Research

Research in the Brook Lab focuses on the  study, control and application of the interaction between unpaired electrons. In addition to the role this plays in understanding covalent bonding, these interactions may have applications in magnetic resonance imaging, information storage and molecular computing. We are focusing our efforts in the following areas:

Synthesis of Verdazyl Free Radicals.

Though most free radicals are reactive species, certain families of stable free radicals can be isolated in air at ambient temperature.  We are particularly interested in verdazylfree radicals which have the general structure shown on the right.

In addition to their stability, these free radicals have three substituents (R1, R3, R5) that can be varied, and two nitrogen lone pairs that can coordinate metal ions.

We are actively developing new routes to verdazyl radicals to allow greater variation in the three substitutents. Some of our synthetic results were reported in 2005 (Paré at al) and 2010 (Richardson et al.).

 

Verdazyl properties and Radical-Radical Interaction.

In synthesizing new verdazyl radicals we are looking to see the effect of varying the substituents, and to link verdazyls together in order to investigate the radical-radical interaction. Recently we have examined the effect of verdazyl subsitituents on the properties of phenols (Chemistruck et al, 2009) and looked at the interaction between radicals linked by a methylene (CH2) group (Brook et al, 2006) The crystal structure of the methylene linked bis-verdazyl is shown below. The effect of the radical-radical interaction is seen in the color of this material - the diradical (seen in solution below right) is orange, whereas the corresponding monoradical is yellow.

 

 

Verdazyl Coordination. 

Metal coordination provides another avenue to modify the verdazyl electronic structure and link free radicals together. Interaction with unpaired electrons on the metal ion generate additional complexity. We have recently reported exceptionally strong ferromagnetic interactions between verdazyl radicals and nickel ions as a result of our novel verdazyl ligand structure. (Richardson et al. 2010). The structure of the nickel complex is shown on the right.

Self-assembly. 

In order to fully explore and apply interactions between unpaired electrons we are investigating self-assembled metal coordination compounds. Our initial foray into this area involved diamagnetic hydrazone ligands and zinc ions, allowing us to use NMR as an analytical tool. This resulted in a joint publication with the research group of Jean-Marie Lehn (Barboiu et al. 2006) and a more recent study using dynamic NMR (Dutta et al. 2011). One of the grid complexes from this paper is shown on the right. We are currently exploring paramagnetic analogs of these initial systems. We are also conducting basic research into the properties of hydrazones as ligands (Wood et al, 2004, Ly et al. 2011)

Techniques.

 In addition to standard techniques of inorganic and organic synthesis, researchers in the Brook lab use a broad variety of analytical and physical methods to identify and characterize free radicals, synthetic intermediates and their metal complexes. These techniques include 1H and 13C NMR, IR, MS, ESR, HPLC, Magnetic susceptibility, UV-vis, cyclic voltammetry, and X-ray diffraction (single crystal and powder).