Square-planar complexes charge transfer

The tetracyanonickelate(II) ion is the most extensively studied square planar complex of nickel(II). TTie electronic spectrum is characterized by d-d bands at 31 000-32 000 cm-1 (eM 500-800) and charge transfer bands (eM = 6000-15 000) at 33 000-37 000 cm-1. In Figure 22 the electronic and MCD spectra of K2Ni(CN)4 are shown. In the MCD spectrum of the low energy band (d-d), since C terms are zero because the ground state is lAlg, the presence of the... 

The octahedral complexes of these ions are, of course, all of the spin-paired type.38 The values of Dq are higher than for, say Co111, so that usually only the Tlg band is observed below the charge transfer bands. The spin-forbidden transitions to the 3Tlg and 3T2g terms can be quite intense (e a 10), presumably because of the very large spin-orbit coupling in some of these ions. Square-planar complexes have been studied.149... 

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. 

The Aig - A2u and Aig - E transitions are allowed, with the Aig Eu transition expected to have considerably greater intensity. Thus a three-band charge transfer spectrum, with an intensity order Ajg - E, > Aig - Aju > Alg - Biu, should he typical of square planar complexes with case 2 type ligands. 

The first part of the lecture will consist of a summary of the facts relating to the principal d orbital ordering in square planar complexes. A short discussion of the main features of intramolecular charge transfer in these complexes will also be presented. 

The nickel(II) dithiocarbamate complexes are neutral, water-insoluble, usually square-planar, species, and they have been studied extensively by a range of physical techniques. The usual methods for the synthesis of dithiocarbamate complexes have been employed in the case of Ni(II), Pd(II), and Pt(II). In addition, McCormick and co-workers (330,332) found that CS2 inserted into the Ni-N bonds of [Ni(aziri-dine)4P+, [Nilaziridinelgf, and [Ni(2-methylaziridine)4] to afford dithiocarbamate complexes. The diamagnetic products are probably planar, but they have properties typical of dithiocarbamate complexes, and IR- and electronic-spectral measurements suggested that they may be examples of N,S-, rather than S,S-, bonded dithiocarbamates. The S,S-bonded complexes are however, obtained, by a slow rearrangement in methanol. The optically active lV-alkyl-iV(a-phenethyl)dithio-carbamates of Ni(II), Pd(II), and Cu(II) (XXIV) have been synthesized, and the optical activity was found to be related to the anisotropy of the charge-transfer transitions (332). 

Dithiomalonaldehyde forms an S,S chelate to platinum(II). The TCNQ charge transfer complex with bis(propene-3-thione-l-thiolato)platinum(II) shows a distorted square planar geometry about platinum with Pt—S distances of 2.282(1) and 2.278(1) A.1834... 

There is another assignment possible for the two charge transfer bands in the square planar halide complexes. The first band cotdd contain both the feu(a) - ( ) and [Pg.242]

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