Cuboidal Core Research Articles

A cuboidal [Cu4(SO4)4] structure supported by β-picoline ligands.

The solid-state structure of the cobalt-β-picoline-sulfate complex tetra-μ3-sulfato-tetra-kis-[bis-(3-methyl-pyridine)-cobalt(II)], [Co4(SO4)4(C6H7N)8], is reported. The tetra-meric cobalt cluster contains a cuboidal core comprised of four cobalt(II) cations and four sulfate anions at alternate cube vertices. The cobalt corners are each capped with two β-picoline ligands. The sulfate anions adopt a rare [3.2110] bridging motif, and the cuboidal cluster is unprecedented in coordination chemistry.

Effect of Ti Addition on the Precipitation Mechanism and Precipitate Size in Nb-Microalloyed Steels

The effect of Ti microalloying on the precipitation of NbC particles in Nb-microalloyed and Nb-Ti-microalloyed steels was investigated by scanning transmission electron microscopy. The experimental results illustrate that NbC precipitates tend to be formed via a conventional “nucleation and growth” mechanism in Ti-free steel, while the particles would be precipitated as a complex form of TiN cuboid core and NbC hemispherical cap in Ti-Nb-microalloyed steel with 0.009 wt.% Ti and 0.0046 wt.% N. Ti microalloying contributed to the refinement of the precipitate size, and an enhancement of the volume fraction of NbC particles was also found based on the experimental observations.

On Runtime Communication and Thermal-Aware Application Mapping and Defragmentation in 3D NoC Systems

Many-core systems connected by 3D Networks-on-Chip (NoC) are emerging as a promising computation engine for systems like cloud computing servers, big data systems, etc . Mapping applications at runtime to 3D NoCs is the key to maintain high throughput of the overall chip under a thermal/power constraint. However, the goals of optimizing both the communication latency and chip peak temperature are contradicting due to several reasons. First, exploiting the vertical TSV links can accelerate communications, while low peak temperature prefers that the tasks to be mapped closer to the heat sink, instead of using the vertical links. Second, mapping tasks in close proximity can reduce communication latency, but at the cost of poor heat dissipation. To address these issues, in this paper, we propose an efficient runtime mapping algorithm to reduce both communication latency and overall application running time under thermal constraint. In essence, this algorithm first selects a 3D cuboid core region of a specific shape for each incoming application by setting the region's number of occupied vertical layers and its distance to the heat sink, in order to optimize its communication performance and peak temperature. Next, the exact locations of the core regions in the chip are determined, followed by a task-to-core mapping. A defragmentation algorithm is also proposed to keep free core regions contiguous. The experimental results have confirmed that, compared to two recently proposed runtime mapping algorithms, our proposed approach can reduce the total running time by up to 48% and communication cost by up to 44%, with a low runtime overhead.

Backbone-Substituted β-Ketoimines and Ketoiminate Clusters: Transoid Li2O2 Squares and D2-Symmetric Li4O4 Cubanes. Synthesis, Crystallography and DFT Calculations

The preparation and crystal structures of four β-ketoimines with bulky aryl nitrogen substituents (2,6-diisopropylphenyl and 2,4,6-trimethylphenyl) and varying degrees of backbone methyl substitution are reported. Backbone substitution “pinches” the chelate ring. Deprotonation with n-butyllithium leads to dimeric Li2O2 clusters, as primary laddered units, with an open transoid geometry as shown by crystal structures of three examples. The coordination sphere of each lithium is completed by one tetrahydrofuran ligand. NMR spectra undertaken in either C6D6 or 1:1 C6D6/d8-THF show free THF in solution and the chemical shifts of ligand methyl groups experience significant ring-shielding which can only occur from aryl rings on adjacent ligands. Both features point to conversion to higher-order aggregates when the THF concentration is reduced. Recrystallization of the materials from hydrocarbon solutions results in secondary laddering as tetrameric Li4O4 clusters with a cuboidal core, three examples of which have been crystallographically characterised. These clusters are relatively insoluble and melt up to 250 °C; a consideration of the solid-state structures indicates that the clusters with 2,6-diisopropylphenyl substituents form very uniform ball-like molecular structures that will only be weakly solvated.

