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 (H 2 NDA) from water in different molar ratios (2:1, 4:1, and 8:1) offer [(HMA + ) 2 (NDA 2- )]·4H 2 O ( 1 ), [(HMA + ) 2 (MA) 2 (NDA 2- )]·8H 2 O ( 2 ), and [(HMA + ) 2 (MA) 2 (NDA 2- )]·10H 2 O ( 3 ), respectively. Among them, sulfonic protons are transferred to the triazine nitrogen atoms of MA, furnishing hydrogen-bonded anionic [(NDA 2- )·H 2 O] ∞ 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 NDA 2- 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 Å 2 ) enclosed by the NDA 2- 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.