Alkali metal compounds of hydroquinone: Synthesis and crystal structure

A number of novel routes to the alkali metal compounds of hydroquinone M-2[p-C6H4O2] (M = Li, Na, K, Rb, Cs) and M[p-C6H4O(OH)] (M = K, Rb, Cs) have been synthetically explored. The selective synthesis of the alkali 4-hydroxyphenolates and 1,4-phenylenediolates is based on optimized reaction conditions (solvents, temperatures). All compounds were structurally characterized by means of powder X-ray diffraction using Rietveld profile refinement including C-C and C-O bond distance restraints. The atomic arrangement of M-2[p-C6H4O2] (M = Na, K) (tetragonal, space group: P4(2)/ncm) is characterized by infinite pillars of (1)(infinity)[(M2O2[3])-O-[3]]-units along the c axis connected by [p-C6H4O2](2-) -anions with stacking direction along c. The coordinatively unsaturated alkali metals, surrounded by three oxygen atoms, exhibit symmetrical (K) as well as asymmetrical (Na) interactions with the phenylene rings. M[p-C6H4O(OH] (M = K, Rb) (tetragonal, space group: P4/n) forms hydrogen-bridged linear chains of [p-C6H4O(OH)](-)-anions along the c direction. The phenylene planes of neighboring chains have an almost orthogonal arrangement while the interchain planes are parallel. K and Rb are fourfold coordinated by two different oxygen coordination spheres.