Hydrogen-bonded 3D like structures of Cu(II)/Zn(II) coordination polymers: photoluminescence, TDDFT study and semiconductive properties

Two Cu/Zn complexes [Cu(4,4'-bipy)(H2O)(2)(ClO4)(2)](n)n(4,4'-bipy) (1) and [Zn(4,4'-bipy)(H2O)(4)](3)(n)6n(4,4'-bipy)6n(ClO4)center dot 2nH(2)O (2) (4,4'-bipy = 4,4'-bipyridine) have been prepared via hydrothermal reactions and characterized by single-crystal X-ray diffraction. Both complexes feature an infinite 1-D chain-like structural motif with the metal ions surrounded by two nitrogen atoms and four oxygen atoms to yield a octahedral configuration. Both complexes have a 3-D coordination polymer network formed by the rich hydrogen-bonding interactions. Powder photoluminescence studies reveal that they have an emission in the blue (1) or red (2) region of the light spectrum. Time-dependent density functional theory investigation discover that the nature of the emission is resulted from the ligand-to-metal charge transfer for 1, as well as ligand-to-ligand charge transfer for 2. Narrow optical band gaps of 1.43 eV (1) and 2.24 eV (2) are found by the solid-state UV/vis diffuse reflectance spectra.