Convenient crystal growth, structural determination and magnetic studies of layered copper hydroxides containing aromatic sulfonates

Abstract

Single crystals of layered copper hydroxides, 1–4, with aromatic sulfonate ions, p-toluenesulfonate, p-ethylbenzenesulfonate, 1-naphthalenesulfonate and 1,5-naphthalenedisulfonate, respectively, were conveniently prepared by hydrolysis of aqueous copper acetate solutions containing the organic sulfonates. X-ray structure analyses revealed that these compounds had alternating stacks of copper hydroxide layers and aggregated layers of the organic ions. The atomic alignment of their copper hydroxide layers was similar to that of the inorganic layer of hydrotalcite, [Mg₆Al₂(OH)₁₆]·CO₃·16H₂O. However, their copper hydroxide layers were not isostructural among 1–4. In the copper hydroxide layers, not only hydroxide ions but also water molecules, acetate ions or the organic sulfonate ions were coordinated to the copper ions. The copper ions exhibited an elongated octahedral geometry in 1 and 2, and an elongated octahedral or square pyramidal geometry in 3 and 4. The organic ions formed a bilayer arrangement in 1 and 2, and a monolayer arrangement in 3 and 4. Magnetic measurements revealed primarily antiferromagnetic interactions between neighbouring copper ions. The magnetic behaviours of these materials resembled the antiferromagnetic ordering behaviour at low temperatures. The maximum values of χ_p were observed at 3.8 K, 3.5 K, 3.2 K and 9.1 K for 1–4, respectively. The exchange coupling constants were estimated from an S = 1/2 Heisenberg model with a two-dimensional triangular lattice magnetic network, where J/k_B = 42.2 K, 36.8 K, 80.1 K and 84.9 K for 1–4, respectively. The magnetic differences in these materials are due to the structural differences in their copper hydroxide layers. Thus, it was demonstrated that hydrolysis methods are suitable for the preparation of single crystals of various copper hydroxide derivatives with organic anions.