Picrate salts with bipyridine derivatives: intramolecular and intermolecular aspects.

Here, we present the preparation and characterization of two novel picrate salts. The 2,2′-bis(pyridinium)ketone picrate, DPK-PA (1), crystallizes in the triclinic system and centrosymmetric space group P 1 ¯ , with unit cell parameters a = 9.378(17) Å, b = 9.790(15) Å, c = 10.141(16) Å, α = 99.63(7)°, β = 99.09(8)°, and γ = 102.55(8)°, while the 4,4′-bis(tert-butyl)-2-pyridine-2-pyridinium picrate, BBBPY-PA (2), crystallizes in the non-centrosymmetric P212121 space group, orthorhombic unit cell parameters a = 6.3902(6) Å, b = 23.416(3) Å, and c = 16.7320(18) Å. Both crystal structures present an ion-pair in the asymmetric unit, one picrate anion, and one bipyridine derivative. In the DPK-PA (1) structure, the molecule of DPK presents one intramolecular N1-H ⋯ N H-bond that contributes to stabilizing the planar conformation of DPK. The absence of intramolecular H-bonding in the BBBPY-PA (2) can be explained by the steric hindrance of the tert-butyl group. For DPK-PA (1) and BBBPY-PA (2), the crystal packing is stabilized N–H ⋯ O strong hydrogen bonding interactions, which could be identified by the Hirshfeld surface analysis and fingerprint plots. The compounds were also studied by UV–Vis and infrared analyses, which may support the statement of the formation of new material. Finally, as an attempt to obtain a molecular system to act as a chemical sensor, we studied the fluorescence of both compounds, in solution and in solid state; however, no fluorescence was observed. [ABSTRACT FROM AUTHOR]