Synthesis, crystal structures, and fluorescence properties of (RS)-2-methylglutarato Zn(II), Cd(II) complexes

Reactions of fresh M(OH)2 (M = Zn2+, Cd2+) precipitate and (RS)-2-methylglutaric acid (H2MGL), 2,2'-bipyridine (bipy), or 1,10-phenanthroline (phen) in aqueous solution at 50 degrees C afforded four new metal-organic complexes [Zn2(bipy)2(H2O)2(MGL)2] (1), [Zn2(phen)2(H2O)(MGL)2] (2), [Cd(bipy)(H2O)(MGL)] center dot 3H2O (3), and [Cd(phen)(H2O)(MGL)] center dot 2H2O (4), which were characterized by single crystal X-ray diffraction, IR spectra, TG/DTA analysis as well as fluorescence spectra. In 1, the [Zn(bipy)(H2O)]2+ moieties are linked by R- and S-2-methylglutarate anions to build up the centrosymmetric dinuclear [Zn2(bipy)2(H2O)2(MGL)2] molecules. In 2, the 1-D ribbon-like chains [Zn2(phen)2(H2O)(MGL)2]n can be visualized as from centrosymmetric dinuclear [Zn2(phen)2(H2O)2(MGL)2] units sharing common aqua ligands. Both 3 and 4 exhibit 1-D chains resulting from [Cd(bipy)(H2O)]2+ and [Cd(phen)(H2O)]2+, respectively, bridged alternately by R- and S-2-methylglutarate anions in bis-chelating fashion. The intermolecular and interchain center dot center dot center dot stacking interactions form supramolecular assemblies in 1 and 1-D chains in 2-4 into 2-D layers. The hydrogen bonded lattice H2O molecules are sandwiched between 2-D layers in 3 and 4. Fluorescence spectra of 1-4 exhibit LLCT * transitions.