In this paper, a facile strategy is reported for the preparation of well-dispersed Pt nanoparticles in ordered mesoporous silica (Pt@OMS) by using a hybrid mesoporous phenolic resin-silica nanocomposite as the parent material. The phenolic resin polymer is proposed herein to be the key in preventing the aggregation of Pt nanoparticles during their formation process and making contributions both to enhance the surface area and enlarge the pore size of the support. The Pt@OMS proves to be a highly active and stable catalyst for both gas-phase oxidation of CO and liquid-phase hydrogenation of 4-nitrophenol. This work might open new avenues for the preparation of noble metal nanoparticles in mesoporous silica with unique structures for catalytic applications.

A series of isoreticular metal–organic frameworks (MOFs; NENU-511–NENU-514), which all have high surface areas and strong adsorption capacities, have been successfully constructed by using mixed ligands. NENU-513 has the highest benzene capacity of 1687 mg g⁻¹at 298 K, which ranks as the top MOF material among those reported up to now. This NENU series has been used for adsorptive desulfurization because of its permanent porosity. The results indicate that this series has a higher adsorptive efficiency in the removal of organosulfur compounds than other MOF materials, especially NENU-511, which has the highest adsorptive efficiency in the ambient atmosphere. This study proves that the design and synthesis of targeted MOFs with higher surface areas and with functional groups present is an efficient method to enhance benzene-storage capacity and the adsorption of organosulfur compounds.

The syntheses of two new heteroleptic cationic iridium complexes containing 2,6-diphenylpyridine (Hdppy) and 2,4,6-triphenylpyridine (Htppy) as the cyclometalated ligands, namely, [Ir(dppy)₂phen]PF₆ (1, phen = 1,10-phenanthroline) and [Ir(tppy)₂phen]PF₆ (2), are described. The X-ray crystal structure of 2 reveals a distorted octahedral geometry around the Ir center and close intramolecular face-to-face π–π stacking interactions between the pendant phenyl rings at the 2-position of the cyclometalated ligands and the NN ancillary ligand. This represents a new π–π stacking mode in charged Ir complexes. Complexes 1 and 2 are green photoemitters: their photophysical and electrochemical properties are interpreted with the assistance of density functional theory (DFT) calculations. These calculations also establish that the observed intramolecular interactions cannot effectively prevent the lengthening of the Ir–N bonds of the complexes in their metal-centered (³MC) states. Complexes 1 and 2 do not emit light in light-emitting electrochemical cells (LECs) under conditions in which the model compound [Ir(ppy)₂phen]PF₆ (3) emits strongly. This is explained by degradation reactions of the ³MC state of 1 and 2 under the applied bias during LEC operation facilitated by the enhanced distortions in the geometry of the complexes. These observations have important implications for the future design of complexes for LEC applications.

Herein, a novel anionic framework with primitive centered cubic (pcu) topology, [(CH₃)₂NH₂]₄[(Zn₄dttz₆)Zn₃]⋅15 DMF⋅4.5 H₂O, (IFMC-2; H₃dttz=4,5-di(1H-tetrazol-5-yl)-2H-1,2,3-triazole) was solvothermally isolated. A new example of a tetranuclear zinc cluster {Zn₄dttz₆} served as a secondary building unit in IFMC-2. Furthermore, the metal cluster was connected by Zn^II ions to give rise to a 3D open microporous structure. The lanthanide(III)-loaded metal–organic framework (MOF) materials Ln³⁺@IFMC-2, were successfully prepared by using ion-exchange experiments owing to the anionic framework of IFMC-2. Moreover, the emission spectra of the as-prepared Ln³⁺@IFMC-2 were investigated, and the results suggested that IFMC-2 could be utilized as a potential luminescent probe toward different Ln³⁺ ions. Additionally, the absorption ability of IFMC-2 toward ionic dyes was also performed. Cationic dyes can be absorbed, but not neutral and anionic dyes, thus indicating that IFMC-2 exhibits selective absorption toward cationic dyes. Furthermore, the cationic dyes can be gradually released in the presence of NaCl.

A series of spiral donor–π–acceptor frameworks (i.e. 2–2, 3–3, 4–4, and 5–5) based on 4-nitrophenyldiphenylamine with π-conjugated linear acenes (naphthalenes, anthracenes, tetracenes, and pentacenes) serving as the electron donor and nitro (NO₂) groups serving as the electron acceptor were designed to investigate the relationships between the nonlinear optical (NLO) responses and the spirality in the frameworks. A parameter denoted as D was defined to describe the extent of the spiral framework. The D value reached its maximum if the number of NO₂ groups was equal to the number of fused benzene rings contained in the linear acene. A longer 4-nitrophenyldiphenylamine chain led to a larger D value and, further, to a larger first hyperpolarizability. Different from traditional NLO materials with charge transfer occurring in the one-dimensional direction, charge transfer in 2–2, 3–3, 4–4, and 5–5 occur in three-dimensional directions due to the attractive spiral frameworks, and this is of great importance in the design of NLO materials. The origin of such an enhancement in the NLO properties of these spiral frameworks was explained with the aid of molecular orbital analysis.

