Cooperative rotation of SiO₄ and VO₅ units in response to Li-ion exchange led to changes in symmetry in VSH-2 framework. The Cs sites are converted into new distorted tetrahedral sites for smaller Li⁺ ions via 2D ion transport along the [011] direction. Exchange of Cs⁺ by Li⁺ is incomplete suggesting the formation of protonated water clusters to counterbalance the net negative framework charge.

Abstract

The accessibility of lithium cations in microporous vanadosilicate VSH-2Cs of composition Cs₂(VO)(Si₆O₁₄) ⋅ 3H₂O was investigated by Single Crystal X-ray Diffraction, Attenuated Total Reflection Fourier Transformed Infrared Spectroscopy and Density Functional Theory calculations. The topological symmetry of VSH-2Cs is described in space group Cmca. After Li-ion exchange, the structure of VSH-2Li adopted monoclinic symmetry (space group C2/c) with a=17.011(2) Å, b=8.8533(11) Å, c=12.4934(16) Å, β=91.677(4)°, V=1880.7(4) ų. The strong interactions between Li ions and oxygen-framework atoms drive the main deformation mechanism, which is based on cooperative rotation of SiO₄ and VO₅ units around their oxygen atoms that behave as hinges. Exchange of Cs⁺ by Li⁺ is incomplete and accompanied by the formation of protonated species to counterbalance the electrostatic charge. The incorporation of protons is mediated by the presence of water dimers in the structural channels. H₂O molecules in VSH-2Li account not only as “space-fillers” after the removal of large Cs ions but also mediate proton transfer to compensate the negative charge of the host vanadosilicate framework.

This study demonstrates the application of terbium and europium based time-gated FRET molecular beacons for multiplexed microRNA biosensing, simplified molecular logic devices, and improved security identification and authentication.

Abstract

Time-resolved or time-gated (TG) biosensing and bioimaging with luminescent lanthanide probes and Förster resonance energy transfer (FRET) have significantly advanced bioanalytical chemistry. However, the development of lanthanide-based molecular beacons (MBs) has been rather limited. Here, we designed DNA stem-loop MB probes against two different microRNAs (miR-21 and miR-27b) using Tb and Eu FRET donors and quenching (BHQ2) and fluorescent (Cy3) FRET acceptors. Limits of detection down to 190 pM and duplexed miR-21/miR-27b quantification at low nanomolar concentrations with Tb-BHQ2 and Eu-BHQ2 TG-FRET MBs demonstrated the versatility and high analytical performance of lanthanide-based MBs. The particular donor-acceptor distances in the Tb-Cy3 MB resulted in inverted nucleic acid target concentration-dependent TG PL intensities in short (e. g., 0 to 40 μs) and long (e. g., 0.1 to 2.1 ms) TG detection windows after pulsed excitation. We showed that this specific feature of our TG-FRET MBs can be adapted to the design of molecular logic devices (NOR, OR, NAND, AND, XNOR, XOR, IMPLEMENT, and INHIBIT). Moreover, the almost unlimited choice of TG detection windows and the distinct spectral features of Tb and Cy3 over a broad visible spectral range could be exploited to devise biophotonic physical unclonable functions for highly secure authentication and identification. Our study manifests the versatility of lanthanides for advanced biophotonic applications.

Abstract

Thanks to an unusual protodemethylation reaction, a series of luminescent cyclometallated platinum(II) complexes can be prepared, which incorporate a rare NC-chelating, pyridyl-pyridylidene ligand, in combination with OO-coordinating acetylacetonate (acac) or NO-coordinating 2-picolinate (pic) or 8-hydroxyquinolate.  The acac and pic complexes show unusual dual emission in a frozen glass.

A series of cyclometallated platinum(II) complexes incorporating a rare, N^C-chelating, pyridyl-pyridylidene ligand are described, in which the coordination sphere is completed by two chlorides or an L X co-ligand, namely O O-coordinating acetylacetonate (acac), or N^O-coordinating 2-picolinate (pic) or 8-hydroxyquinolinate. The acac and pic complexes have been structurally characterized in the solid state by single-crystal X-ray diffraction. These two complexes display red phosphorescence in the solid state at room temperature. In a frozen glass at 77 K, all four complexes show two broad emission bands that span much of the visible spectrum, apparently from two unequilibrated excited states.

Two regioisomers of Zr-p-NO₂Bn-DOTA were isolated and characterized by NMR studies and quantum chemical calculations. As opposed to the side regioisomer, the corner regioisomer exists exclusively as the SAP isomer.

