Hydride ligand interstitial

Hydride ligands are the most versatile of all organometallic ligands. Hydrides can coordinate to a single metal (terminal coordination), bridge two p-R, 4) or three (/U.3-H, 5) metal atoms, or occupy an interstitial position inside a metal polyhedron (6). Hydrides bound to transition metal clusters most commonly bridge two metal atoms. Interconversion... 

Hydride ligands can adopt terminal, bridging or (in metal clusters) interstitial modes of bonding (23.9-23.12). A localized 2c-2e M—H bond is an appropriate description for a terminal hydride, delocalized 3c-2e or 4c-2e interactions describe p-H and P3-H interactions respectively (Figures 23.3a and 23.3b), and a 7c-2e interaction is appropriate for an interstitial hydride in an octahedral cage (Figure 23.3c). 

Treatment of Fel2 with equimolar Li2[PhP(CH2)3] in thf affords the anionic cubane cluster [Li(thf)4][ PhP(CH2)3Fe 4(p4-H)], the first example of a first-row transition metal cluster containing a p4-interstitial hydride ligand ( H NMR 5= —11.2 ppm)."... 

While DFT may or may not be more accurate than MP2 for absolute shielding calculations is debatable, the strength of the DFT method in calculations of shieldings is in the ability of DFT to provide a consistent picture over a wide range of chemical systems, since calculations can be done at a very modest computational cost compared to MP2. Among the successes of the method is in ligand chemical shifts in transition metal complexes. For example, 13C, 170,31P and H chemical shifts for oxo (12,14,15), carbonyl (16-19), interstitial carbide (20), phosphine (21,22), hydride (23), and other ligands have been successfully reproduced to within tens of ppm in... 

An interstitial H atom located in a tetrahedral environment was first reported in 1982, in the tetracapped octahedral cluster [HOsioC(CO)24] . Evidence came from X-ray studies which showed complete coverage of the metal core by carbonyl ligands very similar to that of [OsioC(CO)24] from which it was prepared. It was therefore assumed that the hydride was in an interstitial site, and because the octahedral cavity was already occupied by a carbido-atom it seemed reasonable to assume that the hydride was sited within a tetrahedral cap. The Os satellite pattern associated with the hydride signal in the H NMR spectrum was entirely as would be expected for a tetrahedrally coordinated hydride, which helped to confirm this proposal. 

The first example of a six-coordinate interstitial hydride was [Ru6H(CO)i8] the unexpected location was originally deduced indirectly from the close-packed arrangement of the carbonyl ligands which left no space on the cluster surface for an H atom. This structural assignment has since been vindicated by a neutron diffraction study. Similarly, neutron diffraction studies of the hexacobalt cluster... 

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