- Tetrahedral molecular geometry
In a Tetrahedral molecular geometry a central
atomis located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos −1( −1/3) ≈ 109.5° when all four substituents are the same, as in CH4. This molecular geometryis common throughout the first half of the periodic table. The perfectly symmetrical tetrahedron belongs to point group Td, but most tetrahedral molecules are not of such high symmetry. Tetrahedral molecules can be chiral.
Main group chemistry
Aside virtually all saturated organic compounds, most compounds of Si, Ge, and Sn are tetrahedral. Often tetrahedral molecules feature multiple bonding to the outer ligands, as in
xenon tetroxide(XeO4), the perchlorateion (ClO4 −), the sulfateion (SO42 −), the phosphateion (PO43 −] ). Thiazyl trifluoride, SNF3 is tetrahedral, featuring a sulfur-to-nitrogen triple bond. [G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.]
Ammonia can be classified as tetrahedral, if one considers the lone pair as a ligand as in the language of VSEPR theory. The H-N-H angles are 107°, being contracted from 109.4°, a difference attributed to the influence of the lone pair.
Transition metal chemistry
Again the geometry is widespread, particularly so for complexes where the metal has d0 or d10 configuration. Illustrative examples include
tetrakis(triphenylphosphine)palladium(0), nickel carbonyl, and titanium tetrachloride. Many complexes with incompletely filled d-shells are often tetrahedral, e.g. the tetrahalides of iron(II), cobalt(II), and nickel(II).
Exceptions and distortions
Inversion of tetrahedral occurs widely in organic and main group chemistry. The so-called
Walden inversionillustrates the stereochemical consequences of inversion at carbon. Nitrogen inversionin ammonia also entails transient formation of planar NH3.
Inverted tetrahedral geometry
Geometrical constraints in a molecule can cause a severe distortion of idealized tetrahedral geometry. In compounds featuring "inverted carbon," for instance, the carbon is pyramidal. [Inverted geometries at carbon Kenneth B. Wiberg
Acc. Chem. Res.; 1984; 17(11) pp 379 - 386; DOI|10.1021/ar00107a001] .
Organic molecules displaying inverted carbon are
tetrahedranes and propellanes. Such molecules are typically strained, resulting in increased reactivity.
A tetrahedron can also be distorted by increasing the angle between the two opposite bonds. In the extreme case, flattening results. For carbon this phenomenon can be observed in a class of compounds called the
* [http://www.up.ac.za/academic/chem/mol_geom/tetrahed.htm Examples of Tetrahedral molecules]
* [http://intro.chem.okstate.edu/1314F97/Chapter9/4BP.html Animated Tetrahedral Visual]
* [http://www.elmhurst.edu/~chm/vchembook/204tetrahedral.html Elmhurst College]
* [http://www.phys.ncl.ac.uk/staff/njpg/symmetry/Molecules_pov.html Point group Symmetries]
* [http://www.3dchem.com/ 3D Chem] - Chemistry, Structures, and 3D Molecules
* [http://www.iumsc.indiana.edu/ IUMSC] - Indiana University Molecular Structure Center]
* [http://chemlab.truman.edu/CHEM121Labs/MolecularModeling1.htm Molecular Modeling]
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