Tetrahedral molecular geometry: Difference between revisions
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In a '''tetrahedral molecular geometry''', a central [[atom]] is located at the center with four [[substituent]]s that are located at the corners of a [[tetrahedron]]. The [[bond angle]]s are cos<sup>−1</sup>( |
In a '''tetrahedral molecular geometry''', a central [[atom]] is located at the center with four [[substituent]]s that are located at the corners of a [[tetrahedron]]. The [[bond angle]]s are cos<sup>−1</sup>(−{{frac|1|3}}) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in [[methane]] ({{chem|CH4}})<ref>{{cite web|url=http://maze5.net/?page_id=367|title=Angle Between 2 Legs of a Tetrahedron|website=Maze5.net}}</ref><ref>{{cite journal|doi=10.1021/ed022p145|title=Valence Angle of the Tetrahedral Carbon Atom|first=W. E.|last=Brittin|journal=[[J. Chem. Educ.]]|date=1945|volume=22|issue=3|page=145|bibcode=1945JChEd..22..145B}}</ref> as well as [[Group 14 hydride|its heavier analogues]]. Methane and other perfectly symmetrical tetrahedral molecules belong to [[point group]] T<sub>d</sub>, but most tetrahedral molecules have [[Tetrahedron#Isometries of irregular tetrahedra|lower symmetry]]. Tetrahedral molecules can be [[Chirality (chemistry)|chiral]]. |
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== Examples == |
== Examples == |
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===Main group chemistry=== |
===Main group chemistry=== |
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[[Image:Ch4-structure.png|thumb|right|200px|The tetrahedral molecule methane ( |
[[Image:Ch4-structure.png|thumb|right|200px|The tetrahedral molecule methane ({{chem2|CH4}})]] |
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Aside from 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]] (XeO<sub>4</sub>), the [[perchlorate]] ion ({{ |
Aside from 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]] (XeO<sub>4</sub>), the [[perchlorate]] ion ({{chem2|ClO4-}}), the [[sulfate]] ion ({{chem2|SO4(2-)}}), the [[phosphate]] ion ({{chem2|PO4(3-)}}). [[Thiazyl trifluoride]] ({{chem2|SNF3}}) is tetrahedral, featuring a sulfur-to-nitrogen triple bond.<ref>{{cite book | first1 = G. L. | last1 = Miessler | first2 = D. A. | last2 = Tarr | title = Inorganic Chemistry | edition = 3rd | publisher = Pearson/Prentice Hall | isbn = 0-13-035471-6 | url-access = registration | url = https://archive.org/details/inorganicchemist03edmies }}</ref> |
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Other molecules have a tetrahedral arrangement of electron pairs around a central atom; for example [[ammonia]] ( |
Other molecules have a tetrahedral arrangement of electron pairs around a central atom; for example [[ammonia]] ({{chem2|NH3}}) with the nitrogen atom surrounded by three hydrogens and one [[lone pair]]. However the usual classification considers only the bonded atoms and not the lone pair, so that ammonia is actually considered as [[Trigonal pyramidal molecular geometry|pyramidal]]. The H–N–H angles are 107°, contracted from 109.5°. This difference is attributed to the influence of the lone pair which exerts a greater repulsive influence than a bonded atom. |
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===Transition metal chemistry=== |
===Transition metal chemistry=== |
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[[File:Tetrahedral angle calculation.svg|thumb|230px|Calculating bond angles of a symmetrical tetrahedral molecule using a [[dot product]] ]] |
[[File:Tetrahedral angle calculation.svg|thumb|230px|Calculating bond angles of a symmetrical tetrahedral molecule using a [[dot product]] ]] |
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Again the geometry is widespread, particularly so for complexes where the metal has d<sup>0</sup> or d<sup>10</sup> configuration. Illustrative examples include [[tetrakis(triphenylphosphine)palladium(0)]] (Pd[P( |
Again the geometry is widespread, particularly so for complexes where the metal has d<sup>0</sup> or d<sup>10</sup> configuration. Illustrative examples include [[tetrakis(triphenylphosphine)palladium(0)]] ({{chem2|Pd[P(C6H5)3]4}}), [[nickel carbonyl]] ({{chem2|Ni(CO)4}}), and [[titanium tetrachloride]] ({{chem2|TiCl4}}). Many complexes with incompletely filled d-shells are often tetrahedral, e.g. the tetrahalides of iron(II), cobalt(II), and nickel(II). |
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===Water structure=== |
===Water structure=== |
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In the gas phase, a single water molecule has an oxygen atom surrounded by two hydrogens and two lone pairs, and the |
In the gas phase, a single water molecule has an oxygen atom surrounded by two hydrogens and two lone pairs, and the {{chem2|H2O}} geometry is simply described as [[Bent molecular geometry|bent]] without considering the nonbonded lone pairs. |
