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.

We report the polarized infrared reflectance of β‘ ‘-(ET)2SF5CHFCF2SO3 as a function of temperature. This salt is a derivative of the first fully organic superconductor, β‘ ‘-(ET)2SF5CH2CF2SO3, where the nature of the alkyl group has been modified to contain a chiral center. This small chemical modification has a dramatic effect on the spectral and charge transport properties. The β‘ ‘-(ET)2SF5CHFCF2SO3 complex displays highly anisotropic behavior compared with the superconducting material; the essential difference is observed in the ⊥b direction where the interdimer interaction is weak, in agreement with recent theoretical calculations. The temperature dependence of key anion vibrational modes is discussed in terms of intermolecular hydrogen bonding within the anion pocket. That small chemical modifications of the anion template result in such striking changes in the physical properties suggests that the β‘ ‘-(ET)2SF5RSO3 system is quite close to a Mott phase boundary.

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We report the polarized infrared reflectance spectra and optical conductivity of β‘ ‘-(ET)2SF5RSO3 superconducting (R = CH2CF2), metallic (R = CHF), and metal−insulator (R = CHFCF2) mixed crystal materials. Incorporation of chiral counterions in the superconducting matrix allows us to tune the physical and spectroscopic properties over the composition range by modulating the anion potential. We conclude that the two low-energy electronic excitations at ≈5200 and 9600 cm-1 are spectral manifestations of charge localization in the ET stack, made manifest by both local (anion pocket) and spatial (positional) disorder.

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