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.