X-ray structural studies on some Cu (II), Co (II) and Ni (II) complexes with nicotinic and isonicotinic acid N-oxides

Five new copper(II) complexes with nicotinic and isonicotinic acid N-oxides have been synthesized and their crystal and molecular structures determined by single crystal X-ray diffraction measurements. Catena-diaqua-di-μ-hydroxo-bis-μ-(nicotinato N-oxide)bis-μ-(nicotinato N-oxido)tricopper(II), [Cu₃-(N-nicO)₄(OH)₂(H2O)₂], is a polymeric complex with nicotinato N-oxide bridges between trinuclear structural units. Copper atoms are connected by hydroxo, N-oxide oxygen and carboxylato bridges. Catena-diaqua-bis-μ-(nicotinato N-oxido)copper(II) tetrahydrate, [Cu(N-nicO)₂(H2O)₂]·4H₂O, is an unstable polymeric complex. The decomposition has been studied thermogravimetrically. Dichlorobis(nicotinic acid N-oxide)copper(II), [CuCl₂(N-nicOH)₂] was prepared in ethanol solution. The nicotinic acid N-oxide ligand is coordinated to the copper atom through the N-oxide oxygen atom. Diaquabis(isonicotinato N-oxide)bis(pyridine)-copper(II), [Cu(N-inicO)₂(H₂O)₂(py)₂], a complex unstable in air, was prepared through recrystallization of diaquabis(isonicotinato N-oxide)copper(II) in ethanol - pyridine solution. Pentaaqua-di-μ-hydroxo-bis-μ-(isonicotinato N-oxide)-bis(isonicotinato N-oxide)tricopper(II) dihydrate, [Cu₃(NinicO)₄(OH)₂(H₂O)₅]·2H₂O, is a trinuclear complex with hydroxo and carboxylato bridges between copper atoms. Crystal and molecular structures were also determined for diaquabis(isonicotinato N-oxide)copper(II), [Co(N-inicO)₂(H₂O)₂] and for the isomorphous complexes tetraaquabis(nicotinato N-oxide)cobalt(II), [Co(N-nicO)₂-(H2O)₄], and teraaquabis(nicotinato N-oxide)nickel(II), [Ni(N-nicO)₂(H2O)₄]. The results are summarized and discussed.