scholarly journals On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pair. Addendum

2009 ◽  
Vol 65 (3) ◽  
pp. 401-402 ◽  
Author(s):  
Vasyl Sidey
Keyword(s):  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Valence ◽  
Acta Cryst

Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters [Sidey (2008), Acta Cryst. B64, 515–518] have been illustrated using a simple graphical scheme.

On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pair

2008 ◽  
Vol 64 (4) ◽  
pp. 515-518 ◽  
Author(s):  
Vasyl Sidey
Keyword(s):  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Valence ◽  
Acta Cryst ◽  
Bond Valence Model

Applicability of the Wang–Liebau polyhedron eccentricity parameter in the bond-valence model [Wang & Liebau (2007). Acta Cryst. B63, 216–228] has been found to be doubtful: the correlations between the values of the polyhedron eccentricity parameters and the bond-valence sums calculated for the cations with one lone electron pair are probably an artifact of the poorly determined bond-valence parameters.

Studies on bond and atomic valences. I. correlation between bond valence and bond angles in SbIII chalcogen compounds: the influence of lone-electron pairs

1996 ◽  
Vol 52 (1) ◽  
pp. 7-15 ◽  
Author(s):  
X. Wang ◽  
F. Liebau
Keyword(s):  
Statistical Analysis ◽  
Valence State ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Valence ◽  
Continuous Change ◽  
Oxidation Number ◽  
Electron Pairs ◽  
Atomic Valence ◽  
Bond Valence Parameter

In the present bond-valence concept the bond-valence parameter ro is treated as constant for a given pair of atoms, and it is assumed that the bond valence sij is a function of the corresponding bond length Dij , and that the atomic valence is an integer equal to the formal oxidation number for Vi derived from stoichiometry. However, from a statistical analysis of 76 [SbIIIS n ] and 14 [SbIIISe n ] polyhedra in experimentally determined structures, it is shown that for SbIII—X bonds (X = S, Se), ro is correlated with {\bar \alpha} i , the average of the X—Sb—X angles between the three shortest Sb—X bonds. This is interpreted as a consequence of a progressive retraction of the 5s lone-electron pair from the SbIII nucleus, which can be considered as continuous change of the actual atomic valence act Vi of Sb from +3 towards +5. A procedure is derived to calculate an effective atomic valence eff Vi of SbIII from the geometry, {\bar \alpha} i and Dij , of the [SbIII Xn ] polyhedra, which approximates act Vi and is a better description of the actual valence state of SbIII than the formal valence for Vi . Calculated eff V SbIII are found to vary between +2.88 and +3.80 v.u. for [SbIIIS n ] and between +2.98 and +3.88 v.u. for [SbIIISe n ] polyhedra. It is suggested that a corresponding modification of the present bond-valence concept is also required for other cations with lone-electron pairs.

Influence of polyhedron distortions on calculated bond-valence sums for cations with one lone electron pair

2007 ◽  
Vol 63 (2) ◽  
pp. 216-228 ◽  
Author(s):  
X. Wang ◽  
F. Liebau
Keyword(s):  
Periodic System ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Valence ◽  
Correlation Equations ◽  
Coordination Polyhedra ◽  
Absolute Value ◽  
Whole Number ◽  
Correlation Parameters ◽  
Bond Valence Model

In the present bond-valence model (BVM), the bond-valence parameters r 0 and b are, in general, supposed to be constant for each A–X pair and equal to 0.37 Å for all A–X pairs, respectively. For [A i (X j ) n ] coordination polyhedra that do not deviate strongly from regularity, these suppositions are well fulfilled and calculated values for the bond-valence sums (BVS) i are nearly equal to the whole-number values of the stoichiometric valence. However, application of the BVM to 2591 [L i (X j ) n ] polyhedra, where L are p-block cations, i.e. cations of the 13th to 17th group of the periodic system of elements, with one lone electron pair and X = O−II, S−II and Se−II, shows that r 0i values of individual [LX n ] polyhedra are correlated with the absolute value |Φ i | of an eccentricity parameter, Φ i , which is higher for more distorted [LX n ] polyhedra. As a consequence, calculated (BVS) i values for these polyhedra are also correlated with |Φ i |, rather than being numerically equal to the stoichiometric valence of L. This is interpreted as the stereochemical influence of the lone electron pair of L. It is shown that the values of the correlation parameters and the R 2 values of the correlation equations depend on the position of the L cation in the periodic system of elements, if the correlations are assumed to be linear. This observation suggests that (BVS) L describes a chemical quantity that is different from the stoichiometric valence of L.

