Anisotropic Nuclear Inelastic Scattering of an Iron(II) Molecular Crystal

Abstract

Nuclear inelastic scattering (NIS) spectra were recorded for a monocrystal of the spin-crossover complex [Fe(tptMetame)] (ClO (4))(2) (tptMetame = 1,1,1-tris([N-(2-pyridylmethyl)-N-methylamino]-methyl)ethane) at T = 30 K (low-spin state) and at room temperature (high-spin state) for different crystal orientations. The high energy resolution (0.65 meV) allowed us to resolve individual molecular vibrations which were unambiguously identified by density functional calculations. From the NIS spectra for the first time the angular-resolved iron-partial density of phonon states (PDOS) was extracted. The PDOS corroborates a vibrational entropy difference as driving force of the spin transition.

Vibrational dynamics of biological molecules: Multi-quantum contributions

“…Measurements on oriented samples, such as single crystals, also yield the direction of vibrational motions [10,12,14,18,23,20,26,28]. Other names used for this technique include phonon assisted Mössbauer effect [21,22,25,26], inelastic X-ray scattering of synchrotron radiation [11], nuclear inelastic scattering [18], nuclear inelastic absorption [9], and nuclear resonant inelastic X-ray scattering [29].…”

Measuring velocity of sound with nuclear resonant inelastic x-ray scattering

“…This technique provides the phonon excitation spectrum as seen by the probe nuclei, 3,4,5 and in most cases one can extract the partial vibrational frequency distribution, a function often referred to as the partial phonon density of states (PDOS). The NRIXS method has been applied to various materials, e.g., thin films and multilayers, 6,7,8 nanoparticles, 9,10 crystals with impurities, 11 organic molecules, 12,13,14,15 proteins, 16,17 samples under high pressures, 18 and samples of geophysical interests. 19,20 Most of these samples are compounds, and, while the obtained PDOS gives only part of the lattice dynamics, the low-energy portion of the PDOS provides the Debye sound velocity of the whole sample.…”

“…Here we have shown that the sound velocity vk of a sample in general is obtained by applying a correction factor, the cube root of the modulation factor as given in Eq. (13), to the "mean sound velocity" of Ref. 22.…”

Dynamics of metal centers monitored by nuclear inelastic scattering

“…In addition to the peaks that are assigned to the Fe-S bond stretching modes, a second group of prominent peaks was observed in the NIS spectra, which hardly change their positon upon reduction. In order to assign these peaks to molecular vibrations, DFT calculations have been performed for a series of models of the protein under study, Fe(SH) 4 , Fe(SCH 3 ) 4 and FeCys 4 , i.e. containing 9, 21 and 49 atoms, respectively.…”