Robert J. Balahura

Reactions and X-ray crystal structure of (3-cyano-2,4-pentanedionato-N)pentaamminecobalt(III) perchlorate chloride dihydrate

Abstract The pentaamminecobalt(III) complex with the 3-cyano-2,4-pentanedionate anion coordinated through the nitrile nitrogen has been characterized by X-ray crystallography. The crystals of [(NH3)5CoNCacac](Cl)(ClO4)·2H2O are triclinic, space group P 1 , a = 10.245(2) A, b = 14.071(4) A, c = 6.971(2) A, α = 90.03(3)°, β = 109.86(2)°, γ = 108.91(2)°, V = 887.1 A3, Z = 2, Dc = 1.64 g cm−3, F(000) = 456, Mo-Kα radiation, λ = 0.71069 A, μ(Mo-Kα) = 12.7 cm−1. The structure was determined by the heavy-atom method, and refined by block-diagonal least-squares calculations, R = 0.0537, Rw = 0.0607, for 2499 observed reflections. Principal dimensions are: CoN(NH3) trans to NCacac− 1.940(5), other CoN(NH3) 1.967(2), CoN(NCacac−) 1.911(5) A. The pendant acac moiety is best described in terms of a delocalized bond network with, for example, CC distances in the range 1.44–1.52(1) A. Several reactions involving this free acac group are also described including the preparation and characterization of the dimeric species pentaamminecobalt(III) - μ - (3 - cyano - 2,4 - pentanedionato) - bis(propylenediamine) cobalt(III) perchlorate.

Preparation, characterization, and chromium(II) reduction kinetics of tetrazole complexes of pentaamminecobalt(III)

Complexes de cyano-5-, methyl-5-, carbamoyl-5-tetrazole et de tetrazole non substitue. Cinetique et mecanisme de la reduction des complexes

Reduction of Coprinus macrorhizus peroxidase by dithionite

Abstract The reduction of Coprinus macrorhizus peroxidase (CMP) by dithionite (Fe(III) → Fe(II)) was studied. CMP reacts with the radical SO 2 − derived from the dithionite ion via saturation kinetics: k abs = a [S 2 O 4 2− ] 1/2 (1 + b [S 2 O 4 2− where a = (1.32 ± 0.06) × 10 3 M −1/2 s −1 and b = 9.16 ± 0.75 −1/2 . It is proposed that SO 2 binds initially to the protein in a non-redox step with an equilibrium constant K 2 = (2.5 ± 0.1 ) × 10 5 M −1 , followed by intramolecular electron transfer, with k = 144 ± 6 s −1 .

The reduction of pentaammine(phenanthroline-2-carboxamido-N)cobalt(III) by titanium(III) and vanadium(II)

Abstract Pentaammine(phenanthroline-2-carboxamido- N )cobalt(III) ( I ) reacts with Ti 3+ (aq.) in two separable steps. The first step involves rapid formation of a binuclear intermediate with Ti 3+ forming a chelate with the carboxamido oxygen and the adjacent ring nitrogen. The rate law is k obs = k 1 [Ti 3+ ]+ k r [H + ] where k 1 =240±10 and k r =6.7±0.4 M −1 s −1 at 25 °C and I =1.0 M (LiCl). The second reaction involves electron transfer and follows the rate law k obs = a [H + ] −1 [Ti 3+ ]+ b [H + ] −1 where a =0.0046±0.0005 s −1 and b =(1.3±0.1)x10 −4 M −1 s −1 . The first term in the rate law of the second step is assigned to outer-sphere reduction by Ti(OH) 2+ of the binuclear precursor formed in the first reaction. The second term involves intramolecular electron transfer within the conjugate base of the binuclear precursor with k et , estimated as 0.13 s −1 . The factors affecting intramolecular electron transfer within Co(III)- and Ru(III)-Ti(III) intermediates are discussed. The reaction of I with V 2+ (aq.) also occurs in two distinct reactions. The first reaction follows the same rate law as the analogous Ti 3+ reaction with k 1 =2010±100 and k r =600±50 M −1 s −1 at 25 °C, I =1.0 M (LiClO 4 ). The second reaction is first-order in [V 2+ ] and independent of [H + ] with a second-order rate constant of 0.36 ±0.02 M t1 s −1 . The latter redox reaction is thought to involve outer-sphere reduction of the binuclear precursor formed in the first step.

The reduction of (1-(4-cyanophenyl)-3-hydroxy-2-buten-1-one-N)pentaamminecobalt(III) by chromium(II)

The reduction of the title compound,by chromium(II) is first order in Cr(II) and obeys the rate law kobsd = k1Ka′/(Ka′ + [H+]) at 25.0 °C and I = 1.0 mol L−1 (LiClO4) with k1 = (2.9 ± 0.1) × 104 L mol−1 s−1 and Ka′ = 0.86 ± 0.03 mol L−1. In the rate law, k1 refers to reduction of the 3+ ion above and the Ka′ is the acid dissociation constant for the protonated form of 1. The reduction occurs by a remote attack inner-sphere mechanism with complete transfer of the organic ligand to chromium.

Reactions of co-ordinated nucleophiles. Preparation, characterization, and crystal structure of penta-ammine(phenylthiocarbamato-S)cobalt-(III) perchlorate monohydrate

The title complex [Co(NH3)5(SCONHPh)][ClO4]2 has been prepared by the addition of [Co(NH3)5(OH2)]-[ ClO4]3 to phenyl isothiocyanate in dimethylformamide. A mechanism for formation of the complex is proposed whereby an O-bonded complex is initially formed and then isomerizes rapidly to the stable S-bonded species. The stable complex has been characterized by spectroscopic methods and by X-ray crystallography. Crystals are orthorhombic, space group Pnam, with eight molecules of the hydrate, [Co(NH3)5(SCONHC6H5)][ClO4]2·H2O, in a unit cell of dimensions a = 9.573(5), b= 11.300(5), and c= 37.40(2)A. The structure was refined by full-matrix least-squares calculations to a final R value of 0.096 for 660 ‘ observed ’ reflections. The Co atom is octahedrally co-ordinated [Co–N 1.98–2.02(3), Co–S 2.264(9)A]. An extensive network of hydrogen bonds links the cations, anions, and water molecules.

Double-bridging in inner-sphere electron transfer involving chelates; reduction of bis(pentane-2,4-dionato)ethylenediaminecobalt(III) by chromium(II)

The reduction of bis(pentane-2,4-dionato)ethyl-enediaminecobalt(III) by chromiun(II) occurs by an inner-sphere path involving both single bridged and double transition states in addition to the expected outer-sphere path.