Bromine oxidation of a nickel(II) bis(oxime-imine) complex. Evidence for a single-step outer-sphere two-electron transfer

Journal Article · Wed Sep 23 04:00:00 EDT 1987 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00266a007· OSTI ID:5796756

Lappin, A G; Osvath, P; Baral, S

The kinetics and mechanism of the two-electron oxidation of the sexidentate bis(oxime-imine) complex of nickel(II), (Ni/sup II/L) (I), by bromine have been investigated in bromide ion media over the pH range 3.1-7.6 at 25/sup 0/C and 1.0 M ionic strength. In the presence of an excess of bromine or nickel(II), oxidation is monophasic, and the initial product is (Ni/sup IV/L)/sup 2 +/, a formal nickel(IV) species that undergoes subsequent reactions to give an unknown oxidation product with excess bromine at pH > 6 or to give (Ni/sup III/L)/sup +/ by comproportionation with excess nickel(II) at pH > 5. The sole kinetically important oxidant is Br/sub 2/, and second-order rate constants for reaction of (Ni/sup II/L) and its protonated form (Ni/sup II/LH)/sup +/ are 2.1 x 10/sup 7/ and 7.1 x 10/sup 5/ M/sup -1/ s/sup -1/, respectively. These rate constants are in line with a rate-determining single-electron-transfer reaction, and the proposed mechanism involves formation of a transient ion pair (Ni/sup III/L/sup +/,Br/sub 2//sup -/ in which the rate of subsequent electron transfer is comparable with the rate of ion-pair dissociation. In addition, the pulse-radiolysis technique has been used to investigate the reactions of nickel(II) with Br/sub 2//sup -/ to give (Ni/sup III/L)/sup +/, and rate constants for (Ni/sup II/L) and (Ni/sup II/LH)/sup +/ are 8.5 x 10/sup 8/ and 2.7 x 10/sup 8/ M/sup -1/ S/sup -1/, respectively, at 21/sup 0/C. 34 references, 3 figures, 3 tables.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 5796756
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 26:19; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
AMINES
BROMINE
CHEMICAL REACTIONS
COMPLEXES
DATA
ELEMENTS
EXPERIMENTAL DATA
HALOGENS
HYDROXY COMPOUNDS
IMINES
INFORMATION
NICKEL COMPLEXES
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
OXIMES
TRANSITION ELEMENT COMPLEXES