Water dissociation on alpha1-hafnium and ytterbium substituted Dawson polyoxotungstates: a density functional theory study

Density functional theory (DFT) calculations were devised to get insight into Lewis acidic catalysis by POMs, especially on the intriguing activation of complexed water molecules that was observed in some experimental cases. Computationally, it appears that deprotonation is feasible with [alpha(1)-Hf(H(2)O)P(2)W(17)O(61)](6-), but not with [alpha(1)-Yb(H(2)O)P(2)W(17)O(61)](7-). This reflects the difference of the electronic structures (diamagnetic for hafnium POM, paramagnetic for ytterbium POM). From a mechanistical point of view, indirect Br?nsted catalysis cannot be excluded in the hafnium case, especially for Mannich reactions. But our calculations show that catalysis by [alpha(1)-Yb(H(2)O)P(2)W(17)O(61)](7-) (and presumably all the lanthanide series) proceeds through direct complexation of the substrates to the POM.     

0-D and 1-D inorganic-organic composite polyoxotungstates constructed from in-situ generated monocopper-substituted Keggin polyoxoanions and copper-organoamine complexes

Combination of in-situ generated monocopper^II-substituted Keggin polyoxoanions with copper^II-organoamine complexes under hydrothermal conditions results in seven inorganic-organic composite polyoxotungstates [Cu(en)₂(H₂O)]₂{[Cu(en)₂][α-PCuW₁₁O₃₉Cl]}·3H₂O (1), {[Cu(en)₂(H₂O)][Cu(en)₂]₂[α-PCuW₁₁O₃₉Cl]}·6H₂O (2), {[Cu(en)₂(H₂O)]₂[Cu(en)₂][α-XCuW₁₁O₃₉]}·5H₂O (3/4, X=Si^IV/Ge^IV), {[Cu(deta)(H₂O)₂]₂[Cu(deta)(H₂O)][α-XCuW₁₁O₃₉]}·5H₂O (5/6, X=Ge^IV/Si^IV) and [Cu(dap)₂]₂{[Cu(dap)₂]₂[Cu(dap)₂][α-PCuW₁₁O₃₉]₂} (7) (en=ethylenediamine, dap=1,2-diaminopropane and deta=diethylenetriamine). 1 is an isolated structure whereas 2 is a 1-D chain structure, but both contain [α-PCuW₁₁O₃₉Cl]⁶⁻ polyoxoanions. 3-6 contain the 1-D linear chains made up of [α-XCuW₁₁O₃₉]⁶⁻ polyoxoanions in the pattern of -A-A-A- (A=[α-XCuW₁₁O₃₉]⁶⁻), while 7 demonstrates the first 1-D zigzag chain constructed from [α-PCuW₁₁O₃₉]₂¹⁰⁻ polyoxoanions via [Cu(en)₂]²⁺ bridges in the pattern of -A-B-A-B- (A=[α-PCuW₁₁O₃₉]₂¹⁰⁻, B=[Cu(en)₂]²⁺). The successful syntheses of 1-7 can provide some experimental evidences that di-/tri-/hexa-vacant polyoxoanions can be transformed into mono-vacant Keggin polyoxoanions under hydrothermal conditions.     

Exploring Highly Efficient Broadband Self-Trapped-Exciton Luminophors: from 0D to 3D Materials

The review summarizes our recent reports on brightly-emitting materials with varied dimensionality (3D, 2D, 0D) synthesized using “green” chemistry and exhibiting highly efficient photoluminescence (PL) originating from self-trapped exciton (STE) states. The discussion starts with 0D emitters, in particular, ternary indium-based colloidal quantum dots, continues with 2D materials, focusing on single-layer polyheptazine carbon nitride, and further evolves to 3D luminophores, the latter exemplified by lead-free double halide perovskites. The review shows the broadband STE PL to be an inherent feature of many materials produced in mild conditions by “green” chemistry, outlining PL features general for these STE emitters and differences in their photophysical properties. The review is concluded with an outlook on the challenges in the field of STE PL emission and the most promising venues for future research.     

Amino-carboxylic recognition on surfaces: from 2D to 2D + 1 nano-architectures

The control of the electronic properties of the interfaces between small organic molecules and the substrate is key for the development of efficient and reliable organic-based devices. A promising and widely covered route is to interpose a Self-Assembled Monolayer (SAM) to bridge the molecular film and the electrode. The morphology and the electronic level alignment of the triple substrate-SAM-organic layered system can be tuned by properly selecting the SAM composition. We have recently proposed a novel approach to the problem where, under ultra-high vacuum conditions, a molecular film is anchored to the SAM by exploiting the recognition between molecules functionalized, respectively, with -NH(2) and -COOH end-groups. Here we briefly review the role of the amino-carboxylic interaction in the formation of ordered organic 2-dimensional architectures on solid surfaces. We then describe the anchoring process of carboxylic molecules on amine based SAMs we have recently reported on. New results are presented showing how multiple anchoring sites per molecule may be exploited for tailoring the molecular orientation as well as the density of the anchored molecules.     

