Synthesis, crystal structure and spectroscopic properties of trans-difluoro(1,4,7,11-tetraazaundecane)chromium(III) perchlorate

The structure of trans-[Cr(2,2,3-tet)F2]ClO4 (2,2,3-tet = 1,4,7,11-tetraazaundecane) has been determined by single-crystal X-ray diffraction. The complex crystallizes in the space group P 1 ‾ of the triclinic system with two mononuclear formula units in a cell of dimensions a = 5.6741(11), b = 9.971(2), c = 13.222(3) Å, α = 73.76(3)o, β = 81.08(3)° and γ = 85.12(3)°. The chromium(III) atom is in a slightly distorted octahedral environment coordinated by four N atoms of 2,2,3-tet and two F ligands in a mutually trans (meso RS) geometry. The mean Cr-N(2,2,3-tet) and CrF bond lengths are 2.064(9) and 1.885(7) Å, respectively. The crystal packing is stabilized by several hydrogen bonds. The 5 K sharp-line absorption spectrum and the 298 K FT-infrared and UV–visible spectra have been measured. Using the electronic transitions, a ligand field optimization has been performed to determine the metal-ligand bonding properties of the coordinated atoms. It is found that the fluoride is a strong σ- and π-donor and the nitrogen atoms of the 2,2,3-tet ligand also have strong σ-donor properties toward the chromium(III).