Cyclooligomerisation of the amino acid thiazole 3 is influenced by metal io
ns, with smaller alkali metal ions favouring the formation of the trimer 4,
and larger metal ions (eg Cd2+) enhancing the formation of the tetramer 5.
A crystalline complex obtained be tween the tetramer 5 and Ag BF4 is shown
by X-ray studies to comprise two macrocycles and five silver ions in a 'sa
ndwich' type arrangement.