Distortions of C-60(4-) studied by infrared spectroscopy

The Jahn-Teller effect plays a crucial role in the explanation of the insulating character of A(4)C(60) (A = K, Rb, Cs). To detect possible phase transitions arising from the interplay between the molecular Jahn-Teller distortion and the distorting potential field of the counterions, we measured the mid-IR spectra of A(4)C(60) compounds in the temperature range 90 - 300 K and found significant spectral changes with temperature in all three compounds. We also compare these spectra to that of Na(4)C(60) in its room-temperature polymeric phase, where the distortion is more pronounced and evident from the structure

Temporal trends (1990-2005) in heavy metal accumulation in mosses in Slovakia

Biomonitoring of multielement atmospheric deposition using terrestrialmoss is a well-established technique in Europe. The moss samples of Hylocomium splendens, Pleurozium schreberi and Dicranum sp. were collected in Slovakia. Separately we evaluated the atmospheric deposition in the National Parks (Vysoké Tatry, Nízke Tatry, Západné Tatry -Jelenec, Slovenský raj) and in a landscape protection area (Ve¾ká Fatra). In comparison to the median northern Norway values ofheavy metal contents in moss, the Slovak atmospheric deposition loads of elements were found to be higher. The survey has been repeated and in this paper we report on the temporal trends in the concentration of Cd, Cr, Cu, Fe, Hg, Ni, Pb, V and Zn between 1990 and 2005. Metal- and sites-specific temporal trends were observed. In general, the concentration of Cd, Cr, Cu, Fe, Hg, Ni, Pb, V and Zn in mossesdecreased between 1990 and 2005; the decline was higher for Pb than for Cd. The observed temporal trends for the concentrations in mosses were similar to the trends reported for the modelled total deposition of cadmium, lead and mercury in Europe. The level of elements, determined in bryophytes reflects the relative atmosphericdeposition loads of elements at the investigated sites. Factor analysis was applied to determine possible sources of trace element deposition in the Slovakian mosses

The Co-Ni distribution in decagonal Al69.7(4)Co10.0(4)Ni20.3(4)

The Co-Ni distribution in d-Al69.7(4)Co10.0(4)Ni20.3(4) was investigatedbased on X-ray and neutron diffraction data. The structure was modelledin higher dimensional space using the ‘charge-flipping’ and ‘low-densityelimination’ methods and it was quantitatively refined inthree-dimensional space employing a pseudo-approximant approach. Inhigher-dimensional description, the Co atoms are found at the centre ofone of the two symmetry independent occupation domains, enclosed byregions mainly occupied by Ni. The other occupation domain is mostlyoccupied by Al. In physical space Co atoms are located in the centres ofsmall Al pentagons and form pentagonal units, which are arranged indecagonal rings. On these sites Co is partly substituted by Ni, whileall other transition metal sites are occupied by Ni and to a minordegree by Al. The fraction of Co found on transition metal sitesdecreases with decreasing Co-Co distances, whereby Co is replaced by Ni

Isolation and structure of fullerene photodimer, C-120

Photopolymerization of C60 was performed on a gram scale via a new monomer transport method. After subsequent extractions of the raw polymer in organic solvents, lOOmg dimer and lOmg mixture of soluble oligomers were yielded. The structures of the soluble fractions and the insoluble polymer were studied by optical spectroscopy and x-ray diffraction methods. According to IR and UV-VIS spectroscopic data, the obtained photodimer is identical to the (2+2) cycloadduct C12o prepared previously. In contrast to previous crystallization studies, a fast precipitation of the dimer from toluene gives rise to the formation of a solvent-free microcrystalline solid. The crystal structure of the pure dimer is fee (a= 14.05 A) consisting of closely packed balls with the cycloadduct bonds oriented randomly along the 12 nearest neighbor directions. A linear relationship is found to exist between the fee lattice parameter (a) and the average number of bonded neighbours (nB) in various photopolymerized structures. For insoluble polymers nB«2 is estimated, supporting previous photopolymer models of small ring or branched clusters

