About Electrides and Alkalides

Introduction

Historical

	Alkalides and Electrides can be said to trace their lineage to the
ealiest work on Alkali Metal Ammonia Solutions.  The work on Metal-Ammonia
solutions is extensive and I refer the reader to a good reference [1] on the
subject.

	In the 1960's a great amount of progress in understanding the early
experimental work and the first clear cut identification of Metal anions (M-)
and solvated electrons (e-[solv]) was accomplished [see sec. III. A. ref. 1].
Shortly there after in 1974 the first reported synthesis of a crystal with
Alkali metal anions was reported in the literature [2] with a stoichometry 
of Na+[C222]Na-.

Alkalides

	Alkalides are a class of ionic compounds where the Anions are of the
Type I group (Alkali) elements Na, K, Rb, Cs (no known 'Lithide' exists).
The cation is a alkali cation complexed by a large organic complexant. The
resulting chemical form is A+ [Complexant] B-, where the complexant is  
either a Cryptand, Crown Ether, or Aza-Crown.

        Soon after the discovery of Na+[C222]Na- a number of Alkalides with
similiar stoichiometry were produced and characterized.  The list of
complexants has been extended to include Crown ethers, and Aza-Crowns.
The number of known Alkalides has risen to above 40, with the crystal
structures of at least 16 of them now determined.  It was in 1983 when
the first crystal was reported with the presumed formula A+ [18C6] e- [3]
which was called an Electride.

Electrides

	Electrides are just like Alkalides except that the anion is presumed
to be simply a electron which is localized to a region of the crystal between
the complexed cations.  I say presumed because to date no DIRECT evidence
exists that confirms this view.  But there is strong indirect evidence that
this is indeed the correct view.  (Particularly that the parent Alkalide 
is nearly isostructural to it's Electride.)

	The currently known electride systems have the following properties:

(i)	They are Mott insulators.  With band gaps > 1.9ev.  
(ii)	Optical absorption peak occurs about .6-.9ev (probably bound-bound
        transition).
(iii)	Complexed Cation shows tiny Chemical shift from M+ (indicating 
	e- spends a very small fraction of it's time near the M+ nucleus
(iv)	They tend to decompose at temperatures above 240K.
(v)	Strongest reducing agents currently know.
 
	We feel that these systems are the perfect place to examine how
cavity geometry and connectivity effect the electronic and magnetic properties
of isolated regular arrays of localized electrons.

Our groups results