Proton controlled supramolecular assembly: A comparative structural study of bis(2-guanidinobenzimidazolo)nickel(II) with bis(2-guanidinobenzimidazole)nickel(II) nitrate and 2-guanidinobenzimidazole
Mm. Bishop et al., Proton controlled supramolecular assembly: A comparative structural study of bis(2-guanidinobenzimidazolo)nickel(II) with bis(2-guanidinobenzimidazole)nickel(II) nitrate and 2-guanidinobenzimidazole, SUPRAMOL CH, 13(2), 2001, pp. 293-301
Previously studies have shown that when 2-guanidinobenzimidazole complexes
with a number of transition metal ions it tautomerises so that, in contrast
to the free ligand structure, no intermolecular hydrogen bonding between b
ound ligands occurs. In the present study it is demonstrated that ligand de
protonation to yield bis(2-guanidinobenzimidazolo)nickel(II) restores much
of the original hydrogen bonding capability of the uncomplexed ligand. The
structure of this neutral complex is compared to the previously reported st
ructure of its diprotonated derivative, bis(Z-guanidinobenzimidazole)nickel
(II) nitrate, as well as to the structure of the uncomplexed ligand. In con
trast to the dicationic species, the neutral complex exists in two enantiom
eric forms that assemble to form an extended supramolecular lattice, contai
ning channels through its structure. The walls of the channels are made up
of 'strings' of complex molecules and are held in position by hydrogen bond
ing between the bound ligands and dimethyl sulfoxide (solvent) molecules as
well as water molecules. Some of the solvent molecules lie within the chan
nels and some outside. The hydrogen bonding motif responsible for chain for
mation differs from that found in the free ligand structure.