The dihalide capped trinuclear nickel clusters Ni 3 (μ 3 -X) 2 (μ 2 -dppm) 3 (X = I ( 1a ), Br ( 1b ); dppm = Ph 2 PCH 2 PPh 2 ) were synthesized and converted to their respective monocations [Ni 3 (μ 3 -X) 2 (μ 2 -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 Ni 3 (μ 3 -I) 2 (μ 2 -dppm) 3 ( 1a ) by π-acceptor ligands produces a class of 48-electron trinuclear nickel clusters of the general formula [Ni 3 (μ 3 -L)(μ 3 -I)(μ 2 -dppm) 3 ] + (L = CO ( 2a ); CNR, R = CH 3 ( 3a ), 2,6-(CH 3 ) 2 C 6 H 3 ( 4a ), i -C 3 H 7 ( 5 ), C 6 H 11 ( 6 ), t -C 4 H 9 ( 7 ), CH 2 C 6 H 5 ( 8 ), C 6 H 5 ( 9 ), p -C 6 H 4 I ( 10), p -C 6 H 4 Br ( 11 ), p -C 6 H 4 Cl ( 12 ), p -C 6 H 4 F ( 13 ), p -C 6 H 4 CH 3 ( 14 ), p -C 6 H 4 CF 3 ( 15 ), p -C 6 H 4 OCH 3 ( 16 ), and p -C 6 H 4 CN ( 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 PF 6 - 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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Morgenstern et al. (1996) studied this question.
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