Preparation and spectral characterization of copper(I) halide, nitrate and perchlorate complexes of pyrazinic acid and X-ray crystal structure of polymeric [Cu 2(pyrazinic acid) 2I 2] · 3H 2O

Abstract

Copper(l) salts formed with pyrazinic acid (pyz-H) complexes of the types Cu(pyz-H) 2X · 2H 2O for X  Cl or Br, Cu(pyz-H)X · H 2O for X  Br, NO 3 or ClO 4 and Cu 2(pyz-H) n X 2 · 3H 2O where n = 3 for X  Cl and n = 2 for X  I. The complexes were characterized by elemental analysis, IR and electronic spectra. The overall physical measurements suggest that pyz-H acts as a monodentate ligand in the Cu(pyz-H) 2X · 2H 2O complexes and as a N,O-bidentate neutral ligand in the hydrated 1 : 1 complexes, whereas Cu 2(pyz-H) 3Cl 2 · 3H 2O contains both types of acid molecules. The structure of the trihydrated copper(I) iodide complex of pyrazinic acid, as determined by X-ray crystallography, contains the asymmetric Cu 2(pyz-H) 2I 2 · 3H 2O units which are linked together forming a stair or ribbon polymeric structure with tetrahedral copper(I) environments. The two pyrazinic acid molecules in the asymmetric unit behave differently; one acid molecule acts as a neutral ligand whereas the other functions as a zwitterion. Both molecules, however, act as monodentate ligands. The neutral pyrazinic acid molecule forms hydrogen bonds with two water molecules and the zwitterion binds the third water molecule through a hydrogen bond of the type N H … O. The CuN distances are 2.053(4) and 2.064(5) Å the CuI bond lengths vary from 2.618(1) to 2.645(1) Å, and the CuCu distance within the cyclic Cu 2I 2 unit is 2.771(1) Å.