Synthesis, crystal growth, and optical and magnetic properties of three bimetallic thiocyanates TBi(SCN)5 (T = Mn, Cd) and FeBi(SCN)6

Abstract

In this work, we report the synthesis, crystal growth, and optical and magnetic properties of two new isotypic bimetallic thiocyanates, MnBi(SCN)₅ and CdBi(SCN)₅. The crystal structure of MnBi(SCN)₅ and CdBi(SCN)₅ was determined by single-crystal X-ray diffraction. MnBi(SCN)₅ and CdBi(SCN)₅ crystallize in the triclinic space group P (no. 2) with unit cell parameters of a = 8.0498(5) Å, b = 9.2749(5) Å, c = 10.7779(8) Å, α = 72.752(6)°, β = 68.422(6)°, γ = 87.908(5)° and a = 8.1528(5) Å, b = 9.4008(7) Å, c = 10.9513(8) Å, α = 73.212(6)°, β = 67.963(6)°, γ = 87.879(6)°, respectively. The structure of MnBi(SCN)₅ and CdBi(SCN)₅ contains a three-dimensional (3D) network consisting of pairs of edge-sharing [TN₆] (T = Mn, Cd) octahedra linked through the thiocyanate ligand to similar pairs of edge-sharing [BiS₆] octahedra. A known related structure to this is that of FeBi(SCN)₆, which features a perovskite-like structure consisting of corner-sharing [FeN₆] and [BiS₆] octahedra. In this work, the magnetic properties of MnBi(SCN)₅ and the previously reported FeBi(SCN)₆ were investigated, with the former being found to order antiferromagnetically with a Néel temperature around 12 K. FeBi(SCN)₆ was found to exhibit no magnetic ordering down to 2 K, although isothermal magnetization data indicate that it may order ferromagnetically below 2 K. Density functional theory (DFT) was also employed to explore the electronic structure of MnBi(SCN)₅, which reveals that the Bi–S and Mn–N interactions are crucial for controlling the optical properties of MnBi(SCN)₅. MnBi(SCN)₅ was predicted to be an indirect-gap semiconductor with a bandgap of 2.7 eV, which was reasonably consistent with the UV-vis spectrum measurement of 2.1 eV.