Spin-orbit coupling delocalization

In the experimental UPS of HRe(CO)5 (87, 161, 174) the splitting of the first and second bands is 0.31 eV and that between the second and third bands is 0.34 eV (Fig. 9). These relative spacings are consistent only with Scheme III, thus confirming that the e MO is less stable than the b2 MO. The spin—orbit coupling parameter, f5d(Re), of 0.25 eV deduced from the spectra compares with the range 0.26-0.34 eV estimated for the Re2 cation (136, 156). The reduction of fsd(Re) in HRe(C0)4 is consistent with the delocalization of metal 5d electrons into the 2ir MOs of the CO ligands. 

Several methods exist for calculating g values. The use of crystal field wave functions and the standard second order perturbation expressions (22) gives g = 3.665, g = 2.220 and g = 2.116 in contrast to the experimentaf values (at C-band resolution) of g = 2.226 and g 2.053. One possible reason for the d screpancy if the use of jperfXirbation theory where the lowest excited state is only 5000 cm aboye the ground state and the spin-orbit coupling constant is -828 cm. A complete calculation which simultaneously diagonalizes spin orbit and crystal field matrix elements corrects for this source of error, but still gives g 3.473, g = 2.195 and g = 2.125. Clearly, covalent delocalization must also be taken into account. 

Lindgren et al. studied the excited state and phosphorescence of platinum(II) acetylides (5.9) with the DFT/B3LYP method [103], The calculated UV/Vis absorption spectra revealed that the orientation of the phenyl rings relative to the P-Pt-P axis has a strong correlation with the intensity of the absorption band. The broken symmetry phenomenon was also confirmed in the lowest triplet excited state, which leads to a OC-Ph bond on one side and a C=C=C bond on the opposing side. Quadratic response calculations of spin-orbit coupling showed that the intensity of the phosphorescence of these complexes arises mainly from the a—>n type T- l) transitions localized at the OC-Pt-P fragment, but not from the delocalized 7t—type transitions. The quadratic response calculations also reproduced an increase of xR from PEj to PE2 (5.9), which was also determined experimentally. 

Spin-orbit coupling and delocalization are in competition in a molecule like cyclopropyl bromide for two reasons ... 

The light atoms in tt-radicals results in negligible spin-orbit coupling, in contrast to transition metal complexes. Thus D and E are dominated by dipole-dipole interactions, which can be computed from the crystal structure and delocalized... 

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