Lone Pair Interactions in Zintl Phases and Intermetallic Compounds: Influence on Electronic Properties in Stannides and Plumbides

1998 ◽  
Vol 547 ◽  
Author(s):  
Thomas F. Fässler
Keyword(s):  
Intermetallic Compounds ◽  
Chemical Bond ◽  
Tight Binding ◽  
Lone Pair ◽  
Real Space ◽  
Localized States ◽  
Zintl Phases ◽  
Electron Pairs ◽  
Lone Pairs ◽  
Lone Pair Interactions

AbstractThe phases K6Sn23Bi2, K6Sn25, NaSn5, BaSn3, BaSn5, and K5Pb24 depict the structural transition from Zintl phases with localized chemical bonds to typical intermetallic compounds which may even have superconducting properties. The question of the nature of the chemical bond in these compounds is studied with the help of quantum mechanical calculations. Tight binding band structure calculations and real space representations using the Electron Localization Function (ELF) show that free electron pairs play a crucial role for the description of the chemical bond in polar intermetallic compounds. Interactions between lone pairs have a dominant influence on the electronic structures. The coincident appearance of quasi-molecular localized states in form of lone pairs and disperse delocalized bands at the Fermi level EF is discussed with respect to a ‘chemical view’ of the superconductivity observed for BaSn3, BaSn5, and K5Pb24.

An Exact Approach to the Diluted Hubbard Model

1992 ◽  
Vol 291 ◽  
Author(s):  
Chumin Wang ◽  
O. Navarro ◽  
R. Oviedo-Roa
Keyword(s):  
Dimensional Space ◽  
Tight Binding ◽  
Real Space ◽  
Many Body ◽  
Electron Pairs ◽  
Hubbard Hamiltonian ◽  
Exact Approach ◽  
Higher Dimensional ◽  
Three Body ◽  
Body Correlation

ABSTRACTA new method to solve the extended Hubbard Hamiltonian for systems with few electrons is reported. This method is based on mapping the original many-body problem onto a tight-binding one in a higher dimensional space, which can be solved exactly. For one-and two-dimensional periodic lattices, the real-space pairing problem of two electrons with parallel and anti-parallel spins is analyzed by looking at the binding energy, the coherence length and the mobility of electron pairs. Likewise, some results of the three-body correlation are also reported.

Sulfur(lone-pair)…π interactions with FAD in flavoenzymes

2018 ◽  
Vol 233 (8) ◽  
pp. 531-537
Author(s):  
Rui F.N. Silva ◽  
Antônio César S. Sacco ◽  
Ignez Caracelli ◽  
Julio Zukerman-Schpector ◽  
Edward R.T. Tiekink
Keyword(s):  
Flavin Adenine Dinucleotide ◽  
Lone Pair ◽  
Ring System ◽  
Glutathione Disulfide ◽  
Covalent Interaction ◽  
Lone Pairs ◽  
Oxidoreductase Enzymes ◽  
Gamma S ◽  
Lone Pair Interactions ◽  
Disulfide Reductases

AbstractThe interactions of π-systems with lone-pairs of electrons are known and have been described in biological systems, involving lone-pairs derived from metals, metalloids, sulfur, oxygen and nitrogen. This study describes a bibliographic survey of the disulfide-bound sulfur(lone-pair) interactions with π-systems residing in the flavin adenine dinucleotide (FAD) cofactor of oxidoreductase enzymes (flavoenzymes). Thus, of the 172 oxidoreductase enzymes evaluated for gamma-S(lone-pair)…π(FAD) interactions, 96 proteins (56%) exhibited these interactions corresponding; 61% of 350 the constituent monomers featured at least one gamma-S(lone-pair)…π(FAD) interaction. Two main points of association between the S(lone-pair) and the isoalloxazine moiety of FAD were identified, namely at the centroid of the bond linking the uracil and pyrazine rings (60%), and the centroid of the uracil ring (37%). Reflecting the nature of the secondary structure in three prominent classes of oxidoreductase enzymes: glutathione disulfide reductases (GR; 21 proteins), trypanothione disulfide reductases (TR, 14) and sulfhydryl oxidases (SOX, 22), the approach of the gamma-S(lone-pair) to the FAD residue was to the si-face of the isoalloxazine ring system, i.e. to the opposite side as the carbonyl residue, for all GR and TR examples, and to the re-face for all SOX examples. Finally, the attractive nature of the gamma-S(lone-pair)…π(FAD) interactions was confirmed qualitatively by an examination of the non-covalent interaction plots.

SCALING OF RESISTANCE IN THE TWO-DIMENSIONAL ANDERSON TIGHT-BINDING MODEL OF DISORDERED SYSTEMS II

1994 ◽  
Vol 08 (03) ◽  
pp. 195-203 ◽  
Author(s):  
ANIRBAN SAIN ◽  
ABHIJIT MOOKERJEE
Keyword(s):  
Disordered Systems ◽  
Tight Binding ◽  
Weak Localization ◽  
Real Space ◽  
Two Dimensions ◽  
Localized States ◽  
Two Dimensional ◽  
Binding Model ◽  
Algebraic Decay ◽  
Band Center

Several workers using different numerical methods have in recent times obtained algebraic decay of wave function amplitudes for localized states at the band center of a two-dimensional disordered system. These include vector recursion,1 direct diagonalization,2 and real space renormalization techniques.3 We modify a version of the combined real space renormalization and vector recursion techniques, including the effect of the random environment on the phase differences between the electronic incoming waves through the different incoming leads, to confirm the algebraic or weak localization at the band center of a random tight-binding Anderson model in two dimensions.

