Synthesis, structure, photoluminescence and theoretical calculations on a novel tetranuclear Cd(II) complex based on (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid

A novel tetranuclear cadmium complex {Cd2[(CH3)2PPDA]2(CH3OH)Cl4}2 (1) [(CH3)2PPDA = dimethyl esterification of H2PPDA], was prepared from CdCl2·2.5H2O with (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid (H2PPDA) by solvothermal reaction in methanol, and characterized by single-crystal X-ray diffraction analysis, optical diffuse reflectance and photoluminescence. In 1, cadmium ions are bridged by Cl− ions into a tetranuclear oligomeric chain further connected into a 3D supramolecular network by intermolecular Csingle bondH⋯Cl, Osingle bondH⋯Cl, and Csingle bondH⋯O hydrogen bonds. Compound 1 displays fluorescence with a lifetime value of ~ 5.88 ns in the visible region under visible-light excitation, and the origin of the luminescent emission is primary assigned to the combination of intraligand π–π* transition of (CH3)2PPDA ligand and ligand to ligand charge transfer from Cl− to (CH3)2PPDA which is probed by the density of state (DOS) calculations.