Editing Oxidation state (section)

==== A physical measurement is needed to determine oxidation state ====
* when a [[non-innocent ligand|non-innocent]] [[ligand]] is present, of hidden or unexpected redox properties that could otherwise be assigned to the central atom. An example is the [[nickel]] [[metal dithiolene complex|dithiolate]] complex, {{chem|Ni(S|2|C|2|H|2|)|2|2−}}.<ref name="10.1515/pac-2013-0505" />{{rp|1056–1057}}
* when the redox ambiguity of a central atom and ligand yields dichotomous oxidation states of close stability, thermally induced [[tautomerism]] may result, as exemplified by [[manganese]] [[catecholate]], {{chem2|Mn(C6H4O2)3}}.<ref name="10.1515/pac-2013-0505" />{{rp|1057–1058}} Assignment of such oxidation states requires spectroscopic,<ref>{{cite book|first=C. K.|last=Jørgensen|contribution=Electric Polarizability, Innocent Ligands and Spectroscopic Oxidation States|title=Structure and Bonding|volume=1|pages=234–248|publisher=Springer-Verlag|location=Berlin|date=1966}}</ref> magnetic or structural data.
* when the bond order has to be ascertained along with an isolated tandem of a heteronuclear and a homonuclear bond. An example is [[thiosulfate]] {{chem|S|2|O|3|2−}} having two possible oxidation states (bond orders are in blue and formal charges in green):

::[[File:21oxstate.svg|frameless|500px]]

:The S–S distance measurement in [[thiosulfate]] is needed to reveal that this bond order is very close to 1, as in the formula on the left.