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)]·H2On(1), [Nd(stp)(bipy)(H2O)]·2H2On(2), and [Sm(stp)(bipy)(H2O)]·H2On(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.