Spin equilibrium in iron(II) poly(1-pyrazolyl)borate complexes: low-temperature and high-pressure Moessbauer spectral studies

Long, Gary J.; Hutchinson, Bennett

doi:10.1021/ic00251a023

Cited by 82 publications

(68 citation statements)

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“…fig. Other examples for the influence of pressure on the spin transition have been reported by other groups [29][30][31]. With decreasing iron concentration the spin transition becomes more gradual and approaches finally the simple Boltzmann population of the vibronic manifold of the HS state.…”

Section: -Thermal Spin-crossovermentioning

confidence: 63%

Fascinating electronic games in iron complexes

Gütlich

Jung

1996

Il Nuovo Cimento D

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Coordination compounds of transition metal ions with open-shell electron configurations may exhibit dynamic electronic-structure phenomena, depending on the nature of the coordinating ligand sphere. The change of spin state with temperature (,,thermal spin-crossover,,), light-induced electron transfer processes leading to long-lived metastable charge and spin states (e.g., ,,LIESST, effect), are some of the fascinating electronic games encountered in transition metal compounds, which are presently under extensive study by chemists and physicists. M5ssbauer spectroscopy plays a dominant role in the investigation of such phenomena in iron compounds, as will be demonstrated in this paper. This work will focus on selected examples of ~,thermal spin-crossover~ in iron(II) complexes and switching between different spin states by irradiation with light of different wavelength (LIESST effect), demonstrating that M5ssbauer spectroscopy besides other physical techniques proves to be a highly elegant tool for following the spin state conversion and the concomitant changes of molecular and crystal structure properties. Finally, M5ssbauer emission spectroscopy, both time integral and time differential, has been employed to generate and identify long-lived excited spin states by making use of the nuclear disintegration of 57Co as an intrinsic molecular light source (NIESST=nuclear decay-induced excited-spin-state trapping). Lifetime measurements by optical techniques on LIESST states and by timedifferential M5ssbauer coincidence spectroscopy on NIESST states prove that the relaxation pathways in the mechanisms for LIESST and NIESST are identical.PACS 71.70.Ch -Crystal and ligand fields. PACS 76.80 -MSssbauer effect; other 7-ray spectroscopy. PACS 78.40 -Visible and ultraviolet spectra.

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Section: -Thermal Spin-crossovermentioning

confidence: 63%

Fascinating electronic games in iron complexes

Gütlich

Jung

1996

Il Nuovo Cimento D

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“…Furthermore, in some cases, the application of pressure on a SCO material can even favor the HS state. This non-intuitive behavior was observed in Mössbauer studies in mononuclear phenanthroline [19] or poly(1-pyrazol)borate [20] iron(II) complexes, and was also reported for the two-dimensional compound [Fe(btr) 2 (NCS) 2 ]¨H 2 O (btr = 4,4 1 -bis-(1,2,4-triazole)) [21]. As a general matter, the number of discrepancies between expectations and experiments deserves a further investigation of the application of an external pressure on SCO materials.…”

Section: Introductionmentioning

confidence: 61%

Effects of Internal and External Pressure on the [Fe(PM-PEA)2(NCS)2] Spin-Crossover Compound (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline)

et al. 2016

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Abstract:The spin-crossover properties of the strongly cooperative compound [Fe(PM-PEA) 2 (NCS) 2 ] (with PM-PEA = N-(2 1 -pyridylmethylene)-4-(phenylethynyl)aniline) have been investigated under external in situ pressure, external ex situ pressure and internal pressure. In situ single-crystal X-ray diffraction investigations under pressure indicate a Spin-Crossover (SCO) at about 400 MPa and room temperature. Interestingly, application of ex situ pressure induces the irreversible enlargement of the hysteresis width, almost independently from the pressure value. Elsewhere, the internal pressure effects are examined through the magnetic and photomagnetic investigations on powders of the solid-solutions based on the Mn ion, [Fe x Mn 1´x (PM-PEA) 2 (NCS) 2 ]. Growing the Mn ratio increases the internal pressure, allowing to control the hysteresis width and the paramagnetic residue but also to enhance the efficiency of the photo-induced SCO. The comparison of the quenching and light-induced behaviors reveals a complex phase-diagram governed by internal pressure, temperature and light.

