A new {Cu₃-Gd₂} cluster as a two-in-one functional material with unique topology acting as a refrigerant and adsorbent for cationic dye

A new heterometallic cluster system, [Cu₃Gd₂(H₃btp)₂(OAc)₆]·5H₂O {Cu₃-Gd₂}, is designed by employing 1,3-bis(tris(hydroxymethyl)methylamino)propane (H₆btp) as a ligand. The cluster is characterized by FTIR, TGA, PXRD, SCXRD and topological analyses. The crystallography ascertains the presence of two Cu²⁺ in square pyramidal and one Cu²⁺ in octahedral environments while the two Gd³⁺ ions are in a distorted capped square antiprismatic geometry. The ligand is coordinated in an unusual tri-deprotonated form (H₃btp³⁻). The overall cluster represents a rare example of unique topology [1,2 M3-1]. The M(H) plot recorded at 2 K shows the presence of antiferromagnetic interactions. The cluster exhibits a maximum change in entropy of 15.84 J kg⁻¹ K⁻¹ at 3 K for H = 7 T thus acting as a new class of magnetic molecular cooler. Furthermore, free -OH groups in the architecture of the cluster facilitate the adsorption of aromatic cationic dye, methylene blue (MB), selectively owing to strong O-H⋯π interactions with good recyclability at ambient pH and temperature. This cluster is a rare example among a few reported discrete units showing structure-property relation for adsorption of MB. The present work opens new doors for designing exotic materials having a tunable magnetocaloric effect (MCE) as well as cationic dye adsorption with notable efficacy and presents the first example of a dual functional material as a coolant and an adsorbent.