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

Abstract

The title pyrazine dicarboxamide ligand, N 2,N 3-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—H...O hydrogen bonds, forming layers parallel to the (10\overline{1}) plane, which are in turn linked by offset π–π interactions [intercentroid distances 3.4779 (9) and 3.6526 (8) Å], 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, [μ-(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)3·2CH3CN or [Cu2(HL1−)(CH3CN)4](ClO4)3·2CH3CN (I). In the cation of complex I, the ligand coordinates to the copper(II) atoms in a bis-tridentate fashion. A resonance-assisted O—H...O 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—H...O hydrogen bonds, forming a supramolecular three-dimensional structure.