Electron density and charge distribution around the metal atom in [Cp*Fe(eta 5-As-5)]

Fe-57 Mossbauer effect spectroscopy has been used to study the charge densi ty, charge distribution, and lattice dynamics in the ferrocene-related comp ound [Cp*Fe(eta (5)-As-5)]. The isomer shift (at 90 K) is significantly mor e positive than that observed for the related eta (5)-P-5 homologue reporte d earlier, while the quadrupole hyperfine interaction is essentially the sa me in both compounds, but only about a quarter of that observed in related ferrocenes with only carbon atoms in the ring structure. The temperature de pendence of the recoil-free fraction evidences a discontinuity centered at about 213 K, which is also observed in the DSC data. These data are compare d to related results acquired for homologous ferrocenes with variable ring substitution.