Structural elucidation, EPR and magnetic interpretation of lanthanide (Ln = La, Nd, Sm) compounds with 4,4′-bipyridine and 2-sulfoterephthalate

A series of three lanthanide compounds, namely, {[La(stp)(bipy)(H₂O)]·H₂O}_n(1), {[Nd(stp)(bipy)(H₂O)]·2H₂O}_n(2), and {[Sm(stp)(bipy)(H₂O)]·H₂O}_n(3) has been synthesized through the reaction of 2-sulfoterephthalic acid monosodium salt Na(H₂stp), trivalent lanthanide nitrate [Ln(NO₃)₃·6H₂O] and N-donor ancillary co-ligand, 4,4′-bipyridine (bipy). As a result of the potential coordination modes of the stp ligand and the bipy co-ligand, the aforementioned compounds are arranged in a 2-D network, as evidenced by single-crystal X-ray diffraction technique. In all the three compounds, the Ln ion presents a distorted tricapped trigonal-prismatic coordination geometry. The EPR measurements evidence a diamagnetic behaviour of compound 1 (La³⁺) whereas there exhibits a weak antiferromagnetic coupling between paramagnetic Ln³⁺ions (Nd³⁺and Sm³⁺) for compounds 2 and 3. This is also supported by the magnetic data obtained for compounds 1–3. The encapsulation of the lanthanide coordination polymers displays a moderate luminescent property.