Solid state studies (X-ray and 1H-, 13C-NMR) on (NMe 4) 4− x[H xNi 12(CO) 21] · S ( x=1, S=Me 2CO; x=2, S=2THF)

Abstract

The molecular structures of (NMe 4) 4− x [H x Ni 12(CO) 21] · S ( x=1, S=Me 2CO; x=2, S=2THF) are reported. Both anions are similar and consist of a central Ni 6(CO) 3( μ-CO) 6-layer flanked on both sides by two Ni 3(CO) 3( μ-CO) 3-layers such that the Ni 12-fragment is hexagonal close-packed. The separation between the central Ni 6-plane (B) and the two outer Ni 3-planes (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 1H MAS and 13C CP/MAS NMR spectra are reported for both clusters. For the dihydride, the solid state 1H- and 13C-NMR spectra remain unchanged from low to room temperature and are consistent with the X-ray structure; at room temperature, there are two hydride resonances consistent with them being on the plane of symmetry on opposite sides of the Ni 6-layer and the highfield shift is consistent with them not being in the centre of the Ni 6 octahedral cavity. For [H 2Ni 12(CO) 21] 2−, there is close agreement between the solution and solid state 13CO chemical shifts except for the inner bridging carbonyls which appear in solution as one resonance whereas in the 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 for H movement (probably oscillation about the plane of symmetry) but 13C spectra indicate that the CO’s remain essentially static. For the monohydride, 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 intermediate positions; the low temperature solid state 13CO-NMR spectra appear to be entirely consistent with this structure. At room temperature, there is some coalescence of the 13CO resonances, suggesting some carbonyl movement, but there is no evidence for H-migration from the occupied interstitial octahedral site to the unoccupied octahedral site.