Solvated Electron - Properties

Properties

Focusing on ammonia solutions, all of the alkali metals, as well as Ca, Sr, Ba, Eu, and Yb, dissolve to give the characteristic blue solutions. Other amines, such as methylamine and ethylamine, are also suitable solvents.

A lithium ammonia solution at −60 °C is saturated at about 16 mol% metal (16 MPM in the local jargon). When the concentration is increased in this range electrical conductivity increases from 10−2 to 104 ohm−1cm−1 (larger than liquid mercury). At around 8 MPM, a "transition to the metallic state" (TMS) takes place (also called a "metal to nonmetal transition" (MNMT)). At 4 MPM a liquid-liquid phase separation takes place: the less dense gold-color phase becomes immiscible from a more dense blue phase. Above 8 MPM the solution is bronze/gold-colored. In the same concentration range the overall density decreases by 30%.

Dilute solutions are paramagnetic and at around 0.5 MPM all electrons are paired up and the solution becomes diamagnetic. Several models exist to describe the spin-paired species: as an ion trimer, or as an ion-triple—a cluster of two single-electron solvated-electron species in association with a cation, or as a cluster of two solvated electrons and two solvated cations.

Solvated electrons produced by dissolution of reducing metals in ammonia and amines are the anions of salts called electrides. Such salts can be isolated by the addition of macrocyclic ligands such as crown ether and cryptands. These ligands bind strongly the cations and prevent their re-reduction by the electron.