Wyniki wyszukiwania - BazTech

1

Borowce jako centra kwasów Lewisa w oddziaływaniach międzycząsteczkowych : porównanie z wiązaniami wodorowymi

Grabowski S. J.

Wiadomości Chemiczne

|

2017

|

[Z] 71, 7-8

447--471

EN

The triel bonds are analyzed and compared with the hydrogen bond interaction. The triel bonds belong to the class of interactions that are named as the σ-hole and π-hole bonds. The σ-hole bond is an interaction between the σ-hole characterized by the positive electrostatic potential and the electron rich regions such as lone electron pairs, π-electron systems, in other words, centers paying a role of Lewis bases. The σ-holes may be observed for elements of the 14–18 groups of the periodic system and the corresponding interactions with Lewis bases are named; tetrel, pnicogen, chalcogen, halogen and aerogen bonds, respectively. On the other hand, π-holes also characterized by the positive electrostatic potential are observed for centers in planar molecules or planar fragments of molecules in regions above those planes. π-holes may be attributed to triel centers (13th group of the periodic system). The boron and aluminium trihydrides and trihalides are examples of molecules where triels are characterized by π-holes. The mechanism of the triel bond formation is very similar to the mechanism of the formation of the hydrogen bond. It is the Lewis acid – Lewis base interaction where the electron charge transfer from the base unit to the acid one is observed. Next there is outflow of the electron charge from the triel center to the other parts of the Lewis acid unit; in other words the positive charge of the triel center increases as a result of complexation. The triel bonds are often very strong and often they possess characteristics of typical covalent bonds; this is confirmed by the QTAIM (Quantum Theory of Atoms in Molecules) and NBO (Natural Bond Orbital) approaches. For example, for the triel bonds the bond paths between the triel center and the Lewis base center are observed with the bond critical points (BCPs) attributed to those paths. Similarly for the A-H…B hydrogen bonds the H…B bond paths are observed. The parameters of those BCPs often indicate the covalent character of the triel bonds and analogously those characteristics for H-bonds may also indicate the covalent character of the latter interactions. It is very interesting that the triel bonds are observed experimentally in the real systems; for example in crystal structures. The triel center which is trivalent and possesses the trigonal configuration is hypovalent; it means that the octet rule is not obeyed here because of the valence electrons´ deficiency (the triel center possesses six valence electrons in such species). Thus it may interact with one Lewis base ligand reaching rather stable octet and tetrahedral configuration. If the trivalent triel center interacts with two Lewis base ligands thus it may lead to the configuration of the trigonal bipyramid with the hypervalent and pentavalent triel center. These kinds of the triel species occur in crystal structures that are described here.

2

Struktury krystaliczne soli kwasu szczawiowego i amin alifatycznych

Dziuk B., Ejsmont K., Zaleski J.

Chemik

|

2014

|

Vol. 68, nr 4

391--395

PL

W artykule dokonano analizy struktur krystalicznych soli kwasu szczawiowego i amin alifatycznych. W sieciach tych występuje wielość form ułożenia zarówno jedno-ujemnych jak i dwu-ujemnych anionów kwasu szczawiowego. Jednoujemne aniony mogą tworzyć cykliczne dimery lub układać się w liniowe łańcuchy o charakterze zarówno przypominającym strukturę schodkową jak również łańcuchy mieszane. W przypadku anionów dwu-ujemnych można również wyróżnić łańcuchy liniowe płaskie oraz łańcuchy liniowe, zawierające aniony ułożone względem siebie prostopadle. W celu porównania parametrów geometrycznych wiązań wodorowych typu O–H...O występujących pomiędzy jedno-ujemnymi anionami w krysztale oraz w “fazie gazowej”, przeprowadzono obliczenia kwantowo-mechaniczne metodą MP2.

EN

The article analyses crystalline structures of salts of oxalic acid and aliphatic amine. In such network there is multitude of arrangement forms for both mononegative and binegative oxalic acid anions. Mononegative anions might form cyclic dimers or arrange in linear chains of nature resembling stepwise structure, as well as in mixed chains. For binegative anions it is possible to distinguish linear flat chains and linear chains containing anions arranged perpendicularly to each other. In order to compare geometrical characteristics of hydrogen bonds of type O–H...O connecting mononegative ions in the crystal and in the „gas phase”, the quantum mechanical calculations were carried out using MP2 method.

3

Influence of UV irradiation and temperature on polyamides PA6, PA6,6 and polypropylene PP

Brzozowska-Stanuch A., Rabiej S., Sarna E., Maślanka A.

Polish Journal of Applied Chemistry

|

2011

|

Vol. 55, nr 3-4

115-122

EN

In outdoor applications, all polymer materials weather which causes deterioration of their mechanical properties and has a negative influence on their appearance. In this article, the influence of UV irradiation and high temperature on polyamides PA6, PA6.6 and polypropylene PP and influence of aging parameters on their appearance (the state of surface) and chemical crystal structure have been shown. Microscopic examination of samples has shown that the biggest destruction in the surface of PP occurred in a short time after the beginning of the exposure. The examination of the surface and crystal structure of the materials clearly indicated that during exposure to UV irradiation and temperature degradation in PP materials occurred. Polyamides showed longer reaction time but after some time they also underwent radical changes in their supermolecular structure and they lost their esthetic appearance.

4

Cienkowarstwowe struktury fotowoltaiczne

Olchowik J.

Zeszyty Naukowe Politechniki Rzeszowskiej. Budownictwo i Inżynieria Środowiska

|

2006

|

z. 40 [229]

363-370

PL

Praca poświęcona jest analizie wytwarzania i wykorzystania cienkowarstwowych struktur współczesnych baterii słonecznych. Zjawisko konwersji energii słonecznej odbywa się zazwyczaj w niewielkiej przypowierzchniowej części. półprzewodnikowych struktur krystalicznych. Zatem dla celów użytecznych wykorzystywana jest zaledwie niewielka część materiału, natomiast znaczna jego część stanowi jedynie podstawę konstrukcyjną ogniwa słonecznego.

EN

This work presents the analysis of thin layer technology of modern solar celIs. The photovoltaic conversion is realized in thin region of crystalIine substrates, near the surface. For practical purposes one uses only smalI amount of semiconductor material, but majority of these materials support mechanically PV celIs structures.

5

New magnetic structure in TbMn0.33Ge2 compound

Gil A., Szytuła A.

Prace Naukowe. Chemia / Wyższa Szkoła Pedagogiczna w Częstochowie

|

2001

|

Vol. 5

123--129

EN

A study of the magnetic structure of TbMn0.33Ge2 has been made using a neutron diffractometer of better resolution and new results have been obtained. The paramagnetic neutron diffraction data confirmed the CeNiSi2 - type of crystal structure reported earlier for this compound. The magnetic moments are located on terbium. At 1.5 K Tb magnetic moments have two components: a collinear and sine wave modulated one so the magnetic order at this temperature has a complex character. With increasing temperature, the change of the magnetic structure to the new sine wave modulated one is observed near the Neel temperature TN=28 K.