title: Mononuclear versus dinuclear complex formation in nickel(II) sulfate/phenyl(2-pyridyl)ketone oxime chemistry depending on the ligand to metal reaction ratio: synthetic, spectral and structural studies.
abstract: The reactions of phenyl(2-pyridyl)ketone oxime (py)C(ph)NOH, with nickel(II) sulfate hexahydrate under reflux, in the absence of an external base, have been investigated. The reaction of NiSO4 x 6H2O with two equivalents of (py)C(ph)NOH in H2O/MeOH leads to the dinuclear complex [Ni2(SO4)2[(py)C(ph)NOH]4] (1), while an excess of the organic ligand affords the 1:3 cationic complex [Ni[(py)C(ph)NOH]3](SO4) (2). Compound 1 is transformed into 2 by a reaction with an excess of ligand in refluxing H(2)O/MeOH. Reactions of 1 and 2 with a limited amount of LiOH give the known cluster [Ni6(SO4)4(OH)[(py)C(ph)NO]3[(py)C(ph)NOH]3(H2O)3]. The structures of 1 and 2 have been determined by single-crystal X-ray crystallography. In both complexes the organic ligand chelates through its 2-pyridyl and oxime nitrogen atoms. The metal centers of 1 are bridged by two eta1:eta1:micro sulfato ligands; each metal ion has the cis-cis-trans deposition of the coordinated sulfato oxygen, pyridyl nitrogen and oxime nitrogen atoms, respectively. The cation of 2 is the fac isomer considering the positions of the coordinated pyridyl and oxime nitrogen atoms. The crystal structures of both complexes are stabilized by hydrogen bonds. Compounds 1 and 2 join a small family of structurally characterized metal complexes containing the neutral or anionic forms of phenyl(2-pyridyl)ketone oxime as ligands. The IR spectra of the two complexes are discussed in terms of the nature of bonding and their structures. From the vibrational spectroscopy viewpoint, the SO4(2-) groups in 1 and 2 appear to have lower symmetries compared with those deduced from X-ray crystallography; this is attributed to the participation of sulfates in hydrogen bonding interactions.
authors.affiliation: Department of Chemistry, University of Patras, 265 04 Patras, Greece.
authors.forename: Constantina
authors.initials: C
authors.lastname: Papatriantafyllopoulou
authors.forename: Constantinos G
authors.initials: CG
authors.lastname: Efthymiou
authors.forename: Catherine P
authors.initials: CP
authors.lastname: Raptopoulou
authors.forename: Aris
authors.initials: A
authors.lastname: Terzis
authors.forename: Evy
authors.initials: E
authors.lastname: Manessi-Zoupa
authors.forename: Spyros P
authors.initials: SP
authors.lastname: Perlepes
mesh_terms: D002412:Cations / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D010091:Oximes / Q000138:chemical synthesis* / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D002412:Cations; D002614:Chelating Agents; D008024:Ligands; D010091:Oximes; C528188:phenyl 2-pyridyl ketone oxime; C029938:nickel sulfate; D009532:Nickel