Carbon–boron–nitride heteronanotubes have attracted much interest owing to their adjustable properties and wide applications in many fields. In this work, the structures and first hyperpolarizabilities (β₀) of a series of HA-n and isoelectronic PA-n heteronanotubes are investigated, in which HA-n is composed of a helical C segment and BN segment, and PA-n is composed of an arc C segment and BN segment. Interestingly, the helix C segment in HA-9 leads to a fascinating long-range charge-transfer character. As a result, the β₀ value of HA-9 is 1.80×10⁴ a.u., which is much larger than that of PA-9 (4.99×10³ a.u.). Significantly, the β₀ value of the C segment in HA-9 is 1.72×10⁴ a.u., whereas that of the BN segment in HA-9 is much smaller (7.48×10² a.u.). In this context, the larger β₀ value of HA-9 is essentially induced by the helix topological effect of the C segment. It is our expectation that this new knowledge about heteronanotubes might provide more ideas for further exploration of sp²-hybridized carbon segments with special topologies.

A 2D, extremely stable, metal–organic framework (MOF), NENU-503, was successfully constructed. It displays highly selective and recyclable properties in detection of nitroaromatic explosives as a fluorescent sensor. This is the first MOF that can distinguish between nitroaromatic molecules with different numbers of NO₂ groups.

Eight new iridium(III) complexes 1-8, with 1,3,4-oxadiazole (OXD) derivatives as the cyclometalated C^N ligand and/or the ancillary N^N ligands are synthesized and their electrochemical, photophysical, and solid-state light-emitting electrochemical cell (LEC) properties are investigated. Complexes 1, 2, 7 and 8 are additionally characterized by single crystal X-ray diffraction. LECs based on complexes 1-8 are fabricated with a structure indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/cationic iridium complex:ionic liquid/Al. LECs of complexes 1–6 with OXD derivatives as the cyclometalated ligands and as the ancillary ligand show yellow luminescence (λ_max = 552–564 nm). LECs of complexes 7 and 8 with cyclometalated C^N phenylpyridine ligands and an ancillary N^N OXD ligand show red emission (λ_max 616–624 nm). Using complex 7 external quantum efficiency (EQE) values of >10% are obtained for devices (210 nm emission layer) at 3.5 V. For thinner devices (70 nm) high brightness is achieved: red emission for 7 (8528 cd m⁻² at 10 V) and yellow emission for 1 (3125 cd m⁻² at 14 V).

A systematic density functional study was performed on the structures and bonding features in a homologous metal–metal (M–M) host–guest series M₂@C₅₀X₁₀ (M = Zn, Cd, Hg; X = CH, N, B). Calculations indicated that D_5d conformers are energy minima for Zn₂@C₅₀X₁₀ (X = CH, N) and Cd₂@C₅₀X₁₀ (X = CH, N, B), whereas Zn₂@C₅₀B₁₀ has no imaginary frequency with the lowered C_2h symmetry. Among these hybrid fullerene–metal complexes, those with dizinc and dicadmium guests adopt η⁵/η⁵ coordination, except for an η²/η² case in C_2h-Zn₂@C₅₀B₁₀, to meet appropriate interactions between the metal atom and cage; and the η¹/η¹ coordination mode can only be satisfied in just one (Hg₂@C₅₀N₁₀) of the complexes with Hg–Hg guests, regardless of the enforced coordination surroundings. The nature of metal–cage interactions between M₂²⁺ and C₅₀X₁₀^2– moieties and M–M bonds have been analyzed by means of the topological properties of electron densities and energy-partitioning methods, and results suggest that the two types of interactions are almost similar to those in their M₂(C₅H₅)₂ counterparts.

Two anionic metal–organic frameworks (MOFs) with 1D mesoporous tubes (1) and chiral mesoporous cages (2) have been rationally constructed by means of a predesigned size-extended hexatopic ligand, namely, 5,5′,5′′-(1,3,5-triazine-2,4,6-triyl)tris- (azanediyl)triisophthalate (TATAT). Charge neutrality is achieved by protonated dimethylamine cations. Notably, the two MOFs can be used to separate large molecules based on ionic selectivity rather than the size-exclusion effect so far reported in the literature. Owing to the imino triazine backbone and carboxyl groups of the hexatopic ligand, which provide important host–guest interactions, rare solvatochromic phenomena of 1 and 2 are observed on incorporating acetone and ethanol guests. Furthermore, guest-dependent luminescence properties of compound 2 were investigated, and the results show that luminescence intensity is significantly enhanced in toluene and benzene, while quenching effects are observed in acetone and ethanol. Thus, compound 2 may be a potential material for luminescent probes.

