0000000001306624
AUTHOR
Andreas Hauser
High-spin → low-spin relaxation in the two-step spincrossover compound [Fe(pic)3]Cl2EtOH (pic = 2-picolylamine)
Abstract The spin-crossover compound [Fe(pic) 3 ]Cl 2 EtOH (pic = 2-picolylamine) shows an unusual two-step spin transition. This is thought to be caused by specific nearest-neighbour interactions and short-range correlations and requires a theoretical treatment of the elastic interactions between the spin-changing molecules beyond the mean-field approximation. Such short-range correlations also influence the high-spin → low-spin relaxation following the light-induced population of the high-spin state at cryogenic temperatures, leading to characteristic deviations from the predictions of a mean-field treatment. These deviations are directly observable by comparison of the full and unperturb…
Helium gas pressure cell for pressures up to 1 kbar (0.1 GPa) in conjunction with the cold head of a closed-cycle He refrigerator
A helium gas pressure cell for pressures up to 1 kbar (0.1 GPa) has been developed in conjunction with a closed-cycle He refrigerator allowing variable temperatures between 15 and 300 K. Both cell and refrigerator are equipped with optical windows suitable for photophysical measurements, such as temperature- and pressure-dependent absorption spectroscopy or laser flash photolysis. Examples of measurements on iron(II) spin-crossover systems are given. In these compounds, comparatively small external pressures induce significant changes in the thermodynamic equilibrium as well as in the relaxation dynamics.
Very Long-Lived Photogenerated High-Spin Phase of a Multistable Spin-Crossover Molecular Material
The spin-crossover compound [Fe(n-Bu-im)3(tren)](PF6)2 shows an unusual long relaxation time of 20 h after light-induced excited spin state trapping when irradiating at 80 K. This is more than 40 times longer than when irradiating at 10 K. Optical absorption spectroscopy, magnetometry, and X-ray diffraction using synchrotron radiation were used to characterize and explain the different relaxation behaviors of this compound after irradiation below and above 70 K. Rearrangement of the butyl chains of the ligands occurring during the relaxation after irradiation above 70 K is thought to be responsible for the unusually long relaxation time at this temperature.
Intersystem crossing in Fe(II) coordination compounds
Fe(II) spin-crossover systems can be quantitatively converted from the low-spin (LS) to the high-spin (HS) state well below the thermal transition temperature by irradiating either into the metal-ligand charge transfer or d-d absorption bands, and even in low-spin systems a transient population of the HS state can be achieved. This fact can be made use of to determine HS → LS relaxation rate constants for a wide variety of Fe(II) spin-crossover and low-spin systems. The HS → LS relaxation shows strong deviations from an Arrhenius behaviour, with nearly temperature-independent tunnelling below ∼70 K and a thermally activated process above ∼100 K. The range of more than 12 orders of magnitude…
Time integral and time differential Mössbauer measurements on [57Co/Mn(bipy)3](PF6)2
The Mossbauer emission spectra of nucleogenic iron(II) complexes with a low spin (LS) ground state show two metastable iron(II) high spin (HS) states at low temperatures. In order to identify these metastable HS states, the compound [57Co/Mn(bipyridine)3](PF6)2 has been studied by time differential Mossbauer emission spectroscopy (TDMES) and optical lifetime measurements of excited electronic states in the corresponding Fe-doped Mn compound. The lifetime of one of the HS states of the nucleogenic iron(II) determined by TDMES has been measured to be the same as the lifetime of the laser-excited iron(II) electronic state.