K+···Cπ and K+···F Non-Covalent Interactions in π-Functionalized Potassium Fluoroalkoxides

Secondary interactions stabilize coordinatively demanding complexes of s-block metals [...]

Enantioselective synthesis of tungsten trimetallic cluster chalcogenides

Excision of {W3Q7Br4}n (Q=S, Se) of polymeric phases using chiral diphosphines is a general procedure to synthesize optically pure trinuclear clusters. Chiral transfer from the enantiomerically pure diphosphines (+)-1,2-bis[2,5-(dimethylphospholan-1-yl)]ethane, (R,R)-Me-BPE, (−)-1,2-bis[2,5-(dimethylphospholan-1-yl)]ethane, (S,S)-Me-BPE, and (−)-1,2-bis[2,5-(dimethylphospholan-1-yl)]benzene, (R,R)-DUPHOS, to the inorganic phase affords enantiopure P-[W3S4Br3((R,R)-Me-BPE)3]+, M-[W3S4Br3((S,S)-Me-BPE)3]+ (M-1+), P-[W3Se4Br3((R,R)-Me-BPE)3]+ (P-2+) and P-[W3S4Br3((R,R)-DUPHOS)3]+ (P-3+) clusters. The central W3(μ3-Q)(μ-Q) unit defines an incomplete cuboidal core with the capping chalcogen lying on a threefold axis and an effective C3 symmetry. Symbols P- and M- are used to indicate the rotation of the bromine atoms around the C3 axis, with the chalcogen atom pointing towards the viewer. Invariably, P-W3Q4 complexes are obtained starting from (R,R)-diphosphines, while its M-W3Q4 enantiomer is isolated in the presence of (S,S)-diphosphines. All complexes have been structurally characterized by single crystal X-ray diffraction and their enantiomeric character confirmed by CD spectroscopy.

TiN/NbC Compound Particle Formation during Thin Slab Direct Rolling of HSLA Steel

Compound two‐phase particles were found in thin slab direct rolled Ti‐added Nb high strength low alloy (HSLA) steel after the rough rolling stage of an in‐line strip processing line. The compound two‐phase particles are composed of a cuboid Ti‐rich (TixNb1−x)N (0.73≥x > 0.60) core and an Nb‐rich cap‐shaped epitaxial deposit of (TixNb1−x)C (0.35≥x > 0.06) or NbC formed on the {100}‐type faces of the cuboid (TixNb1−x)N (0.73≥x > 0.60) core. At the interface between the cuboid core and the cap‐shaped deposit, the Ti/(Nb + Ti) atomic ratio was found to increase gradually from a low value of Ti/(Nb + Ti) ≈ 0, on the cap‐side of the particles, to a high value of Ti/(Nb + Ti) ≈ 0.7, on the cuboid core side of the precipitate. The fact that compound TiN/NbC two‐phase particles are present in the matrix indicates that NbC has a greater thermodynamic stability, i.e. a lower solubility, in the presence of TiN precipitates. A kinetic precipitation model is proposed to explain this effect. The model is based on the formation of geometrically necessary dislocation (GND) around TiN precipitates. A high TiN volume fraction leads to a high density of GND and a high density of heterogeneous nucleation sites for NbC. Consequently, the solute Nb content is lowered and the strain accumulation due to the suppression of the inter‐pass recrystallization is limited. This results in the high softening ratio observed in multi‐hit compression test.

