Modern inorganic chemistry

368 THE TRANSITION ELEMENTS

Uf

pink E yellow F

* JNH 3

[Cou(CN) 5 H 2 O]^3 " *™1 [Co«(H 2 O) 6 ]^2 +

red. G pink, aquo-

I cation A

water i

I I

C1

"

[Co'"(CN) 6 ]^3 - [Co"Cl 4 ]^2 - -^ [ComCl 4 ]-

yellow, H blue chloro- non-existent

anion C D

Here, the pink aquo-cation (A) (produced when a cobalt(II) salt
dissolves in water) cannot be oxidised to the + 3 state (B) in aqueous
solution, since B would itself oxidise water to give oxygen. Replace-
ment of the water ligands by chloride alters the shape, colour and
redox potential, but again oxidation of C to D is not possible.
However, replacement of water ligands by ammonia to give E allows
easy oxidation to the stable + 3 complex F. Replacement of water
by cyanide would be expected to give G; in fact this is immediately
oxidised by the solvent water (with evolution of hydrogen) to the

• 3 complex H.

OTHER PROPERTIES

The metals: alloys

Reference has already been made to the high melting point, boiling
point and strength of transition metals, and this has been attributed
to high valency electron-atom ratios. Transition metals quite readily
form alloys with each other, and with non-transition metals; in
some of these alloys, definite intermetallic compounds appear (for
example CuZn, CoZn 3 , Cu 31 Sn 8 , Ag 5 Al 3 ) and in these the formulae
correspond to certain definite electron-atom ratios.

The metals: interstitial compounds

The transition metal structures consist of close-packed (p. 26) arrays
of relatively large atoms. Between these atoms, in the 'holes', small
atoms, notably those of hydrogen, nitrogen and carbon, can be
inserted, without very much distortion of the original metal struc-
ture, to give interstitial compounds (for example the hydrides, p. 113).