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 2 bp4do 2+ as two polymophs of the chloride salt (H 2 bp4do)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 2 Br 8 ] and (H 2 bp4do)(Hbp4do) 4 [Bi 4 Br 18 ]·2H 2 O. The dehydration of this last phase leads to (H 2 bp4do)(Hbp4do) 4 [Bi 4 Br 18 ]. In the structures of (H 2 bp4do)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 2 Br 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.