A new family of heterometal–organic frameworks has been prepared by two synthesis strategies, in which IFMC-26 and IFMC-27 are constructed by self-assembly and IFMC-28 is obtained by stepwise synthesis based on the metalloligand (IFMC=Institute of Functional Material Chemistry). IFMC-26 is a (3,6)-connected net and IFMC-27 is a (4,8)-connected 3D framework. The metalloligands {Ni(H₄L)}(NO₃)₂ are connected by binuclear lanthanide clusters giving rise to a 2D sheet structure in IFMC-28. Notably, IFMC-26-Eu_xTb_y and IFMC-28-Eu_xTb_y have been obtained by changing the molar ratios of raw materials. Owing to the porosity of IFMC-26, Tb³⁺@IFMC-26-Eu and Eu³⁺@IFMC-26-Tb are obtained by postencapsulating Tb^III and Eu^III ions into the pores, respectively. Tunable luminescence in metal–organic frameworks is achieved by the two kinds of doping methods. In particular, the quantum yields of heterometal–organic frameworks are apparently enhanced by postencapsulation of Ln^III ions.

A versatile one-pot strategy was employed to synthesize three cerium(III)-stabilized polyoxotungstates nanoclusters by combining cerium linkers and SeO₃²⁻/TeO₃²⁻ heteroanion templates: K₃₂Na₁₆[{(XO₃)W₁₀O₃₄}₈{Ce₈(H₂O)₂₀}(WO₂)₄- (W₄O₁₂)]⋅n H₂O [X=Se, n=81 (1); X=Te, n=114 (2)] and K₁₂Na₂₂[{(SeO₃)W₁₀O₃₄}₈{Ce₈(H₂O)₂₀}(WO₂)₄- {(W₄O₆)Ce₄(H₂O)₁₄(SeO₃)₄(NO₃)₂}]⋅ 79 H₂O (3), which are the first lanthanide-containing polyoxotungstates with selenium or tellurium heteroatoms. The three clusters were characterized by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric/differential thermal analysis, UV/Vis spectroscopy, ESI-MS, and X-ray photoelectron spectroscopy. Their electrochemical, photoluminescence, and magnetic properties were investigated. Their behavior in solution was studied by transmission electron microscopy, which showed that their single polyoxoanions assemble into intact, uniform-sized, purely inorganic hollow spheres in dilute water/acetone solution.

We design a new type of molecular diode, based on the organoimido derivatives of hexamolybdates, by exploring the rectifying performances using density functional theory combined with the non-equilibrium Green’s function. Asymmetric current–voltage characteristics were obtained for the models with an unexpected large rectification ratio. The rectifying behavior can be understood by the asymmetrical shift of the transmission peak observed under different polarities. It is interesting to find that the preferred electron-transport direction in our studied system is different from that of the organic D-bridge-A system. The results show that the studied organic–inorganic hybrid systems have an intrinsically robust rectifying ratio, which should be taken into consideration in the design of the molecular diodes.

DFT calculations were carried out in order to study the second-order nonlinear optical (NLO) response of a series of proposed 2D polyoxometalate-based terpyridine-substituted compounds. These compounds can be formulated as [Mo₆O₁₇{N₄C₂₅H₁₆(X)₂}{N₄C₂₅H₁₆(X)₂}]^2– (X = H, F, Cl, Br, I, CF₃, or CN), which has a wedge Λ-shaped acceptor––π-conjugated bridge––donor––π-conjugated bridge––acceptor (A-π-D-π-A) configuration. The calculations showed that these compounds possess significantly large molecular second-order polarizabilities that range from approximately 1000 × 10^–30 to 4300 × 10^–30 esu. The combination of trifluoromethyl (CF₃) and cyanide (CN) groups at the end of the terpyridine ligand strengthens the bridge conjugation, which is useful for the enhancement of the NLO response. In addition, the greatest contributions to the β_vec values are dervied from the charge transfer (CT) from the Mo≡N bond and the organoimido ligand to the terpyridine-substituted segments. This report demonstrates that various combinations of the acceptor(s) remarkably affect the second-order NLO response. The electronic transitions to the crucial excited states indicated that the y polarized transition contributed to the off-diagonal second-order polarizabiliy tensor (β_zyy) and that the z polarized transition accounted for the diagonal second-order polarizabiliy tensor (β_zzz). Thus, itsteered towards in-plane nonlinear anisotropy (u = β_zyy/β_zzz) along with a good 2D second-order NLO response. These compounds can be used as good 2D second-order NLO materials from the point of view of their large β values.

The structures and second-order nonlinear optical (NLO) properties of a series of chlorobenzyl-o-carboranes derivatives (1–12) containing different push-pull groups have been studied by density functional theory (DFT) calculation. Our theoretical calculations show that the static first hyperpolarizability (β_tot) values gradually increase with increasing the π-conjugation length and the strength of electron donor group. Especially, compound 12 exhibits the largest β_tot (62.404×10⁻³⁰ esu) by introducing tetrathiafulvalene (TTF), which is about 76 times larger than that of compound 1 containing aryl. This means that the appropriate structural modification can substantially increase the first hyperpolarizabilities of the studied compounds. For the sake of understanding the origin of these large NLO responses, the frontier molecular orbitals (FMOs), electron density difference maps (EDDMs), orbital energy and electronic transition energy of the studied compounds are analyzed. According to the two-state model, the lower transition energy plays an important role in increasing the first hyperpolarizability values. This study may evoke possible ways to design preferable NLO materials.

