Impact of Counteranion on Reversible Spin-State Switching in a Series of Cobalt(II) Complexes Containing a Redox-Active Ethylenedioxythiophene-Based Terpyridine Ligand

Subrata Ghosh; Sounak Ghosh; Sujit Kamilya; Subhankar Mandal; Sakshi Mehta; Abhishake Mondal

doi:10.1021/acs.inorgchem.2c02313

Impact of Counteranion on Reversible Spin-State Switching in a Series of Cobalt(II) Complexes Containing a Redox-Active Ethylenedioxythiophene-Based Terpyridine Ligand

Inorg Chem. 2022 Oct 31;61(43):17080-17088. doi: 10.1021/acs.inorgchem.2c02313. Epub 2022 Oct 20.

Authors

Subrata Ghosh¹, Sounak Ghosh¹, Sujit Kamilya¹, Subhankar Mandal¹, Sakshi Mehta¹, Abhishake Mondal¹

Affiliation

¹ Solid State and Structural Chemistry Unit, Indian Institute of Science, Sir C V Raman Road, Bangalore 560012, India.

PMID: 36264687
DOI: 10.1021/acs.inorgchem.2c02313

Abstract

The self-assembly of a redox-active ethylenedioxythiophene (EDOT)-terpyridine-based tridentate ligand and cobalt(II) unit with different counteranions has led to a series of new cobalt(II) complexes [Co(L)₂](X)₂ (X = BF₄ (1), ClO₄ (2), and BPh₄ (3)) (L = 4'-(3,4-ethylenedioxythiophene)-2,2':6',2″-terpyridine). The impact of various counteranions on stabilization and spin-state switching of the cobalt(II) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, electrochemical, and spectroelectrochemical studies. All three complexes 1-3 consisted of an isostructural dicationic distorted octahedral CoN₆ coordination environment offered by the two L ligands in a bis-meridional fashion and BF₄^-, ClO₄^-, and BPh₄^- as a counteranion, respectively. Complex 2 with ClO₄^- counteranion showed a reversible, gradual, and nearly complete spin-state switching between low-spin (LS) (S = 1/2) and high-spin (HS) (S = 3/2) states, while an incomplete spin-state switching behavior was observed for complexes 1 (BF₄^-) and 3 (BPh₄^-) in the measured temperature range of 350-2 K. The non-covalent cation-anion interactions played a significant role in stabilizing the spin-state in 1-3. Additionally, complexes 1-3 also exhibited interesting redox-stimuli-based reversible paramagnetic HS cobalt(II) (S = 3/2) to diamagnetic LS cobalt(III) (S = 0) conversion, offering an alternate way to switch the magnetic properties.