New coordination polymers and supramolecular complexes generated from oxadiazole-containing organic ligands and inorganic M(II) (M = Zn and Cu) salts

The coordination chemistry of the oxadiazole-containing rigid bidentate ligands 2,5-bis-(4-pyridyl)-1,3,4-oxadiazole (L1) and 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (L2) with inorganic M(II) (M = Zn and Cu) salts has been investigated. Two new coordination polymers (1 and 2) and two new bimetallic macrocyclic supramolecular complexes (3 and 4) were synthesized from solution reactions of L1 and L2 with inorganic M(II) (M = Zn and Cu) salts, respectively. {[Zn(L1)(H2O)(2)(CH3CN)(2)](ClO4)(2).(L1)(CH3CN)(1.5)(CH2Cl2)(0.5)}(n) (1; monoclinic, P2(1)/m, a 7.5755(4) Angstrom, b = 8.3120(16) Angstrom, c = 9.6449(6) Angstrom, beta = 99.9920(10)degrees, Z = 2) was obtained by combination of L1 with Zn(ClO4).6H(2)O in a CH2Cl2/CH3CN mixed-solvent system. The structure features one-dimensional chains that are cross-linked to each other by weak noncovalent pi-pi interactions (alternating face-to-face stacking of coordinated and uncoordinated L1 molecules) to generate a novel two-dimensional network. {[Zn(L1)(H2O)(2)NO3)(2)].2(CH3CN)(2)}(n) (2; monoclinic, C2/c, a = 27.2789(18) Angstrom, b = 11.7378(8) Angstrom, c = 7.3357(5) Angstrom, beta = 101.4270(10)degrees, Z = 4) was obtained by combination of L1 with Zn(NO3)(2).6H(2)O in the same solvent system. It forms with an unique H-bonded three-dimensional framework that contains rhombic channels (crystallographic dimensions, 18 x 10 Angstrom(2)) running down the crystallographic c axis. Inside the channels are double columns of CH3CN molecules, stacked neatly upon one another. [Zn(L2)(H2O)(3)(NO3)](2)(NO3)(2) (3; monoclinic, P2(1)/c, a = 13.8786(7) Angstrom, b = 12.5179(7) Angstrom, c = 9.8966(5) Angstrom, alpha = 97.5790(10)degrees, Z = 2) and {[Cu(L2)(CH3CN)(NO3)](2) (4; triclinic, (P) over bar1, alpha = 7.7416(5) Angstrom, b = 8.5956(5) Angstrom, c = 13.3020(8) Angstrom, alpha = 74.3470(10)degrees, beta = 78.4420(10)degrees, gamma = 86.2340(10)degrees, Z = 1) were generated from the reactions of L2 with Zn(NO3)(2).6H(2)O and Cu(NO3)(2).6H(2)O in a CH2Cl2/CH3CN mixed-solvent system, respectively. Both 3 and 4 adopt a novel bimetallic macrocyclic structural motif, consisting of M-2(L2)(2) (M = Zn and Cu) ringlike units. Hydrogen-bonding interactions in 3 and noncovalent pi-pi interactions in 4 play a significant role in aligning the molecular dimeric squares in the solid state. Compounds 3 and 4 are soluble in both water and organic solvents. In addition, both compounds are luminescent in the solid state and a large red shift in the emission is observed between the free ligand L2 and the ligand incorporated into both complexes 3 and 4.