Selective protonation of a tetraaza macrocyclic copper(II) complex containing two N-acetate pendant arms: short hydrogen-bonded chain structure of the mono-protonated derivative

Two copper(II) complexes [Cu(H2L3)](ClO4)2 (1) and [Cu(HL3)]n(ClO4)n.nCH3CN (2), in which the pendant N-acetate groups of L3 (2,12-bis(2-carboxymethyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[14.4.01.18.07.12]docosane) are fully or partially protonated, have been prepared selectively. The complexes have an octahedral coordination polyhedron. The [Cu(HL3)]+ cations of 2 are linked together by strong intermolecular hydrogen bonding interactions (COH⋯OC) between the N-acetic acid and N-acetate pendant arms, forming an one-dimensional polymer; the acetic acid and acetate groups are also coordinated to the metal ion through the oxygen atoms of the carbonyl units. The complexes 1 and 2 are quite stable in the solid states or in non-aqueous solvents, such as nitromethane and N,N-dimethylformamide, but are readily deprotonated to produce [CuL3] in aqueous solutions.