Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, Prague 6 16610, Czech Republic.
J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague 8 18223, Czech Republic.
J Phys Chem A. 2021 Mar 25;125(11):2276-2283. doi: 10.1021/acs.jpca.0c11237. Epub 2021 Mar 16.
Complexes with two or more magnetically coupled metal ions have attracted considerable attention as catalysts of many vital processes, single-molecule magnets, or spin-crossover compounds. Elucidation of their electronic structures is essential for understanding their catalytic and magnetic properties. Here, we provide an unprecedented insight into exchange-coupling mechanisms between the magnetic centers in six prototypical bis-μ-oxo bimetallic MO complexes, including two biologically relevant models of non-heme iron enzymes. Employing multiconfigurational/multireference methods and related orbital entanglement analysis, we revealed the essential and counterintuitive role of predominantly unoccupied valence metal d orbitals in their strong antiferromagnetic coupling. We found that the participation of these orbitals is twofold. First, they enhance the superexchange between the singly occupied d orbitals. Second, they become substantially occupied and thus directly magnetically active, which we perceive as a new mechanism of the exchange interaction between the magnetic transition metal centers.
具有两个或更多磁耦合金属离子的配合物作为许多重要过程的催化剂、单分子磁铁或自旋交叉化合物引起了相当大的关注。阐明它们的电子结构对于理解它们的催化和磁性质是至关重要的。在这里，我们对六种典型的双 μ-氧桥联双金属 MO 配合物中磁心之间的交换耦合机制提供了前所未有的深入了解，其中包括两个非血红素铁酶的生物相关模型。我们采用多组态/多参考方法和相关的轨道纠缠分析，揭示了主要为空的价金属 d 轨道在其强反铁磁耦合中的重要和违反直觉的作用。我们发现这些轨道的参与有两个方面。首先，它们增强了单占据 d 轨道之间的超交换。其次，它们变得实质性地占据，从而直接具有磁性活性，我们认为这是磁过渡金属中心之间交换相互作用的新机制。
