Low‐wavenumber Raman spectra of the spin‐transition complexes [Fe(NH₂ trz)₃](ClO₄)₂ and [Fe(Htrz)₃](ClO₄)₂

Abstract

Raman spectra of two spin-transition polymers, [Fe(NH 2 trz) 3 ](ClO 4 ) 2 and [Fe(Htrz) 3 ](ClO 4 ) 2 , where NH 2 trz = 4-NH 2 -1,2,4-triazole and Htrz = 1-H-1,2,4-triazole, were investigated. The low-temperature high-spin to low-spin phase transition of [Fe(NH 2 trz) 3 ](ClO 4 / 2 is reported. The increasing intensity of the Fe-N stretching band, which appears in the spectrum of the low-spin state, is plotted against temperature to obtain a representative transition curve.

Photoswitching of the spin crossover polymeric material [Fe(Htrz)2(trz)](BF4) under continuous laser irradiation in a Raman scattering experiment

“…Hereafter the spin state of the [Fe(Htrz) 2 (trz)](BF 4 ) complex will be probed by means of Raman microscopy, where the Raman probe laser will also provide the light excitation allowing thermal effects to be potentially generated. Since several years Raman spectroscopy is a well-recognized technique to characterize the phase transition process in SCO compounds, and especially their thermal hysteresis loops [12,14,[22][23][24][25][26][27][28][29][30][31]. The spin transition phenomenon in [Fe(Htrz) 2 (trz)](BF 4 ) samples has been analyzed recently by Urakawa et al [12] by means of an experimental approach combining Raman spectroscopy and X-ray powder diffraction measurements (XRPD).…”

The Role of Molecular Vibrations in the Spin Crossover Phenomenon

“…The role of molecular vibrations as a primary contributor to the entropy change accompanying SCO, initially suggested by Sorai and Seki from the results of heat capacity measurements [50], has been fully confirmed by all subsequent approaches including vibrational spectroscopy [7][8][9][10][11], SCO models accounting for the role of molecular vibrations [36,48,54,55,58], and DFT calculations [8,65]. While most results point to the prominent contribution of metal-ligand vibrations [7][8][9][10], some recent data indicate that other intra-and intermolecular (lattice) vibrations can make significant contributions as well [11].…”

“…While most results point to the prominent contribution of metal-ligand vibrations [7][8][9][10], some recent data indicate that other intra-and intermolecular (lattice) vibrations can make significant contributions as well [11]. However, their relative contributions are not yet clearly evaluated.…”

“…In most cases variable temperature mid-IR or far-IR techniques have been employed [5,6] while Raman spectroscopy has become only recently a well established technique for the characterization of the SCO phenomenon [7][8][9][10][11]. It is worth noting that IR spectroscopy of SCO complexes is complicated by the fact that the SCO is very sensitive to mechanical treatments (grinding, milling, pressure, etc.…”

Sequence of phase transitions induced by chemical composition and high temperature in [Ba2CaWO6](1−x)[Sr2CaWO6]x double perovskite tungsten oxides

“…We utilizedthe technique of Raman spectroscopy as a very sensitive tool to detect accurately the transitions by showing discontinuities in the pressure and temperature dependences of the stretching, bending and external modes[37][38][39][40]. Raman spectra of [Ba 2 CaWO 6 ] 1-x [Sr 2 CaWO 6 ] x (0.1 ≤ x ≤ 1) were collected in-situ at room-pressure and elevated temperatures, up to 550 o C. The Raman spectra obtained at several temperatures are presented inFig.11.…”