Since the development of the laddering principle in the mid-1980s, it has b
ecome a useful concept for describing structural features in a wide variety
of organoalkali metal (particularly organolithium) and other main-group el
ement oligomers. Here a brief account of the laddering principle is given,
and a two-stage approach to understanding structural diversity is described
for several lithium heterocarboxylates. "Primary laddering" describes the
initial aggregation of monomeric units, whereas "secondary laddering" deals
with the assembly of these primary laddered units into larger structures.
Both homo- and heteromolecular clusters can be formed by these processes. I
n this context, several examples are discussed, with particular emphasis on
the effects of solvation and heteroatoms.