Remarkably short intermolecular Se···Se contacts in Ni(II) diselenophosphinates: interplay of electrostatic and dispersion

Abstract

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 electrostatic and dispersion contributions. Using theoretical methods (DFT-DKH for geometry optimization; electron density, ESP, ELF, SAPT0 for analysis), we find that short Se···Se interactions (< 90%ΣrvdW(Se···Se)) are governed primarily by dispersion forces, whereas longer Se···Se contacts (> 90% ΣrvdW(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.