The thermal motion of gold atoms in metal cluster compounds as determined by Mössbauer and specific heat

¹⁹⁷Au Mössbauer effect spectroscopy and specific heat measurements have been performed as a function of temperature on three gold polynuclear cluster compounds, Au₉(PPh₃)₈](NO₃)₃, Au₁₁(PPh₃)₇(SCN)₃, and Au₅₅(PPh₃)₁₂Cl₆. The Mössbauer data yield information on the vibrational motions of the various distinguishable Au sites, as well as on the motion of the clusters as a whole. The Mössbauer and the specific heat data are successfully described by a superposition of inter- and intra-cluster vibrations. The latter are determined by calculating numerically the normal modes of vibration of the metal cores.