Extended structure constructed from sandwich-type tungstoantimonites fused together by water substitution on the sandwiching metal centers

A polyoxotungstate, {Na₆(H₂O)₁₆}[{Mn₃(H₂O)_6?W(OH)₂}{SbW₉O₃₃}₂]?·?13H₂O (1), has been synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction analysis. Compound 1 exhibits a 1-D chain-like structure composed of the sandwich-type tungstoantimonites fused together by water substitution on the sandwiching metal centers, rarely observed in POM chemistry. Electrocatalytic studies show that 1 has electrocatalytic activity for the reduction of nitrite.     

Construction of 0D to 3D cadmium complexes from different pyridyl diimide ligands

Four semirigid ditopic ligands, N,N'-bis(3-pyridylmethyl)-pyromellitic diimide (L(1)), N,N'-bis(4-pyridylmethyl)-pyromellitic diimide (L(2)), N,N'-bis(3-pyridylmethyl)-naphthalene diimide (L(3)), and N,N'-bis(4-pyridylmethyl)-naphthalene diimide (L(4)), reacted with Cd(NO(3))(2) to result in four cadmium(II) complexes, namely, {[Cd(2)(L(1))(2)(NO(3))(4)(CH(3)OH)(4)]·H(2)O} (1), [Cd(L(2))(NO(3))(2)(CH(3)OH)(2)·Cd(2)(L(2))(3)(NO(3))(4)]·{4(HCCl(3))·2H(2)O}(n) (2), {[Cd(L(3))(2)(NO(3))(2)]}(n) (3), and {[Cd(L(4))(2)(NO(3))(2)]·2(CHCl(3))}(n) (4). These complexes have been characterized by elemental analyses, powder X-ray diffraction, thermogravimetric (TG) analyses, IR spectroscopy, and single-crystal X-ray diffraction. Structural analyses show that four types of structures are formed: (1) a discrete M(2)L(2) ring with two Cd ions and two cis-L(1) ligands comprising a zero-dimensional molecular rectangle (0D), (2) an unusual zigzag linear chain and a one-dimensional ladder existing simultaneously in the crystal lattice (1D), (3) a two-dimensional network of the (4,4) net structure (2D), and (4) an unusual chiral three-dimensional framework with 5-fold interpenetrating diamond (dia) topology (3D). In these complexes, the ligands exhibit different coordination modes and construct various architectures by bridging Cd(NO(3))(2) inorganic building blocks. These results suggest that structural diversity of the complexes is tunable by ligand modifications, that is, varying the ligand spacer bulkiness or substituent position of terminal group. Furthermore, gas adsorption measurements indicate that 4 possesses moderate CO(2) uptake and some adsorption selectivity for CO(2) over N(2).     

Photo-responsive Single-Molecule Magnet Showing 0D to 1D Single-Crystal-to-Single-Crystal Structural Transition and Hysteresis Modulation

Photo-responsive lanthanide-based single-molecule magnets (SMM) hold great promise for future switching and memory devices. Herein, we report a dysprosium phosphonate [Dy^III(SCN)₂(NO₃)(depma)₂(4-hpy)₂] ( 1Dy ), which features a supramolecular framework containing layers of hydrogen-bonding network and pillars of π–π interacted anthracene units. The photocycloaddition reaction of anthracene pairs led to a rapid and reversible single-crystal-to-single-crystal (SC–SC) structural transition to form the 1D coordination polymer [Dy^III(SCN)₂(NO₃)(depma₂)(4-hpy)₂]_n ( 2Dy ), accompanied by photoswitchable SMM properties with the reduction of effective energy barrier by half and the narrowing of the butterfly-like hysteresis loop. The diluted sample showed a photo-induced switch of the blocking temperature (T_B) from 3.8 K for 1Dy@Y to 2.6 K for 2Dy@Y . This work may inspire the construction of lanthanide-based molecular materials with targeted photo-responsive magnetic properties.     

