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Issue 13, 2018
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Multiple spin phases in a switchable Fe(II) complex: polymorphism and symmetry breaking effects

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Polymorphism in spin-crossover (SCO) compounds allows accessing additional forms of switchable materials with diverse transition properties. We have prepared three polymorphs of a new complex [FeLBr(dca)2], where LBr is N,N′-bis[(5-bromo-2-pyridyl)methyl]ethane-1,2-diamine and dca is dicyanamide. They display different SCO properties: the α-form displays a hysteretic one-step switch centered at 134 K, the β-form undergoes hysteretic two-step spin transition with a plateau (T1/2 = 153 and 144 K) and the γ-form remains high spin (HS) over the whole temperature region. The kinetic origin of the hysteresis loop was demonstrated in temperature rate dependent magnetic measurements. Spin transition in the α-form is accompanied by symmetry breaking from a single Fe(II) site in the HS state to two distinct Fe(II) sites in the low spin (LS) state. In the β-form, the single crystal XRD has revealed a re-entrant symmetry change associated with the stepwise transition, with an ordered HS–LS alternating arrangement in the temperature plateau range. The corresponding Mössbauer study demonstrates a complicated evolution of spin transitions in the β-form through three different spin phases within different temperature regions.

Graphical abstract: Multiple spin phases in a switchable Fe(ii) complex: polymorphism and symmetry breaking effects

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Publication details

The article was received on 09 Nov 2017, accepted on 19 Feb 2018 and first published on 28 Feb 2018

Article type: Paper
DOI: 10.1039/C7TC05111E
Citation: J. Mater. Chem. C, 2018,6, 3352-3361

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    Multiple spin phases in a switchable Fe(II) complex: polymorphism and symmetry breaking effects

    H. Hang, B. Fei, X. Q. Chen, M. L. Tong, V. Ksenofontov, I. A. Gural'skiy and X. Bao, J. Mater. Chem. C, 2018, 6, 3352
    DOI: 10.1039/C7TC05111E

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