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Thorn H Dunning - One of the best experts on this subject based on the ideXlab platform.
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hypervalency and recoupled pair bonding in the p block elements
Computational and Theoretical Chemistry, 2011Co-Authors: David E Woon, Thorn H DunningAbstract:Abstract The nature of the bonding in hypervalent molecules has long been a topic of discussion with a number of explanations being offered to rationalize the apparent violation of the octet rule. By examining the formation of the second row fluorides, XF n −1 + F → XF n (X = P, S, Cl), we found that a new type of bond is present in these compounds, the recoupled pair bond , which is distinct from other types of chemical bonds. A recoupled pair bond occurs when it is energetically favorable to uncouple an existing pair of electrons to form bonds, which is favorable for most of the valence s 2 and p 2 pairs in P, S, and Cl. The interplay between the formation of normal covalent bonds and recoupled pair bonds in the XF n species readily explains the structures of these species as well as the large variations observed in the XF n −1 –F bond energies. In addition, the formation of recoupled pair bonds leads to the presence of unexpected low-lying excited states in the XF n molecules. We also consider the significant parallels that exist between the XF n families and the YH n families, where Y = Be, B and C. The latter species also involve recoupled pair bonding, which accounts for the divalence of Be, the trivalence of B and the tetravalence of C without invoking the concept of hybridization.
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recoupled pair bonding in pfn n 1 5
Journal of Physical Chemistry A, 2010Co-Authors: David E Woon, Thorn H DunningAbstract:Following our previous studies of hypervalency in SF n (n = 1−6) and ClF n (n = 1−7), we have characterized the structures and energetics of PF n (n = 1−5) species with RCCSD(T) coupled cluster cal...
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bonding in clfn n 1 7 molecules further insight into the electronic structure of hypervalent molecules and recoupled pair bonds
Journal of Physical Chemistry A, 2009Co-Authors: Lina Chen, David E Woon, Thorn H DunningAbstract:As a result of new studies into the nature of hypervalent molecules, we identified a new type of bond called a recoupled pair bond. Hypervalency or hypercoordination was shown to arise by decoupling a pair of valence electrons, each of which becomes available to participate in a new bond. Energy must be expended to decouple an electron pair, so the first recoupled pair bond is weaker than the analogous covalent bond. However, the second bond, which involves a singly occupied antibonding orbital in the hypervalent fragment, is stronger than the analogous covalent bond. Following an initial study of SF(n) species (n = 1-6), the present work explores the ClF(n) (n = 1-7) series to further examine the explanatory usefulness of the recoupled pair bonding model. Optimized structures and energies of the ground and low-lying excited states of the ClF(n) molecules were determined by employing high level ab initio calculations [MRCI, CCSD(T)] with correlation consistent basis sets. Low-lying states that are due to recoupled pair bonding are found in ClF ((3)Pi) and ClF(2) ((2)A(1), (2)B(1), (2)A', (4)A(2)). The bond energies for F addition to form ClF(2), ClF(4), and ClF(6) were found to be much lower than those leading to ClF, ClF(3), and ClF(5). The same type of oscillation is observed in SF(n) species. The differences between ClF(n) and SF(n) reflect the fact that the 3s(2) and 3p(2) electron pairs are more strongly bound in Cl than in S. This behavior and other trends observed in the ClF(n) species demonstrate the improved predictive ability of the recoupled pair bonding model over other models for describing hypervalent bonding.
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theory of hypervalency recoupled pair bonding in sfn n 1 6
Journal of Physical Chemistry A, 2009Co-Authors: David E Woon, Thorn H DunningAbstract:To gain new insight into the nature of hypervalency, we have characterized the bonding across the entire SFn sequence (n = 1−6) with high-level quantum chemical theory (multireference configuration interaction and coupled cluster calculations using correlation consistent basis sets). In contrast to most previous studies, this work examined both the stable equilibrium structures and the process of SFn−F bond formation. We conclude that two different types of bonding can occur in these species: normal polar covalent bonding and a new type that we call recoupled pair bonding. The two bonding processes can be seen in diatomic SF, where hypervalent behavior first occurs. In the covalently bonded 2Π ground state, the bond is formed by straightforward singlet coupling of electrons in the singly occupied S 3p and F 2p orbitals. But there is also a low-lying 4Σ− excited state where the S 3p2 pair of electrons must first be decoupled so that one of the electrons can singlet couple with the electron in the F 2p orbi...
