Transition Metal Moieties Research Articles

Realizing the Tailored Catalytic Performances on Atomic Pt-Promoted Transition Metal Moieties Implanted Layered Double Hydroxides for Water Electrolysis.

High-performance production of green hydrogen gas is necessary to develop renewable energy generation technology and to safeguard the living environment. This study reports a controllable engineering approach to tailor the structure of nickel-layered double hydroxides via doped and absorbed platinum single atoms (PtSA) promoted by low electronegative transition metal (Mn, Fe) moieties (PtSA-Mn,Fe-Ni LDHs). We explore that the electron donation from neighboring transition metal moieties results in the well-adjusted d-band center with the low valence states of PtSA(doped) and PtSA(ads.), thus optimizing adsorption energy to effectively accelerate the H2 release. Meanwhile, a tailored local chemical environment on transition metal centers with unique charge redistribution and high valence states functions as the main center for H2O catalytic dissociation into oxygen. Therefore, the PtSA-Mn,Fe-Ni LDH material possesses a small overpotential of 42 and 288 mV to reach 10 mA·cm-2 for hydrogen and oxygen evolution, respectively, superior to most reported LDH-based catalysts. Additionally, the mass activity of PtSA-Mn,Fe-Ni LDHs proves to be 15.45 times higher than that of commercial Pt-C. The anion exchange membrane electrolyzer stack of PtSA-Mn,Fe-Ni LDHs(+,-) delivers a cell voltage of 1.79 V at 0.5 A·cm-2 and excellent durability over 600 h. This study presents a promising electrocatalyst for a practical water splitting process.

Atomically Dispersed Transition Metal-Nitrogen-Carbon Electrocatalysts: Design, Synthesis, Characterization, Reactivity and Durability

Platinum group metal-free (PGM-free) catalysts have been targeted as possible Earth Abundant Elements solution to many electrochemical energy conversion technologies. Special attention has been given to PGM-free electrocatalysis with atomically dispersed (AD) transition metal moieties decorated over nitrogen-doped carbonaceous materials (a.k.a. M-N-C catalysts). Major applications for M-N-Cs are in cathode catalysts for oxygen reduction reaction (ORR). 1 These materials are employed across the pH-range: in proton exchange membrane fuel cells (PEMFC), biological (microbial) fuel cells (MFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). We have successfully introduced M-N-C catalysts synthesized by sacrificial support method (SSM) as a hard template approach based on high temperature pyrolysis.2 In most cases a secondary pyrolysis is being performed to promote AD display of the transition metal.3 This talk will address structure-to-property correlations for M-N-C catalysts in ORR based on electrochemical activity obtained in rotating ring-disk electrodes (RRDE) with those spectroscopic and microscopic observations and density functional theory (DFT) calculations of oxygen binding on AD transition metal. We will discuss the role of the AD transition metal, participation of the surface N-groups as co-catalysts/alternative active sites and the possible role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor. M-N-C catalysts performance in single membrane electrode assembly (MEA) fuel cells will also be discussed in the context of its surface chemistry and materials structure/morphology. We will focus on local hydrophobicity of SSM-based M-N-C electrocatalystsand its impact on the MEA performance.A broad spectrum of AD transition metal decorated MNCs have been synthesized and evaluated for catalytic activity in ORR (and other processes). The use of such materials as “active supports” for highly dispersed platinum or platinum alloy nanoparticles will be discussed. New developments in synthesis protocols enabling “green chemistry” scalable solutions will be discussed.

