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Basic of the Chalcogenides
Published in Abhay Kumar Singh, Tien-Chien Jen, Chalcogenide, 2021
Abhay Kumar Singh, Tien-Chien Jen
The chalcogen ‘Se’ atom contains two s and four p electrons in its outermost shell. As the figure shows, it is obvious that out of the three p states, two states can be utilized for the bonding. This leaves one p-state unoccupied, which is activated by two paired electrons of the opposite spin. This is known as non-bonding electron pair or lone-pair electrons. Such non-bonded electrons do not participate in the bonding. Therefore, the bonding is actually due to the remaining two p-states (orbitals) each occupied by single electron. On the other hand, selenium is usually present in 2-fold coordination. The conduction band in Se also initiate from σ* states like Ge. With a remarkable difference the highest occupied VB is formed from non-bonding states instead of the 6 states as shown in Fig. 1.18(b). The unshared or non-bonding electrons states near the original p-state energy acts as the valence band [121, 125]. Hence non-bonding electrons constitute the highest VB band and reveal the conduction properties of chalcogenides. Such materials are also called lone-pair semiconductors [121].
Carbon, Nitrogen, and Sulfur Chemistry
Published in Jerome Greyson, Carbon, Nitrogen, and Sulfur Pollutants and Their Determination in Air and Water, 2020
The remarkable differences in the physical and chemical properties of the hydrides of nitrogen and carbon, ammonia and methane, respectively, are also attributable to the lone pair electrons. Although methane is a relatively unreactive neutral compound that liquefies at very low temperature (-164°C), ammonia is a strong base, is relatively reactive, and liquefies at -33°C. Thus, the lone pair serves to enhance molecular association, to increase reactivity, and as a potential partner with a hydrogen ion in an acid-base interaction.
Chemical Bond I: Lewis Scheme
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
In the years when quantum theory was still under development, but with a periodic table portrait already established, starting from the observed chemical inertia of the noble gases,1 G. N. Lewis posed the conjecture that the formation of a stable molecule is determined by the fact that each of its atoms, sharing electrons with nearest-neighbor atoms, would reach a total number of electrons equal to that of the noble gas closest to it in the periodic table. More precisely, Lewis scheme defines for each atom the number of valence electrons as the difference between the total number of the electrons in the atom and the number of electrons in the noble gas which precedes the atom in the periodic table. Moreover, assuming that the valence electrons in an atom are organized in pairs, the scheme distinguishes in a molecule two types of electron pairs: bond pairs and lone pairs. The total number of electrons in bond and lone pairs pertaining to each atom in a molecule must then be 2, 8, or 18, because this is the number of valence electrons in a noble-gas atom (a circumstance which, in the light of the quantum theory of atoms as seen in the previous chapter, amounts to the number of electrons in a complete electron shell).
Isomerization as a tool to design volatile heterometallic complexes with methoxy-substituted β-diketonates
Published in Journal of Coordination Chemistry, 2018
Vladislav V. Krisyuk, Samara Urkasym Kyzy, Tatyana V. Rybalova, Iraida A. Baidina, Ilya V. Korolkov, Dmitry L. Chizhov, Denis N. Bazhin, Yulia S. Kudyakova
In the first series of experiments, bis-diketonates CuL12 and CuL22 containing CF3 and CH3 substituents, respectively, were used. Co-crystallization of equimolar amounts of trans-CuL12 and Pb(hfac)2 from the solution afforded blue-green crystals of the mixed complex and blue crystals of an excess of the starting Cu complex. The single crystal X-ray diffraction study confirmed that the structural units of the new heterocomplex were tri-nuclear centrosymmetric molecules of composition trans-CuL12(Pb(hfac)2)2 (2). At a ratio of the starting complexes 1:2, co-crystallization results in single-phase product 2. The structure of the tri-nuclear complex is shown in Figure 2, and its molecular packing is illustrated in Figure S1. The main geometrical parameters are listed in Table 3. The Cu complex is located in the center of symmetry and has a trans-configuration. The Pb coordination polyhedron resembles a distorted pentagonal bipyramid where O4 and a lone pair are in axial positions. Provided that geometries are normally defined based upon the locations of atoms, the molecular geometry that observed without regard to the lone pair can be considered as distorted octahedral or distorted pentagonal pyramidal.
