A radical ion-pair complex exhibiting strong C-H⋯O H-bonding interaction, moderately broaden near-IR absorbance and complicated EPR spectrum

An ion-pair complex of [Ni(mnt)₂]^2- with p-N-benzylpyridinium a-nitronyl nitroxide radical cations (p-BzPYNN) in acetonitrile shows a moderate and broad absorbance in near-IR region. In the crystal of this complex, two radical cations form a dimer via strong H-bonding interaction; such kinds of dimers are connected into H-bonding chain by [Ni(mnt)₂]^2- dianions through weak H-bonding interactions. The neighboring H-bonding chains are arranged into supramolecular sheet via π⋯π stacking interactions between the five-membered chelate-ring of anion and the superimposed pyridyl rings of cations. The polycrystalline EPR spectrum exhibits two isotropic EPR signals. Based on the analyses of crystal structure, variable temperature magnetic susceptibility and electronic spectrum, the stronger EPR signal is assigned to the radical cation, the weaker one probably arises from a trace amount of [Ni(mnt)₂]^1- species.