Promoting Oxygen Reduction Reaction on Atomically Dispersed Fe Sites via Establishing Hydrogen Bonding with the Neighboring P Atoms

AbstractSingle atom catalysts (SACs) comprised of nitrogen‐coordinated transition metal (TM–N–C) moieties show encouraging performance towards the oxygen reduction reaction (ORR). Nevertheless, for the reactions involving multiple intermediates, single‐atom sites fail to satisfactorily optimize the adsorption of all intermediates. Here, a facile strategy is reported to construct Fe, P dual‐atom sites in multimodal porous carbon (Fe,P‐DAS@MPC), and its superiority in synergistically boosting ORR is demonstrated. Fe,P‐DAS@MPC exhibits excellent ORR performance with substantially positive onset potential (Eonset = 1.02 V) and half‐wave potential (E1/2 = 0.92 V). Theoretical analysis unveils the cooperative effect of dual‐atom sites composed of adjacent P and Fe atoms, and the aiding of hydrogen bonding interaction can promote the adsorption/desorption of intermediates. Additionally, a Zn–air battery based on the Fe,P‐DAS@MPC shows a high peak power density and exceptional cycling stability. These findings provide a novel avenue towards the design of electrocatalysts with dual‐atom sites for practical energy conversion applications.

Construction and Properties of Ag-I Polymeric Clusters Attach with Nitrogen Heterocyclic Transition Metal Moiety

Construction and Properties of Ag-I Polymeric Clusters Attach with Nitrogen Heterocyclic Transition Metal Moiety

Synthesis of Carbonato- and Doubly Oxido-Bridged Diruthenium(III,IV) Complex and Reactions with Cations.

Doubly oxido-bridged transition metal moieties, {M2(μ-O)2}, play important roles as oxidation reaction centers in nature. This work features a diruthenium(III,IV) complex with a doubly oxido-bridged core {Ru2III,IV(μ-O)2}3+ with a carbonato bridged between the two ruthenium centers, M[{RuIII,IV(ebpma)}2(μ-O)2(μ-O2CO)]2(PF6)3 (M[1CO3]2(PF6)3; Carbonato complex, ebpma; ethylbis(2-pyridymethyl)amine), and explores the interactions of this complex with cations (H+ and M+). M[1CO3]2(PF6)3 was formed via reactions of a singly oxido-bridged complex, [{RuIII,IVCl2(ebpma)}2(μ-O)]PF6·(CH3)2CO, with M2CO3 (M = K, Na) or with CO2(g), adjusted to around pH 12 with NaOH(aq.), in a water-acetone mixed solvent. The Carbonato complex was isolated as a powder in the form of M[1CO3]2(PF6)3 (M = K, Na), because of the interactions between the carbonato moiety and K+ or Na+ in the solid structure. In acidic aqueous solutions, unexpectedly, the carbonato ligand remained bound to the doubly bridged core, {Ru2III,IV(μ-O)2}3+ or {Ru2III,IV(μ-O)(μ-OH)}4+, without decarboxylation even under pH 1.0. Two-step one-protonation/deprotonation occurred reversibly between pH 1.0 and 13.2 to the bridging oxido and carbonato ligands. The structures of the corresponding one- and two-protonated complexes ([1CO3H]2+ and [1CO32H]3+) were successfully characterized.

(Energy Technology Division Research Award Address) Transition Metal-Nitrogen-Carbon Catalysts for Oxygen Reduction Reaction:Surface Chemistry, Morphology and Reactivity

