The coordination chemistry of two symmetric double-armed oxadiazole-bridged organic ligands with copper salts.

Two new symmetric double-armed oxadiazole-bridged ligands, 4-methyl-{5-[5-methyl-2-(pyridin-3-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-3-carboxylate (L1) and 4-methyl-{5-[5-methyl-2-(pyridin-4-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-4-carboxylate (L2), were prepared by the reaction of 2,5-bis(2-hydroxy-5-methylphenyl)-1,3,4-oxadiazole with nicotinoyl chloride and isonicotinoyl chloride, respectively. Ligand L1 can be used as an organic clip to bind Cu(II) cations and generate a molecular complex, bis(4-methyl-{5-[5-methyl-2-(pyridin-3-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-3-carboxylate)bis(perchlorato)copper(II), [Cu(ClO4)2(C28H20N4O5)2], (I). In compound (I), the Cu(II) cation is located on an inversion centre and is hexacoordinated in a distorted octahedral geometry, with the pyridine N atoms of two L1 ligands in the equatorial positions and two weakly coordinating perchlorate counter-ions in the axial positions. The two arms of the L1 ligands bend inward and converge at the Cu(II) coordination point to give rise to a spirometallocycle. Ligand L2 binds Cu(I) cations to generate a supramolecule, diacetonitriledi-μ3-iodido-di-μ2-iodido-bis(4-methyl-{5-[5-methyl-2-(pyridin-4-ylcarbonyloxy)phenyl]-1,3,4-oxadiazol-2-yl}phenyl pyridine-4-carboxylate)tetracopper(I), [Cu4I4(CH3CN)2(C28H20N4O5)2], (II). The asymmetric unit of (II) indicates that it contains two Cu(I) atoms, one L2 ligand, one acetonitrile ligand and two iodide ligands. Both of the Cu(I) atoms are four-coordinated in an approximately tetrahedral environment. The molecule is centrosymmetric and the four I atoms and four Cu(I) atoms form a rope-ladder-type [Cu4I4] unit. Discrete units are linked into one-dimensional chains through π-π interactions.