Nickel covalent radius

Mean cobalt-cobalt and nickel-nickel distances observed in these complexes are very close to interatomic distances determined at ambient temperatures in cobalt and nickel metals (Co-Co 2.489(7) A vs. 2.507 A in a-cobalt (33) Ni-Ni 2.469(6) A vs. 2.492 A in the metal (39)). The mean M-H bond lengths, as well as hydride displacements from M3 faces, are less for nickel in H3Ni4(Cp)4 than for cobalt in HFeCo3(CO)9(P(OMe)3)3. Although the differences are marginally significant within error limits (Ni-H 1.691(8) A vs. Co-H 1.734(4) A displacements from plane Ni3 0.90(3) A vs. Co3 0.978(3) A), they are in the expected direction since the covalent radius should vary inversely with atomic number within a transition series. However, other effects such as the number of electrons in the cluster also can influence these dimensions. 

The P-F bond length is very similar to the free ligand value, and the nickel-phosphorus bond length is very short indeed since the normally accepted covalent radius of phosphorus is 1.1 OA and that of atomic... 

Calculated from the metallic radius of 1.13 A for nickel. All covalent radii used in the table and elsewhere are from L. Pauling, TTie Nature of the Chemical Bond , Cornell, Ithaca, New York, 1960. Calculated from the octahedral nickelfn) radius of 1.39 A. The number of bonds averaged is given in square brackets. 0.03 A has been subtracted from the covalent radius of nitrogen to allow for sp hybridization. In five- and six-membered chelate rings. In four-membered rings the mean Ni-S distance is 2.21 A. See also Table 2. 

Nickel is found in the rare +1 oxidation state in Rb4[Ni2(CN)J. There are two crystallographically independent [Nij(CN)6] anions which contain planar Ni(CN)a units linked together by a strong Ni-Ni bond, so that the co-ordination at each nickel atom is approximately square-planar. The mean angle between the nickel co-ordination planes is 86°. The two Ni-Ni distances are 2.32 and 2.29 A, not significantly different from twice the Pauling covalent radius of nickel (2.30 A). The mean Ni-C distance is 1.91 A. Two crystal structures containing the tetracyanonickelate anion have been described. - ... 

---