One of the main obstacles for global introduction of carbon-neutral hydrogen-based energy technology is the lack of efficient, inexpensive and durable cathode catalysts for the oxygen reduction reaction (ORR). The most effective catalytic materials contain Pt or other metals from Pt group. These platinum group metals (PGM) contribute substantially to the cost of most electrochemical energy technologies (fuel cells, electrolyzers, etc.) due to their scarcity and limited global availability. The search for less expensive materials that use of Earth-abundant elements is crucial and such pursuit has been very active for many years. While the earlier work used molecular catalysts, such as transition metal macrocyclic complexes, especially metal phthalocyanines and metal porphyrins, substantial practical progress has been achieved by introducing materials that are obtained by pyrolysis at high temperatures from organic or organo-metallic precursors that contain nitrogen. Over the last decade, a widespread opinion emerged that such materials can be viewed as graphene derivatives with nitrogen and transition metal moieties displayed in in them, including close structural analogs of MN4centers (resembling those of transition metal chelates), claimed responsible for the ORR activity.1While these pyrolyzed materials exhibit higher activity and promising stability, the nature of the active sites is still a field of debate. This paper will present an opinion on reactivity descriptors for transition metal-nitrogen-carbon (M-N-C) PGM-free catalysts obtained through pyrolysis process. It will discuss the attempts and limitation for de-novo, total chemical synthesis of M-N-C catalysts.2The paper will compare activity of metal-less (metal free) nitrogen doped carbon catalysts3and will point out critical differences between these two classes of PGM-free catalysts for ORR.4It will also introduce the role of surface Lewis basicity of N-containing groups across a range of pH5and will attempt on linking those activity descriptors to both chemistry of the catalyst surface and nano-scale morphology of the catalysts electrolyte interface.6This paper will display a hypothesis on the mechanism of ORR on M-N-C catalysts that is congruent with the findings from pH-dependence, inhibition and kinetic isotope effect studies.7The discussion will lead towards setting a set of realistic, non-formal, structure-based activity loss (durability) descriptors, so lacking in this field that emerges from absolute empiric advance towards a chemical interpretation of the key effects. The paper will discuss PGM-free catalysts interactions with ionomers8 and will provide directions for successful integrating M-N-C materials into membrane-electrode assemblies, as evidenced by nano- and micro-X-ray CT. 9,10 Kishi, et al., Nanomaterials,(2018) DOI: 10.3390/nano8120965Gokhale, et al., ACS Applied Energy Materials, (2018) DOI: 10.1002/celc.201800578Kabir, et al., ACS Applied Materials & Interfaces, 14 (2018) 11623-11632Matanović,et al., Current Opinion Electrochem., (2018) DOI: 10.1016/j.coelec.2018.03.009Rojas-Carbonell et al., ACS Catalysis, 8 (2018) 3041-3053Chen, et al., ACS Applied Energy Materials, 1 (2018) 1942-1949Chen, Iet al., ACS Applied Energy Materials, (2018) DOI: 10.1021/acsaem.8b00959Artyushkova, et al., ACS Applied Energy Materials, 1(2018)68-77Serov, et al., Appl. Catalysis B,237 (2018) 1139-1147J. Normile, et al., Materials Today - Energy, 9 (2018) 187-197

Synthesis of Hybrid Phosphomolybdates and Application as Highly Stable and Effective Catalyst for the Reduction of Cr(VI).

Three hybrid phosphomolybdates were successfully synthesized by hydrothermal method and characterized by a series of physicochemical analysis techniques. X-ray single-crystal structural analysis revealed that three compounds with the reductive polyanionic clusters (MoV) were wrapped by protonated organic component bpp cations (bpp = 1,3-bi(4-pyridyl)propane) through the complex supramolecular hydrogen bonding network. They also have similar molecular formulas: (H2bpp)3[PbM(H2O)2]2H6{M[Mo6O12(OH)3(HPO4)3(PO4)]2}2· nH2O (M = Fe in 1, Zn in 2, n = 4; or M = Mn in 3, n = 6). The oxidation states of all Mo centers in these polyanions are in the form of +5, presenting clusters with the higher negative charge. The feature showed that they were easy to be modified by transition metal and organic moieties, so as to form a high-dimensional structure and produce functional materials with specific properties. Comparison of catalytic ability of three crystals to reduce CrVI using formic acid as reductant, found that crystal 1 was effectively active to this redox reaction. The conversion of CrVI can reach 99% after 120 min of heating in 55 °C water bath, and the conversion of above 95% can still be achieved after 5 recycles of applications.

Extending the Toolbox for the Modular Arrangement of Functions at Xanthene/Dibenzofuran Platforms: Introduction of Directly Linked Transition Metals beside Bismuthanes

XanI2 (4,5‐diiodo‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) and DBFI2 (4,6‐diiododibenzofuran) have been functionalized first with Ph2Bi units through reaction with PhLi and then with Ph2BiCl. The remaining C–I bonds were shown to undergo oxidative additions to M(PPh3)2 species (M = Pd, Ni; generated from employed [M(PPh3)4]), thus giving rise to heterometallic systems [Xan(BiPh2)Pd(PPh3)2I] (2), [Xan(BiPh2)Ni(PPh3)2I] (3), and [DBF(BiPh2)Pd(PPh3)2I] (6), where the bismuthane moieties are positioned vis‐à‐vis a d8‐MII center; treatment of 2 with AgOTf led to an exchange of the iodide ligand at the central nickel atom by a more weakly bound triflate ligand. The developed synthetic strategy can be envisioned to also provide access to combinations of such transition metal moieties with other main group entities for cooperative substrate activation.

