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Issue 38, 2007
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Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(II)

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Abstract

The syntheses of [FeL][BF4]2·H2O, [FeL][ClO4]2·H2O, [FeL][NO3]2·CH3NO2 and [FeL][CF3SO3]2 (L = tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine) are described. The isostructural BF4 and ClO4 salts are high-spin between 5–300 K, while the other two compounds are high-spin at room temperature but undergo gradual high→low spin transitions upon cooling. For [FeL][NO3]2 this transition is centred at 139 K and proceeds to near-completeness, while for [FeL][CF3SO3]2 it is centred at 144 K and only proceeds to 50% conversion. The CF3SO3 salt also undergoes spin-crossover centred at 200 K in (CD3)2CO solution, and exhibits dynamic inversion of its helical ligand conformation. All these compounds except the triflate salt have been crystallographically characterised, and show capped trigonal antiprismatic [6 + 1] coordination geometries. The NO3 and CF3SO3 salts undergo quantitative conversion to trapped, high-spin excited states upon irradiation with a green laser at 10 K (the LIESST effect; LIESST = Light-Induced Excited Spin State Trapping). The thermal stabilities of their LIESST excited states (T(LIESST) = 80–82 K) resemble those found for iron(II) complexes of bidentate N-heterocyclic ligands. Hence, the LIESST properties of [FeL]2+ are those of a complex of three rigid bidentate domains linked by a flexible spacer, rather than of a single encapsulating podand.

Graphical abstract: Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(ii)

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Publication details

The article was received on 13 Jun 2007, accepted on 20 Jul 2007 and first published on 02 Aug 2007


Article type: Paper
DOI: 10.1039/B708971F
Citation: Dalton Trans., 2007,0, 4276-4285
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    Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(II)

    H. Z. Lazar, T. Forestier, S. A. Barrett, C. A. Kilner, J. Létard and M. A. Halcrow, Dalton Trans., 2007, 0, 4276
    DOI: 10.1039/B708971F

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