Conformational analysis of coordination compounds. XI molecular structure of tetraammine-{(±)-pentane-2, 4-diamine) cobalt(III) dithionate

The crystal structure of tetraammine{(±)-pentane-2, 4-diamme)cobalt(III) dithionate dihydrate [Co{(±)-ptn)(NH3)4] (S2O6)1·5, 2H2O has been determined by X-ray structure analysis. The crystals are triclinic with the space group PĪ, with a 11·43, b 11·65, c 7·78 Å, α 100·48°, ß 105·95°, and y 75·95°. The structure has been refined by least-squares methods with anisotropic temperature factors to an R value of 0-043 for 2654 reflections. The six-membered diamine chelate ring has a skew-boat conformation in which the two methyl groups are in equatorial orientations. A strainenergy-minimization calculation for the complex reveals an energy difference of 8·3 kJ mol-1 between the preferred skew-boat conformation and the chair conformation. The calculated minimum-energy geometry for the skew-boat conformation is in good agreement with the observed structure for the chelate ring in the dithionate salt. The 1H n.m.r. spectra of this complex and other complexes of the chiral isomer of pentane-2, 4-diamine are discussed in terms of the observed structures and the conformational analysis