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Cis and trans-Cr–N₂ complexes supported by the diphosphine ligand P{sup Ph}₂N{sup Bn}₂ have been prepared. Positioned pendant amines in the second coordination sphere influence the thermodynamically preferred geometric isomer. Electronic structure calculations indicate negligible Cr–N₂ back-bonding; rather, electronic polarization of N₂ ligand is thought to stabilize Cr–N₂ binding.
[M(EtBTP) 3 ][BPh 4 ] 3 ∙3 CH 3 CN (M=Nd, Am; EtBTP=2,6-bis(5,6-diethyl-1,2,4-triazin-3-yl)pyridine) have been synthesized from reactions of MCl 3 ∙ n H 2 O with EtBTP in acetonitrile followed by anion metathesis. Structural analysis reveals that these compounds contain M 3+ cations bound by tridentate EtBTP ligands to create a tricapped trigonal prismatic geometry around the metal centers. Collection of high-resolution, single-crystal X-ray diffraction data also allowed reduction in bond lengths esd's, such that a slight contraction of Δ=0.0158(18) Å in the Am-N versus Nd-N bond lengths was observed, even though these cations ostensibly have matching ionic radii. Theoretical evaluation revealed enhanced metal–ligand bonding through back donation in the [Am(EtBTP) 3 ] 3+ complex that is absent in [Nd(EtBTP) 3 ] 3+ .
A new triketimine (2,6-Me{sub 2}C{sub 6}H{sub 3}N=CMe){sub 2}CH(2,6-Me{sub 2}C{sub 6}H{sub 3}N=CBu{sup t}) (1) was synthesized by the reaction of imidoyl chloride 2,6-Me{sub 2}C{sub 6}H{sub 3}N=CClBu{sup t} with lithium diketiminate (2,6-Me{sub 2}C{sub 6}H{sub 3}N=CMe){sub 2}CHLi. In the crystalline state, compound 1 exists in the diimineenamine form; in solution, in the triimine form. The metalation of triketimine 1 with n-butyllithium in THF at 0 °C produced lithium triketiminate [(2,6-Me{sub 2}C{sub 6}H{sub 3}N=CMe){sub 2}C(2,6-Me{sub 2}C{sub 6}H{sub 3}N=CBu{sup t})]Li(THF){sub 2} (2). The metathesis reactions of Ln(BH{sub 4}){sub 3}(THF){sub 3} (Ln = Y, Nd) with compound 2 (1: 1 molar ratio, THF) gave the neutral triketiminate bis(borohydride) complexes [(2,6-Me{sub 2}C{sub 6}H{sub 3}N=CMe){sub 2}C(2,6-Me{sub 2}C{sub 6}H{sub 3}N=CBu{sup t})]Ln(BH{sub 4}){sub 2}(THF){sub 2} (Ln = Y (3), Nd (4)). As opposed to the complexes with neutral triketimine, the monoanionic triketiminate ligand is coordinated to Li and Y or Nd cations in a bidentate fashion. Complexes 3 and 4 catalyze the polymerization of rac-lactide and ε-caprolactone; in combination with [Ph{sub 3}C][B(C{sub 6}F{sub 5}){sub 4}] and AlBu{sub 3}{sup i} (1 : 1 : 10 molar ratio), these compounds exhibit catalytic activity in the polymerization of isoprene.
The current discussion on whether scandium, yttrium and lanthanum should represent Group 3 in the Periodic Table or whether lutetium should replace lanthanum in the group has prompted us to further explore the structural chemistry of the Group 3 elements and compare the coordination numbers and coordination geometries adopted. The steric and electronic properties of the coordinated ligands have a major influence on the structures adopted. We report the synthesis and crystal structure determination of an unusual dinuclear scandium complex [(bipy)(NO 3 ) 2 Sc(µ-OH) 2 Sc(NO 3 ) 2 (bipy)] obtained by the reaction of hydrated scandium nitrate with 2,2'-bipyridyl (bipy) in either ethanol or nitromethane. The crystal structure of the complex shows that the scandium centers are eight coordinate, and the structure obtained contrasts with related complexes found in the lanthanide series [Ln(bipy) 2 (NO 3 ) 3 ] and [Ln(phen) 2 (NO 3 ) 3 ] (phen = phenanthroline) and in [M(terpy)(NO 3 ) 3 ] (M = Sc, Er–Lu), where these complexes are all mononuclear.
