bluuebunny/crossref_metadata_2025 huggingface dataset:
Zweikernige Tripod‐Cobalt‐Komplexe mit verbrückenden 1,4,5,8‐Tetraoxonaphthalin und 1,4,9,10‐Tetraoxoanthracen‐Liganden: Strukturen, spektroskopische, magnetische und elektrochemische Eigenschaften
Authors: Heinze Katja , Mann Susanne , Huttner Gottfried , Zsolnai Laszlo
Published: July 2007

Dinuclear Tripod Cobalt Complexes with Bridging 1,4,5,8‐Tetraoxonaphthalene and 1,4,9,10‐Tetraoxoanthracene Ligands: Structures, Spectroscopic, Magnetic, and Electrochemical Properties

The syntheses, structures, optical, magnetic, and redox properties of dinuclear tripodcobalt(II) complexes [tripod = CH3C(CH2PPh2)3] with briding 1,4,5,8‐tetraoxonaphthalene 12‐ and 1,4,9,10‐tetraoxoanthracene 22‐ are described. UV/Vis/NIR spectroscopy indicates interaction between the ligand and the metal orbitals. The magnetic interactions involving the two cobalt(II) centers and the bridging ligand are characterized by EPR spectroscopy and magnetic measurements and are analyzed in terms of qualitative Molecular Orbital calculations. The redox chemistry of these complexes is investigated by cyclic voltammetry and interpreted as metal‐based oxidations and ligand‐based reductions.
The Thermally Induced Solid‐State Polymerization Reaction in Halogenoacetates
Authors: Epple Matthias , Kirschnick Holger
Published: July 2007

Nine salts of halogenoacetic acids MOOC–CH2X were prepared and characterized by their thermochemical reactivity. It was found that in seven cases elimination of MX led to polymerization of the organic part of the molecule. The resulting polyester, polyglycolide, could be isolated easily by washing the reaction product with water. It has a distinct porous morphology. The reaction takes place at moderate temperatures (100200°C).
The Crystal Structure of Bi8(AlCl4)2 and the Crystal Structure, Conductivity, and Theoretical Band Structure of Bi6Cl7 and Related Subvalent Bismuth Halides
Authors: Beck Johannes , Brendel Claus J. , Bengtsson‐Kloo Lars , Krebs Bernt , Mummert Marita , Stankowski Alexander , Ulvenlund Stefen
Published: July 2007

The methods of preparation for Bi8(AlCl4)2 and Bi6Cl7 have been improved and the single crystal structures for these cluster compounds re‐investigated and re‐interpreted. In addition, conductivity measurements and band structure calculations using the tight‐binding approximation have been performed on Bi6Cl7 and related subvalent bismuth halides. – Bi8(AlCl4)2 consists of isolated AlCl4‐ anions and rather undistored square‐antiprismatic Bi82+ clusters with an average Bi–Bi distance of 3.10 Å. Relatively short intercluster Bi–Bi contacts of 3.90 Å suggest weak bonding interactions between the Bi82+ units. In contrast, the structure determination of Bi6Cl7 implies that this structure should be regarded as being composed of discrete Bi95+ clusters and a polymeric BiIII–Cl anionic lattice including infinite, distorted α1[Bi2Cl24+] chains. According to the experimental and theoretical results, the Bi6X7 (X = Cl, Br) family of subvalent bismuth halide compounds are anisotropic semiconductors along the crystallographic c axis. The conductivity is mediated by the onedimensional α1[Bi2Cl24+] chains. These are interconnected with the Bi95+ clusters, which are acting as electron reservoirs. The related BiX (X = Br, I) family of subvalent bismuth halides are shown to be anisotropic semiconductors in the crystallographic b direction.
Zur Transformation des P4‐Tetraeders durch Ni‐Komplexe
Authors: Scheer Manfred , Becker Uta
Published: July 2007

