Square planar complex orbitals

Like palladium(II) and platinum(II), gold(III) has the d8 electronic configuration and is, therefore, expected to form square planar complexes. The d-orbital sequence for complexes like AuC14 is dx2 yi dxy > dvz, dxz > dzi in practice in a complex, most of these will have some ligand character. 

Splitting of d-orbitals in square planar complexes of copper(II), nickel(II) and cobalt(II). Y. Nishida andS. Kida, Coord. Chem. Rev., 1979, 27, 275-298 (94). 

Suggest the form that the orbital energy-level diagram would take for a square planar complex with the ligands in the xy plane, and discuss how the building-up principle applies. Hint The d -orbital has more electron density in the xy plane than the dzx- or d -orbitals but less than the dXJ,-orbital. 

C20-0095. The d i and. y 2- orbitals have the same stability in an octahedral complex. However, in a square planar complex, the orbital is much less stable than the d orbital. Use orbital sketches to... 

Figs. 11 and 12 show typical mo diagrams for square planar and octahedral complexes. Inspection reveals that the metal orbital (z is the axial direction) in a square planar complex is involved in the n bonding system and available for a bonding in the transition state. This is a feature shared by nucleophilic substitution at square planar complexes with the spectacularly associative nucleophilic aromatic substitutions. The octahedral complexes discussed in this chapter... 

If a complex having a coordination number of 4 is produced, only two of the 4p orbitals are used and the hybrid orbital type is dsp2, which is characteristic of a square planar complex. For Ni2+, this is illustrated by the following scheme ... 

FIGURE 17.19 The combinations of metal and ligand orbitals in a square planar complex. Although not shown, the/yand/ orbitals are directed... 

FIGURE 17.20 A molecular orbital energy level diagram for a square planar complex. 

Fig. 4. Energy levels of the d orbitals in a square planar complex.

Complexes of class a metals are more ionic, while those of the class b metals are more covalent. Generally, the metals that form tetrahedral complexes by using sp hybrid orbitals are class a types. Those forming square planar complexes by using dsp hybrid orbitals are normally class b types. 

Briefly, as Prof. Basolo points out in his paper, and Prof. Basolo and Pearson pointed out nicely in a review on the trans effect, the situation in the ir-bonding theory is a stabilization of the trigonal bipyramidal intermediate because there are more orbitals in the trigonal plane available for 7r-bonding in the trigonal bipyramid than in the square planar complex. The same is also true in the --system. The trans effect is directional, and in my opinion, it has to be orbital or quantum mechanical. 

The presence of empty dzb orbitals should play a decisive part in the reduction of O2, as they do in 2 transmission. In the square planar complexes (cf. Fig. 32) investigated by us, this condition is fulfilled only by the attachment of a 5th ligand. We therefore assume that the surface groups of the carbon take effect as... 

This sequence of events may be illustrated by the homogeneous hydrogenation of ethylene in (say) benzene solution by Wilkinson s catalyst, RhCl(PPh3)3 (Ph = phenyl, CeH5 omitted for clarity in cycle 18.10). In that square-planar complex, the central rhodium atom is stabilized in the oxidation state I by acceptance of excess electron density into the 3d orbitals of the triphenylphosphane ligands but is readily oxidized to rhodium (III), which is preferentially six coordinate. Thus, we have a typical candidate for a catalytic cycle of oxidative addition and subsequent reductive elimination ... 

For Cu(II) square-planar complexes, B2g is the ground state, whereas for V02+ complexes (symmetry C4v), the ground state is Bu which is the same as the Big function in Eq. (131). For V02+ complexes, the only changes required in Eq. (131) are that the MO coefficients be different for orbitals of atoms 5 and 6. We shall first consider the case where B is the ground state. 

Determine the qualitative form of the molecular orbitals for the square-planar complex Ni(CN)48-. (Assume that each CN ligand provides one e-type and two vr-type orbitals to the system.)... 

Fjg. 11,12 An octahedral complex (a) undergoing axis elongation such that it becomes tetragonally distorted (bj and finally reaches the square planar limit (c). The a i (d ) orbital may lie below the e idn and dy ) orbitals in the square planar complex... 

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