Charge transfer complexes of diquat and paraquat with halide anions

• Published in: Canadian journal of chemistry 1987-10, Vol.65 (10), p.2425-2427
• Main Authors: Bertolotti, S. G, Cosa, J. J, Gsponer, H. E, Previtali, C. M
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts: preparations and properties; Catalytic reactions; Chemistry; Exact sciences and technology; General and physical chemistry; General. Nomenclature, chemical documentation, computer chemistry; Theory of reactions, general kinetics; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v87-404

The association of methylviologen, 1,1′-dimethyl-4,4′-bipyridynium (PQ 2+ ), with halide and pseudo-halide ions was studied in water at 25 °C by ultraviolet spectrophotometry. A charge transfer band could be observed in the region around 300 nm. From difference absorption measurements the first association constant (K 1 ,) was obtained as 1.7 (Cl − ), 3.3 (Br − ), 3.9 (I − ), 0.7 (CN − ), and 2.0(SCN − ) M −1 . Similar results were obtained for the dication, 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinium (DQ 2+ ), with first association constants 3.3 (Cl − ), 4.1 (Br − ) and 4.6 (I − ) M −1 . First and second (K 2 ) association constants were also determined by a potentiometric technique using ion selective electrodes: K 1  = 2.0 M −1 ; K 2  = 0.4 M −1 for the system PQ 2+ -Cl − and K 1  = 5.3 M −1 ; K 2  = 0.3 M −1 for DQ 2+ Br − .