The Transformation Pathway of the P4Tetrahedron by Ni Complexes

The thermal reaction of [Cp*NiCO]2with white phosphorus in the presence of [Cr(CO)5(thf)] at 70°C produces the bentcyclo‐P4ligand complex4and the Ni2P4prismane5. However under photochemical conditions additional products such ascyclo‐P3complexes6and the Ni2P2tetrahedrane7are also formed.4and5were characterized by NMR, IR, and mass spectroscopy as well as by X‐ray structure analysis. The structures of these products and the experimentals verification of the conversion of4into5or into6and7as well as the cubane analog12gives evidence for a transformation pathway starting from P4tetrahedron via a possible bicyclotetraphosphane intermediate to give the bent P4complex4. From4several pathways are possible; the main route is to form the Ni2P4prismane5. Photochemically a P3/P1fragmentation also occurs, albeit in low yield, to give5and6.
The Chemistry of 1,3,5‐Triazacyclohexane Complexes, 4. Strained 1,3,5‐Triazacyclohexane Complexes of Copper(I) and Copper(II)
Authors: Dag Köhn Randolf , Seifert Guido , Kociok‐Köhn Gabriele
Published: July 2007

In this paper we report on the synthesis and the crystallographic characterization of η3‐1,3,5‐triazacyclohexane (R3TAC) complexes of copper(I) and copper(II). The complexes [{Me3TAC)CuCl2}2] (1), [(iPr3TAC)CuCl2] (2), [{(PhCH2)3TAC}Cu(PPh3)](BF4) (3), and [(iPr3TAC)Cu(PPh3)]‐(BF4) (4) were characterized by X‐ray crystallography. The highly strained and bent Cu–N bonds are longer than in the corresponding complexes of other amine ligands. One methylene carbon atom of the ring comes close to the copper atom (2.55–2.65 Å). However, investigation of the ring deuterated complexes by IR and X‐ray crystallography ([D6]2) showed no clear evidence for attractive C–H–Cu interactions.
Synthese, Eigenschaften und Kristallstrukturen der Titan(III)‐Amido‐Komplexe Ti[N(SiMe3)2]3, [TiCl2{N(SiMe3)2}(THF)2] und [Na(12‐Krone‐4)2][TiCl2{N(SiMe3)2}2]
Authors: Putzer Markus A. , Magull Jörg , Goesmann Helmut , Neumüller Bernhard , Dehnicke Kurt
Published: July 2007

Syntheses, Properties, and Crystal Structures of the Titanium(III) Amido Complexes Ti[N(SiMe3)2]3, [TiCl2{N(SiMe3)2}(THF)2], and [Na(12‐Crown‐4)2][TiCl2{N(SiMe3)2}2]

TiCl3(THF)3 reacts with NaN(SiMe3)2 to furnish [TiCl2{N(SiMe3)2}(THF)2] (1), whereas in the presence of 12‐crown‐4 the ionic amido complex [Na(12‐crown‐4)2][TiCl2{N(SiMe3)2}2] (5) is obtained besides [Na(12‐crown‐4)2][TiCl4(THF)] (4). On the other hand, the titanium(III) amido complex Ti[N(SiMe3)2]3 (2), the crystal structure of which was solved, reacts with NaN(SiMe3)2 in the presence of 12‐crown‐4 with deprotonation of one of the methyl groups to give the carbometalated complex [Na(12‐crown‐4)2][Ti{N(SiMe3)2}2{N(SiMe 3CH2)}] (3).
Steroids as Chiral Ligands: Different Molecular and Crystal Structures of Copper(II) Complexes of Mono‐ and Dideprotonated 16β‐Salicylideneimino‐17β‐hydroxy‐3‐methoxyestra‐1,3,5(10)‐triene
Authors: Krieg Reimar , Dubs Manuela , Görls Helmar , Schönecker Bruno
Published: July 2007

The steroidal 16β‐salicylideneimino‐17β‐hydroxy compound 1, synthesized from the corresponding 16β, 17β‐amino alcohol, served as a new tridentate chiral ligand for Cu2+‐complexation. The X‐ray data for 1 and for two dimeric copper complexes 2 and 3 are presented and discussed. Using copper(II) acetate for complexation, dideprotonation of 1 is observed. The neutral complex 2 obtained is characterized by a central planar four‐membered copper—oxygen ring. The cycloaliphatic 17β‐oxygen anions are bridging atoms; the copper ions are tetracoordinated. Reaction of 1 with copper(II) perchlorate gave only monodeprotonation of the phenolic groups. These oxygen anions are now the bridging atoms; furthermore the two copper ions are bridged by a perchlorate anion. Thus the central four‐membered ring is folded (22°), and the copper ions are hexacoordinated (binding of a molecule of water). The crystal lattices of 2 and 3 are also quite different.
Ethene Polymerization Activity and Coordination Gap Aperture in non‐ansa Alkyl‐substituted Cyclopentadienyl‐ and Phospholyl‐zirconium/MAO Catalysts
Authors: Janiak Christoph , Lange Katharina C. H. , Versteeg Uwe , Lentz Dieter , Budzelaar Peter H. M.
Published: July 2007

