Covalency is Frustrating: La2Sn2O7 and the Nature of Bonding in Pyrochlores under High Pressure-Temperature Conditions.

Natural specimens of the pyrochlore (A2B2O7) compounds have been found to retain foreign actinide impurities within their parent framework, undergoing metamictization to a fully amorphous state. The response to radionuclide decay identifies pyrochlore systems with having high radiation tolerance and tailored use in radioactive waste applications and radionuclide sequestration. High pressure is a powerful pathway to high density states and amorphization with parallels to radiation-induced processes. Here, La2Sn2O7 is evaluated under extreme conditions via the combination of laser heating in a diamond anvil cell with X-ray diffraction and Raman spectroscopy. The measurements are supported by ab initio random structure searching and molecular dynamics calculations. A new ground state at 70 GPa is revealed, and high temperature annealing is fundamental to access its crystalline ground state and fully determine the structure. This crystalline phase ( P21/ c) retains its structural integrity during decompression and is fully recoverable to ambient conditions. The final state of the system is shown to be highly pathway dependent due to the covalent nature of the Sn-O bonding. The Tc pyrochlore, La2Tc2O7, is analyzed for similarities in the bonding to determine the likelihood of an analogous pathway dependency to a final state.

Unexpected reactivity and coordination in gallium(III) and indium(III) chloride complexes with geometrically constrained thio- and selenoether ligands.

Reaction of GaCl(3) with 1 mol equiv of [14]aneS(4) in anhydrous CH(2)Cl(2) gives the exocyclic chain polymer [GaCl(3)([14]aneS(4))] (1) whose structure confirms trigonal bipyramidal coordination at Ga with a planar GaCl(3) unit. In contrast, using [16]aneS(4) and GaCl(3) or [16]aneSe(4) and MCl(3) (M = Ga or In) in either a 1:1 or a 1:2 molar ratio produces the anion-cation complexes [GaCl(2)([16]aneS(4))][GaCl(4)] (2) and [MCl(2)([16]aneSe(4))][MCl(4)] (M = Ga, 3 and M = In, 4) containing trans-octahedral cations with endocyclic macrocycle coordination. The ligand-bridged dimer [(GaCl(3))(2){o-C(6)H(4)(SMe)(2)}] (5) is formed from a 2:1 mol ratio of the constituents and contains distorted tetrahedral Ga(III). This complex is unusually reactive toward CH(2)Cl(2), which is activated toward nucleophilic attack by polarization with GaCl(3), producing the bis-sulfonium species [o-C(6)H(4)(SMeCH(2)Cl)(2)][GaCl(4)](2) (6), confirmed from a crystal structure. In contrast, the xylyl-based dithioether gives the stable [(GaCl(3))(2){o-C(6)H(4)(CH(2)SEt)(2)}] (8). However, replacing GaCl(3) with InCl(3) with o-C(6)H(4)(CH(2)SEt)(2) preferentially forms the 4:3 In:L complex [(InCl(3))(4){o-C(6)H(4)(CH(2)SEt)(2)}(3)] (9) containing discrete tetranuclear moieties in which the central In atom is octahedrally coordinated to six bridging Cl's, while the three In atoms on the edges have two bridging Cl's, two terminal Cl's, and two mutually trans S-donor atoms from different dithioether ligands. GaCl(3) also reacts with the cyclic bidentate [8]aneSe(2) to form a colorless, extremely air-sensitive adduct formulated as [(GaCl(3))(2)([8]aneSe(2))] (10), while InCl(3) gives [InCl(3)([8]aneSe(2))] (14). Very surprisingly, 10 reacts rapidly with O(2) gas to give initially the red [{[8]aneSe(2)}(2)][GaCl(4)](2) (11) and subsequently the yellow [{[8]aneSe(2)}Cl][GaCl(4)] (12). The crystal structure of the former confirms a dimeric [{[8]aneSe(2)}(2)](2+) dication, derived from coupling of two mono-oxidized {[8]aneE(2)}(+•) cation radicals to form an Se-Se bond linking the rings and weaker transannular 1,5-Se···Se interactions across both rings. The latter (yellow) product corresponds to discrete doubly oxidized {[8]aneSe(2)}(2+) cations (with a primary Se-Se bond across the 1,5-positions of the ring) with a Cl(-) bonded to one Se. Tetrahedral [GaCl(4)](-) anions provide charge balance in each case. These oxidation reactions are clearly promoted by the Ga(III) since [8]aneSe(2) itself does not oxidize in air. The new complexes have been characterized in the solid state by IR and Raman spectroscopy, microanalysis, and X-ray crystallography where possible. Where solubility permits, the solution characteristics have been probed by (1)H, (77)Se{(1)H}, and (71)Ga NMR spectroscopic studies.

