Molecular Structures and Photophysical Properties of Dirhodium Fluorophosphine Complexes

The excited state properties of a series of singly bonded dirhodium compounds, consisting of Rh(0)(2), Rh(0)Rh(II)X(2), and Rh(II)(2)X(4) (X = Cl and Br) cores coordinated by three bis(difluorophosphino)methylamine ligands, have been investigated. The newly synthesized complexes with X = Br have been structurally characterized. The mixed-valence complex Rh(2)[&mgr;-CH(3)N(PF(2))(2)](3)Br(2)[(PF(2))CH(3)N(PF(2))] crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 13.868(7) Å, b = 16.090(5) Å, c = 11.614(5) Å, V = 1591(3) Å(3), and Z = 4; the structure was refined to values of R = 0.052 and R(w) = 0.062. Orange crystals of Rh(2)[&mgr;-CH(3)N(PF(2))(2)](3)Br(4) are monoclinic with a C2/c space group: a = 14.62(6) Å, b = 12.20(2) Å, c = 14.33(1) Å; beta = 106.0(2) degrees; V = 2457(11) Å(3); Z = 4; and R = 0.058 and R(w) = 0.056. Crystalline solids and low-temperature glasses of each member of the chloride and bromide series exhibit long-lived red luminescence. Excitation profiles and temperature dependencies of the emission bandwidths and lifetimes for all complexes are characteristic of luminescence originating from a dsigma excited state. Efficient nonradiative decay is observed upon the thermal population of an excited state proximate to the lowest energy emissive excited state of these complexes. The nonradiative decay rate constant 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.