(Quinoline-2-carboxylato-κO)(quinoline-2-carboxylic acid-κO)bis(quinoline-2-carboxylic acid-κ2 N,O)potassium

The K atom in the title complex, [K(C10H6NO2)(C10H7NO2)3], lies on a twofold rotation axis that relates one N,O-chelating quinoline-2-carboxylic acid to the other; their N and O atoms are cis to each other in the distorted octahedral coordination geometry. The K atom is also coordinated by another monodentate quinoline-2-carboxylic acid; the acid is disordered with respect to a monodentate quinoline-2-carboxylate anion; the acid and anion are linked by an O—H⋯O hydrogen bond. An O—H⋯N hydrogen bond links adjacent molecules into a linear chain structure along the a axis.

The K atom in the title complex, [K(C 10 H 6 NO 2 )(C 10 H 7 NO 2 ) 3 ], lies on a twofold rotation axis that relates one N,O-chelating quinoline-2-carboxylic acid to the other; their N and O atoms are cis to each other in the distorted octahedral coordination geometry. The K atom is also coordinated by another monodentate quinoline-2-carboxylic acid; the acid is disordered with respect to a monodentate quinoline-2-carboxylate anion; the acid and anion are linked by an O-HÁ Á ÁO hydrogen bond. An O-HÁ Á ÁN hydrogen bond links adjacent molecules into a linear chain structure along the a axis.

Experimental
Quinoline-2-carboxylic acid (1 mmol, 0.17 g) and methyl-8-hydroxy quinoline (1 mmol, 0.16 g) were dissolved completely in warm acetonitrile; the solution was filtered into a clean beaker for the growth of colorless crystals.
As no potasium salt was used in the attempted co-crystallization of the organic compounds, the potassium in the crystal structure is better attributed to the presence of potassium quinoline-2-carboxylate present in the commercially procured carboxylic acid reagent.

Refinement
Hydrogen atoms were placed in calculated positions (C-H 0.95 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C).
Of the two carboxylic acid hydrogen atoms, that connected to O2 lies on a general position and has full site-occupancy.
That connected to O3 is near the Wyckoff 8c site so that the atom should have only half site-occupancy. The refinement of the two hydrogen atoms with a distance restraint of O-H 0.84±0.01 Å gave satisfactory temperature factors. Fig. 1. Thermal ellipsoid plot (Barbour, 2001) of a portion of the polymeric chain structure of K(C 10 H 6 NO 2 )(C 10 H 7 NO 2 ) 3 at the 70% probability level. Hydrogen atoms are drawn as spheres of arbitrary radius. Symmetry code: i = x, 1 -y, 1/2 -z.