Formation of the 2 : 1 mercury(II) porphyrin complex, Hg2(tpps)2− (H2tpps4−: tetrakis(4-sulfonatophenyl)porphyrin), in aqueous solution has been investigated. Equilibrium studies revealed that main chemical species is Hg2(tpps)2− even in a solution of a 1 : 1 molar ratio of Ctpps/CHg and the Hg2(tpps)2− complex is very stable thermodynamically. EXAFS (extended X-ray absorption fine structure) analysis of the Hg2(tpps)2− complex in aqueous solution showed that the Hg–N bond length within the complex is 215(2) pm and the bond length is much shorter than the Hg–O bond length (240 pm) within the hydrated mercury(II) ion. Thus the very strong Hg–N bond is formed upon the complexation of Hg2(tpps)2− and the strong bond formation supports the high stability of the Hg2(tpps)2− complex. Deformation of Hg2(tpps)2− is also discussed in connection with catalytic effect of mercury(II) on metalloporphyrin formation.
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Tabata et al. (1992) studied this question.
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