Elusive Trimethyllanthanum: Snapshots of Extensive Methyl Group Degradation in LaAl Heterobimetallic Complexes

Reactions of [La(AlMe4)3] and [Y(AlMe4)3] with PMe3 show that the phosphine can cleave Ln--CH3--Al linkages, separating Me3Al(PMe3). PMe3 (3 mol equiv) reacts with [Y(AlMe4)3] to give [(YMe3)n] contaminated with by-products containing phosphorus and aluminum. The La-based analog, [(LaMe3)n], is not formed selectively from the reaction of [La(AlMe4)3] with PMe3 or Et2O, which rather yields insoluble La/Al heterobimetallic products. Three multi-nuclear La-based clusters were obtained from a reaction of [La(AlMe4)3] with PMe3 (1 equiv) and identified by X-ray structure analyses. Each cluster exhibits extensive methyl group degradation and contains methylene, methine, or carbide moieties. [La4Al8(CH)4(CH2)2(CH3)20(PMe3)] has a [La4(CH)4] cuboid core supported by AlMe3, Me2AlCH2AlMe2, and PMe3 ligands. [La4Al8(C)(CH)2(CH2)2(CH3)22(toluene)] also contains a cuboid core, [La3Al(C)(CH)2(CH2)], which includes one exo cubic lanthanum atom, and is supported by AlMe3, Me3AlCH2AlMe2, (AlMe4)-, and toluene ligands. The lanthanum atoms in [La5Al9(CH)6(CH3)30] are arranged in a trigonal bipyramidal fashion with (CH) functionalities capping each face. The [La5(CH)6]3- core is formally balanced by three AlMe2 + moieties and is additionally supported by six AlMe3 ligands. The unit cell contains two independent La5 clusters, one with pseudo-C3h and the other with pseudo-D3 symmetry, as well as two molecules of the separation co-product Me3Al(PMe3).

A Model of the Oxygen-Evolving Center of Photosystem II Predicted by Structural Refinement Based on EXAFS Simulations

A refined computational structural model of the oxygen-evolving complex (OEC) of photosystem II (PSII) is introduced. The model shows that the cuboidal core Mn3CaO4 with a "dangler" Mn ligated to a corner mu4-oxide ion is maximally consistent with the positioning of the amino acids around the metal cluster as characterized by XRD models and high-resolution spectroscopic data, including polarized EXAFS of oriented single crystals and isotropic EXAFS. It is, therefore, natural to expect that the proposed structural model should be particularly useful to establish the structure of the OEC, consistently with high-resolution spectroscopic data, and for elucidating the mechanism of water-splitting in PSII as described by the intermediate oxidation states of the EC along the catalytic cycle.

A Tetracopper(II)-Tetraradical Cuboidal Core and Its Reactivity as a Functional Model of Phenoxazinone Synthase

The coordination chemistry of the tridentate ligand N-(2-hydroxy-3,5-di-tert-butylphenyl)-2-aminobenzylalcohol H3L has been studied with the copper(II) ion. The ligand is noninnocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato [L*]2- radical form. The crystal structure of the synthesized tetracopper(II)-tetraradical complex [CuII4(L*)4] (1), has been determined by X-ray crystallography at 100 K. Variable-temperature (2-290 K) magnetic susceptibility measurements of complex 1 containing eight paramagnetic centers establish the spin ground state to be diamagnetic (St=0) arising from the antiferromagnetic interactions. Electrochemical measurements (cyclic voltammograms and square wave voltammograms) indicate four one-electron reductions of the ligand prior to the reduction of the metal center. Complex 1 is found to catalyze the aerial oxidation of 2-aminophenol to 2-amino-phenoxazine-3-one, thus modeling the catalytic function of the copper-containing enzyme phenoxazinone synthase. Kinetic measurements together with electron paramagnetic resonance and electronic spectral studies have been used to decipher the complex six-electron oxidative coupling of 2-aminophenol. An "on-off" mechanism of the radicals together with redox participation of the metal center is proposed for the catalytic oxidation processes.

