Multinuclear magnetic resonance spectroscopy of spin-admixed S = 5/2, 3/2 iron(III) porphyrins

Article abstract of DOI:10.1021/ic00132a023

A variety of synthetic iron(III) porphyrin complexes (Fe^IIIPorX, X = SO₃CF₃^-, ClO₄^-, and C(CN)₃^-) were examined with multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁹F, and ³⁵Cl). Deviations from NMR Curie law behavior, diminished magnetic moments, and characteristic ESR g = 4 values support previous evidence for the quantum-mechanical admixture of S = 5/2 and S - 3/2 states. NMR studies of titrations with the corresponding tetrabutylammonium salts and dipolar shift calculations show the ligands are coordinated rather than ion paired in solution. Solvent studies indicate more S = 5/2 character is present in aromatic solvents than in chlorinated solvents. Although the tricyanomethanide complex is thought to exhibit a "pure" S = 3/2 state in crystalline form, solution measurements are consistent with spin admixture.