Six N-substituted [n]cyclacene (n = 5, 6, 7,…,10) molecules were designed to study the relationship between the structure and first hyperpolarizability. Their static first hyperpolarizabilities (β₀) were obtained by MP2/6-31 + g(d) level. Two interesting relationships between the β₀ value and the structure have been found: (1) The β₀ value increases with the increase of the number n when n is odd: 3155 ([5]cyclacene) < 48,905 ([7]cyclacene) < < 393,444 ([9]cyclacene), and when n is even: 357,620 ([6]cyclacene) < 618,608 ([8]cyclacene) < 3,513,644 a.u. ([10]cyclacene). (2) The β₀ values (in the range of 357,620 ~ 3,513,644 a.u.) of the N-substituted [n]cyclacene (when n is odd) are much larger (in the range of 3155~393,444 a.u.) than that of the N-substituted [n]cyclacene (when n is even). Furthermore, their frequency-dependent β (−2ω; ω, ω) and β (−ω; ω, 0) (ω = 0.005, 0.01, and 0.0239 a.u.) were also estimated by Møller–Plesset perturbation/6-31 + g(d) level. Among the frequency-dependent β (ω), [10]cyclacene has the largest β (−ω; ω, 0) and β (−2ω; ω, ω) to be 1.2 × 10⁸ (ω = 0.01) and 2.9 × 10⁷ a.u. (ω = 0.005 a.u.), which are much larger than the static β₀ = 3.5 × 10⁶ a.u. by 34 and 8 times. Our present work may offer a new idea in the design of high-performance tubiform nonlinear optical materials. Copyright © 2011 John Wiley & Sons, Ltd.

The unusual properties of species with excess electrons have attracted a lot of interest in recent years due to their wide applications in many promising fields. In this work, we find that the excess electron could be effectively bound by the B atoms of boron nitride nanotube (BNNT), which is inverted pyramidally distributed from B-rich edge to N-rich edge. Further, Li@B-BNNT and Li@N-BNNT are designed by doping the Li atom to the two edges of BNNT, respectively. Because of the interaction between the Li atom and BNNT, the 2s valence electron of Li becomes a loosely bound excess electron. Interestingly, the distribution of the excess electron in Li@N-BNNT is more diffuse and pyramidal from B-rich edge to N-rich edge, which is fascinating compared with Li@B-BNNT. Correspondingly, the transition energy of Li@N-BNNT is 0.99 eV, which is obviously smaller than 2.65 eV of Li@B-BNNT. As a result, the first hyperpolarizability (3.40×10⁴ a.u.) of Li@N-BNNT is dramatically larger (25 times) than 1.35×10³ a.u. of Li@B-BNNT. Significantly, we find that the pyramidal distribution of the excess electron is the key factor to determine the first hyperpolarizability, which reveals useful information for scientists to develop new electro-optic applications of BNNTs.

A method is reported for the first time for the selected-control, large-scale synthesis of monodispersed Fe₃O₄@C core–shell spheres, chains, and rings with tunable magnetic properties based on structural evolution from eccentric Fe₂O₃@poly(acrylic acid) core–shell nanoparticles. The Fe₃O₄@C core–shell spheres, chains, and rings were investigated as anode materials for lithium-ion batteries. Furthermore, a possible formation mechanism of Fe₃O₄@C core–shell chains and rings has also been proposed.

The selected-control preparation of uniform core–shell and yolk–shell architectures, which combine the multiple functions of a superparamagnetic iron oxide (SPIO) core and europium-doped yttrium oxide (Y₂O₃:Eu) shell in a single material with tunable fluorescence and magnetic properties, has been successfully achieved by controlling the heat-treatment conditions. Furthermore, the shell thickness and interior cavity of SPIO@Y₂O₃:Eu core–shell and yolk–shell nanostructures can be precisely tuned. Importantly, as-prepared SPIO@Y₂O₃:Eu yolk–shell nanocapsules (NCs) modified with amino groups as cancer-cell fluorescence imaging agents are also demonstrated. To the best of our knowledge, this is the first report on the selected-control fabrication of uniform SPIO@Y₂O₃:Eu core–shell nanoparticles and yolk–shell NCs. The combined magnetic manipulation and optical monitoring of magnetic–fluorescent SPIO@Y₂O₃:Eu yolk–shell NCs will open up many exciting opportunities in dual imaging for targeted delivery and thermal therapy.

