Discovery of Complex Binding and Reaction Mechanisms from Ternary Gases in Rare Earth Metal–Organic Frameworks

Understanding the selectivity of metal–organic frameworks (MOFs) to complex acid gas streams will enable their use in industrial applications. Herein, ab initio molecular dynamic simulations (AIMD) were used to simulate ternary gas mixtures (H₂O-NO₂-SO₂) in rare earth 2,5-dihydroxyterephthalic acid (RE-DOBDC) MOFs. Stronger H₂O gas-metal binding arose from thermal vibrations in the MOF sterically hindering access of SO₂ and NO₂ molecules to the metal sites. Gas-gas and gas-linker interactions within the MOF framework resulted in the formation of multiple secondary gas species including HONO, HNO₂, NOSO, and HNO₃⁻. Four gas adsorption sites were identified along with a new de-protonation reaction mechanism not observable through experiment. This study not only provides valuable information on competitive gas binding energies in the MOF, it also provides important chemical insights into transient chemical reactions and mechanisms.     

The Shortened Transition Metal–Tellurium Bonds in Organometallic Clusters

The shortening of partly multiple M–Te (M = Mn, Fe, Co, Cr or W) bonds is observed for two classes of organometallic compounds: (1) formally electron-deficient species with additional donor–acceptor interaction between Te lone pairs and half-occupied d-orbitals of M; (2) formally electron-saturated species having additional dative interaction between M lone pairs and LUMO of Te. These compounds could be prepared by two main methods: (a) interaction of [CpMn(CO)₂PhC(O)⁻]Li⁺ with Te proceeds via formation of intermediate {[CpMn(CO)₂]₂Te}²⁻ which is further transformed into binuclear complex [CpMn(CO)₂]₂Te(CH₂Ph)₂ or into trinuclear ditelluride cluster [CpMn(CO)₂]₃Te₂ on one hand or to mixed-metal monotelluride clusters [CpMn(CO)₂]₂TeM(CO)₅ on another hand. (b) treatment of Fe(CO)₅, CpMn(CO)₂(THF) or Me₄C₄Co(CO)₂I with [PhTeI]₄, PhTeI₃ or PhTeI₂HC = CPhI results in different PhTeI-containing complexes of Fe, Mn or Co. The molecular structures of all new compounds were studied by means of X-ray diffraction analyses and the mechanism of M–Te bond shortening is discussed. Proceeding of the international workshop on transition metal clusters, 3–5 July 2008, Université de Rennes 1, Campus de Beaulieu, Rennes, France.     

Sequential Solid-State Transformations Involving Consecutive Rearrangements of Secondary Building Units in a Metal–Organic Framework (MOF)

Solid-state transformations in metal–organic frameworks (MOFs) are important and have led to the creation of new MOF structures. Solid-state transformations from interpenetrated to non-interpenetrated networks involving rearrangement of secondary building units (SBUs) in a single-crystal-to-single-crystal (SCSC) fashion have not been explored to date. Herein, we report the sequential, thermally stimulated solid-state transformations in a barium-organic framework ( UPC-600 ). The two-fold interpenetrated framework of UPC-600 is converted at 373 K into UPC-601 , a non-interpenetrated framework. This proceeds in a SCSC fashion and involves the rearrangement of two proximate rod-shaped SBUs in different nets to generate a new rod-shaped SBU. At 473 K, a continuous solid-state transformation involving a second rearrangement occurred, UPC-601 converted into UPC-602 by the rearrangement of the 1D rod-shaped SBU to a 2D layer SBU. This is the first example of such a thermally driven stepwise transformation involving simultaneous cleavage and regeneration of multiple bonds.     

Role of Mononuclear Rare Earth Metal Complexes in Promoting the Hydrolysis of 2-Hydroxypropyl p-Nitrophenyl Phosphate

Two long-chain multidentate ligands： 2,9-di-（n-2＇,5＇,8＇-triazanonyl）-1,10-phenanthroline （L^1） and 2,9-di- （n-4＇,7＇,10＇-triazaundecyl）-1,10-phenanthroline （L^2） were synthesized. The hydrolytic kinetics of 2-hydroxypropyl p-nitrophenyl phosphate （HPNP） catalyzed by the complexes of L^1 or L^2 with La（Ⅲ） or Gd（Ⅲ） have been studied in aqueous solution at （298.2±0.1） K, I=0.10 mol·dm^-3 KNO3 in pH 7.5-9.1, respectively, finding that the catalytic effect of GdL^1 was the best among the four complexes for hydrolysis of HPNP. Its kLnLH-1, kLnLand pKa are 0.047 mol^-1·L·s^-1, 0.000074 mol^-1·L·s^-1 and 8.90, respectively. This paper expounded the studied result with the structure of the ligands and the properties of the metal ions, and deduced the catalysis mechanism.     