[{Cp2(tBuSe)Nb}2E] (E = O and Se) with bridging oxide or selenide ligands.

The title compounds, mu-oxido-bis[(tert-butylselenolato)bis(eta(5)-cyclopentadienyl)niobium(IV)] toluene solvate, [Nb(2)(C(5)H(5))(4)(C(4)H(9)Se)(2)O] x C(7)H(8), and mu-selenido-bis[(tert-butylselenolato)bis(eta(5)-cyclopentadienyl)niobium(IV)], [Nb(2)(C(5)H(5))(4)(C(4)H(9)Se)(2)Se], consist of niobium(IV) centres each bonded to two eta(5)-coordinated cyclopentadienyl groups and one tert-butylselenolate ligand and are the first organometallic niobium selenolates to be structurally characterized. A bridging oxide or selenide completes the niobium coordination spheres of the discrete dinuclear molecules. In the oxide, the O atom lies on an inversion centre, resulting in a linear Nb-O-Nb linkage, whereas the selenide has a bent bridging group [Nb-Se-Nb = 139.76 (2) degrees]. The difference is attributable to strong pi bonding in the oxide case, although the effects on the Nb-C and Nb-Se(t)Bu bond lengths are small.

[Ge(TenBu)4] - a single source precursor for the chemical vapour deposition of germanium telluride thin films.

Reaction of activated germanium with nBu2Te2 in THF solution was shown to be more effective for the preparation of the germanium(iv) tellurolate compound, [Ge(TenBu)4], than reaction of GeCl4 with LiTenBu in a 1 : 4 molar ratio in THF. The product was characterised by 1H, 13C{1H} NMR spectroscopy and microanalysis and evaluated as a single source precursor for the low pressure chemical vapour deposition of GeTe thin films. Depending upon deposition conditions, either dull grey films (predominantly elemental Te) or highly reflective (GeTe) films were obtained from the pure precursor. Grazing incidence X-ray diffraction shows that the highly reflective films are comprised of the rhombohedral α-GeTe phase, while scanning electron microscopy and energy dispersive X-ray analysis reveal rhomb-shaped crystallites with a 49(1) : 51(1)% Ge : Te ratio. This structure is also confirmed from Raman spectra. Van der Pauw measurements show ρ = 3.2(1) × 10-4 Ω cm and Hall electrical measurements indicate that the GeTe thin films are p-type, with a mobility of 8.4(7) cm2 V-1 s-1 and carrier concentration of 2.5(2) × 1021 cm-3. The high p-type concentration is most likely a result of the substantial Ge vacancies in its sub-lattice, in line with the EDX elemental ratios.

Tin(iv) chalcogenoether complexes as single source precursors for the chemical vapour deposition of SnE2 and SnE (E = S, Se) thin films.

The molecular Sn(iv) complexes, [SnCl4{nBuS(CH2)3SnBu}] (2), [SnCl4(nBu2S)2] (3) and [SnCl4(nBu2Se)2] (4) have been prepared in good yield from reaction of SnCl4 with the appropriate chalcogenoether ligand in anhydrous hexane and, together with the known [SnCl4{nBuSe(CH2)3SenBu}] (1), employed as single source precursors for the low pressure chemical vapour deposition of the corresponding tin dichalcogenide thin films. At elevated temperatures the bidentate ligand precursors, (1) and (2), also form the tin monochalcogenides, SnSe and SnS, respectively. In contrast, (3) gave a mixture of phases, SnS2, Sn2S3 and SnS and (4) gave SnSe2 only. The morphologies, elemental compositions and crystal structures of the resulting films have been determined by scanning electron microscopy, energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction and Raman spectroscopy. Van der Pauw measurements on the SnS2, SnS and SnSe2 films confirm their resistivities to be 2.9(9), 266(3) and 4.4(3) Ω cm, respectively.

