The synthesis of six trinuclear Pn₃L₂ macrobicycles (Pn = As, Sb) was achieved by self-assembly of a pnictogen trichloride and a 2,4,6-trisubstituted-1,3,5-benzenetrimethanethiol ligand. ¹H-NMR spectroscopy reveals self-assembly in 1,1,2,2-tetrachloroethane is dynamic in solution producing two structural isomers. The symmetric and the asymmetric isomers (in which a single chloride ligand is cast in an opposing direction from other chlorides) of the As₃L₂ complexes exist in a ca. 2 : 1 distribution, whereas only the symmetric isomer is observed in solution for Sb₃L₂. Solvent effects appear to influence conformational isomerism and conversion to the final products. Macrobicycles were confirmed by ¹H-NMR spectroscopy and X-ray crystallography and further studied by MP2/LANL2DZ optimizations.