Electron spin resonance (ESR) spectroscopy is a crucial tool, through spin labelling, in investigations of the chemical structure of materials and of the electronic structure of materials associated with unpaired spins. ESR spectra measured in molecular systems, however, are established on large ensembles of spins and usually require a complicated structural analysis. Recently, the combination of scanning tunnelling microscopy with ESR has proved to be a powerful tool to image and coherently control individual atomic spins on surfaces. Here we extend this technique to single coordination complexes—iron phthalocyanines (FePc)—and investigate the magnetic interactions between their molecular spin with either another molecular spin (in FePc–FePc dimers) or an atomic spin (in FePc–Ti pairs). We show that the molecular spin density of FePc is both localized at the central Fe atom and also distributed to the ligands (Pc), which yields a strongly molecular-geometry-dependent exchange coupling.

电子自旋共振 (ESR) 光谱是通过自旋标记研究材料化学结构和与不成对自旋相关的材料电子结构的重要工具。然而，在分子系统中测量的 ESR 光谱建立在大型自旋集合上，通常需要复杂的结构分析。最近，扫描隧道显微镜与 ESR 的结合已被证明是成像和连贯控制表面上单个原子自旋的强大工具。在这里，我们将这项技术扩展到单配位配合物——铁酞菁（FePc）——并研究它们的分子自旋与另一个分子自旋（在 FePc-FePc 二聚体中）或原子自旋（在 FePc-Ti 对中）之间的磁相互作用。