Metal-Organic Frameworks in Germany: from Synthesis to Function

Metal-organic frameworks (MOFs) are constructed from a combination of inorganic and organic units to produce materials which display high porosity, among other unique and exciting properties. MOFs have shown promise in many wide-ranging applications, such as catalysis and gas separations. In this review, we highlight MOF research conducted by Germany-based research groups. Specifically, we feature approaches for the synthesis of new MOFs, high-throughput MOF production, advanced characterization methods and examples of advanced functions and properties

High-Throughput Synthesis of Pillared-Layered Magnesium Tetraphosphonate Coordination Polymers: Framework Interconversions and Proton Conductivity Studies

Novel pillared-layered framework materials were synthesized by high-throughput or microwave-assisted methodology that contain Mg2+ and the zwitterionic linker HDTMP (hexamethylenediamine-N,N,N0,N0-tetrakis(methylenephosphonic acid)). Three compounds were structurally characterized by X-ray powder diffraction. In the compound {Mg[(HO3PCH2)2N(CH2)6N (CH2PO3H2)2](H2O)}n(1), obtained at 140 ºC by hydrothermal or microwave-assisted reaction, the layers are built by isolated Mg2+ octahedra coordinated by oxygen atoms from six different zwitterionic HDTMP ligands. Each amino-bis(methylenephosphonate) moiety links three Mg2+ ions, bridging two of them through one phosphonate group and connecting the third polyhedron in a monodentate fashion. In Compound 2, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n, hydrothermally synthesized at 180 C, the layers are composed of bidentate amino-bis(methylenephosphonate) moieties connected to three Mg2+ ions, with one of the phosphonate groups acting as a bridging ligand. Various subtle structural changes are noted for the other two compounds. Thermodiffraction of 1 reveals that a crystalline-to-crystalline phase transformation occurs concomitantly with its dehydration, leading to a new anhydrous phase, namely, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n(1deh). This process is fully reversible upon equilibrating the solid at room temperature. The reported compounds can adsorb ammonia and CO2. Compound 1 exhibits a moderate proton conductivity, ~1.5 x 10-5 S·cm-1 at 80 ºC and 95% RH, that increases a half order of magnitude after experiencing a complete dehydration/rehydration process

Hochdurchsatz-Untersuchung von anorganisch-organischen Hybridmaterialien: Metall-Phosphonatobenzolsulfonate und Ni-basierte MOFs mit Schaufelrad-Baueinheiten

