A New and Facile Route Using Electride Solutions To Intercalate Alkaline Earth Ions into Graphite

A series of new ternary graphite intercalation compounds (GICs) containing alkaline earth metal cations (M = Mg, Ca, Sr, Ba) and ethylenediamine (en) are reported. These GICs are deep blue to green in color and can be prepared as phase-pure compounds by the direct reaction of graphite powder with the metal in liquid en at mild temperatures (25-100 degrees C) under an inert atmosphere. X-ray diffraction and thermal analyses were employed to determine the structural and compositional details. [Mg-2(en)(2.0)] C-26 and [Ba-2(en)(2.0)]C-34 can be obtained as stage-1 GICs with gallery expansions of 0.55 and 0.46 nm, respectively, indicating the presence of intercalate monolayers with en cointercalates oriented perpendicular to the encasing graphene layers. Reactions with Ca and Sr metals form [Ca(en)(2.0)]C-26 and [Sr(en)(2.0)]C-22, which are stage-1 GICs with intercalate bilayers and gallery expansions of 0.76 nm. Titration indicates that each metal intercalate is associated with a 2-electron reduction process. Details on the effects of reaction time, temperature, and starting stoichiometry on reaction rates and product staging are reported.