EXCITED-STATES OF HOMONUCLEAR-BRIDGED AND HETERONUCLEAR-BRIDGED BIMETALLIC COMPLEXES OF RHODIUM(I), IRIDIUM(I), PLATINUM(II), AND GOLD(I) -TRIPLET MANIFOLD SPLITTINGS, STATE ASSIGNMENTS, AND SYMMETRY CORRELATIONS

Spectral information on [Pt-II(CN)(2)Rh-I((t)BuNC)(2)(mu-dppm)(2)] [PF 6], Pt-2(II)(CN)(4)(mu-dppm)(2), [(AuPtII)-Pt-I(CN)(2)(mu-dppm)(2)][PF 6], [(AuRhI)-Rh-I((t)BuNC)(2)(mu-dppm)(2)][PF6](2), and [(AuIrCl)-Ir-I -Cl-I(CO)(mu-dppm)(2)][PF6] [dppm = bis(diphenylphosphino)methane] is reported. Absorption and excitation spectra at room temperature, relat ive band polarizations at 77 K, temperature-dependent decay times (77- 4 K), and changes in phosphorescence decay rates at 4 K as a function of an applied magnetic field are interpreted in terms of an isolated n d(z2) --> n'p(z) promotion leading to a singlet (fluorescing) state an d triplet (phosphorescing) manifold, the latter split into two levels (10-90 cm(-1)) via spin-orbit coupling. The lower level is forbidden, the upper is quasi-degenerate and (x,y) allowed. These data, complemen ted by those from other analogous complexes, are related to an electro nic model that allows assignments of the symmetries of the singlet sta te and the triplet sublevels in D-4h for homonuclear species with four identical bridging ligands, D-2h for homonuclear bi-bridged species w ith symmetrical nonbridging ligands, and C-2v for heteronuclear mu-dpp m bi-bridged complexes of diverse symmetries. The HOMO of the excited configuration is identified with a unique metal in the heteronuclear s pecies. A correlation exists between the magnitudes of the triplet sub level splittings and the dependence of the rate of decay of the lowest spin level of the manifold on magnetic field strength.