CdS thin films on LiNbO3 (1 0 4) and silicon (1 1 1) substrates prepared through an atom substitution method

CdS thin films on LiNbO₃ (1 0 4) and silicon (1 1 1) substrates were prepared through an atom substitution technique using cadmium nitrate as a reactant in an H₂S atmosphere at 230 °C. X−ray diffraction, scanning electron microscopy and transmission microscopy results indicate that the CdS film grows on LiNbO₃ oriented along the [0 0 1] axis in form of crystallized nanoplates, while that deposited on silicon forms randomly oriented nanoparticles. Investigation of the precursor thin film suggests that CdS forms from the O in the CdO precursor thin film being substituted by S from H₂S in the surrounding environment, which is designated as an atom substitution process. This novel method involving an atom substitution reaction between the CdO precursor thin film and its environment can provide a new low cost approach to the preparation of chalcogenide or other compound thin films. A schematic illustration and corresponding mechanism describing the details of this method are proposed.     

Exploring Group 14 Structures: 1D to 2D to 3D

Various one‐, two‐ and three‐dimensional Group 14 (C, Si, Ge, Sn, and Pb) element structures at P=1 atm are studied in this work. As expected, coordination number (CN)—not an unambiguous concept for extended structures—plays an important part in the stability of structures. Carbon not only favors four‐coordination, but also is quite happy with π‐bonding, allowing three‐ and even two‐coordination to compete. Highly coordinated (CN>4) discrete carbon molecules are rare; that “saturation of valence” is reflected in the instability of C extended structures with CN>4. Si and Ge are quite similar to each other in their preferences. They are less biased in their coordination than C, allowing (as their molecular structures do) CN=5 and 6, but tending towards four‐coordination. Sn and Pb 3D structures are very flexible in their bonding, so that in these elements four‐ to twelve‐coordinate structures are close in energy. This lack of discrimination among ordered structures also points to an approach to the liquid state, consistent with the low melting point of Sn and Pb. The Group 14 liquid structures we simulate in molecular dynamics calculations show the expected, effective, first coordination number increase from 5.1 for Si to 10.4 for Pb. A special point of interest emerging from our study is the instability of potential multilayer graphene structures down Group 14. Only for C will these be stable; for all the other Group 14 elements pristine, unprotected, bi‐ and multilayer graphenes should collapse, forming “vertical” bonds as short as the in‐plane ones.     

Multielectron-transfer reactions at single Cu(II) centers embedded in polyoxotungstates driven by photo-induced metal-to-metal charge transfer from anchored Ce(III) to framework W(VI)

Using carbon monoxide as a probe molecule for the oxidation state of Cu ions, we demonstrated that anchored polynuclear charge-transfer complexes consisting of Ce(III) ions and Cu(II)-substituted Keggin-type polyoxotungstates function as efficient visible-light-driven multielectron-transfer catalysts.     

Experimental and Theoretical Study on p-Chlorofluorobenzene in the S0, S1 and D0 States

The geometric structures and vibration frequencies of \begin{document}$ para $\end{document}-chlorofluorobenzene (\begin{document}$ p $\end{document}-ClFPh) in the first excited state of neutral and ground state of cation were investigated by resonance-enhanced multiphoton ionization and slow electron velocity-map imaging. The infrared spectrum of S\begin{document}$ _0 $\end{document} state and absorption spectrum for S\begin{document}$ _1 $\end{document}\begin{document}$ \leftarrow $\end{document}S\begin{document}$ _0 $\end{document} transition in \begin{document}$ p $\end{document}-ClFPh were also recorded. Based on the one-color resonant two-photon ionization spectrum and two-color resonant two-photon ionization spectrum, we obtained the adiabatic excited-state energy of \begin{document}$ p $\end{document}-ClFPh as 36302\begin{document}$ \pm $\end{document}4 cm\begin{document}$ ^{-1} $\end{document}. In the two-color resonant two-photon ionization slow electron velocity-map imagin spectra, the accurate adiabatic ionization potential of \begin{document}$ p $\end{document}-ClFPh was extrapolated as 72937\begin{document}$ \pm $\end{document}8 cm\begin{document}$ ^{-1} $\end{document} via threshold ionization measurement. In addition, Franck-Condon simulation was performed to help us confidently ascertain the main vibrational modes in the S\begin{document}$ _1 $\end{document} and D\begin{document}$ _0 $\end{document} states. Furthermore, the mixing of vibrational modes between S\begin{document}$ _0 $\end{document}\begin{document}$ \rightarrow $\end{document}S\begin{document}$ _1 $\end{document} and S\begin{document}$ _1 $\end{document}\begin{document}$ \rightarrow $\end{document}D\begin{document}$ _0 $\end{document} has been analyzed.     