Correlations of the distribution of spin states in spin crossover compounds
Abstract Short range correlations of the distribution of high spin (HS) and low spin (LS) states show up in thermal spin transition curves, decay curves of the light induced metastable HS state (LIESST state), and in structural features during the spin transitions. Correlations are due to short range interactions between the spin crossover molecules. Short range interactions may compete with omnipresent long range interactions and give rise to interesting spin transition phenomena. In this paper, the effect of correlations on the thermal spin transition in the mixed crystal system [Fe x Zn 1− x (pic) 3 ]Cl 2 ·EtOH (pic=picolylamine) is discussed. In particular the step in the thermal transi…
Intersystem Crossing and Light-Induced Bistability in Iron(?) Spin-Crossover Compounds
Abstract The dynamics of the high-spin→low-spin intersystem crossing process in iron(?) spin-crossover compounds are strongly influenced by cooperative effects of elastic origin which are due to the large difference in volume between high-spin and low-spin complexes. The deviation from first order kinetics is attributed to a build-up of an internal pressure as the relaxation proceeds, leading to a characteristic self-acceleration. The elastic interactions may lead to a light-induced bistability for systems which otherwise remain in the high-spin state down to cryogenic temperatures.
Light-Induced Excited Spin State Trapping in Iron(II) Complexes
In the course of our studies on the thermally induced high spin (HS) ↔ low spin (LS) transition in iron(II) complexes /1/, \({\!^5{\text{T}}_2}_{\text{g}}\) ↔ \({\!^1{\text{A}}_1}_{\text{g}}\) in the approximation of Oh symmetry, we have observed in 1984 a new photophysical effect /2/: If, at sufficiently low temperature, the solid spin crossover complex is irradiated with green light into the \({\!^1{\text{A}}_1}\)→ \({\!^1{\text{T}}_1}\) ligand field absorption band, the thermodynamically stable LS state can be converted to the metastable HS state and trapped with practically infinite lifetime. We have called this unusual phenomenon “Light-Induced Excited Spin State Trapping (LIESST)”.
The [Fe(etz)6](BF4)2 Spin-Crossover System—Part One: High-Spin ⇌ Low-Spin Transition in Two Lattice Sites
The [Fe(etz),](BF,), spin-cross-over system (etz = 1-ethyl-1 H-tetrazole) crystallizes in space group P1, with the following lattice constants at 298 K: a 10.419(3), b=15.709(1), c = 18.890(2) A = = 71.223(9), =77.986(10), and = 84.62(1)° V = 2862.0(9) A3 and Z = 3. Two nonequivalent lattice sites, one without (site A) and one with (site B) inversion symmetry, are observed. The population of the two sites nA:nB is 2:l. Iron(II) on site A undergoes a thermal low-spin (LS) high-spin (HS) transition with T1/2I, = 105 K. whereas that on site B remains in the high-spin state down to cryogenic temperatures. Application of external pressure of up to 1200 bar between 200 and 60 K does not cause for…
Dynamics of spin state conversion processes in the solid state
High spin (HS) ⇌ low spin (LS) conversions in transition metal complexes are nonradiative transitions between spin states. In this contribution, we present a study of the temperature and pressure dependence of the HS ⇌ LS intersystem crossing dynamics. For some iron(II) spin-crossover complexes, the rate constants were determined by line shape analysis of57Fe Mossbauer spectra. Their temperature dependence is described by an Arrhenius equation, their pressure dependence is interpreted within absolute rate theory. HS → LS conversion rates at low temperatures were determined from the relaxation of light-induced formation of HS states, monitored by optical spectroscopy. Deviations from a simpl…
The [Fe(etz)6](BF4)2 Spin-Crossover System - Part Two: Hysteresis in the LIESST Regime
In the [Fe(etz)6](BF4)2 spincrossover system the iron(II) complexes occupy two nonequivalent lattice sites, sites A and B. Complexes on site A show a thermal high-spin (HS) low-spin (LS) transition at 105 K, whereas complexes on site B remain in the HS state down to 10 K. Complexes on both sites exhibit light-induced spin state conversions (LIESST) at 20 K: LS HS on site A with = 514.5 nm, and HS LS on site B with = 820 nm. The relaxation processes subsequent to the HS LS conversion on site B reveal a light-induced HSLS bistability for the complexes on site B at 70 K. The bistability as well as the absence of a thermal spin transition on site B are attributed to a thermal hysteresis for the…
Advances in Mössbauer Emission Spectroscopy
