Ion pair charge-transfer salts based on protonated bipyridines and [W(CN)6(bpy)]2- anion-structure and properties

• The salts with protonated bipyridines and [W(CN) 6 (bpy)] 2- were synthesized. • The layered structure of salts were compared to their analogues with alkali metal cations. • The dimethyl substituted bipyridine as a cation shows a 3D dimensionality. • The cation-anion distance was discussed in relation to position of the UV-Vis bands. • The ion-pair-charge-transfer transitions were compared to these found in [W(CN) 8 ] 4− analogues. The series of salts with [W(CN) 6 (bpy)] 2− and protonated 2,2′-bpy (1), 4,4′-bpy (2), 4,4′-dimethyl-2,2′-bpy (4), 5,5′-dimethyl-2,2′-bpy (5), 6,6′-dimethyl-2,2′-bpy (6), and dq (3) as cations (where bpy - bipyridine, dq - diquat dication = 1,1′-ethylene-2,2′-bipyridylium ion) were synthesized and characterized. The single-crystal X-ray crystal structures of five salts were determined and described. In the case of unsubstituted bipyridines, the structural studies have shown the presence of only one doubly protonated cation. In turn, the syntheses with the use of dimethyl substituted bipyridines gave salts with two monoprotonated cations. We found that two methyl substituents, increase the hydrophobic properties of cation and convert 2D structure into 3D one. The spectral characteristic (IR and UV-Vis) is presented and the IPCT transitions are discussed and compared with those observed for analogous [W(CN) 8 ] 4− ion salts. The band shift changes were correlated with the N (anion) -N (cation) distances found in the structures.