A Simple,Transition Metal Catalyst-Free Method for the Design of Complex Organic Building Blocks Used to Construct Porous Metal–Organic Frameworks

The design of metal–organic frameworks (MOFs) having large pore sizes and volumes often requires the use of complex organic ligands, currently synthesized using costly and time-consuming palladium-catalyzed coupling chemistry. Thus, in the present work, a new strategy for ligand design is reported, where piperazine and dihydrophenazine units are used as substitutes for benzene rings, which are the basic building block of most MOF ligands. This chemistry, which is based on simple, nucleophilic aromatic substitution (S_NAr) reactions, is used for the transition metal catalyst-free construction of 21 new, carboxylate-based ligands with varying sizes, shapes, and denticity and 15 linear di- and tetra-nitriles. Moreover, to demonstrate the utility of the ligands as building blocks, 16 new structurally diverse MOFs having surface areas up to 3100 m² g⁻¹ were also synthesized.     

Studies on Rare Earth Metal-Hydroboron Componuds(Ⅰ) Syntheses and Properties of Benzoylhydrazine Chelates of Rare Earth Metal (Ⅲ) Dodecahydrododecaborates

In this paper,the bcnzoylhydrazine chelates of rare earth metal (Ⅱ) dodecahydro-dodccaboratcs have been synthesized and eaxmined by elemental analysis,IR spectra and clectroconductar.ee measurements.They have the following formulae [Ln(BH)4]2 (U12H12)3(Ln=La,Pr,Nd,Sm,Eu,Gd,Tb,Ho,Er,Tm,Yb;BH=Benzoylhy-drazint).DTA results point out that these chelalrs are thermally stable.     

Solvent-Driven Reversible Phase Transition of a Pillared Metal–Organic Framework

Over the last decade, the controllable reversible phase transition of functional materials has received growing interest as it shows unique suitability for various technological applications. Although many metal–organic frameworks (MOFs) possess a lamellar structure, the reversible structural transformation of MOFs between their three-dimensional (3D) phase and two-dimensional (2D) phase remains a largely unexplored area. Herein, we report for the first time a europium MOF with unprecedented reversible morphology in different solvents at room temperature. This europium MOF displayed a 3D nanorod morphology in organic solvent and a 2D nanobelt architecture in water. As a proof of concept for potential applications of this reversible-phase-transition MOF, we were able to use a delamination recovery method to load dye molecules that previously could not be loaded into europium MOFs.     

Metal–base pairing in DNA

The use of DNA as a molecular wire in nanoscale electronic architectures would greatly benefit from its capability of sequence-specific self-assembly. Although single electrons and positive charges have been shown to be transmitted by natural DNA over a distance of several base pairs, the high ohmic resistance of unmodified oligonucleotides imposes a serious obstacle. Exchanging some or all of the Watson–Crick base pairs in DNA by metal complexes may solve this problem and evolve DNA-like materials with superior conductivity for future nano-electronic applications. The so-called metal–base pairs are formed from suitable transition metal ions and ligand-like nucleosides which are introduced into both of the two pairing strands by automated DNA synthesis. This review illustrates the basic concepts of metal–base pairing and highlights recent developments in the field.     

Electroactive Metal–Organic Frameworks as Emitters for Self-Enhanced Electrochemiluminescence in Aqueous Medium

Metal–organic frameworks (MOFs) have limited applications in electrochemistry owing to their poor conductivity. Now, an electroactive MOF (E-MOF) is designed as a highly crystallized electrochemiluminescence (ECL) emitter in aqueous medium. The E-MOF contains mixed ligands of hydroquinone and phenanthroline as oxidative and reductive couples, respectively. E-MOFs demonstrate excellent performance with surface state model in both co-reactant and annihilation ECL in aqueous medium. Compared with the individual components, E-MOFs significantly improve the ECL emission due to the framework structure. The self-enhanced ECL emission with high stability is realized by the accumulation of MOF cation radicals via pre-reduction electrolysis. The self-enhanced mechanism is theoretically identified by DFT. The mixed-ligand E-MOFs provide a proof of concept using molecular crystalline materials as new ECL emitters for fundamental mechanism studies.     

Modular Assembly of Host–Guest Metal–Phenolic Networks Using Macrocyclic Building Blocks

The manipulation of interfacial properties has broad implications for the development of high-performance coatings. Metal–phenolic networks (MPNs) are an emerging class of responsive, adherent materials. Herein, host–guest chemistry is integrated with MPNs to modulate their surface chemistry and interfacial properties. Macrocyclic cyclodextrins (host) are conjugated to catechol or galloyl groups and subsequently used as components for the assembly of functional MPNs. The assembled cyclodextrin-based MPNs are highly permeable (even to high molecular weight polymers: 250–500 kDa), yet they specifically and noncovalently interact with various functional guests (including small molecules, polymers, and carbon nanomaterials), allowing for modular and reversible control over interfacial properties. Specifically, by using either hydrophobic or hydrophilic guest molecules, the wettability of the MPNs can be readily tuned between superrepellency (>150°) and superwetting (ca. 0°).     

