Correlated character state complexes

Since n bonding is believed to be more important in low oxidation states, as d orbitals contract with increasing oxidation state leading to poorer dw-pw overlap, this would not be expected on the basis of a 7r-bonding mechanism. Similarly, one can compare /(Pt-P) for pairs of isomers in the +2 and +4 states in a planar platinum(II) complex, the platinum 6s orbital is shared by four ligands whereas in an octahedral platinum(IV) complex it is shared by six ligands. Therefore, the 6s character is expected to be only 2/3 as much in the platinum(IV) complexes, correlating well with the 7(Pt-P) values, which can be taken to be a measure of the a-character in the bond. 

Additional support for the orbital nature of the emissive state in the Pt(diimine)(dithiolate) complexes is obtained from the electrochemical data given in Table III. The formation of the emissive state formally involves oxidation of the HOMO having dithiolate and metal character and reduction of the LUMO, which is diimine localized. There should therefore exist a correlation between the energy of the excited state and the difference between the oxidation and reduction potentials for each complex. Indeed, such a linear correlation was found for the emission energies of the complexes a similar correlation was obtained when absorption energies for the solvatochromic transition were plotted (108). 

In the gase phase, the infrared bands are broad (50 cm ), due to the rotational structure, overlapping vibrations, and hot transitions. In the solid state, the rotational motions are quenched, but due to intermolecular (hydrogen bond) and correlation field interactions, the band positions are shifted and the bands are even broader. The infrared absorptions of matrix-isolated molecules are close to the gas-phase frequencies and exhibit a sharp line-like character (half-widths 0.1 to 2 cm ). Hence the spectra of matrix-isolated molecules are less complicated, and, in comparison to gas phase or solid state spectra, the sensitivity and selectivity of detection increase by a factor of about 10 to 100. Closely spaced vibrations attributed to mixtures of similar molecules, such as conformers, rotamers, molecular complexes, or isotopic species, e.g., H C104 and H CI04, are easily distinguished. 

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