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Venerable "18e Rule" Re-derived
C. R. Landis and F. Weinhold,
"18-Electron Rule and the 3c/4e Hyperbonding Saturation Limit,"
J. Comp. Chem. (2015), DOI: 10.1002/jcc.24001
In a special issue of J. Comp. Chem. memorializing
Prof. P. v.R. Schleyer,
researchers from the University of Wisconsin have
shown that the empirical 18-electron rule of transition metal
chemistry corresponds to an intrinsic saturation limit for the
3c/4e hyperbonding interactions that are a ubiquitous feature
of D-block aggregation phenomena. Such a "rule" therefore
requires no "p-orbital participation,"
"valence shell expansion," or other p-type intrusions into the
Aufbau orbital filling sequence...
Taming Peroxide Instabilities with Hyperconjugation
As reported in
Chemistry World (22 October 2015),
a research team led by Prof. I. V. Alabugin
of Florida State University has employed NBO techniques to unravel the
paradoxical instabilities of peroxide species...
Linear-scaling NAO/NHO/NBO construction
[T. Ohwaki, M. Otari, and T. Ozaki,
"A method of orbital analysis for large-scale first-principles simulations,"
J. Chem. Phys.140, 244105 (2014)]
Researchers from the Nissan Resarch Center, National Institute of Advanced Industrial
Science and Technology (AIST), and Japan Advanced Institute of Science and
Technology (JAIST) have developed an efficient method for calculating NBOs
of a localized reaction region in the framework of DFT-based large-scale O(N)
first-principles MD simulations. The method was demonstrated in a variety
of test models [272-atom molecular electrolyte cluster, 217-atom diamond cell,
147-atom cubeoctahedral Pt cluster, and 192-atom 4x4 Pt(111) slab]
and employed to study reactive ligand
exchanges in a 2176-atom simulation of propylene carbonate/LiBF4 bulk liquid
electrolyte, of importance in development of high-performance ion batteries...
Clashing Hydrogens: Repulsive or Attractive?
[F. Weinhold, P. v.R. Schleyer, and W. C. McKee, J. Comp. Chem.35, 1499-1508 (2014)]
Researchers from the University of Wisconsin and University of
Georgia report on page 1499 (DOI: 10.1002/jcc.23654) that
quantitative NBO-based evaluations of steric (left) and
hyperconjugative (right) interactions in the illustrative
model cis-2-butene demonstrate the dominance of steric repulsions
over attractive 'H-H bonding' in biphenyl and related species,
contrary to inferences based on QTAIM analysis...
NBO Description of an unusual 4-center 2-electron bond
[A. Nova, H.-W. Suh, T. J. Schmeier, L. M. Guard, O. Eisenstein,
N. Hazari, and F. Maseras,
"An unusual example of hypervalent silicon: A five-coordinate silyl group
bridging two palladium or nickel centers through a nonsymmetrical
four-center two-electron bond,"
Angew. Chem. Int. Ed.53,
Researchers from the University of Oslo, ICIQ, Université Montpellier 2
and Yale University have used NBO to describe the electronic structure
of a five-coordinate silyl group bridging two palladium or nickel centers.
Crystallographic characterization revealed a rare square-pyramidal geometry
at Si and an unusual asymmetric M2Si2 core (M=Pd or Ni)
held by two pincer PsiP ligands. DFT calculations showed that the
unusual structure of the core is not imposed by the PSiP ligands.
NBO analysis showed that an asymmetric four-center two-electron (4c/2e) bond
stabilizes the hypervalent Si atoms in the M2Si2 core...
Java-based utility programs to simplify NBO input preparation
Marcel Patek of
marcelpatek.com (Tucson, AZ) is providing a series
of Java-based PC-windows utilities
(Gennbo Helper, Jmol-NBO Visualization
Helper,...) to simplify preparation of $NBO input files
and exhibit Jmol-based orbital imagery. Each utility is
provided with an introductory video to demonstrate usage
and capabilities of the program...
Grid-based NBOs in ONETEP linear-scaling DFT Applications
to protein-protein interactions
[L. P. Lee, D. J. Cole, M. C. Payne, and C.-K. Skylaris,
"Natural Bond Orbital Analysis
in Linear-Scaling Density Functional Theory Calculations: application
to a protein-protein interface"
(J. Comp. Chem.34, 429 (2013)]
Members of the
ONETEP (Order-N Electronic Total Energy Package)
Developers Group of Cambridge U. (UK) and U. Southhampton (UK)
have succeeded in extracting NBOs from large-scale (>8000 atoms)
DFT simulations of the entire protein-protein complex
between human RAD51 and BRCA2, thereby
elucidating the mechanism of interaction in terms of the
location and strength of "energetic hotspots" that contribute
the bulk of the binding energy. The NBO results exhibit the
hyperconjugative interactions between non-bonding
electron pairs and antibonding pi* NBOs that provide a
hitherto unknown stabilization mechanism for the
protein conformation that leads to maximum interaction
between the energetic hotspots...
Plane-wave NBOs in Periodic Systems
[B. D. Dunnington and J. R. Schmidt, J. Chem. Theor. Comp.8, 1902 (2012)]
Prof. J. R. Schmidt and graduate student Benjamin Dunnington (UW-Madison)
have developed an
extension of the Natural Bond Orbital (NBO) orbital
localization procedure to
solid-state periodic systems and surface models.
The resulting NBO analysis yields a chemically-intuitive
"general chemistry" Lewis-like picture of bonding between
catalysts / adsorbate in terms of localized orbitals...
NBO-based "Natural Orbital Fukui Function"
[P. Zhou, P. W. Ayers, S. Liu, and T. Li, Phys. Chem. Chem. Phys14, 9890 (2012)]
Researchers from U. Kentucky, McMaster University,
and U. North Carolina have proposed a new condensed form
of the Fukui function, the natural
orbital Fukui function (NOFF), derived
from natural bond orbital occupancy. It is defined as
the change in natural bond orbital occupancy upon
electronic perturbation (electron addition to, or
depletion from, a molecular system). Applying NOFF to
a series of cycloaddition reactions (e.g., [4 + 2] and
[2 + 1] cycloadditions) illustrates the effectiveness of the concept
in interpreting bond breakage and formation mechanisms....