The syntheses, structures and properties of three new lanthanoid thioarsenates: the only example of thioarsenate acting as a ligand to a lanthanide complex.

Three new lanthanoid thioarsenates [Eu(en)3(η²-AsS4)] (1, en = ethylenediamine), [Er(teta)(en)(η²-AsS4)] (2, teta = triethylenetetramine) and [La2(tepa)2(µ-η¹,η³-AsS3)2] (3, tepa = tetraethylenepentamine) have been solvothermally synthesized and structurally characterized. In compounds 1 and 2, the tetrathioarsenate [AsS4]³â» anions act as η²-AsS4 chelating ligands to the lanthanide complexes [Eu(en)3]³âº/[Er(teta)(en)]³âº, leading to neutral molecules [Eu(en)3(η²-AsS4)]/[Er(teta)(en)(η²-AsS4)], whereas the [AsS3]³â» anion in compound 3 acts as a µ-η¹,η³-AsS3 tetradentate bridging ligand to link [La(tepa)]³âº ions into neutral centrosymmetric [La2(tepa)2(µ-η¹,η³-AsS3)2] moieties, where a new coordination mode of µ-η¹,η³-AsS3 is observed for the [AsS3]³â» ligand. Compounds 1-3 are the only examples of solvothermally synthesized thioarsenates where the [AsS4]³â»/[AsS3]³â» anions act as ligands in the lanthanide complex. Compound 1 exhibits a fluorescence emission at room temperature. Density functional theory calculations for compounds 2 and 3 also have been performed, and the absorption edges of compounds 1-3 have been investigated by UV-vis spectroscopy.