Investigation of the role of morphology on the magnetic properties of Ca2Mn3O8 materials.

Ca2Mn3O8 exhibits a complex layered structure comprised of Mn3O84- layers separated by Ca2+ ions. In contrast with the more traditional triangular delafossite layered materials the Mn3O84- layers additionally exhibit an ordered vacancy, which forms a 'bow-tie' like arrangement of the Mn4+ ions. We report a comprehensive study of the magnetic properties of a series of Ca2Mn3O8 materials with different morphologies. EXAFS and XANES analysis confirm no differences in either manganese environment or oxidation state between materials. Apparent differences in magnetic order from SQUID magnetometry can be rationalised by uncompensated surface spins arising as a result of changes to the surface to volume ratio between morphologies. Furthermore, these data suggest these materials are potentially frustrated in nature, due to the triangular connectivity of Mn4+ spins, with a simple 'spin-up/spin-down' (↑↓) antiferromagnetic model unable to explain the data collected.

Unexpected Cation Dynamics in the Low-Temperature Phase of Methylammonium Lead Iodide: The Need for Improved Models.

High-resolution inelastic neutron scattering and extensive first-principles calculations have been used to explore the low-temperature phase of the hybrid solar-cell material methylammonium lead iodide up to the well-known phase transition to the tetragonal phase at ca. 160 K. Contrary to original expectation, we find that the Pnma structure for this phase can only provide a qualitative description of the geometry and underlying motions of the organic cation. A substantial lowering of the local symmetry inside the perovskite cage leads to an improved atomistic model that can account for all available spectroscopic and thermodynamic data, both at low temperatures and in the vicinity of the aforementioned phase transition. Further and detailed analysis of the first-principles calculations reveals that large-amplitude distortions of the inorganic framework are driven by both zero-point-energy fluctuations and thermally activated cation motions. These effects are significant down to liquid-helium temperatures. For this important class of technological materials, this work brings to the fore the pressing need to bridge the gap between the long-range order seen by crystallographic methods and the local environment around the organic cation probed by neutron spectroscopy.

Niobium tetrahalide complexes with neutral diphosphine ligands.

The reactions of NbCl4 with diphosphine ligands o-C6H4(PMe2)2, Me2PCH2CH2PMe2 or Et2PCH2CH2PEt2 in a 1 : 2 molar ratio in MeCN solution produced eight-coordinate [NbCl4(diphosphine)2]. [NbBr4(diphosphine)2] (diphosphine = o-C6H4(PMe2)2 or Me2PCH2CH2PMe2) were made similarly from NbBr4. X-ray crystal structures show that [NbCl4{o-C6H4(PMe2)2}2] has a dodecahedral geometry, but the complexes with dimethylene-backboned diphosphines are distorted square antiprisms. The Nb-P distances and

PZT-like structural phase transitions in the BiFeO3-KNbO3 solid solution.

Despite the high prominence of the perovskites BiFeO(3) and KNbO(3) the solid solution between the two has received little attention. We report a detailed neutron and synchrotron X-ray powder diffraction, and Raman spectroscopy study which demonstrates an R3c→P4mm→Amm2 series of structural phase transitions similar to that exhibited by the PbZrO(3)-PbTiO(3) solid solution.

Thio-, seleno- and telluro-ether complexes of aluminium(III) halides: synthesis, structures and properties.

