From One-Dimensional Linear Chain to Two-Dimensional Layered Chalcogenides XBi4S7 (X = Mn, Fe): Syntheses, Crystal and Electronic Structures, and Physical Properties

Two ternary-layered chalcogenides, MnBi4S7 (1) and FeBi4S7 (2), have been synthesized by using a conventional solid-state reaction method with sealed evacuated quartz tubes. The two isostructural compounds crystallize in the monoclinic space group C2/m (12), with unit cell parameters (1/2) a = 12.916(12)/12.823(19) Å, b = 3.970(3)/3.987(6) Å, c = 11.0397(15)/11.878(18) Å, β = 104.755(14) /104.38(2), and Z = 2 at room temperature. The remarkable structural features of these are the one-dimensional Heisenberg antiferromagnetic (1D HAF) chain, 1 ∞[XS6], and the two-dimensional [Bi2S3] and [MBi2S4] layers built up from the 1D 1 ∞[XS6] chain, 1 ∞[BiS6], and 1 ∞[BiS5] double chains. Magnetic property measurements indicate strong predominance of antiferromagnetic (AFM) interactions, with Néel temperatures (T N) of 31 K for 1 and 67 K for 2, respectively. The density functional theory (DFT) study indicates that both compounds are indirect-band semiconductors with band gaps of 0.79 eV for 1 and 1.24 eV for 2, respectively.