Molecular Nanomagnets and Dual Property Molecular Materials

Prof. Kim R. Dunbar

 

Our interdisciplinary research project in Nanoscience and Nanotechnology involves the design, preparation and study of the physical properties of high-spin molecules  and polymeric molecule-based materials exhibiting interesting magnetic properties in combination with other useful chemical, -physical, -electrical, or -optical properties.  The quest in this area of research is not just to obtain molecule-based compounds than can behave as classical solid state magnets, showing spontaneous magnetization below a certain temperature Tc, but also to produce materials that may exhibit completely new physical properties or those in which the magnetic properties are combined with other physical properties. Examples of such systems could be materials showing bistability, tunable magnetic ordering temperatures, discrete molecules showing magnetic hysteresis (nanomagnets), hybrid materials coupling magnetism with conductivity or even superconductivity, or with optical properties.  In addition the intriguing phenonmenon of “superparamagnetic behavior” This research requires the application of new synthetic strategies to construct molecules at the mesoscale level as well as the use of techniques that allow for precise control, either in solution or in the solid state, of supramolecular assemblies. It is also important to prepare the new magnetic materials in such a way as to take full advantages of their properties in devices. This includes the formation of thin layers and organized films, encapsulation, intercalation and others.  The use of experimental techniques such as high-field high-frequency EPR and NMR spectroscopies, polarized neutron scattering, magnetic and heat capacity measurements at very low temperatures will be used to characterize the resulting materials and to study the most interesting magnetic phenomena.

 

Slow paramagnetic relaxation was observed at low temperatures in the AC susceptibility measurements in the form of a frequency dependent out-of-phase (cm) signal for the molecule {[MnIII(CN)6]2[MnII(tmphen)2]3} (pictured below). This provides compelling evidence that this cluster, which displays antiferromagnetic coupling to stabilize an S = 11/2 ground state, is a rare example of a cyanide-bridged single-molecule magnet (SMM).

 

Structure of the novel two-dimensional honeycomb magnet {[Co3Cl4(H2O)2[Co(Hbbiz)3]2•3C7H8•9CH3OH}, composed of alternating octahedral and tetrahedral Co(II) ions and the bridging ligand 2,2'-bibenzimidazole (Hbbiz). This new type of structural motif is remarkable in that it self-assemblies in one step from solution, with no templating counterions or solvent molecules.  The result is an interwoven series of cormer and edge-sharing twelve-membered rings. Of high interest in terms of properties is the fact that the Hbbiz ligand promotes magnetic exchange and ultimately magnetic ordering in this system. This material is a very rare example of a molecule-based magnet in which a homometallic network is bridged by closed-shell organic molecules.