Topological description (Nets) of MOFs: a new perspective of analysis in crystal engineering

BERNINI, M.C; GOMEZ, GERMÁN ERNESTO; BRUSAU, E.V; G. E. NARDA; N. SNEJKO; E. GUTIERREZ-PUEBLA; M. A. MONGE

Santa Fe

Congreso; VIII Reunión de la Asociación Argentina de Cristalografía; 2012

Universidad Nacional del Litoral y Asociación Argentina de Cristalografía

From the very earliest days of crystallography, simple inorganic structures were shown as ?ball-and-stick? models in which the balls were the atoms and the sticks corresponded to bonds presumed to exist between nearest-neighbor atoms. It was early realized, particularly by Wells,[1] that such models could be considered as representations or embeddings of special kinds of abstract graphs called nets. A net is just a special sort of graph. It is simple, meaning that there is at most one edge that links any pair of vertices, and there are no loops (edges linking a vertex to itself). A net is also connected, meaning that every vertex is linked to every other by a continuous path of edges. The net of a polyhedron is finite. In crystals we will have infinite nets that are 1D, 2D or 3D. Why should we care about nets and related structural aspects of crystals? First and foremost, as chemists we recognize that the very core of our science lies in describing, and perhaps understanding, how atoms organize themselves, sometimes with our help, in chemical compounds[2]. Such knowledge is also essential to designed synthesis of Molecular Materials, from the simpler Inorganic Complexes, Organic Solvates or Salts (for example, in crystalline drugs), to the more complex structures of Covalent Organic Fameworks (COFs) and Metal Organic Frameworks (MOFs) or Coodination Polymers. In this work, we will put particular emphasis in the analysis of MOFs structures to obtain the ?underlaying topology? that means to extract the innate structure of the net associated with such crystal structure. In this sense, a process of deconstruction allows to simplify the whole structure into its fundamental units without losing their chemical significance. An important next step is the realization that, in fact, certain topologies could be targeted by assembling appropriately shaped components.[3] The discipline of preparing materials of targeted geometry by design is termed reticular chemistry[4]. The objectives of this work is: i) to introduce the corresponding nomenclature necessary to properly describe nets; ii) to show the topological analysis performed with TOPOS program[5] in different kind of molecular materials from polynuclear complexes based on Sc(III) and croconate ligand to 2D and 3D Coordination Polymers based on M(III) and diverse ligands like succinate, 2,2- and 2,3-dimethylsuccinate, 2-fenylsuccinate, 2-aminoterephthalate and 4,4´-hexafluorobisbenzoic acid; iii) to discuss different procedure of simplification applied to MOFs structures containing isolated, clusters and infinite Secondary Building Units. [1] Wells, A. F. Three-Dimensional Nets and Polyhedra; Wiley:New York, 1977. [2] M. O´Keefe, O. M. Yaghi Chem. Rev., 2012, 112 (2), pp 675?702. [3] a) Hoskins, B. F.; Robson, R. J. Am. Chem. Soc. 1990, 112, 1546; [4] O. M. Yaghi, M. O?Keeffe, N. W Ockwig, H. K Chae, M. Eddaoudi, J. Kim, Nature 2003, 423, 705. [5] V. A. Blatov, IUCr CompComm Newsletter, 2006, 7, 4?38; http://www.topos.ssu.samara.ru Keywords: Topology, TOPOS, Nets, Metal-Organic Frameworks, Underlaying Net.