Crystals of Racemic Mimics. Part II. Some Mn(III) and Co(III) compounds crystallizing thus, and remarks on the chirality of atoms containing non-bonded electron pairs as stereogenic centers

Abstract Crystallographically well-documented examples of “Racemic Mimic” pairs remain scarce. We describe two new species belonging to this rare class of pseudo-symmetric crystals, which we term “Racemic Mimics.” The Mn(III) and Co(III) compounds – azido-methanol-((R,R)-N,N′-bis(salicylidene)-1,2-diaminocyclohexane)manganese(III) and (1-cyanoethyl)-pyridine-bis(dimethylglyoximato)cobalt(III) – have been studied in two distinct crystalline forms: (1) a centrosymmetric form [ P 2 1 / n , Z ′ = 1.0] and (2) a Sohncke form [ P 2 1 , Z ′ = 2.0]. In each case, the structures are related by their nearly identical cell constants, with the latter form exhibiting a doubled Z ′ due to the loss of the n-glide plane. Our findings expand the scope of racemic mimicry beyond previously recognized purely organic systems, demonstrating that this phenomenon is more widespread than previously appreciated. Additionally, we highlight the overlooked chirality of the tri-bonded oxygen in the Mn(III) compound, a feature typically disregarded in the Cambridge Structural Database. This work adds another chapter to the intriguing study of racemic mimicry in crystallography.