Metal coordination architectures of 2,3-bis(triazol-1-ylmethyl)quinoxaline: Effect of metal ion and counterion on complex structures

A series of complexes, [ZnLCl2](2) (1), [ZnL2(NO3)(2)](infinity) (2), [MnL2(NO3)(2)](infinity) (3), ([ZnL2(H2O)(2)] (CIO4)(2)(CH3COCH3)(2)}(infinity) (4), {[MnL2(H2O)(2)](ClO4)(2)(CH3COCH3)(2)}(infinity) (5), {[CdL2(H2O)(2)]-(ClO4)(2)(H2O)(6)}(infinity) (6), and {[AgL](ClO4)(H2O)(1.5)}(infinity) (7), based on the flexible ligand 2,3-bis(triazol-1-ylmethyl)quinoxaline (L) were synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, and single-crystal X-ray diffraction. Complex 1 is a dinuclear macrocyclic molecular, which is further linked into a 1D supramolecular chain by intermolecular C-H center dot center dot center dot Cl weak interactions. The metal centers in 2 and 3 coordinate two NO3- anions, and the flexible ligand bridges M(NO3)(2) [M = Zn-II or Mu(II)] units to form 1D chain structures. Complexes 4, 5, and 6 show a 2D network structure with (4,4) topology. As expected, complex 7 has a 1D strand chain structure that is different than other Mu complexes (4, 5, and 6) with the same ligand. These chains are further extended into a 2D supramolecular network by O center dot center dot center dot Ag center dot center dot center dot O weak interactions. In all these complexes, the ligand bridges in a similar mode; however, the complexes have different structures ranging from a dinuclear structure to a 2D network mainly due to the differences in the coordination geometries of the metal centers and counterions. These results reveal that the coordination geometry of metal ions and the coordinating abilities of the counterions play important roles in defining the overall structure of metal-organic frameworks. In addition, the fluorescent properties of complexes 1, 2, 4, 6, 7, and ligand L and the EPR spectra of complex 5 were also investigated. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).