Tetrahedral hydride ligands

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. 

X-ray data suggest that the complexes [CoH P(OPh)3 4], [Ni P(OPh)3 4], [Pt P(OPh)3 4], and [RhH P(OPh)3 4] are iso-morphous. A tetrahedral arrangement of phosphite ligands about the metal atom is to be expected for the nickel(O) and platinum(O) complexes and on the evidence of the x-ray data appears highly probable for the cobalt and rhodium hydride derivatives also. The hydride ligand in the latter complexes is probably located along a C3 axis of the molecule as postulated for the related complex [CoH(CO)4]. 

Figure 58 shows the structure of PtOs3(p-H)2(CO)10 P(cyclo-C6H11)3, which is the first of a series of closo tetrahedral, mixed-ligand clusters. The Pt-capped tetrahedron bears two hydride ligands localized on the longest Pt-Os (Pt-Osl) and Os-Os (Os2-Os3) edges, respectively [123],... 

Similarly, the low-temperature - C and H NMR spectra of [HFe4(CO)i3] indicate the presence of two distinct metal frameworks - a butterfly (4) and a tetrahedral core (5). The first contains a dihapto CO ligand bridging the wingtips whereas the hydride ligand bridges the hinge. 

The details for the synthesis of the activated tetraosmium hydrido cluster [Os4(/r-H)4(CO)io(NCMe)2] 72 have been previously reported the X-ray structure has now been determined. It consists of a tetrahedral metal core with each hydride ligand bridging the four OsOs bonds which are longer (2.915(3)-2.998(3) A) compared to the remaining two (both 2.810(3) A). The two acetonitrile ligands are coordinated to the same osmium atom (OsN = 2.02(4) and 2.07(5) A). The molecule possesses approximate symmetry. 

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