Synthesis, spectroscopic and structural characterization of [Cu(phen)(C5O5)(H2O)]·H2O, [Ni(terpy)(C5O5)(H2O)]·H2O and [Ni(terpy)2](NO3)2·0.5H2O

The new mononuclear complexes [Cu(phen)(C5O5)(H2O)]·H2O (1), [Ni(terpy)(C5O5)(H2O)]·H2O (2) and [Ni(terpy)2](NO3)2·0.5H2O (3) [phen=1,10-phenanthroline, C5O52−=dianion of the 4,5-dihydroxycyclopent-4-ene-1,2,3-trione and terpy=2,2′:6′,2″-terpyridine] have been synthesized and characterized by single-crystal X-ray diffraction. The copper atom of 1 has a distorted square pyramidal environment with two phen-nitrogen and two croconate-oxygen atoms building the equatorial plane and a water molecule in the apical position. The nickel atom of 2 exhibits a distorted NiN3O3 octahedral coordination, which may be described either as tetragonally compressed or as skewed trapezoidal bipyramidal. The nickel atom of 3 is situated on a twofold axis and it has a distorted NiN6 octahedral coordination, with an appreciable tetragonal compression along the N(2)-Ni-N(4) axis [N(2) and N(4) being the central terpy-nitrogens]. The structures of 1 and 2 are compared with related ones from the literature and their potential use as ligands is analyzed.