Electron-sink behaviour of the carbonylnickel clusters [Ni32C6(CO)36]6- and [Ni38C6(CO)42]6-:: Synthesis and characteriztion of the anions [Ni32C6(CO)36]n- (n = 5-10) and [Ni38C6(CO)42]n- (n = 5-9) and crystal structure of [PPh3Me]6[Ni32C6(CO)36]•4 MeCN

The hexacarbide clusters [H6-nNi38C6(CO)(42)](n-) (n = 3, 4, 5, or 6) have been directly obtained from the reaction of [Ni-6(CO)(12)](2-) with C3Cl6, whereas the related anions, [H6-nNi32C6(CO)(36)](n-) (n = 5 or 6), have been obtained by degradation under carbon monoxide of [Ni38C6(CO)(42)](6-), or upon thermal treatment at ca. 110 degrees C of [Ni10C2(CO)(42)](2-) salts. The compound [PPh3Me](6)[Ni32C6(CO)(36)] . 4 MeCN is triclinic, space group P (1) over bar (No 2), with a = 15.974(3), b = 17.474(3), c = 18.200(4) Angstrom, alpha = 61.37(2), beta = 69.31(2), gamma = 72.35(2)degrees and Z = 1; final R = 0.033. The structure of [Ni32C6(CO)(36)](6-) has an idealised O-h symmetry and is based on a truncated octahedral Ni32C6 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 Ni32C6 core is very similar to that found previously in [HNi38C6(CO)(42)](5-), and shows very close interatomic separations. Both [Ni32C6(CO)(36)](6-) and [H6-nNi38C6(CO)(42)](n-) (n = 5 or 6) display electron-sink behaviour. Thus, they have been chemically and electrochemically reduced to their corresponding [Ni32C6(CO)(36)](n-) (n = 7-10), [Ni38C6(CO)(42)](n-) (n = 7-9) and [HNi38C6(CO)(42)](n-) (n = 6-8) derivatives, and several of the involved redox changes show features of electrochemical reversibility. In contrast, both [Ni32C6(CO)(36)](6-) and [H6-nNi38C6(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 [HNi32C6(CO)(36)](5-) and [H6-nNi38C6(CO)(42)](n-) (n = 3, 4, or 5), which could not be validated by IH-NMR spectroscopy.