Layered Rare-Earth Hydroxides Intercalated with Metal Complexes: Copper Malonates Make a Difference

Malonate ligands demonstrate versatility for intercalating metal complexes into layered rare-earth hydroxides (LREHs), enabling controlled tuning of coordination geometry and composition. As a proof of concept, a series of copper(II) malonate complexes with various substituents was synthesized and successfully intercalated into layered yttrium, europium, or terbium hydroxide at room temperature via anion-exchange reactions. The copper content in these hybrid materials increased in the order: butylmalonate < benzylmalonate < cyclopropanedicarboxylate < dimethylmalonate. To further expand the range of accessible metal malonate complexes, dimethyl- and benzylmalonate anions were intercalated into layered yttrium hydroxide for the first time and subsequently metalated in situ, yielding well-defined Cu²⁺ species within the interlayer space without disrupting the host lattice. Density functional theory (DFT) calculations provided insight into the structural arrangements of the copper complexes in the interlayer galleries. Comprehensive characterization of the resulting materials by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), IR, UV-vis, and electron paramagnetic resonance (EPR) spectroscopy confirmed both the successful formation of hybrid structures and elucidated the coordination environment of the intercalated copper species.