A New Family of Bimetallic Framework Materials Showing Reversible Structural Transformations Olha Sereda, † Fritz Stoeckli, † Helen Stoeckli-Evans,* ,† Oleg Dolomanov, ‡ Yaroslav Filinchuk, § and Phil Pattison §,| Institute of Physics, UniVersity of Neucha ˆtel, rue Emile-Argand 11, CH-2009 Neucha ˆtel, Switzerland, Department of Chemistry, Durham UniVersity, Durham, DH1 3LE, U.K., Swiss Norwegian Beamlines at ESRF, BP-220, 38043 Grenoble, France, and Laboratoire de Crystallographie, E ´ cole Polytechnique Fe ´de ´rale de Lausanne, BSP, CH-1015 Lausanne, Switzerland ReceiVed August 11, 2008; ReVised Manuscript ReceiVed April 24, 2009 ABSTRACT: Three new bimetallic framework compounds, namely, (([Cd 3 (tn) 4 ][Co(CN) 6 ] 2 ) · 5H 2 O) ∞ (1), ([Cd(tn)] 3 [Cr(CN) 6 ] 2 ) ∞ (2), and ([Cu 2 (tn) 2 ][Ru(CN) 6 ] · 4H 2 O) ∞ (3), have been prepared in a very simple manner from the ligand 1,3-diaminopropane (tn), the hexacyanometalates [Co(CN) 6 ] 3- , [Cr(CN) 6 ] 3- and [Ru(CN) 6 ] 4- , and a metal(II) sulfate (M II SO 4 :M ) Cd 2+ , Cu 2+ ). They have been characterized by IR, X-ray diffraction, elemental analysis and immersion calorimetry. All three compounds have three-dimensional structures, with both the organic ligand and the cyanide groups acting as bridges. Compounds 1 and 3 have channels occupied by water molecules of crystallization. All three complexes are stable indefinitely when exposed to the air at room temperature; however, when compounds 1 and 3 are heated, they lose the water molecules of crystallization. The powder X-ray diffractograms of these dried and as yet unknown species are different from those of the original compounds. However, in a humid atmosphere both dried compounds readsorb water molecules and revert to the original structures, as shown by powder X-ray diffraction measurements. The adsorption properties of compounds 1 and 3 were studied using immersion calorimetry and in situ powder X-ray diffraction. In the case of compound 3 the heat of the structural transformation on rehydration was found to be ca. 19 ( 3 J/g. Introduction The domain of three-dimensional coordination polymers, or metal-organic frameworks (MOFs) as they are called today, is an intensely studied field of research, and the subject has been reviewed recently by various authors who are extremely active in this field. 1-8 These compounds are of great interest owing to their potential applications in the areas of gas storage, gas separation, and heterogeneous catalysis. 9-22 The majority of these compounds are homometallic and have been formed using organic carboxylates and transition metal salts. 23-28 Some cyanide-bridged inorganic coordination polymers, prepared by assembling cyanometalate anions and transition metal complexes as building blocks, have also been found to have framework structures. The hexacyanometalates, M II (CN) 6 4- and M III (CN) 6 3- , are good building blocks, and a number of multidimensional systems have been synthesized, some with interesting magnetic properties. 29-34 Interest in the gas sorption properties of these compounds has increased in recent years. 35 However, only a small number of coordination polymers based on hexacyano- metalates have been reported as being porous. 36,37 Porous materials that show reversible phase transformations on loss and addition of solvent molecules have also been reported on recently. 38-41 We have focused our efforts on the synthesis of crystalline materials, since the attainment of well-defined structures is intimately linked to an understanding of the design, synthesis and properties of such materials. For example, using hexacy- anochromate(III) it was possible to prepare bimetallic three- dimensional (3D) and chiral one-dimensional (1D) metal-organic cyano-bridged materials which exhibit ferromagnetism. 42 In another case, we have successfully prepared a bimetallic 3D metal-organic cyano-bridged framework material using 4,4′- bipyridine, tetracyanonickelate and copper sulfate. 43 Our interests are in the construction of materials, porous or not, in which such phase transformations take place. 44 Here we report on three new 3D metal-organic cyano-bridged frame- works, prepared in a very simple manner from the ligand 1,3- diaminopropane (tn), the hexacyanometalates [Co(CN) 6 ] 3- , [Cr(CN) 6 ] 3- and [Ru(CN) 6 ] 4- , and a metal(II) sulfate (M II SO 4 : M ) Cd 2+ , Cu 2+ ). In order to explore their potential adsorptive properties and to study the various phase transformations that take place, the techniques of immersion calorimetry and in situ powder X-ray diffraction have been used. Experimental Section Elemental analyses of carbon, hydrogen, and nitrogen were per- formed by the Microanalysis Service of the Laboratory of Pharmaceuti- cal and Organical Propedeutical Chemistry at the University of Geneva (Geneva, Switzerland). Infrared spectra were measured using KBr pellets in the interval of 4000-40 cm -1 using a Perkin-Elmer 1720X FT-IR spectrometer. Thermogravimetric (TG) analyses were carried out using a Mettler 4000 module. Samples were introduced in a closed aluminum oxide crucible and heated at rate 0.1 °C min -1 under nitrogen at atmospheric pressure. DSC measurements were done with a modified differential scanning calorimeter (Mettler Toledo DSC 822e), under N 2 /He at a rate of 1 °C/min. Immersion calorimetry experiments were carried out at 293 K on samples of 0.15-0.20 g using a TIAN-CALVET type calorimeter. 45,46 The outgassed sample was placed in the calori- metric cell which was then immersed into a water bath controlled by a thermoregulator system LUDA MS. The thermal flow was provided by 180 thermocouples of Cu/constantan connected to a nanovoltmeter PREMA 8017. The integral of the curve, V ) f(t), is proportional to the energy generated during the immersion process, Δ i H. The normal calibration of the calorimetry system was carried out with an electrical resistance. The accuracy varies between 4 and 5% depending on the absolute energy liberated in the process and on the amount of solid used. * Corresponding author. Mailing address: Institut de Physique, Universite ´ de Neucha ˆtel, Rue Emile-Argand 11, CH-2009 Neucha ˆtel, Switzerland. E-mail: Helen.Stoeckli-Evans@unine.ch. † University of Neucha ˆtel. ‡ Durham University. § Swiss Norwegian Beamlines at ESRF. | E ´ cole Polytechnique Fe ´de ´rale de Lausanne. CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 7 3104–3110 10.1021/cg800883x CCC: $40.75  2009 American Chemical Society Published on Web 05/07/2009