Nickel tetrahedral clusters

The tetrahedral nickel isonitrile cluster Ni4(CNR)7 (R = cyclohexyl or f-Bu) contains three bridging isonitrile ligands and a terminal one at each nickel (52) the bridging ligands are mobile on the cluster surface and a ligand dissociation step occurs (33, 390, 391). 

The tetrahedral [160-163] and cis-planar [100,134,164-167] structures are characteristic for chelates of type 874 with coordination units NiN4 and MN2S2, respectively, as well as chelates 868 discussed above. Original polyhedral forms were discovered by x-ray diffraction for nickel and palladium ICC of the discussed type 874. It is accepted that, in case of a nickel complex, the compound with a carbon-carbon bond 875 is formed [165,166] formation of palladium chelates is accompanied by the cyclometallation reaction leading to tetranuclear clusters 876, where the tridentate ligand behaves as C,N,S-donor [168]. 

In a difference from above, the nickel and copper ICC 874 (X = O) with coordination unit MN202 evidently have tetrahedral structure, which is also characteristic for analogous cobalt and zinc complexes [169], as proved for a zinc complex by x-ray diffraction. In this respect we note a nonstandard behavior of manganese. As a result of the interaction of the ligand 873 (X = 0, R = H, N02 Ar = C6H4R, R =H, OMe, N02) and the acetate of the metal in methanol, together with an expected ICC of type 874 (X = O, M = Mn) [17], tetrameric cluster structures are formed (4.46) [171] ... 

We have mentioned only in passing other cluster complexes in which a tetrahedral core of 1 carbon and 3 metal atoms is present. Such complexes in which the metal atoms are nickel, ruthenium, and osmium have been prepared XIII (81), XIV (82, 83), and XV (66, 82). Their chemistry remains largely unexplored, except for the transformations of compound XV in strong acid medium which we mentioned in the previous section. 

The structure14 of the gold/nickel cluster has tetrahedral symmetry with the metal core shown in Fig. 16-11. 

Some solid-state metal hydrides are commercially (and in some cases potentially) very important because they are a safe and efficient way to store highly flammable hydrogen gas (for example, in nickel-metal hydride (NiMH) batteries). However, from a structural and theoretical point of view many aspects of metal-hydrogen bonding are still not well understood, and it is hoped that the accurate analysis of H positions in the various interstitial sites of the previously described covalent, molecular metal hydride cluster complexes will serve as models for H atoms in binary or more complex solid state hydride systems. For example, we can speculate that the octahedral cavities are more spacious in which H atoms can rattle around , while tetrahedral sites have less space and may even have to experience some expansion to accommodate a H atom. 

Panda R, Zhang Y, McLanchlan CC, Venkateswara Rao P, Tiago de Oliveira FA, Miinck E, Holm RH (2004) Initial structure modification of tetrahedral to planar nickel(II) in a nickel — iron — sulfur eluster related to the C-cluster of carbon monoxide dehydrogenase. J Am Chem Soe 126(20) 6448-6459. doi 10.1021/ja030627s... 

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