Ionization Differences Between Coordination States of a Cation. Octahedral—Tetrahedral Equilibrium of Transition-Element Chlorides in Dimethylformamide

In a high‐dielectric‐constant, low‐base‐strength medium, such as dimethyl formamide, formation of chloride complexes of the first transition elements in the tetrahedral configuration is promoted. The effect is linked with a greater dissociation (weaker anion complexing) of the octahedral configuration, as indicated by the over‐all equilibrium expression $$2^{\mathrm{oct}}({\mathrm{MCl}}_2{\mathrm{X}}_4{\mathrm{)=}}^{\mathrm{oct}}({\mathrm{MClX}}_5^{+}{\mathrm{)·}}^{\mathrm{tet}}({\mathrm{MCl}}_3\mathrm{X}{)}^{-}\text{+2}\mathrm{X}.$$ The corresponding change in the absorption spectrum has been followed for the chlorides of Mn(II), Fe(II), Fe(III), Co(II), Ni(II), and Cu(II). The spectra with and without added LiCl are described. Some relations to current ligand‐field theories concerning the configuration change are pointed out.