COMMUNICATION The Crystal Structure of Monoaquabis(trans-5-

The crystal structures of copper(II) complexes with pyridine and pyrazine carbo-xylate ligands attract considerable interest, because they show a variety of coordina-tion modes. Molecular chains consisting of Cu(II) ions coordinated by two ligand molecules via their N,O bonding moieties, bridged by the carboxylate oxygen atoms donated by neighbouring ligand molecules, have been observed in the crystals of cop-per(II) picolinate (pyridine-2-carboxylate) [1]. The same molecular pattern is shown by the crystals of copper(II) complex with pyrazine-2-carboxylate ligand [2], al-though the above compounds exhibit different symmetry – triclinic (P1) and mono-clinic (P21/c), respectively. In both complexes, the coordination around the metal ion is octahedral. In the crystals of another copper(II) complex with pyrazine-2-carbo-xylate ligand, the monomeric molecules consist of the central ion chelated by two ligand molecules via their N,O bonding moiety and two axially coordinated water molecules. The resulting octahedron is distinctly elongated along the H2O axis [2,3]. On the other hand, in the crystals of copper(II) isonicotinate (pyridine-4-carboxylate) the metal ion is tetracoordinated with two pyridine nitrogen atoms and two water oxy-gen atoms in trans orientation. The coordination geometry is square planar, the carboxylate groups of both ligand molecules participate only in the hydrogen bond system [4]. Therefore, as a part of our ongoing studies of crystal chemistry of pyridine and pyrazine caboxylate complexes with divalent metal ions, we have determined the crystal structure of the copper(II) complex with another monocarboxylate ligand rep-resented by 5-methylpyrazine-2 carboxylic acid (MPZA). The title compound was obtained by reacting 2 mmols of MPZA (Aldrich) dis-solved in 50 mililiters of boiling water with 50 mililiters of hot aqueous solution of 1 mmol of hydrated copper nitrate. After boiling for 1 hour, the solution was left for crystallization at room temperature. Dark blue, platelike crystals were deposited after standing overnight