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-[mu]₃-iodido-di-[mu]₂-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 [pi]-[pi] inter­actions.