High temperature synthesis of some strontium and barium 2,6-dibenzylphenolates

Direct treatment of HOdbp (= 2,6-dibenzylphenol) with strontium or barium metal in the absence of solvent at high temperature provides the corresponding phenolates Sr(Odbp) 2 and Ba(Odbp) 2. Recrystallisation of Ba(Odbp) 2 from THF gave a good yield of the crystalline dimer [Ba(Odbp) 2(THF)] 2 · 2THF. Attempted recrystallisation of Sr(Odbp) 2 from THF mostly yielded microcrystalline material characterized as [Sr(Odbp) 2] n but on one occasion gave a small crop of crystalline [Sr 9(Odbp) 8(O 2SiMe 2) 4(OH) 2(THF) 6(OH 2) 2] · 6THF derived from the adventitious reaction of Sr(Odbp) 2 with dimethylsilicone grease ({OSiMe 2} ∞). In the solid-state [Ba(Odbp) 2(THF)] 2 · 2THF displays significant intramolecular Ba⋯π-arene interactions with the pendant benzyl substituents. [Sr 9(Odbp) 8(O 2SiMe 2) 4(OH) 2(THF) 6(OH 2) 2] · 6THF features a square prismatic [Sr(O 2SiMe 2) 4] 6− core capped by two inverse crown-like square [Sr 4(Odbp) 4(OH)(L) 4] 3+ units, where L = OH 2 or THF, that are staggered with respect to the cuboidal core.

Directional chemical variations in diamonds showing octahedral following cuboid growth

A progression from cuboid to octahedral growth has been observed in 16 natural diamonds from Yakutian kimberlites. X-ray and cathodoluminescence topography have revealed that the change in morphology of diamonds with cloudy cuboid cores may occur without mixed-habit growth but via generation of numerous octahedral apices on cuboid surfaces and subsequent gradual transformation into regular octahedral morphology. Nitrogen aggregation in both cuboid and octahedral domains of such diamonds suggests that they have had a long residence time under mantle conditions. Micro-inclusions in the cuboid domains of the diamonds testify to the nucleation and growth of cuboid cores from a hydrous-carbonatitic (oxidized) fluid. The transition from cuboid hummocky growth rich in inclusions to octahedral growth without inclusions may be linked to decreasing supersaturation in the parent fluid. Measurements of δ13C and Nppm by ion microprobe show that the chemical variations observed between inner cuboid domains and outer octahedral zones commonly have a systematic character and as such they are probably not due to purely kinetic effects. The peripheral octahedral zones are always enriched in 13C in comparison with inner cuboid ones, and the total nitrogen content decreases with the change from cuboid to octahedral growth. The octahedral outer zones show a gradual progressive increase in δ13C, with an overall change of up to 5‰ from the cuboid core (δ13C usually between −8 and −6‰) to the diamond margin (δ13C usually between −4 and −2‰). Decreases in δ13C of this magnitude with a gradual increase in 13C may be attributed to the Rayleigh fractionation operating on a single parent fluid of close to normal mantle δ13C composition with diamond precipitating by the reduction of carbonatitic fluid in a closed system. However, one sample shows a variation of δ13C of approximately −17 to −6‰ and therefore suggests a possible change of fluid source composition from one containing subducted crustal organic carbon to one with common mantle carbon.

Heterometal cubane-type WFe 3S 4 and related clusters trigonally symmetrized with hydrotris(3,5-dimethylpyrazolyl)borate

