Variable temperature IR spectroscopy and quantum chemistry as the tool for diagnostics of metal spin state

Correlations between metal spin states and vibrational spectra of a trinuclear Fe(II) complex exhibiting spin crossover

“…The actual increase is observed for the corresponding experimental band at 1554 cm À1 at high temperatures (Fig. 3), similar to the case of the abovementioned tris(pyrazol-1-yl)methane, phenanthroline and bipyridine complexes [11,12]. According to the computations (Fig.…”

“…A similar enhancement of IR bands associated with in-plane ring vibrations involving N atoms coordinated to the metal centers was caused by the LS / HS transition of SCO complexes of Fe(II) with tris(pyrazol-1-yl)methane [11] and phenanthroline [12] ligands as well as of tris-bipyridine complexes of Fe(II), Co(II) and Ni(II).12.…”

“…Metalto-ligand bond lengths are predicted with a largest deviation of about 4% from the experiment. Similarly to the mononuclear Fe(II) SCO complexes with tris(pyrazol-1-yl)methane [11] and phenanthroline and bipyridine ligands [12] considered elsewhere, the strongest dependence on the metal spin state is found for the Fe(II)-ligand bonds: 202e222 transition causes elongation of the Fe 2 eN distance by~0.2 Å, whereas other structural parameters including Fe 1,3 eligand bonds remain essentially unchanged. These results are in agreement with the X-ray data [27] for a similar complex with C 2 H 4 OH substituent at N 4 .…”

“…Only the cationic form of the complex was considered computationally. It has been previously shown for Fe(II) SCO complexes with trispyrazol-1-yl-methane [11] and for a Fe(II) SCO polymer based on 4-NH 2 -1,2,4-triazole [26] that counterions had no significant influence on the vibrational properties of these complexes.…”

Spin Crossover in New Iron(II) Coordination Compounds with Tris(pyrazol-1-yl)Methane

“…In [53], the influence of temperature on the character of IR spectra was studied. When the samples are heated (Figure 3), there is a sharp increase in the band intensity at 850 cm −1 and a decrease in the band intensity at 865 cm −1 .…”