THE CRYSTAL-STRUCTURE OF FE(II)((DPG)(3)(BF)(2))CENTER-DOT-2TOLUENE -A STUDY IN THE GEOMETRY OF STRAINED CLATHRO-CHELATE COMPOUNDS

The molecular structure of the clathro-chelate compound Fe((dpg)(3)(BF )(2)).2toluene (dpg = diphenylglyoxime) was determined by X-ray diffra ction methods. It crystallizes in the space group P2(1)/c with a = 12. 006(2), b = 16.957(4), c = 25.301(4) Angstrom, beta = 90.552(14)degree s, V = 5150.7(17) Angstrom(3), Z = 4 and R = 4.18% for the 2255 reflec tions with \F-o\ > 6 sigma(F). The mean Fe-N bond distance is 1.914 +/ - 0.012 Angstrom. The coordination geometry of this compound is interm ediate between octahedral and trigonal prismatic, with a twist angle ( phi) of 23.5 +/- 0.3 degrees from the eclipsed (prismatic) geometry. M olecular mechanics calculations were carried out on the similar model compound M((dmg)(3)(BF)(2)) (dmg =dimethylglyoxime), using a range of M-N bond distances. These calculations predict a twist angle of 18.1 d egrees for the M-N distance observed in Fe((dpg)(3)(BF)(2)). The molec ular mechanics calculations support the proposal that forces other tha n crystal field stabilization energy (such as steric forces) are prima rily responsible for the geometries of clathro-chelate compounds.