The scope of formation and structures of tungsten–iron–sulfur clusters has been explored using reactions based on [(Tp*)WS 3] 1− ( 1) as the ultimate precursor. The reaction system 1/FeCl 2/NaSEt/S affords the cubane cluster [(Tp*)WFe 3S 4Cl 3] 1− ( 2), which with NaSEt is converted to [(Tp*)WFe 3S 4(SEt) 3] 1− ( 3).Clusters 2 and 3 contain the cubane [WFe 3(μ 3-S) 4] 3+ core.Complex 1 with FeCl 2/NaSEt forms [(Tp*)WFe 2S 3Cl 2(SEt)] 1− ( 4) with the cuboidal [WFe 2(μ 2-S) 2(μ 3-S)(μ 2-SR)] 2+ core.Treatment of 2 with excess Et 3P yields the edge-bridged double [(Tp*) 2W 2Fe 6S 8(PEt 3) 4] ( 5) with the [W 2Fe 6(μ 3-S) 6(μ 4-S) 2] core. Reaction of 2 with excess Et 3 P / BH 4 - / HS - leads a mixture of products, from which [(Tp*) 2W 2Fe 5S 9Na(SH)(MeCN)] 3−( 6) was identified.This cluster, as closely related [(Tp) 2Mo 2Fe 6S 9(SH) 2] 3−, exhibits a core topology [W 2Fe 5Na(μ 2-S) 2(μ 3-S) 6(μ 6-S)] very similar to the P N cluster of nitrogenase. All reactions were carried out in acetonitrile. The structures of 2– 6 were established crystallographically as Et 4N + salts. In the cubane series, substitution of tungsten for molybdenum decreases the [MFe 3S 4] 3+/2+ redox potential by ca. 0.20 V but has a negligible effect on electron distribution. This work expands the small set of previously known weak-field W–Fe–S clusters, demonstrates the existence of tungsten-containing edge-bridged double cubanes and clusters with the P N core topology, and introduces a new cuboidal core structure as found in 4 (Tp = hydrotris(pyrazolyl)borate, Tp* = hydrotris(3,5-dimethylpyrazolyl)borate).

Parallels between the Chemistry of Calcium(II) and Ytterbium(II). Synthesis and Crystal Structure of a Calcium Alkoxo-Phosphide Cuboidal Complex

Metathesis between CaI2 and K[P{CH(SiMe3)2}(C6H4-2-OMe)] in THF yields the alkoxo-phosphide complex [Ca{P(CH[SiMe3]2)(C6H4-2-O)}(THF)]4·4THF (2) via a ligand cleavage reaction involving the migration of a methyl group from oxygen to phosphorus. X-ray crystallography shows that 2 contains a Ca4O4 cuboidal core with μ2-phosphide groups bridging four of the faces of the cuboid.

Structure of Azotobacter vinelandii 7Fe ferredoxin at 1.35 Å resolution and determination of the [Fe-S] bonds with 0.01 Å accuracy

The crystal structure of Azotobacter vinelandii ferredoxin I (FdI) at 100 K has been refined at 1.35 Å resolution by full matrix block diagonal least-squares methods with anisotropic temperature factors for all non-hydrogen atoms and with hydrogen atoms included in the model. Fe-S bonds within the [3Fe-4S] + and [4Fe-4S] 2+ clusters of the protein are determined with an accuracy of at least 0.01 Å. Analysis of metric parameters reveals greater variation in bonds and angles within the [3Fe-4S] + cluster than in the [4Fe-4S] 2+ cluster, whereas the opposite is true regarding the cysteine Sγ atoms ligating to the two [Fe-S] cores. The [3Fe-4S] + core is asymmetrically distorted by the protein matrix but relatively uniformly ligated by its three Cys ligands; in contrast the tetrahedral [4Fe-4S] 2+ core is relatively symmetric but non-uniformily ligated by its four Cys ligands, three of which occur in a conserved CysxxCysxxCys residue motif. Comparison of the [3Fe-4S] + clusters in FdI and Desulfovibrio gigas ferredoxin II, refined at 1.7 Å resolution, indicates that within the limit of accuracy of the two refinements the cuboidal core is differently distorted in the two proteins. Comparison of the [3Fe-4S] + core in FdI with the structure of a reduced [Fe 3S 4] o synthetic analog † indicates that the protein-bound cluster displays distortions not intrinsic to the core itself. Nevertheless, both [3Fe-4S] + and [Fe 3S 4] o cores have metric features consistent with expected trends due to net charge on Fe and valency of S, and both exhibit a splayed configuration with respect to their three μ 2S atoms in the absence of a fourth Fe. Comparison of the[4Fe-4S] 2+ cluster in FdI with the structures of [Fe 4S 4] 2+ synthetic analogs shows that the protein bound and synthetic cubanes are very similar in geometric parameters, including the presence of tetragonal distortion in the FdI cluster common to this oxidation state.