Dinuclear CuII and NiII complexes of 3-formylsalicylic acid oxime: cis/trans topology and extension of a cis-CuII2 complex to a pentanuclear CuIICuIIMnIICuIICuII complex

Abstract

3-Formylsalicylic acid oxime (H3L) formed the following dinuclear CuII and NiII complexes: [Cu2(HL)2]·0.5H2O (1), Na[Cu2(HL)(L)]·3H2O (2) and [Ni2(HL)2]·2.5H2O (3). The structures of Na[Cu2(HL)(L)(H2O)] (2′) and [Ni2(HL)2(H2O)4]·8H2O (3′) have been determined by X-ray crystallography. Complex 2 has a cis arrangement of the two ligands providing dissimilar {CuN2O2} and {CuO4} chromophores sharing the two phenolic oxygen atoms. The N2O2 cavity has a hydrogen-bonded N–O⋯H⋯O–N linkage as the lateral chain, and the Cu in this site has a square-pyramidal geometry with a water molecule at the axial site. The Cu in the O4 cavity has a planar geometry. Complex 3 has a trans configuration with respect to its two ligands and each Ni has a six-coordinate geometry with two water molecules at the axial sites. Complex 1 has a trans configuration based on its having a chemical formula and IR spectrum similar to 3. The following interconversion among dinuclear Cu complexes has been established by pH adjustment: trans-[Cu2(HL)2] (1) ⇌ cis-[Cu2(HL)(L)]− (2) ⇌ trans-[Cu2(L)2]2− (water molecules are omitted). On the other hand, 3 showed the following interconversion: trans-[Ni2(HL)2] (3) ⇌ trans-[Ni2(L)2]2−. The cis Cu2 complex 2 was reacted with MnII to afford [Mn{Cu2(HL)(L)}2(H2O)4]·H2O·2DMF (4) that has a linear pentanuclear CuIICuIIMnIICuIICuII structure formed by the coordination of two molecules of 2 to a MnII through a carboxylate group.