Two new neutral thioantimonates(III) were first prepared by the reaction of elemental manganese, antimony, and sulfur in tren (tren = tris(2-aminoethyl)amine, C6H18N4) at 140 degreesC. In the amine-rich compound [Mn(tren)](2)Sb2S5 (1) the trigonal SbS3 pyramids are connected via common corners (S(3)) into the tetradentate [Sb2S5](4-) anion. Four S atoms have bonds to the manganese atoms of the [Mn(tren)(2+)] cations. A special structural feature is the large Sb-S(3)-Sb(a) angle of 134degrees. Density functional calculations clearly demonstrate that this large angle results from the steric interactions between the two Mn(tren) subunits. In the crystal structure of the amine-poorer compound [Mn(tren)](2)Mn2Sb4S10 (2), MnS4 tetrahedra and SbS3 pyramids are linked via common corners and edges to form a new heterometallic [Mn2Sb4S10] core. The [Mn(C6H18N4)(2+)] cations are located at the periphery of the core and are bound to the [Mn2Sb4S10] unit via two S atoms. The thermal behavior of both compounds was investigated using simultaneous thermogravimetry (TG), differential thermoanalysis, and mass spectroscopy. The amine-richer compound 1 decomposes in three steps upon heating. After the first TG step an intermediate phase is formed, which was identified as the amine-poorer compound 2 by X-ray diffraction. Reaction of compound 2 at 140 degreesC with an excess of tren forms the amine-rich compound 1.