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.