The phenomenon of conglomerate crystallization. XXXV. The crystallization behaviour of {cis-α-Co(trien)ox]Cl}2·9H2O (1), cis-β-Co(3,2,3-tet)ox]Cl·4H2O(2), {cis-α-Co(trien)ox]NO3}2· H2O (3), and [mer-Co(dien)ox (NO2)] (4)

Abstract

As expected from previous studies, the four title compounds crystallize as racemates from H2O solutions allowed to evaporate at room temperature (ca. 18° C). All four complexes have been characterized by X-ray crystallography. The outer, six-membered rings in (2) are in the chair conformation; and, in the first three species, the secondary nitrogens are chiral centres. In (1) the five-membered rings of the two cations in the asymmetric unit are characterized: Co(1), δ, δ and λ, with the chiralities of the secondary nitrogens (S) and (S); Co(2), λ, λ and δ, with secondary nitrogens (R) and (R). In (3), the five-membered rings of the two cations in the asymmetric unit are: Co(1), δ, δ and λ, with secondary nitrogens (S) and (S); Co(2), δ, λ and δ, with secondary nitrogens (S) and (S). In (2), the five-membered ring is δ and the chiralities of the secondary nitrogens are (R) and (R). In (4), the unique five-membered ring is λ and the central —NH— fragment lies at a mirror plane. Comparison of the crystallization pathways of these complexes with those of related substances are made, and suggestions as to why (1)–(4) select the racemic crystallization pathway are offered.