02251nas a2200241   4500008004100000245010400041210006900145260000800214300001400222490000700236520143100243100002401674700002601698700001601724700002501740700002201765700001801787700002201805700001801827700001801845700002201863856012401885       2017                        eng d00aSpectroscopic and reactivity comparisons of a pair of bTAML complexes with Fe-V=O and Fe-IV=O units0 aSpectroscopic and reactivity comparisons of a pair of bTAML comp  cJUN  a6352-63610 v563 aIn this report we compare the geometric and electronic structures and reactivities of [Fe-V(O)](-) and [Fe-IV(O)](2-) species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the Fe-O vibration of the [Fe-IV(O)](2-) complex 2 is at 798 cm(-1), compared to 862 cm(-1) for the corresponding [Fe-V(O)](-) species 3, a 64 cm(-1) frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe-O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe-O bond length of 1.59 angstrom, which is 0.05 angstrom shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [Fe-IV(O)](2-)/[Fe-III(OH)](2-) and [Fe-V(O)](-)/[Fe-IV(O)](2-) couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.1 aPattanayak, Santanu1 aJasniewsk, Andrew, J.1 aRana, Atanu1 aDraksharapu, Apparao1 aSingh, Kundan, K.1 aWeitz, Andrew1 aHendrich, Michael1 aQue, Lawrence1 aDey, Abhishek1 aGupta, Sayam, Sen  uhttps://library.ncl.res.in/content/spectroscopic-and-reactivity-comparisons-pair-btaml-complexes-fe-vo-and-fe-ivo-units