Molecular And Solid‐State Structure Of Oxovanadium(IV) Etioporphyrin‐III

Oxovanadium(IV) etioporphyrin‐III, VO‐EtioP‐III is an important member of the petroporphyrin family. It can be isolated from crude oil or synthesized de novo from the dipyrromethene precursors, the latter being the approach we used in our research. The molecular structure of VO‐EtioP‐III was for the first time characterized by single‐crystal X‐ray diffraction. Both terminal alkyls and the axial oxygen atom protrude in the same direction relative to the molecular plane, while rear side of the molecule remains almost flat. This results in a peculiar centrosymmetric packing (space group P21/c, monoclinic system with four molecules per unit cell), in which back‐to‐back oriented molecules form the parallel‐plane dimers. The powder X‐ray diffraction data indicate that the VO‐EtioP‐III films deposited by vacuum evaporation retain a very strong texture, with all molecules standing vertically on the substrate surface. The absorption spectra of films differ from the solution spectra by a large redshift of the Soret‐ and Q‐ band (~30 nm) with hypo‐ and hyperchromic effects, respectively. The former band strongly broadens due to multiple splitting to within 350–520 nm, which is followed by a change of the color from purple (in diluted solutions) to brawn (in films or crystals). Molecular and crystal structure of a synthetic petroporphyrin, oxovanadium(IV) etioporphyrin‐III is described for the first time. Molecules in a crystal are arranged in dimers with the interplane distance of 3.53 Å and slip angle of 20.5°. Absorption spectra of thin crystalline films and liquid‐phase molecular aggregates are similar, but differ noticeably from those of isolated molecules in diluted solutions.