The focus of this Ph.D. work is to systematically investigate the formation of inorganic-organic hybrid materials with different metal ions and polyfunctional organic linkers. The synthesis and characterization of the materials were performed under solvothermal conditions employing high-throughput (HT) methods. The HT methods incorporate the parallelization of individual reactions in miniaturized Teflon® reactors and the subsequent characterization of the crystalline products via automated HT-XRPD analysis. The HT methods have enabled the rapid study of the influences of compositional and process parameters on the formation fields and helped to optimize the synthesis conditions. In the first part of the thesis, the reaction system M2+/H2O3PC6H4SO3H/ NaOH/H2O was investigated (M = Ni,Mg,Cu,Zn,Co,Fe,Mn,Sn,Cd,Sr, Pb and Ba). The evaluation of the metal-ion screening yielded six metal 4-phosphonatobenzenesulfonates with Cu2+, Sn2+ and Pb2+ ions. Further detailed investigation of the molar ratio metal salt : linker : NaOH has helped to pinpoint the specific formation fields of each compound. Various M-O-M polyhedra and clusters are observed in the crystal structures which lead to 2D or 3D networks, especially in copper-based structures. A mixed-linker copper phosphonatosulfonate was also obtained with the auxiliary ligand 4,4’-bipyridine which exhibits an interesting reversible structural transition upon de-/rehydration. The characterization of the metal phosphonatosulfonates was performed with X-ray powder and single crystal X-ray diffraction, magnetic susceptibility measurements, thermogravimetric (TG) analysis, energy-dispersive X-ray (EDX) and CHNS elemental analysis, infrared (IR) spectroscopy and scanning electron microscopy (SEM). The second part of the thesis deals with the discovery and characterization of porous nickel(II) based metal-organic frameworks containing paddle-wheel building units. The dimeric paddle-wheel units are comprised of Ni2+ ions that are coordinated by four equatorial R(COO)- groups and two axial terminal ligands. The reaction system Ni2+/R(COOH)3/ additive / solvent, with R = C6H3, 1,3,5-(C6H4)3C6H3, was systematically investigated through screening of nickel salts, organic bases and solvents at various reaction temperatures. Two nickel(II) based compounds with paddle-wheel units were obtained with 1,3,5- benzenetricarboxylic (H3BTC) and 4,4’,4’’-benzene-1,3,5-triyl-tris-benzoic acid (H3BTB). In addition, two pseudo-polymorphs with the framework composition [Ni2(BDC)2(DABCO)] (H2BDC = terephthalic acid, DABCO = 1,4-diazabicyclo[2.2.2]octane) were discovered. For the phase selective synthesis, the influence of conventional vs. microwave-assisted heating, DABCO amount, stirring, overall concentration and reaction temperature was examined in detail. After the optimization of synthesis conditions, the scale-up of all four nickel(II) paddle-wheel compounds was accomplished and all the compounds were characterized via sorption experiments, IR spectroscopy, elemental analysis, SEM measurements and TG analysis.Der Schwerpunkt dieser Doktorarbeit ist die systematische Untersuchung der Bildung anorganisch-organischer