Structural variations of praseodymium(III) benzoate derivative complexes with dimethylformamide

Eight- or nine-coordinated trivalent praseodymium complexes derived from para-substituted benzoic acids have been synthesized by the reaction of hydrated Pr(OH)₃ with 4-XC₆H₄CO₂H, where X = OMe, H, Cl, NO₂, OH, NH₂ or F, in dimethylformamide [DMF, (CH₃)₂NCHO], and eight single crystal X-ray structures have been determined. For the substituted systems studied, dimeric units hydrogen-bonded into chains or networks are observed in complexes comprising electron-donating groups X, whereas electron-withdrawing groups X form polymeric complexes. However, the steric effect of the ligand and the coordination of solvated molecules also play roles in determining the coordination polyhedra. The coordination geometry of the carboxylate ligand in these complexes is restricted to three types: bidentate chelating (η²); bridging bidentate (μ-η¹:η¹ (O,O′)) and bridging chelating tridentate (μ-η²:η¹). Two geometrical isomers, of [Pr(C₆H₅COO)₃(DMF)(H₂O)]₂, designated as a and b, crystallize in the same monoclinic space group but differ in the arrangement of C₆H₅COO and DMF ligands in their coordination polyhedra. The packing of isomer a is more efficient than that of b, resulting in a smaller unit-cell volume of about 50 ų. Although functional group fingerprints from the p-substitution moieties are well-identified in the vibrational spectra of the complexes, reasons are provided to explain why the correlation between carboxyl group ligation and spectra cannot be readily made. Copyright © 2014 Elsevier Ltd.