title: Stereospecificity in vanadium Schiff base complexes: Formation, crystallization and epimerization processes.
abstract: The structures of two stereoisomers of the chiral anion [VO2(N-salicylidene-isoleucinato)](-) possessing three centers of chirality, the vanadium atom (configuration A/C) and the isoleucine moiety (configuration R/S on alpha and beta carbons), are presented. The absolute configuration of all available stereosiomers, CSS, ARR, CSR and ARS, was determined by electronic circular dichroism (ECD), which allows distinguishing between diastereomers, and by vibrational circular dichroism (VCD) capable of differentiating between all four stereoisomers. The comparison of experimental VCD and infrared (IR) spectra with simulated spectra for band assignment revealed the IR spectra of the diastereomers differing significantly in the CH stretching region of the aromatic part in the molecule. Crystallization from binary systems composed of equal ratio of two stereoisomers of isoleucine, unveiled the lower solubility of CSS and ARR stereoisomers, while a longer crystallization time of the CSR and ARS stereoisomers allowed proceeding the vanadium-catalyzed epimerization, leading to the subsequent presence of the CSS and ARR stereoisomers in the product obtained.
authors: Department of Inorganic Chemistry, Comenius University, Faculty of Natural Sciences, Mlynská dolina, 842 15 Bratislava, Slovakia. Electronic address: krivosudskyl@fns.uniba.sk.
authors: Lukáš
authors: L
authors: Krivosudský
authors: Department of Inorganic Chemistry, Comenius University, Faculty of Natural Sciences, Mlynská dolina, 842 15 Bratislava, Slovakia.
authors: Peter
authors: P
authors: Schwendt
authors: Department of Inorganic Chemistry, Comenius University, Faculty of Natural Sciences, Mlynská dolina, 842 15 Bratislava, Slovakia.
authors: Ján
authors: J
authors: Šimunek
authors: Department of Chemistry, Faculty of Education, J. Selye University, Bratislavská cesta 3322, 945 01 Komárno, Slovakia; Department of Inorganic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 43 Praha 2, Czech Republic.
authors: Róbert
authors: R
authors: Gyepes
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D007536:Isomerism; D012545:Schiff Bases / Q000737:chemistry*; D014639:Vanadium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D012545:Schiff Bases; D014639:Vanadium
keywords: Absolute configuration; Circular dichroism; Infrared spectroscopy; Isoleucine; Schiff bases; Vanadium complexes