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

Treatment of [Fe(OEP)](2)O with trichloroacetic acid (2.5-fold excess) resu lts in the formation of (octaethylporphinato)(trichloroacetato)iron(III). V arious crystalline solvates can be isolated, depending on the crystallizati on solvent. Initial crystallization with CHCl3/hexanes resulted in the isol ation of a monoclinic (P2(1)/n, Z = 4) unsolvated form, [Fe(OEP)(O2C2Cl3)]. This form contains two distinct porphyrin core conformations at the same l attice site; one is domed and the other is ruffled. Subsequent crystallizat ions with CHCl3/hexanes resulted in a new triclinic (P (1) over bar, Z=2) c rystalline form, [Fe(OEP)(O2C2CL2)]. CHCl3; the porphyrin core is slightly ruffled. Crystallization with CH,Cl,/hexanes resulted in the isolation of y et another form (triclinic, P (1) over bar, Z = 4), [Fe(OEP)(O2C2Cl3)]. HO2 C2Cl3, which contains two independent molecules in the unit cell; molecule A is modestly ruffled and molecule B is slightly saddled. All conformations form pi--pi: dimers in the solid state. Temperature-dependent magnetic sus ceptibility measurements showed that [Fe(OEP)(O2C2Cl3)]. CHCl3 contains a h igh-spin iron(III) center; the data for [Fe(OEP)(O2C2Cl3)]. HO2C2Cl3 are un derstood in terms of an admired intermediate-spin state (S = 3/2, 5/2) and are readily fit to a Maltempo model with a ground state multiplet containin g about 78% S = 5/2 character and 22% S = 3/2 character. The structural dat a for [Fe(OEP)(O2C2Cl3)]. CHCl3 are consistent with the observed high-spin state, while data for [Fe(OEP)(O2C2Cl3)]. HO2C2Cl3 are consistent with the admired-spin iron(III) character. The observed core conformations have been described by a normal-coordinate structural decomposition method. (C) 1999 Elsevier Science S.A. All rights reserved.