A Design Criteria to Achieve Giant Ising-Type Anisotropy in CoII-Encapsulated Metallofullerenes

Discovery of permanent magnetisation in molecules just like in hard magnets decades ago led to the proposal of utilising these molecules for information storage devices and also as Q-bits in quantum computing. A significant breakthrough with a blocking temperature as high as 80 K has been recently reported for lanthanocene complexes. While enhancing the blocking temperature further remains one of the primary challenges, obtaining molecules that are suitable for the fabrication of the devices sets the bar very high in this area. Encouraged by the fact that our earlier predictions of potential single-molecule magnets (SMMs) in lanthanide-containing endohedral fullerenes have been verified, here we set out to undertake a comprehensive study on Co^II-ion-encapsulated fullerene as potential SMMs. To study this class of molecules, we have utilised an array of theoretical methods ranging from density functional to ab initio CASSCF/NEVPT2 methods for obtaining reliable estimate of zero-field splitting parameters D and E. Additionally, we have also employed, for the first time a combination of molecular dynamics based on DFT methods coupled with CASSCF/NEVPT2 methods to seek the role of conformational isomers in the relaxation of magnetisation. Particularly, we have studied, Co@C₂₈, Co@C₃₈ and Co@C₄₈ cages and their isomers as potential target molecules that could yield substantial magnetic anisotropy. Our calculations categorically reveal a very large Ising anisotropy in this class of molecules, with Co@C₄₈ cages predicted to yield D values as high as −127 cm⁻¹. Our calculations on the smaller cages reveal the free movement of Co^II ion inside the cage, leading to the likely scenario of faster relaxation of magnetisation. However, larger fullerene cages were found to solve this issue. Further models with incorporating units such as {CoOZn}, {CoScZnN} inside larger fullerenes yield axial zero-field splitting values as high as −200 cm⁻¹ with negligible E/D values. As these units represent a strong axiality coupled with a viable way to obtain air-stable low-coordinate Co^II complexes, this opens up a new paradigm in the search of SMMs in this class of molecules.     

Enantiopure Polyradical Tetrahedral Pd12L6 Cages

The synthesis of cages with a polyradical framework remains a challenging task. Herein is reported an enantiomeric pair of quinoid-bridged polyradical tetrahedral palladium(II) cages that are stabilized by an unusual dianionic diradical form (dhbq^..2−). These cages have been characterized by electron paramagnetic resonance and UV-visible spectroscopy, squid magnetometry and mass spectrometry. Single-crystal-derived X-ray investigations of the iso-structural cages built on fluoranilate linkers confirm the tetrahedral structure of the obtained radical cages. Theoretical calculations showed that the diradical state of the dhbq anions is more stable than the usual monoradical state. A weak ferromagnetic exchange between adjacent radical centers was observed in DFT studies.     

The decoupling of the Pomeranchuk pole from all inelastic processes

It is shown that if α_P(0) = 1, then a factorisable Pomeranchuk pole must decouple from all inelastic vertices, when the Pomeron mass is zero.     

Gamma ray line constraints on effective theories of dark matter

A monochromatic gamma ray line results when dark matter particles in the galactic halo annihilate to produce a two body final state which includes a photon. Such a signal is very distinctive from astrophysical backgrounds, and thus represents an incisive probe of theories of dark matter. We compare the recent null results of searches for gamma ray lines in the galactic center and other regions of the sky with the predictions of effective theories describing the interactions of dark matter particles with the Standard Model. We find that the null results of these searches provide constraints on the nature of dark matter interactions with ordinary matter which are complementary to constraints from other observables, and stronger than collider constraints in some cases.     

Effect of pressure on the structural stability of iron phosphate glass: Role of trace water

Raman and infrared spectroscopic measurements were carried out on 40 mol% Fe₂O₃:60 mol% P₂O₅ iron phosphate glass samples to study the effect of increasing external pressure on the local structure of both anhydrous and water trapped glasses. In-situ high‐pressure Raman measurements, done up to 24.2 GPa on anhydrous samples, revealed hardening of the phonon modes accompanied by a loss of Raman intensity and ultimately leading to complete smearing of modes at very high pressures. These changes were found to be reversible upon quenching the sample back to ambient pressure. Raman and infrared spectroscopy of pressure quenched IPG samples containing trace amounts of water have revealed definite signatures of devitrification at room temperature.     

EPR Spectroscopy of a Family of CrIII7MII (M = Cd,Zn, Mn,Ni) “Wheels”: Studies of Isostructural Compounds with Different Spin Ground States

Spinning wheels : The presented highly resolved multifrequency continuous wave EPR spectra (e.g., see figure) of the heterooctametalic “wheels” Cr₇M provide rare examples of high nuclearity polymetallic systems where detailed information on the spin‐Hamiltonian parameters of the ground and excited spin states is observed.

     

Some consequences of the vanishing of the triple-pomeronchukon-vertex

Starting with the assumption that the triple-pomeronchukon-vertex vanishes when all three pomeronchukons have zero mass, we show that in the absence of pionization, total cross sections would fall at least logarithmically with energy, while the mean multiplicity would approach a constant. Several reasons are presented to suggest that some pionization must occur and that, otherwise, limiting fragmentation itself would vanish. A secondary result, that the P-P-P′ coupling will also vanish in certain regions, is also proved.     

Is corannulene a better diene or dienophile? A DFT analysis

Diels Alder reactivity of corannulene has been probed using density functional theory (DFT) at B3LYP/6‐31G^* level by employing it both as a diene and a dienophile in cycloaddition with ethylene and 1,3‐butadiene as typical partners. Computations reveal that corannulene acts better as a dienophile than as a diene and as a dienophile it undergoes normal electron demand type addition with 1,3‐butadiene, and as a diene corannulene undergoes inverse electron demand type addition with ethylene. When employed as a dienophile the addition takes place preferentially in the rim position than in the spoke position due to strong steric and electronic reasons. Further in the rim addition rim exo approach is favored kinetically and thermodynamically. As a diene, corannulene shows regioselectivity for rim–spoke addition over spoke–spoke addition. Concerted type cycloadditions have been studied and the reactions are seen to take place preferentially on the convex face. The effect of substituents in butadiene on the reactivity and the reaction of butadiene–pentaindenocorannulene (an extended corannulene) system has been investigated for the most favorable rim exo positions. Copyright © 2007 John Wiley & Sons, Ltd.