Porphyrin nanotubes based on self-assembly of Mo(V)-dodecaphenylporphyrin complexes and inclusion of Mo-oxo clusters: Synthesis and characterization by X-ray crystallography and transmission electron microscopy

A saddle-distorted molybdenum(V)-dodecaphenylporphyrin (H₂DPP) complex, [Mo(DPP)(O)(OMe)] (1), was converted to [Mo(DPP)(O)(H ₂O)]⁺ (2) in the course of recrystallization from toluene with vapor diffusion of methanol. The complex 2 was organized via self-assembly to form a porphyrin nanotube having a diameter of 1 nm, concomitant with size-selective inclusion of three kinds of novel tetranuclear Mo(VI)-oxo clusters in the nanotube. This porphyrin nanotube exhibits amphiphilic characteristics, that is, a hydrophobic porphyrin surface and a hydrophilic inner-sphere made of aquo ligands to include ionic and hydrophilic entities. Each nanotube has no direct interaction; however, the toluene molecules of crystallization linked the nanotubes together with intermolecular π-π and CH/π interactions. Transmission electron microscopy measurements and energy-dispersive X-ray analysis revealed that the diameters of porphyrin nanotubes could be altered by the size of the Mo-oxo clusters included and also a porphyrin nanoring could be obtained. These results indicate that a variety of porphyrin nanotubular structures can be fabricated by using DPP complexes via cooperatively template-assisted self-assembly.