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As part of an educational exercise designed to introduce school students to the technique of single‐crystal X‐ray diffraction and enhance their understanding of primary and secondary bonding, a group of nine secondary school students was given the opportunity to prepare new compounds and to solve and refine data collected on the crystalline materials they had prepared. Their investigation of the alkali metal salts of 4‐hydroxybenzoic acid (H2hba) yielded nine new compounds and their structures are described in this article. Whilst the salts might be expected to have similar atomic arrangements, there are significant differences in their structures. Although H2hba is a relatively simple organic molecule, it displays remarkable coordinative flexibility, forming ionic solids containing the uncharged molecule, the monoanion Hhba− or the dianion hba2−. A common feature of the structures is their layered arrangement: alternating hydrophilic layers made up of closely packed metal–oxygen polyhedra separated by the hydrophobic component of the hydroxybenzoate linking units. Close packing of these units seems to be a dominant influence in determining the overall structure. The hydroxybenzoate units are usually both parallel and antiparallel with their immediate neighbours, with packing that can be edge‐to‐face, face‐to‐face or a mixture of the two. Hydrogen bonding plays a key role in the structure of most compounds and a short strong hydrogen bond (SSHB) is observed in two of the networks. The compounds of 4‐hydroxybenzoic acid, C7H6O3, described here are: poly[di‐μ‐aqua‐μ‐4‐oxidobenzoato‐dilithium], [Li2(C7H4O3)(H2O)2]n, 1, poly[triaqua‐μ‐4‐oxidobenzoato‐dilithium], [Li2(C7H4O3)(H2O)3]n, 2, poly[μ‐4‐hydroxybenzoato‐lithium], [Li(C7H5O3)]n, 3, catena‐poly[4‐hydroxybenzoate [[diaquasodium]‐di‐μ‐aqua]], {[Na(H2O)4](C7H5O3)}n, 4, poly[di‐μ‐aqua‐aqua‐μ‐4‐hydroxybenzoato‐potassium], [K(C7H5O3)(H2O)3]n, 5, poly[μ‐aqua‐μ‐4‐hydroxybenzoato‐potassium], [K(C7H5O3)(H2O)]n, 6, poly[aqua‐μ‐4‐hydroxybenzoato‐rubidium], [Rb(C7H5O3)(H2O)]n, 7, poly[aqua‐μ‐4‐hydroxybenzoato‐caesium], [Cs(C7H5O3)(H2O)]n, 8, poly[[μ‐aqua‐aqua(μ‐4‐hydroxybenzoato)(4‐hydroxybenzoic acid)sodium] monohydrate], {[Na(C7H5O3)(C7H6O3)(H2O)2]·H2O}n, 9, poly[[(μ‐4‐hydroxybenzoato)(μ‐4‐hydroxybenzoic acid)rubidium] monohydrate], {[K(C7H5O3)(C7H6O3)]·H2O}n, 10, and poly[[(μ‐4‐hydroxybenzoato)(μ‐4‐hydroxybenzoic acid)rubidium] monohydrate], {[Rb(C7H5O3)(C7H6O3)]·H2O}n, 11. [ABSTRACT FROM AUTHOR]

A new piperazine-derived ligand has been prepared and used to synthesise a porous coordination polymer which displays selective carbon dioxide uptake after solvent exchange and thermal activation. The ligand N,N′-bis(4-carboxyphenylmethylene)piperazine H2L1 was prepared from piperazine in three steps and good yield. A structure containing the deprotonated form K2L1·2H2O was determined and consists of a three-dimensional coordination polymer containing inorganic K2(COO)2(OH2) layers separated by the long organic bridging linker. The free compound H2L1 displays a one-dimensional hydrogen-bonded polymeric structure in the solid state with hydrogen bonding interactions between carboxylic acids and piperazine groups tightly linking molecules together. The two-dimensional polymeric complex [Zn3(L1)2(OH)2]·2DMF·0.5H2O 1 was prepared and analysed in the solid state to reveal tubular one-dimensional channels which, when activated by solvent exchange and evacuation, displayed selective affinity for CO2 over N2 and H2. [ABSTRACT FROM AUTHOR]

In the presence of the Et4N+ cation the chloranilate dianion (can2-) associates with a range of divalent cations, M2+, to yield an isomorphous series of crystalline compounds of composition (Et4N)2[M2(can)3] (M = Mg, Mn, Fe, Co, Ni, Cu, and Zn). The fluoranilate dianion (fan2-) likewise affords the closely related (Et4N)2[Zn2(fan)3]. The structures of (Et4N)2[Zn2(can)3], (Et4N)2[Fe2(can)3], and (Et4N)2[Zn2(fan)3] were determined by single crystal X-ray diffraction. Powder X-ray diffraction indicates that all the members of the can2- series are isomorphous. The structure of (Et4N)2[Zn2(fan)3] is very closely related to the structures of the can2- compounds. The [M2(can)3 2-] n component is present as chicken-wire-like sheets with (6,3) topology. The Et4N+ cation binds sheet to sheet and aligns them so that the large holes within the sheets are arranged one above another, thereby generating spacious channels running perpendicular to the sheets. The solvent molecules present in the channels are ill-defined and easily removed. The (Et4N)2[M2(can)3] structure remains intact after desolvation. The void spaces are calculated to be 39% in the case of the can2- compounds and 43% in (Et4N)2[Zn2(fan)3]. Substantial amounts of CO2 are sorbed at 273 K by (Et4N)2[Zn2(can)3] and (Et4N)2[Zn2(fan)3]. Spectroscopic evidence supports the presence of at least some of the chloranilate in the radical trianion form in (Et4N)2[Fe2(can)3]. [ABSTRACT FROM AUTHOR]