  Investigations of dynamic and thermodynamic properties for a molecular
crystal tris-hexafluoroacetylacetonate-iron $Fe(O_2C_5HF_6)_3$ are presented.
Heat capacity $C_p(T)$ has been measured by adiabatic calorimetry method in the
temperature range $4.8-321 K$. An anomaly with a maximum at $T_c = 44.6 K$ has
been discovered. Intermolecular vibrations spectrum was calculated by lattice
dynamics method in quasiharmonic approximation. Intramolecular frequencies are
found by solving the Schr\"odinger equation in approach of small harmonic
oscillations. In the frequency interval $\approx 30-70 cm^{-1}$ overlapping the
spectrums intra- and intermolecular oscillations has been found. The good
agreement for calculated and experimental $C_p(T)$ occurred to be possible for
two sets of the force constants. These sets describe two phases above and below
$T_c$. The difference between phases is connected with freezing of rotation
$CF_3$ groups. It has been concluded that the interaction between different
modes leads to phase transition and anomaly in heat capacity.
