${\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+},\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+},\left[\mathrm{Co}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{3+},}$
${\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+},\left[\mathrm{Cr}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}}$
$(I)\, [CrCl_2(NO_2)_2(NH_3)_2]^-$ $(II)\, [Co(NO_2)_3(NH_3)_3]$
$(III)\, [PtCl(NO_2)(NH_3 )(py)]$ $(IV)\, [PtBrCl(en)]$
$(I)\,\,\,-\,\,\,(II)\,\,\,-\,\,\,(III)\,\,\,-\,\,\,(IV)$