A new modification of MnSb 2 S 4 was synthesized by solid state reaction of MnS, and Sb 2 S 3 at 500 C. The monoclinic, purple-red compound crystallizes in the HgBi 2 S 4 structure type. Single crystal measurements provided the space group C2/m (no. 12) with a 12.747 (3) A, b 3.799(1) A, c 15.106(3) A, b 113.91(3) , V = 668.7(3) A 3 , and Z 4. The refinement converged to R 0.0403, and wR2 0.1001 for 913 unique reflections and 46 parameters. The crystal structure of MnSb 2 S 4 (mC28) consists of strands of edge-sharing octahedra [MnS 6 ] which are interlinked to layers by distorted square pyramids [SbS 5 ] (d(Sb± ±S) < 3.1 A).MnSb 2 S 4 (mC28) shows a greater distortion of the [Sb± ±S] polyhedra as compared to the [Bi± ±S] polyhedra in analogous MnBi 2 S 4 . This is due to an enhanced stereochemical influence of the lone electron pair of Sb 3 . Raman spectra of MnSb 2 S 4 (mC28) are dominated by n Sb± ±S stretching modes at 300 cm À1 , and at 283 cm À1 , respectively.

The two novel compounds, [Mn(tren)]Sb2S4 (1 and 2), were obtained by the reaction of elemental Mn, Sb, and S in aqueous solutions of tren (tren = tris(2-aminoethyl)amine, C6H18N4) after different reaction times. Compound 1 is formed up to a reaction time of 13 d, and an extension of the reaction time leads to the formation of 2. Both compounds crystallize in monoclinic space groups (1, P2(1)/c; 2, C2/c). In 1, the two unique SbS3 trigonal pyramids share a common S atom to form a Sb2S5 unit. Two S atoms of this group have a bond to Mn2+ yielding a MnSb2S3 heteroring in the boat conformation. The Sb2S5 moieties are joined via common corners into the final undulated [Sb2S4]2- anion which is directed along [001]. The structure of 2 contains the [Mn(tren)]2+ ion, one SbS3 pyramid, and a SbS4 unit. Two symmetry-related SbS4 groups share an edge, forming a Sb2S6 group containing a Sb2S2 ring. This group is joined via corners to two SbS3 pyramids on both sides producing a Sb4S4 ring. The Sb2S2 and Sb4S4 rings are condensed into the final [Sb2S4]2- anion which runs along [010]. The [Mn(tren)] groups are bound to the thioantimonate(III) backbone on opposite sides of the Sb4S4 ring, and a small MnSbS2 ring is formed. In both structures, weak S...H bonds are found which may contribute to the stability of the materials. The two compounds decompose in one step upon heating, and only MnS and Sb2S3 could be identified as the crystalline part of the decomposition products. Both compounds can also be prepared under solvothermal conditions using MnSb2S4 as starting material. Compounds 1 and 2 are obtained from this ternary material in a high yield.

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The electronic band structures of orthorhombic ͑oP28͒ and monoclinic ͑mC28͒ MnSb 2 S 4 were investigated with ab initio calculations in the local spin density approximation to the density functional theory. An analysis of the electronic properties and of the chemical bonding is provided using the augmented spherical wave method considering nonmagnetic, ferromagnetic, ferrimagnetic, and antiferromagnetic model orderings. In agreement with experimental results both modifications of MnSb 2 S 4 are predicted to be antiferromagnetic. While the experimental band gap is missed for the monoclinic polymorph, the calculated band gap for orthorhombic MnSb 2 S 4 is close to the experimental one.