Regioisomer-Dependent Endo- and Exocyclic Coordination of Bis-Dithiamacrocycles

Syntheses
of the regioisomers of bis-dithiamacrocycle and the regioisomer-controlled
endo- and exocyclic coordination behaviors are reported. Direct bis-cyclization
reaction of 1,2,4,5-tetra­(bromomethyl)­benzene with 3,6-dioxa-1,8-octanedithiol
led to a mixture of two bis-dithiamacrocycle regioisomers (ortho-type; o-bis-L and meta-type; m-bis-L) which were separated by recrystallization and column
chromatography. When the two isomers were reacted with AgPF6, o-bis-L gave an endocyclic
one-dimensional (1-D) coordination polymer {[Ag3(o-bis-L)2(CH3CN)]­(PF6)3·2CH3CN}n (1) with a 3:2 (metal-to-ligand) stoichiometry,
while m-bis-L afforded
an exocoordination-based 1-D polymeric complex {[Ag­(m-bis-L)]­(PF6)}n (2) with a 2:2 stoichiometry. The observed
endo- and exocoordination modes depending on the isomers were discussed
in terms of the S···S distances in the bis-dithiamacrocycle
isomers. Due to the closer S···S distance in each macrocyclic
ring, o-bis-L is suitable
for the endocoordination. However, m-bis-L forms an exocyclic complex because the S···S
distance between two macrocyclic rings is shorter than that in one
macrocyclic ring. NMR experiments also revealed that o-bis-L and m-bis-L form the endo- and the exocyclic complexes, respectively,
in solution.