Hybridmaterialien mit verschiedenen Metallionen und polyfunktionellen organischen Linkern. Die Synthese und Charakterisierung der Materialien wurden unter solvothermalen Bedingungen mit Hilfe von Hochdurchsatz (HT)-Methoden durchgeführt. Die HT-Methoden umfassen die Parallelisierung der einzelnen Reaktionen in Miniatur-Teflon® Reaktoren und die anschließende Charakterisierung der kristallinen Produkte mittels automatisierter HT-XRPD Analyse. Diese Methoden ermöglichen die schnelle Untersuchung der Einflüsse von Edukt-Zusammensetzungen und Prozessparametern auf die Kristallbildung. Im ersten Teil dieser Dissertation wurde das Reaktionssystem M2+/H2O3PC6H4SO3H/NaOH/H2O (M = Ni,Mg,Cu,Zn, Co,Fe,Mn,Sn,Cd,Sr,Pb and Ba) erforscht. Die Auswertung des Metallion-Screenings ergab sechs Metall-4-phosphonatobenzolsulfonate mit Cu2+, Sn2+ and Pb2+-Ionen. Weitere detaillierte Untersuchungen bei denen das molare Verhältnis Metallsalzen : Linker : NaOH untersucht wurde, half bei der Bestimmung der spezifischen Phasenbildungsbereiche jeder Verbindung. Unterschiedliche M-O Polyeder und M-O-M Cluster wurden in den Kristallstrukturen beobachtet, die zur Bildung von 2D oder 3D M-O Netzwerken geführt haben, insbesondere in den Kupfer-basierten Verbindungen. Ein Misch-Linker Cu-Phosphonatosulfonat wurde auch mit 4,4’-Bipyridin als Co-Ligand erhalten, das eine reversible Strukturumwandlung unter De-/Rehydratisierung aufweist. Die Charakterisierung der Metallphosphonatosulfonate wurde mittels Röntgenpulver- und Einkristallröntgenbeugung, Magnetsuszeptibilitätsmessungen, thermogravimetrischer Analyse (TGA), energiedispersiver Röntgenspektroskopie (EDX), CHNS Elementaranalyse, Infrarotspektroskopie (IR) und Rasterelektronmikroskopie (REM) durchgeführt. Der zweite Teil dieser Arbeit befasst sich mit der Entdeckung und Charakterisierung poröser Nickel(II)-basierter metall-organischer Gerüstverbindungen mit Schaufelrad-Baueinheiten. Die Schaufelrad-Dimere bestehen aus Ni2+-Ionen, die von vier äquitorialen R(COO)- Gruppen und zwei axialen Liganden umgeben sind. Das Reaktionssystem Ni2+/R(COOH)3/Additiv/Lösungsmittel, mit R = C6H3, 1,3,5-(C6H4)3C6H3, wurde systematisch durch Screening von Nickelsalzen, organischen Basen und Lösungsmitteln bei verschiedenen Reaktionstemperaturen untersucht. Zwei nickelbasierte Verbindungen mit Schaufelrad-Einheiten wurden mit 1,3,5-Benzoltricarbonsäure (H3BTC) and 4,4’,4’’-Benzol-1,3,5-triyl-trisbenzoesäure (H3BTB) erhalten. Zusätzlich wurden zwei Pseudopolymorphe mit der Gerüstzusammensetzung [Ni2(BDC)2(DABCO)] (H2BDC = Terephthalsäure, DABCO = 1,4-diazabicyclo[2.2.2]oktan) entdeckt. Die Optimierung der Reaktionsbedingungen führte zu einphasigen Produkten. Dazu wurde der Einfluss der Heizmethode (konventionelle vs. Mikrowellen-unterstützte Synthese), die DABCO-Menge, das Rühren, die Gesamtkonzentration und die Reaktionstemperaturen untersucht. Nach der Optimierung der Synthese, konnten alle vier Nickel(II)-Verbindungen, die Schaufelrad-Baueinheiten enthalten, in größeren Mengen hergestellt und ausführlich mittels Sorptionsmessung, IR-Spektroskopie, Elementaranalyse, REM und thermogravimetrischer Analyse charakterisiert werden

