A vanadium porphyrin with temperature-dependent phase transformation: Synthesis, crystal structures, supramolecular motifs and properties

A vanadium porphyrin, V(O)TMeOPP (1; TMeOPP=5, 10, 15, 20-tetrakis(4- methoxyphenyl)-21 H, 23H-porphyrin), has been synthesized by solvothermal reactions and characterized by single-crystal X-ray diffractions at room temperature and low temperature to reveal two different structures 1 R and 1 L, respectively. Both 1 R and 1 L crystallized in the orthorhombic system, but their space groups were different: Pbca and Pca2₁ for 1 R and 1 L, respectively. The cell parameters of a, b, and c were different and the cell volume of 1 R was larger than that of 1 L by circa 200 ų. 1 R and 1 L were characteristic of an isolated motif with a five-coordinate vanadium(IV) ion and a saddle-distorted nonplanar porphyrin macrocycle. Molecules of 1 R were interconnected through hydrogen-bonding interactions to yield a 3D framework; whilst for the low-temperature phase 1 L, there were more hydrogen-bonding interactions that link the molecules to construct a more-complex 3D supramolecular network. In a solution of acetone, the title compound exhibited purple and green colors at room temperature and low temperature, respectively, which is unprecedented for vanadium porphyrins. The spectral data of UV/Vis, FT-IR, and MALDI-TOF-MS of 1 R and 1 L are reported together with the electrochemical data.