Alkali metal salts of 4-hydroxybenzoic acid: a structural and educational study

As part of an educational exercise designed to introduce school students the technique single-crystal X-ray diffraction and enhance their understanding primary secondary bonding, a group nine was given opportunity prepare new compounds solve refine data collected on crystalline materials they had prepared. Their investigation alkali metal salts 4-hydroxybenzoic acid (H 2 hba) yielded structures are described in this article. Whilst might be expected have similar atomic arrangements, there significant differences structures. Although H hba is relatively simple organic molecule, it displays remarkable coordinative flexibility, forming ionic solids containing uncharged monoanion Hhba − or dianion 2− . A common feature layered arrangement: alternating hydrophilic layers made up closely packed metal–oxygen polyhedra separated by hydrophobic component hydroxybenzoate linking units. Close packing these units seems dominant influence determining overall structure. The usually both parallel antiparallel with immediate neighbours, that can edge-to-face, face-to-face mixture two. Hydrogen bonding plays key role structure most short strong hydrogen bond (SSHB) observed two networks. acid, C 7 6 O 3 , here are: poly[di-μ-aqua-μ-4-oxidobenzoato-dilithium], [Li (C 4 )(H O) ] n 1 poly[triaqua-μ-4-oxidobenzoato-dilithium], poly[μ-4-hydroxybenzoato-lithium], [Li(C 5 )] catena -poly[4-hydroxybenzoate [[diaquasodium]-di-μ-aqua]], {[Na(H ](C )} poly[di-μ-aqua-aqua-μ-4-hydroxybenzoato-potassium], [K(C poly[μ-aqua-μ-4-hydroxybenzoato-potassium], O)] poly[aqua-μ-4-hydroxybenzoato-rubidium], [Rb(C poly[aqua-μ-4-hydroxybenzoato-caesium], [Cs(C 8 poly[[μ-aqua-aqua(μ-4-hydroxybenzoato)(4-hydroxybenzoic acid)sodium] monohydrate], {[Na(C )(C ]·H O} 9 poly[[(μ-4-hydroxybenzoato)(μ-4-hydroxybenzoic acid)rubidium] {[K(C )]·H 10 {[Rb(C 11