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However in liquid water or in ice, the lone pairs form [[hydrogen bond]]s with neighboring water molecules. The most common arrangement of hydrogen atoms around an oxygen is tetrahedral with two hydrogen atoms covalently bonded to oxygen and two attached by hydrogen bonds. Since the hydrogen bonds vary in length many of these water molecules are not symmetrical and form transient irregular tetrahedra between their four associated hydrogen atoms.<ref>{{cite journal | title = "Tetrahedrality" and the Relationship between Collective Structure and Radial Distribution Functions in Liquid Water | first1 = P. E. | last1 = Mason | first2 = J. W. | last2 = Brady | journal = [[J. Phys. Chem. B]] | year = 2007 | volume = 111 | pages = 5669–5679 | doi = 10.1021/jp068581n | issue = 20}}</ref> |
However in liquid water or in ice, the lone pairs form [[hydrogen bond]]s with neighboring water molecules. The most common arrangement of hydrogen atoms around an oxygen is tetrahedral with two hydrogen atoms covalently bonded to oxygen and two attached by hydrogen bonds. Since the hydrogen bonds vary in length many of these water molecules are not symmetrical and form transient irregular tetrahedra between their four associated hydrogen atoms.<ref>{{cite journal | title = "Tetrahedrality" and the Relationship between Collective Structure and Radial Distribution Functions in Liquid Water | first1 = P. E. | last1 = Mason | first2 = J. W. | last2 = Brady | journal = [[J. Phys. Chem. B]] | year = 2007 | volume = 111 | pages = 5669–5679 | doi = 10.1021/jp068581n | issue = 20}}</ref> |
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==Bitetrahedral structures== |
==Bitetrahedral structures== |
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Many compounds and complexes adopt bitetrahedral structures. In this motif, the two tetrahedra share a common edge. The inorganic polymer [[silicon disulfide]] features an infinite chain of edge-shared tetrahedra. |
Many compounds and complexes adopt bitetrahedral structures. In this motif, the two tetrahedra share a common edge. The inorganic polymer [[silicon disulfide]] features an infinite chain of edge-shared tetrahedra. |
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[[File:Gallium-trichloride-from-xtal-2004-3D-balls.png|thumb|220 px|left|Bitetrahedral structure adopted by |
[[File:Gallium-trichloride-from-xtal-2004-3D-balls.png|thumb|220 px|left|Bitetrahedral structure adopted by {{chem2|Al2Br6}} ("[[aluminium tribromide]]") and {{chem2|Ga2Cl6}} ("[[gallium trichloride]]").]] |
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==Exceptions and distortions== |
==Exceptions and distortions== |
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Inversion of tetrahedral occurs widely in organic and main group chemistry. The so-called [[Walden inversion]] illustrates the stereochemical consequences of inversion at carbon. [[Nitrogen inversion]] in ammonia also entails transient formation of planar |
Inversion of tetrahedral occurs widely in organic and main group chemistry. The so-called [[Walden inversion]] illustrates the stereochemical consequences of inversion at carbon. [[Nitrogen inversion]] in ammonia also entails transient formation of planar {{chem2|NH3}}. |
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===Inverted tetrahedral geometry=== |
===Inverted tetrahedral geometry=== |
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===Tetrahedral molecules with no central atom=== |
===Tetrahedral molecules with no central atom=== |
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A few molecules have a tetrahedral geometry with no central atom. An inorganic example is [[Allotropes of phosphorus#White phosphorus|tetraphosphorus]] ( |
A few molecules have a tetrahedral geometry with no central atom. An inorganic example is [[Allotropes of phosphorus#White phosphorus|tetraphosphorus]] ({{chem2|P4}}) which has four phosphorus atoms at the vertices of a tetrahedron and each bonded to the other three. An organic example is [[tetrahedrane]] ({{chem2|C4H4}}) with four carbon atoms each bonded to one hydrogen and the other three carbons. In this case the theoretical C−C−C bond angle is just 60° (in practice the angle will be larger due to [[bent bonds]]), representing a large degree of strain. |
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== See also == |
== See also == |
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Revision as of 03:38, 10 January 2020
| Tetrahedral molecular geometry | |
|---|---|
 | |
| Examples | CH4, MnO− 4 |
| Point group | Td |
| Coordination number | 4 |
| Bond angle(s) | ≈109.5° |
| μ (Polarity) | 0 |
In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−1⁄3) = 109.4712206...° ≈ 109.5° when all four substituents are the same, as in methane (CH4)[1][2] as well as its heavier analogues. Methane and other perfectly symmetrical tetrahedral molecules belong to point group Td, but most tetrahedral molecules have lower symmetry. Tetrahedral molecules can be chiral.
