188
V. Schünemann
4.2.5 Calculation of Iron Ligand Modes in Chemical
Complexes and Proteins
Vibrational properties of molecules can also be calculated using theoretical models
based on DFT. The first step is finding a structure which resembles at least in the
computer the structure resembling the energy minimum of the molecule. In case
the molecule is large like in case of an iron protein the above mentioned QM/MM
approach can be used to find the ground state of the system. Such a calculation
is performed according to the procedure described in the previous chapter. After
that a normal mode analysis of the whole ground state structure is being performed
which gives all normal modes of the molecule. Once the normal modes have been
obtained vibrational spectra like Infrared and/or Raman spectra can be calculated.
These features are nowadays implemented in DFT software packages. In our case
of special interest are those modes which involve non-null movement of the iron
center, because such modes are directly experimental accessible via nuclear inelastic
scattering (NIS) experiments (see Chap. 1 of this book). It should be noted that
this method is often denoted also as Nuclear Resonance Vibrational Spectroscopy
(NRVS). These techniques deliver the partial density of phonon states (pDOS) and
DFT calculations can be used for mode assignment. Examples for calculating spin
marker bands in spin crossover complexes will be presented in Sect. 4.3.
4.3 Exploring Spin States in Iron(II) Containing
Compounds
The spin state of iron(II) spin crossover (SCO) compounds can be switched reversibly
from the low-spin state (S = 0) to a high-spin state (S = 2) by variation of temperature,
pressure or by irradiation with light [47, 48]. More recently the spin dependent charge
transport properties of SCO molecules have also generated interest for their use in
spintronic devices [49, 50]. Since SCO compounds are also discussed in Chap. 6
of this book by N. Kojima and A. Okazawa, we restrict ourselves to some recent
examples which concern the characterization of polynuclear SCO complexes, light
excited spin states and the characterization of spin marker bands via synchrotron
based NIS [51].
4.3.1 Thermal Spin Crossover (SCO) and Mössbauer
Spectroscopy
The spin crossover between the S = 0 and the S = 2 state of ferrous ions can be
ideally followed by Mössbauer spectroscopy. This has been shown in a plethora
of cases by the group of Gütlich who pioneered the research of the SCO effect by
V. Schünemann
4.2.5 Calculation of Iron Ligand Modes in Chemical
Complexes and Proteins
Vibrational properties of molecules can also be calculated using theoretical models
based on DFT. The first step is finding a structure which resembles at least in the
computer the structure resembling the energy minimum of the molecule. In case
the molecule is large like in case of an iron protein the above mentioned QM/MM
approach can be used to find the ground state of the system. Such a calculation
is performed according to the procedure described in the previous chapter. After
that a normal mode analysis of the whole ground state structure is being performed
which gives all normal modes of the molecule. Once the normal modes have been
obtained vibrational spectra like Infrared and/or Raman spectra can be calculated.
These features are nowadays implemented in DFT software packages. In our case
of special interest are those modes which involve non-null movement of the iron
center, because such modes are directly experimental accessible via nuclear inelastic
scattering (NIS) experiments (see Chap. 1 of this book). It should be noted that
this method is often denoted also as Nuclear Resonance Vibrational Spectroscopy
(NRVS). These techniques deliver the partial density of phonon states (pDOS) and
DFT calculations can be used for mode assignment. Examples for calculating spin
marker bands in spin crossover complexes will be presented in Sect. 4.3.
4.3 Exploring Spin States in Iron(II) Containing
Compounds
The spin state of iron(II) spin crossover (SCO) compounds can be switched reversibly
from the low-spin state (S = 0) to a high-spin state (S = 2) by variation of temperature,
pressure or by irradiation with light [47, 48]. More recently the spin dependent charge
transport properties of SCO molecules have also generated interest for their use in
spintronic devices [49, 50]. Since SCO compounds are also discussed in Chap. 6
of this book by N. Kojima and A. Okazawa, we restrict ourselves to some recent
examples which concern the characterization of polynuclear SCO complexes, light
excited spin states and the characterization of spin marker bands via synchrotron
based NIS [51].
4.3.1 Thermal Spin Crossover (SCO) and Mössbauer
Spectroscopy
The spin crossover between the S = 0 and the S = 2 state of ferrous ions can be
ideally followed by Mössbauer spectroscopy. This has been shown in a plethora
of cases by the group of Gütlich who pioneered the research of the SCO effect by