Abstract
Two compounds 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane catena-tetra-mu-halo-dicuprate(I) with DABCOMe(2) Cu2X4 (1: X = Br, 2: X = I) were synthesized by hydrothermal reaction of copper(I) halides with the corresponding 1,4-diazoniabicyclo[2.2.2] octane (DABCO) dihydrohalides in an acetonitrile/methanol mixture. Both compounds crystallize monoclinically, 1 with a = 9.169(4) angstrom, b = ...
Abstract
Two compounds 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane catena-tetra-mu-halo-dicuprate(I) with DABCOMe(2) Cu2X4 (1: X = Br, 2: X = I) were synthesized by hydrothermal reaction of copper(I) halides with the corresponding 1,4-diazoniabicyclo[2.2.2] octane (DABCO) dihydrohalides in an acetonitrile/methanol mixture. Both compounds crystallize monoclinically, 1 with a = 9.169(4) angstrom, b = 10.916(6) angstrom, c = 15.349(6) angstrom , beta = 93.93(2)degrees, V = 1533(1) angstrom(3), Z = 4, space group P2(1)/n (no. 14) and 2 with a = 15.826(9) angstrom, b = 9.476(5) angstrom, c = 22.90(2) angstrom, beta = 90.56(5)degrees, V = 3434(5) angstrom(3), Z = 8, space group P2(1) (no. 4), respectively (lattice constants refined from powder diffraction data measured at 293 K). The cations in both compounds are formed by in situ N-methylation of DABCOH(2)(2+) cations by methanol in a S(N)2 reaction. Both compounds contain an anionic copper(I) halide chain structure consisting of trans edge-sharing CuX4 tetrahedra. The chains are strongly kinked at every 2nd junction thus forming a zigzag structure. The shortest halide-halide distances are observed between the halide ions of adjacent tetrahedra which are approaching each other due to the kinking. This structure type shows a specific luminescence behavior. Under optical excitation, the compounds exhibit yellow (1) and green (2) emission with photoluminescence quantum yields of Phi(PL) = 52 and 4%, respectively, at ambient temperature. According to DFT and TDDFT calculations, the emission is assigned to be a phosphorescence essentially involving a metal centered transition between the HOMO consisting mainly of copper 3d and halide p orbitals and the LUMO consisting mainly of copper 4s and 4p orbitals. The temperature dependence of the emission spectra, decay times, and quantum yields has been investigated in detail, especially for 1. From the resulting trends it can be concluded that the emission for T <= 100 K stems from energetically lower lying copper halide segments. Such segments represent the structural motif of the halocuprate(I) chains. With increasing temperature energetically higher lying segments are populated which also emit, but open the pathway for thermally activated energy transfer to quenching defects.
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