The quest for a better understanding of ethanol coordination to magnesium and zinc porphyrin: A combined experimental and theoretical study

Abstract

An ethanol coordinated magnesium porphyrin [Mg(TDMPP)(C2H5OH)], (TDMPP = 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)porphyrin), 1 was synthesized and characterized by single crystal X-ray diffraction method along with other standard spectroscopic techniques. This is the first known crystal structure of an alcohol bound magnesium porphyrin of tetraphenylporphyrin derivatives. Crystal structure of the compound shows a weak hydrogen bonding interaction (2.730(4) Å) between OH group of axial ethanol molecule and a peripheral methoxy group of an adjacent porphyrin molecule. This hydrogen bonding results the formation of a weak one-dimensional supramolecular structure. The fluorescence and electrochemical studies have also been performed. To explore the disadvantages of using zinc porphyrins to study chlorophyll type magnesium porphyrins, a comparison of theoretical study using DFT level was performed between compound [Mg(TDMPP)(C2H5OH)], 1 and its zinc counterpart [Zn(TDMPP)(C2H5OH)], 2. Theoretical calculations include optimization of geometry, energy of frontier molecular orbitals (FMOs), electronic transitions and global chemical indices. The global reactivity indices like η, µ and ω derived from theoretical calculations for zinc and magnesium porphyrin supports that magnesium porphyrin is more reactive than the zinc analogue. Furthermore, the Hirshfeld surface analysis was used to quantify the weak intermolecular interactions present in the crystal lattice of compound 1.