Crystal structures of bis- and hexakis[(6,6′-dihydroxybipyridine)copper(II)] nitrate coordination complexes

Abstract

Two multinuclear complexes synthesized from Cu(NO3)2 and 6,6′-dihydroxybipyridine (dhbp) exhibit bridging nitrate and hydroxide ligands. The dinuclear complex (6,6′-dihydroxybipyridine-2κ2N,N′)[μ-6-(6-hydroxypyridin-2-yl)pyridin-2-olato-1:2κ3N,N′:O2](μ-hydroxido-1:2κ2O:O′)(μ-nitrato-1:2κ2O:O′)(nitrato-1κO)dicopper(II), [Cu2(C10H7N2O2)(OH)(NO3)2(C10H8N2O2)] or [Cu(6-OH-6′-O-bpy)(NO3)(μ-OH)(μ-NO3)Cu(6,6′-dhbp)], (I), with a 2:1 ratio of nitrate to hydroxide anions and one partially deprotonated dhbp ligand, forms from a water–ethanol mixture at neutral pH. The hexanuclear complex bis(μ3-bipyridine-2,2′-diolato-κ3O:N,N′:O′)tetrakis(6,6′-dihydroxybipyridine-κ2N,N′)tetrakis(μ-hydroxido-κ2O:O′)bis(methanol-κO)tetrakis(μ-nitrato-κ2O:O′)hexacopper(II), [Cu6(C10H6N2O2)2(CH4O)2(OH)4(NO3)4(C10H8N2O2)4] or [Cu(6,6′-dhbp)(μ-NO3)2(μ-OH)Cu(6,6′-O-bpy)(μ-OH)Cu(6,6′dhbp)(CH3OH)]2, (II), with a 1:1 NO3–OH ratio and two fully protonated and fully deprotonated dhbp ligands, was obtained by methanol recrystallization of material obtained at pH 3. Complex (II) lies across an inversion center. Complexes (I) and (II) both display intramolecular O—H...O hydrogen bonding. Intermolecular O—H...O hydrogen bonding links symmetry-related molecules forming chains along [100] for complex (I) with π-stacking along [010] and [001]. Complex (II) forms intermolecular O—H...O hydrogen-bonded chains along [010] with π-stacking along [100] and [001].

Keywords

• crystal structure
• copper
• dihydroxypyridine
• potential water oxidation catalysts