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+

Abstract

Reactions of [Nb₂(µ-S₂)₂(dtc)₄] 1 (dtc = diethyldithiocarbamate, S₂CNEt₂) with chalcogen-transfer reagents PEt₃Y (Y = Se or Te) were investigated. With PEt₃Se, fully substituted [Nb₂(µ-Se₂)₂(dtc)₄] 2 forms if a catalytic amount of free PEt₃ is present. However PEt₃Te gives [Nb₂(S)(Te₂)(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) Å]. 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 [Nb₂(µ-Se₂)₂(dtc)₄]⁺ at 638 mV vs. NHE. By contrast in the reaction of [Nb₂(µ-S₂)₂(acac)₄] 4 (Hacac = acetylacetone) with PEt₃Te only the sulfur abstraction product [Nb₂(µ-S)₂(acac)₄] 5 formed, which could be more directly prepared from 4 and PEt₃. Crystal structures of 4 and 5 were determined.