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Issue 20, 2018
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Selecting the spin crossover profile with controlled crystallization of mononuclear Fe(III) polymorphs

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Abstract

Two polymorphic species of the [Fe(5-Br-salEen)2]ClO4 compound were obtained, each of them being selectively recovered after evaporation of the solvent at a controlled rate. While polymorph 1a is formed during slow evaporation, fast evaporation favors polymorph 1b. The importance of the evaporation rate was recognized after detailed studies of the reaction temperature, solvent evaporation rate and crystallization temperature effects. The complex in the new polymorphic form 1a showed an abrupt spin crossover at 172 K with a small 1 K hysteresis window and over a narrow 10 K range. 57Fe Mössbauer spectroscopy and differential scanning calorimetry, complemented by X-ray studies for both the high-spin and low-spin forms, were used to further characterize the new polymorphic phase 1a. Both polymorphs are based on the same Fe(III) complex cation hydrogen bonded to the perchlorate anion. These units are loosely bound in the crystals via weak interactions. In the new polymorph 1a, the hydrogen bonds are stronger, while the weak hydrogen and halogen bonds, as well as π–π stacking, create a cooperative network, not present in 1b, responsible for the spin transition profile.

Graphical abstract: Selecting the spin crossover profile with controlled crystallization of mononuclear Fe(iii) polymorphs

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Publication details

The article was received on 18 Jan 2018, accepted on 18 Apr 2018 and first published on 18 Apr 2018


Article type: Paper
DOI: 10.1039/C8DT00227D
Dalton Trans., 2018,47, 7013-7019

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    Selecting the spin crossover profile with controlled crystallization of mononuclear Fe(III) polymorphs

    A. I. Vicente, L. P. Ferreira, M. D. D. Carvalho, V. H. N. Rodrigues, M. M. Dîrtu, Y. Garcia, M. J. Calhorda and P. N. Martinho, Dalton Trans., 2018, 47, 7013
    DOI: 10.1039/C8DT00227D

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