The reaction of AlCl3 with Me2E (E = S, Se or Te) or (n)Bu2E (E = Se or Te) in CH2Cl2 under rigorously anhydrous conditions gave the pseudo-tetrahedral complexes [AlCl3(R2E)]. The [AlX3(Me2E)] (X = Br or I, E = S; X = Br, E = Te) were made from toluene solution since attempted syntheses in CH2Cl2 resulted in substantial chloride incorporation. The synthesis of [(AlCl3)2{o-C6H4(CH2SEt)2}], in which the ligand bridges two tetrahedral aluminium centres, and of the six-coordinate trans-[AlX2{MeE(CH2)2EMe}2][AlX4] (X = Cl or Br, E = S, and X = Cl, E = Se) and cis-[AlI2{MeS(CH2)2SMe}2][AlI4] are reported. The tripodal thioether forms [AlCl3{MeC(CH2SMe)3}], which is a chain polymer with κ(2)-coordinated ligand and a tbp arrangement at Al(iii). Chalcogenoether macrocycle complexes [AlCl3([9]aneS3)], [AlCl2([14]aneS4)][AlCl4] and [AlCl2([16]aneSe4)] [AlCl4] are also described. All complexes were characterised by microanalysis, IR and multinuclear NMR ((1)H, (27)Al, (77)Se or (125)Te) spectroscopy as appropriate. In CH2Cl2 solution [AlCl3(Me2S)] with added Me2S forms [AlCl3(Me2S)2], and the [AlX2{MeS(CH2)2SMe}2][AlX4] exist as mixtures of cis and trans isomers which undergo rapid exchange at ambient temperatures. X-Ray crystal structures are reported for [AlCl3(Me2Se], [AlX3(Me2Te)] (X = Cl or Br), trans-[AlCl2{MeE(CH2)2EMe}2][AlCl4] (E = S or Se), cis-[AlI2{MeS(CH2)2SMe}2][AlI4], [AlCl3{MeC(CH2SMe)3}], and for the sulfonium salt [Me2SH][AlCl4]. The aluminium halide chalcogenoether chemistry is compared with the corresponding gallium and indium systems, and the relative Lewis acidities of the metals discussed. Attempts to use [AlCl3((n)Bu2E)] (E = Se or Te) as LPCVD reagents to form aluminium chalcogenide films were unsuccessful.

Six- and eight-coordinate thio- and seleno-ether complexes of NbF5 and some comparisons with NbCl5 and NbBr5 adducts.

The reaction of RS(CH(2))(2)SR (R = Me, Et or (i)Pr) with NbF(5) produces [NbF(4){RS(CH(2))(2)SR}(2)][NbF(6)] which contain distorted eight-coordinate (dodecahedral) cations and octahedral anions, whereas RSe(CH(2))(2)SeR (R = Me or Bu(n)) form six-coordinate [(NbF(5))(2)(mu-RSe(CH(2))(2)SeR)]. Et(2)S and Me(2)Se (L) also form six-coordinate [NbF(5)(L)], but Me(2)S forms both [NbF(5)(Me(2)S)] and an eight-coordinate cation in [NbF(4)(Me(2)S)(4)][NbF(6)]. MeS(CH(2))(2)SMe forms eight-coordinate cations in [NbX(4){MeS(CH(2))(2)SMe}(2)][NbX(6)] (X = Cl or Br), but other complexes of the heavier halides including [NbX(5)(L)] and [(NbX(5))(2)(mu-L-L)] (L-L = RSe(CH(2))(2)SeR; o-C(6)H(4)(CH(2)SMe)(2) and o-C(6)H(4)(CH(2)SeMe)(2)) contain six-coordinate niobium. The very unstable [NbCl(5)(Me(2)Te)] was characterised spectroscopically, but all other attempts to form telluroether complexes resulted in decomposition, and NbI(5) was reduced even by thioethers. The complexes have been characterised by multinuclear NMR ((1)H, (19)F, (93)Nb, (77)Se or (125)Te), IR and UV/visible spectroscopy, and X-ray crystal structures are reported for [NbF(4){RS(CH(2))(2)SR}(2)][NbF(6)] (R = Me, (i)Pr), [NbF(4)(Me(2)S)(4)][NbF(6)], [NbCl(5)(Me(2)Se)], [NbBr(5)(Me(2)S)], [(NbCl(5))(2){o-C(6)H(4)(CH(2)SMe)(2)}] and [(NbCl(5))(2){MeSe(CH(2))(2)SeMe}]. All the complexes are very moisture sensitive and the fluoride complexes decompose slowly with fluorination of the neutral ligand.

Taking TiF4 complexes to extremes--the first examples with phosphine co-ligands.

