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The dihalide capped trinuclear nickel clusters Ni3(μ3-X)2(μ2-dppm)3 (X = I (1a), Br (1b); dppm = Ph2PCH2PPh2) were synthesized and converted to their respective monocations [Ni3(μ3-X)2(μ2-dppm)3]+ (X = I (1a + ), Br (1b + )) via a single electron oxidation. Clusters 1a and 1a + were characterized by X-ray crystallography. Displacement of a triply-bridging iodide ligand in Ni3(μ3-I)2(μ2-dppm)3 (1a) by π-acceptor ligands produces a class of 48-electron trinuclear nickel clusters of the general formula [Ni3(μ3-L)(μ3-I)(μ2-dppm)3]+ (L = CO (2a); CNR, R = CH3 (3a), 2,6-(CH3)2C6H3 (4a), i-C3H7 (5), C6H11 (6), t-C4H9 (7), CH2C6H5 (8), C6H5 (9), p-C6H4I (10), p-C6H4Br (11), p-C6H4Cl (12), p-C6H4F (13), p-C6H4CH3 (14), p-C6H4CF3 (15), p-C6H4OCH3 (16), and p-C6H4CN (17)). A similar but less extensive study was conducted with the dibromide capped cluster 1b. The X-ray crystal structure of cluster 2a, as the PF6 - salt, was also obtained. Clusters 2−17 possess strikingly similar spectroscopic and electrochemical properties. This is ascribed to the lack of interaction between the a 2 LUMO of clusters 2−17 and the molecular orbitals of the capping π-acceptor ligands. The unexpected appearance of two ν(C⋮N) bands in the FT-IR spectra of clusters 3−17 was demonstrated to be the result of a Fermi resonance involving the ν(C⋮N) fundamental and the first overtone of the ν(N−C(alkyl)) fundamental of the capping isocyanide. In addition, molecular orbital calculations on 1−17 provide insights into the differences in the physical properties and reactivities of clusters of this class capped by π-donor (1) or π-acceptor ligands (2−17).

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The UV-vis and IR spectroelectrochemistry of W2(SBz)2(CO)8* 12 3" (1) in 0.1 (TBA)PF6/CH2CI2 is reported (where SBz~= benzyl mercaptide). The reversible 2e~oxidation of W2(SBz)2(CC))82~i s analyzed in terms of the individual le~redox potentials, E e'_/2-and E by measuring the homogeneous disproportionation constant, Adisp. of the electrochemically generated W2(SBz)2(CO)8~r adical. At 25 ®C, we find KnSf equal to 7500 ± 4000. This value places E 0,-/2-at a potential nearly 0.23 V positive of E ®'0/-(E °'-ß---0.46 V; E ®'0/-= -0.69 V vs aqueous AgCl/Ag). The reversal in positions of the leredox potentials drives the disproportionation reaction and is rationalized to be a consequence of the electronic destabilization of W2(SBz)2(CO)8" relative to W2(SBz)2(CO)82' and W2(SBz)2(CO)8.

Kinetic studies of the reduction of some ethylenediaminetetraacetatocobaltate(III) complexes by hexacyanoferrate(II) have been carried out at 25°and ionic strength 0.59 Min the presence of ascorbic acid (added to drive the reactions to completion). Second-order rate constants for CoEDTA", Co(EDTA)Cl2", and Co(EDTA)OH22~a re 0.21 ± 0.02, 7.0 ± 0.2, and 3.4 + 0.2 M"' sec"1, respectively. The oxidation of CoEDTA2" by Fe(CN)63" has been reexamined at pH 10, and it is found that the primary mononuclear cobalt(III) product is the hexadentate species CoEDTA". The mechanism of these oxidation reduction reactions is assigned on the basis of indirect criteria. It is concluded that although the binuclear, cyanobridged complex (EDTA)CoNCFe(CN) 55" (previously identified by Adamson and Gonick) is the predominant primary product formed by the interaction between CoEDTA2" and Fe(CN)6 3", the binuclear complex is not the immediate precursor of the mononuclear products CoEDTA" and Fe(CN)64". These are formed by an alternate, outer-sphere electron-transfer pathway. An outer-sphere mechanism is also indicated for the Fe(CN)64" reductions of Co(EDTA)OH2" and Co(EDTA)-Cl2".