Palladium-Mediated Carbon-Carbon Bond formation: Methodology and Mechanism. Part I: Palladium-Catalyzed Α-Arylation of Aryl Nitromethanes, Phosphonoacetates, and Phosphine Oxides. Part II: Mechanistic Study of the Palladium-Mediated Chemoselective Activation of C(sp3)-H Bonds

Part I: The catalytic α-arylation of aryl nitromethanes has been a longstanding challenge, due to the reported lack of reactivity of these compounds under cross-coupling conditions. Conditions for this transformation have been developed using mechanistically-driven high-throughput experimentation. The method efficiently provides access to a variety of isolable diaryl nitromethanes, which are useful synthetic intermediates, as well as diaryl ketones and diaryl methyl amines in sequential transformations. Additionally, a one-pot process has been developed for the differential di-arylation of nitromethane. The catalytic α-arylation of phosphonoacetates has also been achieved using mechanistically-driven high-throughput experimentation. α-Arylated phosphonoacetates are biologically active structural motifs, and are synthetically useful in the Horner-Wadsworth-Emmons olefination. The conditions developed provide a significant improvement to the range of accessible phosphonoacetates, as previously reported methods were limited in scope and/or required harsh reaction conditions. The method is useful for both aryl bromide and aryl chloride starting materials at low catalyst loadings, and has been shown to be robust on large scale. The challenging racemic quaternary α-arylation of phosphine oxides has been achieved as well, in 50% yield. Reaction conditions were thoroughly investigated using high-throughput experimentation. Improvements to the yield of the quaternary product were limited by decomposition of both the starting material and the product. More mild conditions with palladium catalysts were investigated, and a preliminary investigation of alternative catalysts was undertaken. The asymmetric quaternary α-arylation reaction was also studied. Part II: A unique C(sp3)–H bond activation of toluene by Pd(OAc)2 was recently discovered. The mechanism of this reaction was studied. The initially proposed mechanism was ruled out, and another mechanism, more consistent with experimental evidence, is proposed. Evidence for a rate-limiting C–H activation event is presented, as is as evidence for radical character in both the oxazolone starting material and toluene coupling partner. Kinetics studies were undertaken, which revealed a completely zero-order reaction, perhaps implicating an intramolecular rate-determining step

