title: Coordination diversity in mono- and oligonuclear copper(II) complexes of pyridine-2-hydroxamic and pyridine-2,6-dihydroxamic acids.
abstract: Solution and solid state studies on Cu(II) complexes of pyridine-2-hydroxamic acid (HPicHA) and pyridine-2,6-dihydroxamic acid (H2PyDHA) were carried out. The use of methanol/water solvent allowed us to investigate the Cu(II)-HPicHA equilibria under homogeneous conditions between pH 1 and 11. In agreement with ESI-MS indication, the potentiometric data fitted very well with the model usually reported for copper(II) complexes of α-aminohydroxamate complexes ([CuL](+), [Cu5(LH-1)4](2+), [CuL2], [CuL2H-1](-)), however with much higher stability of the 12-MC-4 species. A series of copper(II) complexes has been isolated in the solid state and characterized by a variety of spectroscopic methods, X-ray structure analysis, and magnetic susceptibility measurements. The ligands show the tendency to form bi- and trinuclear species with copper(II) ions due to the {(N,N'); (O,O')} bis-(bidentate) chelating-and-bridging mode involving (O,O')-hydroxamate chelate formation combined with (N,N') chelating with participation of the pyridine and hydroxamic nitrogen atoms, so that the hydroxamate groups play a μ2-(N,O)-bridging role. Molecular and crystal structures of three synthesized complexes [Cu3(PicHA-H)2(dipy)2](ClO4)2·4/3DMSO·2/3H2O (1), [Cu2(PyDHA)(dipy)2(ClO4)2]·DMF·H2O (4), and [Cu3(PyDHA-2H)(tmeda)3](ClO4)2 (5) (dipy, 2,2'-dipyridyl; tmeda, N,N,N',N'-tetramethyl-1,2-diaminoethane) have been determined by single crystal X-ray analysis. In 1, two trans-situated doubly deprotonated hydroxamic ligands play a {(O,O')(N,N')}-(bis)bidentate-bridging function forming bridges between the medial, Cu(2) (CuN4), and the terminal, Cu(1) and Cu(3) (CuN2O2), copper(II) ions; the chelating dipy ligands are coordinated to the latter. In 4, the ligand is coordinated in a classical (O,O')-hydroxamate chelating mode with the help of two separate hydroxamic groups while the central tridentate donor compartment remains vacant. In 5, the hydroxamate ligand is coordinated by the {(O,O');(N,N',N″);(O″,O"')}-tridentate-(bis)bidentate mode, bridging three copper(II) ions, while the chelating tmeda ligands are coordinated to all three copper(II) ions. Magnetic susceptibility measurements (1.7-300 K) of powdered samples of the trinuclear complexes 1 and 5 revealed strong antiferromagnetic coupling between the copper(II) ions mediated by the hydroxamate bridges.
authors.affiliation: Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wroclaw, Poland. elzbieta.gumienna-kontecka@chem.uni.wroc.pl
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Gumienna-Kontecka
authors.forename: Irina A
authors.initials: IA
authors.lastname: Golenya
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Szebesczyk
authors.forename: Matti
authors.initials: M
authors.lastname: Haukka
authors.forename: Roland
authors.initials: R
authors.lastname: Krämer
authors.forename: Igor O
authors.initials: IO
authors.lastname: Fritsky
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006877:Hydroxamic Acids / Q000737:chemistry*; D008958:Models, Molecular; D011522:Protons; D011725:Pyridines / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D006877:Hydroxamic Acids; D011522:Protons; D011725:Pyridines; C024588:2,6-pyridinedicarbohydroxamic acid; D003300:Copper