Syntheses and crystal structures of ‘encapsulated’ guanidinium complexes of 27-membered macrocyclic ligands

X-Ray structures of complexes of 2,6-pyrido-27-crown-9 and 1,3-xylyl-27-crown-8 with guanidinium perchlorate show a complementary hydrogen bonding relationship between host and guest; in the former complex the pyridyl nitrogen is used preferentially as a hydrogen binding site; the structures found are compared with those of the protonated 27-membered macrocycle and with 2,6-pyrido-24-crown-8.