X-ray and DFT studies of a mono- and binuclear copper(II) ionic compound containing a Schiff base

In the structure of trans-bis­(ethanol-[kappa]O)tetra­kis­(1H-imidazole-[kappa]N³)copper(II) bis­[[mu]-N-(2-oxidobenzyl­idene)-D,L-glutamato]-[kappa]⁴O¹,N,O^2':O^2';[kappa]⁴O^2':O¹,N,O^2'-bis­[(1H-imidazole-[kappa]N³)cuprate(II)], [Cu(C₃H₄N₂)₄(C₂H₆O)₂][Cu₂(C₁₅H₁₄N₃O₅)₂], both ions are located on centres of inversion. The cation is mononuclear, showing a distorted octa­hedral coordination, while the anion is a binuclear centrosymmetric dimer with a square-pyramidal copper(II) coordination. An extensive three-dimensional hydrogen-bonding network is formed between the ions. According to B3LYP/6-31G* calculations, the two equivalent components of the anion are in doublet states (spin density located mostly on Cu^II ions) and are coupled as a triplet, with only marginal preference over an open-shell singlet.