Two new lanthanide thioantimonates, [Pr(en) 3 (H 2 O)(l 2 -SbS 4 )] and [Gd(en) 4 ]SbS 4 AE0.5en (en = ethylenediamine), were synthesized using the solvothermal method by reacting LnCl 3 , Sb and S in en at 160 °C. The crystal structure of 1 consists of a one-dimensional [Pr(en) 3 (H 2 O)(l 2 -SbS 4 )] 1 neutral chain, in which the SbS 4 3À anion act as a bridging ligand to connect [Pr(en) 3 (H 2 O)] 3+ ions. The Pr 3+ ion is in a nine coordination geometry involving six nitrogen atoms of three bidenate en ligands, two sulfur atoms of two different SbS 4
3À anions, and an oxygen atom of one water molecule to form a distorted monocapped square antiprism. The crystal structure of 2 contains an isolated bicapped trigonal prism complex cation [Gd(en) 4 ] 3+ , a tetrahedral anion SbS 4 3À and half a free en molecule in the asymmetric unit. The structural difference between the two thioantimonates is related with the stability of Pr 3+ and Gd 3+ complexes with en ligands. The band gaps of 2.35 eV for 1, and 3.21 eV for 2 have been derived from optical absorption spectra. Thermogravimetric measurements show that both compounds decompose in two steps in the nitrogen stream.