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(a) Van der Waals representation of the honeycomb-like arrangement of stacks in the crystals of 3a_1 and 3a_2. (b) An isolated dimeric motif was observed in the crystals of 3a_3 and 3b_1. Symmetry-independent macrocycles that constitute the tail-to-tail dimer are shown in different colors as a space-filling model.
