Syntheses, structures, fluorescent properties and natural bond orbital analyses of metal–organic complexes based on 5,6-substituted 1,10-phenanthroline derivatives

Abstract

Six new metal–organic coordination complexes, [Cd(MEDPQ)(2,5-pydc)]n (1), [Cd2(MOPIP)2(2,5-pydc)2]n (2), [Cu2(MOPIP)2(2,5-pydc)2]·H2O (3), [Mn(MOPIP)2(2,5-pydc)]·3H2O (4), [Cd(MOPIP)2(2,6-pydc)]·3H2O (5) and [Cd2(MOPIP)2(2,3-pydc)2·H2O]n (6) (MEDPQ=2-methyldipyrido[3,2-f:2′,3′-h]quinoxaline, MOPIP=2-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline, 2,5-H2pydc=pyridine-2,5-dicarboxylic acid, 2,6-H2pydc=pyridine-2,6-dicarboxylic acid, and 2,3-H2pydc=pyridine-2,3-dicarboxylic acid), have been prepared through hydrothermal reactions. The transformation of coordination modes of transition metal ions and organic carboxylate ligands has a crucial influence on the multinuclear structures of these series. In compounds 1 and 2, binuclear Cd(II) subunits occur, which are connected by 2,5-pydc anions to construct an undulating network. By selecting the different transition metal ions, we get the compounds 3 and 4. For the compound 3, the Cu(II) centers are linked by 2,5-pydc ligands to form a binuclear dimer. Compound 4 shows a mononuclear compound. For complexes 5 and 6, by changing the dicarboxylate ligands, Cd(II) adopts a heptacoordinated mode to form a mononuclear compound and chain framework. In addition, fluorescent properties of 2–4 have been reported.