Syntheses and crystal structures of a new pyrazine dicarboxamide ligand, N2,N3-bis­­(quinolin-8-yl)pyrazine-2,3-dicarboxamide, and of a copper perchlorate binuclear complex

The title pyrazine dicarboxamide ligand, N2 ,N3 -bis(quinolin-8-yl)pyrazine-2,3- dicarboxamide (H2L1), C24H16N6O2, has a twisted conformation with the outer quinoline groups being inclined to the central pyrazine ring by 9.00 (6) and 78.67 (5), and by 79.94 (4) to each other. In the crystal, molecules are linked by C—HO hydrogen bonds, forming layers parallel to the (101) plane, which are in turn linked by offset – interactions [intercentroid distances 3.4779 (9) and 3.6526 (8) A˚ ], forming a supramolecular three-dimensional structure. Reaction of the ligand H2L1 with Cu(ClO4)2 in acetonitrile leads to the formation of the binuclear complex, [-(3-{hydroxy[(quinolin-8-yl)imino]methyl}pyrazin-2-yl)- [(quinolin-8-yl)imino]methanolato]bis[diacetonitrilecopper(II)] tris(perchlorate) acetonitrile disolvate, [Cu2(C24H15N6O2)(CH3CN)4](ClO4)32CH3CN or [Cu2(HL1)(CH3CN)4](ClO4)32CH3CN (I). In the cation of complex I, the ligand coordinates to the copper(II) atoms in a bis-tridentate fashion. A resonance-assisted O—HO hydrogen bond is present in the ligand; the position of this H atom was located in a difference-Fourier map. Both copper(II) atoms are fivefold coordinate, being ligated by three N atoms of the ligand and by the N atoms of two acetonitrile molecules. The first copper atom has a perfect square-pyramidal geometry while the second copper atom has a distorted shape. In the crystal, the cation and perchlorate anions are linked by a number of C— HO hydrogen bonds, forming a supramolecular three-dimensional structure.