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

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 - bipyri-dine, 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 unsub-stituted 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. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Automated summary

A series of salts containing [W(CN)(6)(bpy)](2-) and protonated pyridine-based cations were synthesized and characterized. The structures of five salts were determined using single-crystal X-ray diffraction. It was found that unsubstituted pyridine-based salts have a single doubly protonated cation, while salts with dimethyl-substituted pyridines have two monoprotonated cations. Furthermore, the introduction of two methyl substituents increased the hydrophobicity of the cation and transformed the 2D structure into a 3D structure. The spectral characteristics (IR and UV-Vis) were presented and the IPCT transitions were discussed and compared with analogous [W(CN)(8)](4-) ion salts.