Magnetic and spectroscopic studies of iron and manganese complexes: from molecular materials to catalysis

PhD ceremony: Ms. H. Tchouka, 14.30 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Magnetic and spectroscopic studies of iron and manganese complexes: from molecular materials to catalysis

Promotor(s): prof. B.L. Feringa

Faculty: Mathematics and Natural Sciences

Prussian Blue (PB) (Fe₄[Fe(CN)₆]₃.14H₂O) was discovered in the 18th century and used as a dye. Recently, the chemistry of cyano complexes such as PB and its analogues (PBAs) has attracted renewed interest. Their physical and chemical properties e.g., dimensionality, color, magnetism, electron transfer are useful in a wide range of materials applications, such as magneto-optical devices or as gas storage materials. One of the main challenges in applications in magnetic memory has been to synthesize of PBAs with a Curie temperature close to room temperature. Their properties can be tuned by parameters such as the defects in their structure, the alkali metal or the transition metal used during the synthesis, however, perfect control of these parameters has not yet been established. Most reported PBAs are synthesized from the reaction of a mononuclear hexacyano complex anion ([M(CN)₆]^n-) with a transition metal cation (M^’p+). This thesis shows that the properties of the complexes can be tuned by substituting one of the cyano ligands with an imidazole. The imidazole complex ([Fe^III(CN)₅im]^2-)is prepared from the ethylene diamine complex ([Fe^II(CN)₅im]^3-); a reaction which itself raises new prospects of C-C bond cleavage, which could be of relevance in catalysis. The use of [Fe^III(CN)₅im]^2-as building block leads to a new series of PBAs of the type M[Fe(CN)₅im].xSolvent (M is Mn²⁺, Co²⁺ of Zn²⁺). Their crystalline forms are either two or three dimensional networks, and the presence of the imidazole ligand improves the magnetic behavior of the system by increasing the Curie temperature.