Editing VSEPR theory (section)

===Complexes with strong d-contribution===
[[File:Hexamethyl-tungsten-3D-balls.png|200px|thumb|[[Hexamethyltungsten]], a transition metal complex whose geometry is different from main-group coordination]]
Some transition metal complexes with low d electron count have unusual geometries, which can be ascribed to d subshell bonding interaction.<ref name="d0kaupp">{{cite journal | title = "Non-VSEPR" Structures and Bonding in d<sup>0</sup> Systems | first = Martin | last = Kaupp | journal = [[Angewandte Chemie|Angew. Chem. Int. Ed. Engl.]] | year = 2001 | volume = 40 | issue = 1 | pages = 3534–3565 | doi =  10.1002/1521-3773(20011001)40:19<3534::AID-ANIE3534>3.0.CO;2-#| pmid = 11592184 | url = http://www.chimdocet-inorganica.it/SITO_ESERCIZI/Complementi/COMP1/VSEPREccezioni.pdf}}</ref> [[Ronald Gillespie|Gillespie]] found that this interaction produces bonding pairs that also occupy the respective [[antipodal point]]s (ligand opposed) of the sphere.<ref>{{cite journal | title = An Electron Localization Function Study of the Geometry of d<sup>0</sup> Molecules of the Period 4 Metals Ca to Mn | first1 = Ronald J. | last1 = Gillespie | first2 =  Stéphane | last2 =  Noury | first3 = Julien | last3 = Pilmé | first4 =  Bernard | last4 =  Silvi | journal = [[Inorganic Chemistry (journal)|Inorg. Chem.]] | year = 2004 | volume = 43 | issue = 10 | pages = 3248–3256 | doi =  10.1021/ic0354015| pmid = 15132634 }}</ref><ref name="Fiftyyears"/> This phenomenon is an electronic effect resulting from the bilobed shape of the underlying sd<sup>x</sup> [[hybridization (chemistry)|hybrid orbitals]].<ref>{{cite journal | last1 = Landis | first1 = C. R. | last2 = Cleveland | first2 = T. | last3 = Firman | first3 = T. K. | year = 1995 | title = Making sense of the shapes of simple metal hydrides | journal = [[J. Am. Chem. Soc.]] | volume = 117 | issue = 6| pages = 1859–1860 | doi=10.1021/ja00111a036| bibcode = 1995JAChS.117.1859L }}</ref><ref>{{cite journal | last1 = Landis | first1 = C. R. | last2 = Cleveland | first2 = T. | last3 = Firman | first3 = T. K. | year = 1996 | title = Structure of W(CH<sub>3</sub>)<sub>6</sub> | journal = [[Science (journal)|Science]] | volume = 272 | issue = 5259| pages = 179–183 |doi=10.1126/science.272.5259.179f| doi-access = free }}</ref> The repulsion of these bonding pairs leads to a different set of shapes.

{| class="wikitable" style="margin:1em auto;"
|- 
! Molecule type
! Shape
! Geometry
! Examples
|- 
! ML<sub>2</sub>
| [[Bent molecular geometry|Bent]]
| [[File:Bent-3D-balls.png|100px]]
| [[Titanium dioxide|TiO<sub>2</sub>]]<ref name="d0kaupp"/>
|- 
! ML<sub>3</sub>
| [[Trigonal pyramidal molecular geometry|Trigonal pyramidal]]
| [[File:Pyramidal-3D-balls.png|100px]]
| [[Chromium trioxide|CrO<sub>3</sub>]]<ref name=cdoi>{{Cite journal | doi = 10.1021/ja077984d| title = Probing the Electronic and Structural Properties of Chromium Oxide Clusters {{chem|(CrO|3|)|''n''|-}} and (CrO<sub>3</sub>)<sub>''n''</sub> (''n''&nbsp;= 1–5): Photoelectron Spectroscopy and Density Functional Calculations| journal = Journal of the American Chemical Society| volume = 130| issue = 15| pages = 5167–77| year = 2008| last1 = Zhai | first1 = H. J. | last2 = Li | first2 = S. | last3 = Dixon | first3 = D. A. | last4 = Wang | first4 = L. S. |pmid = 18327905}}</ref>
|-
! ML<sub>4</sub>
| [[Tetrahedral molecular geometry|Tetrahedral]]
| [[File:Tetrahedral-3D-balls.png|100px]]
| [[titanium tetrachloride|TiCl<sub>4</sub>]]<ref name=Housecroft/>{{rp|598–599}}
|- 
! ML<sub>5</sub>
| [[Square pyramidal molecular geometry|Square pyramidal]]
| [[File:Square-pyramidal-3D-balls.png|100px]]
| [[Pentamethyltantalum|Ta(CH<sub>3</sub>)<sub>5</sub>]]<ref>{{cite journal |journal= Coord. Chem. Rev. |volume= 197 |year= 2000 |pages= 141–168 |title= Atomic orbitals, symmetry, and coordination polyhedra |first= R. Bruce |last= King | doi = 10.1016/s0010-8545(99)00226-x }}</ref>
|- 
! ML<sub>6</sub>
| ''C<sub>3v</sub>'' [[Trigonal prismatic molecular geometry|Trigonal prismatic]]
| [[File:Prismatic_TrigonalP.png|100px]]
| [[Hexamethyltungsten|W(CH<sub>3</sub>)<sub>6</sub>]]<ref>{{cite journal|last1=Haalan |first1=A. |last2=Hammel |first2=A.|last3=Rydpal |first3=K. |last4=Volden |first4=H. V.|journal=[[J. Am. Chem. Soc.]]|year=1990|volume=112|pages= 4547–4549|title=The coordination geometry of gaseous hexamethyltungsten is not octahedral|doi=10.1021/ja00167a065|issue=11|bibcode=1990JAChS.112.4547H }}</ref>
|}

The gas phase structures of the triatomic halides of the heavier members of [[alkaline earth metal|group 2]], (i.e., calcium, strontium and barium halides, MX<sub>2</sub>), are not linear as predicted but are bent, (approximate X–M–X angles: [[calcium fluoride|CaF<sub>2</sub>]], 145°; [[strontium fluoride|SrF<sub>2</sub>]], 120°; [[barium fluoride|BaF<sub>2</sub>]], 108°; [[strontium chloride|SrCl<sub>2</sub>]], 130°; [[barium chloride|BaCl<sub>2</sub>]], 115°; [[barium bromide|BaBr<sub>2</sub>]], 115°; [[barium iodide|BaI<sub>2</sub>]], 105°).<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref> It has been proposed by [[Ronald Gillespie|Gillespie]] that this is also caused by bonding interaction of the ligands with the d subshell of the metal atom, thus influencing the molecular geometry.<ref name = "Gillespie&Robinson"/><ref>{{cite journal | doi = 10.1063/1.459748 | title = Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX<sub>2</sub> (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I) | year = 1991 | author = Seijo, Luis | journal = [[J. Chem. Phys.]] | volume = 94 | pages = 3762 | last2 = Barandiarán | first2 = Zoila | last3 = Huzinaga | first3 = Sigeru | issue = 5| bibcode = 1991JChPh..94.3762S | url = https://repositorio.uam.es/bitstream/10486/7315/1/41581_jchemphysseijo_91_jcp_94_3762.pdf | hdl = 10486/7315 | hdl-access = free }}</ref>