Magnetic properties and fluxional behaviour of heteroleptic cyclopentadienyl–dithiolene d1and d0niobium complexes

Abstract

Paramagnetic d1 niobium complexes of general formula [Nb(η-C5H4R)2(dithiolene)][R = SiMe3 or But; dithiolene = C3S52–(4,5-disulfanyl-1,3-dithiole-2-thionate), C3OS42–(4,5-disulfanyl-1,3-dithiol-2-onate) or dddt2–(5,6-dihydro-1,4-dithiine-2,3-dithiolate)] have been prepared and their redox properties studied. The crystal structure determination of [Nb(η-C5H4SiMe3)2(C3S5)] showed that the folding angle of the NbS2C2 plane along the S–S axis is 34(2)°, an intermediate value compared with those of analogous d0(45–50°) and d2(0–10°) complexes, as rationalized by extended-Hückel calculations. The Curie-type temperature dependence of the spin susceptibility of [Nb(cp)2(C3S5)], [Nb(cp)2(C3OS4)] and [Nb(η-C5H4R)2(C3S5)](cp =η-C5H5) demonstrates that the paramagnetic complexes do not interact with each other in the solid state. Cationic d0 complexes were obtained either by chemical oxidation (tetracyanoquinodimethane) of the d1 molecules or from the direct reaction of dddt2– with d0[Nb(η-C5H4R)2Cl2][PF6]. The fluxional behaviour of these d0 complexes has been investigated by temperature-dependent NMR studies and shown to be comparable with that of isoelectronic d0[Ti(cp)2(dithiolene)] complexes.