Dirhenium carbonyl complexes bearing 2-vinylpyridine,morpholine and 1-methylimidazole ligands

Treatment of the labile compound [Re₂(CO)₈(MeCN)₂] with 2-vinylpyridine in refluxing benzene affords exclusively the new compound [Re₂(CO)₈(μ-η¹:η²-NC₅H₄CHCH₂)] (1) in 39% yield in which the μ-η¹:η²-vinylpyridine ligand is coordinated to one Re atom through the nitrogen and to the other Re atom via the olefinic double bond. Reaction of [Re₂(CO)₈(MeCN)₂] with morpholine in refluxing benzene furnishes two compounds, [Re₂(CO)₉(η¹-NC₄H₉O)] (2) and [Re₂(CO)₈(η¹-NC₄H₉O)₂] (3) in 5% and 29% yields, respectively. Reaction of [Re₂(CO)₈(MeCN)₂] with 1-methylimidazole gives [Re₂(CO)₈{η¹-NC₃H₃N(CH₃)}₂] (4) and the mononuclear compound fac-[ReCl(CO)₃{η¹-NC₃H₃N(CH₃)}₂] (5) in 18% and 26% yields, respectively. In the disubstituted compounds 2 and 4, the heterocyclic ligands occupy equatorial coordination sites. The mononuclear compound 5 consists of three CO groups, two N coordinated η¹-1-methylimidazole ligands and a terminal Cl ligand. The XRD structures of complexes 1, 3 and 5 are reported.     

Reactivity of [Re2(CO)8(MeCN)2] With 1-vinylimidazole: X-ray Structures of [Re2(CO)8{η1-NC3H3N(CH=CH2)}2] and [ReCl2(CO)2{η1-NC3H3N(CH=CH2)}2]

Abstract  Treatment of [Re₂(CO)₈(MeCN)₂] with excess 1-vinylimidazole in refluxing benzene gives three new compounds [Re₂(CO)₉{η ¹-NC₃H₃N(CH=CH₂)}] (1), [Re₂(CO)₈{η ¹-NC₃H₃N(CH=CH₂)}₂] (2) and [ReCl₂(CO)₂{η ¹-NC₃H₃N(CH=CH₂)}₂] (3) in 11, 32 and 2% yields, respectively. The solid-state structures of complexes 2 and 3 have been determined by single crystal X-ray diffraction studies. Compound 2 crystallizes in the monoclinic space group C2/c, with lattice parameters a = 13.8378(5) ?, b = 11.8909(5) ?, c = 14.4591(6) ?, β = 116.6470(10)°, Z = 4 and V = 2131.99(15) ?³. Compound 3 crystallizes in the monoclinic space group C2/c, with lattice parameters a = 10.1028(3) ?, b = 13.5640(5) ?, c = 12.5398(4) ?, β = 109.637(2)°, Z = 4 and V = 1618.4(9) ?³. The disubstituted dinuclear compound 2 contains two 1-vinylimidazole ligands coordinated through the imino nitrogen atoms at the equatorial sites, whereas the mononuclear compound 3 contains two carbonyl ligands, two N coordinated η ¹-1-vinylimidazole ligands and two terminal Cl ligands. Graphical Abstract  Two dinuclear complesxes [Re₂(CO)₉{η ¹-NC₃H₃N(CH=CH₂)}] (1) and [Re₂(CO)₈{η ¹-NC₃H₃N(CH=CH₂)}₂] (2) and the mononuclear [ReCl₂(CO)₂{η ¹-NC₃H₃N(CH=CH₂)}₂] (3) were obtained from the reaction of [Re₂(CO)₈(MeCN)₂] with excess 1-vinylimidazole at 80 °C. The X-ray structrures of 2 and 3 are described.      

Long-lasting hydrophilicity on nanostructured Si-incorporated diamond-like carbon films

We investigated the long-lasting hydrophilic behavior of a Si-incorporated diamond-like carbon (Si-DLC) film by varying the Si fraction in DLC matrix through oxygen and nitrogen plasma surface treatments. The wetting behavior of the water droplets on the pure DLC and Si-DLC with the nitrogen or oxygen plasma treatment revealed that the Si element in the oxygen-plasma-treated Si-DLC films played a major role in maintaining a hydrophilic wetting angle of <10° for 20 days in ambient air. The nanostructured patterns with a roughness of ～10 nm evolved because of the selective etching of the carbon matrix by the oxygen plasma in the Si-DLC film, where the chemical component of the Si-Ox bond was enriched on the top of the nanopatterns and remained for over 20 days.     

