3 is labile and can be substituted by sterically less-crowded groups such as dimethylamido or azido that yield the presumably monomeric compounds 4 and 5, respectively. A similar treatment of 6 with sodium azide yields the dimeric azido derivative 7. Reacting [WCl(2)(Nt-Bu)(2)py(2)] directly with an excess of sodium azide leads to the dimeric bis-azide species [[W(Nt-Bu)(2)(N(3))(mu(2)-N(3))py](2)]. The new compounds were fully characterized by single-crystal X-ray diffractometry (except 2, 4, and 5), NMR, IR, and mass-spectroscopy as well as elemental analysis. Compound 5, [W(N(3))(Nt-Bu)(2)[(Ni-Pr)(2)CNi-Pr(2)]], can be sublimed at 80 degrees C, 1 Pa.