Abstract

A combination of NMR studies and quantum chemical calculations were employed to investigate the structure and energetics of Zr⁴⁺ chelates of pNO₂Bn-DOTA. We have demonstrated that two discrete regioisomeric chelates are generated during the complex formation. The nitrobenzyl substituent can adopt either an equatorial corner or side position on the macrocyclic ring. These regioisomers are incapable of interconversion and were isolated by HPLC. The corner isomer is more stable than the side, and the SAP conformer of both regioisomers is energetically more favorable than the corresponding TSAP conformer.

The π-system in a series of three fac-[Mn(α-diimine)(CO)₃Br] complexes is extended from 2,2′-bipyridine (bpy) to 2-(2-pyridyl)quinoline (pq) to 2,2′-biquinoline (bqn). The effects on photochemical mechanism, electrochemistry, and electroreduction of CO₂ is observed via cyclic voltammetry, bulk electrolysis, and UV-vis and IR spectroscopies.

Abstract

The complex [Mn(bpy)(CO)₃Br], has been previously studied as both an electrocatalyst and a photocatalyst, in conjugation with a photosensitizer, for CO₂ reduction to CO. This study considers the relationship between this catalytic activity and the steric and electronic nature of the aromatic diimine ligand. To this end, the π-system in the bidentate ligand is increased step-wise from 2,2′-bipyridine (bpy) to 2-(2-pyridyl)quinoline (pq) to 2,2′-biquinoline (bqn) in a series of three fac-[Mn(α-diimine)(CO)₃Br] complexes. It is found that the propensity of these complexes to photochemically dimerize trends with the energy of the α-diimine π* energy. Electrochemically, it is observed that the second reduction event in these systems becomes increasingly thermodynamically favorable and approaches the potential of the first reduction event as the π-system expands. In fac-[Mn(bqn)(CO)₃Br], the second reduction is more favorable than the first reduction, precluding the formation of a dimer intermediate; even though, chemical reduction of fac-[Mn(bqn)(CO)₃Br] confirms that the dimer, [Mn(bqn)(CO)₃Br]₂ is able to form and not prevented by steric considerations. Though the second reduction potential is more positive for bqn and pq than for bpy, the CO₂ reduction mechanism changes such that the overpotential for carbon dioxide reduction occurs at more negative potentials, leading to a decrease in overall catalytic activity.

Ligands derived from cis,cis-1,3,5-triaminocyclohexane (TACH) have been prepared with pendant heterocycles that serve as outer-sphere H-bond donors. Upon coordination to Cu(I), the facially coordinating N ₃ ligands create a hydrogen-bonding cavity that stabilizes (pseudo)halide anions. Reaction of the TACH-based ligands with divalent cations revealed a range of protonation states, coordination geometries, and H-bonding interactions.

Abstract

With the aim of constructing hydrogen-bonding networks in synthetic complexes, two new ligands derived from cis,cis-1,3,5-triaminocyclohexane (TACH) have been prepared that feature pendant pyrrole or indole rings as outer-sphere H-bond donors. The TACH framework offers a facial arrangement of three N-donors, thereby mimicking common coordination motifs in the active sites of nonheme Fe and Cu enzymes. X-ray structural characterization of a series of Cu^I-X complexes (X=F, Cl, Br, NCS) revealed that these neutral ligands (H₃L^R, R=pyrrole or indole) coordinate in the intended facial N ₃ manner, yielding four-coordinate complexes with idealized C ₃ symmetry. The N−H units of the outer-sphere heterocycles form a hydrogen-bonding cavity around the axial (pseudo)halide ligand, as verified by crystallographic, spectroscopic, and computational analyses. Treatment of H₃L^pyrrole and H₃L^indole with divalent transition metal chlorides (M^IICl₂, M=Fe, Cu, Zn) causes one heterocycle to deprotonate and coordinate to the M(II) center, giving rise to tetradentate ligands with two remaining outer-sphere H-bond donors. Further ligand deprotonation is observed upon reaction with Ni(II) and Cu(II) salts with weakly coordinating counteranions. The reported complexes highlight the versatility of TACH-based ligands with pendant H-bond donors, as the resulting scaffolds can support multiple protonation states, coordination geometries, and H-bonding interactions.

Pyridinophane aryl manganese(III) fluoro complexes were synthesized via transmetalation from Zn-CF₃ reagent and alpha-fluoride elimination to generate Mn^III fluoride and difluorocarbene. Carbene formation was confirmed by trapping by alkenes to give difluoropropanation product.

