The phenomenon of conglomerate crystallization: Part 52. Stereochemical control of the crystallization pathway by small alterations of ligands

Abstract

The X-ray structure analysis of mer- trans-[Co(aepn)Cl 2(OH 2)](ClO 4)·H 2O ( 1) (aepn= N-(2-aminoethyl)-1,3-propanediamine) reveals that the compound crystallizes in an enantiomorphic space group P2 12 12 1 implying a spontaneous resolution of its racemic solution, known as conglomerate crystallization. Substitutions of the two chloride ligands with bromides result in the isostructural compound mer- trans-[Co(aepn)Br 2(OH 2)](ClO 4)·H 2O ( 2), which also crystallizes as a conglomerate in the space group P2 12 12 1. Meanwhile, a substitution of the coordinated OH 2 of 1 with NH 3 gives mer- trans-[Co(aepn)Cl 2(NH 3)](ClO 4) ( 3), which crystallizes as a simple racemate in P2 1/ n space group. When N-(3-aminopropyl)-1,3-propanediamine (dpt) is used instead of aepn in the preparation of 1, it gives racemic crystals of mer- trans-[Co(dpt)Cl 2(OH 2)](ClO 4) ( 4) whose molecular packing pattern is identical to that of 3. In the conglomerate structures, the protons of coordinated water ligand are strongly hydrogen-bonded to the oxygen of a water of crystallization to form a spiral packing structures. In the packing structures of 3 and 4, two molecules of opposite chirality are brought together around a crystallographic center of inversion by hydrogen bonds of the protons of the corresponding tridentate amine ligand with oxygens of perchlorate anion.