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C. Knoll, M. Seifried, D. Müller, P. Weinberger:
"Variable Temperature ATR-IR Spectroscopy as a Valuable Tool for the In Situ Spin-State Detection of Iron(II) Spin Crossover Complexes";
Vortrag: ICAVS 8, Wien; 12.07.2015 - 17.07.2015; in: "ICAVS8 Abstracts Oral", (2015), ISBN: 978-3-200-04205-6; S. 164 - 165.

Variable temperature vibrational spectroscopy has proved a valuable tool for structural characterization of iron(II) coordination compounds undergoing a high-spin (HS) ↔ low-spin (LS) transition. MIR- and FIR-spectroscopy of iron(II) compounds allows not only for the observation of the first order structural phase transition, but also concomitant for an in-situ detection of the spin state [1]. The reason for this is the drastic bond strength change of the Fe-N bonds due to the spin transition.

Especially, temperature-dependent FIR-spectroscopy is an often neglected technique, mainly due to the obstacle of sensitivity and sample preparation. It has been shown that in the FIR region there is a vibrational mode of the iron(II) coordination center towards the centroids of the coordination octahedron formed by the six coordinating nitrogen atoms of the tetrazole ligands [2]. The calculations reveal that this N3-Fe-N3´ vibrational mode is almost totally decoupled from any other atomic motions of the rest of the molecule. Therefore, this absorption feature can be used for the quantification of the high spin and low spin species, respectively, thus allowing for a very sensitive in-situ determination of the ratio between the high spin and low spin compounds. The molecular spin transition properties derived by variable vibrational spectroscopy is compared to complementary physico-chemical characterizations by UV-VIS-NIR spectroscopy, SQUID/VSM and 57Fe-Mössbauer spectroscopy [3]
Herein we present an innovative custom-made setup for both temperature-dependent MIR and FIR-spectroscopy based on a PIKE Technologies ATR-Unit with a Perkin Elmer Spectrum 400 FT-MIR/FIR combination (see Fig. 1).
The resulting spectra during the observation of a phase transition using the novel ATR-setup are compared to calculated spectra for detailed assignments using DFT. The DFT calculations implemented in the Gaussian 09 software package [4] used for the free ligands the basis set 6-311G++ (2d,3p) and SDD for the complexes for the B3LYP functionals.

1 Weinberger P., Matthias G., (2004) Vibrational Spectroscopy 34(1), 175-186.
2 Valtiner M., Paulsen H., Weinberger P. and Linert W., (2007) MATCH Communications in Mathematical and in Computer Chemistry, 57, 749-761.
3 Reissner M., Weinberger P., Wiesinger G., Hilscher G., Mereiter K., Linert W., (2009) Hyperfine Interactions, 191, 81-86.
4 Gaussian 09, Revision C.01, M. J. Frisch et al. Gaussian, Inc., Wallingford CT, (2010)

variable temperature ATR-IR, iron(II), spin corossover

http://publik.tuwien.ac.at/files/PubDat_239840.pdf