Hollow mesoporous SiO₂ (mSiO₂) nanostructures with movable nanoparticles (NPs) as cores, so-called yolk-shell nanocapsules (NCs), have attracted great research interest. However, a highly efficient, simple and general way to produce yolk-mSiO₂ shell NCs with tunable functional cores and shell compositions is still a great challenge. A facile, general and reproducible strategy has been developed for fabricating discrete, monodisperse and highly uniform yolk-shell NCs under mild conditions, composed of mSiO₂ shells and diverse functional NP cores with different compositions and shapes. These NPs can be Fe₃O₄ NPs, gold nanorods (GNRs), and rare-earth upconversion NRs, endowing the yolk-mSiO₂ shell NCs with magnetic, plasmonic, and upconversion fluorescent properties. In addition, multifunctional yolk-shell NCs with tunable interior hollow spaces and mSiO₂ shell thickness can be precisely controlled. More importantly, fluorescent-magnetic-biotargeting multifunctional polyethyleneimine (PEI)-modified fluorescent Fe₃O₄@mSiO₂ yolk-shell nanobioprobes as an example for simultaneous targeted fluorescence imaging and magnetically guided drug delivery to liver cancer cells is also demonstrated. This synthetic approach can be easily extended to the fabrication of multifunctional yolk@mSiO₂ shell nanostructures that encapsulate various functional movable NP cores, which construct a potential platform for the simultaneous targeted delivery of drug/gene/DNA/siRNA and bio-imaging.

The geometric and electronic structures and photophysical properties of anilido-pyridine boron difluoride dyes 1–4, a series of scarce 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives with large Stokes shift, are investigated by employing density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to shed light on the origin of their large Stokes shifts. To this end, a suitable functional is first determined based on functional tests and a recently proposed index—the charge-transfer distance. It is found that PBE0 provides satisfactory overall results. An in-depth insight into Huang–Rhys (HR) factors, Wiberg bond indices, and transition density matrices is provided to scrutinize the geometric distortions and the character of excited states pertaining to absorption and emission. The results show that the pronounced geometric distortion due to the rotation of unlocked phenyl groups and intramolecular charge transfer are responsible for the large Stokes shift of 1 and 2, while 3 shows a relatively blue-shifted emission wavelength due to its mild geometric distortion upon photoemission, although it has a comparable energy gap to 1. Finally, compound 4, which is designed to realize the rare red emission in BODIPY derivatives, shows desirable and expected properties, such as high Stokes shift (4847 cm⁻¹), red emission at 660 nm, and reasonable fluorescence efficiency. These properties give it great potential as an ideal emitter in organic light-emitting diodes. The theoretical results could complement and assist in the development of BODIPY-based dyes with both large Stokes shift and high quantum efficiency.

Much effort has been devoted to investigating the unusual properties of the π electrons in Möbius cyclacenes, which are localized in a special region. However, the localized π electrons are a disadvantage for applications in optoelectronics, because intramolecular charge transfer is limited. This raises the question of how the intramolecular charge transfer of a Möbius cyclacene with clearly localized π electrons can be enhanced. To this end, [8]Möbius cyclacene ([8]MC) is used as a conjugated bridge in a donor–π-conjugated bridge–acceptor (D–π–A) system, and NH₂-6-[8]MC-10-NO₂ exhibits a fascinating spiral charge-transfer transition character that results in a significant difference in dipole moments Δμ between the ground state and the crucial excited state. The Δμ value of 6.832 D for NH₂-6-[8]MC-10-NO₂ is clearly larger than that of 0.209 D for [8]MC. Correspondingly, the first hyperpolarizability of NH₂-6-[8]MC-10-NO₂ of 12 467 a.u. is dramatically larger than that of 261 a.u. for [8]MC. Thus, constructing a D–π–A framework is an effective strategy to induce greater spiral intramolecular charge transfer in MC although the π electrons are localized in a special region. This new insight into the properties of π electrons in Möbius cyclacenes may provide valuable information for their applications in optoelectronics.

Drying-tube-shaped single-walled carbon nanotubes (SWCNTs) with multiple carbon ad-dimer (CD) defects are obtained from armchair (n,n,m) SWCNTs (n=4, 5, 6, 7, 8; m=7, 13). According to the isolated-pentagon rule (IPR) the drying-tube-shaped SWCNTs are unstable non-IPR species, and their hydrogenated, fluorinated, and chlorinated derivatives are investigated. Interestingly, chemisorptions of hydrogen, fluorine, and chlorine atoms on the drying tube-shaped SWCNTs are exothermic processes. Compared to the reaction energies for binding of H, F, and Cl atoms to perfect and Stone–Wales-defective armchair (5,5) nanotubes, binding of F with the multiply CD defective SWCNTs is stronger than with perfect and Stone–Wales-defective nanotubes. The reaction energy for per F₂ addition is between 85 and 88 kcal mol⁻¹ more negative than that per H₂ addition. Electronic structure analysis of their energy gaps shows that the CD defects have a tendency to decrease the energy gap from 1.98–2.52 to 0.80–1.17 eV. After hydrogenation, fluorination, and chlorination, the energy gaps of the drying-tube-shaped SWCNTs with multiple CD defects are substantially increased to 1.65–3.85 eV. Furthermore, analyses of thermodynamic stability and nucleus-independent chemical shifts (NICS) are performed to analyze the stability of these molecules.