(Invited) Platinum Group Metal-Free Oxygen Reduction Electrocatalysts: Structure-to-Property Relationships and Design Directions

Platinum group metal-free (PGM-free) electrocatalysts draw much attention these days as low-temperature (polymer electrolyte) fuel cell technology is approaching its broad market introduction. Among several competing chemistries, catalysts based on metal-nitrogen-carbon (M-N-C) materials system are by far the most popular choice. UNM have developed and commercialized catalysts from this class obtained by pyrolysis of N-containing organic precursor (N and C source) and transition metal salt (Fe, Co, Mn or combination of more than one metal). The pyrolysis is carried after integration of the precursors with a sacrificial support (usually mono-dispersed silica powder) through ball-milling. After the pyrolysis, the silica support is removed by leaching with HF. The catalysts are usually re-pyrolyzed and a second acid wash is carried out to remove remaining of metallic, oxide or carbide particles from the nano-composite. The resulting catalysts show high graphitic content (exceeding 80%) and atomically dispersed transition metal (usually less than 1%). Both nitrogen and transition metal moieties are integrated into the carbonaceous structure as defects in graphene. Design for performance of this type of catalysts depends on an understanding the nature and of these transition metal and nitrogen sites and the ways they participate in the oxygen reduction reaction (ORR). The structure-to-property relationships in these materials will be discussed here through correlating of theirs observed electrocatalytic activity in Rotating Ring-Disk Electrode (RRDE) and performance in single Membrane Electrode Assembly (MEA) polymer electrolyte fuel cells with results of X-ray photoelectron (XPS), X-ray absorption (XAS) and Mössbauer spectroscopy charaterization. We have introduced Density Functional Theory (DFT) calculations of core level binding energy shifts as a powerful tool for interpretation of XPS spectra of such catalysts.1-3 A combination of XPS and first principles calculations of nitrogen-containing model electrocatalysts4-5 was further used to elucidate the chemical nature of the nitrogen defects. We will discuss here how hydrogenation and protonation of different nitrogen-containing defects play a major role in ORR activity of the PGM-free catalysts across different pH ranges. This paper will place a particular emphasis on elucidating the role of nitrogen- and Fe-N-containing in-plane and edge defects on the acid-base steps in ORR catalysis and thus regulation PGM-free catalysts reactivity and selectivity. The nature of Fe-N-containing in-plane and edge defects pre-determines their association with the micro-pores (edge defects) or with the extended graphene surface (in-plane defects). This sets the stage for a “first order” dependence of chemistry of the active site and the morphology of the carbonaceous material, which is the catalysts’ backbone (see the Figure for conceptual illustration). We have shown that these correlations are more pronounced when MEA performance data are being used. In this case, we observe a strong anti-correlation of the overall performance with the “stacking number” of the graphitic domains in these catalysts, which lead us to conclude that in-plane defects are the predominant contributors to catalytic activity in fuel cells.6 Further discussion will bring the importance of these two classes of active sites in different modes of MEA performance loss and will serve as a guide for both active and durable PGM-free Polymer Electrolyte Fuel Cell (PEMFC) cathode catalysts and catalyst layer design. K. Artyushkova, et al., Chem. Commun., 49 (2013) 2539-2541S. Kabir, et al., Phys. Chem. Chem. Phys., 17 (2015) 17785-17789S. Kabir, et al., Surf. Interface Anal., 48 (2016) 293-300I. Matanovic, et al., J. Phys. Chem. C, 120 (2016) 29225-29232K. Artyushkova, et al., J. Phys. Chem. C, 121 (2017) 2836–2843M. Workman, et al., ACS Energy Letters, 2 (2017) 1489-1493 Figure 1

