Editing Coordination complex (section)

===Color of transition metal complexes===
Transition metal complexes often have spectacular colors caused by electronic transitions by the absorption of light. For this reason they are often applied as [[Pigment#Physical basis|pigments]]. Most transitions that are related to colored metal complexes are either d–d transitions or [[charge transfer band]]s.  In a d–d transition, an electron in a d&nbsp;orbital on the metal is excited by a photon to another d orbital of higher energy, therefore d–d transitions occur only for partially-filled d-orbital complexes (d<sup>1–9</sup>). For complexes having d<sup>0</sup> or d<sup>10</sup> configuration, charge transfer is still possible even though d–d transitions are not. A charge transfer band entails promotion of an electron from a metal-based orbital into an empty ligand-based orbital ([[Charge transfer complex|metal-to-ligand charge transfer]] or MLCT).  The converse also occurs: excitation of an electron in a ligand-based orbital into an empty metal-based orbital ([[Charge transfer complex|ligand-to-metal charge transfer]] or LMCT). These phenomena can be observed with the aid of electronic spectroscopy; also known as [[UV-Vis]].<ref>{{cite book |last1= Harris |first1= D. |last2= Bertolucci |first2= M. |title= Symmetry and Spectroscopy |year= 1989 |publisher= Dover Publications | isbn= 9780486661445 }}</ref> For simple compounds with high symmetry, the d–d transitions can be assigned using [[Tanabe–Sugano diagram]]s.  These assignments are gaining increased support with [[computational chemistry]].

{| class="wikitable"
|+ Colours of Various Example Coordination Complexes
|-
! &nbsp;
! Fe<sup>2+</sup>
! Fe<sup>3+</sup>
! Co<sup>2+</sup>
! Cu<sup>2+</sup>
! Al<sup>3+</sup>
! Cr<sup>3+</sup>
|-
! [[Metal ions in aqueous solution|Hydrated Ion]]
| style="background: #CBE9AD;" | {{tooltip|2=Hexaaquairon(2+) cation|[Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>|dotted=no}}     <br/>Pale green<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #EAD558;" | {{tooltip|2=Hexaaquairon(3+) cation|[Fe(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup>|dotted=no}}    <br/>Yellow/brown<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #FF99CB;" | {{tooltip|2=Hexaaquacobalt(2+) cation|[Co(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>|dotted=no}}<br/>Pink<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #C7D9F1;" | {{tooltip|2=Hexaaquacopper(2+) cation|[Cu(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup>|dotted=no}}<br/>Blue<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #F2F2F2;" | {{tooltip|2=Hexaaquaaluminium(3+) cation|[Al(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup>|dotted=no}}<br/>Colourless<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #D7E3BD;" | {{tooltip|2=Hexaaquachromium(3+) cation|[Cr(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup>|dotted=no}}<br/>Green<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
|-
! (OH)<sup>−</sup>, dilute
| style="background: #92D14F;" | {{tooltip|2=Tetraaquadihydroxidoiron|[Fe(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>2</sub>]|dotted=no}} <br/>Dark green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #9B752A;" | {{tooltip|2=Triaquatrihydroxidoiron|[Fe(H<sub>2</sub>O)<sub>3</sub>(OH)<sub>3</sub>]|dotted=no}}<br/>Brown<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #8AE5D6;" | {{tooltip|2=Tetraaquadihydroxidocobalt|[Co(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>2</sub>]|dotted=no}}<br/>Blue/green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #8EB2E2;" | {{tooltip|2=Tetraaquadihydroxidocopper|[Cu(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>2</sub>]|dotted=no}}<br/>Blue<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #FFFFFF;" | {{tooltip|2=Triaquatrihydroxidoaluminium|[Al(H<sub>2</sub>O)<sub>3</sub>(OH)<sub>3</sub>]|dotted=no}}<br/>White<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #76923D;" | {{tooltip|2=Triaquatrihydroxidochromium|[Cr(H<sub>2</sub>O)<sub>3</sub>(OH)<sub>3</sub>]|dotted=no}}<br/>Green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
|-
! (OH)<sup>−</sup>, concentrated
