Structural and Spectroscopic Properties of Trans-dichlorobis(2,2-dimethyl-1,3-diaminopropane)chromium(III) Chloride

The structure of trans-[CrCl(2)(Me(2)tn)(2)]Cl (Me(2)tn=2,2-dimethylpropane-1,3-diamine) has been determined by a single-crystal X-ray diffraction study at 150K. The analysis reveals that there are two independent Cr(III) complex cations in the structure, one with crystallographic inversion symmetry and the other with two-fold rotation symmetry, which are conformational isomers of each other. In both conformations, the chromium atom adopts a distorted octahedral structure with the four nitrogen atoms of two Me(2)tn ligands occupying the equatorial plane and two chlorine atoms occupying trans-axial positions. The six-membered chelate rings are in stable chair conformations with N-Cr-N angles of 87.03(8) degrees and 88.99(8) degrees . The two chelate rings in the centrosymmetric complex cation 1 are anti, while those in the rotation-symmetric complex cation 2 are in syn conformations. The mean Cr-N and Cr-Cl bond lengths are 2.0922 and 2.3253 A, respectively. The infrared and UV-visible absorption spectra of trans-[CrCl(2)(Me(2)tn)(2)]Cl have also been measured. The resolved band maxima of the electronic d-d spectrum are fitted with a secular determinant for a quartet energy state of the d(3) configuration in a tetragonal field including configurational but neglecting spin-orbit coupling. It is confirmed that the nitrogen atoms of the Me(2)tn ligand have a strong sigma-donor character, but the chloro ligand has weak sigma- and pi-donor properties toward the chromium(III) ion.