The phenomenon of conglomerate crystallization. VIII. Spontaneous resolution in coordination compounds. VI. The chiral behaviour of [ trans-( P, or M)-Co(NH 3) 2 (NO 2) 4] − anions, dissymmetric by virtue of their propeller conformation

Abstract

Octahedral coordination compounds chiral by virtue of having fixed propeller conformations are, apparently, quite rare. Despite the fluxionality of the anion [ trans-( P, or M)-Co(NH 3) 2(NO 2) 4] −, it is possible to establish its chiroptical properties in the solid. Our studies of its salts suggest that, conformationally, it is relatively impervious to the nature of the compensating cation and to variations in packing forces. Consequently, a useful method of determining the chiral symbol of this anion is proposed based on that of stereochemically rigid cations with which it forms diastereoisomeric salts. In the case of solutions of the ions [ cis-Co(en) 2(NO 2) 2] + and [ trans-Co(NH 3) 2(NO 2) 4] −, the crystals obtained from a conglomerate are expected to contain Λ(δλ)-(−) 589-[ cis-Co(en) 2(NO 2) 2][ trans-( P)- Co(NH 3) 2(NO 2) 4] and Λ(δλ)-(+) 589-[ cis-Co(en) 2(NO 2) 2][ trans-( M)-Co(NH 3) 2(NO 2) 4].