Cocrystallization of chiral cobalt complexes via formation of quasiracemates

Starting from the enantiomerically pure or racemic nucleophile 1-phenylethy lamine (L) chiral cobalt complexes with the general formula [Co(Hdmg)(2)XL] (Hdmg = dimethylglyoximate, X =CN, NO2) were obtained as homochiral or het erochiral crystalline solids, respectively. The: crystal structures of the resulting cyano and nitro complexes were determined by single crystal X-ray diffraction. The homochiral solids crystallize in space group P2(1) with t wo molecules per asymmetric unit, the racemates ill P2(1)/c With only one i ndependent molecule. From a solution containing equimolar amounts of enanti omerically pure S-L cyano and X-L nitro complexes a stable and well-ordered binary solid could be crystallized and structurally characterized. The mol ecular constituents of opposite chirality are arranged in pairs ill the vic inity of pseudo inversion centers forming a quasi-racemate in space group P 2(1). The driving force for the formation of this cocrystal is discussed in terms of intermolecular geometry and energy: The crystal structures of all five complexes are similar with respect to lattice parameters and inter mo lecular arrangement, but comparisons based on space filling and lattice ene rgy confirm higher packing efficiency For the racemates and the quasi-racem ate than for the enantiopure compounds.