Toward a Rational Design of 3d-4f Heterometallic Coordination Polymers based on Mixed Valence Copper Centers

In the present work, we report two new Cu^I/Cu^II-Gd^III mixed valence heterometallic coordination polymers (HCP), [Gd(H₂O)₄Cu^IICu^I(IDC)₂] (1) and [Gd₂(H₂O)₂(C₂O₄)₂Cu^II(IDC)₂Cu^I ₂(4,4′-bipy)]·4.5H₂O (2) obtained under solvothermal synthesis using 1H-imidazole-4,5-dicarboxylic acid (H₃IDC) as a principal N,O-bifunctional organic linker. In both compounds, the stabilization of the Cu^I cations is achieved only by the coordination of N-atoms belonging to the organic ligands. While 1 presents a two-dimensional honeycomb network obtained by the coordination of single organic linker (IDC^3-), 2 contains three different organic ligands (IDC^3-, C₂O₄ ^2-, and 4,4′-bipy), which allow the construction of a three-dimensional network. From a magnetic point of view, 1 and 2 behave as simple paramagnets at high temperature, presenting ferromagnetic interactions below 50 K, and a positive magnetic coupling constant of J = 0.60 cm^-1 and J = 0.22 cm^-1 was obtained for 1 and 2 respectively. To the best our knowledge, 1 and 2 correspond to the second and third reported examples containing a Cu^I/Cu^II mixed valence system assembled with Gd^III cations, thus enriching the chemistry involved in 3d-4f metal-organic materials.