Crystal structures of two SmIII complexes with dipicolinate [DPA]2− ligands: comparison of luminescent properties of products obtained at different pH values

Abstract

The formation of the two title compounds, Na3[Sm(DPA)3]·14H2O trisodium tris(pyridine-2,6-dicarboxylato-κ3O2,N,O6)samarate(III) tetradecahydrate, Na3[Sm(C7H3NO4)3]·14H2O, and catena-poly[[[diaqua(6-carboxypyridine-2-carboxylato-κ3O2,N,O6)samarium(III)]-μ-pyridine-2,6-dicarboxylato-κ4O2,N,O6:O2] tetrahydrate], {[Sm(C7H3NO4)(C7H4NO4)(H2O)2]·4H2O}n, depends on the pH value adjusted with NaOH solution. In both crystal structures, the coordination spheres of the SmIII cations were found to be best described by a tricapped trigonal prism (TTP), with a more regular O6N3 donor set for Na3[Sm(DPA)3]·14H2O than that of O7N2 for [Sm(DPA)(HDPA)(H2O)2]·4H2O. The supramolecular features of both crystal structures are dominated by O—H...O hydrogen bonds between water molecules and the O atoms of the dipicolinato ligands. Samples were made from solutions at pH = 2, pH = 5, pH = 7, and pH = 10, and the crystals present in each sample were ground to a powder. The powder samples were analyzed with powder X-ray diffraction and luminescence spectroscopy. The splitting of the bands in the luminescence spectra recorded on powders at 77 K was observed to vary with the pH.

Keywords

• crystal structure
• luminescence
• samarium(iii)
• pxrd
• hydrogen bonding