Name: Ms. Sukanya Bagchi

Title: Switchable Magnetic Materials based on Spin State Switching and Single Molecule Magnets

Date &Time : Friday, 24th May 2024 at 11.00 a.m.

Venue: Rajarshi Bhattacharya Memorial Lecture Hall, Chemical Sciences Building

Molecular Magnets have been a subject of interest among researchers due to their potential application towards the data storage devices, molecular switches and sensors, spintronics and quantum computing.1-2 They encompass various systems, includingspin crossover (SCO), single molecule magnets (SMMs), single chain magnets (SCMs), electron transfer systems,valence tautomersetc. Of these intriguing topics, my Ph.D. thesis is based on Stimuli-responsive SCO systems and Lanthanide based SMMs.

SCO systems are of contemporary interest to the research community as they represents a group of molecules that respond to stimuli such as heat (temperature variations), light, pressure, pH, etc., and can change their spin states and hence their observable physical properties. Transition metal complexes with the configuration of 3d4-7generally show this property in an octahedral coordination environment when the octahedral splitting energy (Do) is comparable to the pairing energy (P) and contributes to the world of multifunctional bistable materials.3Therefore, SCO systems have potential applications as switches, sensors and in spintronics.1In my thesis, Iexplored the various avenues of Mn(III) based SCO systems, studied the magneto-structural aspects, andcarried out spectroscopic and electrochemical studies. Itried to tune the SCO temperature of these systems by ligand modification, alteration of counter anions, etc.4Mn(III), a d4 system in Oh surrounding is Jahn Teller active metal center and shows distinct structural changes associated with SCO at different temperatures. It can change the spin state from high spin to low spin on temperature variation when the ligand field and orientation and cooperativity of the systems are properly tuned.3,4We explored the effect of counter anions and ligand substitutions in shaping the SCO profiles of Mn(III) mononuclear systems via. modifying the cooperativity of these systems.

SMMsbridge the gap between the Classical and the Quantum world. As the name suggests, they are magnets of molecular origin and do not require long-range ordering as in classical magnets. Scientists are investigating to tune the blocking temperature (the temperature below which SMMs can retain its magnetization in the absence of an applied external field)of these systems to use them as qubits for data storage and aid in Quantum Computing and Spintronics.5, 6 These systems require a high spin ground state and high uniaxial anisotropy is desirable so that the effective energy barrier between the bistable magnetic spin ground state is enhanced and thereby the longevity of data storage. To investigate this research area, I have used several lanthanide (III) ions, namely Dy(III), Nd(III), Ho(III), Er(III), Tb(III), to prepare a series of SMMs. Dy(III) complexes7 showed SMM behaviour at zero applied DC field and the other lanthanides displayed field induced slow relaxation of magnetization confirming the SMM behaviour.7 Lanthanides are also known for their luminescence, and attempts are being made to use them in luminescence thermometry.5 We explored the photoluminescence properties of the synthesized complexes and studied the temperature-dependent photoluminescence behaviour to unravel its potential in luminescence thermometry.7We explored the effect of counter anions and ligand substitutions and tried to tune the slow relaxation of magnetization in Ln(III) SMMs by tuning the anisotropy of these systems.Proper utilization of these stable molecular systems with precise modifications will show bright prospects in the field of molecular switches and memory devices.

1. Coronado, E., Molecular magnetism: from chemical design to spin control in molecules, materials and devices. Nat. Rev. Mater.,2019,5, 87-104.

2. Kahn, O., Molecular magnetism. Wiley-VCH New York (N.Y.): New York (N.Y.), 1993.

3. Olguín, J., Unusual metal centres/coordination spheres in spin crossover compounds. Coord. Chem. Rev.,2020,407, 213148 – 213177.

4. Ghosh, S.; Bagchi, S.; Das, M.; Kamilya, S.; Mondal, A., Stepwise spin-state switching in a manganese(III) complex. Dalton Trans.,2020,49, 14776-14780; Ghosh, S.; Bagchi, S.; Kamilya, S.; Mondal, A., Effect of ligand substituents and tuning the spin-state switching in manganese(iii) complexes. Dalton Trans.,2021,50, 4634-4642; Ghosh, S.; Bagchi, S.; Kamilya, S.; Mehta, S.; Sarkar, D.; Herchel, R.; Mondal, A., Impact of counter anions on spin-state switching of manganese(III) complexes containing an azobenzene ligand. Dalton Trans.,2022,51, 7681-7694, Bagchi, S.; Kamilya, S.; Mehta, S.; Mandal, S.; Bandyopadhyay, A.; Narayan, A.; Ghosh, S.; Mondal, A., Spin-state switching: chemical modulation and the impact of intermolecular interactions in manganese(iii) complexes. Dalton Trans., 2023, 52, 11335-11348; Bagchi, S.; Mandal, S.; Mondal, A. Impact of (TBA)2[Ni(mnt)2] as Counter Anion on the Spin Crossover Profile of a Mn(III) Mononuclear Complex (manuscript under preparation).

5. Marin, R.; Brunet, G.; Murugesu, M., Shining New Light on Multifunctional Lanthanide Single-Molecule Magnets. Angew. Chem. Int. Ed., 2021,60, 1728-1746.

6. Dey, A.; Kalita, P.; Chandrasekhar, V., Lanthanide(III)-Based Single-Ion Magnets. ACS Omega,2018,3 (8), 9462-9475.

7. Bagchi, S.; Kamilya, S.; Mehta, S.; Rouzières, M.; Herchel, R.; Ghosh, S.; Mondal, A. Tuning Magnetic Anisotropy and Luminescence in a Series of Dysprosium Complexes containing b-diimine Ligand (submitted); Bagchi, S.; Kamilya, S.; Mehta, S.; Rouzières, M.; Herchel, R.; Ghosh, S.; Mondal, A. Luminescence HolmiumIII Mononuclear Single Molecule Magnet (manuscript under preparation); Bagchi, S.; Kamilya, S.; Mehta, S.; Rouzières, M.; Herchel, R.; Ghosh, S.; Mondal, A. Probing of Magnetic and Optical Properties in Mononuclear Neodymium(III) Complexes (manuscript under preparation).