Dinuclear niobium(III), tantalum(III) and tantalum(IV) complexes with thioether and selenoether ligands

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 <P-Nb-P angles are very similar in the two types, but Nb-Cl distances are ∼0.1 Å 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(Me2PCH2CH2PMe2)] 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 (31)P{(1)H} NMR spectra, they are formulated as halide-bridged dimers [(diphosphine)X2Nb(μ-X)4NbX2(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)2PEt2}}2{μ-Et2P(CH2)2PEt2}] 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.

Chalcogenoether complexes of Nb(v) thio- and seleno-halides as single source precursors for low pressure chemical vapour deposition of NbS2 and NbSe2 thin films

A series of thioether complexes of NbSCl₃ has been prepared and selected examples demonstrated as precursors to 3R-NbS₂ films; deposition of 2H-NbSe₂ from [NbSe₂Cl₃(SeⁿBu₂)] is also reported.

Niobium tetrachloride complexes with thio-, seleno- and telluro-ether coordination – synthesis and structures

Six- and eight-coordinate complexes of NbCl₄ with thio- seleno- and telluro-ethers are described and the structures of representative examples determined.

Developments in the chemistry of the hard early metals (Groups 1–6) with thioether, selenoether and telluroether ligands

Key developments in the coordination chemistry of the soft, neutral chalcogenoether ligands towards hard s-, f- and early d-block ions, and their prospects for various applications are discussed.