New metal chalcogenides found in Mn_N-1(Gd_2-xIn_x)S_N+2 (N = 3, 4, 5): syntheses, structures, and magnetic properties

Three new metal chalcogenides have been identified in Mn_N-1(Gd_2-xIn_x)S_N+2 with N = 3, 4, and 5 via a flux-growth synthesis. All compounds crystallize in the same space group of orthorhombic Cmcm with cell constants: Mn₂GdInS₅ (1), a = 3.789(1) Å, b = 12.411(1) Å, and c = 15.489(1) Å; Mn₃Gd₂S₆ (2), a = 3.778(1) Å, b = 12.505(2) Å, and c = 19.114(2) Å; Mn₄Gd₂S₇ (3), a = 3.769(1) Å, b = 12.466(2) Å, and c = 22.289(3) Å. Compounds 1-3 form a homologous series through the modulation of the MnS unit, whose structures represent a complete system of the corresponding lillianites (^N1,N2L) of ^3,3L, ^4,4L and ^5,5L. The gradually wider slabs formed in the series result in a monotonic increase along the c dimensions from 1 to 3. Crystal 3 is the first to achieve a predicted structure of ^5,5L. Mn₂GdInS₅ (1) displays a weak antiferromagnetic (AFM) ordering at 10 K and the Weiss constant (θ) of -0.76 K. Mn₂Gd_1.5In_0.5S₅ (1a), an isostructure of 1, shifts the AFM transition temperature to 12 K and possesses a slightly larger θ constant of -6.06 K. Mn₄Gd₂S₇ (3), featuring the thickest slabs in this series, shows a significant antiferromagnetic behavior beginning at a high temperature of 70 K and has a largest θ constant of -40.25 K. A small amount of impurity α-Gd₂S₃ with an AFM transition temperature around 4 K was characterized in sample 3, which does not interfere with the magnetic ordering of 3 at much higher temperatures. These magnetic chalcogenides display band gaps of 1.66 eV for 1, 1.75 eV for 1a, and 1.44 eV for 3.