Planar metal complexes

The most interesting work on the isocyanide complexes of the elements in this subgroup has been done with rhodium and iridium. For the most part, the work is involved with the oxidative addition reactions of d square-planar metal complexes. 

Steric hindrance is well known to slow down the rates of ligand substitution reactions in square-planar metal complexes. An example for which steric hindrance controls the aquation rate is complex 9. The effect of 2-picoline on the rate of hydrolysis of CP trans to NH3 (cis to 2-picoline) is dramatic, being about 5 times as slow as the analogous CP ligand in the nonsterically hindered 3-picoline complex (Table I) (44). 

In many planar metal complexes it is not possible to record an ENDOR spectrum which only contains contributions from Bo orientations in the complex plane. This is due to the fact that in the powder EPR spectrum the high- or low-field turning points may arise from extra absorption peakssl which do not correspond to directions of the principal axes. ENDOR spectra observed near the in-plane region of such a powder EPR spectrum are due to molecules oriented along a large number of B0 directions (in- and out-of-plane), so that the orientation selection technique is no longer effective. 

Since many planar metal complexes have nearly axially symmetric g and AM tensors, two-dimensional powder ENDOR spectra can easily be obtained from such compounds oriented in nematic glasses84. As mentioned, interpretation of this type of spectra will be discussed in Sect. 4.3. 

Oxidative addition of dihydrogen commonly involves transformation of a d8 square planar metal complex into a d6 octahedral metal complex, or similar transformations involving d2 — d°, d10 —> d8 etc. The oxidative addition of... 

The mechanism by which the d-d transitions gain intensity still remains to be determined. For octahedral and square planar complexes which have a center of symmetry, the transitions are partly inhibited. Slightly disorted octahedral and square planar metal complexes may have a fractional part of a d-d transition allowed, and this static distortion mechanism may be responsible for some intensity in many cases (I, 2). The fact that when Co(acac)3 catalyst was utilized in the oxidation, its absorption wavelength remained unchanged and its coefficient increased,... 

A Molecular Orbital Theory for Square Planar Metal Complexes... 

Various efforts have been made to evaluate the d-orbital splittings in square planar metal complexes, and to assign the observed d-d spectral bands.2-8 The most complete calculation has been made for Pt8+ complexes by Fenske, Martin and Ruedenberg,6 and considerable confidence may be placed in their ordering of the d-orbitals. However, for other complexes the d-ordering may depend on the metal ion and the type of ligand under consideration. 

It is the purpose of this paper to develop a molecular orbital theory for square planar metal complexes. Both the spectral and magnetic properties of typical square planar complexes of Ni2+, Pda+, Pts+ and Au8+ will be considered m order to arrive at consistent values for the molecular orbital energies. However, in contrast to previous workers, effort will be concentrated on the assignments of the charge transfer bands of representative square planar complexes. 

Fig. 1.—A molecular orbital coordinate system for a square planar metal complex.

Fig. 3.—Molecular orbital energy level scheme for square planar metal complexes in which the ligands themselves have a r-orbltal system (case 2).

Spectral Properties of Square Planar Metal Complexes. A. Halide Complexes (Case 1).—The com-... 

Magnetic Properties of Square Planar Metal Complexes.—The magnetic susceptibility of the diamagnetic d square planar metal complexes is given by... 

Table t Dipole Moments (jif and Relaxation Times (t) of Square-planar Metal Complexes [M(RCS—CHCOR lil... 

I. Alkorta et al., Chiral discrimination in binuclear square planar metal complexes of group 10. Inorg. Chem. Commun. 9, 712-715 (2006)... 

The combination of dithiolene and diimine chelating ligands in square-planar ds complexes gives rise to a unique CT excited state, and complexes of this class have been the subject of a rich and growing amount of research in recent years. The Pt(diimine)(dithiolene) complexes were among the earliest examples of emission from square-planar metal complexes in fluid solution. Luminescence from room temperature solutions of Pt(diimine)(mnt) complexes with diimine = bpy, phen, or an alkyl- or aryl-substituted derivative was reported in 1990 by Zuleta et al. (98, 99), following an initial report on similar complexes with a 1,1-dithiolate. 

With the unsymmetric bis-carbene palladium(II) complexes conung from Foley s research group, we are again on firm ground a square planar metal complex and sterically innocent wingtip groups (methyl, benzyl, p-Bu -benzyl) let us suspect the preferred formation of a chelate complex and this is indeed what is observed [316]. 

The crystal field theory as applied to octahedral, tetragonal, tetrahedral and sejuare planar metal complexes... 

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