David E Woon - One of the best experts on this subject based on the ideXlab platform.
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hypervalency and recoupled pair bonding in the p block elements
Computational and Theoretical Chemistry, 2011Co-Authors: David E Woon, Thorn H DunningAbstract:Abstract The nature of the bonding in hypervalent molecules has long been a topic of discussion with a number of explanations being offered to rationalize the apparent violation of the octet rule. By examining the formation of the second row fluorides, XF n −1 + F → XF n (X = P, S, Cl), we found that a new type of bond is present in these compounds, the recoupled pair bond , which is distinct from other types of chemical bonds. A recoupled pair bond occurs when it is energetically favorable to uncouple an existing pair of electrons to form bonds, which is favorable for most of the valence s 2 and p 2 pairs in P, S, and Cl. The interplay between the formation of normal covalent bonds and recoupled pair bonds in the XF n species readily explains the structures of these species as well as the large variations observed in the XF n −1 –F bond energies. In addition, the formation of recoupled pair bonds leads to the presence of unexpected low-lying excited states in the XF n molecules. We also consider the significant parallels that exist between the XF n families and the YH n families, where Y = Be, B and C. The latter species also involve recoupled pair bonding, which accounts for the divalence of Be, the trivalence of B and the tetravalence of C without invoking the concept of hybridization.
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recoupled pair bonding in pfn n 1 5
Journal of Physical Chemistry A, 2010Co-Authors: David E Woon, Thorn H DunningAbstract:Following our previous studies of hypervalency in SF n (n = 1−6) and ClF n (n = 1−7), we have characterized the structures and energetics of PF n (n = 1−5) species with RCCSD(T) coupled cluster cal...
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bonding in clfn n 1 7 molecules further insight into the electronic structure of hypervalent molecules and recoupled pair bonds
Journal of Physical Chemistry A, 2009Co-Authors: Lina Chen, David E Woon, Thorn H DunningAbstract:As a result of new studies into the nature of hypervalent molecules, we identified a new type of bond called a recoupled pair bond. Hypervalency or hypercoordination was shown to arise by decoupling a pair of valence electrons, each of which becomes available to participate in a new bond. Energy must be expended to decouple an electron pair, so the first recoupled pair bond is weaker than the analogous covalent bond. However, the second bond, which involves a singly occupied antibonding orbital in the hypervalent fragment, is stronger than the analogous covalent bond. Following an initial study of SF(n) species (n = 1-6), the present work explores the ClF(n) (n = 1-7) series to further examine the explanatory usefulness of the recoupled pair bonding model. Optimized structures and energies of the ground and low-lying excited states of the ClF(n) molecules were determined by employing high level ab initio calculations [MRCI, CCSD(T)] with correlation consistent basis sets. Low-lying states that are due to recoupled pair bonding are found in ClF ((3)Pi) and ClF(2) ((2)A(1), (2)B(1), (2)A', (4)A(2)). The bond energies for F addition to form ClF(2), ClF(4), and ClF(6) were found to be much lower than those leading to ClF, ClF(3), and ClF(5). The same type of oscillation is observed in SF(n) species. The differences between ClF(n) and SF(n) reflect the fact that the 3s(2) and 3p(2) electron pairs are more strongly bound in Cl than in S. This behavior and other trends observed in the ClF(n) species demonstrate the improved predictive ability of the recoupled pair bonding model over other models for describing hypervalent bonding.
