Photometric study on the reaction between 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis-(4-methylpyridyl)porphine and various metal ions

The chelate forming reaction between 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-methylpyridyl)por-phine (OBTMPyP) and various metal ions, which belong mainly to 4th period and 7th-12th groups in the periodic table, was examined by the observing the absorption spectra. Because one chemical spicy, H-OBTMPyP, which is one pro-tonated compound at an N atom of pyroll ring among 4 pyroll rings, was observed at pH 9.0, this pH was used to measure the changes of absorption spectra with metal ions. From these changes of absorption spectra of OBTMPyP with metal ions, OBTMPyP were seen to react easily with Cu²⁺, Zn²⁺, Mn²⁺, or Co²⁺ ion without other additional reagent or heating within 1 min at over 25°C. On the other hand, OBTMPyP reacted little with Ni²+, and was not all with Fe3+ (or Fe²⁺ reduced by ascorbic acid from Fe³⁺) under the same conditions. 5,10,15,20-tetrakis(4-methylpyridyl)porphine (TMPyP) also did not reacted metal ions above these conditions. The λ_max of each Soret band diFfered. The stability constants (Ka value) of Cu-, Zn-, Mn- and Co-OBTMPyP was calculated by the change in absorbance of each band, and was 2.6×10⁵, 3.6×10⁵, 2.7×10⁵ and 2.9×10⁵ (dm³/mol), respectively. It was revealed that OBTMPyP and metal ions reacted at molar ratio of 1:1, and octabromination of porphine rings improved the reactivity with these ions.