The ethene polymerization activities of a series of Cp'(C5H5)ZrCl2 and Cp'2ZrCl2 pre‐catalysts (Cp' = C5HMe4, C4Me4P, C5Me5, C5H4tBu, C5H3‐1,3‐tBu2, C5H2‐1,2,4‐tBu3) together with (C5H5)2ZrCl2 have been correlated with the coordination gap aperture. In the case of the mixed substituted C5R5‐nR'n ligands, the coordination gap aperture has been determined with the help of the cyclopentadienyl cone angle and the bending angle at zirconium. A hindered rotatability of the tert‐butyl substituted systems has been evaluated by molecular modeling calculations and was included in the gap aperture estimation. Deviations from the activity—gap aperture correlation in the case of the phospholyl (C4Me4P) systems could be accounted for in terms of adduct formation between aluminum species and the phosphorus donors. These Lewis acid/base adducts form in an equilibrium reaction at high Al/Zr ratios, as shown by 31P NMR. Ab initio calculations on model L2TiMe+ complexes (L = C5H5, C5H4N and C5H4P) for the insertion of ethene in the TiMe bond suggest a high electronic similarity for phospholyl and cyclopentadienyl. The 91Zr‐NMR data (chemical shift and line width) for the above zirconocene series are reported. The 91Zr chemical shift values increase with a good linear correlation to the number of methyl or tert‐butyl groups, which is traced to the additive electron donating effect of the alkyl groups. The hyperconjugative donor effect of a tert‐butyl group is found here to be 1.25 times that of a methyl group. The X‐ray structure of (C5H3‐1,3‐tBu2)(C5H5)ZrCl2 has been determined (monoclinic, P21/n, a = 6.631(3), b = 18.843(9), c = 15.265(5) Å, β = 91.3°, Z = 4).
Selenocyanato Derivatives of Hydro‐closo‐borates: Syntheses and Crystal Structures of (PPh4)2[SeCN)BnHn–1] (n = 6, 10, 12)
Authors: Nachtigal Christiane , Steuer Boris , Preetz Wilhelm
Published: July 2007

The hydro‐closo‐borates [BnHn]2– (n = 6, 10, 12) react with (SeCN)2 in organic media to yield derivatives with one SeCN group bound via Se to the Bn polyhedra. This was verified by single‐crystal X‐ray structural analysis of the isotypical (P1¯) tetraphenylphosphonium salts (PPh4)2[(SeCN)B6H5] (1), (PPh4)2[1‐(SeCN)B10H9] (2) and (PPh4)2[(SeCN)B12H11] (3) The 11B‐NMR spectra reveal the features of monosubstituted hydro‐closo‐borates. The 77Se‐NMR resonances are observed in the downfield region between δ = −22.6 and −78.8 characteristic of Se‐bonded SeCN groups.
Layered Ternary and Quaternary Metal Chalcogenides
Authors: Pell Michael A. , Ibers James A.
Published: July 2007

The syntheses, crystal structures, and physical properties of some recently discovered layered ternary and quaternary chalcogenides are reviewed. One component of these systems is an alkali metal or thallium; another is a d‐, f‐, or p‐ block metal.
Synthesis of Functionalized Carbamates through a Palladium‐Catalyzed Reductive Carbonylation of Substituted Nitrobenzenes
Authors: Wehman Petra , Borst Leo , Kamer Paul C. J. , Leeuwen Piet W. N. M. Van
Published: July 2007

The palladium‐catalyzed reductive carbonylation of ortho and para‐substituted nitrobenzenes has proven to be an attractive route for the synthesis of functionalized carbamates. For the Pd(1, 10‐phenanthroline)2(triflate)2 catalyst system, the scope of the reaction has been studied. Substrates with electron‐donating substituents at the para position were found to decrease the catalytic activity, most probably as a result of their relatively low oxidizing capacity. the selectivity towards the desired carbamate, however, was increased for these substrates. Under the influence of electron‐withdrawing substituents the azoxybenzene and azobenzene derivatives became important side products. Introduction of large steric hindrance at the ortho position of the nitro substrates gave rise to an interesting side reaction, viz. methoxylation of the aromatic ring. The methoxylation reaction appeared to occur on an intermediate species in the catalytic cycle. Several functionalities have shown to be resistant to the reaction conditions required for the conversion ot the nitro group. Especially with 4‐nitrobenzoic acid, an extremely high activity and selectivity was found, thus yielding a very convenient synthesis for N‐protected amines containing carboxylic acid function.
Triphenylphosphonio‐Substituted 1,2,3,4‐Triazaphospholes and 1,2,4‐Diazaphospholes
Authors: Schrödel Hans‐Peter , Schmidpeter Alfred
Published: July 2007

