Structural Complexity and Magnetic Orderings in a Large Family of 3d–4f Heterobimetallic Sulfates

The synthesis of a large family of heterobimetallic lanthanide copper sulfates was realized via stoichiometric hydrothermal reactions among Ln₂O₃, CuO, and H₂SO₄, giving rise to four distinct phases, namely Ln₂Cu­(SO₄)₂(OH)₄ (Ln = Sm–Ho) (LnCuSO₄-1), Ln₄Cu­(SO₄)₂(OH)₁₀ (Ln = Tm–Lu) (LnCuSO₄-2), LnCu­(SO₄)­(OH)₃ (Ln = Nd–Gd, except Pm) (LnCuSO₄-3), and LnCu­(SO₄)­(OH)₃ (Ln = Dy–Lu) (LnCuSO₄-4), with completely different topologies. The passage from LnCuSO₄-1 and LnCuSO₄-3 to LnCuSO₄-2 and LnCuSO₄-4 across the 4f series, respectively, can be ascribed to the effect of lanthanide contraction, which progressively induces shrinking of the Ln–O distance, reduction in the Ln coordination number, and eventually structural transitions. The incorporation of identical 3d–4f metal ions into different spin–lattices, in conjunction with substitution of diverse Ln³⁺ cations within the same spin–lattice, gives rise to tunable magnetic properties varying from ferromagnetic ordering in GdCuSO₄-3 and HoCuSO₄-4 to antiferromagnetic ordering in YbCuSO₄-4, and to paramagnetic correlations found in GdCuSO₄-1 and YbCuSO₄-2.