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“…The simplicity of the optical detection of the usually LS-red HS-white and the associated magnetic 40 changes for iron(II) SCO compounds stimulate the interest for potential information storage, 5 , 6 display devices, 2,6 and sensors. 7,8,9,10,11,12 The iron complexes of hydrotris(pyrazolyl)borato ligands exhibit such a SCO phenomenon between LS-red HS-white 45 states 13,14,15,16,17,18,19 and the transition temperatures (T 1/2 ) were found to vary strongly with the substituents on the pyrazolyl rings or on the boron atom. 18,20 The interplay of the steric effects of substituents with the different sizes of the LS and HS Fe(II) ions was demonstrated to be the decisive factor in controlling the 50 relative stability of the spin states.…”

Section: Introductionmentioning

confidence: 99%

Solvent-triggered relaxative spin state switching of [Fe(HB(pz)₃)₂] in a closed nano-confinement of NH₂-MIL-101(Al)

et al. 2016

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Synthesis of the NH 2 -MIL-101(Al) Metal-Organic Framework (MOF) with bis(hydrotris(pyrazolyl)borato)iron(II), [Fe(HB(pz) 3 ) 2 ], added to the reaction medium yielded [Fe(HB(pz) 3 ) 2 ]@NH 2 -MIL101(Al) encapsulation products, further denoted as S@Ms, in a course of a 'bottle-around-the-ship' assembly. [Fe(HB(pz) 3 ) 2 ] is a spin-crossover (SCO) compound with a gradual spin transition at 290-440K for the bulk material (repeated cycles), associated with a pronounced colour change from the red low spin (LS) state to the white high-spin 10 (HS) state. The identity of S@Ms, with a maximum loading of iron complex at ~11 wt% (0.16 molecules per Al 3 OL 3 moiety), was confirmed by PXRD and spectroscopic evidences. The entrapped complex, which is stable in air, and cannot be removed by vacuum drying is confined in the cages of the framework. N 2 and CO 2 gas adsorption measurements on the dry S@M composite with different iron complex loadings confirm the absence of most of the initial NH 2 -MIL-101(Al) porosity. The S@M composite material demonstrate a gradual thermally induced transition from red low-spin (LS) state to light yellow HS state, associated with the colour of the matrix, 15 chiefly over the range 300-450 K, which is close to the 290-440 K temperature range for [Fe(HB(pz) 3 ) 2 ]. The thermally induced HS form of S@M does not return to LS upon cooling to room temperature, and the metastable HS form relaxes only very slowly, which becomes noticeable only after weeks of storage. Rapid, almost complete relaxation and decrease of magnetic moment for up to ~97% of the whole sweep could be triggered by addition of n-hexane, as evidenced by change of colour and magnetic measurements. Via mechanic stress akin to action of capillary forces, the adsorbed liquid effectively amplifies the otherwise very weak 'matrix effect' by increasing the 20 effective local pressure imposed on the transiting molecules, thus favouring even further the LS state. The immersion of the dried composites into practically any typical solvents, incl. MeOH, DMSO, DMF, i PrOH, BuOH, t-BuOH, THF, ethylacetate, CH 2 Cl 2 , CHCl 3 CCl 4 , toluene, mesitylene, cyclohexane also induces a spin state change, which is evidenced by change of colour. The effect is fully reversible: the metastable HS state could be reinstated upon drying the sample at elevated temperature and subsequent cooling. The materials were thoroughly characterized by AAS, PXRD, gas sorption analysis, IR spectroscopy, magnetic measurements, and optical 25 reflectivity measurements. Thereby a novel MOF-based material with isolated SCO units is proposed, which demonstrate a salient relaxative 'solvent assisted matrix-effect' on metastable entrapped sites, potentially suitable for light-driven single-unit addressability.

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Spin equilibrium in iron(II) poly(1-pyrazolyl)borate complexes: low-temperature and high-pressure Moessbauer spectral studies

Cited by 82 publications

References 0 publications

Fascinating electronic games in iron complexes

Fascinating electronic games in iron complexes

Effects of Internal and External Pressure on the [Fe(PM-PEA)2(NCS)2] Spin-Crossover Compound (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline)

Solvent-triggered relaxative spin state switching of [Fe(HB(pz)₃)₂] in a closed nano-confinement of NH₂-MIL-101(Al)

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Spin equilibrium in iron(II) poly(1-pyrazolyl)borate complexes: low-temperature and high-pressure Moessbauer spectral studies

Cited by 82 publications

References 0 publications

Fascinating electronic games in iron complexes

Fascinating electronic games in iron complexes

Effects of Internal and External Pressure on the [Fe(PM-PEA)2(NCS)2] Spin-Crossover Compound (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline)

Solvent-triggered relaxative spin state switching of [Fe(HB(pz)3)2] in a closed nano-confinement of NH2-MIL-101(Al)

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Solvent-triggered relaxative spin state switching of [Fe(HB(pz)₃)₂] in a closed nano-confinement of NH₂-MIL-101(Al)