Three new [XC(O)NH]P(O)[N(CH2C6H5)2]2phosphoric triamides (X= CClF2, 3-F-C6H4and 3,5-F2-C6H3): a database analysis of tertiary N-atom geometry in compounds with a C(O)NHP(O)[N]2core

2012 ◽  
Vol 68 (10) ◽  
pp. o399-o404 ◽  
Author(s):  
Mehrdad Pourayoubi ◽  
Jerry P. Jasinski ◽  
Samad Shoghpour Bayraq ◽  
Hossein Eshghi ◽  
Amanda C. Keeley ◽  
...  
Keyword(s):  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Angle ◽  
Carbonyl Groups ◽  
Database Analysis ◽  
Acta Cryst ◽  
Phosphoric Triamide ◽  
Minimal Deviation ◽  
Structural Database ◽  
Phosphoric Triamides

In the phosphoric triamidesN,N,N′,N′-tetrabenzyl-N′′-(2-chloro-2,2-difluoroacetyl)phosphoric triamide, C30H29ClF2N3O2P, (I),N,N,N′,N′-tetrabenzyl-N′′-(3-fluorobenzoyl)phosphoric triamide, C35H33FN3O2P, (II), andN,N,N′,N′-tetrabenzyl-N′′-(3,5-difluorobenzoyl)phosphoric triamide, C35H32F2N3O2P, (III), the tertiary N atoms of the dibenzylamido groups havesp2character with minimal deviation from planarity. The sums of the three bond angles about the N atoms in (I)–(III) deviate by less than 8° from the planar value of 360°. The geometries of the tertiary N atoms in all phosphoric triamides with C(O)NHP(O)[N]2skeletons deposited in the Cambridge Structural Database [CSD; Allen (2002).Acta Cryst.B58, 380–388] have been examined and the bond-angle sums at the two tertiary N atoms (SUM1 and SUM2) and the parameter ΔSUM (= SUM1 − SUM2) considered. It was found that in compounds with a considerable ΔSUM value, the more pyramidal N atoms are usually oriented so that the corresponding lone electron pair isantiwith respect to the P=O group. In (I), (II) and (III), the phosphoryl and carbonyl groups, separated by an N atom, areantiwith respect to each other. In the C(O)NHP(O) fragment of (I)–(III), the P—N bond is longer and the O—P—N angle is contracted compared with the other two P—N bonds and the O—P—N angles in the molecules. These effects are also seen in analogous compounds deposited in the CSD. Compounds with [C(O)NH]P(O)[N]X(X≠ N), such as compounds with a [C(O)NH]P(O)[N][O] skeleton, have not been considered here. Also, compounds with a [C(O)NH]2P(O)[N] fragment have not been reported to date. In the crystal structures of all three title compounds, adjacent molecules are linkedviapairs of P=O...H—N hydrogen bonds, forming dimers withCisymmetry.

Two new thiophosphoramide structures:N,N′,N′′-tricyclohexylphosphorothioic triamide andO,O′-diethyl (2-phenylhydrazin-1-yl)thiophosphonate

2014 ◽  
Vol 70 (12) ◽  
pp. 1147-1152 ◽  
Author(s):  
Mehrdad Pourayoubi ◽  
Mozhgan Abrishami ◽  
Václav Eigner ◽  
Marek Nečas ◽  
Michal Dušek ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Angle ◽  
Mirror Plane ◽  
Acta Cryst ◽  
Bond Lengths ◽  
Planar Configuration ◽  
Structural Database ◽  
The Ideal

The compoundN,N′,N′′-tricyclohexylphosphorothioic triamide, C18H36N3PS or P(S)[NHC6H11]3, (I), crystallizes in the space groupPnmawith the molecule lying across a mirror plane; one N atom lies on the mirror plane, whereas the bond-angle sum at the other N atom has a deviation of some 8° from the ideal value of 360° for a planar configuration. The orientation of the atoms attached to this nonplanar N atom corresponds to anantiorientation of the corresponding lone electron pair (LEP) with respect to the P=S group. The P=S bond length of 1.9785 (6) Å is within the expected range for compounds with a P(S)[N]3skeleton; however, it is in the region of the longest bond lengths found for analogous structures. This may be due to the involvement of the P=S group in N—H...S=P hydrogen bonds. InO,O′-diethyl (2-phenylhydrazin-1-yl)thiophosphonate, C10H17N2O2PS or P(S)[OC2H5]2[NHNHC6H5], (II), the bond-angle sum at the N atom attached to the phenyl ring is 345.1°, whereas, for the N atom bonded to the P atom, a practically planar environment is observed, with a bond-angle sum of 359.1°. A Cambridge Structural Database [CSD; Allen (2002).Acta Cryst. B58, 380–388] analysis shows a shift of the maximum population of P=S bond lengths in compounds with a P(S)[O]2[N] skeleton to the shorter bond lengths relative to compounds with a P(S)[N]3skeleton. The influence of this difference on the collective tendencies of N...S distances in N—H...S hydrogen bonds for structures with P(S)[N]3and P(S)[O]2[N] segments were studied through a CSD analysis.

