Remarkably short intermolecular Se⋯Se contacts in Ni(ii) diselenophosphinates: interplay of electrostatic and dispersion forces†

We report the discovery of remarkably short intermolecular Se⋯Se contacts (3.242–3.751 Å) and a novel supramolecular _Se/^Se\_Se/^Se zigzag pattern in Ni(II) diselenophosphinate complexes. The monoclinic polymorph of [Ni(Se₂PPh₂)₂], along with [Ni(Se₂PPh₂)₂(Pz)₂] and the 1D polymer [Ni(Se₂PPPh₂)₂(3,3′-bipy)]_n, exhibit this zigzag pattern with one short (avg. 3.35 Å) and two longer (avg. 3.68 Å) Se⋯Se contacts between adjacent NiP₂Se₄ units. In contrast, the orthorhombic [Ni(Se₂PPh₂)₂] and the 1D polymer [Ni(Se₂PPPh₂)₂(4,4′-bipy)]_n display chain-like intermolecular Se⋯Se contacts of about 3.51 Å. Employing a multifaceted approach, we elucidate the nature of the interactions, distinguishing between the electrostatic and dispersion contributions. Using theoretical methods (DFT-DKH for geometry optimization; electron density, ESP, ELF, and SAPT0 for analysis), we find that short Se⋯Se interactions (<90%∑r_vdW(Se⋯Se)) are governed primarily by dispersion forces, whereas longer Se⋯Se contacts (>90% ∑r_vdW(Se⋯Se)) are mainly attributed to electrostatic forces, typical of σ-hole interactions. Notably, we document an unprecedented Se⋯Se contact of 3.242 Å, which, to our knowledge, is the shortest proven non-covalent Se⋯Se interaction reported to date. This finding not only confirms the existence of Se⋯Se interactions, but also highlights their potential strength and importance in coordination chemistry, an aspect that has not been thoroughly explored in previous studies.