Several products resulting from the condensation of the bis‐(trimethylsilyl)ylide 1 with PCl3 serve as synthetic equivalents of a phosphoniophosphaethyne. Cycloaddition reactions with azides lead to phosphonio‐1,2,3,4‐triazaphosphole cations 5, 7 and to the zwitterionic phosphonio‐1,2,3,4‐triazaphospholide 6. The latter readily undergoes a cycloreversion yielding a phosphoranediyl diazomethane 12 as intermediate. Its cycloaddition affords the diphosphonio‐1,2,4‐diazaphosholide chloride 9a as the final product. 9a is a remarkably stable and unreactive derivative of the two‐coordinate phosphorus. By HCL it is protonated at a nitrogen atom to give dication without any tendency to associate with the chloride counterions.
Bildung und Charakterisierung des Dinatrium‐tetraphosphendiids (tBu3Si)NaP–PP–PNa(SitBu3) und seines Dimeren
Authors: Wiberg Nils , Wörner Angelika , Karaghiosoff Konstantin , Fenske Dieter
Published: July 2007

Reaction of P4 in THF or DME with 2 R*Na (R* = SitBu3) at –78°C leads quantitatively to deep red THF or DME adducts of R*NaP–PP–PNaR* (3). According to 31P NMR, the P4 skeleton 3 is cis‐configurated. On the other hand, reaction of P4 in TBME with 2 R*Na at ‐78°C leads quantitatively to (R*NaP)4 (4), a [2+2] cycloadduct of 3, the Na4P8 skeleton of which according to X‐ray structure analysis forms a double cube with four P atoms in the second layer and two P and two Na atoms in alternating positions in the first and in the third layer (the Na atoms are coordinated with donors). By resolving the THF adduct 3 in TBME (the TBME adduct of 4 in THF) the compound 4 (the compound 3) is rapidly formed under reversal of the P–PP–P configuration by way of [2+2] cycloaddition (by way of [2+2] cycloreversion). 3 and 4 are sensitive to oxidation and to protolysis. With TCNE, 3 is oxidized to R*2P4 (bicyclic P4 skeleton), with CF3SO3H, 3 may be transformed into R*3P5Na2 X 4 THF or in (R*P3)3 and R*PH2.
1,2‐FDTA: A Ferrocene‐Based Redox‐Active EDTA Analogue with a High Ca2+/Mg2+and Ca2+/Sr2+ Selectivity in Aqueous Solution
Authors: Plenio Herbert , Burth Dirk , Vogler Raphael
Published: July 2007

1, 2‐Ferrocenemethylenediyldiamino tetraacetate (1,2‐FDTA) is a redox‐active relative of EDTA and was synthesized in the reaction of 1,2‐bis(chloromethyl)ferrocene with iminodiacetate methyl ester followed by cleavage of the ester with methanolic KOH. Potentiometric determination of the stability constants of the complexes of 1,2‐FDTA with the alkaline earth metal ions showed this ligand to display a higher Ca2+/Mg2+ and Ca2+/Sr2+ selectivity (Ca2+ log K = 6.56, Mg2+ log K = 4.65, Sr2+ log K = 3.32) than EDTA itself. The redox potential of 1,2‐FDTA‐Ca2+ determined in aqueous solution by cyclic voltammetry was found to be anodically shifted by +50 mV with respect to that of the calcium free complex. Consequently the redox‐inactive calcium can be determined electrochemically in aqueous solution with a high selectivity with respect to the other alkaline earth metal ions.
Gold(1) Complexes of Ketiminophosphanes and ‐phosphane Sulfides
Authors: Schneider Wolfgang , Bauer Andreas , Schier Annette , Schmidbaur Hubert
Published: July 2007

