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Bis-meridional Fe2+ spincrossover complexes of phenyl and pyridyl substituted 2-(pyridin-2-yl)-1,10-phenanthrolines

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Abstract

A series of Fe2+ SCO complexes of substituted 2-(pyridin-2-yl)-1,10-phenanthrolines 2 was prepared and the SCO (spincrossover) properties were characterized in the solid state (X-ray crystallography, SQUID magnetometry) and in solution (VT-1H NMR spectroscopy), augmented by theoretical modelling. Bis-meridional coordination of the tridendate 2a–c and tetradentate 2d ligands gives octahedral and distorted trigonal-dodecahedral complexes [Fe(2)2]2+, respectively, which were identified as SCO complexes with the transition temperature T1/2 below room temperature. SCO in the solid state is limited to bromo-substituted [Fe(2a)2]2+ (Dalton Trans., 2017, 46, 6218–6229) and [Fe(2b)2]2+ with a pyridine-appended phenyl group, whereas solution state NMR studies reveal SCO behaviour for all complexes, which is in agreement with DFT derived results. As anticipated from its N6(+2) coordination in the HS state, DFT structure modelling of [Fe(2d)2]2+ identified deviation from a structure-conserving SCO reaction coordinate; that is, Fe–N breathing is accompanied by a change in the coordination number. Accordingly, a remarkably slow SCO is observed in [Fe(2d)2]2+, owing to an extended coordinate. De-novo defined characteristic temperatures T(τHSLS) are introduced as structure-dependent parameters deemed to define the onset of phenomenological “slow” SCO. The rich phenomenology of the NMR spectra of [Fe(2)2]2+ is identified to be largely controlled by the dynamics of spin-state exchange and a qualitative illustration of the NMR-reporters of SCO is suggested.

Graphical abstract: Bis-meridional Fe2+ spincrossover complexes of phenyl and pyridyl substituted 2-(pyridin-2-yl)-1,10-phenanthrolines

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Publication details

The article was received on 26 Jun 2017, accepted on 01 Dec 2017 and first published on 04 Dec 2017


Article type: Paper
DOI: 10.1039/C7DT02320K
Citation: Dalton Trans., 2018, Advance Article
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    Bis-meridional Fe2+ spincrossover complexes of phenyl and pyridyl substituted 2-(pyridin-2-yl)-1,10-phenanthrolines

    H. Petzold, P. Djomgoue, G. Hörner, C. Lochenie, B. Weber and T. Rüffer, Dalton Trans., 2018, Advance Article , DOI: 10.1039/C7DT02320K

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