Benzene Trisulfonic Acid (H3BTS) as Analogue of Trimesic Acid for Building Open Frameworks: The First Rare Earth Examples [La(BTS)(H2O)5] and [RE(BTS)(H2O)4] (RE = Nd,Sm, Eu)

The reaction of benzene 1,3,5‐trisulfonic acid (H₃BTS) with the hydroxides RE(OH)₃ (RE = La, Nd, Sm, Eu) in aqueous solution afforded the sulfonates [La(BTS)(H₂O)₅] and [RE(BTS)(H₂O)₄] (RE = Nd, Sm, Eu). Single crystal investigations were performed for the lanthanum and the europium compound, respectively. [La(BTS)(H₂O)₅] is triclinic [P$bar{1}$ , Z = 2, a = 783.18(6) pm, b = 1056.94(8) pm, c = 1082.38(8) pm, α = 114.860(2)°, β = 96.655(3)°, γ = 104.402(3)°] whereas [Eu(BTS)(H₂O)₄] exhibits monoclinic symmetry [P2₁/n, Z = 4, a = 767.61(5) pm, b = 1730.2(1) pm, c = 1134.06(8) pm, β = 108.375(8)°]. Despite these crystallographic differences, the structural features of the lanthanum and europium compounds are very similar. They show the metal ions connected by BTS anions to layers that are further linked by hydrogen bonds. Interestingly, only two of the three sulfonate groups are connected to rare earth ions, whereas the third remains uncoordinated and acts as acceptor within the hydrogen bonds. According to powder XRD measurements the neodymium and samarium sulfonates are isotypic with the europium compound. The thermal analyses of the compounds show the dehydration in a temperature range between 100 and 300 °C, whereas the decomposition of the organic ligands takes place at temperatures as high as 550 °C. Thus the anhydrous sulfonates are much more stable than comparable salts of trimesic acid. The residues of the thermal decompositions were identified by XRD experiments.