Does oxidation state have a definition?
Professor Pavel Karen at our department has led a IUPAC work group that has worked with this question.
In 2009, IUPAC established a task group to find out whether oxidation state can be defined with anything else than just algorithms how to calculate it.
The work of group led by Pavel Karen included analysis of the present use of oxidation state and evaluations of its value on about 100 example cases.
In an iterative circle, three subsequently feasible definitions emerged as the case solutions worked out by the chairman were commented by group members.
The results of this research have been published in the IUPAC Technical Report http://dx.doi.org/10.1515/pac-2013-0505 which concludes:
Oxidation state is an atom’s charge after ionic approximation of its bonds; the atom that reversibly contributes more to a molecular orbital keeps that orbital’s electrons while bonds between atoms of the same element are divided equally.
Based on bonding rather than mere composition, such a definition yields oxidation-state values also in networks of crystalline solids or in clusters.
As for the latter, a bistable oxidation state of a single suitable atom in a cluster embedded in a conductive network might represent the information-storage unit in flash memory devices of the future.