The crystal structure of a complex formed from isonitrosoacetophenone and potassium o-nitrophenolate having the formula KC₆H₄(NO₂)OHONCHC(O)C₆H₅ has been determined. The crystals are monoclinic and have space group P2₁/c with Z= 4, a= 10·826(4), b= 5·581(3), c= 24·559(10)Å, and β= 102°4′(1′). 1557 independent reflections collected on an automatic diffractometer were used to refine the structure by full-matrix least-squares methods to a conventional R of 0·053.

The potassium is surrounded by eight electron-rich atoms of the ligands. Seven of these are oxygen atoms and one is the oxime-nitrogen atom. The two ligands may be regarded as chelates; the o-nitrophenol forms a six-membered ring and the isonitrosoacetophenone ligand makes a five-membered ring by the interaction of the potassium ion with the keto-oxygen atom and the oxime-nitrogen atom. Two oxygen atoms from the o-nitrophenolate interact with two symmetry-related potassium ions and thereby form a polymeric sequence parallel to the b-axis. The o-nitrophenolate is connected to the isonitrosoacetophenone by an apparently symmetrical hydrogen bond of length 2·51 Å. The dimensions of the o-nitrophenolate ligand indicate a significant contribution of a quinonoid form.