Group 9 cobalt

Cobalt is less reactive than Fe (e.g. see equation 22.75) Co does not react with O2 unless heated, although when very finely divided, it is pyrophoric. It dissolves slowly in dilute mineral adds (e.g. reaction 22.76), but concentrated HNO3 makes it passive alkalis have no effect on the metal. 

Cobalt reacts at 520K with F2 to give C0F3, but with CI2, Br2 and I2, C0X2 is formed. Even when heated, cobalt does not react with H2 or N2, but it does combine with B, C (see Section 14.7), P, As and S. 

The blue, low-spin [Co(OH2)6] ion can be prepared in situ by electrolytic oxidation of aqueous C0SO4 in acidic solution at 273 K. A more convenient method for routine use is to dissolve solid [Co(NH3)6][Co(C03)3] (a stable, sparingly soluble salt, made according to scheme 22.77) in aqueous nitric or perchloric acid. The acid is chosen so as to ensure precipitation of [Co(NH3)s]X3 (equation 22.78), leaving [Co(OH2)e] in solution. 

The [Co(OH2)6] ion is a powerful oxidant (equation 22.79) and is unstable in aqueous media, decomposing to Co(II) with the liberation of ozonized O2. The [Co(OH2)6] ion is best isolated as the sparingly soluble blue alum CsCo(S04)2 12H20, although this decomposes within hours on standing. Complex formation with, for example, bpy, NH3, RNH2 or [CN] greatly stabilizes Co(III) as equations 22.80-22.83 illustrate. 

Replacing aqua by ammine ligands, for example, results in a dramatic change in E° (equations 22.79 and 22.81) and shows that the overall stability constant of [Co(NH3)6] is 10 greater than that of [Co(NH3)6]. Much of this difference arises from LFSEs  

Cobalt is less reactive than Fe (e.g. see equation 21.72) Co does not react with O2 unless heated, although when very 

The trend in decreasing stability of high oxidation states on going from Mn to Fe continues along the row Table 

Alfred Werner (working at the University of Zurich) was awarded the Nobel Prize for Chemistry in 1913 for his pioneering work that began to unravel the previous mysteries of the compounds formed between i-block metal ions and species such as H2O, NH3 and halide ions. A famous problem that led to Werner s theory of coordination concerns the fact that C0CI3 forms a series of complexes with NH3  

In addition to the hexaaqua ion, high-spin Fe(II) complexes include [Fe(en)3]. Its magnetic moment of 5.45//b is larger than the spin-only value of 4.90/xb and reflects orbital contributions for the configuration tjg fig. Although iron(II) favours an octahedral arrangement of donor atoms, there are some tetrahedral complexes, for example [FeCm (eq. 21.73), [FeBr4], [Fey and [Fe(SCN)4] . 

The amido complex [Fe N(SiMePh2)2 2l is an unusual example of 2-coordinate Fe(ll) (see Section 19.7). 

Attempts to prepare binary iron nitrosyl complexes by treatment of Fe(CO)3Cl with AgPFs or AgBF4 lead to Fe(NO)3(ri -PF6) and Fe(NO)3(T -BF4) rather than salts containing naked [Fe(NO)3] ions the r notation indicates that the anions coordinate through the metal centre through one F atom. 

Explain why there is an orbital contribution to the magnetic moment of [Fe(en)3].  

---

Catalysts Prepared from Metal Carbonyls of Group 9 Cobalt, Rhodium and Iridium 331... 

Ring enlargement to r/3-oxocyclobutenyl complexes, by carbonyl insertion into the three-membered ring, is generally observed in reactions of group 9 cobalt carbonyl anions with cyclopropenylium cations (equation 197)271 275. Formation of j/ -oxocyclobutenyl complexes also occurs with nitroso iron carbonyl anions270,275. These reactions are usually... 

The major route to -cyclopropenylium complexes L M(C3R3) (metallatetrahedranes) is by oxidative addition reactions of cyclopropenylium salts to transition metal complexes of groups 5 (V), 6 (Mo, W), 8 (Fe, Ru), 9 (Co, Rh, Ir) and 10 (Ni, Pd, Pt). The addition is frequently accompanied by loss of one or more carbonyl, olefin or halogen auxiliary ligand. Concurrent formation of oxocyclobutenyl complexes by carbonyl insertion into the cyclopropenyl ring is often observed in reactions with group 9 cobalt triad and early transition metal complexes. 

---