The first soft donor adducts of TiF(4), [TiF(4)(diphosphine)] (diphosphine = o-C(6)H(4)(PMe(2))(2), R(2)P(CH(2))(2)PR(2), R = Me or Et) have been prepared from [TiF(4)(MeCN)(2)] and the diphosphines in rigorously anhydrous CH(2)Cl(2), as extremely moisture sensitive yellow solids, and characterised by multinuclear NMR ((1)H, (31)P, (19)F), IR and UV/vis spectroscopy. The crystal structure of [TiF(4){Et(2)P(CH(2))(2)PEt(2)}] has been determined and shows a distorted six-coordinate geometry with disparate Ti-F(transF) and Ti-F(transP) distances and long Ti-P bonds. Weaker soft donor ligands including Ph(3)P, Ph(2)P(CH(2))(2)PPh(2), o-C(6)H(4)(PPh(2))(2), Ph(2)As(CH(2))(2)AsPh(2), o-C(6)H(4)(AsMe(2))(2) and (i)PrS(CH(2))(2)S(i)Pr do not form stable complexes with TiF(4), although surprisingly, fluorotitanate(IV) salts of the previously unknown doubly protonated ligand cations [LH(2)][Ti(4)F(18)] (L = o-C(6)H(4)(PPh(2))(2), o-C(6)H(4)(AsMe(2))(2) and (i)PrS(CH(2))(2)S(i)Pr) are formed in some cases as minor by-products. The structure of [o-C(6)H(4)(PPh(2)H)(2)][Ti(4)F(18)] shows the first authenticated example of a diprotonated o-phenylene-diphosphine. The synthesis and full spectroscopic characterisation are reported for a range of TiF(4) adducts with hard N- or O-donor ligands for comparison purposes, along with crystal structures of [TiF(4)(thf)(2)], [TiF(4)(Ph(3)EO)(2)]·2CH(2)Cl(2) (E = P or As), and [TiF(4)(bipy)].

Isolation and structures of sulfonium salts derived from thioethers: [{o-C(6)H(4)(CH(2)SMe)(2)}H][NbF(6)] and [{[9]aneS(3)}H][NbF(6)].

Two very unusual sulfonium salts, [{o-C(6)H(4)(CH(2)SMe)(2)}H][NbF(6)] and [{[9]aneS(3)}H][NbF(6)], obtained from reaction of the thioethers with NbF(5) in CH(2)Cl(2) solution, are reported and their structures described; the eight-coordinate tetrafluoro Nb(v) cation of the dithioether is obtained from the same reaction.

Preparation and properties of cyclic and open-chain Sb/N-donor ligands.

The preparations of both open-chain and cyclic mixed-donor Sb/N ligands, MeN(CH2-2-C6H4)2SbMe (1), MeN(CH2-2-C6H4SbMe2)2 (2), CH2{CH2N(Me)CH2-2-C6H4SbMe2}2 (3) and CH2{CH2N(Me)CH2-2-C6H4}2SbMe (4), are described via reaction of chlorostibines with dilithio-reagents, and their spectroscopic properties established. Air-stable stibonium derivatives of (3) and (4) have been isolated by treatment of the compounds with excess MeI, which leads to quaternisation at the Sb atoms exclusively. A crystal structure of a bis(stibonium) derivative of (3), [CH2{CH2N(Me)CH2-2-C6H4SbMe3}2]I2, reveals hypervalency at Sb through long-range Sb...N interactions (ca. 2.87 A), giving pseudo-five-membered rings fused to the aromatic rings, and distorted trigonal bipyramidal coordination at Sb. The coordinating properties of compounds (1) to (4) have been investigated through their reactions with Cu(I), Mn(I), Mo(0) and Pt(IV) reagents, and for (1) and (4) by reaction with Fe(0), giving [Fe(CO)4(L)]. The spectroscopic data (IR, 1H, 13C{1H}, 55Mn, 63Cu, 95Mo and 195Pt NMR), mass spectrometry and microanalyses for this series of complexes confirm that coordination occurs via the Sb donor atoms in all cases, with N-coordination only present in fac-[Mn(CO)3(2)](CF3SO3). Crystal structures of [Cu(2)2]BF4, [Mo(CO)4(2)] and [PtMe3I(2)] confirm the coordination modes, showing (2) functioning as a wide-angle bidentate distibine. The structures also show the amine N-donor atoms in the complexes are involved in a hypervalent SbN interaction (ca. 3.0 A) with one of the coordinated Sb atoms in each ligand, leading to significant differences in the conformations of the carbon backbones linking the Sb and N atoms. Reaction of Na3[RhCl6].12H2O with one mol equiv. of (2), (3) or (4) leads to the bis-ligand complex [RhCl2(2)2]Cl and the 1 : 1 Rh : L complexes [RhCl2(3)]Cl and [RhCl3(4)], both of which involve coordination via the Sb and N donor atoms.

