Structure determination of a twinned Rb(H₂NC₁₀H₆SO₃) · H₂O crystal and comparison to related alkali metal aminonaphthalenesulfonates

Rb(H₂NC₁₀H₆SO₃)·H ₂O crystallizes in space group P2₁ with two formula units in the asymmetric unit, the crystal being twinned by a 180° rotation about [1 0 0]. The structure was determined from X-ray diffraction data, and refined, based on two twin components, to yield a final R value of 0.0557 for 2754 reflections. The structure consists of alternating layers of aminonaphthalenesulfonate and rubidium ions. There are two distinct rubidium environments, the metal ions linked by the sulfonate groups and bridging water molecules into an infinite sheet. The sulfonate groups are bidentate, monodentate and bridging, all oxygen atoms being bound to at least one metal. The amino groups do not participate in coordination to the metal. Aromatic moieties from neighboring hydrophilic metallo-layers interleave to form the hydrophobic layers. There is some similarity to the analogous sodium and potassium structures, however the rubidium compound is distinguished by an infinite cationic layer, rather than columns observed for the other two structures.