Interaction of hydrogen sulfide with the pristine and B&N-doped beryllium oxide nanotube: DFT study
Published in Journal of Sulfur Chemistry, 2021
One of the helpful and efficient methods to investigate the adsorption properties within a H2S the pure-, B&N-doped BeONTs is the natural bond orbital (NBO) analysis. This method reveals us the charge transfer between donor electron orbital and electron acceptor orbital, and it is used to determine an accurate Lewis structure [70]. In this method, the second-order perturbation energy E(2) is used to analyze the behavior of bonding interactions, strength of the electronic delocalization, and charge transfer effects in the molecular systems [71]. The E(2) value is calculated by Equation (6). where and are orbital energies and Fij is the off–diagonal NBO Fock matrix element and qi is the donor orbital occupancy. The values of E(2), electron donor, and acceptor orbitals i and j for all systems are given in Tables S1 and S2 (in supplementary data). The NBO results indicate A(I), A(III), D(I) D(II), and D(III) adsorption models, transfers of have most interactions with E(2) values from 5.34 to –5.9 kcal/mol and the least interaction is occurred in the B(I), B(II), and B(III) models with E(2) values from 0.43 to –0.77 kcal/mol. On the other hand, oxygen atoms with lone pair play an important role in the formation of a stable bond in this system. As it can be seen the most interaction of lone pair (n) for D(II) model is between has the most interaction with E(2) values from 6.20 kcal/mol. The least interaction occurred in the C(III) model with E(2) value 1.38 kcal/mol. Inspection of results demonstrates that between E(2) values of the charge transfer, there is a following order: D > A > C > B; and for charge transfer is in the order: D > B > A > C. It is noticeable that the charge transfer from donor orbital to acceptor orbital at B&N-doped BeONTs is more than pristine, B, and N doped.
Air dehumidification with advance adsorptive materials for food drying: A critical assessment for future prospective
Published in Drying Technology, 2021
Mohamad Djaeni, Dewi Qurrota A’yuni, Misbahudin Alhanif, Ching Lik Hii, Andri Cahyo Kumoro
Since adsorbent characteristics determine the successful operation of adsorptive dehumidification system, many efforts have been devoted to the designing and developing adsorbents for efficient air dehumidification.[21,38] For dehumidification application, the ideal solid adsorbent materials are porous materials with an excellent adsorption capacity, as supported by superior physical and chemical properties, including specific surface area, pore size, pore volume, tunable functionality,[44] and appropriate adsorption sites.[45] This is owing to the fact that adsorbents with higher specific surface area and porosity and pore volume will generally exhibit a higher water vapor adsorption capacity.[46] However, the adsorption process on the porous structure is also strongly affected by the operating pressure.[47] In addition, the capability of nanosized porous materials to adsorb water vapor depends on the existence of hydrophilic sites, which represent their water affinity can mainly be fulfilled by oxygen functional groups (aliphatic).[48–50] The literature clearly explains that the presence of hydrophilic sites significantly improves the water vapor adsorption on the adsorbent surface (e.g., silica and carbon black).[51] In contrast, adsorbents with hydrophobic sites cannot adsorb a significant amount of water vapor, especially at a relatively low-pressure operation. In addition to the adsorbent characteristics, adsorbate properties also demonstrate a pivotal role in the adsorption process. The water molecules in air dehumidification are small with the size below 3 Ao. Wang et al.[21] described that the water molecules can actively undergo intermolecular interactions with each other through hydrogen bonding mechanism. The oxygen atom of a water molecule has two lone pairs of electrons, each of which can form a hydrogen bond with the hydrogen atom of another neighboring water molecule. This molecular interaction takes place in such a way that every water molecule can exist in H-bonded configuration with up to four other water molecules.[21]