“G ütlich,Bill,Trautw ein: Mössbauer S pectroscopy and T ransition Metal C hemistry@ Springer-Verlag 2009” AX Trautwein: Pressure-induced changes studied by synchrotron radiation Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of synchrotron radiation AX Trautwein , H Paulsen, H Winkler Universität Lübeck, Germany H Giefers, G Wortmann Universität Paderborn, Germany H Toftlund Syddansk Universitaet, Odense, Denmark JA Wolny Technische Universität Kaiserslautern, Germany AI Chumakov, O Leupold ESRF, Grenoble, France
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AX Trautwein: Pressure-induced changes studied by synchrotron radiation Pressure-induced changes of the vibrational modes of spin- crossover complexes.
AX Trautwein: Pressure-induced changes studied by synchrotron radiation Method nuclear resonant scattering (NFS and NIS) using synchrotron radiation storage ring at ESRF, Grenoble, France NIS NFS
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“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation
Pressure-induced changes of the vibrational modes of spin-crossover complexes studied by nuclear resonance scattering of
synchrotron radiation
AX Trautwein, H Paulsen, H WinklerUniversität Lübeck, Germany
H Giefers, G WortmannUniversität Paderborn, Germany
H ToftlundSyddansk Universitaet, Odense, Denmark
JA WolnyTechnische Universität Kaiserslautern, Germany
AI Chumakov, O LeupoldESRF, Grenoble, France
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation
Material• iron(II) complexes STP and ETP: STP = [Fe(1,1,1-tris{[N-(2-pyridylmethyl)- N-methylamino]methyl}ethane)](ClO4)2
ETP = [Fe ……………..butane)](ClO4)2
• first coordination sphere of iron is a distor- ted [FeN6] octahedron with C3 symmetry
• STP and ETP exhibit transition from the low-spin (LS, S = 0) to the high-spin (HS, S = 2) state by increasing temperature
• spin-transition complexes are promising materials for optical information storage gand display devices (Gütlich et al., Angew. Chemie Int. Ed. Engl. 33, 2024 (1994)
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation
Method
nuclear resonant scattering (NFS and NIS) using synchrotron radiation
Undulator
Premonochromator
Detector (APD)
Detector (APD)
Sample
High resolutionmonochromator
Si(4 2 2)
Si(12 2 2)Si(1 1 1)
storage ring at ESRF, Grenoble, France
NIS
NFS
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation
NIS absorption probability S(E, k)
consists of a zero-phonon (elastic) and of a multi-phonon (inelastic) part S(E, k) = fLM(k) δ(0) + fLM(k) Σn Sn(E, k)
• at 30 K (LS, open circles): fLM ~ 0.9;
room temp. (HS, closed circles): fLM ~ 0.15• negative energy accounts for annihilation, positive energy for creation of mole- cular vibrations• NIS spectrum reflects in its inelastic part (inset) drastic hardening of vibrational modes
when decreasing temperature
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation
Fe
FeN
N
N
N
N
N
N
N
Fe(3d)
eg
t2g
Fe-N distance
antibonding
LS (S=0)
antibondingHS
(S=2)
Orbital scheme for spin transitionLS becomes energetically favored over HS due to smaller volume
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation
Angular-resolved molecular vibrations
• NIS study of a single crystal of STP at 30 K, with mol. orientations k_|_ a and k || a (a is along the C3 symmetry axis of the molecular complex)
• NIS intensity yields partial density of states: PDOSmol = Σj δ(E – hωj) (k · uj)2
ωj = vibrational frequencies of the molecule uj = projection of the jth eigenvector in the subspace of iron coordinates k = normalized wave vector of the photons (synchrotron beam)
→ only those vibrational modes are NIS visible that are connected with a
mean square displacement of the iron nucleus along the wave vector k
“Gütlich, Bill, Trautwein: Mössbauer Spectroscopy and Transition Metal Chemistry@Springer-Verlag 2009”
AX Trautwein: Pressure-induced changes studied by synchrotron radiation