Solutions of s-block metals in liquid NH3 All of the group 1 metals and the group 2 metals Ca, Sr and Ba dissolve in liquid NH3 to give metastable solutions from which the group 1 metals can be recovered unchanged. The group 2 metals are recoverable as solids of composition [M(NH3)6 ]. Yellow [Li(NH3)4] and blue [Na(NH3)4] may also be isolated at low temperatures. Dilute solutions of the metals are bright blue, the colour arising from the short wavelength tail of a broad and intense absorption band in the infrared region of the spectrum.
The electronic spectra in the visible region of solutions of all the s-block metals are the same, indicating the presence of a species common to all the solutions: this is the solvated
electron (eq. 9.26).