The epoxidation of cyclic alkenes with molecular oxygen was efficiently completed in excellent epoxide yield using a novel ruthenium complex as catalyst under mild reaction conditions.

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The structure of the title pentadentate ligand as its hemi­hydrate, C19H17N5O2·0.5H2O, is different from the structure of a similar tridentate ligand reported previously [Qi et al. (2001). Acta Cryst. E57, o749–o750; Yang et al. (2001). Acta Cryst. E57, o1161–o1162]. The two pyridine side arms are not in the same plane, owing to their rotation around an axis between the pyridine ring and the methyl­ene group. There is an intermolecular hydrogen bond between the ligand and the disordered lattice water mol­ecule.

Key indicatorsSingle-crystal X-ray study T = 294 K Mean '(C±C) = 0.004 A Ê R factor = 0.031 wR factor = 0.072 Data-to-parameter ratio = 17.5For details of how these key indicators were automatically derived from the article, see