Syntheses and magnetic properties of new tellurite-sulfate compounds M2(TeO3)(SO4)·H2O (M = Co, Mn) with a layer structure showing a distorted honeycomb spin-lattice

Anhydrous copper tellurite disulfate Cu3TeO3(SO4)2 featuring the coexistence of spin singlets and a long-range antiferromagnetic order

Anhydrous copper tellurite sulfate, Cu₃TeO₃(SO₄)₂, has been synthesized via vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization M, magnetic susceptibility χ, specific heat C_p and X-band electron spin resonance, a long-range antiferromagnetic order at T_N = 13 K and an H-T magnetic phase diagram have been established. One-third of Cu²⁺ ions were found to form magnetically silent dimers. A peak in dielectric permittivity ε, which accompanies the Néel order, allows considering Cu₃TeO₃(SO₄)₂ as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters.

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.

A Large Family of Centrosymmetric and Chiral f-Element-Bearing Iodate Selenates Exhibiting Coordination Number and Dimensional Reductions

The exploration of phase formation in the f-element-bearing iodate selenate system has resulted in 14 novel rare-earth-containing iodate selenates, Ln(IO₃)(SeO₄) (Ln = La, Ce, Pr, Nd; LnISeO-1), Ln(IO₃)(SeO₄)(H₂O) (Ln = Sm, Eu; LnISeO-2), and Ln(IO₃)(SeO₄)(H₂O)₂·H₂O (Ln = Gd, Dy, Ho, Er, Tm, Yb, Lu, Y; LnISeO-3), as well as two new thorium iodate selenates, Th(OH)(IO₃)(SeO₄)(H₂O) (ThISeO-1) and Th(IO₃)₂(SeO₄) (ThISeO-2). LnISeO-3 and ThISeO-2 crystallize in the chiral space group P2₁2₁2₁, while LnISeO-1, LnISeO-2, and ThISeO-1 crystallize in the centrosymmetric space group P2₁/c. The numbers of both coordinating and hydrating water molecules crystallized in LnISeO-1, LnISeO-2, and LnISeO-3 increase along these three series, in line with the increasingly negative values of hydration enthalpies of heavier trivalent lanthanide ions. Such a systematic change in compositions, especially the first coordination sphere of Ln, further induces structural rearrangements, including coordination number and dimensional reductions. More specifically, the structures of LnISeO-1, LnISeO-2, and LnISeO-3 have undergone transitions from 2D Ln-oxo layers with 10-coordinate Ln centers to 1D Ln-oxo chains with 9-coordinate Ln centers and then to 0D Ln-oxo monomers with 8-coordinate Ln centers, respectively. The formation and characterization of this large family of Ln/Th iodate selenates suggest that such a mixed-anion system not only exhibits richer structural chemistry but also can be capable of generating intriguing properties, such as the second-harmonic generation (SHG) effect.