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Salt induced micelle-to-vesicle transitions of ionic surfactants depend on the surfactant chain length, headgroup structure, counterion type and concentration, but the interfacial molarities of counterions and water that balance the hydrophobic effect are difficult to determine. In anionic micelles of twin-tailed sodium bis(2-ethylhexyl)sulfosuccinate (AOT), the chemical trapping (CT) method provides estimates of the interfacial molarities of anionic headgroups (RSO3−m) and neutral (H2Om) nucleophiles during salt induced transitions of AOT micelles to vesicles. Product yields were measured by HPLC from the competitive dediazoniation reaction using a specially designed hydrophobic probe, 4-hexadecyl-2,6-dimethylbenzenediazonium cation, 16-ArN2+. The reactions were run at constant concentration of 15 mM AOT mixed with 0 to 50 mM added salts, containing cations of different sizes and valences including tetraalkylammonium cations (MR4+, R = 1–4) and metal cations (M1–3+). Parallel reactions in aqueous salt solutions with a short chain analog, 1-ArN2+, were used as references to calculate interfacial molarities. Aggregates were structurally characterized by TEM and DLS. Typically, interfacial RSO3− molarities increase with added salts from 1 to 2 M and water molarities decrease from about 40 to 20 M with the micelle to vesicle transition. These changes are consistent with the ion-pair/hydration model, in which the added cations form neutral but polar ion-pairs with RSO3− that have a lower demand for hydration and water was released into the surrounding aqueous phase. The extent of ion-pairing increases with cation size, charge and hydrophobicity and decreases with interfacial water molarity, which permits tighter interfacial packing and vesicle formation at lower added salt concentrations. [ABSTRACT FROM AUTHOR]

Exploration of the catalytic activity of low-dimensional transition metal (TM) or noble metal catalysts is a vital subject of modern materials science because of their instrumental role in numerous industrial applications. Recent experimental advances have demonstrated the utilization of single atoms on different substrates as effective catalysts, which exhibit amazing catalytic properties such as more efficient catalytic performance and higher selectivity in chemical reactions as compared to their nanostructured counterparts; however, the underlying microscopic mechanisms operative in these single atom catalysts still remain elusive. Based on first-principles calculations, herein, we present a comparative study of the key kinetic rate processes involved in CO oxidation using a monomer or dimer of two representative TMs (Pd and Ni) on defective TiO2(110) substrates (TMn@TiO2(110), n = 1, 2) to elucidate the underlying mechanism of single-atom catalysis. We reveal that the O2 activation rates of the single atom TM catalysts deposited on TiO2(110) are governed cooperatively by the classic spin-selection rule and the well-known frontier orbital theory (or generalized d-band picture) that emphasizes the energy gap between the frontier orbitals of the TM catalysts and O2 molecule. We further illuminate that the subsequent CO oxidation reactions proceed via the Langmuir–Hinshelwood mechanism with contrasting reaction barriers for the Pd monomer and dimer catalysts. These findings not only provide an explanation for existing observations of distinctly different catalytic activities of Pd@TiO2(110) and Pd2@TiO2(110) [Kaden et al., Science, 2009, 326, 826–829] but also shed new insights into future utilization and optimization of single-atom catalysis. [ABSTRACT FROM AUTHOR]

In our efforts toward the rational design and systematic synthesis of porous 3D MOFs, three 3D frameworks of Zn-MOFs ([Zn(BDC)(TIB)]·3H2O (Zn-MOF-1) (TIB = 1,3,5-tri(1H-imidazol-1-ly) benzene and H2BDC = 1,4-dicarboxybenzene), [Zn(BDA)(TIB)2/3]n (Zn-MOF-2) (H2BDA = 4,4′-biphenyl-dicarboxylic acid) and [Zn3(BDC)2(BDA)(TIB)2]n (Zn-MOF-3)) were successfully synthesized, based on different multicarboxylate ligands through solvothermal reactions. The resulting MOFs show similar 3D structures with different pore sizes which lead to distinct selective adsorption for organic dyes. Remarkably, Zn-MOF-1 exhibits an excellent capacity to adsorb CR (congo red) with high selectivity, and it maintains an almost identical adsorption performance after being recycled several times. [ABSTRACT FROM AUTHOR]

An extremely thermostable magnesium metal–organic framework (Mg-MOF) is reported for use as a highly selective and sensitive, instantaneous and colorimetric sensor for Eu3+ ions. There has been extensive interest in the recognition and sensing of ions because of their important roles in biological and environmental systems. However, only a few of these systems have been explored for specific rare earth ion detection. A robust microporous Mg-MOF for the recognition and sensing of Eu3+ ions with high selectivity at low concentrations in aqueous solutions has been synthesized. This stable metal–organic framework (MOF) contains nanoscale holes and non-coordinating nitrogen atoms inside the walls of the holes, which makes it a potential host for foreign metal ions. Based on the energy level matching and efficient energy transfer between the host and the guest, the Mg-MOF sensor is both highly selective and sensitive as well as instantaneous; thus, it is a promising approach for the development of luminescent probing materials with unprecedented applications and its use as an Eu3+ ion sensor. [ABSTRACT FROM AUTHOR]

