SOLUTION CHEMISTRY OF CHALCOHALIDE HEXANUCLEAR RHENIUM CLUSTER MONOANIONS - SUBSTITUTION-REACTIONS AND STRUCTURAL AND LSIMS CHARACTERIZATION OF THE HETEROSUBSTITUTED CLUSTER DIANIONS, (N-BU(4)N)(2)[RE(6)Q(5)ECL(8)](Q=S,E=S,SE Q=SE,E=S,SE,TE)

The gentle, efficient, and specific substitution of one face-bridging inner chloride ligand (Cl-i) upon reaction of (n-Bu(4)N)[Re(6)Q(5)(i)Cl(3)(i)(Cl-6(a))] (Q = S, Se) with [(CH3)(3)Si](2)E (E = O, S, Se, Te) reagents provides at room temperature and in high yields the tetrabutylammonium salts of the chalcogen-enriched,eventually heterosubstituted, hexanuclear molecular cluster dianions (n-Bu(4)N)2[Re(6)S(5)(i)E(i)Cl(2)(i)(Cl-6(a))] (E = 0, 1; S, 2; Se, 3) and (n-Bu(4)N)2[Re(6)Se(5)(i)E(i)Cl(i)(2)-(Cl-6(a))] (E = S, 4; Se, 5; Te, 6). The latter have been fully characterized by liquid secondary negative ion mass spectrometry (LSIMS). The crystal structures of (n-Bu(4)N)(2)Re6S5OCl8 and (n-Bu(4)N)(2)Re6Se5TeCl8 have been determined. Crystal data for 1: P2(1)/a, a = 18.377(1) Angstrom, b = 16.138(6) Angstrom, c = 18.257(3) Angstrom, beta = 92.16(1)degrees, V = 5410(2) Angstrom(3), Z = 4. Crystal data for 6: P2(1)/n, a = 12.877(2) Angstrom, b = 11.312(8) Angstrom, c = 18.613(3) Angstrom, beta = 90.11(1)degrees, V = 2711(2) Angstrom(3), Z = 2. There is a significant contraction of the single octahedron face capped by the oxygen atom in the oxo sulfide rhenium cluster [Re6S5OCl8](2-). The values of the Re-Cl-a distances in both structures complement earlier structural studies and confirm that this distance increases with the molecular cluster charge. Molecular orbital calculations of the extended Huckel type for the series of model molecular clusters (Re6S4Cl4i)-Cl-i(Cl-6), [(Re6S5Cl3i)-Cl-i(Cl-6(a))](-), [(Re6S6Cl2i)-Cl-i(Cl-6(a))](2-), [(Re6S7Cli)-Cl-i(Cl-6(a))](3-), and [Re6S8i(Cl-6(a))](4-), as well as [(Re6S5OCl2i)-O-i-Cl-i(Cl-6(a))](2-), demonstrate that the thermalized average Re-Cla overlap population decreases with the increase in cluster charge, a genuine electronic effect which supports the conclusion that the actual Re-Cl-a distances in a given structure is specific of the cluster anion charge. The shrinking of the ore-capped Res face on the contrary is not an electronic effect but is more the result of a steric adjustment.