Stereospecific formation of vanadium mandelato complexes with [Fe(2,2′-bipyridine)3]2+ as a counter ion

Abstract

Two vanadium complexes of mandelic acid having [Fe(bpy)3]2+ as counterion, [Fe(bpy)3][V2O4(rac-mand)2]·4.9H2O·0.1CH3CN (1, FeV2L2) and (H3O)[Fe(bpy)3]4[V3O7(S-mand)2]3·28H2O (2, FeV3L2) (bpy = 2,2’-bipyridine, mand2– = mandelato ligand, C8H6O32–) have been synthesized and characterized by single crystal X-ray diffraction and spectral methods. The FeSO4—bpy—KVO3—H2mand—H2O—CH3CN system exhibits a stereospecific behaviour: while from the system including racemic mandelic acid only the complex of the V2L2 type (1) could be obtained in crystalline form, the system with S-mandelic acid afforded the V3L2 (2) complex as the single crystalline product. All vanadium atoms exhibit tetragonal pyramidal coordination geometry with oxygen donor atoms of the oxido ligands and carboxylate anion. The stereospecific behaviour was investigated using the 51 V NMR spectroscopy, which revealed different composition of systems with racemic mandelic acid and S-mandelic acid after some preliminary period (≈ 15 days). The compound 2 is chiral non-racemic compound (space group P21212), the structure of which contains Δ-[Fe(bpy)3]2+ cations and [V3O7(S-mand)2]3– anions.Graphical abstract