H-Bonds, π-Stacking and (Water)O-H/π Interactions in (µ₄-EDTA)Bis(Imidazole) Dicopper(II) Dihydrate

• Main Authors: Jeannette Carolina Belmont-Sánchez, María Eugenia García-Rubiño, Antonio Frontera, Josefa María González-Pérez, Alfonso Castiñeiras, Juan Niclós-Gutiérrez
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Crystals
• Subjects: crystal structure; copper(II); EDTA; imidazole; polymer; H-bonding
• Online Access: https://www.mdpi.com/2073-4352/11/1/48

We synthesized and studied the polymeric compound {[Cu₂(µ₄-EDTA)(Him)₂] 2H₂O}_n (<b>1</b>). The single-crystal structure is reported along with an in depth characterization of its thermal stability (TGA), spectral properties (FT-IR, Vis-UV and RSE), and magnetic behavior. The crystal consists of infinite 2D-networks built by centrosymmetric dinuclear motifs, constructed by means of a bridging <i>anti,syn</i>-carboxylate group from each asymmetric unit. Each layer guides Him ligands toward their external faces. They are connected by intermolecular (Him)N-H···O(carboxylate) bonds and antiparallel π–π stacking between symmetry related pairs of Him ligands, and then pillared in a 3D-network with parallel channels, where disordered water molecules are guested. About half of the labile water is lost from these channels over a wide temperature range (r.t. to 210 °C) before the other one, most strongly retained by the cooperating action of (water)O1-H(1A)···O(carboxylate) and (water) O1-H(1B)···π(Him) interactions. The latter is lost when organic ligands start to burn. ESR spectra and magnetic measurements indicated that symmetry related Cu(II) centers connected by the bridging carboxylate groups behave magnetically not equivalently, enabling an exchange interaction larger than their individual Zeeman energies.