Redes metalo-orgânicas baseadas em ligandos tetrafosfonato

Doutoramento em QuímicaRedes Metalo-Orgânicas (MOFs) são materiais híbridos porosos e cristalinos que têm registado um rápido desenvolvimento dadas as suas propriedades excecionais e o grande número de potenciais aplicações, tais como adsorção e separação de gases, catálise, aplicações em biomedicina, dispositivos eletrónicos ou sensores óticos, entre outras, bem como a sua infinita variabilidade química e diversidade topológica sem precedente. Particularmente, MOFs baseadas em lantanídeos e (poli)fosfonatos têm atraído a atenção de investigadores de todas as partes do mundo, principalmente pelos diferentes usos dos ácidos difosfónicos, que são, em geral, facilmente obtidos comercialmente. Para além da sua notável diversidade estrutural, ligandos (poli)fosfonato possuem vantagens relativamente a outros ligandos mais comumente usados, como os carboxilatos (ou aqueles baseados em aminas), contribuindo com a sua notável robustez térmica, mecânica e química para a obtenção de novos materiais. O grupo de investigação em MOFs da Universidade de Aveiro tem preparado novos materiais a partir da combinação de ligandos orgânicos com grupos fosfonato e, principalmente, lantanídeos. Esta dissertação descreve os resultados mais recentes nesta área envolvendo a síntese de MOFs multidimensionais baseadas em dois ligandos fosfonato tetrapodais. Os ligandos orgânicos usados neste projeto foram desenhados e preparados após seleção e otimização das condições reacionais e métodos de síntese. Reações entre estes ligandos orgânicos e catiões lantanídeo levaram à formação de várias famílias de MOFs 2D e 3D. A preparação destes materiais envolveu o uso de métodos de síntese distintos: síntese hidro(solvo)térmica, evaporação lenta e síntese por irradiação de micro-ondas. A seleção criteriosa dos ligandos orgânicos mostrou ter um papel fundamental na topologia final dos materiais: a presença de um certo grau de flexibilidade por parte do ligando orgânico teve como consequência uma grande variedade estrutural de MOFs obtidas, tanto 2D como 3D. As reações com um outro ligando que apresenta maior rigidez requereram a presença de um segundo ligando (auxiliar) para facilitar a formação da rede. A estrutura cristalina dos materiais foi resolvida através de difração de raios-X de monocristal, técnica usada em conjunto com várias outras técnicas de caracterização de compostos em estado sólido (FT-IR, microscopia eletrónica (SEM e EDS), RMN em estado sólido, análise elementar e termogravimétrica e difração de raios-X de pós). A estabilidade térmica dos materiais reportados foi ainda abordada de forma comparativa, verificando-se que alguns compostos obtidos apresentam robustez e estabilidades térmicas excecionais, num caso particular até cerca dos 800 ºC. As propriedades intrínsecas de algumas MOFs foram também investigadas. Estudos de fotoluminescência revelaram que o ligando orgânico derivado do bifenilo é um sensibilizador apropriado para catiões Tb3+, levando à formação de materiais emissores de luz verde intensa. Os materiais obtidos também mostraram possuir elevada atividade catalítica, em meio heterogéneo, nomeadamente na reação de abertura do anel epóxido do óxido de estireno e na proteção do benzaldeído pela formação do correspondente acetal (reações na presença de metanol), bem como excelente condução protónica a humidades elevadas, tendose registando valores entre os mais elevados para este tipo de materiais híbridos.Metal-Organic Frameworks (MOFs) are hybrid porous crystalline materials which have developed rapidly due to their outstanding properties and myriad of potential applications such as gas storage, separations, catalysis, biomedicine, electronic devices, optical sensors, among several others, as well as their endless chemical variability and unprecedented diversity of pore structure and topology. Particularly, MOFs based on lanthanide (poly)phosphonates have attracted worldwide research attentions, mainly because of the different uses of diphosphonic acid molecules, which are, in general, readily available from commercial sources. Besides their remarkable structural diversity, (poly)phosphonate linkers offer advantages over the more widely used carboxylate (or nitrogen-based) molecules for developing new materials, prompted by their notable chemical, mechanical and thermal robustness. The MOF research group at the University of Aveiro has prepared MOFs from the combination of phosphonate organic linkers as primary building units (PBUs) with, mainly, lanthanides. This thesis presents the last findings in this area involving the synthesis of multidimensional MOFs based on two tetrapodal phosphonate ligands. The organic PBUs were designed and prepared by selecting and optimizing the best reaction conditions and synthetic routes. The self-assembly between phosphonate PBUs and lanthanide cations led to the formation of several 2D and 3D families of isotypical MOFs. The preparation of these materials was achieved using distinct synthetic approaches: hydro(solvo)thermal, slow evaporation and microwave-assisted synthesis. The selection of the organic PBUs had an important role in the final architectures: a certain degree of flexibility present in the phosphonate ligand afforded a large variety of MOF architectures, both 2D and 3D. The self-assembly using a more rigid organic ligand required an ancillary ligand for the reaction to occur. The crystal structure of these materials was successfully unveiled by single-crystal X-ray diffraction used in tandem with standard solid-state characterization techniques (FT-IR, electron microscopy (SEM and EDS), solid-state NMR, elemental and thermogravimetric analyses and powder X-ray diffraction). Thermal stability of the reported networks was also addressed in a comparative fashion with some MOF materials exhibiting remarkable thermal stabilities and robustness, in one particular case up to ca. 800 ºC. The intrinsic properties of some MOFs were also investigated. Photoluminescence studies revealed that the biphenyl-based organic PBU is a suitable sensitizer of Tb3+, leading to the isolation of intense green-emitting materials. Materials also exhibited high heterogeneous catalytic activity in the ring-opening reaction of styrene oxide and acetalization of benzaldehyde with methanol, as well as excellent protonic conductivity at high humidities, with registered values (in all these studies) among the highest for this type of hybrid materials