Jahn-Teller distortion in Cs4C60 studied by vibrational spectroscopy

We have measured the infrared spectra of Cs(4)C(60) in the temperature range 220 - 450 K. Two anomalies in the low-frequency modes at 270 K and 400 K point to changes in molecular or crystal structure. The most probable explanation is a rotator phase above 400 K and a fully ordered phase below 220 K; the intermediate structure is one where molecular Jahn-Teller distortions compete with crystal field effects

Bis(tetra­propyl­ammonium) di-μ3-iodido-di-μ2-iodido-diiodidodi­pyridine­tetra­copper(I)

The title compound, (C12H28N)2[Cu3.194I6(C5H5N)2] was prepared from reaction of copper powder, copper(I) oxide, hydro­iodic acid, tetra­propyl­ammonium iodide and pyridine under hydro­thermal conditions. In the centrosymmetric Cu4I6 2− anion, one Cu site is in a trigonal-planar coordination while the second Cu site, which is only partially occupied [site occupancy of 0.5968 (16)], is surroundedby three iodine atoms and one pyridine molecule in a distorted tetrahedral coordination

A fázisprobléma megoldásának új módszerei = New methods for solving the phase problem

A kristályos anyagok szerkezetének ab initio meghatározásához megkerülhetetlen a krisztallográfiai fázisprobléma megoldása. Kutatásunk során erre a feladatra dolgoztunk ki új eljárást, amely a klasszikus direkt módszertől teljesen különböző elven működik. A töltésalternáló (charge flipping) módszer meglepően merész alapfeltevése az, hogy kellően jó felbontás esetén a megoldáshoz nincs szükség sem előzetes kémiai vagy szimmetria ismeretekre, sem az atomicitás elvére vagy statisztikus fázisösszefüggésekre. Szükségesek viszont a cella ürességét kihasználó gyenge perturbációk, amelyekkel a hiányzó fázisok terének nagy dimenziószámát le lehet csökkenteni. A megvalósított algoritmus a valós és reciprok terek között gyors Fourier-transzformációval iterál, a valós térben az elektronsűrűség előjelét egy kis küszöbszint alatt megváltoztatja, míg a reciprok térben csak a gyenge reflexiók fázisait tolja el. Az iterációs folyamat nem igényel külső beavatkozást: a megoldást valamely jósági tényező hirtelen zuhanása jelzi. Könnyű adaptálhatóságának köszönhetően a töltésalternálás módszere az első közlemény megjelenése óta rohamosan terjed. Alkalmazhatósága mára a diffrakciós szerkezetmeghatározás több területén nyert bizonyosságot; a listán egykristály és pordiffrakciós adatok, periodikus, pszeudoszimmetrikus és modulált szerkezetek, ill. kvázikristályok is vannak. Az algoritmust már három felhasználói programcsomag kínálja alternatívaként nehéz esetek elemzésére. | The solution of the crystallographic phase problem is essential for the ab inito determination of crystalline structures. For this purpose we developed a new method called charge flipping. It is based on principles very different from that of classical direct methods. The primary assumption of charge flipping is the following: given sufficiently high-resolution diffraction data, we need neither preliminary information on chemical composition or symmetry, nor the principle of atomicity or statistical phase relations. Instead, we must rely on the emptiness of the unit cell and decrease the dimensionality of the missing phases through small perturbations. The new algorithm iterates between the real and reciprocal spaces by the fast Fourier transform, in real space it changes the sign of electron density below a small positive threshold, while in reciprocal space it shifts the phases of weak reflections. The whole process is deterministic and proceeds without user intervention, the solution is signified by a sharp drop of some figure of merit. Due to its deceptive simplicity and easy implementation the charge flipping method quickly propagates. Its applicability is already proven in several fields of structural science, the list contains using single crystal and powder data of periodic, pseudo-symmetric and modulated structures and also quasicrystals. The algorithm is already offered as an alternative by three user programs for the treatment of difficult cases

A fázisprobléma megoldásának új módszerei II. = New methods for solving the phase problem II.

