FULL PAPER DOI:10.1002/ejic.201300906 Cation Exchange in Layered Copper(II) Coordination Polymers Krapa Shankar, [a] Babulal Das, [a] and Jubaraj B. Baruah* [a] Keywords: Materials science / Organic-inorganic hybrid composites / Layered compounds / Coordination polymers / Carboxylate ligands / Ion exchange The covalently linked anionic layers of a series of Cu II 2,3- pyridinecarboxylate anions containing organic cations are characterized. Depending on the cations, mononuclear, dinu- clear or polynuclear complexes are formed. The complex with adeninium cations is mononuclear, whereas the com- plexes bearing cations of 4-aminobenzylamine, 1,5-diami- nopentane, and 5-aminoquinoline are dinuclear, and com- plexes bearing cations of isopropylamine, ethylenediamine, 1,8-diaminooctane, N,N,N',N'-tetramethylethylenediamine, tris(2-aminoethyl)amine, 1,4-diazabicyclo[2.2.2]octane, imid- azole, pyridine, 8-hydroxyquinoline, and cytidine are coordi- nation polymers. All of the complexes other than the one bearing tris(2-aminoethyl)amine cations have lamellar struc- tures. The polynuclear complex anion with tris(2-amino- ethyl)amine trications exhibits an unusual –3 charge for the Introduction Hybrid materials that form layerlike structures have been continuously applied in materials chemistry as advanced materials. [1] Their role in catalysis [2] and molecular recogni- tion [3] features regularly in everyday science. Guanidinium sulfonates, ammonium trimesates, polyoxometalates, vana- dates, phosphates, and various metal carboxylates are com- monly used to generate layered structures. [4] Layered struc- tures made up of VO 5 and PO 4 polyhedra easily hold am- monium cations in their layered structures. [5] Among the carboxylates, 2,6-pyridinedicarboxylate commonly forms layered structures through π–π interactions, [6] whereas 2,3- pyridinedicarboxylate [7] forms layered structures through covalently linked polymeric anions. Protonated cytosine as- semblies have been held in the layers of metal oxalates [8] and metal dipicolinates. [9] However, difficulties arise in pro- cessing such structures formed either from anion assemblies or from polymeric anions of hybrid materials owing to their low solubility and poor crystallizability as well as to the [a] Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India E-mail: juba@iitg.ernet.in http://www.iitg.ernet.in/juba Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201300906. Eur. J. Inorg. Chem. 2013, 6147–6155 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 6147 polynuclear anionic nodes. The 1H,9H-adeninium cationic dimers are stabilized in the interstices of mononuclear Cu II quinolinate complex anions. The interlayer separations in the layered polymers varied from 8.5 to 15.9 Å and are guided by the cations. Biologically relevant cytidinium cations are trapped in the layers of polymeric anions. The complexes bearing organocations undergo exchange of the organic cat- ions with alkali, alkaline earth, or transition metal ions or with smaller cations without disturbance of the polymeric in- organic layer. The exchange of the cytidinium cations by metal ions resulted in polymeric complexes in which the cat- ionic organic layer is replaced by a layer of aquated metal cations. The thermochemical properties, electron paramag- netic resonance (EPR) spectroscopy, and solid-state conduc- tance of the complexes are described. exchange of the central metal ions. Further complications arise in the choice of appropriate inorganic and organic parts of the layers with lower toxicity for biological studies. In this regard, the biomolecules used for the formation of assemblies and metal–organic frameworks [10] would provide a relationship between materials and living sciences. Cytid- ine is a commonly used carbohydrate-containing nucleotide for the study of metal–nucleotide interactions; [11] it forms interesting assemblies when coordinated to copper ions. [12] The copper cytidine complexes bind carbon dioxide to pro- vide interesting assembled structures. [13] Generally, assembl- ies formed by the direct coordination of cytidine to copper ions have less scope for ligand exchange. However, assembl- ies generated from the polymeric-anion-embedding cytosin- ium cation will provide easy access to the exchange of cytid- ine by other cationic species. Further, a coordination poly- mer that forms a layered structure would be easy to trans- form to different species through manipulation by top- down or bottom-up approaches. To meet these challenges and to exchange biologically important molecules from the layered structures, we adopted the design principle shown in Scheme 1. On the basis of these design principles, we show the arrangement of various cations, including a nu- cleobase, in layered structures and demonstrate the ex- change of the later from a copper 2,3-pyridinedicarboxylate framework by a wide range of cations.