The reactions of chloro(dimethyl sulfide)gold(I) with equivalent quantities of the ketiminophosphane diphenyl(diphenylmethyleneamino)phosphane (1a) or its sulfide (1aS) lead to high yields of stable, crystalline 1 : 1 complexes with AuCl units attached to the phosphorus and sulfur atom, respectively. Tris(diphenylmethyleneamino)phosphane (1c) gives the related complex (Ph2CN)3PAuCl with the gold atom also selectively P‐bound. Bis(diphenylmethyleneamino)phenyl‐phosphane (1b) could not be used because of its limited stability. Single‐crystal X‐ray diffraction studies have shown that there is no auxiliary coordination of the metal center by the imino functions of the ligands. The geometry of the P/SAuCl moieties deviates only very slightly from linearity. The angle at the sulfur atom in (Ph2CN)Ph2PSAuCl is very small [94.30(3)°], but despite of the resulting rather open coordination there are no discernible intra‐ or intermolecular contacts in the lattice. Such contacts are also absent with (Ph2CN)Ph2PAuCl and (Ph2CN)3PAuCl owing to the bulk of the ligands. The 1 : 1 complexes do not react with an excess of (Me2S)AuCl. This finding, and the molecular structures of the 1 : 1 complexes, show very consistently that both phosphane and sulfide donors are far superior as ligands for gold(I) as compared to ketimine donor molecules.
Tetraphenyl rac‐3,3,7,7‐Tetramethyl‐trans‐5 palladatricyclo[4.1.0.02,4]‐heptane‐1,2,4,6‐tetracarboxylate: A New PTH Derivative and the First X‐ray Crystallographic Study of a Bis(acetone)palladium(II) Complex
Authors: Hashmi A. Stephen K. , Naumann Frank , Bats Jan W.
Published: July 2007

The title compound rac‐9 and its bis(acetone) complex rac‐10 were prepared, and the latter investigated by X‐ray structure analysis. rac‐10 proves that the coordination of the weak donor acetone, an easily substitutable ligand in PTHs and related compounds, is an essential point for dissolving these coordination polymers, and thus allowing catalysis reactions in such solvents. Furthermore rac‐10 shows only a small deviation from the square‐planar coordination expected for Pd11. This indicates that the strong deviation from planarity observed in complexes with more sterically demanding, bidentate ligands is caused by steric interactions with the substituents on the PTH, rather than by electronic effects.
Interactions in Molecular Crystals, 118. The Sodium(benzo‐15‐crown‐5) Salt of 2, 6‐Di(tert‐butyl)‐4‐methylphenol, a Sodium Phenolate with an Extremely Short Na+…O− Distance: Structure and Density Functional Calculations
Authors: Bock Hans , Dienelt Rüdiger , Näther Christian , Havlas Zdenek
Published: July 2007

The structure of crystals, isolated in low yield, from the attempted metallation of diphenylmethane in tetrahydrofuran solution containing benzo‐15‐crown‐5 at a sodium metal mirror is determined, surprisingly, to be the sodium (benzo‐15‐crown) salt of 2,6‐di(tert‐butyl)‐4‐methylphenol, an antioxidative stabilizer to prevent ether peroxide formation. The structure of the solvent‐shared contact ion pair (monoclinic P21/n, Z = 4, R1 = 0.06) proves a strong Na+…O− interaction at the extremely short distance of only 216 pm, a sixfold O‐coordination of the Na+ cation in a pentagonal pyramid, and a hemispherical distortion of the crown ether. Density functional calculations at the B3LYP/6‐31G* level, based on the structural data, reproduce, within a one‐dimensional hypersurface approach, the rather short Na+…O− distance, and predict Mulliken charges of +0.32 for Na′ and ‐0.71 for 0−, as well as a considerable polarization of the trialkyl phenolate anion.
Diastereoselective Synthesis and Molecular Structure of a Bicyclic and a Cage Phosphane
Authors: Bekiaris Georgios , Lork Enno , Offermann Werner , Röschenthaler Gerd‐Volker
Published: July 2007

