Molecular Structures and Photophysical Properties of Dirhodium Fluorophosphine Complexes

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Abstract
The excited state properties of a series of singly bonded dirhodium compounds, consisting of Rh02, Rh0RhIIX2, and RhII2X4 (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 Rh2[μ-CH3N(PF2)2]3Br2[(PF2)CH3N(PF2)] crystallizes in the orthorhombic space group P212121 with a = 13.868(7) Å, b = 16.090(5) Å, c = 11.614(5) Å, V = 1591(3) Å3, and Z = 4; the structure was refined to values of R = 0.052 and Rw = 0.062. Orange crystals of Rh2[μ-CH3N(PF2)2]3Br4 are monoclinic with a C2/c space group: a = 14.62(6) Å, b = 12.20(2) Å, c = 14.33(1) Å; β = 106.0(2)°; V = 2457(11) Å3; Z = 4; and R = 0.058 and Rw = 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 dσ* 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 102−103 and 103−104 greater than that of the emissive excited state for complexes with X = Cl and Br, respectively.