Structure–property relationships: Polymorphism, solvates, and clay behavior in the one-dimensional coordination polymer chains [Ag(L)(NO 3 )](H 2 O) n , L = ethanediyl bis(isonicotinate), n = 0, and 2 Adeline Y. Robin a , Jorge L. Sague Doimeadios a , Antonia Neels b , Tu ¨ nde Vig Slenters a , Katharina M. Fromm a, * a University of Basel, Department of Chemistry, Spitalstrasse 51, CH-4056 Basel, Switzerland b University of Neucha ˆtel, Institut de Microtechnique, Rue Emile-Argand 11, BATIMENT G, Case postale 158, CH-2009 Neucha ˆtel, Switzerland Received 16 June 2006; accepted 20 July 2006 Available online 10 August 2006 Inorganic Chemistry – The Next Generation. Abstract The system AgNO 3 and L (L = ethanediyl bis(isonicotinate)) yielded so far five different compounds from a THF/H 2 O mixture (or acetonitrile) when reacted in a ratio 1:1. Three solvent-free compounds possess the same chemical composition, [Ag(L)NO 3 ], but different structures and thus different properties. Additionally, two solvates [Ag(L)NO 3 ] Æ nH 2 O with one or two water molecules have been iden- tified. One of the solvates can be reversibly transformed into one of the solvent free compounds. This clay-like property depends strongly on the structure observed in the solid state, namely on the coordinating function of the nitrate ions with respect to silver cations. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Coordination polymer networks; Metal-organic frameworks; Silver nitrate; Polymorphs; Clay-like behavior; Solvates; Supramolecular iso- mers; X-ray crystal structures 1. Introduction Controlled porosity in materials is a widely studied topic in chemistry, as open frameworks with micro- or nanome- tre-sized spaces can be used in gas and liquid separation, gas storage, sensors, molecular recognition, anions/cations exchange, heterogeneous catalysis etc. [1]. Indeed, porous materials allow the reversible passage of host molecules through the guest materials via the surface holes. The advantage of introducing organic molecules in such frame- works is the control of the material design: architecture choice, functionality of the pores and increasing selectivity. A particular case of interest for intercalation is found in the research on layered materials acting as mineral clays for the reversible intercalation of guest molecules [2,3]. The coordination polymers derived from silver ions Ag I with N-donor ligands are well-known for making simple, one-dimensional motifs when the two-coordinate metal ion reacts with a bipyridine-type ligand [4,5]. Ag I has a preference for linear geometry in these cases. Nevertheless, as the coordination sphere of Ag I is very flexible, it can adopt coordination number between two and six, the geometry changing from linear to octahedral. The coordi- nation geometries of Ag I are often distorted owing to the inherent lack of ligand field stabilization effects (Soft Lewis Acid). The reaction of silver salts with the linear 4,4 0 - bipyridine ligand affords either a linear [6–8] or tetrahedral geometry [9], depending on the ratio of 4,4 0 -bipyridine to silver, 1:1 or 2:1, respectively. The same compounds can also lead to other architecture with a ‘‘T-shaped’’ moiety 0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2006.07.086 * Corresponding author. Tel.: +41 61 267 1004; fax: +41 61 267 1021. E-mail address: katharina.fromm@unibas.ch (K.M. Fromm). URL: http://www.chemie.unibas.ch (K.M. Fromm). www.elsevier.com/locate/ica Inorganica Chimica Acta 360 (2007) 212–220