Substitution of bridging S2 ligands in the [Nb2(μ-S2)2]4+ core:: a simple route to [Nb2(Se2)2]4+, [Nb2(S)(Te2)]4+ and [Nb2(S)2]4+

Reactions of [Nb-2(mu-S-2)(2)(dtc)(4)] 1 (dtc = diethyldithiocarbamate, S2CNEt2) with chalcogen-transfer reagents PEt3Y (Y = Se or Te) were investigated. With PEt3Se, fully substituted [Nb-2(mu-Se-2)(2)(dtc)(4)] 2 forms if a catalytic amount of free PEt3 is present. However PEt3Te gives [Nb-2(S)(Te-2)(dtc)(4)]3 which has a new core with two different chalcogens acting as bridges. The structures of both 2 and 3 were determined by X-ray analysis [2: Nb-Nb 2.974(2), Se-Se 2.303(2). 3: Nb-Nb 2.920(4), Te-Te 2.648(3) Angstrom]. Electrochemistry of 2 and 3 was studied and a reversible one-electron oxidation was found for 2, giving a blue ESR-active (19-plet, g = 2.0489, A = 52.5 G) species [Nb-2(mu-Se-2)(2)(dtc)(4)](+) at 638 mV vs. NHE. By contrast in the reaction of [Nb-2(mu-S-2)(2)(acac)(4)] 4 (Hacac = acetylacetone) with PEt3Te only the sulfur abstraction product [Nb-2(mu-S)(2)(acac)(4)] 5 formed, which could be more directly prepared from 4 and PEt3. Crystal structures of 4 and 5 were determined.