After effects following nuclear transformation have been extensively studied in a large variety of matrices by Mossbauer Emission Spectroscopy (MES). The branching ratios of transient atomic charge states and energetically unstable states of the environment, excitations of electronic ligand field states and populations out of equilibrium within the electronic ground state manifold have been studied. Recent developments and also new insights and understandings of different aspects of the aftereffects of radioactive decay of57Co in semiconductors and molecular crystals are reviewed. A detailed picture of the decay process within the electronic states of the nucleogenic Fe3+ species could be o…
A polymeric two-dimensional mixed-metal network. Crystal structure and magnetic properties of {[P(Ph)4][MnCr(ox)3]}
Abstract The mixed-metal ferromagnet {[P(Ph) 4 ][MnCr(ox) 3 ]} n , where Ph is phenyl and ox is oxalate, has been prepared and a two-dimensional network structure, extended by Mn(II)-ox-Cr(III) bridges, has been determined from single crystal X-ray data. Crystal data: space group R 3 c , a = b =18.783(3), c =57.283(24) A, α=β=90, γ=120°, Z =24 (C 30 H 20 O 12 PCrMn). The magnetic susceptibility data obey the Curie-Weiss law in the temperature range 260–20 K with a positive Weiss constant of 10.5 K. The temperature dependence of the molar magnetization exhibits a magnetic phase transition at T c =5.9 K. The structure is discussed in relation to the strategy for preparing molecular based ferr…
Cooperativity in the Iron(II) Spin-Crossover Compound [Fe(ptz)6](PF6)2 under the Influence of External Pressure (ptz = 1-n-Propyltetrazole)
The iron(II) spin-crossover compound [Fe(ptz)(6)](PF(6))(2) (ptz = 1-propyltetrazole) crystallizes in the triclinic space group Ponemacr;, with a = 10.6439(4) Å, b = 10.8685(4) Å, c = 11.7014(4) Å, alpha = 75.644(1) degrees, beta = 71.671(1) degrees, gamma = 60.815(1) degrees, and Z = 1. In [Fe(ptz)(6)](PF(6))(2), the thermal spin transition is extremely steep because of cooperative effects of elastic origin. The transition temperature at ambient pressure is 74(1) K. An external pressure of 1 kbar shifts the transition temperature to 102(1) K, corresponding to a stabilization of the low-spin state, which is smaller in volume. The volume difference between the high-spin and the low-spin stat…
Cooperative effects on the HS→LS relaxation in the [Fe(ptz)6](BF4)2 spin-crossover system
Abstract The high-spin to low-spin (HS→LS) relaxation in the [Fe(ptz) 6 ](BF 4 ) 2 spin-crossover system deviates strongly from first-order kinetics because of cooperative effects of elastic origin. The shift in horizontal and vertical displacement of the potential wells of the initial and final state relative to each other due to the build-up of an “internal” pressure is estimated from spectroscopic measurements. The HS→LS relaxation as such is described by the theory of nonadiabatic multiphonon relaxation in the strong-coupling limit, with a Huang—Rhys factor S ≈ 45 which is much larger than the reduced energy gap p . The sigmoidal relaxation curves in [Fe(ptz) 6 ](BF 4 ) 2 result when a …
Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds
In iron(II) spin-crossover compounds, the transition from the 1A1 low-spin state at low temperatures to the 5T2 high-spin state at elevated temperatures is accompanied by a large increase in metal-ligand bond lengths. The resulting elastic interactions may be pictured as an internal pressure which is proportional to the concentration of the low-spin species. Because pressure stabilises the low-spin state relative to the high-spin state this results in a positive feedback. Thermal transition curves in neat iron(II) spin-crossover compounds are thus invariable much steeper than in diluted mixed crystals, and the high-spin→low-spin relaxation following the light-induced population of the high-…
Optical investigation of spin-crossover in cobalt(II) bis-terpy complexes
Abstract The spin transition of the [Co(terpy) 2 ] 2+ complex (terpy = 2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy) 2 ](ClO 4 ) 2 shows an asymmetric absorption band at 14 400 cm −1 with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing te…
Excited-state lifetimes of [Fe (bipy)3]2+ and [Fe(phen)3]2+
Abstract In the low-spin [Fe(bipy)3]2+ (bipy = 2,2′,bipyridine) and [Fe(phen)3]2+ (phen = 1,10-phenanthroline) complexes an excited high-spin 5T2 ligand field state can be populated by irradiating into the 1MLCT absorption band at 530 nm. The lifetimes of this excited state at low temperatures are reported for [Fe(bipy)3]2+ doped into [Zn(bipy)3] (PF6)2 and [Zn(bipy)3] (BF4)2 and for [Fe(phen)3]2+ and [Fe(bipy)3]2+ embedded in the ion exchange polymer Nafion. For [Fe(bipy)3]2+ in [Zn(bipy)3](PF6)2 the observed lifetimes decrease from 1600 ns at 10 K to 14 ns at 125 K.