Density functional theory (DFT) calculations were performed for three ruthenium/nitrous oxide(N₂O) adducts, Ru^IICl₂(η¹-N₂O)(P–N)(PPh₃) {P–N = [o-(dimethylamino)phenyl]diphenylphosphane} (1), Ru^II(η¹-N₂O)(TMP)(THF) (TMP = dianion of tetramesitylporphyrin, THF = tetrahydrofuran) (2), and [PW₁₁O₃₉{Ru^II/(η¹-N₂O/H₂O)}]^n– (3). The bonding interactions between the N₂O molecule and the metal–ruthenium fragment were determined from the energy-decomposition analysis (EDA) and their electronic structures. The results show that the bonding in the ruthenium(II)/N₂O adducts 1–3 can be interpreted in terms of weak donor–acceptor interactions between the N₂O molecule and the ruthenium(II) center. The geometrical optimization of the polyoxometalate (POM) adduct 3 indicates a bent Ru–NNO linkage, which effectively enhances donor–acceptor interactions with the quasi π-symmetry orbital. The mono-ruthenium(II) substituted Keggin-type POM adduct 3 is a potential reagent for the activation of the N₂O molecule because of the strong Ru–NNO bond and the significant RuNN–O π*-antibonding orbital character relative to adducts 1 and 2, according to our DFT calculations.

On the basis of the famous staggered biphenalenyl diradical π dimer 1, the eclipsed biphenalenyl (1 a), with no centrosymmetry, was obtained by rotating a layer of 1 by 60° around its central axis. Furthermore, the central carbon atoms of 1 and 1 a were substituted by boron and nitrogen atoms to form 2 and 2 a with a novel 2e–12c bond. We found that the novel 2e–12c bond is formed by the electron pair of the occupied orbital of the phenalenyl monomer substituted by the nitrogen atom and the unoccupied orbital of the phenalenyl monomer substituted by the boron atom. As a result of the novel 2e–12c bond, 2 and 2 a exhibit a fascinating interlayer charge-transfer transition character, which results in a significant difference in the dipole moments (Δμ) between the ground state and the crucial excited state. The values of Δμ for 2 and 2 a are 6.4315 and 6.9253 Debye, clearly larger than the values of 0 and 0.0015 Debye for 1 and 1 a. Significantly, the boron/nitrogen substitution effect can greatly enhance the first hyperpolarizabilities (β₀) of 2 and 2 a with a novel 2e–12c bond compared with 1 and 1 a with a traditional 2e–12c bond: 0 and 19 a.u. for 1 and 1 a are much lower than 3516 and 12272 a.u. for 2 and 2 a. Furthermore, the interaction energies (E_int)of 2 and 2 a are larger than those of 1 and 1 a, which could be considered as a signature of reliability for the newly designed dimers. Our present work will be beneficial for further theoretical and experimental studies on the properties of molecules with the novel 2e–12c bond.

In this paper, the preparation of ascorbic acid (AA)-doped polyoxometalate (SiW₁₂-AA) microtubes is described. The SiW₁₂-AA microtubes convert to heteropoly blue microtubes upon exposure to ammonia gas, which is an ammonia-triggered solid–solid redox reaction between AA molecules and polyoxometalates, and can possibly be applied to a chemical sensor for detecting ammonia and volatile organic amines. Furthermore, the SiW₁₂-AA microtubes have been applied to the in situ synthesis of Ag nanoparticles (NPs) through the redox reaction between the AA component and Ag⁺ ions occurring on the surfaces of the SiW₁₂-AA microtubes to give silver NPs immobilized on polyoxometalate microtubes (Ag@SiW₁₂).

An optical oxygen sensor based on an Eu^III complex/polystyrene (PS) composite nanofibrous membrane is prepared by electrospinning. The emission intensity of [Eu(TTA)₃(phencarz)] (TTA=2-thenoyltrifluoroacetonate, phencarz=2-(N-ethylcarbazolyl-4)imidazo[4,5-f]1,10-phenanthroline) decreases with increasing oxygen concentration, and thus the [Eu(TTA)₃ (phencarz)]/PS composite nanofibrous membranes can be used as an optical oxygen-sensing material based on emission quenching caused by oxygen. Elemental analysis, UV/Vis absorption spectra, scanning electron microscopy (SEM), fluorescence microscopy, luminescence-intensity quenching Stern–Volmer plots, and excited-state decay analysis are used to characterize the obtained oxygen-sensing materials. A high sensitivity (I_N2/I_O2) of 3.38 and short response and recovery times (t=5.0, t=8.0 s) are obtained. These results are the best values reported for oxygen sensors based on Eu^III complexes. The high surface area-to-volume ratio and porous structure of the electrospun nanofibrous membranes are taken to be responsible for the outstanding performance.

