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N Unit (n + unit)

Distribution by Scientific Domains

Chemistry	60%

Selected Abstracts

Sodium Hydro(isothiocyanato)borates: Synthesis and Structures

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2004
Heinrich Nöth
Abstract Sodium thiocyanate reacts in THF solution with 18-crown-6 to give the molecular compound Na(18-crown-6)(THF)NCS (3) with the N atom of the NCS anion oriented towards Na+. The same reaction with 15-crown-5 yields the ion pair Na(15-crown-5)NCS (4). In contrast, Na(NCS)(py)4, obtained by treating a solution of Na(H3BNCS) in THF with pyridine, yields Na(py)4(NCS) (5), which has a chain structure with hexacoordinate Na atoms coordinated to five N atoms and an S atom. Na(NCS) in THF adds 1 equiv. of BH3 to give Na(H3BNCS)·nTHF. Addition of 18-crown-6 to this solution yields crystals of the salt [Na(18-crown-6)(THF)2][H3BNCS] (1), as shown by X-ray crystallography. Both the cation and the anion show site disorder. However, when 15-crown-5 is used for complexation, the salt [Na(15-crown-5)(THF)][H3BNCS] (2) can be isolated. Its anion shows an almost linear B,N,C,S unit. Only a mixture of (catecholato)(isothiocyanato)borates results on treating Na(NCS) in THF with catecholborane. However, the borate Na[catB(NCS)2] is readily formed by adding Na(NCS) to B -(isothiocyanato)catecholborane. Single crystals of this compound were obtained as the salt [Na(18-crown-6)(THF)2][catB(NCS)2] (6). On the other hand, the reaction of Na(NCS) with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF yields Na[(9-BBN)NCS)]·nTHF, and, on addition of 18-crown-6, the complex [Na(18-crown-6)(THF)2][(9-BBN)NCS] was isolated. Suitable crystals for X-ray structure determination were, however, only obtained by crystallization from tetrahydropyran. This solvate has the rather unusual structure [Na(18-crown-6)(thp)2][{(9-BBN)NCS}2Na(thp)4] (8). The sodiate anion has an Na atom coordinated by two S and four O atoms. DFT calculations support these experimental results: The (isothiocyanato)borates are more stable than the thiocyanato isomers. For the latter a bent structure of the B,S,C,N unit with a B,S,C bond angle of 105.7° is predicted. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Double anomeric effects and a hydrogen-bonded supramolecular motif in N,N,-bis(3-nitrophenyl)methanediamine

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2009
Zhenfeng Zhang
In the title compound, C13H12N4O4, the molecule lies on a crystallographic twofold axis. Molecules are linked into complex sheets parallel to (100) via one N,H...O and two C,H...O hydrogen bonds. Within the molecule, the 3-nitroanilino fragment is essentially planar, and the C,N,C,N,C fragment assumes a nearly perpendicular/perpendicular conformation, with C,N,C,N torsion angles of 81.18,(18)°, which is controlled by a pair of adjacent anomeric interactions. The findings constitute the first demonstration of two anomeric effects existing in one N,C,N unit. [source]

Threshold optimization for weighted voting classifiers

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2003
G. Levitin
Abstract Weighted voting classifiers considered in this paper consist of N units each providing individual classification decisions. The entire system output is based on tallying the weighted votes for each decision and choosing the one which has total support weight exceeding a certain threshold. Each individual unit may abstain from voting. The entire system may also abstain from voting if no decision support weight exceeds the threshold. Existing methods of evaluating the reliability of weighted voting systems can be applied to limited special cases of these systems and impose some restrictions on their parameters. In this paper a universal generating function method is suggested which allows the reliability of weighted voting classifiers to be exactly evaluated without imposing constraints on unit weights. Based on this method, the classifier reliability is determined as a function of a threshold factor, and a procedure is suggested for finding the threshold which minimizes the cost of damage caused by classifier failures (misclassification and abstention may have different price.) Dynamic and static threshold voting rules are considered and compared. A method of analyzing the influence of units' availability on the entire classifier reliability is suggested, and illustrative examples are presented. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 322,344, 2003. [source]

Continuous accumulation games on discrete locations

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2002
Kensaku Kikuta
Abstract In an accumulation game, a HIDER attempts to accumulate a certain number of objects or a certain quantity of material before a certain time, and a SEEKER attempts to prevent this. In a continuous accumulation game the HIDER can pile material either at locations $1, 2, ,, n, or over a region in space. The HIDER will win (payoff 1) it if accumulates N units of material before a given time, and the goal of the SEEKER will win (payoff 0) otherwise. We assume the HIDER can place continuous material such as fuel at discrete locations i = 1, 2, ,, n, and the game is played in discrete time. At each time k > 0 the HIDER acquires h units of material and can distribute it among all of the locations. At the same time, k, the SEEKER can search a certain number s < n of the locations, and will confiscate (or destroy) all material found. After explicitly describing what we mean by a continuous accumulation game on discrete locations, we prove a theorem that gives a condition under which the HIDER can always win by using a uniform distribution at each stage of the game. When this condition does not hold, special cases and examples show that the resulting game becomes complicated even when played only for a single stage. We reduce the single stage game to an optimization problem, and also obtain some partial results on its solution. We also consider accumulation games where the locations are arranged in either a circle or in a line segment and the SEEKER must search a series of adjacent locations. © 2002 John Wiley & Sons, Inc. Naval Research Logistics, 49: 60,77, 2002; DOI 10.1002/nav.1048 [source]

Structural phase transition in [NH3(CH2)5NH3]BiCl5: thermal and vibrational studies

JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2005
H. Jeghnou
Abstract An x-ray diffraction study carried out on the pentylenediammonium pentachlorobismuthate (III) compound [NH3(CH2)5NH3]BiCl5 indicated that it is orthorhombic with a P212121(Z = 4) space group. Differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were also made, which showed that this compound undergoes a unique phase transition at high temperatures. The infrared and Raman spectra recorded at room temperature were interpreted on the basis of data published in the literature. The Raman bands observed below 300 cm,1 are very characteristic of the anions, which are made of isolated (BiCl52, )n units composed of BiCl63, octahedra. Raman spectra recorded at various temperatures confirmed the contribution to the phase-transition mechanism of both the anion and cation motions. Copyright © 2005 John Wiley & Sons, Ltd. [source]