Solid state studies (X-ray and H-1-, C-13-NMR) on (NMe4)(4-x)[HxNi12(CO)(21)]center dot S (x = 1, S = Me2CO; x = 2, S = 2THF)

The molecular structures of (NMe4)(4-x)[HxNi12(CO)(21)] S (x = 1, S = Me2CO ; x = 2, S = 2THF) are reported. Both anions are similar and consist of a c entral Ni-6(CO)(3)(mu-CO)(6)-layer flanked on both sides by two Ni-3(CO)(3) (mu-CO)(3)-layers such that the Ni-12-fragment is hexagonal close-packed. T he separation between the central Ni-6-plane (B) and the two outer Ni-3-pla nes (A, C) is consistent with H-occupancy of either one (x = 1) or both (x = 2) of the two octahedral metal cavities. Variable temperature solid state H-1 MAS and C-13 CP/MAS NMR spectra are reported for both clusters. For th e dihydride, the solid state H-1- and C-13-NMR spectra remain unchanged fro m low to room temperature and are consistent with the X-ray structure; at r oom temperature, there are two hydride resonances consistent with them bein g on the plane of symmetry on opposite sides of the Ni-6-layer and the high field shift is consistent with them not being in the centre of the Ni-6 oct ahedral cavity. For [H2Ni12(CO)(21)](2-), there is close agreement between the solution and solid state (CO)-C-13 chemical shifts except for the inner bridging carbonyls which appear in solution as one resonance whereas in th e solid state occur as two resonances due to the bridging CO's being either above or below the Ni-6-plane. At higher temperatures, there is evidence f or H movement (probably oscillation about the plane of symmetry) but C-13 s pectra indicate that the CO's remain essentially static. For the monohydrid e, three of the bridging CO's are almost co-planar with the Ni-6-plane, one , C6, is significantly bent towards the hydride and two CO's are in interme diate positions; the low temperature solid state (CO)-C-13-NMR spectra appe ar to be entirely consistent with this structure. At room temperature, ther e is some coalescence of the (CO)-C-13 resonances, suggesting some carbonyl movement, but there is no evidence for H-migration from the occupied inter stitial octahedral site to the unoccupied octahedral site. (C) 1999 Publish ed by Elsevier Science S.A. All rights reserved.