The structures of the hypho-compounds B5H 12− and B6H14: Application of the combined ab initio/IGLO/NMR method

1991 ◽  
Vol 2 (4) ◽  
pp. 499-506 ◽  
Author(s):  
Michael Bühl ◽  
Paul Von Ragué Schleyer ◽  
Michael L. McKee
Keyword(s):  
Ab Initio ◽  
Nmr Method

4,6-Dicarba-8-thia-arachno-nonaborane(10) Revisited. Theoretical Refinement of Its Structure

1999 ◽  
Vol 64 (6) ◽  
pp. 993-1000 ◽  
Author(s):  
Drahomír Hnyk ◽  
Matthias Hofmann ◽  
Paul von Ragué Schleyer
Keyword(s):  
Raman Spectroscopy ◽  
Ab Initio ◽  
Chemical Shifts ◽  
Structural Features ◽  
Ir And Raman Spectroscopy ◽  
Nmr Method ◽  
Ir And Raman ◽  
Rule Out

The structure of the nine-vertex arachno-thiadicarbaborane C2SB6H10 has been established employing the ab initio/IGLO/NMR method. Theoretical IGLO 11B chemical shifts support C and S atom placements at the 4, 6 and 8 positions, respectively, and unambiguously rule out the 4,6,5-C2SB6H10 structural alternative, suggested earlier on the basis of IR and Raman spectroscopy. Important structural features of the 4,6,8-C2SB6H10 geometry include a small B(7)-S(8)-B(9) angle (MP2(fc)/6-31G*: 97.9°) and long S-B bonds (MP2(fc)/6-31G*: 1.905 and 1.924 Å) compared to B-B bonds spanning the 1.71-1.85 Å range.

Two Forgotten Ten-Vertex arachno Triheteroboranes: arachno-5,6,9-C2SB7H11 and arachno-5,6,9-C3B7H13, Their Molecular Structure Determination by ab initio/NMR Approach and Synthesis of the Thiacarbaborane

2002 ◽  
Vol 67 (6) ◽  
pp. 813-821 ◽  
Author(s):  
Drahomír Hnyk ◽  
Josef Holub
Keyword(s):  
Molecular Structure ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Sulfur Atom ◽  
Structure Determination ◽  
Chemical Shifts ◽  
Parent Compound ◽  
Symmetry Reduction ◽  
Geometrical Parameters ◽  
Nmr Method

A solution of nido-5,6-C2B8H12 reacted in the presence of Et3N with sulfur to yield the first mixed triheteroborane based on the [arachno-B10H14]2- framework (C2v symmetry), i.e. arachno-5,6,9-C2SB7H11. This compound is isoelectrolobal with known arachno-5,6,9-C3B7H13. The structures of these two ten-vertex arachno triheteroboranes have been established by the ab initio/IGLO (and GIAO-SCF)/NMR method. The presence of three heteroatoms and the absence of the hydrogen atom bridging the 5 and 10 atoms are responsible for a symmetry reduction from C2v to C1 in both compounds. The carbon atoms are compressed toward the center and the sulfur atom is pushed away from the center of the respective cluster relative to the positions they would have in [arachno-B10H14]2-. These distortions from the parent compound are well described by the MP2/6-31* geometrical parameters. A good fit between the computed and measured 11B chemical shifts revealed that the MP2/6-31G* internal coordinates are good representations of the molecular geometries of these two ten-vertex arachno heteroboranes.

Ein 2 π-Vierring-Aromat mit stark reduzierter 1,3-Wechselwirkung / A Four-Membered 2 π Aromatic System with Strongly Reduced 1,3-Interaction

1991 ◽  
Vol 46 (8) ◽  
pp. 1085-1090 ◽  
Author(s):  
Monika Pilz ◽  
Jürgen Allwohn ◽  
Michael Bühl ◽  
Paul von Ragué Schleyer ◽  
Armin Berndt
Keyword(s):  
Ab Initio ◽  
Aromatic System ◽  
Ring Carbon ◽  
Folding Angle ◽  
Nmr Method

2,4-Dicyclopropyl-1,3-diduryl-1,3-dihydro-1,3-diborete (1 e) has the most strongly deshielded ring carbon atoms (δ13C = 186.7 ppm) and the longest C 1–C3 distance (196.6(5) pm) observed so far for 1,3-dihydro-1,3-diboretes. Its folding angle along the C 1–C 3 bond, however, is only slightly reduced (δ = 45°). For the planar (α = 0) unsubstituted 1,3-dihydro-1,3-diborete (1 f′) the corresponding data are calculated by the combined ab initio/IGLO/NMR method to be δ13C = 302 ppm and C 1–C3 218.3 pm. Comparison of these data with those of 1 a and 1 b shows that the bonding 1,3-interaction in 1 e is strongly reduced.

Ab initio band theory approach to electron energy loss near edge structures

1988 ◽  
Vol 46 ◽  
pp. 506-507
Author(s):  
Xudong Weng ◽  
O.F. Sankey ◽  
Peter Rez
Keyword(s):  
Ab Initio ◽  
Local Density ◽  
Interpolation Method ◽  
Atomic Orbital ◽  
Plane Waves ◽  
Large Set ◽  
Theory Approach ◽  
Band Theory ◽  
Atomic Orbitals ◽  
Pseudopotential Calculations

Single electron band structure techniques have been applied successfully to the interpretation of the near edge structures of metals and other materials. Among various band theories, the linear combination of atomic orbital (LCAO) method is especially simple and interpretable. The commonly used empirical LCAO method is mainly an interpolation method, where the energies and wave functions of atomic orbitals are adjusted in order to fit experimental or more accurately determined electron states. To achieve better accuracy, the size of calculation has to be expanded, for example, to include excited states and more-distant-neighboring atoms. This tends to sacrifice the simplicity and interpretability of the method.In this paper. we adopt an ab initio scheme which incorporates the conceptual advantage of the LCAO method with the accuracy of ab initio pseudopotential calculations. The so called pscudo-atomic-orbitals (PAO's), computed from a free atom within the local-density approximation and the pseudopotential approximation, are used as the basis of expansion, replacing the usually very large set of plane waves in the conventional pseudopotential method. These PAO's however, do not consist of a rigorously complete set of orthonormal states.

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