scholarly journals Towards a quantitative bond valence description of coordination spheres – the concepts of valence entropy and valence diversity coordination numbers

2019 ◽  
Vol 75 (1) ◽  
pp. 86-96 ◽  
Author(s):  
Piotr A. Guńka ◽  
Janusz Zachara
Keyword(s):  
Coordination Number ◽  
Shannon Entropy ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Bond Valence ◽  
Coordination Numbers ◽  
Close Relationship ◽  
Coordination Spheres ◽  
Relationship Of

Two novel definitions of chemical coordination numbers – valence entropy coordination number n VECN and valence diversity coordination number n VDCN – are proposed. Their originality stems from the fact that they are the first definitions based solely on bond valences. The expressions for them are derived from their definitions and their properties are studied. The unexpected close relationship of n VECN to Shannon entropy and n VDCN to diversity are revealed and the names of the new coordination numbers are taken therefrom. Finally, as an example, a study of arsenic(III) lone electron pair stereoactivity with respect to AsIII coordination number is carried out to demonstrate the usefulness and advantages of the new definitions as well as to compare them with the existing ones.

The Contribution To Bond Valences By Lone Electron Pairs

2004 ◽  
Vol 848 ◽  
Author(s):  
Xiqu Wang ◽  
Friedrich Liebau
Keyword(s):  
Coordination Sphere ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Lone Pair ◽  
Bond Valence ◽  
Alkali Cations ◽  
Continuous Increase ◽  
Electron Pairs ◽  
Effective Valence

ABSTRACTBond valence sums (BVS) calculated for lone-pair cations are found increasingly higher than their formal valences as the retraction of the lone electron pair (LEP) from the nucleus is more pronounced. The increase in BVS is interpreted as a continuous increase of an effective valence of an atom that is a measure of its actual ability to bind other atoms without changing its formal valence. How the LEP of a lone-pair cation affects the effective valence of other atoms in a structure is studied by bond valence calculations for specific structures. For structures rich in alkali cations, it is found that the high effective valence of the lone-pair cations tends to be balanced by low effective valence of alkali cations. The LEP transfers bonding power or effective valence from the alkali cations to the lone-pair cations by joining the coordination sphere of the alkali cations.

Synthesis, Electronic Structure and Anti-Cancer Activity of the Phenyl Substituted Pyrazolo[1,5-a][1,3,5]triazines

2021 ◽  
Vol 25 ◽  
Author(s):  
Evgenia S. Veligina ◽  
Nataliya V. Obernikhina ◽  
Stepan G. Pilyo ◽  
Oleksiy D. Kachkovsky ◽  
Volodymyr S. Brovarets
Keyword(s):  
Electronic Transition ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Anti Cancer ◽  
Protein Molecules ◽  
Biological Affinity ◽  
Cancer Types ◽  
Derivatives Of ◽  
Cancer Activity

: Background: Synthesis of a series of 2-(dichloromethyl)pyrazolo[1,5- a][1,3,5]triazines was carried out and evaluated in vitro for their anticancer activity against a panel of 60 cell lines derived from nine cancer types. The joint quantum-chemical and experimental study of the influence of the extended πconjugated phenyl substituents on the electron structure of the pyrazolo[1,5-a][1,3,5]triazines as Pharmacophores were performed. It is shown that the decrease in the barriers to the rotation of phenyl substituents in compounds 1-7 possibly leads to an increase in the anti-cancer activity, which is in agreement with the change in the parameter biological affinity ϕ0. Analysis of the S0 → S1 electronic transitions (π→π*) of the pyrazolo[1,5-a][1,3,5]triazines shows that an increase in their intensity correlates with anti-cancer activity. Thus, the introduction of phenyl substituents increases the likelihood of investigated pyrazolo[1,5-a][1,3,5]triazines interacting with protein molecules (Biomolecule) by the π stacking mechanism. In both methyl and phenyl derivatives of pyrazolo[1,5-a][1,3,5]triazines, the second electronic transition includes the n-MO (the level of the lone electron pair in two-coordinated nitrogen atoms). The highest intensity of the η→π* electronic transition is observed in pyrazolo[1,5-a][1,3,5]triazine with pyridine residue, which does not exhibit anti-cancer activity, but exhibits antiviral activity [13]. It can be assumed that the possibility of the formation of [Pharmacophore-Biomolecule] complex by hydrogen bonding ([H-B]) mechanism with protein molecules increases.

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