A krisztallográfiai fázisprobléma megoldására általunk felfedezett charge flipping módszert több, a gyakorlatban azonnal alkalmazható irányba fejlesztettük tovább. Új algoritmusváltozatokat, adatkezelést, paraméterválasztást vezettünk be, amellyel egyrészt gyorsabban, másrészt jobb minőségben oldhatók meg a kristályszerkezetek. A fejlesztések új alkalmazásokat is lehetővé tettek; az algoritmus egyik változata a negatív szórássűrűségű neutrondiffrakciós adatok, míg egy másik, különböző típusú, súlyosan hiányos adatok esetén működik kiválóan. Utóbbi esetben, akár a krisztallográfiai irodalomban szokásos adatok 1/8-val is lehetséges jó minőségű szerkezetmeghatározás. A kristályos alapállapot elméletével is részletesen foglalkoztunk. Az atomok közötti Fourier-transzformálható kölcsönhatások és a kristályos rend kapcsolatának matematikailag egzakt leírását adtuk egyes speciális, a puhaanyag-fizikához köthető esetekben. Kristályok helyett molekulák azonos replikáin alapul az atomi szerkezet meghatározásának egy teljesen új módszere, az egyrészecske-leképezés. A kísérlet csak szabadelektron-lézereknél lehetséges, és még számos kihívást jelent. Ezek közül mi az adatelőkészítés problémáját oldottuk meg, iterációs módszert alkottunk, amely az ismeretlen orientációjú és rendkívül zajos 2D diffrakciós képeket szerkezetmeghatározásra alkalmas 3D adatkészletté alakítja. | Our charge flipping method, that solves the crystallographic phase problem, was further developed with practical utilization in mind. We introduced new algorithm variants, data treatments and parameter choices, that helped to determine crystal structures both faster and at better quality. These developments also allowed new applications; one of the algorithm variants works well in the case of negative scattering density, and an other in various instances of seriously incomplete data. In the latter case, high quality structure determination is feasible using only 1/8-th of the data expected in the crystallographic literature. We also investigated the ground state of crystals with mathematical rigour. The relationship of Fourier-transformable atomic interactions and crystal order was described, the special cases treated are related to soft matter physics. Our third theme is single particle imaging, a new method of structure determination that is not based on crystals but on molecular replicas. The experiment is only made possible by free electron lasers, and it still poses a number of challenges. We worked on the problem of data preparation, and solved it by creating an iterative procedure that is capable of composing a single high-quality 3D dataset from the large number of noisy 2D images of unknown orientation

Structural differences arise between fruit cuticles of two apple cultivars during long term cold storage

Apple fruits are covered by hydrophobic cuticle that provides protection against desiccation, pathogens, excessive water absorption and radiation. The features of cuticle affect the quality and storability of the fruits. It was aimed to evaluate the correlation between peel ultrastructure and weight loss in fruits covered by waxy bloom (cv. Florina) and without bloom (cv. Red Rome van Well) during 4-month cold storage. SEM (scanning electron microscopy) was used for visualization of the fruit surface and fruit weight was also measured. Several studies have revealed that there may be correlation between the ultrastructure of cuticle and its water permeability. Our results confirmed this phenomenon in case of two cultivars. The weight loss per fruit surface area unit of ‘Florina’ was found significantly higher than that of ‘Red Rome van Well’. At the same time the cuticular surface of the fruits contained more micro-cracks in case of the former cultivar. These data confirmed the relationship between the density of cuticular micro-cracks and the water vapour permeability. We concluded that this feature is more significant than the amount of natural waxy bloom on fruit surface