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Although metalloenzymes possessing metal\u2010oxo units at their active site are typically associated with outer\u2010sphere electron transfer (OSET) processes, biomimetic models, in contrast, have been found to manifest either an inner\u2010sphere electron transfer (ISET) or OSET mechanism. This distinction is clearly illustrated through the behaviour of [(N4Py)Mn<jats:sup>IV<\/jats:sup>(O)]<jats:sup>2+<\/jats:sup> (<jats:bold>1<\/jats:bold>) and [(N4Py)Fe<jats:sup>IV<\/jats:sup>(O)]<jats:sup>2+<\/jats:sup> (<jats:bold>2<\/jats:bold>) complexes, where complex <jats:bold>1<\/jats:bold> showcases an OSET mechanism, while complex <jats:bold>2<\/jats:bold> exhibits an ISET mechanism, especially evident in their reactions involving C\u2212H bond activation and oxygen atom transfer reactions in the presence of a Lewis\/Bronsted acid. However, the precise reason for this puzzling difference remains elusive. This work unveils the origin of the perplexing inner\u2010sphere vs outer\u2010sphere electron transfer process (ISET vs OSET) in [(N4Py)Mn<jats:sup>IV<\/jats:sup>(O)]<jats:sup>2+<\/jats:sup> (<jats:bold>1<\/jats:bold>) and [(N4Py)Fe<jats:sup>IV<\/jats:sup>(O)]<jats:sup>2+<\/jats:sup> (<jats:bold>2<\/jats:bold>) species in the presence of Bronsted acid. The calculations indicate that when the substrate (toluene) approaches both <jats:bold>1<\/jats:bold> and <jats:bold>2<\/jats:bold> that is hydrogen bonded with two HOTf molecules (denoted as <jats:bold>1\u2010HOTf<\/jats:bold> and <jats:bold>2\u2010HOTf<\/jats:bold>, respectively), proton transfer from one of the HOTf molecules to the metal\u2010oxo unit is triggered and a simultaneous electron transfer occurs from toluene to the metal centre. Interestingly, the preference for OSET by <jats:bold>1\u2010HOTf<\/jats:bold> is found to originate from the choice of Mn<jats:sup>IV<\/jats:sup>=O centre to abstract spin\u2010down (\u03b2) electron from toluene to its \u03b4(d<jats:sub>xy<\/jats:sub>) orbital. On the other hand, in <jats:bold>2\u2010HOTf<\/jats:bold>, a spin state inversion from triplet to quintet state takes place during the proton (from HOTf) coupled electron transfer (from toluene) preferring a spin\u2010up (\u03b1) electron abstraction to its \u03c3<jats:sup>*<\/jats:sup>(d<jats:sub>z<\/jats:sub><jats:sup>2<\/jats:sup>) orbital mediated by HOTf giving rise to ISET. In addition, <jats:bold>2\u2010HOTf<\/jats:bold> was calculated to possess a larger reorganisation energy, which facilitates the ISET process via the acid. The absence of spin\u2010inversion and smaller reorganisation energy switch the mechanism to OSET for <jats:bold>1\u2010HOTf<\/jats:bold>. Therefore, for the first time, the significance of spin\u2010state and spin\u2010inversion in the electron transfer process has been identified and demonstrated within the realm of high\u2010valent metal\u2010oxo chemistry. This discovery holds implications for the potential involvement of high\u2010valent Mn\u2010oxo species in performing similar transformative processes within Photosystem II.<\/jats:p>","DOI":"10.1002\/asia.202300773","type":"journal-article","created":{"date-parts":[[2023,10,19]],"date-time":"2023-10-19T07:29:07Z","timestamp":1697700547000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Unravelling the Effect of Acid\u2010Driven Electron Transfer in High\u2010Valent Fe<sup>IV<\/sup>=O\/Mn<sup>IV<\/sup>=O Species and Its Implications for Reactivity"],"prefix":"10.1002","volume":"18","author":[{"given":"Neethinathan Johnee","family":"Britto","sequence":"first","affiliation":[{"name":"Department of Chemistry Indian Institute of Technology Bombay, Powai  Mumbai 400 076 India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Asmita","family":"Sen","sequence":"additional","affiliation":[{"name":"Department of Chemistry Indian Institute of Technology Bombay, Powai  Mumbai 400 076 India"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6133-3026","authenticated-orcid":false,"given":"Gopalan","family":"Rajaraman","sequence":"additional","affiliation":[{"name":"Department of Chemistry Indian Institute of Technology Bombay, Powai  Mumbai 400 076 India"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2023,11,6]]},"reference":[{"key":"e_1_2_8_1_1","unstructured":"\u00a0"},{"key":"e_1_2_8_2_2","doi-asserted-by":"crossref","first-page":"13","DOI":"10.1021\/acscentsci.8b00698","volume":"5","author":"Guo M.","year":"2018","journal-title":"ACS Cent. 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