Protonated N,N'-Dioxide-4,4'-bipyridine, an Interesting Synthon for the Building of Polar H-Bonded Networks?

A slow liquid-gas diffusion method in strong acid conditions has allowed stabilizing for the first time in the solid state the diprotonated form of the 4,4′-bipyridine-N,N′-dioxide (bp4do), H 2bp4do 2+ as two polymophs of the chloride salt (H 2bp4do)Cl 2, while in the presence of a metallic salt M (III)Br 3 (M = Bi, Sb), the monoprotonated form Hbp4do + is mainly stabilized as (Hbp4do) 2[Sb 2Br 8] and (H 2bp4do)(Hbp4do) 4[Bi 4Br 18] •2H 2O. The dehydration of this last phase leads to (H 2bp4do)(Hbp4do) 4[Bi 4Br 18]. In the structures of (H 2bp4do)Cl 2 salts, the hydroxyl H atoms point toward the chloride anions leading to close (O)H•••Cl contacts in the range 1.831-1.839 Å. A one-dimensional network of H-bonded Hbp4do + cations is found in the structure of (Hbp4do) 2[Sb 2Br 8], whereas H-bonded supramolecular cations of five entities are found in the structures of bromobismuthate salts. In all the halometallate structures, X-ray analyses (293 K and 120 K data) did not allow us to locate the acid H atoms of protonated bp4do molecules certainly due to a disorder phenomenon but also revealing an asymmetrical H-bonding situation. The bromobismuthate hybrids are nonlinear optical active with a powder second harmonic generation efficiency being half that of urea.