Nickel electronic configurations

Note. The electronic configuratioa of any element can easily be obtained from the periodic table by adding up the numbers of electrons in the various quantum levels. We can express these in several ways, for example electronic configuration of nickel can be written as ls 2s 2p 3s 3d 4s. or more briefly ( neon core ) 3d 4s, or even more simply as 2. 8. 14. 2... 

With an atomic number of 28, nickel has the electron configuration [Ar]45 34f (ten valence electrons). The 18-electron rule is satisfied by adding to these ten the eight electrons from four carbon monoxide ligands. A useful point to remember about the 18-electron rule when we discuss some reactions of transition-metal complexes is that if the number is less than 18, the metal is considered coordinatively unsaturated and can accept additional ligands. 

Often, to save space, electron configurations are shortened the abbreviated electron configuration starts with the preceding noble gas. For the elements sulfur and nickel,... 

By considering electron configurations, suggest a reason why iron(III) is readily prepared from iron(ll) but the conversion of nickel(II) and cobalt(II) into nickel(III) and cobalt(III), respectively, is much more difficult. 

Among many examples of -orbital interaction, only the following two are selected to illustrate the feature of HO—LU conjugation. One is the cyclooctadiene-transition metal complex ">. The figure indicates the symmetry-favourable mode of interaction in a nickel complex. The electron configuration of nickel is (3d)8 (4s)2. The HO and LU of nickel can be provided from the partly occupied 3d shell from which symmetry-allowed occupied and unoccupied d orbitals for interaction with cyclo-octadiene orbitals are picked up. 

This complex is diamagnetic, indicating that the nickel atoms have attained the electronic configuration of krypton, and the infrared spectrum shows... 

Fig. 7.113. d-Electron configuration of transition-metal ions at the surface of perovskites, for the case of magnanites and of nickelates (below). (Reprinted from J. O M. Bockris and T. Ottagawa, J. Phys. Chem., 87 2966,1983.)... 

Indicate the position of iron, cobalt, and nickel in Mendeleev s periodic table of the elements, the electron configurations and sizes of their atoms, and their oxidation states. Explain the observed law of the change in the characteristic oxidation states in the series iron-cobalt-nickel. Why do the elements of the iron family fail to exhibit the highest oxidation state corresponding to the number of the group in the periodic table which they belong to ... 

Nickel, heated gently in a stream of CO, forms the carbonyl Ni(CO)4. Carbonyls of other metals have been prepared by reduction of the halides with other metals in the presence of CO under high pressure. All carbonyls have 18-electron configurations the formulae of the carbonyls of metals with even atomic numbers thus can be easily found, e.g. Ni(CO)4, Fe(CO)5, Cr(CO)6 and Mo(CO)6. 

Otherwise, unusual valency states are often observed in cyanide complexes. A Mn complex K5Mn(CN)6 has been reported here the stable 18-electron configuration causes the valency of manganese to take the very unusual value of one, and the compound is formed in spite of the extremely unfavourable cation anion ratio. Still more remarkable are the complex nickel cyanides. KGN and Ni(CN)2 form a complex K2Ni(CN)4, in which sixteen electrons are involved in the bond formation. The diamagnetism and the square structure of the Ni(CN)4 ion show that the bonding is due to dsp2 hybridization. 

With this structure the nickel atom lias achieved the krypton electron configuration its outer shell contains five unshared pairs (in the five M orbitals) and five shared pairs (occupying the 4s4p3 tetrahedral bond orbitals). The Ni—C bond length expected for this structure is about 2.16 A, as found by use of the tetrahedral radius 1.39 A obtained by extrapolation from the adjacent values in Table 7-13 (Cu, 1.35 A Zn, 1.31 A). 

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. 

The electronic configuration of a nickel(III) complex is d1. In a tetragonal ligand field3034 the ground configuration will be (dXzdyz)4(dxy)2(dziy(dx2 yi)° for a square planar or elongated octahedral complex and (dJ idyi)4(dj y)2(dx2 y2)1(d )0 f°r a compressed octahedron. In the first case the EPR spectra will show g > 11 = 2.00 while in the latter situation the pattern gy 2.00 will be observed.3035,3036... 

Nickel(IV) complexes have a d6 electronic configuration and are always diamagnetic or weakly paramagnetic with a temperature-independent magnetic susceptibility. The characterization of these complexes is generally based on the stoichiometry and the electrochemical behaviour. 

The starting point for most of the redox chemistry considered in this review is the nickel(II) ion. The nickel(II) ion has a d8 electronic configuration and, with weak-field ligands such as H20, it forms a six-coordinate ion with approximately octahedral symmetry and a paramagnetic (two unpaired electrons) 3A2 ground state. The characteristic solution chemistry of six-coordinate nickel(II) is well documented and, in particular, the substitution behavior has been extensively studied and is the subject of recent reviews (11, 12). It is a labile ion with solvent exchange rates around 104 sec-1 at 25°C and activation parameters are consistent with dissociatively activated interchange behavior (13). 

With its 3d84,r2 electron configuration, nickel forms Ni2 ions. Having a nearly complete 3d subshell, nickel does not yield a 3d electron as readily as iron and cobalt, and trivalent and tetravalent forms are known only in the hydrated oxides. Ni203 and Ni()2. and a few complexes. 

Ferrocene is only one of a large number of compounds of transition metals with the cyclopentadienyl anion. Other metals that form sandwich-type structures similar to ferrocene include nickel, titanium, cobalt, ruthenium, zirconium, and osmium. The stability of metallocenes varies greatly with the metal and its oxidation state ferrocene, ruthenocene, and osmocene are particularly stable because in each the metal achieves the electronic configuration of an inert gas. Almost the ultimate in resistance to oxidative attack is reached in (C5H5)2Co , cobalticinium ion, which can be recovered from boiling aqua regia (a mixture of concentrated nitric and hydrochloric acids named for its ability to dissolve platinum and gold). In cobalticinium ion, the metal has the 18 outer-shell electrons characteristic of krypton. 

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