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摘要
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 <P-Nb-P angles are very similar in the two types, but Nb-Cl distances are similar to 0.1 angstrom longer in the square antiprismatic complexes. These paramagnetic (d(1)) complexes were also characterised by microanalysis, magnetic measurements, IR and UV-visible spectroscopy. Using a 1 : 1 molar ratio of NbCl4 : diphosphine (diphosphine = Me2PCH2CH2PMe2, Et2PCH2CH2PEt2, Cy2PCH2CH2PCy2 and Ph2PCH2CH2CH2PPh2) afforded [NbCl4(diphosphine)], and [NbBr4(Me(2)PCH(2)CH(2)PMe2)] was obtained similarly. These 1 : 1 complexes are unstable in solution, preventing X-ray crystallographic study, but based upon their diamagnetism, IR, UV-visible and P-31{H-1} NMR spectra, they are formulated as halide-bridged dimers [(diphosphine)X2Nb(mu-X)(4)NbX2(diphosphine)], with single Nb-Nb bonds and chelating diphosphines. The Nb(IV) complexes are prone to hydrolysis and oxidation in solution and the structures of the Nb(V) complexes [NbBr4(Me2PCH2CH2PMe2)(2)][NbOBr4(MeCN)] with a dodecahedral cation, and [{NbOCl3{Et2P(CH2)(2)PEt2}}(2){mu-Et2P(CH2)(2)PEt2}] which contains seven-coordinate Nb(V) centres with a symmetrical diphosphine bridge, are reported. The structure of niobium tetrabromide, conveniently made from NbCl4 and BBr3, is a chain polymer with edge-linked NbBr6 octahedra and alternating long and short Nb-Nb distances, the latter ascribed to Nb-Nb bonds.
- 出版日期2016