Structural, photophysical and magnetic properties of transition metal complexes based on the dipicolylamino-chloro-1,2,4,5-tetrazine ligand
International audience; The ligand 3-chloro-6-dipicolylamino-1,2,4,5-tetrazine (Cl-TTZ-dipica) 1, prepared by the direct reaction between 3,6-dichloro-1,2,4,5-tetrazine and di(2-picolyl)-amine, afforded a series of four neutral transition metal complexes formulated as [Cl-TTZ-dipica-MCl2]2, with M = Zn(II), Cd(II), Mn(II) and Co(II), when reacted with the corresponding metal chlorides. The dinuclear structure of the isostructural complexes was disclosed by single crystal X-ray analysis, clearly indicating the formation of [MII–(μ-Cl)2MII] motifs and the involvement of the amino nitrogen atom in semi-coordination with the metal centers, thus leading to distorted octahedral coordination geome…
Thermal- and photoinduced spin-state switching in an unprecedented three-dimensional bimetallic coordination polymer.
The compound {Fe(pmd)[Ag(CN)2][Ag2(CN)3]} (pmd=pyrimidine) was synthesized and characterized. Magnetic, calorimetric and single crystal visible spectroscopic studies demonstrate the occurrence of a two-step high-spin (HS) right arrow over left arrow low-spin (LS) transition. The critical temperatures are T(c1)=185 and T(c2)=148 K. Each step involves approximately 50 % of the iron centers, with the low-temperature step showing a hysteresis of 2.5 K. The enthalpy and entropy variations associated with the two steps are DeltaH(1)=3.6+/-0.4 kJ mol(-1) and DeltaS(1)=19.5+/-3 J K(-1) mol(-1); DeltaH(2)=4.8+/-0.4 kJ mol(-1) and DeltaS(2)=33.5+/-3 J K(-1) mol(-1). Photomagnetic and visible spectros…
Stimuli responsive hybrid magnets : tuning the photoinduced spin-crossover in Fe(III) complexes inserted into layered magnets
The insertion of a [Fe(sal_2 trien)]^+ complex cation into a 2D oxalate network in the presence of different solvents results in a family of hybrid magnets with coexistence of magnetic ordering and photoinduced spin crossover (LIESST effect) in compounds [Fe^{III}(sal_2 trien)][Mn^{II}Cr^{III}(ox)_3]·CHCl_3 (1·CHCl_{3}) [Fe^{III}(sal_{2} trien)][Mn^{II}Cr^{III}(ox)_{3}]·CHBr_{3} (1·CHBr_{3}) and [Fe^{III}(sal_{2} trien)][Mn^{II}Cr^{III}(ox)_{3}]·CH_{2}Br_{2} (1·CH_{2}Br_{2}). The three compounds crystallize in a 2D honeycomb anionic layer formed by Mn^{II} and Cr^{III} ions linked through oxalate ligands and a layer of [Fe(sal_{2} trien)]^{+} complexes and solvent molecules (CHCl_{3} CHBr_{…
CCDC 1045096: Experimental Crystal Structure Determination
Related Article: Iuliia Nazarenko, Flavia Pop, Qinchao Sun, Andreas Hauser, Francesc Lloret, Miguel Julve, Abdelkrim El-Ghayoury, Narcis Avarvari|2015|Dalton Trans.|44|8855|doi:10.1039/C5DT00550G
CCDC 929206: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 929201: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 1045094: Experimental Crystal Structure Determination
