Hydrate Stabilization in the Three-Dimensional Hydrogen-Bonded Structure of the Brucinium Compound, Bis(2,3-dimethoxy-10-oxostrychnidinium) Biphenyl-4,4′-disulfonate Hexahydrate

Abstract

The crystal structure of the 2:1 proton-transfer compound of brucine with biphenyl-4,4 ′ -disulfonate, bis(2,3-dimethoxy-10-oxostrychnidinium) biphenyl-4,4 ′ -disulfonate hexahydrate (1) has been determined at 173 K. Crystals are monoclinic, space group P2₁ with Z = 2 in a cell with a = 8.0314(2), b = 29.3062(9), c = 12.2625(3) Å, β = 101.331(2)°. The crystallographic asymmetric unit comprises two brucinium cations, a biphenyl-4,4 ′ -disulfonate dianion and six water molecules of solvation. The brucinium cations form a variant of the common undulating and overlapping head-to-tail sheet sub-structure. The sulfonate dianions are also linked head-to-tail by hydrogen bonds into parallel zig-zag chains through clusters of six water molecules of which five are inter-associated, featuring conjoint cyclic eight-membered hydrogen-bonded rings [graph sets R ³₃ (8) and R ³₄ (8)], comprising four of the water molecules and closed by sulfonate O acceptors. These chain structures occupy the cavities between the brucinium cation sheets and are linked to them peripherally through both brucine N⁺–H···O_sulfonate and O_carbonyl···H–O_water to sulfonate O bridging hydrogen bonds, forming an overall three-dimensional framework structure. This structure determination confirms the importance of water in the stabilization of certain brucine compounds which have inherent crystal instability.

Graphical Abstract

The crystal structure determination of the 2:1 proton-transfer brucinium compound, bis(2,3-dimethoxy-10-oxostrychnidinium) biphenyl-4,4′-disulfonate hexahydrate shows the presence of two independent brucinium cations which form into semi-associated sheet substructures. The disulfonate dianions and the associated water molecules of solvation occupy the interstitial cavities between the brucinium substructures with which they are hydrogen-bonded, giving a three-dimensional framework structure.