The title compound Mn(3)Sb(2)S(6)(C(6)H(18)N(4)) (C(6)H(18)N(4) = triethylenetetramine) was obtained under solvothermal conditions by reacting Mn, Sb, S, and the amine at 140 degrees C for 7 days. The compound crystallizes in the triclinic space group P1 with a = 6.645(1) A, b = 8.667(1) A, c = 9.660(1) A, alpha = 90.82(2) degrees , beta = 109.70(2) degrees , gamma = 110.68(2) degrees , Z = 1, and V = 484.4(1) A(3). The Mn(4)Sb(2)S(6) double-heterocubane unit is the main motif in the structure of the title compound, which results from the interconnection of two SbS(3) trigonal pyramids, two MnS(6) octahedra, and two MnS(4)N(2) octahedra. The two N atoms completing the environment of the latter Mn(2+) ions belong to the tetradentate amine; i.e., the amine acts in a bidentate manner. The Mn(4)Sb(2)S(6) groups are joined by corner sharing of the MnS(6) octahedra, yielding one-dimensional linear Mn(3)Sb(2)S(6) rods along [100]. The two other N atoms of the amine molecule act in a bidentate manner to Mn(2+) ions of neighboring rods, thus producing layers within the (010) plane. Within the rods, the arrangement of the Mn(2+) ions in triangles leads to a chain of Mn(2+) diamonds connected via opposite corners. For the magnetic properties, each edge connecting the Mn(2+) ions represents a superexchange path due to coupling of the Mn(2+) centers via S bridges. The resulting Mn(2+) triangles give rise to substantial competing interaction and magnetic frustration. Below about 100 K, a gradual buildup of short-range antiferromagnetic correlations is observed. At lower temperatures, long-range antiferromagnetic interactions occur with T(N) = 2.90 K, as indicated by a lambda-type anomaly in the heat capacity curve. The analysis of the magnetic and heat capacity data evidences that the magnetic properties are essentially determined by the one-dimensional character of the Mn(3)Sb(2)S(6) chain. In addition, significant magnetic frustration due to the arrangement of the Mn(2+) ions in a triangular configuration cannot be neglected.