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

摘要

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] 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.