Examples
Main group chemistry
Aside from 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 perchlorate ion (ClO−4), the sulfate ion (SO2−4), the phosphate ion (PO3−4). Thiazyl trifluoride (SNF3) is tetrahedral, featuring a sulfur-to-nitrogen triple bond.[3]
Other molecules have a tetrahedral arrangement of electron pairs around a central atom; for example ammonia (NH3) with the nitrogen atom surrounded by three hydrogens and one lone pair. However the usual classification considers only the bonded atoms and not the lone pair, so that ammonia is actually considered as pyramidal. The H–N–H angles are 107°, contracted from 109.5°. This difference is attributed to the influence of the lone pair which exerts a greater repulsive influence than a bonded atom.
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) (Pd[P(C6H5)3]4), nickel carbonyl (Ni(CO)4), and titanium tetrachloride (TiCl4). Many complexes with incompletely filled d-shells are often tetrahedral, e.g. the tetrahalides of iron(II), cobalt(II), and nickel(II).
Water structure
In the gas phase, a single water molecule has an oxygen atom surrounded by two hydrogens and two lone pairs, and the H2O geometry is simply described as bent without considering the nonbonded lone pairs.
However in liquid water or in ice, the lone pairs form hydrogen bonds with neighboring water molecules. The most common arrangement of hydrogen atoms around an oxygen is tetrahedral with two hydrogen atoms covalently bonded to oxygen and two attached by hydrogen bonds. Since the hydrogen bonds vary in length many of these water molecules are not symmetrical and form transient irregular tetrahedra between their four associated hydrogen atoms.[4]
Bitetrahedral structures
Many compounds and complexes adopt bitetrahedral structures. In this motif, the two tetrahedra share a common edge. The inorganic polymer silicon disulfide features an infinite chain of edge-shared tetrahedra.
Exceptions and distortions
Inversion of tetrahedral occurs widely in organic and main group chemistry. The so-called Walden inversion illustrates the stereochemical consequences of inversion at carbon. Nitrogen inversion in 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" tetrahedral geometry at a carbon atom, all four groups attached to this carbon are on one side of a plane.[5] The carbon atom lies at or near the apex of a square pyramid with the other four groups at the corners.[6][7]
The simplest examples of organic molecules displaying inverted tetrahedral geometry are the smallest propellanes, such as [1.1.1]propellane; or more generally the paddlanes,[8] and pyramidane ([3.3.3.3]fenestrane).[6][7] Such molecules are typically strained, resulting in increased reactivity.
Planarization
A tetrahedron can also be distorted by increasing the angle between two of the bonds. In the extreme case, flattening results. For carbon this phenomenon can be observed in a class of compounds called the fenestranes.[citation needed]
Tetrahedral molecules with no central atom
A few molecules have a tetrahedral geometry with no central atom. An inorganic example is tetraphosphorus (P4) which has four phosphorus atoms at the vertices of a tetrahedron and each bonded to the other three. An organic example is tetrahedrane (C4H4) with four carbon atoms each bonded to one hydrogen and the other three carbons. In this case the theoretical C−C−C bond angle is just 60° (in practice the angle will be larger due to bent bonds), representing a large degree of strain.
See also
References
- ^ "Angle Between 2 Legs of a Tetrahedron". Maze5.net.
- ^ Brittin, W. E. (1945). "Valence Angle of the Tetrahedral Carbon Atom". J. Chem. Educ. 22 (3): 145. Bibcode:1945JChEd..22..145B. doi:10.1021/ed022p145.
- ^ Miessler, G. L.; Tarr, D. A. Inorganic Chemistry (3rd ed.). Pearson/Prentice Hall. ISBN 0-13-035471-6.
- ^ Mason, P. E.; Brady, J. W. (2007). ""Tetrahedrality" and the Relationship between Collective Structure and Radial Distribution Functions in Liquid Water". J. Phys. Chem. B. 111 (20): 5669–5679. doi:10.1021/jp068581n.
- ^ Wiberg, Kenneth B. (1984). "Inverted geometries at carbon". Acc. Chem. Res. 17 (11): 379–386. doi:10.1021/ar00107a001.
- ^ a b Joseph P. Kenny; Karl M. Krueger; Jonathan C. Rienstra-Kiracofe; Henry F. Schaefer III (2001). "C5H4: Pyramidane and Its Low-Lying Isomers". J. Phys. Chem. A. 105 (32): 7745–7750. Bibcode:2001JPCA..105.7745K. doi:10.1021/jp011642r.
- ^ a b Lewars, E. (1998). "Pyramidane: an ab initio study of the C5H4 potential energy surface". Journal of Molecular Structure: THEOCHEM. 423 (3): 173–188. doi:10.1016/S0166-1280(97)00118-8.
- ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "paddlanes". doi:10.1351/goldbook.P04395
External links
- Examples of Tetrahedral molecules
- Animated Tetrahedral Visual
- Elmhurst College
- Interactive molecular examples for point groups
- 3D Chem – Chemistry, Structures, and 3D Molecules
- IUMSC – Indiana University Molecular Structure Center]
- [1]
- Molecular Modeling
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| Coordination number 9 | |