Synthesis, characterisation and structures of thio-, seleno- and telluro-ether complexes of indium(III) halides.

The indium(III) halo-bridged octahedral dimers [InX(2)(L-L)(mu-X)(2)InX(2)(L-L)] (X = Cl: L-L = MeS(CH(2))(2)SMe, MeSe(CH(2))(2)SeMe, (n)BuSe(CH(2))(2)Se(n)Bu), the ionic trans-[InX(2)(L-L)(2)][InX(4)] (X = Cl: L-L = (i)PrS(CH(2))(2)S(i)Pr; X = Br: L-L = MeS(CH(2))(2)SMe, (i)PrS(CH(2))(2)S(i)Pr, MeSe(CH(2))(2)SeMe), cis-[InCl(2)(thiamacrocycle)][InCl(4)] (thiamacrocycle = [12]aneS(4) or [14]aneS(4)) and the neutral, octahedral [InCl(3)([9]aneS(3))] and [InCl(3){MeC(CH(2)SMe)(3)}] were obtained in good yield by the reaction of 1:1 molar ratios of InX(3) with the ligand in anhydrous CH(2)Cl(2) solution. The distorted tetrahedral [InX(3)(Me(2)Se)] (X = Cl, Br or I) and [InX(3)(Me(2)Te)] (X = Br or I) were obtained from 1:3 and 1:2 molar ratios respectively of InX(3) and Me(2)E (E = Se or Te) also in CH(2)Cl(2). The ligand-bridged, distorted tetrahedral dimers [(InCl(3))(2){micro(2)-o-C(6)H(4)(CH(2)SMe)(2)}] and [(InCl(3))(2){micro(2)-MeTe(CH(2))(3)TeMe}] are formed even from a 1:1 In:ligand ratio. Key structure types were confirmed from crystal structures of [InCl(2){RSe(CH(2))(2)SeR}(micro-Cl)(2)InCl(2){RSe(CH(2))(2)SeR(2)}] (R = Me or (n)Bu), trans-[InX(2){(i)PrS(CH(2))(2)S(i)Pr}(2)][InX(4)] (X = Cl or Br), trans-[InBr(2){MeSe(CH(2))(2)SeMe}(2)][InBr(4)], cis-[InCl(2)([14]aneS(4))][InCl(4)] and [InBr(3)(Me(2)Se)]. The bulk complexes have been characterised by IR and Raman spectroscopy and microanalyses, while (1)H, (77)Se{(1)H} and (125)Te{(1)H} NMR spectroscopy show that the compounds are extremely labile in solution and undergo rapid dynamic exchange equilibria. Comparisons are drawn between these structurally rather diverse In(III) chalcogenoether complexes and the corresponding Ga(III) species (all of which are neutral and involve distorted tetrahedral coordination). The reaction of TlCl(3) with Me(2)E (E = Se or Te) shows that chlorination of Me(2)E rather than adduct formation occurs, while no reaction occurred between TlCl(3) and Me(2)S, consistent with Tl(III) being a very poor Lewis acid.

Preparation and structures of tellurium(IV) halide complexes with thioether coordination.

The first chalcogenoether complexes of Te(iv) chloride and bromide are prepared by reaction of the thioether with a suspension of TeX(4) in anhydrous CH(2)Cl(2), and the products characterised by IR, Raman, (1)H and (125)Te{(1)H} NMR spectroscopy and microanalysis. The structures of the distorted octahedral chelate complexes [TeX(4){RS(CH(2))(2)SR}] (X = Cl or Br; R = Me or (i)Pr) and the centrosymmetric halo-bridged dimers [{X(3)(Me(2)S)Te}(2)(micro-X)(2)] (X = Cl or Br) involving Te(iv) are reported and the structures interpreted in terms of a three-centre-four-electron bonding model, with weak, secondary Te-S interactions. The structure of a unique Te(ii) thioether complex, [TeCl{(i)PrS(CH(2))(2)S(i)Pr}][Te(2)Cl(9)] obtained as a decomposition product from a sample of [TeCl(4){(i)PrS(CH(2))(2)S(i)Pr}], in which a Te(ii) thioether cation and Te(iv) chloride anion are weakly associated via micro(2)- and micro(3)-bridging Cl ligands, is also described. In this case distortions in the coordination environment at the Te(ii) ion are attributed to the effects of the Te-based lone pairs.

