Hydrogen Bonds Regulate Paramagnetic Spin Delocalization in Ferric Hemes

However, systematic control over hydrogen-bond-mediated spin delocalization has not been achieved in a synthetic system. Here, we combine experiment and theory to demonstrate that hydrogen bonds provide a tunable pathway for spin delocalization from a paramagnetic iron center into the distal secondary coordination sphere.

Using a series of five-coordinate biphenolato Fe(III) porphyrin complexes with systematically varied hydrogen-bond strengths, we establish a well-defined noncovalent framework for controlling spin propagation. Paramagnetic ¹H and ¹⁹F NMR spectroscopy reveals pronounced hyperfine shifts within the hydrogen-bonded distal environment, whereas no measurable spin delocalization is detected in analogous complexes lacking hydrogen bonds.