Impact of counter anions on spin-state switching of manganese(iii) complexes containing an azobenzene ligand

Ghosh, S and Bagchi, S and Kamilya, S and Mehta, S and Sarkar, D and Herchel, R and Mondal, A (2022) Impact of counter anions on spin-state switching of manganese(iii) complexes containing an azobenzene ligand. In: Dalton Transactions, 51 (19). pp. 7681-7694.

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Abstract

Four mononuclear manganese(iii) complexes coordinated with photo-active hexadentate azobenzene ligands, [Mn(5azo-sal2-323)](X) (X = Cl, 1; X = BF4, 2; X = ClO4, 3; X = PF6, 4), were prepared. The impact of various counter anions on the stabilization and switching of the spin state of the manganese(iii) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, and spectroelectrochemical studies, along with theoretical calculations. All four complexes consisted of an isostructural monocationic distorted octahedral MnN4O2 coordination environment offered by the hexadentate ligand and Cl−, BF4−, ClO4−, and PF6− as counter anions respectively. Complex 1 with a spherical Cl− counter anion showed a reversible and gradual spin-state switching between low-spin (LS) (S = 1) and high-spin (HS) (S = 2) states above 400 K, where non-covalent cation-anion interactions played a significant role in stabilizing the LS state. While, irrespective of the shape of the counter anion, complexes 2-4 remained in the HS state throughout the measured temperature range of 300-2 K, where strong π-π interaction between the azobenzene motifs among cationic units played a substantial role in stabilizing the HS state. Furthermore, magnetic data analyses revealed significantly large zero-field splitting in the S = 1 state for 1 (D = 19.4 cm−1, E/D = 0.008) in comparison with that in the S = 2 state for 2-4 (D = 3.99-4.97 cm−1, E/D = 0.002-0.195). Spectroelectrochemical investigations revealed the quasi-reversible reduction and oxidation of the manganese(iii) center to manganese(ii) and manganese(iv), respectively. A detailed theoretical calculation at the DFT and CASSCF level of theory was carried out to better understand the magneto-structural correlation.

Item Type:	Journal Article
Publication:	Dalton Transactions
Publisher:	Royal Society of Chemistry
Additional Information:	The copyright for this article belongs to the Royal Society of Chemistry.
Keywords:	Azobenzene; Manganese compounds; Negative ions; Single crystals; Spectroelectrochemistry; Spin dynamics, Counter anions; Hexadentate; High spin state; Manganese complex(III); Manganese(III); Spin state; Spin-state switching; Structural investigation; Theoretical calculations; Variable temperature, Ligands
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	21 Sep 2022 09:47
Last Modified:	21 Sep 2022 09:47
URI:	https://eprints.iisc.ac.in/id/eprint/76936

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