Halocuprate(i) zigzag chain structures with N-methylated DABCO cations - bright metal-centered luminescence and thermally activated color shiftsDedicated to Prof. Dr. Henri Brunner on the occasion of his 80th birthday.Electronic supplementary information (ESI) available: IR spectra of 1, 2, DABCOH2Br2, and DABCOH2I2H2O; experimental and simulated powder diffraction patterns of 1 and 2. CCDC 1410360 and 1410361. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/

Two compounds 1,4-dimethyl-1,4-diazoniabicyclo[2.2.2]octane catena -tetra-μ-halo-dicuprate( i ) with DABCOMe 2 Cu 2 X 4 ( 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) Å, b = 10.916(6) Å, c = 15.349(6) Å, β = 93.93(2)°, V = 1533(1) Å 3 , Z = 4, space group P 2 1 / n (no. 14) and 2 with a = 15.826(9) Å, b = 9.476(5) Å, c = 22.90(2) Å, β = 90.56(5)°, V = 3434(5) Å 3 , Z = 8, space group P 2 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 CuX 4 tetrahedra. The chains are strongly kinked at every 2 nd 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 Φ 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. Two halocuprate( i ) chain structures were synthesized and studied with respect to their emission properties that are governed by two interacting chain segments.