Niobium and Tantalum

Niobium tetrahalide complexes with neutral diphosphine ligands

“…Phosphine complexes of niobium chlorides and bromides are known in oxidation states II-V, and with a wide range of stoichiometries and structures, [1][2][3] and we recently reported six-and eight-coordinate phosphine complexes with NbF5. 4 Whilst the complexes of niobium(V) chloride and bromide are mononuclear and based upon six-or eight-coordinate metal centres, those in lower oxidation states are more varied.…”

“…14,15 The chemistry of Nb(IV) chloride with bidentate group 16 ligands has also proved to be complicated, and in order to obtain a better understanding of the latter, we explored some chemistry with diphosphine ligands, and describe our results below. Only a few complexes of types [NbCl4(diphosphine) 2] or [NbCl4(diphosphine)] have been described previously, 16,17 and none have been structurally characterised. The structure of [TaCl4(Me2PCH2CH2PMe2)2] 18 has been determined, but curiously the tantalum is coordinated in a square antiprismatic geometry, whilst the Nb(V) or Ta(V) complexes are dodecahedral.…”