STRUCTURE AND OPTICAL SPECTROSCOPY OF [RH(2-PHENYLPYRIDINE)2(2,2'-BIPYRIDINE)]PF6 AND RELATED COMPLEXES

The crystal structure of [Rh(phpy)2(bpy)]PF6 (phpyH = 2-phenylpyridine, bpy = 2,2'-bipyridine) is determined and described. Crystallographic data at 100 K: chemical formula C32H24F6N4PRh, orthorhombic crystal system, space group Pbca (No. 61), Z = 8, a = 10.821 (1) angstrom, b = 15.798 (1) angstrom, c = 33.328 (3) angstrom, V = 5697.4 (9) angstrom3. There is one complex cation, i.e. two crystallographically inequivalent phpy- ligands, per asymmetric unit. Polarized single-crystal absorption spectra of [Rh(phpy)2(bpy)]PF6 and excitation and site-selective luminescence spectra of [Rh(thpy)2(bpy)]+ and [Rh(thpy)(phpy)(bpy)]+ (thpyH = 2-thienylpyridine) doped into [Rh(phpy)2(bpy)]PF6 are reported and interpreted on the basis of the crystal structure of [Rh(phpy)2(bpy)]PF6. The two lowest-energy excitations of [Rh(phpy)2(bpy)]PF6, and also of [Rh(phpy)2(bpy([BPh4, [Rh(phpy)2(en)]PF6, and [Rh(phpy)2-(en)]BPh4 (BPh4- = tetraphenylborate anion, en = ethylenediamine), are found in the region between 21 400 and 22 200 cm-1 with an energy splitting ranging from 22 to 242 cm-1. They are assigned to electronic transitions involving the phpy- ligands. The third excited state of [Rh(phpy)2(bpy)]PF6 lies 967 cm-1 above the first excited state and is ascribed to an analogous transition involving the bpy ligand. The polarization properties of these three lowest-energy transitions and the crystal structure of [Rh(phpy)2(bpy)]PF6 show that the transition moments are parallel to the ligand planes: The bpy transition is short-axis polarized, and the two phpy- transitions are oriented approximately parallel to the respective Rh-N(phpy-) bonds. It is concluded that the three lowest-energy excited states are essentially 3pipi* states, localized on the three ligands of the complex. They have a small admixture of the lowest-energy 1dpi* excitations through spin-orbit coupling.