Ternary copper(II) complexes with N-carboxymethyl-l-prolinato(2−) ion and imidazole or creatinine: A comparative study of the interligand interactions influencing the molecular recognition and stability

The compounds {[Cu(CMP)(Him)] · H2O}n (I) and [Cu(CMP)(crea)H2O] · 3H2O (II) were synthesized and characterized by X-ray diffraction, thermal, spectral and magnetic methods (CMP = N-carboxymethyl-;l-prolinato(2−) ion, Him = imidazole and crea = creatinine). Appropriate structural comparison with other compounds such as {[Cu(CMP)(H2O)] · H2O}n, [Cu(crea)2Cl2] and [Cu(dipeptide)(crea)(H2O)x] · nH2O (x = 0 or 1) have been made in order to prove that crea can act as an imidazole-like ligand (because it is able to promote the same fac- to mer-CMP tridentate conformational change in copper(II) complexes) as well as to discuss the interligand interactions which control the 'Cu(CMP) complex-crea, molecular recognition processes. In contrast to that found in related ternary complexes, we have concluded that direct CMP-crea interligand interactions are missing in the Cu-CMP-crea complex due to the inappropriate correspondence between the donor and/or acceptor H-bonding properties of these ligands. CMP can only act as H-acceptor by its two terminal carboxylate group, and crea can display H-donor and H-acceptor roles by its exocyclic -NH2 and O moieties, respectively. That promotes the reinforcement of the Cu-N(crea) bond by a bridge -N-H(crea)⋯O(aqua) (2.867(3) Å, 176.4°).