Transfer of chirality from ligands to metal centers: recent examples

Recent examples of "chiral at metal" complexes and assemblies that are produced by chirality transfer of information from enantiopure ligands to metal ions are reported. They highlight the new progress that has been made in this area in the last two years and the new tendencies that such a topic is following. Besides the fundamental aspects related to the stereoselective synthesis of chiral complexes, the progress in diverse classes of chiral complexes for applications in materials science (chiral switches and molecular machines, biological mimics, CPL probes, etc.) is reported.     

Heteronuclear 1D and 2D NMR Resonances Detected by Chemical Exchange Saturation Transfer to Water

A method to detect NMR spectra from heteronuclei through the modulation that they impose on a water resonance is exemplified. The approach exploits chemical exchange saturation transfers, which can magnify the signal of labile protons through their influence on a water peak. To impose a heteronuclear modulation on water, an HMQC‐type sequence was combined with the FLEX approach. 1D ¹⁵N NMR spectra of exchanging sites could thus be detected, with about tenfold amplifications over the ¹⁵N modulations afforded by conventionally detected HMQC NMR spectroscopy. Extensions of this approach enable 2D heteronuclear acquisitions on directly bonded ¹H–¹⁵N spin pairs, also with significant signal amplification. Despite the interesting limits of detection that these signal enhancements could open in NMR spectroscopy, these gains are constrained by the rates of solvent exchange of the targeted heteronuclear pairs, as well as by spectrometer instabilities affecting the intense water resonances detected in these experiments.     

Designing a 0D/1D S-Scheme Heterojunction of Cadmium Selenide and Polymeric Carbon Nitride for Photocatalytic Water Splitting and Carbon Dioxide Reduction

Constructing photocatalysts to promote hydrogen evolution and carbon dioxide photoreduction into solar fuels is of vital importance. The design and establishment of an S-scheme heterojunction system is one of the most feasible approaches to facilitate the separation and transfer of photogenerated charge carriers and obtain powerful photoredox capabilities for boosting photocatalytic performance. Herein, a zero-dimensional/one-dimensional S-scheme heterojunction composed of CdSe quantum dots and polymeric carbon nitride nanorods (CdSe/CN) is created and constructed via a linker-assisted hybridization approach. The CdSe/CN composites exhibit superior photocatalytic activity in water splitting and promoted carbon dioxide conversion performance compared with CN nanorods and CdSe quantum dots. The best efficiency in photocatalytic water splitting (10.2% apparent quantum yield at 420 nm irradiation, 20.1 mmol g⁻¹ h⁻¹ hydrogen evolution rate) and CO₂ reduction (0.77 mmol g⁻¹ h⁻¹ CO production rate) was achieved by 5%CdSe/CN composites. The significantly improved photocatalytic reactivity of CdSe/CN composites primarily originates from the emergence of an internal electric field in the zero-dimensional/one-dimensional S-scheme heterojunction, which could greatly improve the photoinduced charge-carrier separation. This work underlines the possibility of employing polymeric carbon nitride nanostructures as appropriate platforms to establish highly active S-scheme heterojunction photocatalysts for solar fuel production.     

Diastereoselective cycloaddition of alkylidenecyclopropane nitrones from palladium(0)-catalyzed nucleophilic substitution of asymmetric 1-alkenylcyclopropyl esters by amino acids

The asymmetric construction of perhydropyrrolo[3,4-b]pyridine derivatives was performed by chemo- and regioselective formation of enantiopure alkylidenecyclopropane nitrones, followed by diastereoselective intramolecular 1,3-dipolar cycloaddition. The resulting spirocyclopropane isoxazolidines then underwent thermally induced regioselective ring expansion into optically active diazaheterocycles.     

Carbohydrate-coated nanocapsules from amphiphilic rod-coil molecule: binding to bacterial type 1 pili

Stable carbohydrate-coated nanocapsules designed as multivalent nanoscaffolds for selective interactions with receptors are able to encapsulate guest molecules within their interior and to bind efficiently to FimH adhesin of bacterial type 1 pili.     

