Synthesis and Magnetic Properties of the KCu(IO₃)₃ Compound with [CuO₅]_∞ Chains

The new quaternary iodate KCu(IO₃)₃ has been prepared by hydrothermal synthesis. KCu(IO₃)₃ crystallizes in the monoclinic space group P2₁/n with unit cell parameters a = 9.8143(4) Å, b = 8.2265(4) Å, c = 10.8584(5) Å, β = 91.077(2)°, and z = 4. The crystals are light blue and translucent. There are three main building units making up the crystal structure: [KO₁₀] irregular polyhedra, [CuO₆] distorted octahedra, and [IO₃] trigonal pyramids. The Jahn-Teller elongated [CuO₆] octahedra connect to each other via corner sharing to form [CuO₅]_∞ zigzag chains along [010]; the other building blocks separate these chains. The Raman modes can be divided into four groups; the lower two groups into mainly lattice modes involving K and Cu displacements and the upper two groups into mainly bending and stretching modes of [IO₃E], where E represents a lone pair of electron. At low temperatures, the magnetic susceptibility is characterized by a broad maximum centered at ∼5.4 K, characteristic for antiferromagnetic short-range ordering. Long-range magnetic ordering at T _C = 1.32 K is clearly evidenced by a sharp anomaly in the heat capacity. The magnetic susceptibility can be very well described by a spin S = 1/2 antiferromagnetic Heisenberg chain with a nearest-neighbor spin exchange of ∼8.9 K.