Selective adenine/cytosine cations in one-dimensional coordination polymers of manganese (II) and copper (II) 2,3-pyridinedicarboxylates Babulal Das a , Athanassios K. Boudalis b , Jubaraj B. Baruah a, ⁎ a Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, Assam, India b Institute of Materials Science, NCSR "Demokritos", 15310 Aghia Paraskevi Attikis, Greece abstract article info Article history: Received 27 April 2010 Accepted 30 June 2010 Available online 16 July 2010 Keywords: Coordination polymer 2,3-Pyridinedicarboxylic acid Copper(II) Manganese(II) Nucleobase Magnetochemistry One-dimensional coordination polymer {[1H,9H-ade] 2 [MnL 2 ]∙4H 2 O} n (1) and {[1H,3H-cyt] 2 [CuL 2 ]∙6H 2 O} n (2) (ade = adenine, cyt = cytosine, L = dianion of 2,3-pyridinedicarboxylic acid) are selectively synthesized and variable-temperature magnetic susceptibility measurements revealed weak antiferromagnetic interactions within the chains of 1 and 2 (J =−0.29 cm −1 for 1 and J =−0.03 cm −1 for 2, according to the −2J ij S i S j HDvV Hamiltonian formalism). © 2010 Elsevier B.V. All rights reserved. The organic cations sandwiched between layers of metal-organic frameworks (MOF) serve as adjustable components to tune structure and properties [1–9]. Layered solid comprising of organic, metal phosphonate or metal halide anions are widely used in the synthesis and design of inorganic–organic lamellar solids [10–12]. Our interest in this branch of chemistry is fueled from the formation of (a) inorganic/organic layered solids in these metal-organic frameworks and (b) studies on metal–nucleobase bindings that provides under- standing on the role of metal ions in the function of nucleic acids, especially in genetic information transfer [13–17]. Molecular recog- nition of these nucleobases, such as adenine and cytosine cations in their most stable tautomeric forms, by artificial receptors such as metal oxalato and metal malonato complexes have been reported recently [18,19]. Studies concerning these nucleobases are carried out in the gas phase [20] or aqueous media [21]. Some studies on nucleobases are directed towards pharmaceuticals [22–27], construc- tion of ligands [28,29], stabilization of noncanonical tautomers through interactions with metal ions [30], development of artificial receptors for specific DNA/RNA base recognition and determination of therapeutic agents [31]. The coordination chemistry of heteroatom- containing dicarboxylic acids such as 2,6- and 2,3-pyridinedicar- boxylic acid is diverse [32–35]. However, there are also examples of cationic polymeric complexes of 2,3-pyridinedicarboxylate anions [36]. These polymeric structures hold cations in the interstices between different layered structures. In this work we show the stabilization of organocations as illustrated in Fig. 1, in the crystal lattice of manganese(II) and copper(II) 2,3-pyridinedicarboxylate coordination polymers. The reactions of 2,3-pyridinedicarboxylic acid with manganese(II) or copper(II) acetate, followed by reaction with adenine or cytosine under ambient conditions, led to the formation of [1H,9H]-adenine and [1H,3H]-cytosine cations (Scheme 1) in the interstices of metal 2,3-pyridine dicarboxylato polymeric anionic frameworks [37]. Both the adenine/cytosine cations are found to interact with the polymeric chain through electrostatic and hydrogen bonding interactions through Watson–Crick (abbreviated as W-C) face of the nucleobase. The structure of the complex {[1H,9H-ade] 2 [MnL 2 ] n ∙ 4H 2 O} n (1) consists of a chain of [MnL 2 ] 2− units, flanked by two stacks of 1H, 9H- adenine cations. The coordination polyhedron of the manganese (II) ion is distorted octahedral, bearing an O 4 N 2 donor atom set. The coordination mode adopted by the ligand isμ-(κ 3 N,O 2 :O 3 ), i.e. a 2- position carboxylato O atom and the pyridine N atom chelate one manganese atom and a 3-position carboxylato O atom coordinates to another manganese atom (Fig. 2a). The adenine cation (adenine protonated at N1 and N9 sites is most stable [38]) is strongly bound to the polymeric framework. The striking feature of complex 1 is the charge assisted hydrogen bonding between the uncoordinated O 2 atom and the protonated nitrogen of adenine at N1 position (d D∙∙∙H , 1.667 Å, d D∙∙∙A , 2.592 Å; b D-H∙∙∙A, 1580) (Fig. 2c). The amino group of the Watson–Crick face of the adenine cation is not hydrogen bonded with the polymeric anion, but to two crystallized water molecules. The interstitial spaces of the polymeric chain of anionic frameworks of coordination polymer accommodate the discrete adenine cations. The water molecules of crystallization occupy the interstitial space Inorganic Chemistry Communications 13 (2010) 1244–1248 ⁎ Corresponding author. E-mail address: juba@iitg.ernet.in (J.B. Baruah). 1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2010.06.052 Contents lists available at ScienceDirect Inorganic Chemistry Communications journal homepage: www.elsevier.com/locate/inoche