With the increasing penetration of electronic loads and distributed energy resources, conventional load models cannot capture their dynamics. Therefore, a new comprehensive composite load model is developed by Western Electricity Coordinating Council (WECC). However, this model is a complex high-order non-linear system with multi-time-scale property, which poses challenges on power system studies with heavy computational burden. In order to reduce the model complexity, the authors firstly develop a large-signal order reduction (LSOR) method using singular perturbation theory. In this method, the fast dynamics are integrated into the slow ones to preserve transient characteristics of the former. Then, accuracy assessment conditions are proposed and embedded into the LSOR to improve and guarantee the accuracy of reduced-order model. Finally, the reduced-order WECC composite load model is derived by using the proposed algorithm. Overall, simulation results show that the reduced-order large-signal model significantly alleviates the computational burden while maintaining similar dynamic responses as the original composite load model.
Strong-field hexadentate ligands were synthesized and coordinated to cobalt metal centers to result in three new low-spin to low-spin Co(III/II) redox couples. The ligand backbone has been modified with dimethyl amine groups to result in redox potential tuning of the Co(III/II) redox couples from –200 to –430 mV versus Fc +/0 . The redox couples surprisingly undergo a reversible molecular switch rearrangement from five-coordinate Co(II) to six-coordinate Co(III) despite the ligands being hexadentate. The complexes exhibit modestly faster electron self-exchange rate constants of 2.2–4.2 M –1 s –1 compared to the high-spin to low-spin redox couple [Co(bpy) 3 ] 3 + /2 + at 0.27 M –1 s –1 , which is attributed to the change in spin state being somewhat offset by this coordination switching behavior. The complexes were utilized as redox shuttles in dye-sensitized solar cells with the near-IR AP25 + D35 dye system and exhibited improved photocurrents over the [Co(bpy) 3 ] 3 + /2 + redox shuttle (19.8 vs 18.0 mA/cm 2 ). Finally, future directions point toward pairing the low-spin to low-spin Co(II/III) tunable series to dyes with significantly more negative highest occupied molecular orbital potentials that absorb into the near-IR where outer sphere redox shuttles have failed to produce efficient dye regeneration.
Abstract γ‐alumina is one of the oldest and most important commercial catalytic materials with high surface area and stability. These attributes enabled its use as the first commercial large‐scale heterogeneous catalyst for ethanol dehydration. Despite progress in materials characterization the nature of the specific sites on the surface of γ‐alumina that are responsible for its unique catalytic properties has remained obscure and controversial. By using combined infrared spectroscopy, electron microscopy and solid‐state nuclear magnetic resonance measurements we identify the octahedral, amphoteric (O) 5 Al(VI)‐OH sites on the (100) segments of massively restructured (110) facets on typical rhombus‐platelet γ‐alumina as well as the (100) segments of irrational surfaces (invariably always present in all γ‐alumina samples) responsible for its unique catalytic activity. Such (O) 5 Al(VI)‐OH sites are also present on the macroscopically defined (100) facets of γ‐alumina with elongated/rod‐like geometry. The mechanism by which these sites lose ‐OH groups upon thermal dehydroxylation resulting in coordinatively unsaturated penta‐coordinate Al +3 O 5 sites is clarified. These coordinatively unsaturated penta‐coordinate Al sites produce well‐defined thermally stable Al‐carbonyl complexes. Our findings contribute to the understanding of the nature of coordinatively unsaturated Al sites on the surface of γ‐alumina and their role as catalytically active sites.
