H3Ni4 4, neutron diffraction

Neutron Diffraction Studies of Tetrahedral Cluster Transition Metal Hydride Complexes HFeCo3(CO)9-(P(OCH3)3)3 and H3Ni4(C5H5)4... 

One motivation to carry out a neutron diffraction investigation of H3Ni4(Cp)4 was to check the possibility of disorder of the hydride ligands over all four faces of the Ni4 tetrahedron. The hydrides were not located from the x-ray data (33, 34). Rather, their positions were inferred from the deviations of the structure from strict tetrahedral symmetry. The observed Cp(i)-Cn-Cp( ) angles (see Table IV) are distorted from the tetrahedral value such that Cp(2), Cp(3), and Cp(4) are bent away from Cp(l). The face defined by Ni(2), Ni(3), and Ni(4) therefore could be expected to be vacant. Our neutron results indicate, that this is indeed the case, with no evidence for disorder of the hydride ligands on the nuclear density maps. 

Fig- 55. a The structure of H3Ni4Cp4, determined by a neutron diffraction study (Ref. 232). One of the CsHs rings has been removed for clarity, b The H3Ni4 core of this molecule, which resembles a cube with a missing comer... 

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