An unusual two-dimensional hydrogen-bonding network in bis(2,9-dimethyl-1,10-phenanthrolin-1-ium) peroxodisulfate dihydrate.

The title compound, 2C(14)H(13)N(2)(+).S(2)O(8)(2-).2H(2)O, is a protonated amine salt which is formed from two rather uncommon ionic species, namely a peroxodisulfate (pds(2-)) anion, which lies across a crystallographic inversion centre, and a 2,9-dimethyl-1,10-phenanthrolin-1-ium (Hdmph(+)) cation lying in a general position. Each pds(2-) anion binds to two water molecules through strong water-peroxo O-H...O interactions, giving rise to an unprecedented planar network of hydrogen-bonded macrocycles which run parallel to (100). The atoms of the large R(8)(8)(30) rings are provided by four water molecules bridging in fully extended form (...H-O-H...) and four pds(2-) anions alternately acting as long (...O-S-O-O-S-O...) and short (...O-S-O...) bridges. The Hdmph(+) cations, in turn, bind to these units through hydrogen bonds involving their protonated N atoms. In addition, the crystal structure also contains pi-pi and aromatic-peroxo C-H...O interactions.