Effect of Auxiliary Ligands on the Architectures of Manganese Complexes Constructed by N-Heterocyclic Ligands: Syntheses, Structures, and Properties

Abstract

Two manganese complexes based on N-heterocyclic ligands, [Mn(bqdca)(2,2'-bipy)(H2O)2]n (1), Mn0.5(4,4'-bipy) (H2O)2?0.5bqdca?2H2O (2) (H2bqdca = 2, 2'-biquinoline-4, 4'-dicarboxylic acid, 2, 2'-bipy = 2, 2'-bipyridine, 4, 4'-bipy = 4, 4'-bipyridine), have been synthesized by hydrothermal methods based on Pearson?s acid-base theory and structurally characterized. In Complex 1, the Mn ions are bridged by bqdca2- anions to form one-dimensional chains, which are further linked by hydrogen bonds to generate a two-dimensional layered structure. In Complex 2, each Mn ion was coordinated by 4, 4'-bipy and water molecules to generate a mononuclear structure accompanied by bqdca2- anion balancing valences. The intermolecular hydrogen bonds can link them to construct a three-dimensional supramolecular structure. The different structures of Complexes 1 and 2 illustrate the great influence of the N-heterocyclic auxiliary ligands on the self-assembly of coordination architectures. 2,2'- bipy and 4,4'-bipy ligands all act as terminal ligands. In addition, Complexes 1 and 2 exhibit the photoluminescent emission at 455 nm and 463 nm, and 455 nm and 465 nm in the solid state, respectively, which may be attributed to intraligand transitions. The redshifts of Complexes 1 and 2 may be due to the ligand-to-metal charge transfer, comparing to the H2bqdca ligand.. KEYWORDS :Crystal structure, Manganese complex, N-Heterocyclic ligand, Photoluminesce.