Synthesis and Characterization of Anionic Lanthanide(III) Complexes with a Bidentate Sulfonylamidophosphate (SAPh) Ligand

A series of new anionic lanthanide­(III) complexes with the general formula NEt4[LnL4] (1-Ln; HL = dimethyl­[(4-methylphenyl)­sulfonyl]­amidophosphate; Ln = La, Nd, Eu), were synthesized and characterized by IR, UV–vis, and NMR spectroscopies, the differential scanning calorimetry method, thermogravimetric and X-ray analysis, and photoluminescence measurements. Single-crystal structures of NEt4[EuL4] (1-Eu) were determined at 293 and 100 K and evidenced the single-crystal-to-single-crystal phase transition. Both phases are in the monoclinic crystal system in centrosymmetric groups of the same Laue class. The room temperature structure is in C2/c (No. 15), while low-temperature structure is in the P21/c (No. 14) space groups. The coordination environment geometry around the central europium­(III) ion is a distorted square antiprism in both polymorphs, while the peripheral methoxy and tolyl groups show different orientations. This phenomenon indicates the occurrence of a thermally driven second-order phase transition during the cooling–heating process. The europium­(III) complex exhibits an unusual emission spectrum, clearly dominated by the 5D0–7F4 bands, and an emission decay time equaling 3.5 ms, being among the highest values known for europium coordination compounds