Related Article: Iuliia Nazarenko, Flavia Pop, Qinchao Sun, Andreas Hauser, Francesc Lloret, Miguel Julve, Abdelkrim El-Ghayoury, Narcis Avarvari|2015|Dalton Trans.|44|8855|doi:10.1039/C5DT00550G
CCDC 929203: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 1045095: Experimental Crystal Structure Determination
Related Article: Iuliia Nazarenko, Flavia Pop, Qinchao Sun, Andreas Hauser, Francesc Lloret, Miguel Julve, Abdelkrim El-Ghayoury, Narcis Avarvari|2015|Dalton Trans.|44|8855|doi:10.1039/C5DT00550G
CCDC 929204: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 1848631: Experimental Crystal Structure Determination
Related Article: Teresa Delgado, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif, Céline Besnard|2018|J.Am.Chem.Soc.|140|12870|doi:10.1021/jacs.8b06042
CCDC 1045093: Experimental Crystal Structure Determination
Related Article: Iuliia Nazarenko, Flavia Pop, Qinchao Sun, Andreas Hauser, Francesc Lloret, Miguel Julve, Abdelkrim El-Ghayoury, Narcis Avarvari|2015|Dalton Trans.|44|8855|doi:10.1039/C5DT00550G
CCDC 929205: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 1848628: Experimental Crystal Structure Determination
Related Article: Teresa Delgado, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif, Céline Besnard|2018|J.Am.Chem.Soc.|140|12870|doi:10.1021/jacs.8b06042
CCDC 1857201: Experimental Crystal Structure Determination
Related Article: Teresa Delgado, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif, Céline Besnard|2018|J.Am.Chem.Soc.|140|12870|doi:10.1021/jacs.8b06042
CCDC 929202: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 929207: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 1848626: Experimental Crystal Structure Determination
Related Article: Teresa Delgado, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif, Céline Besnard|2018|J.Am.Chem.Soc.|140|12870|doi:10.1021/jacs.8b06042
CCDC 929208: Experimental Crystal Structure Determination
Related Article: Miguel Clemente-León, Eugenio Coronado, Maurici López-Jordà, João C. Waerenborgh, Cédric Desplanches, Hongfeng Wang, Jean-François Létard, Andreas Hauser , and Antoine Tissot|2013|J.Am.Chem.Soc.|135|8655|doi:10.1021/ja402674x
CCDC 1045097: Experimental Crystal Structure Determination
Related Article: Iuliia Nazarenko, Flavia Pop, Qinchao Sun, Andreas Hauser, Francesc Lloret, Miguel Julve, Abdelkrim El-Ghayoury, Narcis Avarvari|2015|Dalton Trans.|44|8855|doi:10.1039/C5DT00550G
CCDC 1848629: Experimental Crystal Structure Determination
Related Article: Teresa Delgado, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif, Céline Besnard|2018|J.Am.Chem.Soc.|140|12870|doi:10.1021/jacs.8b06042
CCDC 1848627: Experimental Crystal Structure Determination
Related Article: Teresa Delgado, Antoine Tissot, Laure Guénée, Andreas Hauser, Francisco Javier Valverde-Muñoz, Maksym Seredyuk, José Antonio Real, Sébastien Pillet, El-Eulmi Bendeif, Céline Besnard|2018|J.Am.Chem.Soc.|140|12870|doi:10.1021/jacs.8b06042