A purple-emitting luminescence complex [Cd(bpdc)(phen)₂(H₂O)]·6H₂O: Synthesis, structure and spectral properties

A supramolecular Cd(II) complex[Cd(bpdc)(phen)₂(H₂O)]·6H₂O (1) was synthesized with 2, 4'-biphenyldicarboxylic acid (H₂bpdc) and 1, 10-phenanthroline (phen) under hydrothermal conditions and characterized by single-crystal X-ray diffraction elemental analysis, and IR spectrum. Single-crystal X-ray analysis reveals complex 1 crystalizes in the triclinic P1 space group, the metal center Cd(II) ion is six-coordinated and exhibits a distorted octahedron geometry arrangement. 3D supramolecular structure could be formed taking into account two kinds of hydrogen bonds and π- π interactions. At the same time, we discussed the luminescent properties of complex 1 in the solid-state as well as in the solvents at different temperatures. When excited at 350 nm, in the solid state at 298 K, 1 has purple luminescence with emission band at 390 nm; in the solid state at 77 K, 1 displays two emission bands at 380 and 520 nm. Because the vibration structure is more defined at low temperature, at 298 K, 1 also has purple luminescence in DMSO and CH₃OH solutions with emission bands at 380 and 375 nm, which are blue-shifted compared with solid-state maximum emission band. These all can be attribute to the π* →π transition based on the coordinate ligands. The fluorescence decay curves of complex 1 indicate that the processes of decay consist of two components. At 298 K, the lifetime of 1 is longer in DMSO solution (τ₁=1.73 μs and τ₂=14.07 μs) than that in CH₃OH solution (τ₁=1.21 μs and τ₂=12.44 μs). Moreover, the lifetime of 1 is longer at 77 K (τ₁=1.96 μs and τ₂=16.11 μs) than that at 298 K in the solid state (τ₁=1.20 μs and τ₂=11.34 μs). The results might be caused by the increase in radiative rate and decrease in non-radiative rate at low temperature.