Preparation and properties of sterically demanding and chiral distibine ligands.

A series of new rigid distibines, 1,8-bis(R(2)Sb)naphthalene (R = Me: (); R = Ph: ()), and chiral distibines, 2,2'-bis(R(2)Sb)-1,1'-binaphthyl (R = Me: (); R = Ph: () obtained as racemic mixtures) and the discrete enantiomers of 4,5-bis((R(2)Sb)methyl)-2,2-dimethyl-1,3-D/L-dioxolane (R = Me: () (l), () (d); R = Ph: () (l), () (d)) have been obtained in high yields, using either electrophilic halostibine reagents with di-lithium reagents (()-()) or nucleophilic stibide reagents with dibromo-derivatives (()-()). The distorted octahedral complexes [Mo(CO)(4)(L)], L = ()-(), planar [PtCl(2)(L)], L = (), (), (), (), and neutral, five-coordinate [RhCl(cod)(L)], L = (), (), (), are reported and trends in the spectroscopic data are discussed in terms of the ligand donor properties. Crystal structures of () and [Mo(CO)(4)()] reveal significant structural changes occur upon coordination, and these are also reflected in the solution NMR spectroscopic parameters. Changes in the C-Sb-C angles and C-Sb bond distances upon coordination of () are discussed in term of increased s/p orbital mixing. Air oxidation of () forms a very unusual stibine oxide, the structure of which shows a distorted Sb(4)O(4) cubane core (bridging O atoms) with two orthogonal naphthalene units.

Synthesis, chemistry and structures of complexes of the dioxovanadium(V) halides VO2F and VO2Cl.

[VO2F(L-L)] (L-L = 2,2'-bipyridyl, 1,10-phenanthroline, Me2N(CH2)2NMe2) and [VO2F(py)2] (py = pyridine) have been prepared from the corresponding [VOF3(L-L)] or [VOF3(py)2] and O(SiMe3)2 in MeCN solution. VO2F (itself made from VOF3 and O(SiMe3)2 in MeCN) forms [Me4N][VO2F2] with [Me4N]F, but does not react with neutral N- or O-donor ligands. VO2Cl, prepared from VOCl3 and ozone, reacts with 2,2'-bipyridyl or 1,10-phenanthroline to form [VO2Cl(L-L)], with pyridine or pyridine-N-oxide (L) to produce [VO2Cl(L)2], and with OPPh3 or OAsPh3 (L') gives [VO2Cl(L')]. A second product from the OPPh3 system is the ionic [VO2(OPPh3)3][VO2Cl2] containing a trigonal bipyramidal cation. Neither VO2F nor VO2Cl form isolable complexes with MeCN, thf or MeO(CH2)2OMe, and both are reduced by P-, As-, S- or Se-donor ligands. [Ph4As][VO2X2] (X = F or Cl) react with 2,2'-bipyridyl to form [VO2X(2,2'-bipyridyl)], but similar reactions with weaker O-donor ligands fail. The complexes have been characterised by IR, multinuclear NMR (1H, 19F, 51V or 31P) and UV-visible spectroscopy. X-ray crystal structures are reported for [VO2F(py)2], [VO2Cl(L)2] (L = py or pyNO) and [VO2(OPPh3)3][VO2Cl2].

Communication in platinum ethynylchalcogenophenes.

A series of alkynylchalcogenophene platinum(II) complexes have been synthesized and characterized by multinuclear NMR and UV-visible absorption spectroscopies; the NMR spectra show unprecedented long-range heteronuclear coupling, and clear correlations emerge between spectroscopic data and theoretical analysis of their electronic structures.