Compounds of formula (IIa):
are provided where:
X is a group capable of being cleaved from the α-carbon atom to form an ion of formula (I')
C is a carbon atom bearing a single positive charge or a single negative charge;
The invention further provides compounds of formula (IIb):
where:
X is a counter-ion to C.
The compounds of formula (IIa) and (IIb) may form ions of formula (I') by either cleaving the C-X bond between X and the α-carbon atoms in the case of the compounds of formula (IIa) or dissociating X in the case of compounds of formula (IIb).