Infinite Water Chains Trapped in an Organic Framework Constructed from Melamine with 1,5-Naphthalenedisulfonic Acid via Hydrogen Bonds

Cocrystallizations of melamine (MA) with 1,5-naphthalenedisulfonic acid (H2NDA) from water in
different molar ratios (2:1, 4:1, and 8:1) offer [(HMA+)2(NDA2-)]·4H2O (1), [(HMA+)2(MA)2(NDA2-)]·8H2O (2), and
[(HMA+)2(MA)2(NDA2-)]·10H2O (3), respectively. Among them, sulfonic protons are transferred to the triazine nitrogen
atoms of MA, furnishing hydrogen-bonded anionic [(NDA2-)·H2O]∞ chains. In 1, the adjacent HMA+ cations form
cationic (HMA+)∞ ribbons via pairs of N−H···N hydrogen bonds (

(8) synthon), and the ribbons connect to each
other through NDA2- anions as well as lattice water molecules via hydrogen bonds and C−H···π, π···π, and
electrostatic interactions to form a 3D structure. In 2 and 3, only half of the MA molecules are protonated, resulting
in cationic (MA·HMA+)∞ ribbons via N−H···N hydrogen bonds. In 2, hydrophilic channels (size 3.9 × 6.1 Å2) enclosed
by the NDA2- anions and (MA·HMA+) cations are found to host a pair of zigzag water chains, which are interlinked
through sulfonate oxygen atoms via hydrogen bonds into a double water chain. In 3, similar 1D channels are also
found to accommodate a pair of water chains in each channel via hydrogen bonds.