This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2011 New J. Chem., 2011, 35, 1211–1218 1211 Cite this: New J. Chem., 2011, 35, 1211–1218 [K 2 Mn 5 {Mo(CN) 7 } 3 ]: an open framework magnet with four T c conversions orchestrated by guests and thermal historywz Julie Milon, ab Philippe Guionneau, c Carine Duhayon ab and Jean-Pascal Sutter* ab Received (in Montpellier, France) 2nd November 2010, Accepted 10th January 2011 DOI: 10.1039/c0nj00860e The 3D metal organic framework of formula [K 2 (H 2 O) 4 Mn 5 (H 2 O) 8 (MeCN){Mo(CN) 7 } 3 ]2H 2 O, 1a, gives rise to four ferri-magnets with distinct sets of attributes attained by controlled and sequential variation of its sorption state and a structural transition. 1a is prepared by solution (H 2 O) chemistry at ambient conditions by assembling the heptacyanomolybdate building unit {Mo(CN) 7 } 4 with Mn(II) in the presence of MeCN. The resulting open-framework is achieved only with the small cyanide ligand that also ensures noteworthy magnetic performances. Its potential porosity (28% of solvent accessible volume) is sufficient to observe fast and efficient sorption processes that permit converting the attributes (T c and H c ) of the corresponding magnets. It is shown that the magnetic ordering temperature T c increases from 61 K (for 1a) to 82 K after solvent release whereas this T c is 72 K upon the structural transition taking place for the guest-free magnet. A fourth magnet with T c = 61 K is generated by H 2 O uptake. Concomitantly the coercive fields H c vary between 70 and 1770 Oe. These processes, including the structural phase transition, are reversible by means of basic levers, i.e. thermal processing and H 2 O sorption, allowing inter-conversion among three of the four magnets. The crystal structure analysis for 1a, the XRPD for 1b, 1c, and 1d, the magnetic behavior for the four magnets, and TGA data are reported. Introduction Molecule-based solids represent a rare opportunity to combine, adjust, and inter-relate structural and physical functionalities to develop multi-property materials. The rational and resourceful design methodology to achieve supramolecular architectures with tailored properties opened the way to more elaborated materials that combine two or more physical and/or chemical properties with synergetic interactions. For instance, the design of molecular materials with relevant magnetic properties has been one of the main challenges over the last two decades. 1 Presently, particular attention is devoted to materials for which the magnetic attributes (i.e. ordering temperature, T C ; coercive field, H C ) can be reversibly modulated in the solid state because of prospective relevance of such materials in technological applications such as information storage, switches, sensors, etc. Among the approaches envisioned to achieve such switchable magnets, porous magnets are attracting an increasing interest and several examples of magnetic behaviors driven by the sorption state or the nature of the guest molecules have been reported. 2–4 Four main causes for the changing of the magnet’s features with the sorption states can be identified. The first is a modification of the network dimensionality. Examples comprise the magnetic sponges initially described by Kahn and coworkers. 5–7 Stricto sensu these are not porous materials because in their fully solvated state the solids are formed by discrete molecular units (binuclear {Co–Cu} complexes for Kahn’s compounds). However, upon solvent release these molecules assemble in the solid state leading to 2D or 3D coordination polymers. This structural reorganization induces a dramatic modification of the magnetic behavior. Whereas the initial hydrated compounds exhibit a paramagnetic behavior, the final degassed solids are ferri-magnets. Upon re-solvation, the magnetic ordering is lost and the initial behaviors are recovered. Here, the modulation of the magnetic properties is driven by a changing of the network dimensionality induced by the sorption–desorption process. A shift of the magnetic ordering temperature, T c , to higher temperatures usually comes with the increase of the dimensionality. Several open framework magnets that exhibit T c conversion behaviors are based on dimensionality changes (typically 2D 2 3D). 8–13 The deformation of the framework as a function of the sorption state or of the guest molecules is a further source for a CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse, France. E-mail: sutter@lcc-toulouse.fr b Universite ´ de Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France c CNRS, Universite ´ de Bordeaux, ICMCB, 87 Av. Doc. A. Schweitzer, 33608 Pessac, France w Electronic supplementary information (ESI) available. CCDC reference number 699019. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c0nj00860e z This article is part of a themed issue on Molecular Materials: from Molecules to Materials, commissioned from the MolMat2010 conference. NJC Dynamic Article Links www.rsc.org/njc PAPER