Stereoselective formation and spectroscopic studies of [Cr(edda or eddp)(N[sbnd]N)]-type complexes (edda = ethylenediamine-N,N′-diacetate; eddp = ethylenediamine-N,N′-dipropionate)

Abstract

[Cr(edda or eddp)(NN)]-type complexes (edda = ethylenediamine-N,N′-diacetate, eddp = ethylenediamine-N,N′-dipropionate; NN = 1,2-ethanediamine (en), 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen)) were formed with stereoselectivity. These complexes were characterized by UV–Vis and IR absorption spectra and X-ray crystal analysis. The chromium atom is coordinated to a bidentate N,N-ligand and a tetradentate −O,N,N,O−-ligand, producing a distorted CrN4O2 octahedral molecular geometry. The edda ligand coordinates to the chromium atom through two oxygen and two nitrogen atoms. The anionic oxygen atoms of the edda ligand occupy positions trans to each other. The crystal structures are stabilized by several intermolecular NH⋯O and/or OH⋯O hydrogen bonding interactions. In the tetrahydrate [Cr(edda)(bpy)] (1b), the solid-state structure has a notable feature of hydrogen bonding interactions among the water molecules, and the four water molecules form a (H2O)4 chain consisting of OH⋯O hydrogen bonds between complex cations. In the anhydride [Cr(edda)(en)] (1e), each complex cation is connected to two adjacent cations through N(edda)H⋯O(edda) hydrogen bonds and to two perchlorate anions through N(en)H⋯O hydrogen bonds to construct a two-dimensional sheet structure. The optically active [Cr(edda)(bpy)] (1b) and [Cr(edda)(phen)] (1p) could be isolated by fractional resolution using the [Sb2(d-tart)2]2− anion. However, both isomers were readily racemized, even in an acidic aqueous solution, within a period of 3 h. The eddp ligand in [Cr(eddp)(phen)] (2p) and [Cr(eddp)(bpy)] (2b) coordinates to the chromium atom through two oxygen and two nitrogen atoms. The anionic oxygen atoms of the eddp ligand occupy positions cis to each other. The NCrO angles of the β-alaninato (six-membered) ring in the eddp ligand are larger than those of the glycinato (five-membered) ring in the edda ligand. The formation of only the cis isomer in the eddp complex is caused by the relaxation of the strain on the β -alaninato ring.