THE PHENOMENON OF KRYPTORACEMIC CRYSTALLIZATION. PART 1. COUNTERION CONTROL OF CRYSTALLIZATION PATHWAY SELECTION. PART 4. THE CRYSTALLIZATION BEHAVIOR OF (+/−)-[Co(tren)(NO2)2]Br(I), (+/−)-[Co(tren)(NO2)2]2Br(ClO4) · H2O(II), (+/(−)-[Co(tren)(NO2)2]ClO4(III) AND ATTEMPTS TO SOLVE THE STRUCTURE OF (+/−)-[Co(tren)(NO2)2]NO3(IV)

Abstract

Abstract Racemic aqueous solutions of (+/−)-[Co(tren)(NO2)2]Br (I), (+/−)-[Co(tren)(NO2)2]ClO4 (III) and [Co(tren)(NO2)2]NO3(IV) crystallize as racemates. By contrast, the double salt, (+/−)-[Co(tren)(NO2)2]2Br(ClO4) · H2O(II), produces kryptoracemic crystals belonging to the enantiomorphic space group P212121 (No. 19). The former three species crystallize with one molecule in the asymmetric unit; in the latter, a racemic pair is the asymmetric unit, a fact which is hidden by the enantiomorphic nature of its space group – thus the name of the crystallization phenomenon reported. In (II) pairs of cations are related by an approximate, non-crystallographic, inversion center. The crystal structure and polarity of (I) and the absolute configuration of (II) were determined by refinement. The crystalline contents of (I) to (III) consist of infinite strings of hydrogen bonded cations, the counter ions and (where relevant) waters of crystallization acting as a hydrogen-bonding glue linking the spiral strings In (...