THE CHEMISTRY OF OCTAHEDRAL RHENIUM CLUSTERS
Abstract
The reaction of rhenium metal is Na(,2)CO(,3) with gaseous H(,2)S st 750-900(DEGREES)C yields transparent red Na(,4){Re(,6)S(,8)}S(,2)(S(,2)), and a Re(III) compound containing Re(,6) octahedra in a cube of sulfide ions. Additional sulfide as well as disulfide ions bridge octahedra. It is interesting to note that this compound possesses structural features similar to those of the isoelectronic Mo(II) octahedral cluster compounds such as {Mo(,6)Cl(,8)}Cl(,4), in which halides bridge the clusters along their 4-fold axes, and the various Chevrel phases, M(,x)Mo(,6)S(,8), in which intercluster bridging is accomplished by the positioning of clusters so that cluster sulfides occupy the exo positions of neighboring clusters. Na(,4){Re(,6)S(,8)}S(,2)(S(,2)) reacts with acid to give semiconducting black Na(,1.5){Re(,6)S(,8)}S(,2)(S(,2)) with only slight changes in cell dimensions. The structure of the black compound shows that the Re(,6)S(,6) unit, sulfide and disulfide bridges remain intact. Sodium sites are partially occupied. The oxidation of the 24 electron Re(,6) cluster is accompanied by an expansion of the Re(,6) cluster and shifts in the far IR spectra which are consistent with weakening of the Re-Re bonds. The black compound can be reduced by butyl lithium. An analogous set of reactions can be carried out in the Cs(,4){Re(,6)S(,8)}SS(,2/2)(S(,2))(,3/2) system, which is synthesized by replacing Na(,2)CO(,3) with Cs(,2)CO(,3) in the original synthesis. This system possesses a terminal sulfide in place of a bridging disulfide, and is therefore a 23 electron system. The measured paramagnetism of Cs(,4){Re(,6)S(,8)}SS(,2/2)(S(,2))(,3/2) confirms the notion of a 23 electron system.
Degree
Ph.D.
Subject Area
Chemistry
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