Crystalline-State Reaction of Cobaloxime Complexes by X-Ray Exposure. X. Structural Requirement for the Racemization of the 1-Methoxycarbonylethyl Group

Article abstract of DOI:10.1107/S0108768184002512

Two crystalline forms of bis(dimethylglyoximato)-<(S)-1-methoxycarbonylethyl><(R)-α-methylbenzylamine>cobalt(III) (dimethylglyoximato is 2,3-butanedione dioximato), C20H32CoN5O6, , were obtained from an aqueous methanol solution and their structures were determined by X-ray analysis.From (I): M_r=497.4, triclinic, P1, a=8.637(1), b=8.955(2), c=8.094(1) Angstroem, α=105.71(1) deg, β=100.18(2) deg, γ=96.23(2) deg, V=585.0(2) Angstroem³, F(000)=262, D_x=1.412 g cm^-3, Z=1, μ(Mo Kα)=8.11 cm^-1.From (II): monoclinic, P2₁, a=8.017(3), b=16.715(6), c=8.972(3) Angstroem, β=101.88(3) deg, V=1176.5(7) Angstroem³, D_x=1.404 g cm^-3, Z=2, μ(MoKα)=8.04 cm^-1.Both structures were solved by direct methods and refined by block-diagonal least squares.The final R values were 0.052 (2646 reflections) and 0.046 (2697 reflections) for forms (I) and (II), respectively.The two different forms result from a conformational change around the Co-C and Co-N bonds.Neither form was racemized by X-rays at room temperature.The chiral methoxycarbonylethyl (mce) group in each crystal is isolated from the other mce groups and the cavity for the mce group is small for the racemization of the bulky mce group.The structures are compared with those of related crystals and the structural requirement for the racemization of the mce group in the crystalline state is discussed.