Two nitrato-iron(III) porphyrinates [Fe(4-Me-TPP)(NO₃)] 1 and [Fe(4-OMe-TPP)(NO₃)] 2 are reported. Interestingly, [Fe(4-Me-TPP)(NO₃)] 1 has nitrate ion coordinated as monodentate (by single oxygen atom), while [Fe(4-OMe-TPP)(NO₃)] 2 has nitrate coordination through bidentate mode. Compound 1 was found serendipitously in the reaction of [Fe(4-Me-TPP)Cl] with nitrous acid, which was performed for the synthesis of nitro-iron(III) porphyrin, [Fe(4-Me-TPP)NO₂]. The compound 2 was synthesized by passing NO₂ gas through a solution of [Fe(4-OMe-TPP)]₂O. Upon passing NO₂ gas through a solution of a 𝜇-oxo-dimer, [Fe(4-Me-TPP)]₂O also produces 1. It is interesting that in more electron-rich porphyrin 2, binding of the nitrate in a symmetrical bidentate way while in less electron-rich porphyrin 1, binding of the anion is unidentate by a terminal oxygen atom. However, it is expected that the energy difference between the monodentate and bidentate coordination mode is very small and the interchange between these coordination is possible. Upon passing NO₂ gas through a solution of 𝜇-oxo-dimeric iron(III) porphyrin, the nitrato-iron(III) porphyrin forms first, that later gets oxidized to 𝜋-cation radical to yield hydroxy-isoporphyrin in the presence of trace amount of water. These nitrato-iron(III) porphyrinates in moist air slowly converted back to their respective 𝜇-oxo-dimeric iron(III) porphyrins.

A magnesium porphyrin compound, [Mg(TMPP)(H ₂O)].(CH ₃COCH ₃)2H ₂O 1 (TMPP = 5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrin) has been synthesized and characterized using single crystal X-ray diffraction and other spectroscopic analysis. The luminescence properties of compound 1 were studied at different concentrations. At higher concentration (3×10 ⁻³ M), treatment of 1 with cholesterol enhanced the luminescence when excited at Soret band, demonstrating the role of lipid in controlling porphyrin-porphyrin interaction for tuning the bulk photophysical properties. However, at lower concentration (10 ⁻⁵ M) of porphyrin, there was no significant change in luminescence intensity in the presence of cholesterol. It suggests some role of lipids in light harvesting systems where chlorophyll is present at higher concentration.

The crystal structure of the compound, Zn(II) 5,10,15,20-tetrakis(meta-methoxyphenyl)porphyrin chloroform trisolvate, [ZnT(m-OCH₃)PP]·3CHCl₃ 1 reveals that it forms a weak one-dimensional chain structure through interaction between Zn of porphyrin and the oxygen atom of the methoxy group of a neighbouring porphyrin. The zinc–oxygen interaction observed in compound 1 is compared with Zn(II) 5,10,15,20-tetrakis(para-methoxyphenyl)porphyrin [ZnT(p-OCH₃) PP] 2 and Zn(II) 5,10,15,20-tetrakis(3,4,5-tri-methoxyphenyl)porphyrin

[ZnT(3, 4, 5-triOCH₃)PP] 3 to understand the preferred methoxy-position ofinteraction. The strength of the non-covalent zinc–oxygen (methoxy group of a neighboring porphyrin) interaction in compound 1 is in between that of similar interactions observed in compounds 2 and 3. The Mulliken charge analysis using theoretical calculation at the DFT level shows that the meta-methoxy oxygenhas a higher probability of binding to the metal than the para-methoxy oxygen. In the presence of nucleophiles, the formation of one-dimensional chain structure stops due to the binding of the nucleophiles to the metal zinc. The photoluminescence and differential scanning calorimetric studies were also performed for compound 1.