Capped Nanojars: Synthesis, Solution and Solid-State Characterization, and Atmospheric CO2 Sequestration by Selective Binding of Carbonate

Nanojars are a class of supramolecular anion-incarcerating coordination complexes that self-assemble from Cu²⁺ ions, pyrazole, and a strong base in the presence of highly hydrophilic anions. In this work, we show that if the strong base (e.g., NaOH or Bu₄NOH) is replaced by a weak base such as a trialkylamine, capped nanojars of the formula [{Cu₃(μ₃-OH)(μ-pz)₃L₃}CO₃⊂{Cu(μ-OH)(μ-pz)}_n] (pz = pyrazolate anion; L = neutral donor molecule; n = 27-31) are obtained instead of the conventional nanojars. Yet, to obtain capped nanojars, the conjugate acid side product originating from the weak base must be separated by transferring it to water either by precipitation of the water-insoluble capped nanojars or by liquid-liquid extraction. Full characterization using electrospray ionization mass spectrometry, UV-vis and variable-temperature ¹H NMR spectroscopy in solution, and single-crystal X-ray diffraction, elemental analysis, and solubility studies in the solid state reveals similarities as well as drastic differences between capped nanojars and nanojars lacking the [Cu₃(μ₃-OH)(μ-pz)₃L₃]²⁺ cap. Acid-base reactivity studies demonstrate that capped nanojars are intermediates in the pH-controlled assembly-disassembly of nanojars. During the self-assembly of capped nanojars, CO₂ is selectively sequestered from air in the presence of other atmospheric gases and converted to carbonate, the binding of which is selective in the presence of NO₃^-, ClO₄^-, BF₄^-, Cl^-, and Br^- ions.

Self-Assembly of Antiferromagnetically-Coupled Copper(II) Supramolecular Architectures with Diverse Structural Complexities

The self-assembly of 2,6-diformyl-4-methylphenol (DFMP) and 1-amino-2-propanol (AP)/2-amino-1,3-propanediol (APD) in the presence of copper(II) ions results in the formation of six new supramolecular architectures containing two versatile double Schiff base ligands (H₃L and H₅L1) with one-, two-, or three-dimensional structures involving diverse nuclearities: tetranuclear [Cu₄(HL²⁻)₂(N₃)₄]·4CH₃OH·56H₂O (1) and [Cu₄(L³⁻)₂(OH)₂(H₂O)₂] (2), dinuclear [Cu₂(H₃L1²⁻)(N₃)(H₂O)(NO₃)] (3), polynuclear {[Cu₂(H₃L1²⁻)(H₂O)(BF₄)(N₃)]·H₂O}_n (4), heptanuclear [Cu₇(H₃L1²⁻)₂(O)₂(C₆H₅CO₂)₆]·6CH₃OH·44H₂O (5), and decanuclear [Cu₁₀(H₃L1²⁻)₄(O)₂(OH)₂(C₆H₅CO₂)₄] (C₆H₅CO₂)₂·20H₂O (6). X-ray studies have revealed that the basic building block in 1, 3, and 4 is comprised of two copper centers bridged through one μ-phenolate oxygen atom from HL²⁻ or H₃L1²⁻, and one μ-1,1-azido (N₃⁻) ion and in 2, 5, and 6 by μ-phenoxide oxygen of L³⁻ or H₃L1²⁻ and μ-O²⁻ or μ₃-O²⁻ ions. H-bonding involving coordinated/uncoordinated hydroxy groups of the ligands generates fascinating supramolecular architectures with 1D-single chains (1 and 6), 2D-sheets (3), and 3D-structures (4). In 5, benzoate ions display four different coordination modes, which, in our opinion, is unprecedented and constitutes a new discovery. In 1, 3, and 5, Cu(II) ions in [Cu₂] units are antiferromagnetically coupled, with J ranging from −177 to −278 cm⁻¹.

Accessing the inaccessible: discrete multinuclear coordination complexes and selective anion binding attainable only by tethering ligands together

The use of tethers between ligands allows for the preparation of novel multimetallic complexes, not obtainable without tethers, and leads to unexpected properties, such as selective binding of the carbonate vs. sulfate anion by nanojars.

Stabilization of Cu7 clusters in azide networks: syntheses, structures and magnetic behaviour

Two new azide bridged copper(II) coordination polymer compounds, [Cu7(N3)14(C3H10N2)(C4H13N3)]n (I) and [Cu7(N3)14(C3H10N2)(C5H15N3)2]n (II) [where C3H10N2 = 1,2-diaminopropane (1,2-DAP); C4H13N3 = diethylenetriamine (DETA); C5H15N3 = N-2-aminoethyl-1,3-propanediamine (AEDAP)] were prepared by employing a room temperature diffusion technique involving three layers. Single crystal studies reveal that both compounds I and II, have similar connectivity forming Cu7 clusters through end-on (EO) bonding of the azide. The Cu7 clusters are connected through end-to-end (EE) connectivity of the azides forming three-dimensional structures. Magnetic studies confirmed the ferromagnetic interactions within the Cu7 units and revealed the occurrence of concomitant ferro- and antiferro-magnetic interactions between these clusters. As a result I behaves as a weak-ferromagnet with TC = 10 K.