MOLECULAR-STRUCTURES AND PHOTOPHYSICAL PROPERTIES OF DIRHODIUM FLUOROPHOSPHINE COMPLEXES

The excited state properties of a series of singly bonded dirhodium co mpounds, consisting of Rh-2(0), Rh(0)Rh(II)X(2), and Rh(2)(II)X(4) (X = Cl and Br) cores coordinated by three bis(difluorophosphino)methylam ine ligands, have been investigated. The newly synthesized complexes w ith X = Br have been structurally characterized. The mixed-valence com plex Rh-2[mu-CH3N(PF2)(2)]Br-3(2)[(PF2)CH3N(PF2)] crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 13.868(7) Angstrom, b = 16.090(5) Angstrom, c = 11.614(5) Angstrom, V = 1591(3) Angstrom(3), and Z = 4; the structure was refined to values of R = 0.052 and R(w) = 0.062. Orange crystals of Rh-2[mu-CH3N(PF2)(2)]Br-3(4) are monoclini c with a C2/c space group: a = 14.62(6) Angstrom, b = 12.20(2) Angstro m, c = 14.33(1) Angstrom; beta = 106.0(2)degrees; V = 2457(11) Angstro m(3); Z = 4; and R = 0.058 and R(w) = 0.056. Crystalline solids and lo w-temperature glasses of each member of the chloride and bromide serie s exhibit long-lived red luminescence. Excitation profiles and tempera ture dependencies of the emission bandwidths and lifetimes for all com plexes are characteristic of luminescence originating from a d sigma excited state. Efficient nonradiative decay is observed upon the therm al population of an excited state proximate to the lowest energy emiss ive excited state of these complexes. The nonradiative decay rate cons tant of the upper excited state is 10(2)-10(3) and 10(3)-10(4) greater than that of the emissive excited state for complexes with X = Cl and Br, respectively.