Substitution of bridging S_2 ligands in the [Nb_2(#mu#-S_2)_2]~(4+) core: a simple route to [Nb_2(Se_2)_2]~(4+), (Nb_2(S)(Te_2)_2)~(4+) and [Nb_2(S)_2]~(4+)

摘要

Reactions of [Nb_2(#mu#-S_2)_2(dtc)_4] 1 (dtc=diethyldithiocarbamate, S_2CNEt_2) with chalcogen-transfer reagents PEt_3Y (Y = Se or Te) were investigated. With PEt_3Se, fully substituted [Nb_2(#mu#-Se_2)_2(dtc)_4] 2 forms if a catalytic amount of free PEt_3 is present. However PEt_3Te 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)A]. 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 PEt_3Te only the sulfur abstraction product [Nb_2(#mu#-S)_2(acac)_4] 5 formed, which could be more directly prepared from 4 and PEt_3. Crystal structures of 4 and 5 were determined.