We use concepts from organic chemistry to design tailor-made ligands. These designed ligands are then used to form metal complexes where the metal center is in a defined and confined environment. Principles from organometallic synthesis, classical coordination chemistry, and (sometimes) photochemistry and microwave irradiation are used for the synthesis of the metal complexes. Such a holistic approach helps us to generate target oriented metal complexes for catalysis and for inducing switchable properties. Working under an inert atmosphere helps us to detect reactive species with relevance to catalysis. Furthermore, controlled synthesis of reactive metal complexes is useful for probing (catalytic) reaction mechanisms.
The initial characterization of all compounds is performed by 1D 1H and 13C NMR spectroscopy. For compounds that contain relevant heteroatoms, additionally, 31P, 19F, 15N and so on are performed as well. Multidimensional NMR spectroscopy is sometimes used for the thorough assignments of all the nuclei in a compound. Additionally, we use both multinuclear and multidimensional NMR spectroscopy for characterizing catalytic intermediates. Such measurements provide us with invaluable information regarding catalytic reaction mechanisms. We also sometimes use NMR spectroscopy for investigating paramagnetic compounds. Variable temperature NMR spectroscopy on paramagnetic compounds provide very useful information regarding spin state switching in solution.
Electroactive organic compounds and their metal complexes are at the heart of our research. To decipher their electron transfer properties, we usually use a combination of CV and DPV. The same methods are also used to investigate electrocatalytic processes such as H2 activation and production, CO2 reduction and C-C bond formation reactions. Additionally, bulk electrolysis is used for studying the electrocatalytic reactions. An important current focus is the use of electrochemical methods for the investigation of reaction mechanisms of electrocatalytic reactions.
Besides NMR spectroscopy, IR spectroscopy is extremely powerful for gaining structural information of molecules. Often this method is used as a simple characterization tool. However, we also use IR spectroscopy in combination with electrochemistry (IR spectroelectrochemistry). Such an approach allows us to gather structural information on chemical systems in their various redox states. IR spectroelectrochemistry also provides useful information on the charge distribution in molecules. Additionally, IR spectroelectrochemistry helps us in determining the donor properties of new redox-active ligands and in probing mechanisms of electrocatalytic reactions.
Many compounds synthesized in our labs are strongly colored. Hence, absorption spectroscopy in the visible region is extremely useful for the characterization of such compounds. As one focus of our research is the generation of visible and NIR electrochromic dyes, the combination of electrochemistry and UV-vis-NIR spectroscopy (spectroelectrochemistry) is widely used in our labs. This combination allows use to determine optical switching in the visible and the NIR region. Additionally, we use UV-vis-NIR spectroelectrochemistry to gain information on the electronic structures of the compounds in their various redox states, to investigate electron transfer processes, and to investigate electrocatalytic reaction mechanisms.
Synthesizing and characterizing paramagnetic compounds is one of the priorities in our group. These compounds, which sometimes get a step-motherly treatment from chemists, can be characterized through EPR spectroscopy. Additionally, we routinely generate short-lived radical intermediates through in-situ electrolysis, and the method of EPR spectroelectrochemistry comes in very handy for the characterization of such species. Apart from characterizing paramagnetic species, we use EPR spectroscopy also to investigate reactive intermediates of catalytic reactions that involve radical intermediates. Furthermore, EPR spectroscopy is a useful method while investigating magnetically switchable molecules. While we can perform X-band EPR spectroscopy in our own labs, high frequency EPR measurements are sometimes carried out in joint projects with our collaborators.
For an inorganic chemist, the epitome of structural characterization is single crystal X-ray diffraction. We often characterize all our metal complexes through this method. In cases, where information from spectroscopic methods are not sufficient for the prediction of the structure of a new compound, information from single crystal X-ray diffraction is extremely useful. Additionally, for paramagnetic compounds, this method delivers direct structural information on the samples, which is otherwise hard to obtain through other methods. In some cases, intermediates obtained from chemical reactions are investigated with single crystal X-ray diffraction to obtain valuable information about the reaction mechanism.
In modern chemistry, DFT calculations play a vital role in elucidating diverse chemical and physical properties of chemical compounds. In our group, DFT calculations are used to probe the electronic structures of metal complexes, and to complement and comprehend the spectroscopic data obtained from several spectroscopic techniques. Such a combined theoretical and experimental approach helps us in understanding our systems better, and also provides us with some predictive power over newly synthesized systems. While basic DFT is carried out in the group itself, we collaborate with expert theoreticians on advanced problems.
Light is an extremely powerful, benign and environmentally friendly source for carrying out various chemical reactions including catalysis. In our laboratories, we use light for both catalysis, as well as for bond activation reactions resulting in highly reactive and exotic chemical species. In many cases, it is not possible to carry out these light-induced reactions through normal thermal means. A first focus of these investigations is to convert light into useful chemistry. However, the mid- and long-term goals of these projects are to understand the photochemical landscapes of such species, and to correlate these with the observed chemical reactivity. Many of the spectroscopic methods mentioned above are combined with photochemical reactions to probe mechanisms. Additionally, we collaborate with photochemists and photophysicists to have a closer look at the excited states of these molecules.