Titanium thiosalicylate complexes: functional metalloligands for the construction of redox-active heterometallic architectures

The titanium complex [TiCp*(thiosal)(thiosalH)] (1) has been synthesised by reaction of [TiCp*Me3], Cp* = η5-C5Me5, with thiosalicylic acid (H2thiosal). Complex 1 reacts with [M(μ-OH)(COD)]2 (M = Rh, Ir) to yield the corresponding early-late heterobimetallic complexes [TiCp*(thiosal)2M(COD)] (M = Rh (2); Ir (3)). Carbon monoxide replaces the COD ligand in 2 and 3 leading to the respective dicarbonyl complexes [TiCp*(thiosal)2M(CO)2] (M = Rh (4); Ir (5)). Compound 4 reacts with PPh3 to yield the monocarbonyl derivative [TiCp*(thiosal)2Rh(CO)(PPh3)] (6). The reaction of compound 1 with LinBu yields the tetrametallic complex [{TiCp*(thiosal)2Li}2(THF)3(H2O)] (7). Compound 7 reacts with [RuCp*Cl(COD)] yielding the heterometallic complex [TiCp*(thiosal)2RuCp*] (8). The molecular structures of compounds 4, 5 and 7 have been studied by X-ray diffraction. From cyclic voltammetric (CV) and square wave voltammetric (SWV) experiments, we observed that attachment of the titanium moiety of precursor 1 to a late transition metal moiety through the sulfur atoms has a significant influence on the reduction behaviour of the Ti(iv) metal centre. Thus, monometallic 1 exhibits an irreversible reduction process at -1.15 V vs. SCE, whereas the CVs of heterobimetallic compounds 2-6 are characterized by the reversible or quasi-reversible one-electron reduction of the Ti(iv)/Ti(iii) system, suggesting a significant stabilization of the Ti(iii) reduced species. Likewise, substitution of the M(COD) diolefin fragment in 2 and 3 by the M(CO)2 carbonyl-containing moiety (in compounds 4 and 5) leads to a significant anodic shift in the titanium E1/2 reduction redox potentials.

Transition Metal Functionalization of P4 Using a Diarylgermylene Anchor.

The manipulation of white phosphorus (P4) has been a long-standing challenge for chemists. While the holy grail remains at finding a method to catalytically activate and functionalize P4 to yield new organophosphorus compounds, fundamental research lies in developing procedures to control the reactivity of elemental phosphorus. In this work, Lewis acidic transition metal moieties M(CO)5 (M = Cr, Mo, W) and AuCl react with P4 derivatized with a low valent germanium compound. For both M(CO)5 and AuCl, bis-functionalized products can be formed; however the monosubstituted derivatives are found to be more stable, and the decomposition can be monitored by 31P{1H} NMR spectroscopy. The selective reactivity of white phosphorus, once a P-P bond has been activated, is a key step in yielding new organophosphorus compounds.

(Invited) High-Performance PGM-Free Electrocatalysts for the Polymer Electrolyte Fuel Cell Cathode

