The crystallization behavior of (±)-cis-α-[Co(dmtrien)(NO2)2]Cl· 0.5H2O 1 and (±)-cis-α-[Co(dmtrien)(NO2)2]I 2† (dmtrien = 3,6-dimethyl-3,6-diazaoctane-1,8-diamine)

Abstract

The compound (±)-cis-α-[Co(dmtrien)(NO₂)₂]Cl·0.5H₂O 1 has been found to crystallize as a kryptoracemate in the space group C2 (Z = 4) with a racemic pair as the asymmetric unit, whereas (±)-cis-α-[Co(dmtrien)(NO₂)₂]I 2 crystallizes as a simple racemate, as expected (dmtrien = 3,6-dimethyl-3,6-diazaoctane-1,8-diamine). For 1 the two cations in the asymmetric unit had the conformations Δ(λδλ), Co(1), and Λ(δλδ), Co(2), and those of the chiral, methylated, nitrogens of Co(1) are (S,S) while those of Co(2) are (R,R). Compound 2 crystallizes as a racemate in the space group Pccn (Z = 8); the anions are in a general position but there are two half cations sitting at two-fold axes of the space group. For 1, Co(1) and Co(2) cations form separate spiral strings which extend through the length of the a axis, and these strings are held together by hydrogen bonds to the anions and waters of crystallization. Each string contains, exclusively, cations of single chirality and layers of homochiral strings define the ab plane of the crystals. Each layer is of opposite chirality to the pair of adjacent ones. In 2 the packing is different in that there are strings made exclusively of either Co(1) or Co(2) running along the diagonal of the bc plane, as well as [–Co(1)–Co(2)–Co(1)–Co(2)–]_n . . . strings running parallel to the c axis.