Crystal and molecular structure of unsymmetrical N-methyl-substituted μ-oxo diiron(III) tetraphenylporphyrin

Abstract

The complex [(NCH 3TPP)Fe IIIOFe III(TPP)]ClO 4, where TPP is the dianion of meso-tetraphenylporphyrin and NCH 3TPP is the monoanion of N- methyl- meso-tetraphenylporphyrin, has been characterized by single-crystal X-ray structure analysis. The compound crystallizes in the space group P2 1/ c with cell dimensions (133 K) of a = 16.605(5), b = 16.827(3), c = 28.075(9) Å, β = 105.30(2)° with Z = 4. The structure has been refined to an R index on F of 0.074 on the basis of 8396 reflections (Mo Kα). The discrete (NCH 3TPP)Fe IIIO unit exhibits a highly distorted square pyramidal coordination about iron(III) with the oxo ligand occupying the apical position (Fe(2)O(1) = 1.740(4) Å). The N-methylated porphyrin ligand forms three strong bonds to iron(III) (Fe(2)N(121) = 2.053(5) Å; Fe(2) N(122) = 2.055(6) Å; Fe(2)N(124) = 2.066(6) Å) together with a weaker one (Fe(2)N(123) = 2.257(5)Å) between the methylated nitrogen atom and the iron(III) atom. The Fe III displacement above the N(121), N(122), N(124) reference plane is 0.526(2) Å and the dihedral angles between pyrrole rings and the reference plane are: N-methylated 33.1(2)°, opposite 5.1(2)°, adjacents −12.3(2)° and −13.2(2)°. The first example of ferric ion coordination by N- methylporphyrin has been compared to the ferrous analogue. The discrete (TPP)Fe IIIO unit exhibits a square pyramidal coordination with an apical position of the oxo ligand Fe(1)O(1) = 1.767(4) Å) and the average Fe(1)N bond length in the range characteristic for high-spin ferric porphyrins (Fe(1)N av = 2.066(6) Å). The Fe(1)O(1)Fe(2) angle is distinctly non-linear with a value 165.4(3)° due to the steric interaction imposed by the N-methylated pyrrole ring. The facing porphyrins are twisted by 30.2(2)° with respect to one another.