Observation of the correlation between the phonon frequency and long-range magnetic ordering on a MnW octacyanide molecule-based magnet

We show an anomalous change in the phonon frequency at the magnetic phase transition on a cyanide-bridged bimetal assembly, Mn3[W(CN)8]2(pyrimidine)4·6H2O. This compound shows a frequency shift in the CN stretching mode below the magnetic phase transition temperature (TC). First-principles phonon mode calculation and molecular orbital calculation suggest that the frequency shift of the CN stretching mode is due to the competition of the magnetic energy and the elastic energy. This work demonstrates that a specific change in the phonon frequency is induced by long-range magnetic ordering in flexibly structured matter.