Selenadiazolopyridine: A Synthon for Supramolecular Assembly and Complexes with Metallophilic Interactions

The synthesis and characterization of the complexes of Cu­(I), Ag­(I), Cu­(II), and Co­(II) ions with 1,2,5-selenadiazolopyridine (psd) is reported. The following complexes have been prepared: [Cu<sub>2</sub>(psd)<sub>3</sub>(CH<sub>3</sub>CN)<sub>2</sub>]<sup>2+</sup>2­(PF<sub>6</sub><sup>–</sup>); [(CuCl)<sub>2</sub>(psd)<sub>3</sub>]; [Cu<sub>2</sub>(psd)<sub>6</sub>]<sup>2+</sup>2­(ClO<sub>4</sub>)<sup>−</sup>; [Ag<sub>2</sub>(psd)<sub>2</sub>]<sup>2+</sup>2­(NO<sub>3</sub>)<sup>−</sup>; [Ag<sub>2</sub>(psd)<sub>2</sub>]<sup>2+</sup>2­(CF<sub>3</sub>COO)<sup>−</sup>; [Cu­(psd)<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub>]<sup>2+</sup>2­(ClO<sub>4</sub>)<sup>−</sup>·(psd)<sub>2</sub>; [Cu­(psd)<sub>4</sub>(H<sub>2</sub>O)]<sup>2+</sup>2­(ClO<sub>4</sub>)<sup>−</sup>·(CHCl<sub>3</sub>); [Cu­(psd)<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub>]<sup>2+</sup>2­(NO<sub>3</sub>)<sup>−</sup>·(H<sub>2</sub>O)·(psd)<sub>2</sub>, and [Co­(psd)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]<sup>2+</sup>2­(ClO<sub>4</sub>)<sup>−</sup>·(psd)<sub>2</sub>. The electronic structure of ligand psd, in particular the bond order of Se–N bonds, has been probed by X-ray diffraction, <sup>77</sup>Se NMR, and computational studies. A detailed analysis of the crystal structures of the ligand and the complexes revealed interesting supramolecular assembly. The assembly was further facilitated by the presence of neutral ligands for some complexes (Cu­(II) and Co­(II)). The molecular structure of the ligand showed that it was present as a dimer in the solid state where the monomers were linked by strong secondary bonding Se···N interactions. The crystal structures of Cu­(I) and Ag­(I) complexes revealed the dinuclear nature with characteristic metallophilic interactions [M···M] (M = Cu, Ag), while the Cu­(II) and Co­(II) complexes were mononuclear. The presence of M···M interactions has been further probed by Atoms in Molecules (AIM) calculations. The paramagnetic Cu­(II) and Co­(II) complexes have been characterized by UV–vis, ESI spectroscopy, and room temperature magnetic measurements.