Synthesis and structure of a hexaazamacrocyclic copper(II) complex with maleato ligand

A hexaazamacrocyclic copper(II) complex Cu(L)(H₂O) (O₂CCH = CHCO₂)⋅H₂O (1) (L = 3,10-bis(2-hydroxyethyl)-1,3,5,8,10,12-hexaazacyclotetradecane) was prepared and structurally characterized by a combination of analytical, spectroscopic, and crystallographic methods. In complex 1, the coordination geometry about the copper(II) ion is six-coordinate with four equatorial nitrogen atoms from the macrocycle and two oxygen atoms from the axial maleato and aqua ligands. In 1, the one end of the maleato ligand coordinates to the central copper atom, while the other end is not bonded. The macrocycle and the axial ligands are highly involved in multiple types of hydrogen bonding interactions, resulting in the stabilization of the maleato ligand as a “coordinated ligand counter anion.”