Alkaline-earth metal phosphonocarboxylates: Synthesis, structures, chirality, and luminescence properties

Six new alkaline-earth metal carboxyphosphonates [Mg(H₂O)(H ₂PMIDA)] (1), [Sr(H₂O)(H₂PMIDA)] (2), [Sr ₂(H₂O)(PMIDA)] (3), [Sr₂(HPO ₄)(H₂PMIDA)] (4), [Ba₂(HPO₄)(H ₂PMIDA)] (5), and [Ba₂(H₂O)(H ₂PMIDA)₂] (6) (H₄PMIDA = N-(phosphonomethyl) iminodiacetic acid) have been synthesized solvothermally in order to study the coordination behavior of H₄PMIDA towards alkaline-earth metal ions (Mg²⁺, Sr²⁺, and Ba²⁺) and the structural features of the resulting polymeric compounds. The newly synthesized compounds have been characterized by elemental analysis, UV-Vis spectrometry, IR spectroscopy, thermogravimetry analysis, solid state ³¹P MAS NMR, powder X-ray diffraction analysis and single crystal X-ray diffraction techniques. The single crystal structure analysis revealed structural variability of the prepared compounds. Compounds 1, 2, 4 and 5 are three-dimensional with the H₂PMIDA skeletons connecting the inorganic parts to each other, whereas compound 3 has a layered structure. Compounds 2, 4 and 5 contain helical structural motifs. In addition, the extrinsic luminescent properties of Eu(iii)- and Tb(iii)-doped compounds 1, 4 and 5 have also been studied.