Ultrawideline dynamic nuclear polarization (DNP)-enhanced 195 Pt solid-state NMR (SSNMR) spectroscopy and theoretical calculations are used to determine the coordination of atomic Pt species supported within the pores of metal–organic frameworks (MOFs). The 195 Pt SSNMR spectra, with breadths reaching 10,000 ppm, were obtained by combining DNP with broadbanded cross-polarization and CPMG acquisition. Although the DNP enhancements in static samples are lower than those typically observed under magic-angle spinning conditions, the presented measurements would be very challenging using the conventional SSNMR methods. The DNP-enhanced ultrawideline NMR spectra served to separate signals from cis - and trans -coordinated atomic Pt 2+ species supported on the UiO-66-NH 2 MOF. Here, the data revealed a dominance of kinetic effects in the formation of Pt 2+ complexes and the thermodynamic effects in their reduction to nanoparticles. A single cis-coordinated Pt 2+ complex was confirmed in MOF-253.
The trivalent f-element coordination chemistry of a novel aminopolycarboxylate complexant was investigated. The novel reagent is an octadentate complexant that resembles diethylenetriamine-N,N,N',N",N"-pentaacetic acid (DTPA), but a single N-acetate pendant arm was substituted with a N-2-pyrazinylmethyl functional group. Thermodynamic studies of ligand protonation and trivalent lanthanide, americium and curium, complexation by N-2-pyrazinylmethyldiethylenetriamine-N,N',N",N"-tetraacetic acid (DTTA-PzM) emphasize the strong electron withdrawing influence of the N-2-pyrazinylmethyl group. Particularly, DTTA-PzM is more acidic compared to a N-2-pyridinylmethyl-substituted structural equivalent, DTTA-PyM, with a substantial lowering of pK7, corresponding to the protonation of a second aliphatic amine site. The participation of the pyrizyl nitrogen in the metal ion coordination sphere is observed from the fluorescence lifetime decay measurements of metal hydration and the interpretation of the stability constants for ML– and MHL(aq) complexes. The overall conditional stability constants for the trivalent f-element complexation by DTTA-PzM complexes decrease, relative to DTTA-PyM, as expected based on the lower basicity of pyrazine in water relative to pyridine. Replacement of the N-2-pyridinylmethyl group with N-2-pyrazinylmethyl, while enhancing the total acidity of DTTA-PzM, also reduces its softness, as manifested by a small lowering of β 101 Am/Nd and liquid–liquid separation of trivalent lanthanides from trivalent americium. Despite this, the 4f/5f separation is doubled when DTTA-PzM replaces DTPA as an aqueous complexant in solvent extraction.
Tetraazamacrocycles have been very extensively exploited as transition metal ligands for a variety of purposes, including catalysis, medical imaging, pharmaceuticals, etc. However, the pentaazamacrocycles are much less commonly used for similar purposes because of poor availability, difficulties in their synthesis, and less well-known metal coordination properties. 1,4,7,10,13-pentaazacyclopentadane (15aneN5) was initially synthesized by a published synthetic route, which we simplified and shortened with minimal drop in yield. Eight different transition metal complexes were made using typical complexation methods. X-ray crystallography of multiple novel complexes yielded insight into the flexibility in coordination geometry of this interesting macrocycle as well as the first crystal structures of 15aneN5 with Cr 3+ , Mn 3+ , Fe 3+ , Co 3+ , Cu 2+ , and Ru 2+ . A parameter to quantify the coordination geometry adopted by the ligand was devised and applied to all known crystal structures of its metal complexes. Lastly, oxidation of 15aneN5 to a novel diimine macrocycle was observed during complexation with ruthenium.