Synthesis and in situ Investigation of Inorganic Organic Hybrid Compounds Based on Metalphosponates and Bismuthcarboxylates

Die hier vorliegende Arbeit beschäftigt sich mit der Synthese und Charakterisierung von neuen anorganisch-organischen Hybridverbindungen und den in situ Untersuchungen ihrer Kristallisation. Den Hauptteil dieser Arbeit machten dabei die Untersuchung polyfunktionalisierter Metallphosphonate und Bismutcarboxylate aus. Die Kristallisationsprozesse wurden mittels energiedispersiver Röntgenbeugung (EDXRD) untersucht. Die Produktbildung von Cu2(O3P-C2H4-SO3(OH)(H2O)2]*3H2O und [Cu2(O3P-C2H4-SO3(OH)(H2O)] verläuft über das metastabile hydratisierte Intermediat [Cu2(O3P-C2H4-SO3(OH)(H2O)2] *4H2O, während bei der Kristallisation von Ca(O3P-C2H4-NH2) das Intermediat [Ca(OH) (O3P-C2H4-NH3)]*2H2O beobachtet wird. Die Kristallstrukturen beider Intermediate und von Ca(O3P-C2H4-NH2) wurden hierbei aus Röntgenpulverdaten bestimmt. EDXRD Untersuchungen der Bildung von M(HO3P-CH2)2-NHCH2-C6H4-COOH (M = Mn2+, Co2+, Fe2+, Ni2+), zeigten verschiedene Reaktionszeiten und Intermediate in Abhängigkeit des Metallions. Die Kristallisation von Sm(O3P-C4H8-SO3)(H2O), Co-CPO-27 und Ni-CPO-27 wurden in situ untersucht und unter Verwendung des Avrami bzw. Gualtieri Modells war es möglich die Geschwindigkeitskonstanten und Arrhenius-Akti\-vierung\-senergien der Reaktionen sowohl unter mikrowellenunterstützten als auch konventionellen Synthesebedingungen zu bestimmen. Mikrowellenunterstütze Synthesemethoden konnten ebenfalls genutzt werden um die Verbindungen [Ni(m-[(HO3PCH2)2NHCH2]2C6H4)] *H2O, [Cd(p-[(HO3PCH2)2NHCH2]2C6H4)] und [Zn(p-[(HO3PCH2)2NHCH2]2C6H4)H2O] zu synthetisieren und ihre Kristallstrukturen konnten mittels Röntgenpulverbeugung bestimmt bzw. aus kristallographischen Zusammenhängen hergeleitet werden. Unter Verwendung von H3BTB und Bi(NO3)3*5H2O war es möglich das erste hoch poröse Bismutcarboxylat Bi(BTB) (H3BTB=1,3,5-Benzoltrisbenzoesäure) herzustellen, welches eine scheinbare spezifische Oberfläche von 1150 m2/g aufweist. Die Verbindung ist für die Hydroxymethylierung von Furan katalytisch aktiv. Die Kristallstruktur wurde aus einer Kombination von Elektronenbeugungsdaten, Rietveld-Verfeinerung und DFT Rechnungen bestimmt. Ebenso wurde zum ersten Mal die Kristallisation von Bismutcarboxylaten in situ untersucht. Es wurde gezeigt, dass in Abhängigkeit der verwendeten Linkermoleküle Pyromellitsäure (H4Pyr), Trimellitsäure (H3Tri) und Trimesinsäure (H3BDC) unter ansonsten ähnlichen Reaktionsbedingungen isolierbare, nicht isolierbare oder gar keine Intermediate bei der Bildung von Bi(HPyr), Bi(Tri)(H2O) und (Bi2(O)(OH)(HBTC)(NO3)) entstehen.This thesis deals with the synthesis and characterization of new inorganic-organic hybrid compounds and the in situ investigations of their crystallization. The main part of this work deals with metalphosphonates and bismuthcarboxylates. The crystallization was investigated by in situ energy dispersive X-ray diffraction (EDXRD). The product formation of [Cu2(O3P-C2H4-SO3(OH)(H2O)2]*3H2O and [Cu2(O3P-C2H4-SO3(OH)(H2O)] proceeds through the metastable hydrated intermediate [Cu2(O3P-C2H4-SO3(OH)(H2O)2]*4H2O, while in the crystallization of Ca(O3P-C2H4-NH2) the intermediate [Ca(OH)(O3P-C2H4-NH3)]*2H2O is observed. The crystal structure of both intermediates and Ca(O3P-C2H4-NH2) were determined from X-ray powder diffraction data. In situ EDXRD investigations of the formation of M(HO3P-CH2)2NHCH2-C6H4-COOH (M = Mn2+, Co2+, Fe2+, Ni2+), Ca(O3P-C2H4-NH2) revealed different reaction times and intermediates depending on the metal ion used. The in situ investigation of the crystallization of Sm(O3P-C4H8-SO3)(H2O), Co-CPO-27 and Ni-CPO-27 allowed the extraction of rate constants and Arrhenius activation energies for the crystallization under microwave-assisted as well as conventional syntheses methods using the model of Avrami and Gualtieri. Microwave-assisted heating was also used to synthetize the compounds [Ni(m-[(HO3PCH2)2NHCH2]2C6H4)] *H2O, [Cd(p-[(HO3PCH2)2NHCH2]2C6H4)] and [Zn(p-[(HO3PCH2)2NH-CH2]2C6H4)H2O]. Their crystal structures were determined from X-ray powder diffraction or derived from crystallographic relations. The use of H3BTB (1,3,5-benzenetrisbenzoicacid) and Bi(NO3)3*5H2O allowed the synthesis of the first highly porous bismuth carboxylate Bi(BTB) with a specific surface area of 1150 m^2/g (BET). The compound is catalytic active in the hydroxymethylation of furan. The crystal structure was determined by a combination of electron diffraction, Rietveld refinement and DFT calculations. In addition in situ EDXRD was employed to investigate the crystallization of bismuth carboxylates for the first time. Depending on the linkermolecule pyromellitic acid (H4Pyr), trimellitic acid (H3Tri) and trimesic acid (H3BDC) under similar reaction intermediates occur that were isolated and fully characterized