A dramatic increase in the second-order nonlinear optical (NLO) response of terpyridine-substituted hexamolybdates has been observed from 886.55 × 10^–30 esu (system 1) to 4622.92 × 10^–30 esu (system 7). The dipole polarizabilities and second-order nonlinear optical (NLO) properties of terpyridine derivatives of hexamolybdates have been investigated by using time-dependent density functional theory (TDDFT). The quantum mechanical design suggests that [Mo₆O₁₈(N₄C₂₅H₁₄(CF₃)₂ (CN)₂)]^2– (system 7) is the best choice among all studied systems to improve nonlinearity. The electron-withdrawing ability of electron-acceptor groups (F, Cl, Br, I, CF₃, and CN) at the end of the terpyridine ligand directs the charge transfer (CT) from the POM cluster to the terpyridine segment along the z axis, which leads to an efficient second-order NLO molecular design. These small changes in molecular composition by substitution may have disproportionately huge effects on the NLO properties, which can be attributed to the so-called “butterfly effect”.

The preparation of exquisite hierarchical worm-like Co_1−xS (x=0.75) microtubes by a one-pot complex–surfactant-assisted hydrothermal method is successfully achieved for the first time. The hierarchical structures of the microtube wall are assembled from numerous interleaving hexagonal nanoplates. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy were used to characterize the samples. The experimental results indicate that the “soft template” surfactant cetyltrimethylammonium bromide and the chelating ethylenediamine both play important roles for the formation of hierarchical Co_1−xS microtubes. A possible formation mechanism for the growth processes is proposed. Additionally, the electrochemical and magnetic properties of Co_1−xS microtubes were systematically studied.

The bonding characteristics, first hyperpolarizabilities, and origin of the nonlinear optical (NLO) properties of aryloxido and salicylaldehydo derivatives of [XW₅O₁₈]^3– (X = Zr or Ti) have been investigated using density functional theory (DFT). The flexible bonding behavior of the linkage oxygen (O_L) atom attracted our attention initially, and NBO analysis revealed that there aret two different kinds of π-interactions involving the O_L atom in these systems. In two aryloxido derivatives (systems 1 and 2), O_L–metal π-interactions are largely O_L–M p-d in character, whereas in the salicylaldehydo derivatives (system 3) we observed another kind of π-interaction, namely O_L–C p-p π-bonding. The differences in molecular composition in our studied systems are very slight. However, the β₀ values differ significantly. Thus, system 3 has the largest β₀ value(559.27 × 10^–30 esu), which is 170 times larger than that of system 1. This variation can be traced to the different electronic transitions and charge-transfer characteristics. The heteropolyanion cluster and organic ligand are both electron-rich groups. A small change in molecular composition or architecture can therefore significantly modify the configuration and overlapping of molecular orbitals, thus causing a “butterfly effect” upon the electronic transitions and charge-transfer characteristics.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The second-order polarizabilities, transition moments, and density of states of aryldiazenido hexamolybdates derivatives were investigated by density functional theory (DFT). System 2 [Mo₆O₁₈(N₂C₆H₅)]^3– has a considerably large second-order polarizability, 14.50 × 10^–30 esu, and it is larger than that of system 1 [Mo₆O₁₈(N₂C₆H₄NO₂)]^3– due to the absence of nitro group in the aryldiazenido ligand. The aryldiazenido ligand acts as an electron donor and the polyanion acts as an electron acceptor. The substitution of an amino(-NH₂) group in the ortho/para positions on the aryldiazenido segment leads to a substantially higher nonlinear optical (NLO) response. The introduction of an electron donor(-NH₂) in the ortho, meta, para, and ortho/para positions on the aryldiazenido ligand significantly enhances the second-order polarizabilities of aryldiazenido hexamolybdates in comparison to the electron acceptor (-NO₂) as in system 1, because the electron-donating ability was reasonably enhanced when the electron donor is attached to the aryldiazenido ligand. Furthermore, orbital analysis shows that incorporation of another phenyl (aromatic) ring in the aryldiazenido ligand leads to a maximum NLO response by reverting the direction and degree of charge transfer (CT), which might result from the C=C π-conjugated bridge. System 8 [Mo₆O₁₈ (N₂C₁₄H₁₁)]^3– possesses a strikingly large and conspicuous static second-order polarizability (β_vec) computed to be 210.21 × 10^–30 esu. The NLO response can be tuned by subtle changes in the aryldiazenido segment; the present investigation provides important insight into the NLO properties of (aryldiazenido) hexamolybdate derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Two isostructural compounds, {[Cu₂(DF)₂H₂O]₂SiW₁₂O₄₀}·2H₂O (1) and {[Cu₂(DF)₂H₂O]₂GeMo₁₂O₄₀}·2H₂O (2) (DF = 4,5-diazafluoren-9-one), were synthesized and characterized by routine methods and single-crystal X-ray diffraction. In the compounds, each Keggin cluster links five copper dimers [Cu₂(DF)₂H₂O]²⁺ in an unusual asymmetrical pentacoordination mode to form 3D networks with left- and right-handed helical chains. Notably, by comparing 1 and 2 with other helical compounds with Keggin clusters as connectors, we found that the pitches of those compounds are mainly dominated by the coordination modes of the Keggin clusters, suggesting that the Keggin clusters are pitch-tunable synthons. Furthermore, the luminescent and electrochemical properties of the title compound were studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

