Pancě Naumov,*,† Stanislav Chizhik,‡,§ Manas K. Panda,† Naba K. Nath,† and Elena Boldyreva*,‡,§ †New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab Emirates ‡Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of Russian Academy of Sciences, ul. Kutateladze, 18, Novosibirsk 630128, Russia Novosibirsk State University, ul. Pirogova, 2, Novosibirsk 630090, Russia

Mechanically Responsive Molecular Crystals

The hyperfine structure in the Mossbauer spectrum of Fe57 in ferrocene and in related compounds shows that the bonding of the iron atom is not affected by ring substitution. The temperature dependence of the fraction of recoil‐free absorption events in these compounds indicates that the Debye temperature is low (∼150°K) and that the optical modes make only a minor contribution to the reduction of the recoil‐free fraction at low temperature.

Fe57 Mössbauer Effect in Ferrocene Derivatives

The second part of this compendium concludes with a collection of phase change enthalpies of organic molecules inclusive of C11–C192 reported over the period 1880–2015. Also included are phase change enthalpies including fusion, vaporization, and sublimation enthalpies for organometallic, ionic liquids, and a few inorganic compounds. Paper I of this compendium, published separately, includes organic compounds from C1 to C10 and describes a group additivity method for evaluating solid, liquid, and gas phase heat capacities as well as temperature adjustments of phase changes. Paper II of this compendium also includes an updated version of a group additivity method for evaluating total phase change entropies which together with the fusion temperature can be useful in estimating total phase change enthalpies. Other uses include application in identifying potential substances that either form liquid or plastic crystals or exhibit additional phase changes such as undetected solid–solid transitions or behave ani...

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Phase Transition Enthalpy Measurements of Organic and Organometallic Compounds and Ionic Liquids. Sublimation, Vaporization, and Fusion Enthalpies from 1880 to 2015. Part 2. C11–C192

In order to determine quantitative information about chemical bonding in metallocenes, we investigated the electronic structure of the cobaltocene molecule by EPR and magnetic susceptibility measurements at 42°K and by optical spectroscopy at 77°K Diamagnetic ruthenocene, weakly paramagnetic nickelocene, and paramagnetic cobaltocene single crystals as well as polycrystalline ferrocene served as host systems From the poorly resolved optical spectra of pure cobaltocene, approximate ligand field parameters were determined The magnetic properties (gtensor,cobalt hfs tensor) of the lowest Kramers doublet are explained in terms of the relative magnitudes of (a) spin‐orbit coupling, (b) static orthorhombic distortion, and (c) vibronic coupling (dynamic Jahn‐Teller effect) in the orbitally degenerate 2 E 1g ground state From the analysis of the EPR data of cobaltocene‐doped ruthenocene, we conclude that covalency effects and vibronic interactions (``Ham effect'') are of comparable importance resulting in a drastic modification of the magnetic parameters compared to a free Co2+ ion in a static crystal field In agreement with earlier qualitative and semiquantitative predictions, considerable covalency of the singly occupied e 1 g * orbital ( 42%± 5% ligand, 58%± 5% cobalt 3d character) was found The strong change of the EPR parameters going from the ruthenocene to the ferrocene host lattice originates mainly in a strongly enhanced static orthorhombic splitting parameter in the tighter packed ferrocene environment In cobaltocene single crystal, magnetic dipole‐dipole interactions broaden the EPR lines beyond detection even at 2°K Nickelocene, an S =1 case with a large positive zero field splitting, behaves as a pseudodiamagnet at liquid helium temperature; exchange interactions with the cobaltocene dopant cause significant modifications of the g values but leaves the cobalt hfs tensor almost unaffected

Electronic Structure and Dynamic Jahn‐Teller Effect of Cobaltocene from EPR and Optical Studies

New types of phase transitions occurring in molecule-based materials have recently drawn great attention, in which electrons are directly involved In this paper are given calorimetric investigations aimed at the elucidation of the mechanisms governing such phase transitions as (i) spin crossover phenomena occurring between high- and low-spin states in transition-metal complexes, (ii) intramolecular electron transfers in mixed-valence complexes, (iii) neutral-to-ionic transitions due to charge transfer mechanism, and (iv) thermochromic phenomena due to a change in coordination geometry Since a change in the electronic state is strongly coupled with a change in the lattice, it turns out that the transition mechanisms always include interplays with various molecular motions in the lattice In all these systems, a large change in the electronic energy is compensated by the entropy term due to these molecular motions

G. L. Kington

Papers

The thermodynamic properties of ferrocene. Part 1.—The low-temperature transition in ferrocene crystals