We report the far-infrared spectra of the molecular nanomagnet Mn12-acetate (Mn12) as a function of temperature (5-300 K) and magnetic field (0-17 T). The large number of observed vibrational modes is related to the low symmetry of the molecule, and they are grouped together in clusters. Analysis of the mode character based on molecular dynamics simulations and model compound studies shows that all vibrations are complex; motion from a majority of atoms in the molecule contribute to most modes. Three features involving intramolecular vibrations of the Mn12 molecule centered at 284, 306 and 409 cm −1 show changes with applied magnetic field. The structure near 284 cm −1 displays the largest deviation with field and is mainly intensity related. A comparison between the temperature dependent absorption difference spectra, the gradual low-temperature cluster framework distortion as assessed by neutron diffraction data, and field dependent absorption difference spectra suggests that this mode may involve Mn motion in the crown.

We report the polarized infrared reflectance spectra, optical conductivity, and electronic band structure of metallic β′′-(ET) 2 SF 5 CHFSO 3 and compare our results with those of the β′′-(ET) 2 SF 5 CH 2 CF 2 SO 3 superconductor and the β′′-(ET) 2 SF 5 CHFCF 2 SO 3 metal/insulator material. We discuss the electronic structure of these organic molecular solids in terms of band structure, many-body effects, and disorder. On the basis of spectral similarities between the superconductor and metallic salts and structural differences in the anion pocket of all three, we conclude that the unusual electronic excitations observed in the β′′-(ET) 2 SF 5 -CHFCF 2 SO 3 metal/insulator material are not caused by electron correlation but are due to disorder-related localization.

We report the temperature-dependent infrared spectra of pure, deuterated, Zn-doped, and 2,6-dimethyl-substituted samples of the S ) 1 / 2 , one-dimensional Quantum Heisenberg Antiferromagnet (QHAF) copper pyrazine dinitrate (Cu(C 4 H 4 N 2 )(NO 3 ) 2 ). Of the more than 100 vibrational modes observed in the spectra, nearly one-third of them unexpectedly soften throughout the temperature range of investigation (300-5 K). We discuss the temperature dependence of the vibrational spectra in terms of several different models for mode softening. On the basis of detailed structural information and a comparison of the infrared spectra between pure copper pyrazine dinitrate and its chemically modified relatives, we conclude that the unusual softening observed in this low-dimensional molecular magnet is due to enhanced interchain hydrogen bonding with decreasing temperature.