An unsystematic molecule PPV-Alq₃ [3-(4-((E)-2-(8-hydroxy-3-(4-styrylstyryl)quinolin-Alq₂-6-yl)vinyl)- styryl)-6-(4-styrylstyryl)quinolin-8-olate-Alq₂; q=8-quinolinolate], which combines poly(p-phenylenevinylene) with tris(8-quinolinolate)aluminum, has been studied using a localized-density-matrix method. The absorption spectra and electronic transition properties were analyzed and compared with both intermediate neglect of the differential overlap method and the localized-density-matrix method. Great efforts have been made on investigating conjugated system on the absorption properties as these can be particularly important for many applications. Two different absorptions of the special molecule, tris(8-quinolinolate)aluminum grafted on poly(p-phenylenevinylene) units, were further discussed with density matrices. For the molecule, the first absorption peak is at 413 nm near the purple light. Two 8-hydroxyquinolines have very slight electronic transition properties. Another absorption peak is at 237 nm. The second characteristic peak of molecule is completely different from that of the first one, which comes from contribution of 8-hyroxyquinolines in the two different side chains. Our studies show that electronic transition properties of poly(p-phenylenevinylene) can be effectively tuned by grafting tris(8-quinolinolate)-aluminum on poly(p-phenylenevinylene) from the standpoint of transition energies, frontier molecular orbitals and density matrices.

Five compounds based on [MnMo₉O₃₂]⁶⁻: (Himi)₆[MnMo₉O₃₂] (1) (imi=imidazole), Na₂(Himi)₄[MnMo₉O₃₂]⋅2 H₂O (2), Na₃(Himi)₃[MnMo₉O₃₂] (3), D-NH₄Mn_2.5[MnMo₉O₃₂]⋅11 H₂O (4 a), and L-NH₄Mn_2.5[MnMo₉O₃₂]⋅11 H₂O (4 b) were prepared and characterized. X-ray crystallographic analysis revealed that compounds 1 and 2 with imidazole molecules as linkers are racemic compounds; compound 3 is a racemic solid solution of Na⁺ cations and the polyoxoanion [MnMo₉O₃₂]⁶⁻; and compounds 4 a and 4 b are enantiomers. In compound 4, the homochiral polyoxoanions [MnMo₉O₃₂]⁶⁻ are connected by Mn²⁺ cations to form a unique (4⁵⋅6)(4⁷⋅6⁸) topology net framework. By adjusting the linkers from imidazole molecules to Na⁺ and finally Mn²⁺ cations, the chiral polyoxoanions [MnMo₉O₃₂]⁶⁻ were changed from a racemic compound to a conglomerate. This means that spontaneous resolution can be efficiently realized by connecting homochiral polyoxoanions into one-dimensional (1D), 2D, and 3D structures, with an emphasis on using appropriate linkers with substantial interaction strength, directionality, and enantioselectivity.

Four enantiomerically pure 3D chiral POM-based compounds, [Ni₂(bbi)₂(H₂O)₄V₄O₁₂]⋅2 H₂O (1 a and 1 b) and [Co(bbi)(H₂O)V₂O₆] (2 a and 2 b) (bbi=1,1′-(1,4-butanediyl)bisimidazole) based on the achiral ligand, different vanadate chains, and different metal centers have been synthesized by hydrothermal methods. Single-crystal X-ray diffraction analyses revealed that 1 a and 1 b, and 2 a and 2 b, respectively, are enantiomers. In 1 a and 1 b two kinds of vanadate chains with different screw axes link Ni cations to generate 3D chiral inorganic skeletons, which are connected by the achiral bbi ligands to form complicated 3D 3,4-connected chiral self-penetrating frameworks with (7²⋅8)(7²⋅8²⋅9²)(7³⋅8²⋅10) topology. They represent the first examples of chiral self-penetrating frameworks known for polyoxometalate (POM) systems. Contrary to 1 a and 1 b, in 2 a and 2 b the vanadate chains link Co^II cations to generate 3D chiral inorganic skeletons, which are assembled from two kinds of heterometallic helical units of opposite chirality along the c axes. The chiral inorganic skeletons are connected by bbi to form 3D 3,4-connected chiral POM-based frameworks with (6²⋅8)₂(6²⋅8²⋅10²) topology. It is believed that the asymmetrical coordination modes of the metal cations in 1 a–2 b generate the initial chiral centers, and that the formation of the various helical units and the hydrogen bond interactions are responsible for preservation of the chirality and spontaneous resolution when the chirality is extended into the homochiral 3D-networks. This is the first known report of chiral POM-based compounds consisting of 3D chiral inorganic skeletons being obtained by spontaneous resolution upon crystallization in the absence of any chiral source, which may provide a rational strategy for synthesis of chiral POM-based compounds by using achiral ligands and POM helical units.