Structural Induction via Solvent Variation in Assemblies of Triphenylboroxine and Piperazine—Potential Application as Self-Assembly Molecular Sponge

Abstract

This study examined the direct effect of solvent on the chemical composition and structure of supramolecular assemblies formed from triphenylboroxine ((PhBO) 3 ) and piperazine (ppz) through N→B bonds. Oxygen-containing solvents with a molecular size smaller than 4.1 Å produce 1D polymeric structures (1:1 boroxine/piperazine) of compositions {(PhBO) 3 (ppz)} n •nTHF (1a• THF) and {(PhBO) 3 (ppz)} n •nAcetone (1a•Acetone), in which the boroxine B 3 O 3 rings are linked through N→B bonded piperazine molecules in a cis-conformation. In both cases, a pseudocavity is generated between two polymer chains, which is occupied by a solvent molecule interacting through bifurcated N−Hbonds with one of the chains. In contrast, oxygen-based solvents with a size larger than 6.3 Å give rise to discrete 2:1 assemblies, {(PhBO) 3 } 2 (ppz)•2Ethyl acetate (2•AcOEt) and {(PhBO) 3 } 2 (ppz)•2Pentanone (2•Pentanone), with the piperazine molecule bridging two B 3 O 3 rings and interacting with two solvent molecules via N−H•••O hydrogen bonds. In chloroform or dichloromethane 2:3 adducts, {(PhBO) 3 } 2 (ppz) 3 •4CHCl 3 (3•CHCl 3 ) and {(PhBO) 3 } 2 (ppz) 3 •2.09CH 2 Cl 2 (3•CH 2 Cl 2 ), were obtained, with N−H•••N interactions formed between the piperazine molecules directing the crystal lattice. Finally, unlike with THF and acetone, the presence of two coordination sites in dioxane gives rise to a 1D polymeric 1:1 clathrate-type assembly with trans-conformation, {(PhBO) 3 (ppz)} n •3.5nDioxane (1b•Dioxane). In accordance with the structural characterization, the thermogravimetric analysis of compounds 1−2 evidenced relatively high decomposition (solvent elimination) temperatures for the inclusion complexes derived from oxygen-containing solvents (T peak = 76.4 to 145.4 °C). On the contrary, solvates based on halogenated solvents (3•CHCl 3 and 3•CH 2 Cl 2 ) or 1,4-dioxane started to decompose already at room temperature. In view of potential applications for the storage and structural characterization of volatile or highly reactive reagents, a final inclusion experiment was carried out with racemic 1,2-epoxybutane. As expected, the resulting N→B bonded inclusion complex exhibited a 1:1 cis-polymeric structure, in which the guest molecules were bonded by bifurcated N pip −H•••O epoxy •••H−N pip hydrogen bonds.

Efficient Conversion of CO2 via Grafting Urea Group into a [Cu2(COO)4]-Based Metal–Organic Framework with Hierarchical Porosity

“…The yields of cyclic carbonates decreased to 78%, 50%, and 43% for butylene oxide, 1,2-epoxy-3-allyloxypropane, and glycidyl phenyl ether, respectively (Table ). This may be related to the slow diffusion of large-sized substrates into the framework with the increase of molecule size from 4.2 × 2.6 × 1.8 Å 3 of propylene oxide to 9.4 × 4.3 × 2.3 Å 3 of glycidyl phenyl ether . Moreover, the interaction strength between the substrates and the active sites may also affect the catalytic activity.…”

Effect of chemical substitution on the construction of boroxine-based supramolecular crystalline polymers featuring B←N dative bonds

“…10 g , h Recently, the B←N dative bond has appeared to serve as a good alternative to traditional non-covalent and metal–coordinate bonds, to build supramolecular network/host–guest-based crystalline assemblies, for various applications. 11–20 In general, the donation of electrons from the N-donor ligand to the electron-deficient boron atom (empty p-orbital) stabilizes such type of bonding. It has also been observed that the electronic properties of the interacting partner strongly influence the strength of the B←N dative bond.…”

Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline

“…The Laplacian vs distance plot (see Figure 6a in ref ) shows a “heap”, where the Laplacian changes its sign, and this corresponds to the overall lability of this particular bond. This feature has recently been used to construct various B–N bonded networks …”

“…in ref122) shows a "heap", where the Laplacian changes its sign, and this corresponds to the overall lability of this particular bond. This feature has recently been used to construct various B−N bonded networks 128. Similarly to the B−N case, all B−O bonds exhibit the closedshell character, which is manifested by the positive Laplacian.…”