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theory of hypervalency recoupled pair bonding in sfn n 1 6
Journal of Physical Chemistry A, 2009Co-Authors: David E Woon, Thorn H DunningAbstract:To gain new insight into the nature of hypervalency, we have characterized the bonding across the entire SFn sequence (n = 1−6) with high-level quantum chemical theory (multireference configuration interaction and coupled cluster calculations using correlation consistent basis sets). In contrast to most previous studies, this work examined both the stable equilibrium structures and the process of SFn−F bond formation. We conclude that two different types of bonding can occur in these species: normal polar covalent bonding and a new type that we call recoupled pair bonding. The two bonding processes can be seen in diatomic SF, where hypervalent behavior first occurs. In the covalently bonded 2Π ground state, the bond is formed by straightforward singlet coupling of electrons in the singly occupied S 3p and F 2p orbitals. But there is also a low-lying 4Σ− excited state where the S 3p2 pair of electrons must first be decoupled so that one of the electrons can singlet couple with the electron in the F 2p orbi...
Agnie M. Kosmas - One of the best experts on this subject based on the ideXlab platform.
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Research Article Theoretical Investigation of Halogen-Oxygen Bonding and Its Implications in Halogen Chemistry and Reactivity
2013Co-Authors: Agnie M. KosmasAbstract:Trends in the properties of normal valent and multivalent halogen-oxygen bonding are examined for the isomers of the halogen polyoxide families of the types (YXO2) and (YXO3), Y=Cl, Br, I, H, CH3, X=Cl, Br, I. A qualitative model is formulated on the relationship between the X-O bond distance variations, the ionic character of the bonding, and the degree of halogen valence. The relative stability and enthalpy of formation of each species are also suggested to correlate with the ionic nature of the X-O bonding and the electrostatic character of the Y, YO fragments. In the model presented, halogen Hypervalence is interpreted to be the result of partial p → d promotion of lone-pair valence electrons followed by the formation of two, four, or six additional pd hybrid bonds around the halogen atom. Copyright © 2007 Agnie Mylona Kosmas. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1
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Theoretical Investigation of Halogen-Oxygen Bonding and Its Implications in Halogen Chemistry and Reactivity
Bioinorganic Chemistry and Applications, 2007Co-Authors: Agnie M. KosmasAbstract:Trends in the properties of normal valent and multivalent halogen-oxygen bonding are examined for the isomers of the halogen polyoxide families of the types (YXO2) and (YXO3), Y = Cl, Br, I, H, CH3, X = Cl, Br, I. A qualitative model is formulated on the relationship between the X−O bond distance variations, the ionic character of the bonding, and the degree of halogen valence. The relative stability and enthalpy of formation of each species are also suggested to correlate with the ionic nature of the X−O bonding and the electrostatic character of the Y, YO fragments. In the model presented, halogen Hypervalence is interpreted to be the result of partial p → d promotion of lone-pair valence electrons followed by the formation of two, four, or six additional pd hybrid bonds around the halogen atom.
Maosheng Miao - One of the best experts on this subject based on the ideXlab platform.
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structural evolution of carbon dioxide under high pressure
Journal of the American Chemical Society, 2013Co-Authors: Maosheng MiaoAbstract:Using an efficient structure search method based on a particle swarm optimization algorithm, we study the structural evolution of solid carbon dioxide (CO2) under high pressure. Our results show that, although it undertakes many structural transitions under pressure, CO2 is quite resistive to structures with C beyond 4-fold coordination. For the first time, we are able to identify two 6-fold structures of solid CO2 with Pbcn and Pa3 symmetries that become stable at pressures close to 1 TPa. Both structures consist of a network of C-O octahedra, showing Hypervalence of the central C atoms. The C-O bond length varies from 1.30 to 1.34 A at the 4-fold to 6-fold transition, close to the C-O distance in the transition state of a corresponding S(N)2 reaction. It has been a longstanding and challenging objective to stabilize C in a hypervalent state, particularly when it is bonded with nonmetallic elements. Most of the work so far has focused on synthesizing organic molecules with a high coordination number of C. Our results provide a good measure of the resistivity of C toward forming hypervalent compounds with nonmetallic elements and of the barrier of reaction involving C-O bonds.
