Synthesis, Structural, Photophysical, Electrochemical Redox and Axial Ligation Properties of Highly Electron Deficient Perchlorometalloporphyrins and Selective CN‒ Sensing by Co(II) Complexes
Nivedita Chaudhri, R. J. Butcher, Sankar Muniappan
A straightforward synthetic route has been used to synthesize highly nonplanar electron deficient perchlorometalloporphyrins. Herein, we report the synthesis and characterization of MTPP(NO2)Cl7 where (M = CoII, NiII, CuII and ZnII). Further, we examined their electronic spectral and electrochemical redox properties and the results are compared with MTPPCl8. MTPP(NO2)Cl7 exhibited red-shifted ( ̴ 10-15 nm) absorption spectra relative to MTPPCl8 due to strong electron withdrawing nature of nitro group. Mixed β-substitution alters the electrochemical redox properties to such an extent that an appreciable increment in anodic shift in reduction potential (200-300 mV) is observed for MTPP(NO2)Cl7 relative to MTPPCl8 whereas only a minimal shift (15-50 mV) in the oxidation potential is observed. Nonplanarity of macrocyclic core was investigated by Single crystal X-ray analysis and DFT calculations. Higher ΔCβ (0.706 Å) for 1d as compared to 2d (0.642 Å) is undoubtedly signifying nonplanarity induced by nitro group. To substantiate the effect of mixed substitution, we performed axial ligation studies of Zn(II) complexes with nitrogenous bases and basic anions and found higher logβ2 values as well as a linear relation between logβ2 and pKa as compared to perbromoporphyrins. Highly electron deficient β-substituted Co(II) porphyrins (1a and 2a) were utilized as novel sensors for selective rapid visual detection of CN− ions.