(Isocyano group)⋯lone pair interactions involving coordinated isocyanides: experimental, theoretical and CSD studies

CrystEngComm ◽  
2020 ◽  
Vol 22 (7) ◽  
pp. 1154-1159 ◽  
Author(s):  
Alexander S. Mikherdov ◽  
Svetlana A. Katkova ◽  
Alexander S. Novikov ◽  
Mariia M. Efremova ◽  
Elena Yu. Reutskaya ◽  
...  
Keyword(s):  
Lone Pair ◽  
Carbon And Nitrogen ◽  
Lone Pairs ◽  
Lone Pair Interactions ◽  
Pair Interactions

Both carbon and nitrogen centers in the coordinated isocyano group are capable of acting as a π-hole donor toward lone pairs.

A study of lone-pair interactions of tetracyclic diamines by ultraviolet photoelectron spectroscopy

1986 ◽  
Vol 64 (4) ◽  
pp. 760-763 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Douglas Neve Butler ◽  
Sushil Datta
Keyword(s):  
Photoelectron Spectroscopy ◽  
Lone Pair ◽  
Photoelectron Spectra ◽  
Ultraviolet Photoelectron Spectroscopy ◽  
First Report ◽  
Lone Pairs ◽  
Nitrogen Lone Pair ◽  
Lone Pair Interactions ◽  
Pair Interactions ◽  
Hydrogen Bonded

The ultraviolet photoelectron spectra of 2,7-diazatetracyclo[3.3.3.0.4,90.8,11]undecane (1) and its N,N-dimethyl- and methylene-bridged analogues 2 and 3 are documented. The spectrum of 2, which exhibits a nitrogen lone-pair splitting of 0.95 ± 0.1 eV, is interpreted on the basis of an interaction of "inside" lone pairs of the 1,2-diamine. Apparently this is the first report of a study of such an interaction. The spectrum of 1 is consistent with our view that 1 is an intramolecularly hydrogen bonded species in which the lone pairs are "inside–outside".

Theoretical perspective of the lone pair activity influence on band gap and SHG response of lead borates

RSC Advances ◽  
2015 ◽  
Vol 5 (97) ◽  
pp. 79882-79887 ◽  
Author(s):  
Danni Li ◽  
Qun Jing ◽  
Chen Lei ◽  
Shilie Pan ◽  
Bingbing Zhang ◽  
...  
Keyword(s):  
Band Gap ◽  
Theoretical Perspective ◽  
Lone Pair ◽  
Red Shift ◽  
Lone Pairs

Metal lone pairs play an important role in determining the SHG enhancement and bandgap red shift.

Anomalous stabilizing and destabilizing effects in some cyclic π-electron systems

1993 ◽  
Vol 71 (8) ◽  
pp. 1123-1127 ◽  
Author(s):  
Peter Politzer ◽  
M. Edward Grice ◽  
Jane S. Murray ◽  
Jorge M. Seminario
Keyword(s):  
Ab Initio ◽  
Lone Pair ◽  
Electrostatic Potentials ◽  
Electron Delocalization ◽  
Isodesmic Reaction ◽  
Computational Studies ◽  
Electron Systems ◽  
Molecular Electrostatic Potentials ◽  
Lone Pairs

Ab initio computational studies have been carried out for three molecules that are commonly classed as antiaromatic: cyclobutadiene (1), 1,3-diazacyclobutadiene (7), and 1,4-dihydropyrazine (6). Their dinitro and diamino derivatives were also investigated. Stabilizing or destabilizing energetic effects were quantified by means of the isodesmic reaction procedure at the MP2/6-31G*//HF/3-21G level, and calculated molecular electrostatic potentials (HF/STO-5G//HF/3-21G) were used as a probe of electron delocalization. Our results do not show extensive delocalization in the π systems of any one of the three parent molecules. The destabilization found for 1 and 7 is attributed primarily to strain and to repulsion between the localized π electrons in the C=C and C=N bonds, respectively. However, 6 is significantly stabilized, presumably due to limited delocalization of the nitrogen lone pairs. NH2 groups are highly stabilizing, apparently because of lone pair delocalization. NO2 is neither uniformly stabilizing nor destabilizing.

scholarly journals Unexpectedly Large Couplings Between Orthogonal Units in Anthraquinone Polymers

2019 ◽  
Author(s):  
Rocco Peter Fornari ◽  
Piotr de Silva
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Lone Pair ◽  
Localized States ◽  
Ab Initio Molecular Dynamics ◽  
Coupling Mechanism ◽  
Functional Theory ◽  
Pi Interactions

Directly linked polyanthraquinones have relatively large electronic couplings between charge-localized states despite near-orthogonality of the monomer units. By using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations, we investigate this unusual coupling mechanism and show that this is due to strong lone pair-pi interactions, which are maximized around orthogonal conformations. We find that such materials are largely resilient to dynamic disorder and are promising for organic electronics applications.

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