The role of symmetry breaking in the structural trapping of light-induced excited spin states

Kulmaczewski, Rafał; Trzop, Elżbieta; Cook, Laurence J. Kershaw; Collet, Éric; Chastanet, Guillaume; Halcrow, Malcolm A.

doi:10.1039/c7cc07990g

Cited by 43 publications

(72 citation statements)

References 27 publications

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“…The latter is the only structure:function relationship we have identified which accounts for all the outlier compounds in group 3. We therefore suggest the Fe N bond lengths in the high-spin state are the biggest contributor to 39 That gives a predicted T(latt) = 147 K, or T½(solid) = 68 K, from the correlation in Figure 4. SCO in [Fe(1-bpp)2] 2+ and [Fe(3-bpp)2] 2+ derivatives rarely extends below 100 K, [39][40][41] where they become kinetically trapped in their high spin states.…”

Section: T½(solid)mentioning

confidence: 79%

Relationship between the Molecular Structure and Switching Temperature in a Library of Spin-Crossover Molecular Materials

et al. 2019

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Structure:function relationships are surveyed relating the spin-crossover (SCO) midpoint temperature (T½) in the solid state, for 43 members of the iron(II)/dipyrazolylpyridine family of SCO compounds. The difference between T½ in the solid state and in solution [T(latt)] is proposed as a measure of the lattice contribution to the transition temperature. Negative linear correlations between SCO temperature and the magnitude of the rearrangement of the coordination sphere during SCO are evident among isostructural or near-isostructural subsets of compounds; that is, a larger change in molecular structure during SCO stabilizes the high-spin state of a material. Improved correlations are often obtained when T(latt), rather than the raw T½ value, is considered as the measure of SCO temperature. Different lattice types show different tendencies to stabilize the high-spin or low-spin state of the molecules containing them, which correlates with the structural changes that most influence T(latt) in each case. These relationships are mostly unaffected by the SCO cooperativity in the compounds, or by the involvement of any crystallographic phase changes. One or two materials within each subset are outliers in some or all of these correlations however which, in some cases, can be attributed to small differences in their ligand geometry or unusual phase behavior during SCO. A reinvestigation of the structural chemistry of [Fe(3-bpp)2][NCS]2•nH2O (3-bpp = di{1H-pyrazol-3-yl}pyridine; n = 0 or 2), undertaken as part of this study, is also presented. .

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Section: T½(solid)mentioning

confidence: 79%

Relationship between the Molecular Structure and Switching Temperature in a Library of Spin-Crossover Molecular Materials

et al. 2019

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“…Deviations from the "family line" can also find their origin not at the coordination sphere scale but at the crystal packing scale. For example, recently, compounds from the bpp family [Fe(L 1 ) 2 ](BF 4 ) 2 ·S were shown to deviate from the T 0 = 150 K line due to a photo-induced crystallographic phase transition [41]. Various solvates of the [Fe(…”

Section: Iii2-further Predictive Abilitiesmentioning

confidence: 99%

“…However, such deviation can also come from crystal packing effects. We mentioned the occurrence of a structural transition upon irradiation [41] and also the effect of internal pressure due to metal dilution [29]. Depending on the size of the host ion [57], the internal pressure can be tuned and the effect on the T(LIESST) recorded.…”

Section: Iv2-t(liesst) Is Not a Critical Temperature!mentioning

confidence: 99%

A critical review of the T(LIESST) temperature in spin crossover materials − What it is and what it is not

Chastanet¹,

Desplanches²,

Baldé³

et al. 2018

Chem.Sq.

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Light-Induced Excited Spin-State Trapping has been studied since 1982 in solution and 1984 in solid state as it offers a reversible way of photoswitching the electronic configuration of spin crossover systems. Since then, the lifetime of the photo-induced state was deeply investigated through kinetics measurements. In 1998, a fast and easy way to record the limit temperature above which the photo-induced state is erased, denoted T(LIESST), was introduced. This procedure has been widely used in the spin crossover community due to its easiness and its efficiency to provide detailed information on the photo-induced state. Correlations between T(LIESST) and structural parameters have been proposed for instance. However, it intrinsically contains drawbacks that can lead to misinterpretation of behaviours and can lead to an over-estimation of its scope. This review aims to present and discuss not only the correct way to measure T(LIESST) but also the essential contributions it has brought and the limits not to be exceeded in its interpretation.

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“…Previous studies have demonstrated an empirical relation between T 1/2 and T (LIESST): T (LIESST)= T 0 −0.3× T 1/2 , with T 0 =150 K for tridentate ligands such as the bpp ligand ,,,. Taking for T 1/2 the mean value of T 1/2↓ and T 1/2↑ , T 1/2 can be evaluated at 392 and 425 K respectively for the two hysteresis cycles.…”

Section: Resultsmentioning

confidence: 99%

Solvatomorphism‐Induced 45 K Hysteresis Width in a Spin‐Crossover Mononuclear Compound

Djemel

Stefańczyk

Marchivie

et al. 2018

Chemistry A European J

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Spin-transition compounds are coordination complexes that can present two stable or metastable high-spin and low-spin states at a given temperature (thermal hysteresis). The width of the thermal hysteresis (difference between the maximum and minimum temperature between which the compound exhibits bi-stability) depends on the interactions between the coordination complexes within the compound, and which may be modulated by the absence or presence of solvent within the structure. The new compound [Fe(3-bpp) ][Au(CN) ] (1, 3-bpp=2,6-di-(1H-pyrazol-3-yl)pyridine) was synthesized and its properties were compared with those of the solvated compound [Fe(3-bpp) ][Au(CN) ] ⋅2 H O (1.H O) already described. 1 has a two-steps thermal hysteresis of 45 K, in contrast to the compound 1.H O which exhibits a gradual conversion without hysteresis. This hysteretic transition is accompanied by a reversible reconstructive structural transition and twinning. This stepped behaviour is also observed in the photomagnetic properties despite the low efficiency of photoswitching. Single-crystal photocrystallographic investigations confirm this low conversion, which we attributed to the high energy cost to form the high-spin structure, whose symmetry differs from that of the low-spin phase.

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The role of symmetry breaking in the structural trapping of light-induced excited spin states

Cited by 43 publications

References 27 publications

Relationship between the Molecular Structure and Switching Temperature in a Library of Spin-Crossover Molecular Materials

Relationship between the Molecular Structure and Switching Temperature in a Library of Spin-Crossover Molecular Materials

A critical review of the T(LIESST) temperature in spin crossover materials − What it is and what it is not

Solvatomorphism‐Induced 45 K Hysteresis Width in a Spin‐Crossover Mononuclear Compound

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