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

Abstract

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°).