Influence of copper substitution on the interaction of ethylene over iron clusters: a theoretical study

We report the results of density functional theory (DFT) calculations of ethylene adsorption over the most stable pure and bimetallic clusters of Fe(n)Cu(m) (2 ≤ m+n ≤ 4), in two adsorption modes of π and di-σ. Our results show that the quality of interaction of ethylene with iron center in bimetallic clusters of iron-copper is characteristically different from what is found over pure iron. Over the range of our studies for dimers, trimers, and tetramers, whether for π or di-σ mode, alloying iron clusters results in a substantial improvement in adsorption of ethylene over cluster and exhibits a notable increase in binding and interaction energies compared with pure iron clusters. One of the interesting features of this adsorption is that ethylene never orients toward di-σ mode for Cu-Cu or Fe-Cu bonds, and π orientation is strongly preferred. Ethylene adsorption in di-σ coordination is accompanied by the sever restructuring, larger deformation energy, and the larger interaction energy. In the next part, we answer this question of how electronic perturbations induced by copper atoms can enhance the activity of iron toward ethylene. This interpretation is done within the framework of natural bond orbital (NBO) and natural resonance theory (NRT) analyses. Different reaction pathways detected by NRT analysis (donor-acceptor, metallacyclic, and carbanion) reveal interesting aspects of differences between the nature of metal-alkene coordination in bimetallic and purely metallic clusters.     

Amine-controlled assembly of metal-sulfite architecture from 1D chains to 3D framework

Whereas open-framework materials have been made in a variety of chemical compositions, few are known in which 3-connected SO3(2)- anions serve as basic building units. Here, we report four new metal-sulfite polymeric structures, (ZnSO3)Py (1, py = pyridine), (ZnSO3)2(2,2'-bipy)H2O (2, 2,2'-bipy = 2,2'-bipyridine), (ZnSO3)2(TMDPy) (3, TMDPy = 4,4'-trimethylenedipyridine), and (MnSO3)2en (4, en = ethylenediamine) that have been synthesized hydrothermally and structurally characterized. In these compounds, low-dimensional 1D and 2D inorganic subunits are assembled into higher 2D or 3D covalent frameworks by organic ligands. In addition to the structure-directing effect of organic ligands, the flexible coordination chemistry of Zn2+ and SO3(2)- also contributes to the observed structural diversity. In compounds 1-3, Zn2+ sites alternate with trigonal pyramidal SO3(2)- anions to form three types of [ZnSO3]n chains, whereas in compound 4, a 2D-corrugated [MnSO3]n layer is present. Compound 1 features a rail-like chain with pendant pyridine rings. The pi-pi interaction between 2,2'-bipy ligands is found between adjacent chains in compound 2, resulting in 2D sheets that are further stacked through interlayer hydrogen bonds. Compound 3 exhibits a very interesting inorganic [(ZnSO3)2]n chain constructed from two chairlike subunits, and such chains are bridged by TMDPy ligands into a 2D sheet. In compound 4, side-by-side helical chains permeate through 2D-corrugated [MnSO3]n layers, which are pillared by neutral ethylenediamine molecules into a 3D framework that can be topologically represented as a (3,6)-connected net. The results presented here illustrate the rich structural chemistry of metal-sulfites and the potential of sulfite anions as a unique structural building block for the construction of novel open-framework materials, in particular, those containing polymeric inorganic subunits that may have interesting physical properties such as low-dimensional magnetism or electronic properties.     

Novel inorganic-organic hybrids constructed from multinuclear copper cluster and Keggin polyanions: from 1D wave-like chain to 2D network

Two novel inorganic-organic hybrids constructed from Keggin-type polyanions and multinuclear copper clusters based on 1-H-1,2,3-benzotriazole (HBTA), [Cu(I)(8)(BTA)(4)(HBTA)(8)(SiMo(12)O(40))]·2H(2)O (1) and [Cu(II)(6)(OH)(4)(BTA)(4)(SiW(12)O(40))(H(2)O)(6)]·6H(2)O (2), have been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction, elemental analyses, IR spectra and thermogravimetric (TG) analyses. In compound 1, eight Cu(I) ions were linked by twelve HBTA/BTA ligands to form an octanuclear Cu(I) cluster, which is connected by SiMo(12)O(40)(4-) anion with two bridging O atoms and two terminal O atoms to construct a one-dimensional (1D) wave-like chain. The octanuclear copper unit represents the maximum subunit linked just by amine ligands in the POMs system. In 2, four BTA ligands linked five Cu(II) ions constructing a pentanuclear "porphyrin-like" subunit, which is connected by another Cu(II) ion to form a 1D metal-organic band. The SiW(12)O(40)(4-) polyanions as tetradentate inorganic linkages extend the 1D band into a two-dimensional (2D) network with (8(3))(2)(8(5)·10) topology. To the best of our knowledge, compounds 1 and 2 represent the first examples of inorganic-organic hybrids based on metal-HBTA multinuclear subunits and polyoxometalates. The photocatalysis and electrochemical properties have been investigated in this paper.