New lanthanide thioantimonate(V) compounds, [Ln(en)(3)(H2O)(x)(mu(3-x)-SbS4)] (en = ethylenediamine, Ln = La, x = 0, Ia; Ln = Nd, x = 1, Ib) and [Ln(en)(4)]SbS(4)(.)0.5en (Ln = Eu, IIa; Dy, IIb; Yb, IIc), were synthesized under mild solvothermal conditions by reacting Ln(2)O(3), Sb, and S in en at 140 degrees C. These compounds were classified as two types according to the molecular structures. The crystal structure of type I (Ia and Ib) consists of one-dimensional neutral [Ln(en)(3)(H2O)(x)(mu(3-x)-SbS4)](infinity) (x = 0 or 1) chains, in which SbS43- anions act as tridentate or bidentate bridging ligands to interlink [Ln(en)(3)](3+) ions, while the crystal structure of type II (IIa, IIb, and IIc) contains isolated [Ln(en)(4)](3+) cations, tetrahedral SbS43- anions, and free en molecules. A systematic investigation of the crystal structures of the five lanthanide compounds, as well as two reported compounds, clarifies the relationship between the molecular structure and the entity of the lanthanide(III) series, such as the stability of the lanthanide(III)-en complexes, the coordination number, and the ionic radii of the metals.