Is building molecular solid-state structures as easy as playing with Lego?

Licentiate thesis, 2008

Crystal engineering is a science dealing with molecular solid-state compounds. One major development in the last ten years has been the description of structures as if they were forming network. In this simplified approach to the structures where atoms, molecules, and molecular ions are replaced by a construction of edges and nodes forming a net. Some of these assemblies are made by combining organic ligands and metal ions, and they are sometimes referred to as Metal Organic frameworks (MOF). The interest in MOFs comes from the specific structure of some of them. They can have large void in the assembly and the cavities can be surrounded by different molecular functions, which are useful for some application, for example gas storage, such as hydrogen, or gas separation. For these reasons the interest in MOFs has increased during the last ten years. The thesis will first give some useful definitions for the project and then a description of different crystal structures and the elaboration of the frameworks associated to them. The compounds described are made from covalent bonds with the example of three different barium oxalates: (Ba(C2O4)·2H2O, Ba(C2O4)(H2C2O4)·2H2O, and Ba2(C2O4)(HC2O4)2·2H2O,), or by hydrogen bonds with cobalt biimidazole used as starting building block: [Co(H2biim)3](ox)2Cl2, [Co(H2biim)3][Co(ox)3]·H2O, [Co(H2biim)3][Cr(ox)3]·H2O , and [Co(C6H6N6)3][C4HO4]·2H2O, or a mix of covalent and hydrogen bonds in [Ca[Co(en)(oxalato)2]2]n, and finally a structure formed by weak hydrogen bonds ([C12H7N2O2]Cl).