Nickel atom clustering

H. Basch, M. D. Newton and J. W. Moskowitz, The electronic structure of small nickel atom clusters , J. Chem. Phys. 73 4492 (1980). 

Fig. 31. Models for Nickel atoms clusters, a) Bulk cluster, b) (111) surface cluster, c) (100) surface cluster, d) (110) surface cluster. In b) and d) the dotted lines show the relationship with the planes of a).

In the first example (46), hydrogen adsorption on different sites of a nickel crystal was studied by considering the interaction of a hydrogen atom with a limited number of metal atoms. The nickel crystal was truncated to obtain the clusters shown in Fig. 31, containing 13,10, 9 and 8 nickel atoms, and representing models for the bulk crystal and for the (111), (100) and (110) surfaces respectively. The nearest-neighbour distance in all clusters was... 

For mixed lanthanide-transition metal clusters, Yukawa et al. have synthesized an octahedral [SmNi6] cluster by the reaction of Sm3+ and [Ni(pro)2] in nonaque-ous medium [66-68]. The six [Ni(pro)2] ligands use 12 carboxylate oxygen atoms to coordinate to the Sm3+ ion, which is located at the center of an octahedral cage formed by six nickel atoms. The coordination polyhedron of the central Sm3+ ion may be best described as an icosahedron. The [SmNir, core is stable in solution but the crystal is unstable in air. The cyclic voltammogram shows one reduction step from Sm3+ to Sm2+ and six oxidation steps due to the Ni2+ ions. Later, similar [LaNis] and CjdNif> clusters were also prepared. 

A similar reaction can be written for the [Fe] hydrogenases with a Fe-[4Fe-4S] complex replacing the nickel. Note that the nickel atom in the NiFe cluster, and the Fe-[4Fe-4S] sites are nearest to the electron carrier [4Fe-4S] clusters, indicating that electron transfer occurs through these atoms. The other atom in each of the centres is an iron atom with -CN and -CO ligands, and it seems likely that this is a binding site for hydride (Fig. 8.1). 

The CASSCF/CASPT2 calculations were performed with an active space including the five nd, the (n + l)s, the three (n+ l)p orbitals, and a second set of nd orbitals to account for the double shell effect. The importance of including a second 3d shell in the active space was detected in an early study of the electronic spectrum of the nickel atom [2]. This had already been suggested from MRCI results [1]. The results obtained by RT at about the same time indicated that such effects are effectively accounted for when a method is used that includes cluster corrections to all orders, like the QCI method used by them [3]. This result will hold true also for the less approximate coupled cluster method CCSD(T). 

This electronic explanation of the synergy between Co or Ni and Mo does not give any direct information on the structure of the active phase except that cobalt or nickel atoms should be bonded to molybdenum atoms through bridging sulfur atoms according to the molecular model used by the authors. The precise structure of this pseudobinary cluster is as yet unknown, but... 

The Ni3S2 fragments in the two complexes (263) and (265) have a trigonal bipyramidal geometry with the two S atoms in the apical positions and the three nickel atoms in the equatorial plane, as found in other organometaUic compounds which contain the same Ni unit.1939 The formation of the enneanuclear complex (264), on the contrary, is exceptional and no other complex of this stoichiometry was isolated with analogous tertiary phosphines, with selenium, or with metals other than nickel. It is not possible to assign any definite oxidation number to nickel in complex (264). The lack of two electrons with respect to the situation of nine nickel(II) ions was reported to be essential for the existence of complex (264) because the oxidation is spontaneous and its reduction invariably leads to the decomposition of the cluster compound.19 ... 

The soluble hydrogenase from the hydrogen-oxidizing bacterium N. opaca is one of a class of hydrogenases that contain flavin and use nicotinamide adenine dinucleotide (NAD) as electron acceptor. The protein consists of four dissimilar subunits and contains approximately four atoms of nickel, one FMN, three [Fe-4S] clusters, one [2Fe-2S] cluster, and up to one [3Fe-xS] cluster (82). Two of the nickel atoms were readily removed by dialysis, in contrast to the nickel in most hydrogenases. The enzyme would only catalyze electron transfer from hydrogen to NAD if cations, of which Ni2+ is the most effective, were added. In the absence of the cations, the enzyme could be separated as... 

Examples of nickel complexes are rare and are confined to three reported nickel carbonyl clusters containing interstitial germanium or tin atoms (90). The reaction between [Ni6(CO)l2]2 and GeCl4 affords two species, [Ni10Ge(CO)2o]2 , 79, and [Ni12Ge(CO)22]2, 80. The former structure is based on a pentagonal antiprismatic framework of nickel atoms with an... 

The metal(O) isocyanide clusters Ni4(CNBu )7 (45)5 (60), Pt3(CNBu )6 (46) (23) and Pt7(CNXylyl),2 (47) (20) have been characterized crystallographi-cally. In the nickel complex the nickel atoms define the vertices of a highly compressed C3v tetrahedron, with each nickel having a terminal isocyanide and three basal nickel atoms joined by three four-electron donor isocyanide ligands. The unusual feature of the structure of Pt7(CNXylyl),2 is that one... 

The final three structures in this section are clusters. The first cluster structural type is formulated as Ni3S2(S2COR)2(Ph2PCH2CH2PPh2) and is found for R = Me, shown in Fig. 62, and Et (115). The structure comprises a triangle of nickel atoms [Ni- Ni range from 2.7243(7) to 2.8990(8) A] capped on either side by a p3-sulfido atom. Two of the nickel atoms are each chelated by a... 

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