Investigations of 2-Thiazoline-2-thiol as a Ligand: Synthesis and X-ray Structures of [Mn2(CO)7(μ-NS2C3H4)2] and [Mn(CO)3(PPh3)(κ2-NS2C3H4)]

Abstract  Treatment of Mn₂(CO)₁₀ with 2-thiazoline-2-thiol in the presence of Me₃NO at room temperature afforded the dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) in 51 and 34% yields, respectively. Compound 1 was quantitatively converted into 2 when reacted with one equiv of Me₃NO. Reaction of 1 with triphenylphosphine at room temperature furnished the mononuclear complex [Mn(CO)₃(PPh₃)(κ ²-NS₂C₃H₄)] (3) in 66% yield. All three new complexes have been characterized by elemental analyzes and spectroscopic data together with single crystal X-ray diffraction studies for 1 and 3. Compound 1 crystallizes in the orthorhombic space group Pbca with a = 12.4147(2), b = 16.2416(3), c = 19.0841(4) ?, β = 90°, Z = 8 and V = 3848.01(12) ?³ and 3 crystallizes in the monoclinic space group P 2₁/n with a = 10.41730(10), b = 14.7710(2), c = 14.9209(2) ?, β = 91.1760(10)°, Z = 4 and V = 2295.45(5) ?³. Graphical Abstract  Two new dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) were formed when [Mn₂(CO)₁₀] was treated with 2-thiazoline-2-thiol in the presence of Me₃NO. Compound 2 reacts with PPh₃ to give the monomeric complex [Mn(CO)₃(PPh₃ )(κ ²-NS₂C₃H₄)]. The structures of 1 and 3 were established by crystallography. Shishir Ghosh, Faruque Ahmed, Rafique Al-Mamun, Daniel T. Haworth, Sergey V. Lindeman, Tasneem A. Siddiquee, Dennis W. Bennett, Shariff E. Kabir Investigations of 2-thiazoline-2-thiol as a ligand: Synthesis and X-ray structures of [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] and [Mn(CO)₃ (PPh3)(κ ²-NS₂C₃H₄)].      

Reactivity of [Re2(CO)8(MeCN)2] with thiazoles: Hydrido bridged dirhenium compounds bearing thiazoles in different coordination modes

Reactions of the labile compound [Re₂(CO)₈(MeCN)₂] with thiazole and 4-methylthiazole in refluxing benzene afforded the new compounds [Re₂(CO)₇{μ-2,3-η²-C₃H(R)NS}{η¹-NC₃H₂(4-R)S}(μ-H)] (1, R = H; 2, R = CH₃), [Re₂(CO)₆{μ-2,3-η²-C₃H(R)NS}{η¹-NC₃H₂(4-R)S}₂(μ-H)] (3, R = H; 4, R = CH₃) and fac-[Re(CO)₃(Cl){η¹-NC₃H₂(4-R)S}₂] (5, R = H; 6, R = CH₃). Compounds 1 and 2 contain two rhenium atoms, one bridging thiazolide ligand, coordinated through the C(2) and N atoms and a η¹-thiazole ligand coordinated through the nitrogen atom to the same Re as the thiazolide nitrogen. Compounds 3 and 4 contain a Re₂(CO)₆ group with one bridging thiazolide ligand coordinated through the C(2) and N atoms and two N-coordinated η¹-thiazole ligands, each coordinated to one Re atom. A hydride ligand, formed by oxidative-addition of C(2)-H bond of the ligand, bridges Re-Re bond opposite the thiazolide ligand in compounds 1-4. Compound 5 contains a single rhenium atom with three carbonyl ligands, two N-coordinated η¹-thiazole ligands and a terminal Cl ligand. Treatment of both 1 and 2 with 5 equiv. of thiazole and 4-methylthiazole in the presence of Me₃NO in refluxing benzene afforded 3 and 4, respectively. Further activation of the coordinated η¹-thiazole ligands in 1-4 is, however, unsuccessful and results only nonspecific decomposition. The single-crystal XRD structures of 1-5 are reported.     

Flow characteristics of slot jet impingement on a wedge

An experimental investigation is made to study the flow characteristics of slot jet impingement on a wedge whose included angle is 90 degrees. The aim of this investigation is to study the characteristics of the flow field near the wedge surface for various parameters. The different parameters like, jet velocity, slot width, distance of wedge vertex from the jet exit and the inclination of the wedge to jet axis are systematically varied to see their effect on the flow field. The flow field near the wedge vertex is similar to stagnation point flow. Far away from the vertex, the flow field is like that of wall jet. Near the vertex, very large variations of static pressure are observed in streamwise and transverse directions. This is due to large streamwise curvature and stagnation of flow. The transverse pressure gradient slowly decays in the streamwise direction, as a result, the velocity profiles are different from the similarity profiles of stagnation point flow and wall jet in the respective regions. Experiments are conducted for slot widths of 10 mm, 15 mm and 30 mm each for the distance between slot and wedge vertex of 80 mm, 120 mm and 240 mm. The static pressure and velocity profiles are measured by calibrated disk type static pressure probe and pitot tube respectively at various streamwise locations.Es wurde eine experimentelle Studie über die Strömmungscharakteristiken eines auf einem rechtwinkligen Keil auftretenden Spaltstrahls durchgeführt. Das Ziel dieser Untersuchungen ist die Studie des Strömungsverhaltens in Keilnähe, in Abhängigkeit verschiedener Parameter wie Strahlgeschwindigkeit, Spaltbreite, Entfernung der Keilspitze und Winkel zwischen Strahlachse und Keil. Diese Parameter werden systematisch variiert um deren Einfluß auf das Strömungsverhalten zu bestimmen. Die Strömung an der Keilspitze ist ähnlich der Staupunktströmung. Weit hinter der Spitze gleicht das Strömungsfeld dem eines auf einer Wand auftreffenden Strahls. In Nähe der Keilspitze sind die Änderungen des statischen Drucks in Strömungsrichtung und quer zur Strömung groß. Grund dafür sind die starke Krümmung der Strömung und die Stagnation der Strömung. Der Druckgradient in Querrichtung nimmt langsam in Strömungsrichtung ab, daher unterscheiden sich die Geschwindigkeitsprofile von den Ähnlichkeitsprofilen der Staupunktströmung und des Wandstrahls in den jeweiligen Bereichen. Die Versuche wurden für Spaltbreiten von 10, 15 und 30 mm und Keilentfernungen von 80, 120 und 240 mm durchgeführt. Der statische Druck und die Geschwindigkeitsprofile wurden mit kalibrierten scheibenförmigen Drucksonden bzw. einer Pitot-Sonde an verschiedenen Orten gemessen.     

