Comparison of structural variations of Ln(III) compounds with (pyrazol-1-yl)acetic acid

As a continuation of our previous studies of light lanthanides (La, Ce, Pr, and Nd) with (Pyrazol-1-yl)acetic acid (L), we reacted L with the heavier lanthanides in aqueous solution at pH 5 and synthesized lanthanide complexes of the general formula [Ln(L)3(H2O)2]·H2O (Ln = Eu, 1; Gd, 2; Dy, 3; Ho, 4; Er, 5; Yb, 6; Lu, 7) and [HoL(NO3)2(H2O)3] (8). All complexes were characterized by single crystal X-ray diffraction analysis revealing one-dimensional chain formations. Three distinct crystallographic structures are governed by the different coordination modes of the carboxylate groups in L: terminal bidentate, bridging bidentate and tridentate coordination in 1–3, terminal and bridging bidentate coordination in 4–7, and bridging bidentate coordination in 8. The solid state UV–Vis–NIR diffuse reflectance spectra and the solution UV–Vis–NIR absorption spectra differ, suggesting different coordination environments in solution and solid state. The coordination-induced shifts of the 13C NMR signals for [Lu(L)3(H2O)2]·H2O (7) in D2O show that the carboxylate groups of the ligand are coordinated with the Lu(III) ion in solution.

Graphical abstractA series of lanthanide complexes with (pyrazol-1-yl)acetic acid (L), Ln(L)3(H2O)2]·H2O (Ln = Eu, 1; Gd, 2; Dy, 3; Ho, 4; Er, 5; Yb, 6; Lu, 7) and [HoL(NO3)2(H2O)3] (8), have been synthesized and structurally characterized. Spectroscopic studies of these complexes reveal different coordination in solution and solid state.Figure optionsDownload full-size imageDownload as PowerPoint slide