Gadolinium chloride hexahydrate and its intercalation into synthetic saponite: structure, characterization and slow magnetic relaxation of the intercalated sample

Abstract

The intercalation of [Gd(H₂O)₆Cl₂]⁺ cations into synthetic saponite (Sap) was investigated via direct exchange of the sodium ions by the complex cation along with chloride anions. The final intercalated sample (Gd-Sap) was characterized using powder X-ray diffraction, thermogravimetric analysis, and also, for the first time, magnetic measurements. The results reveal that during the intercalation procedure, the chlorido ligands surrounding the central Gd(III) atom were released from its coordination sphere and associated with Na⁺ cations in the solution. Furthermore, a significant increase in the d₀₀₁ value of the intercalated saponite and its EDX spectra confirmed the presence of the hydrated Gd³⁺ ions in the Sap interlayers. The thermal stability of the intercalated sample containing Gd³⁺ ions was lower than that of the initial [Gd(H₂O)₆Cl₂]Cl complex (1). DC and AC magnetic study of the Gd-Sap sample revealed slow magnetic relaxation with two relaxation channels. X-ray single crystal structure analysis of 1 was conducted at two temperatures (173 and 293 K) and confirmed its ionic character. The central Gd(III) atom exhibited slightly deformed square antiprismatic coordination with an O₆Cl₂ donor set. The formation of the supramolecular assembly is controlled by hydrogen bonds of an O–H⋯Cl nature. The investigation of static magnetic response is consistent with that of a S = 7/2 Heisenberg magnet with small single-ion anisotropy and weak antiferromagnetic magnetic coupling. The magnetic relaxation is found to be mediated by a combination of two relaxation processes. The slow process is determined by transitions among various energy levels in a multilevel spin system induced by the lattice degrees of freedom, whereas the fast process is tentatively ascribed to the phonon bottleneck effect.