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 alpha= 9.378(17) angstrom, b= 9.790(15) angstrom, c= 10.141(16) angstrom, alpha=99.63(7)degrees, beta= 99.09(8)degrees, and gamma= 102.55(8)degrees, while the 4,4 '-bis(tert-butyl)-2-pyridine-2-pyridinium picrate, BBBPY-PA (2), crystallizes in the non-centrosymmetric P2(1)2(1)2(1) space group, orthorhombic unit cell parameters alpha= 6.3902(6) angstrom, b= 23.416(3) angstrom, and c = 16.7320(18) angstrom. Both crystal structures present an ion-pair in the asym-metric 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 Hir-shfeld 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.