Abstract

We report the synthesis of cyclometalated monoaryl Mn^III fluoro complexes using bis(trifluoromethyl)zinc reagent, Zn(CF₃)₂(DMPU)₂, under mild conditions via a reaction pathway that involves initial transmetalation followed by α-fluorine elimination. The formation of difluorocarbene in these reactions was detected by trapping experiments. Such facile difluorocarbene generation from Mn^III results in moderate enhancement of difluoropropanation and difluoropropenation of alkenes and alkynes using Zn(CF₃)₂(DMPU)₂ at lower temperature (20–60 °C) and short reaction time, suggesting potential application of manganese(III) perfluoroalkyl complexes as reactive species for carbene transfer reactivity.

An efficient photocatalytic system with earth abundant carbon dots and a series of cobalt thiosemicarbazone catalysts was designed and studied. All prepared photocatalysts produced hydrogen, reaching a rate of 358 μmol g_NCdot ⁻¹ h⁻¹ upon light irradiation in water.

Abstract

In order to diminish environmental issues such as global warming due to increased carbo dioxide (CO₂) emissions, considerable efforts have been made in the research community. Photocatalytic hydrogen (H₂) production is a very important way towards this goal, since sunlight is an abundant source of energy and H₂ is a clean fuel, producing no greenhouse gases. Inexpensive, stable and non-toxic carbon dots were easily synthesized and used as photosensitizers in water in the presence of a series of molecular cobalt catalysts (CoTSC). The catalysts were thiosemicarbazone-based complexes able to transfer electrons for hydrogen evolution reaction. Under visible light irradiation, the nitrogen-doped carbon dots (NCdots) transfer the photoexcited electrons to the catalyst, producing an activity of 358 μmol g_NCdot ⁻¹ h⁻¹ (TON_Co=570) for CoTSC−N(CH₃)₂CN after 24 h of irradiation. These types of molecular catalysts display great activity and stability in combination with the easily synthesized and modified carbon dot materials.

Regio- and stereoisomerism of N,N-dialkylamide ligands was shown to impact plutonium recovery by promoting or demoting inner or outer sphere complexes, both controlled by steric hindrance effects.

Abstract

The relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid-liquid extraction (LLE) by using the N,N-di-(2-ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ-isomer) and N-(2-ethylhexyl)-N-(oct-3-yl)butyramide (EHOBA or αβ-isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)- and (S,S)-diastereoisomers, and were all assessed for Pu^IV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect Pu^IV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV-vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α-position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)-isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes.

The formation, structures and thermal and solution stability of cerium(IV) complexes with bidentate phosphine oxides are reported. Complexes with flexible ligand architecture tend to be less stable showing decomposition to Ce(III) in solution. The decomposition products of the thermal decomposition in the solid state have been identified by infrared spectroscopy.

Abstract

The reactions between ceric ammonium nitrate, (NH₄)₂Ce(NO₃)₆, (CAN) and the bidentate phosphine oxides, 4,5-bis(diphenylphosphine oxide)-9,9-dimethylxanthene (L¹), oxydi-2,1-phenylene bis(diphenylphosphine dioxide) (L²), 1,2-bis(diphenylphosphino)ethane dioxide (L³) and 1,4-bis(diphenylphosphino)butane dioxide, L⁴ have been investigated. The crystal structures of the molecular Ce(NO₃)₄L¹ (1), and ionic [Ce(NO₃)₃L³ ₂][NO₃]⋅CHCl₃ (3), [Ce(NO₃)₃L³ ₂][NO₃] (4) and the polymeric [Ce(NO₃)₃L⁴ _1.5] [NO₃] (5) and the cerium(III) complex [Ce(NO₃)₂L¹ ₂][NO₃] (2) are reported. The thermal stability of the complexes has been examined by thermogravimetry with the gaseous decomposition products analysed by infrared spectroscopy. Evolution of CO₂ is found for both Ce(III) and Ce(IV) complexes with the later also forming NO₂. The formation of the complexes in solution has been studied by ³¹P NMR spectroscopy and further complexes [Ce(NO₃)₃L¹ ₂]⁺[NO₃]⁻ and [Ce(NO₃)₂L¹ ₃]²⁺2[NO₃]⁻ identified in CD₃CN solution. The complex (1) exists as a single molecular species in solution and is stable in dichloromethane whilst (3) decomposes on standing in both CD₂Cl₂ and CD₃CN to Ce(III) containing species. Complexes of L² have been identified by solution ³¹P NMR spectroscopy and these decompose in solution to give Ce(NO₃)₃L² ₂. This study represents the first structural characterisations of Ce(IV) complexes with bidentate phosphine oxides.