The Cambridge Structural Database in chemical education: analysis of hydrogen-bonded networks in salts of hexaaqua metal ions with organic counter-ions

This paper describes a laboratory course that introduces basic crystallographic data analysis to chemistry students encountering for the first time the world of crystals and crystal structures. The aim of the course is to provide students with direct contact with crystal structures and hands-on experience in structure analysis. To this end, a set of appropriately simple inorganic molecular structures was selected, consisting of salts of hexaaqua metal ions with organic counter-ions. By exploiting the crystallographic tools available in the Cambridge Structural Database program Mercury, students learn how to visualize and analyse a set of atomic coordinates. In this way they learn how to extract bonding and structural information concerning intramolecular interactions in both salt components. Intermolecular interactions are next analysed by looking closely at supramolecular motifs and packing patterns generated by hydrogen bonds. This pragmatic approach turned out to be effective and extremely useful for summarizing many chemical concepts learned by students during a bachelor degree course in chemistry. The experience provides at the same time some basic capabilities for properly managing crystal structure analysis.

Engineering a Highly Defective Stable UiO-66 with Tunable Lewis- Brønsted Acidity: The Role of the Hemilabile Linker

The stability of metal-organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H₂SO₄, the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD₃CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity.

Crystal Engineering with the New Linker Tolanedisulfonic Acid (H2 TDS): Helical Chains in Zn(TDS)(DMA)3 , Linear Chains in Zn(TDS)(NMP)3 , and Complex Anions in [HDMA]2 [Zn(TDS)2 (DMA)3 ](DMA)2

Reaction of 4,4'-tolanedisulfonic acid, H2 TDS, with zinc hydroxide in dimethylacetamide, DMA, under solvothermal conditions led to the coordination polymer Zn(TDS)(DMA)3 (I). In the crystal structure [trigonal, P32 21, Z=3, a=1175.0(1) pm, c=1949.5(1) pm, R1 ; wR2 (Io > 2σ(Io ))=0.0393; 0.0921] the disulfonate anions linked the Zn(2+) ions into helical chains according to ∞ (1) [Zn(DMA)3/1 (TDS)2/2 ] (I) causing the chirality of the compound. By using higher concentrations of H2 TDS in the starting mixture the compound [HDMA]2 [Zn(TDS)2 (DMA)3 ](DMA)2 (II) was formed. The structure [monoclinic, Cc, Z=4, a=1201.5(1) pm, b=1996.0(1) pm, c=2749.2(2) pm, β=101.897(2)°, R1 ; wR2 (Io > 2σ(Io ))=0.0699; 0.2017] displayed the complex anion [Zn(TDS)2 (DMA)3 ](2-) which was a perfect cut-off of the helical chain in I. Charge compensation was achieved by protonated DMA molecules. If N-methylpyrrolidone, NMP, was chosen as a solvent, the sulfonate Zn(TDS)(NMP)3 (III) [monoclinic, I2/a, Z=4, a=1575.7(1) pm, b=1077.3(1) pm, c=1870.0(1) pm, β=101.189(9)°, R1 ; wR2 (Io > 2σ(Io ))=0.0563; 0.1320] was obtained. Similarly to the findings for I, the formation of chains according to ∞ (1) [Zn(NMP)3/1 (TDS)2/2 ] was observed. However, due to the more bulky NMP molecules these chains were no longer helical but straight instead.

1,4-Benzenedisulfonic acid (H2BDS) as terephthalic acid analogue for the preparation of coordination polymers: the examples of M(BDS)(NMP)3 (M = Mn, Fe, Co; NMP = N-methylpyrrolidone)

1,4-Benzenedisulfonic acid, the sulfo analogue of terephthalic acid, has been successfully used for building coordination polymers of Co, Mn, and Fe.

A cyclic tetranuclear cuboid type copper(ii) complex doubly supported by cyclohexane-1,4-dicarboxylate: molecular and supramolecular structure and cyclohexane oxidation activity

A rare isolated tetranuclear 3d complex with a single metal CDC cuboid cage. It catalyzes cyclohexane peroxidative oxidation without any promoter.

1,2,4,5-Benzenetetrasulfonic acid and 1,4-benzenedisulfonic acid as sulfo analogues of pyromellitic and terephthalic acids for building coordination polymers of manganese

New polysulfonic acids have been used for the preparation of manganese coordination polymers.

Crystal structure of di-acetato-bis-pyridine-palladium(II), [Pd(C2H3O2)2(C5H5N)2], C14H16N2O4Pd

C14H16N2O4Pd, monoclinic, P21/c (no. 14), a = 7.7797(4) Å, b = 11.7520(6) Å, c = 8.0914(4) Å, β = 90.754(2)°, V = 739.7 Å3, Z = 2, Rgt(F) = 0.0186, wRref(F2) = 0.0437, T = 153 K.

Hexaaqua-copper(II) bis-(tetra-fluorido-borate)-pyrazine 1,4-dioxide (1/3)

The crystal structure of the title compound, [Cu(H2O)6](BF4)2·3C4H4N2O2, comprises discrete [Cu(H2O)6](2+) cations and BF4 (-) anions along with three equivalents of pyrazine 1,4-dioxide (pzdo). The hexa-aqua-copper(II) ion and all three pzdo mol-ecules lie about crystallographic inversion centers. The lattice is supported by an extensive hydrogen-bonding network. O-H⋯O hydrogen bonding between the [Cu(H2O)6](2+) and pzdo units creates a pseudo-hexa-gonal lattice parallel to the bc plane. The BF4 (-) anions lie in the voids of that lattice, held in place by O-H⋯F hydrogen bonds, and also generate BF4 (-)-pzdo-BF4 (-)-pzdo stacks via short F⋯N contacts [2.866 (3)-3.283 (4) Å].