A new double negative metamaterial for multi-band microwave applications

This paper reveals the design and analysis of a new split-H-shaped metamaterial unit cell structure that is applicable for multi-band frequency range, and it shows negative permeability and permittivity at those frequency bands. In the basic design, the two separate split square resonators have been added by a metal link to form H-shape unit structure. Moreover, the analyses and comparison of the 1 × 1-array, 2 × 2-array structures and 1 × 1, 2 × 2 unit cell configurations have been investigated. All these configurations demonstrate its multi-band operating frequency (S-band, C-band, X-band, K _u -band) with double negative characteristics. The equivalent circuit model for the unit cell is presented to demonstrate the validation of the resonant behavior. The commercially available finite-difference time-domain based simulation software CST microwave studio has been used to get the reflection and transmission parameters of the unit cell. In summation, the material also exhibits single negative characteristics in the multi-band frequency range if it is projected on the 20 × 20 mm² substrates. The simplicity, scalability, double negative characteristics, and multi-band operations have made this design novel in the electromagnetic paradigm.     

Performance of convex underestimators in a branch-and-bound framework

The efficient determination of tight lower bounds in a branch-and-bound algorithm is crucial for the global optimization of models spanning numerous applications and fields. The global optimization method \(\alpha \)-branch-and-bound (\(\alpha \)BB, Adjiman et al. in Comput Chem Eng 22(9):1159–1179, 1998b, Comput Chem Eng 22(9):1137–1158, 1998a; Adjiman and Floudas in J Global Optim 9(1):23–40, 1996; Androulakis et al. J Global Optim 7(4):337–363, 1995; Floudas in Deterministic Global Optimization: Theory, Methods and Applications, vol. 37. Springer, Berlin, 2000; Maranas and Floudas in J Chem Phys 97(10):7667–7678, 1992, J Chem Phys 100(2):1247–1261, 1994a, J Global Optim 4(2):135–170, 1994), guarantees a global optimum with \(\epsilon \)-convergence for any \(\mathcal {C}^2\)-continuous function within a finite number of iterations via fathoming nodes of a branch-and-bound tree. We explored the performance of the \(\alpha \)BB method and a number of competing methods designed to provide tight, convex underestimators, including the piecewise (Meyer and Floudas in J Global Optim 32(2):221–258, 2005), generalized (Akrotirianakis and Floudas in J Global Optim 30(4):367–390, 2004a, J Global Optim 29(3):249–264, 2004b), and nondiagonal (Skjäl et al. in J Optim Theory Appl 154(2):462–490, 2012) \(\alpha \)BB methods, the Brauer and Rohn+E (Skjäl et al. in J Global Optim 58(3):411–427, 2014) \(\alpha \)BB methods, and the moment method (Lasserre and Thanh in J Global Optim 56(1):1–25, 2013). Using a test suite of 40 multivariate, box-constrained, nonconvex functions, the methods were compared based on the tightness of generated underestimators and the efficiency of convergence of a branch-and-bound global optimization algorithm.     

Deterministic global derivative-free optimization of black-box problems with bounded Hessian

Obtaining guaranteed lower bounds for problems with unknown algebraic form has been a major challenge in derivative-free optimization. In this work, we pre     

Electronic,optical and bonding properties of MgCO3

The electronic, optical and bonding properties of MgCO₃ (magnesite, rhombohedral calcite-type structure) are calculated using a first-principles density-functional theory (DFT) method considering the exchange-correlation function within the local density approximation (LDA) and the generalized gradient approximation (GGA). The indirect band gap of magnesite is estimated to be 5.0 eV, which is underestimated by ～1.0 eV. The fundamental absorption edge, which indicates the exact optical transitions from occupied valence bands to the unoccupied conduction band, is estimated by calculating the photon energy dependent imaginary part of the dielectric function using scissors approximations (rigid shift of unoccupied bands). The optical properties show consistent results with the experimental calcite-type structure and also show a considerable optical anisotropy of the magnesite structure. The density of states and Mulliken population analyses reveal the bonding nature between the atoms.