Ni IV Complexes

Ni(IV) complexes have a d configuration and the favourite geometry is octahedral with low spin (t2g) electron arrangement, indicating that they are likely to be diamagnetic like Co(III) complexes. 

Grind your preparation to a fine powder. Use the powder for measuring the effective magnetic moment and recording its ir spectrum. Compare with the precipitated complex in Sec. 15.3.2. 

Use ice cold KOH solution to dissolve the prepared complex to give 3 x 10 M solution at pH 12 and run its spectrum in 1 cm cell over the range 200-750 nm. Comment on the spectrum. 

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Indeed, as far as the stabilization of Cu(III) complexes is concerned, deprotonated amides proved to be suitable ligands (as has been discussed for Ni(IV) complexes). For instance, Figure 123 shows the strictly planar geometry of the oxamidate Cu(III) complex [CuL]-.181... 

The effect of coordination in stabilizing higher stales of oxidation is seen in the occurrence of irontIV) in certain cationic complexes, such as [FctCI) 2C<,Hj(As(CH i ) (FeClr) tel. the corresponding nickelllVi, Ni(IV), complex). 

The reaction of Ni(dmpe)2 (dmpe = bis(dimethyl-phosphino)ethane) with 1,2-disilylbenzene (10) has formed a number of interesting bis(silyl) species (11-13) that seem to be intermediates leading to the rare tetiasilyl Ni(IV) complex (14) and the (apparently) Ni(III)-Ni(III) dimer bearing /u-silylene moieties (15), as shown in Scheme 15. ... 

In contrast to the situation with Pt, there are few examples of addition of Sn-X or Sn-R bonds to Ni or Pd centers, although the Ni(0) complex [Ni(PPh3)3] has been reported to react with R3SnCl by a double oxidative addition to give stable, colorless Ni(IV) complexes of the type [NiCl2(SnR3)2(PPh3)2] . 

Ni(II) and Ni(IV) complexes with chelating 2-acylphenolato ligand undergo several unique reactions including the transmetalation as mentioned below. The nickel(II) complex with a 2-acylphenoxido ligand, Ni[CO-C6H2(Me)(t-Bu)-... 

The 1 2 molar reaction of the Ni(IV) complex with CoMe(PMe3)4 produces the complexes formed through a complex reaction pathway involving transmetalation (Eq. 5.68) [214],... 

Copper ions catalyze a variety of inorganic redox reactions. The kinetics and mechanisms of some of these reactions were analyzed in detail. Thus, the reduction of V(IV) by Sn(II) and Ge(II) is catalyzed by Cu ions in the presence of high concentrations of Cl. The mechanism involves the reduction of Cu(II) by Sn(II) or by Ge(II) followed by the reduction of V(IV) by Cu(I) (134). These reactions proceed via the inner-sphere mechanism (134). Also the copper-catalyzed reduction of peroxonitrite by sulfite (135), the copper-catalyzed reduction of a Ni(IV) complex by thiols (136), and the reduction of superoxide boimd to binuclear cobalt(III) complexes by thiols (137) and by ascorbate (138) follow analogous inner-sphere mechanisms. Copper ions also catalyze the reduction of peroxide-boimd Cr(IV) by ascorbate(i39). 

The first diamagnetic Ni(IV) complexes have been prepared (R = Me, Bu), and the methyl derivative has been structurally characterised (Scheme... 

Interest in Ni(IV) complexes arises from their d configuration like Co(lII) complexes. Hence Ni(IV) complexes are expected to be octahedral diamagnetic and kinetically inert. This facilitates their preparation and characterisation. 

When a nickel (II) chloride solution is made alkaline and the resulting hydroxide is oxidised with chlorine and treated with an alkaline solution of dimethylglyoxime, the Ni(IV) complex is formed. This is taken up in an anion exchange resin and when eluted, the solution produced can be vacuum dried to get the crystalline complex. 

Fig. 2. Rates of aquation of nCo(en)2LCl]"+ as a function of L. The ascending curves indicate increasing SnI character (left branch) and increasing Sn2 character (right branch) in the reaction mechanism., ds isomer O, trans isomer , unknown structure L, 0 is hypothetical analogous Ni(IV) complex.

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