Research efforts in the Lemaire group are very multi-faceted. In general terms, we are interested in the preparation and properties of new hybrid inorganic/organic materials. This work encompasses basic and advanced organic synthetic techniques, in particular, for the preparation of new ligands, as well as coordination and polymer chemistry.
Students in my lab obtain a plethora of new skills and are exposed to a number of exotic techniques to probe electronic and magnetic properties. We have our own inert-atmosphere facilities to carefully prepare sensitive materials (Innovative Technologies glove box and Schlenk lines), as well as an in-house UV-VIS-NIR spectrophotomer (Shimadzu 3600), FTIR spectrometer (Shimadzu IRAffinity), and electrochemistry equipment (Bioanalytical Systems Inc.). Our spectrophotometer is equipped with a Specac low temperature cell with temperature controller so that we can study the variable temperature optical properties of our materials.
We have also established very fruitful collaborations with crystallographers and physicists and have the ability to investigate the structural, magnetic and Mössbauer properties of our systems.
Current research plans fall within two general themes, which are considered to be the most active areas of research in the field. These include synthetic efforts toward new multifunctional materials we are also exploring new avenues toward the synthesis of high-spin molecules as new families of single molecule magnets.
Multifunctional materials: Spin-crossover, valence tautomerism, and conductivity
One of the most exciting developments in the field of molecular materials is a new focus toward the preparation of materials that exhibit combinations of unusual and generally disparate properties, known in the literature as “multifunctional materials”. The motivation for this work is generally two-fold: Primarily, this is basic exploratory research because combining properties that typically do not exist together in nature within a single material should lead to the discovery of new and unusual properties. On the other hand, there are other interesting applied considerations, for example, using one property in the material to control the other, which has implications for sensory materials, molecular electronics or information storage. We are interested in the preparation of systems that exhibit bistable magnetic or optical properties and at the same time are electrically conducting. Our approach is to combine these properties in an intramolecular fashion by preparing conducting metallopolymers (Wolf class I, II, or III) containing spin-crossover or valence tautomeric substituents. Our intramolecular approach should lead to stronger property-property interactions and, therefore, make these materials potentially much more useful.
New synthetic pathways toward high-spin molecules
High-spin molecules are defined as molecular species containing at least two unpaired electrons, and in which the local magnetic interactions between these electrons result in, at a minimum, an S = 1 ground state. Generally, the local spin-spin interaction in high-spin molecules is ferromagnetic (magnetic dipoles align parallel to one another); however, antiferromagnetic interactions can result in high-spin ground states when the aligning spin vectors are unequal (ferrimagnetism). A challenge in materials chemistry is to design molecules containing many unpaired electrons, but doing this in a rational manner so that the magnetic interactions are ferromagnetic: This is a rather difficult challenge, but the potential benefits are enormous! Under particular conditions, high-spin molecules can exhibit single molecule magnetism, which basically means that a single molecule can exhibit magnetic properties (such as thermal hysteresis and remnance) that are analogous that of a bulk magnet! If data storage using the magnetic dipole of a single molecule as a “bit” is achievable, we have the opportunity to dramatically increase magnetic storage capacities, or computer “speeds”.
Most high-spin molecules are prepared serendipitously by coordination of paramagnetic transition metal ions with bridging ligands. Some excellent examples of high-spin molecular species have been reported, but magnetic interactions between metal ions through diamagnetic bridging ligands tend to be extremely weak. One of the major synthetic challenges is to design molecular systems with high-spin ground states that are well isolated, energetically speaking, from other spin excited states. We propose to do this using paramagnetic bridging ligands designed from known or newly developed families of stable free radicals. In this manner, the local magnetic interactions are direct, between metal and coordinated ligand. Interactions of this type are known to be very strong.
Students in my lab obtain a plethora of new skills and are exposed to a number of exotic techniques to probe electronic and magnetic properties. We have our own inert-atmosphere facilities to carefully prepare sensitive materials (Innovative Technologies glove box and Schlenk lines), as well as an in-house UV-VIS-NIR spectrophotomer (Shimadzu 3600), FTIR spectrometer (Shimadzu IRAffinity), and electrochemistry equipment (Bioanalytical Systems Inc.). Our spectrophotometer is equipped with a Specac low temperature cell with temperature controller so that we can study the variable temperature optical properties of our materials.
We have also established very fruitful collaborations with crystallographers and physicists and have the ability to investigate the structural, magnetic and Mössbauer properties of our systems.
Current research plans fall within two general themes, which are considered to be the most active areas of research in the field. These include synthetic efforts toward new multifunctional materials we are also exploring new avenues toward the synthesis of high-spin molecules as new families of single molecule magnets.
Multifunctional materials: Spin-crossover, valence tautomerism, and conductivity
One of the most exciting developments in the field of molecular materials is a new focus toward the preparation of materials that exhibit combinations of unusual and generally disparate properties, known in the literature as “multifunctional materials”. The motivation for this work is generally two-fold: Primarily, this is basic exploratory research because combining properties that typically do not exist together in nature within a single material should lead to the discovery of new and unusual properties. On the other hand, there are other interesting applied considerations, for example, using one property in the material to control the other, which has implications for sensory materials, molecular electronics or information storage. We are interested in the preparation of systems that exhibit bistable magnetic or optical properties and at the same time are electrically conducting. Our approach is to combine these properties in an intramolecular fashion by preparing conducting metallopolymers (Wolf class I, II, or III) containing spin-crossover or valence tautomeric substituents. Our intramolecular approach should lead to stronger property-property interactions and, therefore, make these materials potentially much more useful.
New synthetic pathways toward high-spin molecules
High-spin molecules are defined as molecular species containing at least two unpaired electrons, and in which the local magnetic interactions between these electrons result in, at a minimum, an S = 1 ground state. Generally, the local spin-spin interaction in high-spin molecules is ferromagnetic (magnetic dipoles align parallel to one another); however, antiferromagnetic interactions can result in high-spin ground states when the aligning spin vectors are unequal (ferrimagnetism). A challenge in materials chemistry is to design molecules containing many unpaired electrons, but doing this in a rational manner so that the magnetic interactions are ferromagnetic: This is a rather difficult challenge, but the potential benefits are enormous! Under particular conditions, high-spin molecules can exhibit single molecule magnetism, which basically means that a single molecule can exhibit magnetic properties (such as thermal hysteresis and remnance) that are analogous that of a bulk magnet! If data storage using the magnetic dipole of a single molecule as a “bit” is achievable, we have the opportunity to dramatically increase magnetic storage capacities, or computer “speeds”.
Most high-spin molecules are prepared serendipitously by coordination of paramagnetic transition metal ions with bridging ligands. Some excellent examples of high-spin molecular species have been reported, but magnetic interactions between metal ions through diamagnetic bridging ligands tend to be extremely weak. One of the major synthetic challenges is to design molecular systems with high-spin ground states that are well isolated, energetically speaking, from other spin excited states. We propose to do this using paramagnetic bridging ligands designed from known or newly developed families of stable free radicals. In this manner, the local magnetic interactions are direct, between metal and coordinated ligand. Interactions of this type are known to be very strong.
