Structural diversity in two dimensional chiral coordination polymers involving 4,4 0 -bipyridine and L-cysteate as bridging ligands with Zn and Cd metal centres: Synthesis, characterization and X-ray crystallographic studies Amal Cherian Kathalikkattil, P.S. Subramanian, Eringathodi Suresh ⇑ Analytical Science Discipline, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), G.B. Marg, Bhavnagar 364 002, Gujarat, India article info Article history: Received 30 May 2010 Received in revised form 16 September 2010 Accepted 27 September 2010 Available online xxxx Keywords: Supramolecular chemistry Chiral coordination polymers L-cysteic acid Gas adsorption N-donor ligand X-ray crystal structures abstract Two chiral coordination polymers involving amino acid backbone L-cysteic acid (H 2 L-cys) and N-donor ligand 4,4 0 -bipyridine (4,4 0 -bpy) [{Cd(L-cys)(4,4 0 -bpy)(H 2 O)}3.5H 2 O] n 1, [{Zn 2 (L-cys) 2 (4,4 0 -bpy) 2 (H 2 O) 4 } (H 2 O)(4,4 0 -bpy)] n 2 with rectangular grids have been synthesized. Both compounds are insoluble in com- mon polar/non-polar solvents and well characterized by various physico-chemical techniques such as CHN, IR, TGA, NMR, solid state CD and single crystal X-ray diffraction methods. Complexes 1 and 2 com- prise L-cysteate dianions self assembled into chiral coordination polymers by bridging the adjacent metal centres through the carboxylate oxygen generating one-dimensional helical chains. The helical chains are pillared by 4,4 0 -bpy generating two dimensional network. Complex 1 generates two dimensional (4,4) rectangular grid network with dimension 4.77 Å 11.74 Å (based on d CdCd ) involving with the edge sharing L-cys and 4,4 0 -bpy ligands, respectively. Complex 2 possesses a brick-wall type (6,3) network topology with edge lengths of the grids 11.42 Å 10.11 Å based on d ZnZn . Lattice water molecules are encapsulated between the adjacent rectangular grids via hydrogen bonding interactions. One 4,4 0 -bpy moiety is stacked between the adjacent layers of brick-wall network via weak pp interaction with the edge sharing N-donor ligand. Even though both the complexes are rigid and stable, N 2 adsorption studies by these complexes revealed not much promising results. The terminal protruding sulphonate groups, angular orientation of the grids within the two-dimensional network and interpenetration of the adjacent offset sheets concomitantly prevent the formation of through tubular channels. Flexible coordination geometry around the metal centre and the versatile coordination mode of the amino car- boxylate group from the L-cys moiety are accountable for the variation of the appealing network topology in these complexes. Chiral nature is established by solid state CD spectrum which shows a positive cotton effect for both complexes. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Metal–organic frameworks (MOFs) also known as coordination polymers are inorganic–organic hybrid solids with infinite network structures built from organic ligands such as linkers and metal ions as connecting points [1]. Metal organic frameworks can be con- structed via two kinds of interactions viz., coordinate covalent bond and weaker intermolecular forces such as hydrogen bonding and pp stacking interactions. By the judicious choice of the ligand moiety and inorganic nodal points of transition metals possessing versatile coordination geometry, multidimensional MOFs can be constructed. In recent years, research in the area of MOFs has grown rapidly because these materials can be con- structed from designer building blocks with unique properties, for a wide range of potential applications in gas storage [2], sepa- ration [3], heterogeneous catalysis, non-linear optics [4], enantio- selective separations and heterogeneous asymmetric catalysis [5,6]. The importance of chirality in biological processes and the increasing demand of materials for enantioselective separation and catalysis have encouraged extensive research in the area of chiral coordination polymers. Optically pure amino acids have been successfully used to craft chiral helical coordination polymers [7,8]. Achiral ligands such as multi-carboxylates can also introduce chirality by coordinating with the metal centre in the formation of helical chains [9]. The use of organic enantiopure chiral building blocks for the construction of extended frameworks has been shown to be a useful method for the synthesis of homochiral mate- rials with aesthetic multi-dimensional network topology [10]. Syn- thesis of molecular chiral metal complexes is of current interest, and increasing research in this area can be noted in coordination and supramolecular chemistry not only for their extended multi- dimensional structures but also for various application in gas adsorption properties and catalysis [6a,10b–e]. 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.09.049 ⇑ Corresponding author. Tel.: +91 2782567760; fax: +91 2782567562. E-mail addresses: esuresh@csmcri.org, sureshe123@rediffmail.com (E. Suresh). Inorganica Chimica Acta xxx (2010) xxx–xxx Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica Please cite this article in press as: A.C. Kathalikkattil et al., Inorg. Chim. Acta (2010), doi:10.1016/j.ica.2010.09.049