Two series of lanthanide-based coordination polymers, [Ln(HCPOB)(CPOB)(H2O)2]n [Ln = Eu(a1), Gd(a2), Tb(a3), Dy(a4), Ho(a5), Er(a6)] and [Ln(HCPOB)(CPOB)]n [Ln = Eu(b1), Gd(b2), Tb(b3), Dy(b4), Ho(b5), Er(b6)], have been synthesized using an asymmetric semi-rigid V-shape multicarboxylate ligand [H4CPOB = 2-(4-carboxyphenoxy)benzoic acid] by a hydrothermal method at different temperatures. Series a were obtained at 130 °C and have one-dimensional (1D) chain architectures, while series b were synthesized at 180 °C and exhibit three-dimensional (3D) structures. Interestingly, temperature-dependent XRD patterns for 1D compounds indicate that the 1D structure changes to form the 3D coordination polymers on heating the crystals. Single crystals of series a can transform into crystals of series b without any significant change in crystal quality. The variations from 1D to 3D coordination structures are attributed to variable coordination modes of multicarboxylate ligand H2CPOB. In addition, we have studied the luminescent properties of Eu3+, Tb3+, and Dy3+ compounds of series a and series b, and found that series a give very weak luminescence because of coordinated water molecules existing in the complexes. Due to the “antenna effect” or “luminescence sensitization”, series b exhibit much stronger fluorescent intensity than that of series a. [ABSTRACT FROM AUTHOR]

A novel 3D microporous compound [Zn3(Httca)2(4,4′-bpy)(H2O)2]n (MOF–COOH) containing uncoordinated carbonyl groups pointing to the pores was prepared. The uncoordinated carbonyl groups in the channels can act as postsynthetic modification sites for cation exchange. The MOF–COOH compound can effectively and selectively serve as an antenna for sensitizing the visible-emitting Tb3+ cation. [ABSTRACT FROM AUTHOR]

Exploration of the catalytic activity of low-dimensional transition metal (TM) or noble metal catalysts is a vital subject of modern materials science because of their instrumental role in numerous industrial applications. Recent experimental advances have demonstrated the utilization of single atoms on different substrates as effective catalysts, which exhibit amazing catalytic properties such as more efficient catalytic performance and higher selectivity in chemical reactions as compared to their nanostructured counterparts; however, the underlying microscopic mechanisms operative in these single atom catalysts still remain elusive. Based on first-principles calculations, herein, we present a comparative study of the key kinetic rate processes involved in CO oxidation using a monomer or dimer of two representative TMs (Pd and Ni) on defective TiO2(110) substrates (TMn@TiO2(110), n = 1, 2) to elucidate the underlying mechanism of single-atom catalysis. We reveal that the O2 activation rates of the single atom TM catalysts deposited on TiO2(110) are governed cooperatively by the classic spin-selection rule and the well-known frontier orbital theory (or generalized d-band picture) that emphasizes the energy gap between the frontier orbitals of the TM catalysts and O2 molecule. We further illuminate that the subsequent CO oxidation reactions proceed via the Langmuir-Hinshelwood mechanism with contrasting reaction barriers for the Pd monomer and dimer catalysts. These findings not only provide an explanation for existing observations of distinctly different catalytic activities of Pd@TiO2(110) and Pd2@TiO2(110) [Kaden et al., Science, 2009, 326, 826-829] but also shed new insights into future utilization and optimization of single-atom catalysis.

Two pairs of novel enantiomerically chiral clusters R/S-[NaMn(II)Mn(III)3L3(μ3-O)] (R/S-1) and R/S-[Na2Mn(II)2Mn(III)6L6(μ3-O)2] (R/S-2) have been obtained via the self-assembly of R/S-H2L Schiff base ligands and different auxiliary ligands (N3(-), dca(-)) with divalent manganese salt in an air-exposed methanol-ethanol solution. The structures of R/S-1 and R/S-2 were characterized by single-crystal X-ray diffraction analysis and powder X-ray diffraction. When the dicyanamide anion serves as an auxiliary ligand in the assembling reaction system, a pair of enantiomeric clusters R/S-[NaMn(II)Mn(III)3L3(μ3-O)] (R-1 and S-1) with a trigonal bipyramid configuration were obtained, while another pair of enantiomeric clusters R/S-[Na2Mn(II)2Mn(III)6L6(μ3-O)2] (R-2 and S-2) were formed in the case of the azide. Interestingly, the skeleton configuration of R/S-2 can be described as a 3-fold EO-azide bridging double trigonal bipyramid of [NaMn(II)Mn(III)3L3(μ3-O)]2via Mn(II) vertices. Circular dichroism (CD) spectra demonstrated the enantiomeric nature of the two pairs of clusters. Detailed direct current (DC) magnetic susceptibility studies in the temperature range 2-300 K suggested that R-1 and R-2 showed predominantly antiferromagnetic interactions between the manganese centers.