Metallohexacycles containing 4′-aryl-4,2′:6′,4′′-terpyridines: conformational preferences and fullerene capture

Abstract

4′-(4-Biphenylyl)-4,2′:6′,4′′-terpyridine (1) reacts with ZnCl2 or ZnBr2 to produce discrete metallohexacycles instead of the expected one-dimensional coordination polymers. Structural determination of [{ZnCl2(1)}6] and [{ZnBr2(1)}6] reveals that the metallomacrocycles adopt a conformation in which the biphenyl domains are in an alternating up/down arrangement (conformer I). The hexamers pack into tubes; within each tube, biphenyl domains of every second hexamer are interdigitated, and these assemblies then interlock to produce a rigid architecture supported by pyridine–phenyl face-to-face contacts. π-Stacking between 4,2′:6′,4′′-tpy domains operates between adjacent tubes. Reaction of ZnCl2 or ZnBr2 with 4′-(2′,3′,4′,5′,6′-pentafluorobiphenyl-4-yl)-4,2′:6′,4′′-terpyridine (2) leads to [{ZnCl2(2)}6] and [{ZnBr2(2)}6], each crystallizing in two conformations; the centrosymmetric chair-conformer (II) is dominant with respect to the tub-like conformer I. Both conformers pack into tube assemblies, but that consisting of conformer II is less rigid than that of I. Reaction of 4′-(4-(naphthalen-1-yl)phenyl)-4,2′:6′,4′′-terpyridine (3) with ZnCl2 or ZnBr2 leads to [{ZnX2(2)}6] (X = Cl, Br) in conformer I; disordering of the naphthyl substituents is problematic. Assembly of the metallohexacycle in the presence of C60 results in the formation of the host–guest complex [2{ZnCl2(3)}6·C60]·6MeOH·16H2O. The [{ZnCl2(3)}6] units assemble into a tube-like array that mimics that observed in the parent host. In the host–guest complex, each crystallographically-ordered C60 is trapped between six ordered naphthyl units, three from one hexamer and three from its interdigitated partner, and the C60–six-naphthyl unit sits centrally within a second [{ZnCl2(3)}6] macrocycle. In contrast to previously described tube-like host–guest assemblies featuring fullerene entrapment, [2{ZnCl2(3)}6·C60] is unusual in having an ordered array of C60 molecules present in every other available cavity, despite the fact that sterically, the ‘empty’ cavity could, in principle, host a C60 guest.