CONFORMATIONAL DIVERSITY IN (OCTAETHYLPORPHINATO)(TRICHLOROACETATO)IRON(III) DERIVATIVES

Abstract Treatment of [Fe(OEP)] 2 O with trichloroacetic acid (2.5-fold excess) results in the formation of (octaethylporphinato)(trichloroacetato)iron(III). Various crystalline solvates can be isolated, depending on the crystallization solvent. Initial crystallization with CHCl 3 /hexanes resulted in the isolation of a monoclinic ( P 2 1 / n , Z =4) unsolvated form, [Fe(OEP)(O 2 C 2 Cl 3 )]. This form contains two distinct porphyrin core conformations at the same lattice site; one is domed and the other is ruffled. Subsequent crystallizations with CHCl 3 /hexanes resulted in a new triclinic ( P 1 , Z =2) crystalline form, [Fe(OEP)(O 2 C 2 Cl 3 )]·CHCl 3 ; the porphyrin core is slightly ruffled. Crystallization with CH 2 Cl 2 /hexanes resulted in the isolation of yet another form (triclinic, P 1 , Z =4), [Fe(OEP)(O 2 C 2 Cl 3 )]·HO 2 C 2 Cl 3 , which contains two independent molecules in the unit cell; molecule A is modestly ruffled and molecule B is slightly saddled. All conformations form π–π dimers in the solid state. Temperature-dependent magnetic susceptibility measurements showed that [Fe(OEP)(O 2 C 2 Cl 3 )]·CHCl 3 contains a high-spin iron(III) center; the data for [Fe(OEP)(O 2 C 2 Cl 3 )]·HO 2 C 2 Cl 3 are understood in terms of an admixed intermediate-spin state ( S =3/2, 5/2) and are readily fit to a Maltempo model with a ground state multiplet containing about 78% S =5/2 character and 22% S =3/2 character. The structural data for [Fe(OEP)(O 2 C 2 Cl 3 )]·CHCl 3 are consistent with the observed high-spin state, while data for [Fe(OEP)(O 2 C 2 Cl 3 )]·HO 2 C 2 Cl 3 are consistent with the admixed-spin iron(III) character. The observed core conformations have been described by a normal-coordinate structural decomposition method.