MAGNETIC-PROPERTIES AND FLUXIONAL BEHAVIOR OF HETEROLEPTIC CYCLOPENTADIENYL-DITHIOLENE D(1) AND D(0) NIOBIUM COMPLEXES

Paramagnetic d(1) niobium complexes of general formula [Nb(eta-C(5)H(4 )R)(2)(dithiolene)] [R = SiMe(3) or Bu(t); dithiolene = C3S52- (4,5-di sulfanyl-1,3-dithiole-2-thionate), C3OS42- (4,5-disulfanyl-1,3-dithiol -2-onate) or dddt(2-) (5,6-dihydro-1,4-dithiine-2,3-dithiolate)] have been prepared and their redox properties studied. The crystal structur e determination of [Nb(eta-C(5)H(4)SiMe(3))(2)(C3S5)] showed that the folding angle of the NbS2C2 plane along the S-S axis is 34(2)degrees, an intermediate value compared with those of analogous d(0) (45-50 deg rees) and d(2) (0-10 degrees) complexes, as rationalized by extended-H uckel calculations. The Curie-type temperature dependence of the spin susceptibility of [Nb(cp)(2)(C3S5)], [Nb(cp)(2)(C3OS4)] and [Nb(eta-C( 5)H(4)R)(2)(C3S5)] (cp = eta-C5H5) demonstrates that the paramagnetic complexes do not interact with each other in the solid state. Cationic d(0) complexes were obtained either by chemical oxidation (tetracyano quinodimethane) of the d(1) molecules or from the direct reaction of d ddt(2-) with d(0) [Nb(eta-C(5)H(4)R)(2)Cl-2][PF6]. The fluxional behav iour of these d(0) complexes has been investigated by temperature-depe ndent NMR studies and shown to be comparable with that of isoelectroni c d(0) [Ti(cp)(2)(dithiolene)] complexes.