METAL-METAL BONDING IN PENTANUCLEAR BOW-TIE METAL SULFIDO CLUSTERS - SYNTHETIC AND STRUCTURAL STUDIES ON THE CATIONIC PENTANUCLEAR CLUSTERS2)(MU(3)-S)(2)M(MU(3)-S)(2)(IRCP-ASTERISK)(2)](N+) (M = FE, CO, NI, N= 1, 2)

Reactions of [CpMCl(mu(2)-SH)(2)MCp*Cl] (1, M = Ir; 2, M = Rh; Cp* = eta(5)-C5Me5) with excess FeCl2. 4H(2)O in THF grave the paramagnetic trinuclear clusters [(CpM)(2)(mu(3)-S)(2)FeCl2] (3, M = Ir; 4, M = Rh ), which were further converted into the dicationic 78e(-) pentanuclea r bow-tie cluster CpIr)(2)(mu(3)-S)(2)Fe(mu(3)-S)(2)(IrCp*)(2)](2+) ( 5) by treatment with NaBPh4. When complex 1 was allowed to react with CoCl2 and NiCl2. 6H(2)O or Ni(cod)(2) (cod cyclooctadiene), the relate d pentanuclear 79e(-) and 80e(-) bow-tie clusters (CpIr)(2)(mu(3)-S)( 2)M(mu(3)-S)(2)(IrCp)(2)](2+) (6, M = Co; 7, M = Ni) were obtained di rectly, respectively. Cyclic voltammograms of 5[BPh4](2), 6[BPh4](2), and 7[BPh4](2) showed two reversible reduction waves at -0.25 to -0.43 V and -1.04 to -1.34 V. In both redox couples, the redox potential wa s in the order Fe < Co < Ni. One-electron reduction of clusters 5[BPh4 ](2), 6[BPh4](2), and 7[BPh4](2) with Co(eta(5)-C5H5)(2) gave the corr esponding monocationic pentanuclear 79-81e(-) bow-tie clusters [(CpIr )(2)(mu(3)-S)(2)(mu(3)-S)(2)(IrCp)(2)](+) (8, M = Fe; 9, M = Co; 10, M = Ni). The molecular structures of 3, 4, 5[BPh4](2). CH2Cl2, 6[CoCl3 (NCMe)](2), 7[NiCl4]. CH2Cl2, 8[BPh4], 9[BPh4], and 10[BPh4] were unam biguously determined by X-ray diffraction study. The structures of the pentanuclear bow-tie cluster cores remarkably changed stepwise as the core electrons increased from 78 to 81. Two of the M-Ir (M = Fe, Co) bonds in the 79e(-) clusters 6 and 8 show significant elongation in co mparison with the Fe-Ir bonds in the 78e- cluster 5. Two different typ es of the bow-tie structures were observed for the 80e(-) clusters 7 a nd 9. Cluster 7 has a Z-shaped metal core with only two Ni-Ir bonds, w hile in cluster 9, the six metal-metal bonds in the bow-tie structure are retained with slight elongation of the Co-Ir bonds in comparison w ith the corresponding dication 6. The 81e(-) cluster 10 has two normal Ni-Ir bonds and one long Ni-Lr bonding interaction with the fourth no nbonding Ni-Ir contact. This structural variation is interpreted in te rms of the total electron counts and molecular orbital calculations of the clusters.