Conformational diversity in (octaethylporphinato)(trichloroacetato)iron(III) derivatives

Treatment of [Fe(OEP)]2O 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 CHCl3/hexanes resulted in the isolation of a monoclinic (P21/n, Z=4) unsolvated form, [Fe(OEP)(O2C2Cl3)]. This form contains two distinct porphyrin core conformations at the same lattice site; one is domed and the other is ruffled. Subsequent crystallizations with CHCl3/hexanes resulted in a new triclinic (P1̄, Z=2) crystalline form, [Fe(OEP)(O2C2Cl3)]·CHCl3; the porphyrin core is slightly ruffled. Crystallization with CH2Cl2/hexanes resulted in the isolation of yet another form (triclinic, P1̄, Z=4), [Fe(OEP)(O2C2Cl3)]·HO2C2Cl3, 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)(O2C2Cl3)]·CHCl3 contains a high-spin iron(III) center; the data for [Fe(OEP)(O2C2Cl3)]·HO2C2Cl3 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)(O2C2Cl3)]·CHCl3 are consistent with the observed high-spin state, while data for [Fe(OEP)(O2C2Cl3)]·HO2C2Cl3 are consistent with the admixed-spin iron(III) character. The observed core conformations have been described by a normal-coordinate structural decomposition method.