4,15-Dimethyl-7,12-diazo-niatri-cyclo-[,7]hexa-deca-1(12),2,4,6,13,15-hexa-ene dibromide monohydrate

Acta Crystallogr E Crystallogr Commun. 2020 Aug 18;76(Pt 9):1467-1471. doi: 10.1107/S2056989020011147. eCollection 2020 Sep 1.


The title compound, C16H20N2 2+·2Br-·H2O (1) is a member of the class of compounds called viologens. Viologens are quaternary salts of di-pyridyls and are especially useful as redox indicators as a result of their large negative one-electron reduction potentials. Compound 1 consists of a dication composed of a pair of 4-methyl-pyridine rings mutually joined at the 2-position, with a dihedral angle between the pyridine rings of 62.35 (4)°. In addition, the rings are tethered via the pyridine nitro-gen atoms by a tetra-methyl-ene bridge. Charge balance is provided by a pair of bromide anions, which are hydrogen bonded to a single water mol-ecule [D O⋯Br = 3.3670 (15) and 3.3856 (15) Å]. The crystal structure of 1, details of an improved synthesis, and a full analysis of its NMR spectra are presented.

Keywords: atropisomer; crystal structure; synthesis; viologen.

Grant support

This work was funded by NSF grant CHE1625732 to Sean Parkin.