Acemetacin monohydrate

The structure of the title compound (systematic name: 2-{2-[1-(4-chloro­benzo­yl)-5-meth­oxy-2-methyl-1H-indol-3-yl]acet­oxy}­acetic acid monohydrate, C₂₁H₁₈ClNO₆·H₂O) contains one-dimensional infinite hydrogen-bonded chains. Mol­ecules of acemetacin, a nonsteroidal anti-inflammatory drug, and water are linked by three independent O—H...O bonds. The central unit in each chain consists of a sequence of alternating centrosymmetric R₄⁴(12) and R₄⁴(18) rings, which are edge-fused. Each ring links two acemetacin and two water mol­ecules. A comparison with seven related structures reveals that mol­ecules of acemetacin, indomethacin and their analogues can adopt two principal conformations.