Alkali-metal complexes. Part 8. Crystal structures of potassium quinolin-8-olate–quinolin-8-ol(1/1) and –quinolin-8-ol(1/2)

Abstract

The crystal structures of the complexes K(quin)·Hquin (1) and K(quin)·2Hquin (2)(Hquin = quinolin-8-ol) have been determined. Crystals of (1) are monoclinic, with a= 6.375(3), b= 12.616(3), c= 19.366(4)Å, β= 90.76(4)°, Z= 4, and space group P2₁/c; full-matrix least-squares refinement with isotropic vibration parameters for the hydrogen atoms has given an R factor of 0.076 5 for 1 302 reflections. The structure consists of centrosymmetrical dimers in which each potassium ion is six-co-ordinated by a chelating anion and by two chelated neutral molecules, the oxygen and nitrogen atoms of the last molecules being shared with the other potassium ion in the dimer. The dimers are held in chains along the a axis by centrosymmetric pairs of short, but not symmetric, O–H ⋯ O hydrogen bonds (O–H 0.92, H ⋯ O 1.52, and O ⋯ O 2.430 Å). Complex (2) is triclinic, with a= 7.601(4), b= 11.803(3), c= 14.108(3)Å, α= 70.42(1), β= 104.51(3), γ= 104.27(3)°, Z= 2, and space group P. Least-squares refinement with isotropic vibration parameters for hydrogen and anisotropic vibration parameters for the other atoms has led to R= 0.068 3 for 1 935 observations. In the centrosymmetrical dimeric molecules each potassium ion is seven-co-ordinate approximately in a pentagonal bipyramid. The equatorial plane is formed by two nearly parallel neutral chelating molecules and by the nitrogen atom of the chelating anion, the oxygen atom of which forms one apex of the pentagonal bipyramid. The other apex is occupied by a nitrogen atom of a neutral ligand in the other half of the dimer. Both of the hydrogen atoms on the chelating neutral molecules of one potassium ion are directed towards the same anionic oxygen in a neighbouring molecule across a centre of symmetry (O ⋯ O 2.599 and 2.566 Å). Thus, alternate centres of symmetry along the a axis relate (i) the co-ordination dimmers, and (ii) two pairs of hydrogen bonds. Because the neutral molecules are approximately parallel these contacts are reinforced by stacking effects.