Chromium(II) complexes of o-phenylenediamine. The crystal and molecular structures of bis(o-phenylenediamine-κN)-bis(thiocyanato-κN)chromium(II) and bis(o-phenylenediamine-κ2N,N′) bis(o-phenylenediamine-κN)chromium(II) trifluoromethanesulphonate

Abstract

The following chromium(II) complexes of o-phenylenediamine (opd) have been isolated: [Cr(opd)₂(NCS)₂], [Cr(opd)₄]Br₂, [Cr(opd)₂I₂]·1.5EtOH, [Cr(opd)Cl₂], [Cr(opd)₆]Cl₂ and [Cr(opd)₄][CF₃SO₃]₂. From the patterns of bands assigned to NH₂ and CN stretching vibrations in the infrared spectra the first two complexes contain monodentate diamine, the next two bidentate diamine and the last two both mono- and bi-dentate diamine; thus [Cr(opd)₆]Cl₂ is more correctly formulated as [Cr(opd)₄]Cl₂·2opd. Crystal-structure determinations confirm the assignments for [Cr(opd)₂(NCS)₂] and [Cr(opd)₄][CF₃SO₃]₂. The thiocyanato complex crystallises in the monoclinic space group P2₁/c with a= 11.027(3), b= 5.828(2), c= 13.431(2)Å, β= 103.93(2)° and Z= 2. The structure was refined to R= 0.040 for 1551 observed reflections. There are trans-planar units in which the bond distances are Cr-NH₂(monodentate diamine) 2.160(2) and Cr-NCS 2.036(2)Å, with S atoms of isothiocyanato groups of adjacent units in axial positions, Cr-S 2.972(2)Å forming a thiocyanato bridged structure. The triflate crystallises in the orthorhombic space group Pbca, with a= 8.978(8), b= 22.455(7), c= 16.842(2)Å and Z= 4. The structure was refined to R= 0.061 for 1863 observed reflections. The co-ordination sphere consists of two bidentate diamine molecules, mean Cr-N 2.119 Å, with two more distant, axially positioned, monodentate molecules at 2.669(5)Å. In accordance with its structure [Cr(opd)₂(NCS)₂] exhibits antiferromagnetic behaviour as does [Cr(opd)Cl₂] which is a chloride-bridged polymer. The triflate and the remaining complexes show simple paramagnetic behaviour (90–300 K). Attempts to prepare a chromium (II) complex of a tetraazamacrocyclic ligand by reaction of the o-phenylenediamine complexes with acetylacetone were unsuccessful; either no reaction took place or the benzodiazepinium chloride was isolated.