Cephalexin: a channel hydrate

The antibiotic cephalexin systematic name: d ‐7‐(2‐amino‐2‐phenyl­acet­amido)‐3‐methyl‐8‐oxo‐5‐thia‐1‐aza­bi­cyclo­4.2.0]oct‐2‐ene‐2‐carboxyl­ic acid] forms a range of isomorphic solvates, with the maximum hydration state of two water mol­ecules formed only at high relative humidities. The water content of the structure reported here (C₁₆H₁₇N₃O₄S·1.9H₂O) falls just short of this configuration, having three independent cephalexin mol­ecules, one of which is disordered, and 5.72 observed water mol­ecules in the asymmetric unit. The facile nature of the cephalexin solvation/desolvation process is found to be facilitated by a complex channel structure, which allows free movement of solvent in the crystallographic a and b directions.