Pressure is an energy density. When a material is compressed, it rises its energy, which is a way to induce structural transformations. The higher the pressure, the more sever can be the transforamtions, ranging from simple crystal packing modifications and conformational rearrangements of a molecule to stretching/compression of some strong chemical bond and solid state chemical reactions. In this project we investigate some representative example of each kind of transformation. In particualr, we analyse conformational rearrangements in organometallic molecules, breathing effect in metal-organic frameoworks, pressure induced changes of the Jahn Teller distortions in magnetic coordination polymers and chemical reactions in organic crystals (in particular nucleophilic additions).

Lay summary

The goal of this project is that of using pressure as a medium to induce structural modifications in crystalline phases of organic and metal organic molecules or polymers, with the intent to discover new forms of the materials, potentially with new properties.

In this study, we have so far characterized the transformation occurring in metal carbonyl dimers under pressure, in particular clarifying the stereochemistry of the high pressure form of Mn2(CO)10, which was still matter of debate, lacking of X-ray diffraction analysis.

Moreover, we have investigated several coordination polymers. Some of them are magnetically active, due to the presence of a magnetic metal ion. In particular we have studied the [CuF2(H2O)2](pyrazine)x (x=1,2) system, known to undergo sequential orbital ordering as a function of pressure. We have discovered one new high pressure phase and an ambient phase of new stoichiometry. The kinetics of these transformation is investigated, with a new high pressure technique (results will be submitted for publication soon).

Other coordination polymers are metal organic frameworks based on benzotriazole-5-carboxylate as anionic linker and Zn, Co, Mn as metal connectors. These MOF are flexible enough to show the so-called breathing effect, i.e. contraction expansion of the pores due to desorption or adsorption of (small) guest molecules. we found new interesting phases, pressure or temperature induced, that demonstrate the occurrence of coordination by the guest molecules. These results are going to be submitted for publication.

Th most appealing results of our study are the functionalization of some organic molecules (dicarboxylic acids and aromatic annulenes) that bring to pre-reactive states and eventually to pressure induced polymerization, all step characterized by synchrotron X-ray diffraction.