Kinetics of the Dissociation of Transition Metal Complexes with α,α-Dipyrrolylmethene in Acetic Acid–Benzene as a Binary Proton-Donating Solvent

The kinetics of the dissociation of Co(II), Ni(II), and Zn(II) complexes with 4,4-dibutyl-3,3,5,5-tetramethyldipyrrol-2,2-ylmethene was studied in acetic acid–benzene as a binary proton-donating solvent. The metal nature was found to affect the kinetic parameters of the process. Assumptions were made about the limiting step of the process and the effectiveness of d metal ions in the template synthesis of porphyrins from dipyrrolylmethenes.     

Dynamic PdII/CuI Multimetallic Assemblies as Molecular Models to Study Metal–Metal Cooperation in Sonogashira Coupling

Cooperation between two different metals plays a crucial role in many synergistic catalytic reactions, such as the Sonogashira C−C cross-coupling reaction, where an interaction between the Pd and Cu centers is proposed in the transmetalation step. Although several heterobimetallic Pd/Cu complexes were proposed as structural models of the active species in Sonogashira coupling, the detailed understanding of the metal–metal cooperation in transmetalation is still lacking in current systems. In this work, we report a stepwise and systematic approach to building heteromultimetallic Pd/Cu assemblies as a tool to study metal–metal cooperativity. We obtained fully characterized Pd/Cu multimetallic assemblies that show reactivity in alkyne activation, formation of catalytically relevant aryl/acetylide species, and C−C elimination, serving as functional models for Sonogashira reaction intermediates. The combined experimental and DFT studies highlight the importance of ligand-controlled coordination geometry, metal–metal distances and dynamics of the multimetallic assembly for transmetalation step.     

Oxidative Dehydrogenation of Isobutane to Isobutylene over F￣－ Modified Rare Earth Metal Oxide Catalysts

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Ring-Opening Copolymerization of 2,2-Dimethyltrimethylene Carbonate and ε-Caprolactone Using Rare Earth Aryloxides Substituted by Various Alkyl Groups

A variety of single component rare earth aryloxides substituted by various alkyl groups [Ln(OAr)₃] such as methyl, isopropyl, tert‐butyl have been surveyed in the ring‐opening copolymerization of 2,2‐dimethyltrimethylene carbonate (DTC) and ε‐caprolactone (ε‐CL). It was worthwhile to note that activity of the catalyst varied with both the ligands' structure and the number of alkyl groups on phenyl ring. The stronger ability of electron‐donation of alkyl groups on phenyl ring, and the more numbers of alkyl groups on phenyl ring, the higher catalytic activity. The experimental results show that lanthanum tris(2,4,6‐tri‐tert‐butylphenolate) [La(OTTBP)₃] exhibits highest activity in all lanthanum aryloxides. ¹H NMR spectral data of copolymer obtained showed that the polymerization mechanism is in agreement with the coordination insertion mechanism.     

Liquid–Liquid–Liquid Micro Extraction Combined with CE for the Determination of Rare Earth Elements in Water Samples

A simple method for determination of rare earth elements (REEs) by liquid–liquid–liquid microextraction (LLLME) coupled with capillary electrophoresis and ultraviolet technique was developed. In the LLLME system, 40 mmol L^?1 4-benzoyl-3-methy-1-phenyl-5-pyrazolinone (PMBP) acted as extractant and 4% (v/v) formic acid was used as back-extraction solution. The parameters influencing the LLLME, including the type of the organic solvent, sample pH, formic acid concentration, PMBP concentration, extraction time, volume of organic solvent, stirring rate and phase volume ratio, were investigated. Under the optimized conditions, the detection limits (S/N = 3) of REEs were in the range of 0.19–0.70 ng mL^?1. The developed method was successfully applied to the determination of trace amounts of REEs in water samples.     

Synergistic Effect of Novel Synergists–Transition Metal Ion-incorporated Nickel Phosphates with Intumescent Flame Retardants in Polypropylene

The two kinds of transition metal ion-incorporated nickel phosphates (TMIVSB-1) were synthesized by the hydrothermal method. The flame retardancy and thermal behavior of intumescent flame retardants (IFR), with and without TMIVSB-1 for PP, were investigated by LOI, UL-94 test, thermogravimetric analyses (TGA) and cone calorimetry. TMIVSB-1 can obviously improve the flame retardant behavior of IFR systems according to the results of LOI values and UL-94 test. The results of LOI show that 2 wt% TMIVSB-1 can increase the LOI value by 3–5 unit compared with that of PP/IFR composite. The UL-94 test shows that PP with 20% IFR burns and has no rating, but the addition of a small content 2 wt% of TMIVSB-1 with 18 wt% of IFR can reach a UL-94 V-0 rating. TGA results show that the thermal stability of PP/IFR/TMIVSB-1 increases obviously more than that of PP/IFR when the temperature is above 265°C. From cone calorimetry results, it can be observed that the HRR peaks are not obviously decreased, but the burning time of PP/IFR/FeVSB-1 (351s) and PP/IFR/ZnVSB-1 (380s) is obviously prolonged compared with that of PP/IFR (303s). The real time FTIR spectra (RTFTIR) demonstrates that the addition of TMIVSB-1 further staves the decomposition of the PP composites. The scanning electron microscopy (SEM) indicates the quality of char forming of PP/IFR/ TMIVSB-1 is superior to that of PP/IFR.