Nickel oxide coordination number

Oxide ratio, 18 815 Oxides, 16 598 acidic, 22 190-191 bond strengths and coordination numbers of, 22 570t diorganotin, 24 819 glass electrodes and, 14 28 gold, 22 707 iron, 14 541-542 lead, 14 786-788 manganese, 15 581-592 nickel, 27 106-108 niobium, 27 151 plutonium, 29 688-689 in perovskite-type electronic ceramics, 14 102... 

Nickel forms a large number of complexes with various anions (monoden-tate, bidentate, and polydentate) and many neutral ligands. The most common coordination numbers of the metal in these complexes are six and four while the metal is usually in +2 oxidation state, Ni2+. Also, some complexes of three and five coordinations exist. Several zero valent nickel complexes, such as nickel tetracarbonyl, and a number of substituted carbonyl complexes are well known. 

Most of the nickel compounds in the solid state and almost all in aqueous solution contain the metal in the oxidation state +2, which, by consequence, can be considered the ordinary oxidation state for nickel in its compounds. The electronic structure and stereochemistry of nickel(II) were reviewed in 1968.6 The most stable electronic configuration of the free Ni ion is [Ar]3d8 which is also the ground state configuration in its complexes. The overwhelming majority of nickel(II) complexes have coordination numbers of four, five and six. Complexes with coordination numbers of three, seven and eight are still quite rare. 

In this section we will briefly review some complexes of nickel with -coordinated fragments or molecules. In this case the assignment of an oxidation number to the nickel atom in a formal sense may be questionable, owing to the extensive rearrangement of the electronic distribution in the molecule with respect to the starting species. 

Reaction of (COD)2Ni with acetylacetone (73) produces orange crystalline 7r-(4-cyclooctenyl)acetylacetonatonickel(II) which sublimes in vacuo at about 60°C and melts with decomposition at 75°C. The reaction involves a proton transfer from acetylacetone to the COD ring with a concomitant change of the nickel oxidation number from zero to two. A structural analysis (412) has shown an essentially square planar coordination about the nickel (Fig. 4) with a C=C length of 1.42 A and a Ni-C distance of 2.03 A, [these values are very close to those observed for the complex (C2H4)Ni[P(C,iH5)3].2 (122)], and a Ni CH, distance of 1.95 A. 

In order to confirm the nickel oxidation state in the active entity and to study the influence of the composition of its coordination sphere [coordination number, nature of the trialkylphosphine (TAP) ligands] on the catalytic performances, we have used a set of silica-supported unsaturated Ni complexes [58] with a given number of TAP ligands of different electronic and steric properties [59,60],... 

Mononuclear thiolate complexes containing nickel sites in different oxidation state as [Ni(SC5H40)2] and [Ni(SC6H40)2] were described by KOckerling and Henkel (1993). With respect to the chemical as well as electrochemical properties of the nickel sites of various dehydrogenases, [Ni(SC6H40)2] is a relevant model complex of coordination number four. 

PRACTICE EXAMPLE A What are the coordination number and oxidation state of nickel in the ion [Ni(CN)4l] ... 

A nickel complex, namely Ni(CO)4, was the first reported (1890) coordination compound of a metal in a low oxidation state.13 Today the number of the nickel(O) complexes is enormous and is still increasing. 

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