Journal of Chemical Crystallography, Vol. 33, No. 4, April 2003 ( C  2003) Crystal structures of bis(4-dimethylaminopyridinium) tetrachlorocobaltate(II) and bis-[1,3-di (ammoniummethyl)benzene]tetrachlorocobaltate(II) Salim Haddad, (1) Ashwani Vij, (2) and Roger D. Willett (3)∗ Received April 14, 2002 The crystal structures consist of organoammonium cations hydrogen bonded to tetrahedral CoCl 2− 4 anions. In the 4-dimethylaminopyridinium salt, [(CH 3 ) 2 NC 5 H 5 NH] 2 CoCl 4 , pairs of cations hydrogen bond in an asymmetric fashion to two of the chlorines in each anion. The planar cations form two sets of π –π stacks, first parallel to the a axis and the second parallel to the b axis. The anions lie between these two nonintersecting sets of stacks. In contrast, for the second compound, [C 6 H 4 (CH 2 NH 3 ) 2 ]CoCl 4 , the tetrahedral CoCl 2− 4 anions form layers lying parallel to the bc plane. The 1,3-di(ammoniummethyl)benzene cations crosslink adjacent anionic layers, forming a lamellar structure of alternating organic and inorganic layers. KEY WORDS: Tetrachlorocobaltate(II); π –π stacking. Introduction The role of weak intermolecular interactions in the determination of crystal structures is one of the principal avenues of investigation now be- ing probed in crystal engineering studies. Interac- tions such as hydrogen bonding and π –π stacking play a very important role in the organization of structural units in areas ranging from biochem- istry to material science. While much of the inter- est has focused on strictly organic systems, 1 recent advances have been made in understanding how to use these concepts in hybrid organic/inorganic (1) Department of Chemistry, University of Jordan, Amman, Jordan. (2) University Research Office, University of Idaho, Moscow, Idaho 83844. (3) Department of Chemistry, Washington State University, Pullman, Washington 99164. ∗ To whom correspondence should be addressed. E-mail: Willett@mail.wsu.edu systems. The control of these interactions will be important in the design of materials with specific types of properties, such as conductivity or mag- netic behavior. 2 Several recent studies have examined how metal halide oligomers can be tied together via the 4,4 ′ -bipyridinium cation (and related cations) into chains, layers, etc. 3 In these systems, the mono- directional nature of the two N---H hydrogen bonding moieties gives strong control of the struc- tural linkages, while the planar nature of the cation allows for efficient π –π stacking. More recently, a number of authors have examined the crystal packing effects in (spyH) 2 CuBr 4 salts, where spy represents a substituted pyridine molecule. 4 Here control of the interactions are important magnet- ically because of the importance of Br···Br con- tacts as magnet exchange pathways. 5 Again, the N---H moiety provides hydrogen bonding capa- bilities, but now there is no control of the linkage 245 1074-1542/03/0400-0245/0 C  2003 Plenum Publishing Corporation