Pulse radiolysis nickel complexes

The Ni1 complexes may exist in different isomeric forms, and the form obtained may depend upon whether pulse radiolysis of electroreduction are employed to synthesize them.2323 Usually, isomeric integrity of tmc nickel complexes is not maintained upon going from Ni11 to Ni1 ... 

Nickel(II) complexes with the ligands (76b) and (76d) have been reduced in aqueous solution by solvated electrons with the aid of the pulse radiolysis technique.314 The decay kinetics and the behaviour of these complexes as bases and as reducing agents have also been studied. 

Pulse radiolysis is a very powerful technique which can be employed to form solutions of nickel(III) and nickel(IV) complexes. The complexes cannot generally be isolated in the solid state, but their properties can be directly investigated by several physicochemical techniques. 

Redox reactions involving the nickel(IV) complex are also subject to divalent metal ion catalysis (170, 171). Oxidations of the two-electron reductant ascorbate (40) and the one-electron reductant [Fe(CN)6]4-(172) have been examined in some detail. Both reactions have as the rate-determining step the transfer of one electron from the reductant to nickel(IV) in an outer-sphere process to give an undetected nickel(III) transient. Spectroscopic properties of the nickel(III) species have been determined by pulse radiolysis (41). 

There is an extensive chemistry of the nickel(I) ion generated by pulse radiolysis which is beyond the scope of this review. Complexes with saturated amines such as 1,2-diaminoethane have been studied by this method and by the y radiolysis of aqueous glasses, but the species formed have no more than a transient existence. The imine ligands phen and bpy offer a more attractive environment for nickel(I) by allowing electron delocalization over the ligand n system (178,179). A number of complexes of these ligands have been reported in y-radiolysis studies. The EPR spectra indicate that reduction is primarily metal centered with a significant orbital contribution. Electrochemical reduction of [NiH(bpy)3]2+ in anhydrous acetonitrile results in [Ni (bpy)3] +, which can be detected by EPR methods. The reduction potential is reported to be —1.55 V but the complex is thermodynamically unstable with... 

Other Univalent Metal Ions.—The reductions of cobalt(iri) complexes by univalent zinc, cadmium, and nickel ions have been studied in aqueous solutions, using pulse radiolysis techniques. Radiolysis of aqueous solutions of bivalent metal salts and cobalt(m) complexes involve reactions of the type (5)—(7). When the cobaltic complex concentrations are... 

Other Studies.— The kinetics and mechanisms of reactions of tptz (5) complexes of cobalt(ii), copper(ii), and nickel(u) with water and with hydroxide have been established and compared. Covalent hydrates are believed to be important intermediates in aquation of the [M(tptz)(OH2)3] + complexes. Kinetics of aquation of the anions [M(acac)a] (M = Co, Cr, or Ru) have been studied in pulse radiolysis experiments. All three steps were monitored for the cobalt(n) complex, but the first step for the chromium(ii) complex was too fast to follow and, predictably, all steps for the ruthenium(ir) complex were too slow to follow by this technique. The mechanism of acac loss is thought to involve equilibrium... 

Reactions in Water.—A preliminary report has indicated that the rate of water exchange in the five-co-ordinate Co complex of (7) is particularly low for this metal (4.2 X 10 s at 25 °C) the activation parameters are given as A/f = 36.5 1.4 kJ mol and AS = — 34 4 JK mol. A preliminary application of conductometric pulse radiolysis to the dissociation of Co -amine chlorides has yielded results consistent with those obtained by other methods. The very small effect exerted by nickel(ii)-bound pyridine on the lability of the remaining water molecules has already been mentioned. An interesting preliminary report has indicated that the substitution reactions of Cu complexes are relatively slow in the absence of Jahn-Teller distortions [as, for example, in the trigonal-bipyramidal complex with (8) see Table 7]. 

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