Iron(III) and manganese(III) complexes of a pseudocalixarene tetraiminotetraphenol macrocyclic ligand: structure, magnetism and electrochemistry

Abstract

The pseudocalixarene tetraiminotetraphenol macrocyclic ligand H4L has been structurally characterized and used to synthesize the complexes [Fe^III₂L(NO₃)₂(H₂O)₂] (1), [Fe^III₂L(Cl)₂]∞ (2), [{Fe^III₂L(μ-O)}₂]·2CH₃CN·H₂O (3), [Mn^III2L(Cl)₂]·3H2O (4) and [Mn^III2L(OAc)₂]·5H₂O (5). The crystal structures of 3 and 4 have been determined. Variable-temperature (2–295 K) magnetic susceptibility measurements have been carried out for 3 and the data have been fitted to the spin Hamiltonian H = −2JS₁.S₂ with J = −45 cm⁻¹. Cyclic voltammetric measurements carried out for 1 in N,N-dimethylformamide have revealed the presence of two reversible redox couples with E_1/2 = −180 and −280 mV, which coalesced into a single couple with E_1/2 = −220 mV with the addition of excess NaNO₃. The two manganese(III) complexes undergo quasi-reversible reduction in methanol at the same potential with E_1/2 = −240 mV.