A new three-dimensional, hydrogen-bonded metal-pteridine complex: synthesis, characterization and crystal structure of diaqua bis(1,3-dimethylpteridine-2,4(1H,3H)-dione-O4,N5) copper(II) nitrate dihydrate

Abstract

In absolute methanol, copper(II) nitrate reacted with 1,3-dimethyl-(1H, 3H)-pteridin-2,4-dione (1,3-dimethyllumazine, DMLM) giving a complex with formula [Cu(DMLM)2(H2O)2] (NO3)2 · 2H2O. This compound has been characterized by means of analytical techniques (elemental analysis and TG), spectral methods (IR, UV-vis-NIR, EPR), magnetic measurements (77–290 K) and single-crystal X-ray diffraction. The copper(II) ion occupies an inversion centre and exhibits an elongated octahedral coordination. The equatorial plane consists of two N(5) atoms of the pteridine ligands and two oxygen atoms from water molecules, and the two axial sites are occupied by two O(4) atoms of the ligands. The non-coordinated water molecules and nitrate anions, as well as the pteridine ligands are involved in a two-dimensional H-bond network, the metal-pteridine moieties being linked to the non-coordinated water molecules and nitrate anions of neighbouring molecules through the O(2) atom of the pteridine ligands. The molecules are packed in planes parallel to the b-axis, these planes being stacked at a mean distance of 3.297A˚to each other. A three-dimensional arrangement is defined by the involvement of the coordinated water molecules in a hydrogen bond with one oxygen atom from the uncoordinated water and another oxygen from the nitrate group of the adjacent layers.