The activity of oxygen reduction reaction (ORR) catalysts often determine performance of polymer electrolyte fuel cells (PEFCs) as measured by their power output, open circuit voltage, and fuel conversion efficiency. Currently, Pt-nanoparticle catalysts, either supported on high surface-area carbons or prepared in a form of contiguous thin layer on conductive or non-conductive supports, represent the state of the art in ORR electrocatalysis at the PEFC cathode. However, the high and variable price and scarceness of Pt have limited its widespread implementation in the -temperature fuel cells to date, especially in automotive transportation. Under these circumstances, platinum group metal-free (PGM-free) ORR catalysts have received growing attention in recent years as a possible replacement for Pt-based formulations. The progress achieved since the development of the first nature-inspired electrocatalysts of oxygen reduction in the seminal work by Jasinski in the 1960s (Nature 201, 1212, 1964), which mostly happened through the broad implementation of the high-temperature synthesis approach, makes replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this this presentation, we will summarize recent progress in research targeting development of high-performance PGM-free catalysts for oxygen reduction reaction (ORR) at Los Alamos National Laboratory. Two approaches will be discussed in a greater detail: (i) the approach involving fine-tuning of the catalyst porosity and surface area using pore-forming compounds and (ii) the method specifically focusing on the development of atomically dispersed transition metal moieties and avoiding the formation of transition metal-rich nanoparticles during the heat treatment of catalyst precursors. We will demonstrate the impact that porosity/surface area optimization, through the use of either pore formers (cyanamide, ZnCl2) precursor templating (metal organic frameworks) or both, can have on the fuel cell performance of PGM-free catalysts. We will also show how modifications to the electrode structure through the change in the ionomer content and ionomer equivalent weight can lead to substantial improvements in the fuel cell performance at both low- and high current densities (aerial power density of more than 0.50 W/cm2 in H2-air testing at 80°C). Finally, we will recapitulate the challenges still facing PGM-free research that, in spite of all the progress achieved in recent years, is yet to produce materials capable of competing with the incumbent Pt-based catalysts in terms of oxygen reduction activity, performance durability, and cost (specifically, when extended to the overall cost of a fuel cell stack). Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.

Supramolecular Organometallic Gels Based on Neutral Platinum-Acetylide Moiety

Supramolecular gels, as a family of classical soft materials, have received considerable attention because of their wide potential applications in catalysis, chemical sensing, drug delivery carrier, and many other areas. Recently, it was found that the introduction of metal moieties, especially the transition metal moieties into the gelator allows for the additional scope for tuning gel properties such as catalytic activity, magnetism, and photoand electrochemistry. Neutral platinum-acetylide complex have been investigated in many respects from supramolecular chemistry to materials science during the past two decades because of their attractive properties such as well-defined linear geometry, synthetic accessibility and intriguing photoproperties. In this review article, we summarize the recent results in the investigation of supramolecular organometallic gels based on neutral platinum-acetylide moieties. These systems are classified based on the skeleton of the gelator building blocks and divided into two main parts, conjugated phenylene cored platinum-acetylide derivatives as well as other platinum-acetylide derivatives containing various functional groups.

Synthesis and spectroscopic studies of transition-metal fullerene supramolecular systems

Abstract A new ligand has been designed that provides a relatively simple framework to build supramolecular systems containing both fullerene and transition metal moieties. The modular framework of the ligand allows for the easy design of more complex systems. Analysis of absorption and emission spectra suggests significant photoinduced charge transfer between the two moieties. More complex systems and the excited-state photophysics of the presented systems are being studied.

Facile synthesis and photochromic properties of diarylethene‐containing terpyridine and its transition metal (Zn2+/Co2+/Ru2+) complexes

Several transition metal complexes based on 2,3‐bis(2,4,5‐trimethyl‐3‐thienyl)maleic anhydride (DTE) bearing terpyridine (TPY) have been designed and synthesized. Furthermore, the photochromism of the free ligand and the influence of transition metal moieties on the photochemical properties have been thoroughly characterized by monitoring the changes in their UVvis spectra. Compounds 3–6 all display excellent response to UV irradiation, especially Co complex 5 with optimum sensitivity that took only 5 s to reach photostationary state. The photochromic properties of DTE unit have been found to be strongly influenced by the bridging transition metals, as complexes 4 (L–Zn–L) and 6 (L–Ru–L) exhibit much better photochromic properties in tetrahydrofuran solution than complex 5 (L–Co–L) and the free ligand 3 (L). It is worth noting that the optical/chemical thermal stabilities of photochromic compounds 3–6 are all greatly improved after the precursor functionalized with TPY and further coordinated with metal ions. Copyright © 2012 John Wiley & Sons, Ltd.

ChemInform Abstract: Organometallic Acetylides of PtII, AuI and HgII as New Generation Optical Power Limiting Materials

AbstractReview: 106 refs.

