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

The X-ray structure analysis of mer-trans-[Co(aepn)Cl-2(OH2)](ClO4). H2O (1 ) (aepn =N-(2-aminoethyl)-1,3 -propanediamine) reveals that the compound cr ystallizes in an enantiomorphic space group P2(1)2(1)2(1) implying a sponta neous resolution of its racemic solution, known as conglomerate crystalliza tion. Substitutions of the two chloride ligands with bromides result in the isostructural compound mer-trans-[Co(aepn)Br-2(OH2)](ClO4). H2O (2), which also crystallizes as a conglomerate in the space group P2(1)2(1)2(1). Mean while, a substitution of the coordinated OH2 of 1 with NH3 gives mer-trans- [Co(aepn)Cl-2(NH3)](ClO4) (3), which crystallizes as a simple racemate in P 2(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(OH2)](ClO4) (4) whose molecular packing pattern is ident ical to that of 3. fn the conglomerate structures, the protons of coordinat ed water ligand are strongly hydrogen-bonded to the oxygen of a water of cr ystallization to form a spiral packing structures. In the packing structure s of 3 and 4, two molecules of opposite chirality are brought together arou nd a crystallographic center of inversion by hydrogen bonds of the protons of the corresponding tridentate amine ligand with oxygens of perchlorate an ion. (C) 1999 Elsevier Science Ltd. All rights reserved.