Water-Soluble Squaramide Dihydrates: N‑Methylation Modulates the Occurrence of One- and Two-Dimensional Water Clusters through Hydrogen Bonding and Dipolar Interactions

• Published in: Crystal growth & design 2018-08, Vol.18 (8), p.4420-4427
• Main Authors: Ximenis, Marta, Pitarch-Jarque, Javier, Blasco, Salvador, Rotger, Carmen, García-España, Enrique, Costa, Antonio
• Format: Article
• Language: English
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/acs.cgd.8b00401

Water confined in molecular size domains is distinct to bulk water. The altered interactions between adjacent water molecules, and between water molecules and molecular wall components of the confinement system, determine aspects of important phenomena in material science, biology, and nanotechnology. The structural determination of confined water, however, has proven to be challenging. Here, we describe the crystal structures of three related squaramides 1–3 whose molecular structures are modulated by the gradual incorporation of N-methyl groups to the squaramide moiety. The three squaramides differ in their hydrogen bonding capabilities due to the different degree of N-methylation of each one. Thus, while 1·2H2O forms narrow tapes of water molecules, the monomethylated squaramide 2·2H2O produces two-dimensional water layers, and the dimethylated squaramide 3·2H2O develops polymeric one-dimensional water chains. Our observations show that N-methylation heavily alters the interplay between H-bonding and dipolar stacking, the two supramolecular interactions that govern the structural arrangement of squaramides 1–3, hence modulating the arrangement of the water molecules within the crystals.