A series of complexes {[NBu 4 ][LCu II (O 2 CR)] (R = -C 6 F 5 , -C 6 H 4 (NO 2 ), -C 6 H 5 , -C 6 H 4 (OMe), -CH 3 , and -C 6 H 2 ( i Pr) 3 )} were characterized (with the complex R = -C 6 H 4 (m-Cl) having been published elsewhere (Mandal et al. J. Am. Chem. Soc. 2019, 141, 17236)). All feature N,N',N"-coordination of the supporting L 2– ligand, except for the complex with R = -C 6 H2( i Pr) 3 , which exhibits N,N',O-coordination. For the N,N',N"-bound complexes, redox properties, UV–vis ligand-to-metal charge transfer (LMCT) features, and rates of hydrogen atom abstraction from 2,4,6,-tri-t-butylphenol using the oxidized, formally Cu(III) compounds LCu III (O 2 CR) correlated well with the electron donating nature of R as measured both experimentally and computationally. Specifically, the greater the electron donation, the lower is the energy for LMCT and the slower is the reaction rate. The results are interpreted to support an oxidatively asynchronous proton-coupled electron transfer mechanism that is sensitive to the oxidative power of the [Cu III (O 2 CR)] 2+ core.
Abstract A promising metal-organic complex, iron (Fe)-NTMPA 2 , consisting of Fe(III) chloride and nitrilotri-(methylphosphonic acid) (NTMPA), is designed for use in aqueous iron redox flow batteries. A full-cell testing, where a concentrated Fe-NTMPA 2 anolyte (0.67 M) is paired with a Fe-CN catholyte, demonstrates exceptional cycling stability over 1000 charge/discharge cycles, and noteworthy performances, including 96% capacity utilization, a minimal capacity fade rate of 0.0013% per cycle (1.3% over 1,000 cycles), high Coulombic efficiency and energy efficiency near 100% and 87%, respectively, all achieved under a current density of 20 mA·cm - ². Furthermore, density functional theory unveils two potential coordination structures for Fe-NTMPA 2 complexes, improving the understanding between the ligand coordination environment and electron transfer kinetics. When paired with a high redox potential Fe-Dcbpy/CN catholyte, 2,2′-bipyridine-4,4′-dicarboxylic (Dcbpy) acid and cyanide (CN) ligands, Fe-NTMPA 2 demonstrates a notably elevated cell voltage of 1 V, enabling a practical energy density of up to 9 Wh/L.
The formation of C–N bonds from molecular dinitrogen (N 2 ) offers a synthetic route to value-added nitrogen-containing compounds without relying on prefunctionalized nitrogen sources. Here, this Perspective highlights recent advances in forming C–N bonds from N 2 with homogeneous transition metal complexes. After discussing how transition metal complexes activate N 2 through various coordination modes, we focus on the reactivity of reduced nitrogen intermediates with different kinds of carbon sources. Carbon electrophiles and nucleophiles enable C–N bond formation via insertion, substitution, or radical pathways. Cycloaddition reactions, particularly involving polarized N 2 ligands and unsaturated carbon electrophiles, offer routes to more complex products. We describe efforts to achieve catalytic turnover and emphasize the remaining obstacles to catalytic C–N bond construction.
The syntheses of the first homoleptic U(III) and U(IV) amidate complexes are described here. These can be interconverted by chemical reduction/oxidation, showing an unusual change in coordination number from four in the U(III) complex to eight in the U(IV) complex in the solid state structures.
