Stereochemistry of the Diquat Ion in the Crystalline Dibromide Salt

The crystal and molecular structure of dipyrido[1,2-a:2',1'-c]pyrazinium dibromide monohydrate

“…The C-N+-C angles within the pyridinium rings are slightly greater than 120 ° in agreement with previous results (Singh, 1965;Hanic, 1966;Colleter & Gadret, 1968;Derry & Hamor, 1969).…”

“…Nevertheless, the observed bond lengths can be rationalized to some extent in terms of the five possible non-excited valence bond structures [formulae (I) and (IV), together with the three other canonicals * Even if the cation is involved in (unsymmetrical) charge transfer interactions with the bromide ions, these would not be expected to lead to measurable changes in the dimensions of the cation (Prout & Murray-Rust, 1969). Thus the carbon-nitrogen bond lengths of 1.365 to 1.40A are greater than those found in pyridinium derivatives such as pyridoxine hydrochloride (Hanic, 1966), ethionamide hydrochloride (Colleter & Gadret, 1968), diquat dibromide (Derry & Hamor, 1969), 1,1'-tetramethylene-2,2'-bipyridylium dibromide (Derry & Hamor, 1970), and paraquat salts with chlorometallate anions (Prout & Murray-Rust, 1969;Russell & Wallwork, 1969), where they range from 1.33 to 1.36A, but are shorter than the standard C(aromatic)-N single bond length of 1.43.~, (Sutton, 1965).…”

“…The relationship between stereochemistry and herbicidal activity in bipyridylium salts has been discussed by Boon (1964Boon ( , 1967 and the crystal structures of diquat dibromide and the inactive tetramethylene analogue (Ill) have been determined and reported in preliminary form (Derry & Hamor, 1969. In this paper we describe the crystal structure of (I) as part of our programme of structural investigations on 2,2'-bipyridylium salts.…”

Competitive and non-competitive adsorption/desorption of paraquat, diquat and difenzoquat in vineyard-devoted soils

“…A planar conformation is more stable in the reduced form than a twisted one, because the bond connecting the two pyridinium rings bears more double-bond character in the reduced form than in the oxidized form [23]. The diquat ion is, in the same way, not strictly planar [24]; the dihedral angle between the rings is −20 • [25]. Instead, DFQ has not planar structure.…”

Diquats with Robust Chirality: Facile Resolution, Synthesis of Chiral Dyes, and Application as Selectors in Chiral Analysis

“…[1] Electrond eficient systemsb ased on diquat and paraquat [2] have been also instrumental as buildingb locks for supramolecular chemistry, [3] as well as in the design of electron-transfer systems. [1] Electrond eficient systemsb ased on diquat and paraquat [2] have been also instrumental as buildingb locks for supramolecular chemistry, [3] as well as in the design of electron-transfer systems.…”