New syntheses of image (Q = S, Se) complexes with bidentate ligands, their isomerism and electronic structure

Mechanochemical synthesis was used to prepare a series of [Nb2(μ-Q2)2(LL)4] complexes with various bidentate ligands (Q = S, Se; LL is oxalate, dithiocarbamates, xanthates, acetylacetonate and dithiophosphate). The reactions always give two isomers which differ by the relative orientation of the chelate rings, as was shown by 77Se, 13C and 31P NMR techniques. Crystal and molecular structures of centrosymmetric isomers of [Nb2(μ-Se2)2(acac)4], [Nb2(μ-Q2)2(n -Bu2NCS2)4], [Nb2(μ-Se2)2((i -PrO)2PS2)4], and of the non-centrosymmetric isomers of [Nb2(μ-S2)2(i -Bu2NCS2)4] and [Nb2(μ-Se2)2(EtOCS2)4] · CHCl3 were determined. Quantum chemical calculations were used to establish the HOMO–LUMO composition of several View the MathML sourceNb2(S2)24+ complexes, to probe the extent of M–M bonding and to interpret the electronic spectra. Mass-spectrometry and thermogravimetric data are also reported.