Polyoxometalate associated ion-pair solid based on a crown ether inclusion complex: Synthesis, structure and spectroscopy Tanmay Chatterjee, Monima Sarma, Samar K. Das * School of Chemistry, University of Hyderabad, P.O. Central University, Hyderabad 500 046, Andhra Pradesh, India article info Article history: Received 28 May 2010 Received in revised form 9 July 2010 Accepted 9 July 2010 Available online 21 July 2010 Keywords: Crown ether Isopolyanion Supramolecular chemistry X-ray crystallography Spectroscopy abstract A supramolecular complex, in which a mono-protonated ortho-phynelenediamine (OPDAH) + is included in the cavity of a crown ether (18-crown-6, 18C6) and a tetrabutyalammonium cation are associated with an isopolyanion [Mo 6 O 19 ] 2 resulting in the formation of compound [Bu 4 N][OPDAH(18C6)][Mo 6 O 19 ](1). Compound 1 has been isolated as a single crystalline material at room temperature from MeCNACH 3- COOH solvent system through a one-pot synthesis that includes OPDA, 18-crown-6 and [Bu 4 N] 2 [Mo 6 O 19 ]. Compound 1 has been characterized through routine spectroscopic analyses (IR, 1 H NMR) and elemental analysis including its structural determination through single crystal X-ray crystallography. Crystal data for 1: monoclinic, C2/c, a = 17.5055(10) Å, b = 16.2661(9) Å, c = 37.006(2) Å, b = 94.8510(10)°, V = 10499.7(10) Å 3 , Z = 8, R 1 = 0.0571, wR 2 = 0.1214. Extensive supramolecular hydrogen bonding and p-stacking interactions have been observed in the crystal packing of 1. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Supramolecular assemblies from organic and/or inorganic molecular building blocks are of considerable interest owing to their topological diversities and importance in the area of host– guest chemistry since the last few decades [1–7]. Crown ethers or macrocyclic poly-ethers, an unanticipated discovery of Pedersen [8–10], have been extensively used in the area of supramolecular chemistry as a consequence of their potential applications in molecular recognition, transportation and catalysis [11–16]. These macrocycles have selective complexation aptitude for cationic spe- cies. Common crown-type poly-ethers consist of O, N, S, etc. as the hetero atoms which can encapsulate a cation (for example, a metal ion) via coordinate–covalent bonds or a hydrogen containing cat- ion (for example, H 3 O + , RNH þ 3 , etc.) via hydrogen bonding interac- tions. These macrocycles have repeating AOACH 2 ACH 2 AOA units (in the case of the oxy-crown ethers), which are saturated in nat- ure, thereby making the crown ethers structurally flexible. Guest inclusion capability of such macrocycles is controlled by their cav- ity sizes. 18-crown-6 (18C6) and its derivatives are good hosts for ammonium ions (NH þ 4 ; RNH þ 3 , etc.). Polyoxometalates (POMs), on the other hand, are metal–oxide based cluster anions with potential electronic, structural and topo- logical diversities [17–19]. These macro-anions comprise of edge shared {MO 6 } octahedra (M = Mo, W, etc.) and bear oxygen atoms on their surfaces, that can participate in hydrogen bonding interac- tion with a donor atom or can coordinate to a metal ion too. Incor- poration of supramolecular complexes of the crown ethers with the polyoxometalates (POMs) opens a new area of inorganic–or- ganic hybrid materials that has drawn significant interest in the contemporary research [20–33]. We [20–22], Wang and co-work- ers [23–28] and others [29–33] have reported several crown ether–POM based solids in this category. This class of compounds is known to play an important role as far as separation chemistry is concerned [34–36]. Very recently we have analyzed supramolecular contacts (inter- molecular association) between crown ether inclusion complexes of simple tetrahedral symmetrical (T d ) molecular cation, ammo- nium ion ðNH þ 4 Þ and POM cluster anions [22]. In case of the crown ethers with smaller cavity size (for example, 18-crown-6 and its derivatives), the ammonium ion associates the macrocycle via N + AHO hydrogen bonding interactions using three NAH bonds of the tetrahedral cation, while the fourth NAH bond is involved in N + AHA (A = acceptor) supramolecular interaction with an available acceptor atom (for example, O atom of a POM cluster an- ion). We have observed that, bridging oxygen atom instead of ter- minal oxygen atom of the POM anion has been used as the hydrogen bond acceptor site, possibly because of more efficient crystal packing in the former case [22]. However, both the simple ammonium ion ðNH þ 4 Þ and organic ammonium ions (RANH þ 3 or ArANH þ 3 ) have tetrahedral geometry. The only structural difference between them is that, the latter one has hydrophobic alkyl or aryl group. Again among the alkyl and phenyl groups, the phenyl ring (of the aromatic amines) might undergo p-stacking interactions in the crystal lattice with the generation of a totally different type 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.07.020 * Corresponding author. Tel.: +91 40 2301 1007; fax: +91 40 2301 2460. E-mail address: skdsc@uohyd.ernet.in (S.K. Das). Journal of Molecular Structure 981 (2010) 34–39 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc