Synthesis, structure and magnetic properties of two selenites, Li2Mn2.5(SeO3)4 and Li2Co3(SeO3)4 with a one-dimensional spin-chain

Two transition metal selenites Li 2 Mn 2.5 (SeO 3 ) 4 and Li 2 Co 3 (SeO 3 ) 4 were synthesized using hydrothermal and solid-state reactions, respectively. Both compounds form similar three-dimensional (3D) frameworks featuring twisted one-dimensional (1D) chains, where transition metal polyhedra connect through shared corners or edges. However, Li 2 Co 3 (SeO 3 ) 4 and Li 2 Mn 2.5 (SeO 3 ) 4 exhibit distinct structural features. The former contains one type of [4 + 2] Li, two different CoO 6 octahedra, and two SeO 3 pyramids. The latter possesses one type of [5 + 1] Li, one Mn 3+ O 6 octahedron, one Mn 2+ O 5 square-pyramid, and two SeO 3 pyramids. Consequently, the lithium polyhedron undergoes unusually strong irregular distortions in the cobalt compound, but experiences strong distortions in the manganese compound. Magnetic measurements confirm that Li 2 Co 3 (SeO 3 ) 4 with a S  = 3/2 uniform spin chain structure possess a long-range antiferromagnetic ordering and field-induced spin-flip transition at 2K, where the fitting via the Bonner–Fisher model with interchain mean-field corrections yields J intra /k B  = -4.32(2) K, J inter /k B  = −0.64(10) K, g  = 2.34(3). Systematic distortion regularities in central metal cation polyhedra emerge from quantifying the ratio of SeO 3 groups to total cation polyhedra within lithium transition metal selenites.