The crystal structures of the ligand N-(quinolin-8-yl)pyrazine-2-carboxamide and of a tetranuclear copper(II) complex

Abstract

The title tridentate ligand, C14H10N4O, N-(quinolin-8-yl)pyrazine-2-carboxamide (HL1), crystallizes with three independent molecules (A, B and C) in the asymmetric unit. All three molecules are relatively planar (r.m.s. deviations are 0.068, 0.055 and 0.06 Å, respectively), with the NH H atom forming three-centered (bifurcated) intramolecular N—H...N hydrogen bonds in each molecule. There is also an intramolecular C—H...O contact present in each molecule, involving the benzene ring of the quinoline unit and the amide carboxamide O atom. In the crystal, the three molecules stack in columns with the various molecules being linked by offset π-π interactions [intercentroid distances vary from 3.367 (5) to 3.589 (5) Å], forming layers parallel to the ab plane. The title complex, [Cu4(C42H44N8O16)]·2CH3OH, {hexa-μ-acetato-1:2κ2 O:O′;2:3κ8 O:O′;3:4κ2 O:O′-dimethanol-1κO,2κO-bis[N-(quinolin-8-yl)pyrazine-2-carboxamide]-1κ3 N,N′,N′′;4κ3 N,N′,N′′-tetracopper(II) methanol disolvate} (I), was obtained by the reaction of HL1 with Cu(CH3CO2)2. It consists of a tetranuclear complex with a central tetrakis(μ-acetato)dicopper paddle-wheel moiety linked on either side via bridging acetato ions to a mononuclear copper(II)–(L1) complex; it crystallizes as a methanol disolvate. The complex possesses inversion symmetry, being located about a center of symmetry situated at the mid-point of the Cu...Cu bond of the paddle-wheel moiety. In the crystal, the complex molecules are linked by O—H...O hydrogen bonds, forming chains along the [01\overline{1}] direction, which are linked by offset π–π interactions [intercentroid distance = 3.7367 (11) Å] and C—H...O hydrogen bonds, leading to the formation of a supramolecular framework.