Electron-Sink Behaviour of the Carbonylnickel Clusters (Ni_(32)C_6(CO)_(36))~(6-) and (Ni_(38)C_6(CO)_(42))~(6-): Synthesis and Characterization of the Anions (Ni_(32)C_6(CO)_(36))~(n-) (n = 5-10) and (Ni_(38)C_6(CO)_(42))~(n-) (n = 5-9) and Crystal

摘要

The hexacarbide clusters [H_(6-n)Ni_(38)C_6(CO)_(42)]~(n-) (n=3,4,5, or 6) have been directly obtained from the reaction of [Ni_6(CO)_(12)]~(2-) with C_6Cl_6, whereas the related anions, [H_(6-n)Ni_(32)C_6(CO)_(36)]~(n-) (n = 5 or 6), have been obtained by degradation under carbon monoxide of [Ni_(38)C_6(CO)_(42)]~(6-), or upon thermal treatment at ca. 110 deg C of [Ni_(10)C_2(CO)_(16)]~(2-) salts. The compound [PPh_3Me]_6[Ni_(32)C_6(CO)_(36)] (centre dot) 4 MeCN is triclinic, space group P1-bar (No 2), with a = 15.974(3), b = 17.474(3), c = 18.200(4) A, #alpha# = 61.37(2), #beta# = 69.31(2), #gamma# = 72.35(2) deg and Z = 1; final R = 0.033. The structure of [Ni_(32)C_6(CO)_(36)]~(6-) has an idealised O_h symmetry and is based on a truncated octahedral Ni_(32)C_6 framework, with all edges spanned by bridging carbonyl groups. The six interstitial carbide atoms are lodged in square-antiprismatic cavities. The overall geometry of the Ni_(32)C_6 core is very similar to that found previously in [HNi_(38)C_6(CO)_(42)]~(5-), and shows very close interatomic separations. Both [Ni_(32)C_6(CO)_(36)]~(6-) and [H_(6-n)Ni_(38)C_6(CO)_(42)]~(n-) (n = 5 or 6) display electron-sink behaviour. Thus, they have been chemically and electrochemically reduced to their corresponding [Ni_(32)C_6(CO)_(36)]~(n-) (n = 7-10), [Ni_(38)C_6(CO)_(42)]~(n-) (n = 7-9) and [HNi_(38)C_6(CO)_(42)]~(n-) (n = 6-8) derivatives, and several of the involved redox changes show features of electrochemical reversibility. In contrast, both [Ni_(32)C_6(CO)_(36)]~(6-) and [H_(6-n)Ni_(38)C_6(CO)_(42)]~(n-) (n = 5 or 6) support only one partially reversible oxidation step. Their different behaviour upon protonation or oxidation is an indirect, but unambiguous, proof of the hydride nature of [HNi_(32)C_6(CO)_(36)]~(5-) and [H_(6-n)Ni_(38)C_6(CO)_(42)]~(n-) (n = 3, 4 or 5), which could not be validated by ~1H-NMR spectroscopy.