Four new complexes, (NH{sub 4}){sub 11.9}[Ln{sub 4.7}(MoO{sub 4})(H{sub 2}O){sub 23}(Mo{sub 7}O{sub 24}){sub 4}]{center_dot}xH{sub 2}O (Ln=Pr, x=34 (1); Ln=Nd, x=19 (2)), [NH{sub 4}]{sub 28}[Ce{sub 8}(MoO{sub 4}){sub 2}(H{sub 2}O){sub 31}(Mo{sub 7}O{sub 24}){sub 8}]{center_dot}74H{sub 2}O (3), and (NH{sub 4}){sub 26}[CoPr{sub 8}(MoO{sub 4}){sub 2}(H{sub 2}O){sub 33}(Mo{sub 7}O{sub 24}){sub 8}]{center_dot}54H{sub 2}O (4) have been synthesized and characterized by single-crystal and powder X-ray diffraction, CHN elemental analyses TGA analyses, IR and UV-Vis spectroscopy. Complex 1-3 are 0D compounds constructed by the connection between Ln{sup III} ions and [Mo{sub 7}O{sub 24}]{sup 6-} unit. In complex 4, the existence of Co{sup II} connects the polyanion clusters into 1D chain. The introduction of 3d metal (cobalt cation) and 4f metal (Ln=Pr{sup III}, Nd{sup III}, Ce{sup III}) encourages the coordination capability for [Mo{sub 7}O{sub 24}]{sup 6-} unit, which shows interesting coordination modes. The [Mo{sub 7}O{sub 24}]{sup 6-} unit in 1-4 shows three new coordination modes, connecting up to four metal cations. Complexes 1-4 show antiferromagnetic behavior via variable temperature magnetic study. The photoluminescence spectrum indicates the photoluminescence property for 4. - Graphical abstract: Heptamolybdate anion shows extraordinary coordination geometry in the presence of both lanthanide cation (Pr{sup III}) and transitional metal cation (Co{sup II}), which give rise to a new 4d-4f-3d complex. Black-Small-Square Highlights: Black-Right-Pointing-Pointer A new 4d-4f-3d complex that containing 1D chain was obtained and discussed. Black-Right-Pointing-Pointer New coordination geometry with higher coordination number of heptamolybdate. Black-Right-Pointing-Pointer Series of heptamolybdate contained complexes were synthesized and characterized. Black-Right-Pointing-Pointer Complexes mentioned above show antiferromagnetic behavior.
Cu(II) cations in the presence of diamine ligands such as tetramethylethylendiamine (TMEDA) react with Na2SeO3 to produce the heteroleptic selenite copper compound of formula [Cu-3(TMEDA)(3)(SeO3)(2)(H2O)(4)] (NO3)(2). In the cationic moiety two copper atoms are linked by two selenite anions through the O-Se-O bridge. One of the two bridging selenite anion coordinates to a third copper atom through the third oxygen atom. Reaction of Cd(CH3COO)(2)center dot 2H(2)O with Na2SeO3 in the presence of ligand with softer character such as thiourea [(NH2)(2)CS; tu] or selenourea [(NH2)(2)CSe; tu] in aqueous solution afforded the complex [{Cd(tu)(2)SeO3}(2)], whose structure has been elucidated by X-ray diffraction analysis. It is the first reported example of a molecular cadmium selenite complex. Two cadmium cations stabilized by the coordination of four ancillary thiourea soft ligands, are linked together by two bridging selenite ions through O and O-Se-O bridges. A comparison between the coordination mode of the selenite ion in those cadmium and copper complexes and in inorganic extended CdSeO3 and hydrated CuSeO3 phases is also reported. (C) 2017 Elsevier B.V. All rights reserved.
In extreme-scale computing environments such as the DOE Leadership Computing Facilities scientific workflows are routinely used to coordinate software processes for the execution of complex, computational applications that perform in-silico experiments. Monitoring the performance of workflows without also simultaneously tracking provenance is not sufficient to understand variations between runs, configurations, versions of a code, and between changes in an implemented stack, and systems, i.e. the variability of performance metrics data in their historical context. We take a provenance-based approach and demonstrate that provenance is useful as a tool for evaluating and optimizing workflow performance in extreme-scale HPC environments. We present Chimbuko, a framework for the analysis and visualization of the provenance of performance. Chimbuko implements a method for the evaluation of workflow performance from multiple components that enables the exploration of performance metrics data at scale.