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Structural Evolution of Carbon Dioxide under High Pressure
2013Co-Authors: Maosheng MiaoAbstract:Using an efficient structure search method based on a particle swarm optimization algorithm, we study the structural evolution of solid carbon dioxide (CO2) under high pressure. Our results show that, although it undertakes many structural transitions under pressure, CO2 is quite resistive to structures with C beyond 4-fold coordination. For the first time, we are able to identify two 6-fold structures of solid CO2 with Pbcn and Pa3̅ symmetries that become stable at pressures close to 1 TPa. Both structures consist of a network of C–O octahedra, showing Hypervalence of the central C atoms. The C–O bond length varies from 1.30 to 1.34 Å at the 4-fold to 6-fold transition, close to the C–O distance in the transition state of a corresponding SN2 reaction. It has been a longstanding and challenging objective to stabilize C in a hypervalent state, particularly when it is bonded with nonmetallic elements. Most of the work so far has focused on synthesizing organic molecules with a high coordination number of C. Our results provide a good measure of the resistivity of C toward forming hypervalent compounds with nonmetallic elements and of the barrier of reaction involving C–O bonds
Dietmar Stalke - One of the best experts on this subject based on the ideXlab platform.
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thf li2 h2cs ntbu 2 2 synthesis polymorphism and experimental charge density to elucidate the bonding properties of a lithium sulfur ylide
Organometallics, 2008Co-Authors: Stephan Deuerlein, Dirk Leusser, Ulrike Flierler, Holger Ott, Dietmar StalkeAbstract:Sulfur ylides (R2S+−−CR2) are widely used in organic synthesis for stereoselective epoxidations, cyclopropane formations, and ring expansion reactions. Nevertheless, their electronic properties are still under debate, because their ylenic textbook formulation (R2S═CR2) contradicts the reactivity. In order to elucidate the electronic situation in a sulfur ylide, we present an experimental charge density study via multipole refinement and subsequent topological analysis based on high-resolution X-ray data of [(thf)Li2{H2CS(NtBu)2}]2 (1). The title compound is of special interest, since additionally the formal hypervalency can be investigated along with the controversial interaction between a carbanion with a Li3 triangle. As a prerequisite for these studies, the polymorphism and synthesis of 1 were investigated. The findings clearly support the ylidic, non-hypervalent description of the molecule. The ylidic carbanion was determined to be 6-fold coordinated with three single bonds to the sulfur atom and both...
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metal coordination to the formal pn bond of an iminophosphorane and charge density evidence against hypervalent phosphorus v
Chemistry: A European Journal, 2004Co-Authors: Nikolaus Kocher, Dirk Leusser, Alexander Murso, Dietmar StalkeAbstract:: The iminophosphorane Ph(2)P(CH(2)Py)(NSiMe(3)) (1) was treated with deprotonating alkali metal reagents to give [(Et(2)O)Li[Ph(2)P(CHPy)(NSiMe(3))]] (2), [[Ph(2)P(CH(2)Py)(NSiMe(3))]Li[Ph(2)P(CHPy)(NSiMe(3))]] (3) and [[Ph(2)P(CH(2)Py)(NSiMe(3))]Na[Ph(2)P(CHPy)(NSiMe(3))]] (4). We report their coordination behaviour in solid-state structures and NMR spectroscopic features in solution. Furthermore, we furnish experimental evidence against hypervalency of the phosphorus atom in iminophosphoranes from experimental charge-density studies and subsequent topological analysis. The topological properties, correlated to the results from NMR spectroscopic investigations, illustrate that the formal P=N double bond is better written as a polar P(+)--N(-) single bond. Additionally, the effects of metal coordination on the bonding parameters of the iminophosphorane and the related anion are discussed.