1 research outputs found
FTIR Study of Thermally Induced Magnetostructural Transitions in Breathing Crystals
“Breathing
crystals” based on copperÂ(II) hexafluoroacetylacetonates and
pyrazolyl-substituted nitronyl nitroxides comprise the exchange-coupled
clusters within the polymeric chains. Owing to an interplay of exchange
interaction between copperÂ(II) and nitroxide spins and Jahn–Teller
nature of copperÂ(II) complex, the breathing crystals demonstrate thermally
and light-induced magnetostructural transitions in many aspects similar
to the classical spin crossover. Herewith, we report the first application
of variable temperature (VT) far/mid Fourier transform infrared (FTIR)
spectroscopy and mid FTIR microscopy to breathing crystals. This VT-FTIR
study was aimed toward clarification of the transitions mechanism
previously debated on the basis of superconducting quantum interference
device, X-ray diffraction, and electron paramagnetic resonance data.
VT-FTIR showed the onset of new vibrational bands during phase transitions
occurring at the expense of several existing ones, whose intensity
was significantly reduced. The most pronounced spectral changes were
assigned to corresponding vibrational modes using quantum chemical
calculations. A clear-cut correlation was found between temperature-dependent
effective magnetic moment of studied compounds and the observed VT-FTIR
spectra. Importantly, VT-FTIR confirmed coexistence of two types of
copperÂ(II)–nitroxide clusters during gradual magnetostructural
transition. Such clusters correspond to weakly coupled and strongly
coupled spin states, whose relative contribution depends on temperature.
The pronounced difference in the VT-FTIR spectra of two states in
breathing crystals is a fingerprint of magnetostructural transition,
and understanding of these characteristics achieved by us will be
useful for future studies of breathing crystals as well as their diamagnetic
analogues