Syntheses, Structure, and Magnetic Properties of New 3d–4f Heterometallic Hydroxysulfates Ln₂Cu(SO₄)₂(OH)₄ (Ln = Sm, Eu, Tb, or Dy) with a Two-Dimensional Triangle Network

A series of 3d–4f hydroxysulfates Ln₂Cu­(SO₄)₂(OH)₄ (Ln = Sm, Eu, Tb, or Dy) have been successfully obtained by the conventional hydrothermal method. These compounds crystallize in the monoclinic system in space group P2₁/c, showing a layered structure. The layers are built by the LnO₉ polyhedra and CuO₄ planar squares, which are separated by SO₄^2– tetrahedra. The topological structure of Sm³⁺ ions shows a distorted honeycomb lattice, while Cu²⁺ ions are located at the center of a honeycomb framework forming a triangle lattice. Magnetic measurements reveal that the isostructural Ln₂Cu­(SO₄)₂(OH)₄ exhibits different magnetic behaviors at low temperatures, which may be attributed to the different contribution of 3d–4f couplings.