Hydrogen Bonding in the Water Stabilized Structure of the Modified Unsymmetrically Substituted Viologen Chromophore, N-ethyl-N′-(2-phosphonoethyl)-4,4′-bipyridylium Dichloride

Abstract

The crystal structure of the modified unsymmetrically N,N′-substituted viologen chromophore, N-ethyl-N′-(2-phosphonoethyl)-4,4′-bipyridinium dichloride 0.75 hydrate (1) has been determined. Crystals are triclinic, space group P−1 with Z = 2 in a cell with a = 7.2550(1), b = 13.2038(5), c = 18.5752(7) A, α = 86.495(3), β = 83.527(2), γ = 88.921(2)°. The two independent but pseudo-symmetrically related cations in the asymmetric unit form one-dimensional hydrogen-bonded chains through short homomeric phosphonic acid O–H···O links [2.455(4), 2.464(4) A] while two of the chloride anions are similarly strongly linked to phosphonic acid groups [O–H···Cl, 2.889(4), 2.896(4) A]. The other two chloride anions together with the two water molecules of solvation (one with partial occupancy) form unusual cyclic hydrogen-bonded bis(Cl···water) dianion units which lie between the layers of bipyridylium rings of the cation chain structures with which they are weakly associated. The crystal structure determination of unsymmetrically substituted viologen N-ethyl-N′-(2-phosphonoethyl)-4,4′-bipyridylium dichloride 0.75 hydrate shows the presence of strong intermolecular phosphonate O–H···O and O–H···Cl interactions together with unusual cyclic hydrogen-bonded bis(chloride···water) dianion units giving one-dimensional chain structures.