The local structure around the cobalt(II) ion in the reaction intermediate formed during the metal substitution reaction of the homodinuclear mercury(II) porphyrin (5,10,15,20-tetrakis(4- sulfonatophenyl)porphyrin; H2tpps4- ) complex with a cobalt(II) ion in an acetate buffer has been determined by the stopped-flow EXAFS method. The structure of the reactant and the product of the above reaction has also been determined by the same method. The coordination geometry around the cobalt(II) ion in the heterodinuclear intermediate, [Hg(tpps)Coll]2- , is six-coordinate octahedral with four additional water and/or acetate oxygen atoms. The Coll-N and Coll-O bond lengths in the intermediate are 212(2) and 221(1) pm, respectively. The product, [Coll(tpps)]4-, has a six-coordinate octahedral structure, the Coll-N and Coll-O bond lengths being 203(1) and 215(1) pm, respectively. The Coll-N bond length in the intermediate is ca. 9 pm longer than that in the product. The Coll-O bond length in the intermediate is also ca. 9 pm longer than that of 212(1) pm in the reactant, the cobalt(II) acetato complex, and ca. 6 pm longer than that in the product. The longer Coll-O bond in the intermediate as compared to those in the reactant and in the product appears to be responsible for the instability of the intermediate. The oxidized product, [Colll(tpps)]3-, has a six-coordinate structure with two additional Colll-O bonds. The Colll-N and Colll-O bond lengths are 189(1) and 197(2) pm, respectively, and are much shorter than those in [Coll(tpps)]4-.
Synthesis of Ti3AuC2, Ti3Au2C2 and Ti3IrC2 by noble metal substitution reaction in Ti3SiC2 for high-temperature-stable Ohmic contacts to SiC