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Homochiral Mn3+ Spin-Crossover Complexes: A Structural and Spectroscopic Study

Year: 2022

Type: article

Abstract: Structural, magnetic, and spectroscopic data on a Mn 3+ spin-crossover complex with Schiff base ligand 4-OMe-Sal 2 323, isolated in crystal lattices with five different counteranions, are reported.Complexes of [Mn(4-OMe-Sal 2 323)]X where X = ClO 4 -(1), BF 4 -(2), NO 3 -(3), Br -(4), and I -(5) crystallize isotypically in the chiral orthorhombic space group P2 1 2 1 2 with a range of spin state preferences for the [Mn(4-OMe-Sal 2 323)] + complex cation over the temperature range 5-300 K. Complexes 1 and 2 are high-spin, complex 4 undergoes a gradual and complete thermal spin crossover, while complexes 3 and 5 show stepped crossovers with different ratios of spin triplet and quintet forms in the intermediate temperature range.High-field electron paramagnetic resonance was used to measure the zero-field splitting parameters associated with the spin triplet and quintet states at temperatures below 10 K for complexes 4 and 2 with respective values: D S=1 = +23.38(1)cm -1 , E S=1 = +2.79(1)cm -1 , and D S=2 = +6.9(3)cm -1 , with a distribution of E parameters for the S = 2 state.Solid-state circular dichroism (CD) spectra on high-spin complex 1 at room temperature reveal a 2:1 ratio of enantiomers in the chiral conglomerate, and solution CD measurements on the same sample in methanol show that it is stable toward racemization.Solid-state UV-vis absorption spectra on high-spin complex 1 and mixed S = 1/S = 2 sample 5 reveal different intensities at higher energies, in line with the different electronic composition.The statistical prevalence of homochiral crystallization of [Mn(4-OMe-Sal 2 323)] + in five lattices with different achiral counterions suggests that the chirality may be directed by the 4-OMe-Sal 2 323 ligand.

Source: Inorganic Chemistry

DOI: 10.1021/acs.inorgchem.1c03379