Synthesis and Electronic Structure of a Tetraazanaphthalene Radical-Bridged Yttrium Complex

Taming radical anions with highly electropositive metal ions poses a grand synthetic challenge owing to the high reactivity of such compounds originating from the unpaired electron. A successful synthetic metal radical match elicits a desire to thoroughly understand the electronic structure of a given metal radical pairing, which may inform about the potential physical properties pertaining to spintronics and magnetism relevant for future technologies. Here, the 1,4,5,8-tetraazanaphthalene (tan) ligand was utilized in the synthesis of (Cp*₂Y)₂(μ-tan), 1, using the doubly reduced version K₂tan and Cp*₂Y-(BPh₄) following a salt metathesis reaction. Chemical oxidation of 1 yielded [(Cp*₂Y)₂(μ-tan^•)]-[BArF₂₀], 2, containing a tan^-• radical anion. 2 constitutes the first d-block coordination compound bearing a tan radical. 1 and 2 were studied through X-ray crystallography, electrochemistry, and spectroscopy. The radical nature of 2 was uncovered by cw-EPR spectroscopy and density functional theory (DFT) computations. All findings suggest major changes in the spin and charge distributions of this organic radical ligand when it is metalated. In fact, the results demonstrate that the tan^-• radical is more stable when coordinated to a transition metal than in its free nature, and thus, this insight is relevant for the development of future spintronic technologies.