Nano-sized toroidal copper(II)-hydroxide/pyrazolate assemblies, lined by H-bond donors on the inside and hydrophobic on the outside, selectively extract sulfate from mixtures with nitrate or perchlorate. Tetrabutylammonium “lids” seal the “nano-jars” and render the encapsulated sulfate anion completely buried and inaccessible, so that it is not precipitated by Ba²⁺ ions.

The present study demonstrates that the pyrazole-4-sulfonate anion (4-SO₃-pzH = L⁻) is a versatile ligand for the preparation of layered, 3-D solid state lattices. The ligand itself can coordinate to metals with both its sulfonate group and aromatic N-atom, as well as participate in hydrogen bonding both as donor and acceptor, and form various extended π–π networks. Five new complexes with Rb⁺ , Cs⁺ , Mg²⁺ , Sr²⁺ and Cu²⁺ have been prepared and characterized including single crystal X-ray diffraction: RbL, tetragonal I4₁/a, a = 9.7332(4) Å, b = 9.7332(4) Å, c = 29.941(1) Å, V = 2836.5(2) Å, Z = 16; CsL, monoclinic P2₁/c, a = 8.821(1) Å, b = 8.109(1) Å, c = 9.889(2) Å, β = 91.560(3)°, V = 707.1(2) Å, Z = 4; Mg(H₂O)₆L₂, triclinic P, a = 7.0543(7) Å, b = 7.7307(8) Å, c = 8.6389(9) Å, α = 72.572(2)°, β = 74.370(2)°, γ = 76.045(2)°, V = 426.22(8) Å, Z = 1; SrL₂, triclinic P, a = 6.027(2) Å, b = 7.243(3) Å, c = 14.186(5) Å, α = 92.491(8)°, β = 101.383(7)°, γ = 97.471(7)°, V = 426.22(8) Å, Z = 2; Cu(H₂O)₂L₂·4H₂O, monoclinic P2₁/c, a = 9.032(1) Å, b = 13.297(1) Å, c = 7.7103(9) Å, β = 109.747(2)°, V = 871.5(2) Å, Z = 2. The varying size and charge of the cations in these five complexes produce unique, alternating inorganic–organic layered materials. We find a correlation between the size and charge of cations and the coordination mode of the ligand as well as hydration of the metal, but no correlation between the nature of the cation and the thickness of the inorganic/organic layers. We conclude that the overall 3-D structure of these layered materials is determined by a subtle balance between the coordination preferences of the metal ion and an intricate lattice of hydrogen bonds and aromatic interactions. Ligand HL and its complexes with Na, K, Rb, Cs, Mg, Ca, Sr and Ba were tested as potential corrosion inhibitors of copper metal surfaces at three different pH values (2, 3, and 4). All the above mentioned compounds show significant corrosion inhibition at pH 4 and 3, while no activity is observed at pH 2. The correlation of inhibition activity with pH of ligand HL and its different metal complexes is discussed.

Five compounds based on the versatile pyrazole-4-sulfonate anion (4-SO₃-pzH = L⁻) were synthesized by the reaction of ligand HL with ZnO, CdCO₃, Ag₂O, NaOH and NH₃ , respectively. Crystals of Zn(4-SO₃-pzH)₂(H₂O)₂, Cd(4-SO₃-pzH)₂(H₂O)₂, Ag(4-SO₃-pzH), Na(4-SO₃-pzH)(H₂O) and NH₄(4-SO₃-pzH) were obtained from aqueous solutions upon evaporation, and were characterized by single-crystal X-ray diffraction, IR and NMR spectroscopy, thermogravimetric analysis and copper corrosion inhibition experiments. We found that the non-isomorphous, 3-dimensional inorganic–organic layered solid state structure of these compounds is determined by an intricate interplay between the size, charge and coordination preference of the cation, and an extended lattice of hydrogen bonds and aromatic interactions. Ligand L⁻ incorporates a host of different binding capabilities (metal coordination through the pyrazole N-atom and/or the sulfonate O-atom, hydrogen-bonding both as donor and acceptor, π–π and C–H⋯π interactions). Thin films formed by these complexes on copper metal surfaces were studied by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. ZnL₂, CdL₂, AgL and NH₄L, in addition to the free ligand HL, were tested as corrosion inhibitors on copper metal surfaces at three different pH values (2, 3 and 4), and the corrosion rates were quantified. Significant corrosion protection was observed with all compounds at pH 4 and 3.

Colored pseudorotaxane solutions can be used to assess temperature changes over large temperature windows. The color intensity of our novel pseudorotaxane systems decreases gradually from −50 to +50 °C with no shift in absorption maximum, making these and similar pseudorotaxanes attractive candidates for single-wavelength colorimetric temperature sensors.