Structural and luminescence modulation in 8-hydroxyquinolinate-based coordination polymers by varying the dicarboxylic acid.

Two Zn(ii) and Cd(ii) coordination polymers [ZnL2·2DMF] (1) and [CdL(OAc)] (2) were first synthesized by treating a novel 2-substituted 8-hydroxyquinolinate ligand HL involving a pyridyl group with zinc or cadmium salts. Two dicarboxylic acid ligands (H2BDC = 1,4-benzenedicarboxylic acid; H2BPDC = 4,4'-biphenyldicarboxylic acid) are employed as secondary auxiliary ligands to perform a systematic study on the structural diversities in the M(ii)-quinolinate frameworks. By introducing two dicarboxylate anions in the reaction system, four new polymers [Zn2L2(BDC)] (3), [Zn3L2I2(BPDC)·2MeOH·8H2O] (4), [Cd2L2(BDC)] (5) and [Cd2L2(BPDC)·2MeOH·4H2O] (6) were obtained. Complex 1 possesses a two-dimensional (2D) square grid containing meso-helical chains. Complex 2 is a 2D network fabricated by binuclear {Zn2} secondary building units (SBUs). Complexes 3 and 5 show a kind of 2D structure constructed by cyclic hexamers Zn6L4, which are divided into half by the coordinated BDC. In complex 4, the BPDC ligands bridge the 1D M(ii)-L chains into a 2D layered structure. Complex 6 presents an interesting 3D structure, in which the BPDC ligands link the binuclear Cd(ii) units into many meso-helical chains along the a and b axes. The diverse structures of complexes 1-6 indicate that the skeletons of dicarboxylate anions play an important role in the assembly of such different frameworks. Moreover, distinct fluorescence properties (emission wavelength and lifetime) of the complexes 1-6 were observed in the solid state.