Different coordination environments of iron(III) and pseudopolymorphism in complexes with dipicolinic acid and 2-amino-6-picoline. The influence of molar ratio and solvent type

Three iron(III) compounds of dipicolinic acid (dipicH2) and 2-amino-6-picoline (Hamp-6-pic), formulated as (Hamp-6-pic)[Fe(dipic)2][Fe(dipic)(NO3)(H2O)2]·2H2O (1), (Hamp-6-pic)[Fe(dipic)2]·H2O (2) and {(Hamp-6-pic)[Fe(dipic)2]}2·H2O (3) (Hamp-6-pic+ = 2-amino-6-picolinium), were prepared and characterized by spectroscopic methods (IR and UV–Vis) and their molecular and crystal structures were determined by X-ray crystal structure analysis. Compound 1 was prepared by the reaction of Fe(NO3)3·6H2O with dipicolinic acid and 2-amino-6-picoline in aqueous solution in a molar ratio of 1:1:1, while 2 was obtained by the same reaction but in a molar ratio of 2:2:1. Recrystallization of 2 in a mixture of methanol and ethanol led to the formation of 3. The neutral complex [Fe(dipic)(NO3)(H2O)2] is co-crystallized with (Hamp-6-pic)[Fe(dipic)2] in 1. Fe(III) ion is seven-coordinated (in a distorted pentagonal-bipyramidal geometry) by a tridentate dipicolinate and a bidentate nitrate ion and the coordination is completed by two water molecules in axial positions. Complexes 2 and 3 are examples of pseudopolymorphs which differ in the number of co-crystallized water molecules and in the crystal system (monoclinic (2) or triclinic (3)).

Two Fe(III) complexes, (Hamp-6-pic)[Fe(dipic)2][Fe(dipic)(NO3)(H2O)2]·2H2O (1) and (Hamp-6-pic)[Fe(dipic)2]·H2O (2) (Hamp-6-pic+ = 2-amino-6-picolinium), with different coordination environments of the Fe(III) ions, were prepared by varying the ligand-to-metal molar ratio, and {(Hamp-6-pic)[Fe(dipic)2]}2·H2O (3) was obtained by recrystallization of 2 in a mixture of methanol and ethanol. All the compounds were characterized by spectroscopic (IR and UV–Vis) methods and elemental analysis, whilst their crystal structures were revealed by X-ray structural analysis.Figure optionsDownload as PowerPoint slide