Synthesis of unsymmetrical pendant-armed and phosphonic acid-pendant-armed cross-bridged tetraazamacrocycles

The synthesis of a variety of cross-bridged tetraazamacrocycles bearing phosphonate pendant arms and their corresponding phosphonic acid derivatives as well as their Cu(II) complexes are presented. The half-life of decomplexation of Cu(II)·51 in 5M HCl at 90°C was found to be 3.8 hours. Ligand 51 showed faster complexation kinetics relative to known cross-bridged tetraazamacrocycles bearing ionizable pendant arms. The biodistribution of 64Cu(II)·51 was studied in male rats and indicated an improved blood and liver clearance and higher bone retention of 64Cu(II)·51 relative to 64Cu(II)·10.*. The formation of a single pendant-armed cross-bridged cyclam is presented through an unusual single alkylation of cross-bridged cyclam. Several experiments were implemented to probe the origin of the selectivity of the reaction including computational studies, 1D 1H NMR and 2D NMR experiments. Monoamide ligand 64 was used as a springboard for the formation of several unsymmetrical pendant-armed cross-bridged cyclams.*. Attempts were made toward the synthesis of two potential bifunctional chelators for radiopharmaceuticals, each bearing only one phosphonic acid pendant arm and one free carboxylate for conjugation to somatostatin analogues.*

Use of the Advantages of Titanium in the Metal: Organic Framework

Titanium is one of the most attractive elements, due to its unique advantages such as stability, recyclability, activity under light absorption, cheapness, and safety. The special characteristics of titanium include different oxidation states, high coordination number of Ti4+, and the ability to form strong bonds with oxygen and different ligands, making it a good candidate for the construction of the new composite named metal–organic framework or briefly MOF. MOFs are composites that have opened a new window toward the scientific world due to their special structure that makes them have some properties, including the highest surface activity, high porosity, tunable pore, and high flexibility in design that make them useful in different applications, such as gas storage and separation, liquid separation and purification, electrochemical energy storage, catalysis, and sensing. Titanium, due to the mentioned properties, has been used as a node in the structure of different MOFs and applied in different fields

Organophosphorus Chemistry 2018

Organophosphorus chemistry is an important discipline within organic chemistry. Phosphorus compounds, such as phosphines, trialkyl phosphites, phosphine oxides (chalcogenides), phosphonates, phosphinates and >P(O)H species, etc., may be important starting materials or intermediates in syntheses. Let us mention the Wittig reaction and the related transformations, the Arbuzov- and the Pudovik reactions, the Kabachnik–Fields condensation, the Hirao reaction, the Mitsunobu reaction, etc. Other reactions, e.g., homogeneous catalytic transformations or C-C coupling reactions involve P-ligands in transition metal (Pt, Pd, etc.) complex catalysts. The synthesis of chiral organophosphorus compounds means a continuous challenge. Methods have been elaborated for the resolution of tertiary phosphine oxides and for stereoselective organophosphorus transformations. P-heterocyclic compounds, including aromatic and bridged derivatives, P-functionalized macrocycles, dendrimers and low coordinated P-fragments, are also of interest. An important segment of organophosphorus chemistry is the pool of biologically-active compounds that are searched and used as drugs, or as plant-protecting agents. The natural analogue of P-compounds may also be mentioned. Many new phosphine oxides, phosphinates, phosphonates and phosphoric esters have been described, which may find application on a broad scale. Phase transfer catalysis, ionic liquids and detergents also have connections to phosphorus chemistry. Green chemical aspects of organophosphorus chemistry (e.g., microwave-assisted syntheses, solvent-free accomplishments, optimizations, and atom-efficient syntheses) represent a dynamically developing field. Last, but not least, theoretical approaches and computational chemistry are also a strong sub-discipline within organophosphorus chemistry