| style="background: #92D14F;" | {{tooltip|2=Tetraaquadihydroxidoiron|[Fe(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>2</sub>]|dotted=no}} <br/>Dark green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #9B752A;" | {{tooltip|2=Triaquatrihydroxidoiron|[Fe(H<sub>2</sub>O)<sub>3</sub>(OH)<sub>3</sub>]|dotted=no}}<br/>Brown<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #8AE5D6;" | {{tooltip|2=Tetraaquadihydroxidocobalt|[Co(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>2</sub>]|dotted=no}}<br/>Blue/green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #8EB2E2;" | {{tooltip|2=Tetraaquadihydroxidocopper|[Cu(H<sub>2</sub>O)<sub>4</sub>(OH)<sub>2</sub>]|dotted=no}}<br/>Blue<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #FFFFFF;" | {{tooltip|2=Tetrahydroxidoaluminium|[Al(OH)<sub>4</sub>]<sup>−</sup>|dotted=no}}<br/>Colourless<br/>Solution
| style="background: #C3D59B;" | {{tooltip|2=Hexahydroxidochromate(3−) anion|[Cr(OH)<sub>6</sub>]<sup>3−</sup>|dotted=no}}<br/>Green<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
|-
! NH<sub>3</sub>, dilute
| style="background: #92D14F;" | {{tooltip|2=Hexaammineiron|[Fe(NH<sub>3</sub>)<sub>6</sub>]<sup>2+</sup>|dotted=no}}<br/>Dark green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #9B752A;" | {{tooltip|2=Hexaammineiron|[Fe(NH<sub>3</sub>)<sub>6</sub>]<sup>3+</sup>|dotted=no}}<br/>Brown<br/> {{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #D3D359;" | {{tooltip|2=Hexaamminecobalt(2+) cation|[Co(NH<sub>3</sub>)<sub>6</sub>]<sup>2+</sup>|dotted=no}}<br/>Straw coloured<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #548DD4;" | {{tooltip|2=Tetraamminediaquacopper(2+) cation|[Cu(NH<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup>|dotted=no}}<br/>Deep blue<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #FFFFFF;" | {{tooltip|2=Triamminealuminium|[Al(NH<sub>3</sub>)<sub>3</sub>]<sup>3+</sup>|dotted=no}}<br/>White<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #CC0099;" | {{tooltip|2=hexaamminechromium(3+) cation|[Cr(NH<sub>3</sub>)<sub>6</sub>]<sup>3+</sup>|dotted=no}}<br/>Purple<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
|-
! NH<sub>3</sub>, concentrated
| style="background: #92D14F;" | {{tooltip|2=Hexaammineiron|[Fe(NH<sub>3</sub>)<sub>6</sub>]<sup>2+</sup>|dotted=no}}<br/>Dark green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #9B752A;" | {{tooltip|2=Hexaammineiron|[Fe(NH<sub>3</sub>)<sub>6</sub>]<sup>3+</sup>|dotted=no}}<br/>Brown<br/> {{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #D3D359;" | {{tooltip|2=Hexaamminecobalt(2+) cation|[Co(NH<sub>3</sub>)<sub>6</sub>]<sup>2+</sup>|dotted=no}}<br/>Straw coloured<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #548DD4;" | {{tooltip|2=Tetraamminediaquacopper(2+) cation|[Cu(NH<sub>3</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>2+</sup>|dotted=no}}<br/>Deep blue<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
| style="background: #FFFFFF;" | {{tooltip|2=Triamminealuminium|[Al(NH<sub>3</sub>)<sub>3</sub>]<sup>3+</sup>|dotted=no}}<br/>White<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #CC0099;" | {{tooltip|2=hexaamminechromium(3+) cation|[Cr(NH<sub>3</sub>)<sub>6</sub>]<sup>3+</sup>|dotted=no}}<br/>Purple<br/>{{tooltip|2=Suspended in solution|Solution|dotted=no}}
|-
! (CO<sub>3</sub>)<sup>2-</sup>
| style="background: #92D14F;" | {{tooltip|2=Iron(II) carbonate|FeCO<sub>3</sub>|dotted=no}}<br/>Dark green<br                            />{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
| style="background: #9B752A;" | {{tooltip|2=Iron(III) carbonate|Fe<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>|dotted=no}}<br/>Brown<br                            />{{tooltip|2=Precipitates from solution|Precipitate+bubbles|dotted=no}}
| style="background: #FF99CB;"| {{tooltip|2=Cobalt(II) carbonate|CoCO<sub>3</sub>|dotted=no}}<br/>Pink<br/>{{tooltip|2=Precipitates from solution with an effervescence of Carbon Dioxide|Precipitate|dotted=no}}
| style="background: #8AE5D6;" | {{tooltip|2=Copper(II) carbonate|CuCO<sub>3</sub>|dotted=no}}<br/>Blue/green<br/>{{tooltip|2=Precipitates from solution|Precipitate|dotted=no}}
|}