Synthesis, photophysical, cyclic voltammetry properties, and molecular structure study of novel (5,10,15,20-tetratolylphenyl porphyrinato)zinc(II) with pyrazine

Abstract

The precursor (5,10,15,20)-tetratolylporphyrin (H2TTP) (1) and Zn(II) complex (5,10,15,20)-tetratolylporphyrinato)zinc(II) [Zn(TTP)] (2) have been synthesized and utilized to afford a novel complex (3) bearing pyrazine as fifth coordination site on axial position, i.e. (pyrazine)(5,10,15,20-tetratolylporphyrinato)zinc(II) hemi-pyrazine hemidichloromethane solvate [Zn(TTP) (pyz)]0.0.5(pyz.CH2Cl2). Photophysical, electrochemical and X-ray diffraction were investigated. The single-crystal X-ray analysis indicated that in complex (3) (i) Zn(II) ion is penta coordinated, (ii) slight displacement of Zn atom by −0.28 Å towards the axial ligand (pyrazine) and (iii) the crystal lattice is made up of two dimensional layers stabilised by C−H…Cg intra- and intermolecular interactions (Cg is the centroid of pyrrole ring). Optical absorption studies revealed a redshifted of the Soret (B) and Q bands of the Zn-porphyrins complexes. Contrarily, a hypsochromic shift of Q bands in emission spectra of the complexes is noted as compared to the H2TPP. Lifetime of the electrons in (1–3) were determined and compared. Overall, this study would assist in understanding the impact of incorporation of pyrazine at the axial position on optical and electronic properties. Cyclic voltammetry (CV) was applied for the study of the electrochemical behavior of both (2) and (3) complexes in 0.2 M Tetra-n-butyl ammonium perchlorate (TBAP) solution in CH2Cl2. The results of electrochemical confirmed the potentials redox peaks shift more negative ca 60 mV to that is caused by the coordination of pyrazine ligand.