Organometallic acetylides of PtII, AuI and HgII as new generation optical power limiting materials

Within the scope of nonlinear optics, optical power limiting (OPL) materials are commonly regarded as an important class of compounds which can protect the delicate optical sensors or human eyes from sudden exposure to damaging intense laser beams. Recent efforts have been devoted to developing organometallic acetylide complexes, dendrimers and polymers as high performance OPL materials of the next generation which can favorably optimize the optical limiting/transparency trade-off issue. These metallated materials offer a new avenue towards a new family of highly transparent homo- and heterometallic optical limiters with good solution processability which outperform those of current state-of-the-art visible-light-absorbing competitors such as fullerenes, metalloporphyrins and metallophthalocyanines. This critical review aims to provide a detailed account on the recent advances of these novel OPL chromophores. Their OPL activity was shown to depend strongly on the electronic characters of the aryleneethynylene ligand and transition metal moieties as well as the conjugation chain length of the compounds. Strategies including copolymerization with other transition metals, change of structural geometry, use of a dendritic platform and variation of the type and content of transition metal ions would strongly govern their photophysical behavior and improve the resulting OPL responses. Special emphasis is placed on the structure-OPL response relationships of these organometallic acetylide materials. The research endeavors for realizing practical OPL devices based on these materials have also been presented. This article concludes with perspectives on the current status of the field, as well as opportunities that lie just beyond its frontier (106 references).

Studies on the Reactivity of [Ge9]4− towards [Fe(cot)(CO)3]: Synthesis and Characterization of [Ge8Fe(CO)3]3− and of the Anionic Organometallic Species [Fe(cot)(CO)3]−

Reaction of cyclooctatetraene (COT) iron(II) tricarbonyl, [Fe(cot)(CO)(3)], with one equivalent of K(4)Ge(9) in ethylenediamine (en) yielded the cluster anion [Ge(8)Fe(CO)(3)](3-) which was crystallographically-characterized as a [K(2,2,2-crypt)](+) salt in [K(2,2,2-crypt)](3)[Ge(8)Fe(CO)(3)]. The chemically-reduced organometallic species [Fe(η(3)-C(8)H(8))(CO)(3)](-) was also isolated as a side-product from this reaction as [K(2,2,2-crypt)][Fe(η(3)-C(8)H(8))(CO)(3)]. Both species were further characterized by EPR and IR spectroscopy and electrospray mass spectrometry. The [Ge(8)Fe(CO)(3)](3-) cluster anion represents an unprecedented functionalized germanium Zintl anion in which the nine-atom precursor cluster has lost a vertex, which has been replaced by a transition-metal moiety.

ChemInform Abstract: Synthesis and Reactivity of Arenes Coordinated to Cyclopentadienyliron Cations

Abstract Over the past few decades, there has been tremendous interest in the chemistry of arenes coordinated to transition metal moieties due to their applications in the fields of organic and polymer synthesis. The electrophilicity of coordinated arenes allows for reactions with a number of carbon-, oxygen-, nitrogen- and sulfur-containing nucleophiles. This review describes the synthesis and reactivity of both mono- and polyiron arene complexes. Spectroscopic and electrochemical methods for the characterization of these coordination compounds are presented. The important synthetic applications of arene cyclopentadienyliron complexes are also described.

Functionalized Porous Silicas with Unsaturated Early Transition Metal Moieties as Hydrogen Storage Materials: Comparison of Metal and Oxidation State

Hexagonally packed mesoporous silica (HMS) grafted with titanium, vanadium, and chromium organometallic fragments possessing metal oxidation states between (II) and (IV) were synthesized and characterized by XRD, nitrogen adsorption, XPS, and elemental analysis. These materials were then tested for their excess hydrogen storage capacity, with the purpose in mind of subtracting out the physisorption component and establishing which transition metal fragments and oxidation states functioned as the most effective binding sites for hydrogen. By varying the metal type and the metal oxidation state, as well as the ligand environment by exchanging the alkyl group with hydride via hydrogenolysis, the effects of these variations on the H2 adsorption capacity of the metal center as well as on the binding enthalpies of these systems were investigated. This study demonstrated that titanium is more effective at hydrogen binding than vanadium and chromium. Hence, HMS silica grafted with benzyl titanium(III) fragments c...