Overlap square-planar complexes

The general molecular orbital energy level schemes arrived at for square planar complexes are given in Fig. 2 (case 1) and Fig. 3 (case 2). Group molecular orbital overlap integrals (for Ni(CN)42-) and ligand exchange interactions are summarized in Table II. 

In the structure of Zeise s salt, the ethylene occupies the fourth coordination site of the square planar complex with the C C axis perpendicular to the platinum-ligand plane. In this compound, the dsp2 hybridised s orbital of Pt overlaps with / -bonding... 

Determine the energies of the d orbitals predicted by the angular overlap model for a square-planar complex ... 

NO BF3, SOo, tetracyanoethylene, and O2 to form a series of well characterized products. The variations in reactivity toward such molecules as SOo, Oo, and BF that is observed among the many known square-planar complexes were attributed to the following factors (15) (a) the electron affinity of the covalent molecule, (b) the nucleophilicity of the metal in the complex, and (c) the ability of d orbitals on the metal to overlap effectively with suitable orbitals on the electrophile. Molecules such as Oo and SO2 are most appropriately viewed as tt acids of considerable electron affinity, although they do have some ability to act as (T donors, and also as Lewis (cr-bonding) acids. 

The trans influence of a ligand is the ability of a ligand to weaken the bond trans to itself in a complex. Gold(I) and gold(III) complexes are, in the simplest treatment, considered to use sp and dsp hybrid orbitals in forming linear and square planar complexes respectively. A good o donor, L, tends to concentrate gold 6s character in the AuL bond and the trans bond must then overlap with an orbital of low s character. A weaker and more ionic bond is then formed. 

Divalent late transition metals like cobalt (d ), nickel (d ), and copper (d ) in the first row of the d-block can use five 3d orbitals, one 4s orbital, and three 4p orbitals to form 4-, 5-, or 6-coordinate complexes. As a general rule, if there are N ligands in the first-shell coordination sphere of a transition metal complex, then there should be N bonding molecular orbitals, N anti-bonding molecular orbitals, and 9-N nonbonding molecular orbitals. Exceptions to this rule occur in some square-planar complexes in which three orbitals with the same symmetry properties overlap and form chemical bonds. Usually, some coordination sites in the first-shell of the... 

This results in at least a partial double bond between M and the olefin and some restricted rotation of the olefin relative to the metal might be expected. Rotation could be about the M-olefin bond or about the C=C axis. The M(L)3(olefin) compounds normally have the C=C axis perpendicular to the plane of the MfL), unit, while M(L)4(olefin) compounds have the olefin in the trigonal plane with the C=C axis parallel to the trigonal plane. The theoretical analysis of Hoffmann and co-workers " suggests that the orientation of the olefin in the square planar complexes is controlled by steric factors, while the trigonal bipyramidal complexes prefer ethylene in the trigonal xy plane to give better overlap with the hybridized orbital compared to the unhybridized d orbital. 

Figure 9-14 Overlap of the metal d valence orbitals with the ligand valence orbitals in a square-planar complex.

A crystal-structure determination on [Ni(PhCH2CS2)2] showed evidence of a Ni-Ni bond (Ni—Ni distance, 256 pm) in a bridging, acetate-cage, binuclear complex (363). Each nickel atom is 5-coordinate and is in a tetragonally distorted, square-pyramid spectroscopic evidence for a Ni-Ni bond has been obtained (364). The polarized crystal spectra showed more bands than predicted for a mononuclear, diamagnetic, square-planar nickel(Il), and the spectra are indicative of substantial overlap of the d-orbitals between the two nickel atoms. The bis(dithiobenzation)nickeKII) complex was found to exhibit unusual spectrochemical behavior (365). 

Electronic stmcture calculations reveal that the actual EEG in linear Au(l) and square-planar Au(lll) complexes is not merely a matter of 5d occupation. Instead, the EEG is markedly determined by AO populations, including Au core 5p as well as valence 6p orbitals and further by the charge in the overlap area (AOAuAOug) and on the ligands (Table 7.14). 

In the early stage of the development of molecular conductors based on metal complexes, partially oxidized tetracyanoplatinate salts (for example, KCP K2 [Pt(CN)4]Br0.30-3H2O) and related materials were intensively studied [6], In this system, the square-planar platinum complexes are stacked to form a linear Pt-atom chain. The conduction band originates from the overlap of 5dz2 orbitals of the central platinum atom and exhibits the one-dimensional character. 

Group Overlap Integrals an Liganx>-Ligand Interactions for Square Planar Metal Complexes... 

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