Coordination-Driven Self-Assembly of Discrete Molecular Nanotubular Architectures

Two new M8L4 tetrafacial nanotubes (T1 and T3) of different lengths have been synthesized in water using ligands L1 and L2, respectively, with acceptor cis-[(dch)Pt(NO3)2] (M) using coordination-driven self-assembly [where dch is 1,2-diaminocyclohexane, L1 is 1,4-di(pyrimidin-5-yl)benzene, and L2 is 4,4′- di(pyrimidin-5-yl)-1,1′-biphenyl]. In addition to complex T1, a tetrahedral cage of composition [M12(L1)6] (T2) was also formed in the self-assembly reaction of ligand L1 with cis-[(dch)Pt(NO3)2]. The precise composition of the products (T1 and T2) in solution was confirmed by 1H NMR and ESI–MS. Pure tube T1 was separated out by a crystallization technique and fully characterized by 1H NMR and X-ray diffraction. Temperature- and concentration-dependent NMR studies indicated no equilibrium between T1 and T2 in the solution phase, and the proportion of T1 and T2 in the mixture depends on the temperature of the reaction. In contrast to ligand L1, the self-assembly of the longer ligand, L2, with cis-[(dch)Pt(NO3)2] gave only tetrafacial tube [M8(L2)4] (T3) without any tetrahedral cage.