COMPLEXATION WITH LIGANDS CONTAINING A DIPYRIDYLMETHANE UNIT - STRUCTURES OF A FREE LIGAND AND 2 COPPER(II) COMPLEXES

The crystal structures of the metal-free ligand ,6'-(1-methoxypropylid ene)bis(2-pyridinecarboxylic acid) monohydrate, C16H16N2O5.H2O (1), th e complex '-[1-(2-pyridylmethoxy)propylidene]bis(2-pyridine- carboxyla to-N,O)}copper(II), [CU(C21H17N3O5)(H2O)] (2), and the dimeric complex ethoxy)[3-(3-pyridylmethoxy)phenyl]methylene)bis(2 carboxylato)-N,N', O,O'':N'']dicopper(II) monohydrate, [Cu-2(C26H19N3O6)(2)].H2O (3), hav e been studied by X-ray diffraction, In the crystal of (1) the dipyrid ylmethane moiety adopts an anti conformation, with the two aromatic ri ngs almost perpendicular to each other. This molecular conformation, a s well as the crystal packing, are stabilized by hydrogen bonds involv ing the water molecule, The Cu-II ion in (2) has square-pyramidal coor dination, with the apex position occupied by the water O atom, The aro matic are slightly bent from the plane formed by the two N atoms the t wo carboxylic O atoms of the ligand molecule. The apical water O atoms link successive molecules into infinite chains via hydrogen bonds, Th e chains, held together by weak electrostatic interactions besides the van der Waals forces, are arranged so as to Copies form a layer struc ture. (3) also contains a five-coordinate Cu-II ion with a square-pyra midal coordination polyhedron. The axial position is occupied by an N atom, N(22), belonging to the pendant arm of the neighbouring molecule . Thus, (3) forms a dimer although the crystallographic asymmetric uni t contains only half the dimeric formula unit. The water O atom, havin g only a half site occupation, does not coordinate to the Cu ion. In t he crystal the dimeric molecules stack, with alternating orientation, along the unique b axis.