Éva Kováts

Bio: Éva Kováts is an academic researcher from Hungarian Academy of Sciences. The author has contributed to research in topics: Cubane & Fullerene. The author has an hindex of 12, co-authored 49 publications receiving 469 citations.

Rotor–stator molecular crystals of fullerenes with cubane

Abstract: Cubane (C8H8) and fullerene (C60) are famous cage molecules with shapes of platonic or archimedean solids. Their remarkable chemical and solid-state properties have induced great scientific interest. Both materials form polymorphic crystals of molecules with variable orientational ordering. The idea of intercalating fullerene with cubane was raised several years ago but no attempts at preparation have been reported. Here we show that C60 and similarly C70 form high-symmetry molecular crystals with cubane owing to topological molecular recognition between the convex surface of fullerenes and the concave cubane. Static cubane occupies the octahedral voids of the face-centred-cubic structures and acts as a bearing between the rotating fullerene molecules. The smooth contact of the rotor and stator molecules decreases significantly the temperature of orientational ordering. These materials have great topochemical importance: at elevated temperatures they transform to high-stability covalent derivatives although preserving their crystalline appearance. The size-dependent molecular recognition promises selective formation of related structures with higher fullerenes and/or substituted cubanes.

Molecular and spin dynamics in the paramagnetic endohedral fullerene Gd3N@C80

Abstract: Gd3N@C80 endohedral fullerene, a starting material for a potential magnetic resonance imaging contrast agent, is investigated by high-frequency electron spin resonance (ESR) and SQUID magnetometry. The magnetic moments of the three Gd ions of the endohedral Gd3N molecule are ferromagnetically aligned at low temperatures and are uncorrelated at high temperatures. The 4 T broad 210 and 315 GHz ESR spectra measured at 2 K are well-described by a single transition between the lowest Zeeman levels of static molecules shifted by fine structure effects. At higher temperatures there is a gradual transition to a rotating state. At ambient temperatures the rotation frequency is much larger than the fine structure broadening, and a single ESR line is observed at a gyromagnetic ratio of g = 1.995.

Effects of Precursors and Plasma Parameters on Fullerene Synthesis in RF Thermal Plasma Reactor

Abstract: Synthesis of fullerenes from graphite powders of different grade was studied in a radiofrequency (RF) plasma reactor. Dependence of fullerene yield on the properties and feed rate of precursors and on the helium content of plasma gas was studied in details. The fullerene yield was influenced by the mean size and the thermal conductivity of graphite particles on the one hand, and the helium content of the gas phase on the other. Soot containing fullerene mixture of 5.9% was produced in best conditions found in this work. The main component of the fullerene mixture was C60. In addition, it contained about 30% of C70 (corresponding to a C60/C70 mass ratio of 2.64). Higher fullerenes such as C84 were also detected by mass spectroscopy (MS) and high performance liquid chromatography (HPLC).

Structural study of C60 and C70 cubane

Abstract: Fullerenes and cubane (CgHg) form new high-symmetry heteromolecular crystals and C 60 -cubane and C 70 -cubane are the first members of this family. We present the results of a detailed structural study in a wide temperature range, from 100 K to 470 K. The structure of these compounds is based on the well-known face centered cubic (fcc) C 60 lattice. In the highest symmetry case freely rotating fullerenes occupy the fcc lattice sites, and cubanes fill the octahedral voids. We found various phase transitions on lowering the temperature. As expected, the free rotation of fullerenes becomes hindered and orientational ordering appears. The orientational transition temperature is exceptionally low, which can be explained by the combination of the high symmetry environment of fullerenes, the perfect match of convex fullerene and concave cubane molecular surfaces and the significantly expanded fullerene lattice.

Polymerization of the rotor-stator compound C60 -cubane under pressure

Abstract: Cubane, C8H8, can be inserted into the octahedral voids of fullerene lattices to create a family of rotor-stator compounds. We have investigated the structural phase behavior of C60 center dot C8H8 ...

Dynamic molecular crystals with switchable physical properties

Abstract: The development of molecular materials whose physical properties can be controlled by external stimuli - such as light, electric field, temperature, and pressure - has recently attracted much attention owing to their potential applications in molecular devices. There are a number of ways to alter the physical properties of crystalline materials. These include the modulation of the spin and redox states of the crystal's components, or the incorporation within the crystalline lattice of tunable molecules that exhibit stimuli-induced changes in their molecular structure. A switching behaviour can also be induced by changing the molecular orientation of the crystal's components, even in cases where the overall molecular structure is not affected. Controlling intermolecular interactions within a molecular material is also an effective tool to modulate its physical properties. This Review discusses recent advances in the development of such stimuli-responsive, switchable crystalline compounds - referred to here as dynamic molecular crystals - and suggests how different approaches can serve to prepare functional materials.

Hierarchy of Supramolecular Synthons: Persistent Carboxylic Acid···Pyridine Hydrogen Bonds in Cocrystals That also Contain a Hydroxyl Moiety

Abstract: A Cambridge Structural Database (CSD) analysis was conducted in order to evaluate the hierarchy of supramolecular heterosynthons that involve two of the most relevant functional groups in the context of active pharmaceutical ingredients, carboxylic acids and alcohols, in competitive environments. The study revealed that 34% of the 5690 molecular carboxylic acid entries and 26% of the 25 035 molecular alcohol entries form supramolecular homosynthons, whereas the remaining entries form supramolecular heterosynthons with other functional groups, in particular Narom, CONH2, C−O−C, C═O, and chloride anions. Further refinement of this raw data revealed the following: 98% occurrence of the COOH···Narom supramolecular heterosynthon in the 126 crystal structures that contain acid and pyridine moieties in the absence of other hydrogen bond donors or acceptors; and 78% occurrence of the OH···Narom supramolecular heterosynthon in 228 crystal structures that contain hydroxyl and pyridine moieties (excluding intramolec...

Crystalline molecular machines: function, phase order, dimensionality, and composition

Abstract: The design of molecular machines is stimulated by the possibility of developing new materials with complex physicochemical and mechanical properties that are responsive to external stimuli. Condensed-phase matter with anisotropic molecular order and controlled dynamics, also defined as amphidynamic crystals, offers a promising platform for the design of bulk materials capable of performing such functions. Recent studies have shown that it is possible to engineer molecular crystals and extended solids with Brownian rotation about specific axes that can be interfaced with external fields, which may ultimately be used to design novel optoelectronic materials. Structure/function relationships of amphidynamic materials have been characterized, establishing the blueprints to further engineer sophisticated function. However, the synthesis of amphidynamic molecular machines composed of multiple “parts” is essential to realize increasingly complex behavior. Recent progress in amphidynamic multicomponent systems suggests that sophisticated functions similar to those of simple biomolecular machines may eventually be within reach.