Crystal Structure and Absolute Configuration of a Cobalt(III) Complex of a Linear Tetradentate Ligand: (+)₄₇₀-Δ-β-cis-Dinitro(5-methyl-1,4,8,11-tetraazaundecane)coball(III) Bromide

The crystal structure and absolute configuration of a Co(III) complex of a linear tetradentate ligand, (+)₄₇₀-Δ-β-cis-Dinitro(5-methyl-1,4,8,11-tetraazaundecane)coball(III), [Co{NH₂(CH₂)₂NH(CH₂)₂CH(CH₃)NH(CH₂)₂NH₂}(NO₂)₂]Br, have been determined by X-ray diffraction methods. The crystals are monoclinic, with a = 13.383 (9), b = 7.724 (5), c = 7.554 (5)Å,β= 110.94 (2)°, space group P2₁, and Z= 2. A set of 2570 observed hkl reflections was obtained by counter methods. The molecular structure was determined by Patterson methods and refined by least squares to R₁= 0.034 with the adjustment of 270 variables. The absolute configuration was determined with the aid of 200 selected hkl reflections. The cation adopts the β-cis geometry, with the substituent methyl group adjacent to the out-of-plane chelate ring. The arrangements at the asymmetric centers are S for each nitrogen atom and R for the carbon atom. The five-membered rings both have the λ conformation, and the six-membered ring has the chair conformation, with the substituent methyl group in an equatorial position. The coordination around the cobalt atom is slightly distorted from octahedral, with angles between adjacent coordinated atoms varying from 85.0 (2) to 93.7 (2)°. The average Co-N(ligand) distance is 2.000 (2) Å, for three of the ligand atoms, but the in-plane terminal amino group has Co-N = 1.968 (4) Å. The Co-NO₂ distances are 1.936 (2) Å.