A two‐step formal insertion of 1,1,1,5,5,5‐hexafluoro‐ (2a) and 1,111‐trifluoropentane‐2,4‐dione (2b) into the P‐H bonds of phosphane gave the primary a‐hydroxyphosphanes 3 and 4, precursors for the resulting secondary phosphanes, 6,9‐dioxa‐2‐phosphabicyclo[3.3.l]nonane (6a) and 2,4,8‐trioxa‐6‐phosphaadamantane (7), both formed diastereospecifically. The molecular structures of 6a and 7 were established by single‐crystal X‐ray structure analysis which revealed two independent molecules for 6a in the unit cell possessing a chair‐boat conformation with a C‐P‐C angle of 95.4(2)°, and a characteristic heteroadamantane geometry for 7, with the corresponding angle being smaller by 4.9°.
Synthetic and Structural Studies of 1‐Sila‐2,5‐diaryltetrazenes
Authors: Frenzel Andrea , Buffy Jarrod J. , Powell Douglas R. , West Robert , Müller Thomas
Published: July 2007

The reaction between aryl azides and lithiated aryl amines leads to tetrazenes 3 and 9 which contain a chain of four nitrogen atoms. Reaction with different halosilanes gives the cyclic silatetrazenes 10, 12, and 15 where substitutents on the silicon vary form alkyl to hydrogen and chlorine atoms. The structures of 10, 12, and 15 in the solid state are reported. Variation of the solvent and the Lewis acidity of the halosilane influence the ratio of silatetrazene to side products, bissilyated amines. These effects are studied for different halosilanes.
Synthesis and Structure of Trimethyllead Niobocene Dihydride
Authors: Nikonov Georgii, I. , Avtomonov Evgeni V. , Massa Werner
Published: July 2007

The reaction of niobocene trihydride [Cp2NbH3] with ClPbMe3 in the presence of amine affords the plumbido dihydride complex [Cp2NbH2(PbMe3)] (1). Compound 1 represents the first example of a stable complex with neighbouring hydride and terminal plumbyl substituents. The structure of this compound has been established by NMR and IR spectroscopy and confirmed by an X‐ray structure analysis.
Steric Effects on Base Adduct Formation and Crystal Structures of Diastereomers of a Nickel(II) Schiff Base Complex
Authors: Jäger Ernst‐G. , Schuhmann Kerstin , Görls Helmar
Published: July 2007

Reaction of the ligand meso‐H2L, derived from cis‐diaminocyclohexane and ethyl cyano(ethoxymethylene)acetate, with nickel(II) acetate gives meso‐NiL. Spectrophotometric titration of RR‐NiL and meso‐NiL with various nitrogen bases reveals a strong influence of the steric hindrance of the diaminocyclohexanediyl bridge in meso‐NiL on the base adduct stability. The structures of RR‐NiL and meso‐NIL have been established by X‐ray diffraction.
Contribution to the Chemistry of Boron, 240 . Studies on Benzo‐1,3,2‐diphosphaborolanes, Benzo‐1,4,2,3‐diphosphadiborinanes and Benzo‐1,5,2,3,4‐diphosphatriborepanes
Authors: Kaufmann Bernhard , Jetzfellner Ralf , Nöth Heinrich , Schmidt Martin , Leissring Elke , Issleib Kurt
Published: July 2007

A series of benzo‐ 1,3,3‐diphosphaborolanes C6H4(PR)2BR' (R = H, iPr, SiMe3; R' = R2N, R) has been prepared by several routes and characterized by spectroscopic and – in part – by X‐ray diffraction methods. They feature pyramidal P atoms with the substituents in antiperiplanar positions. The P atoms act as coordination sites for the (CO)5Cr fragment. In contrast to the R2N‐bearing benzo‐1,3,2‐diphosphaborolanes, the derivative C6H4(PH)2BCMe3 (4f) dimerizes by additional B–P bond formation to produce a pentacyclic system (4f)2. – The reaction of C6H4(PHNa)2 with B2(NMe2)2Cl2 in THF/hexane yields the acyclic phosphanylborane Me2NB(PH–C6H4PH2)2 (15). However, if C6H4[P(iPr)Li]2 is allowed to react with B2(NMe2)2Cl2, the benzo‐1,4,2,3‐diphosphadiborinane 13 is obtained, together with its rearrangement product 2‐bis(dimethylamino)borylbenzo‐1,3,2‐diphosphaborolane 14 which dimerizes to (14)2. — In contrast, the almost planar ring of the 2,3‐dimesitylbenzo‐1,4,2,3‐diphosphadiborinane (16) possesses P and B atoms with a planar geometry. Short B–B and B–P bonds suggest that this new heterocycle can be regarded as a 6π electron system. Moreover, the benzo‐1,5,2,3,4‐diphosphatriborepane 18 forms readily forms readily from C6H4(PHNa)2 and Br(Me2N)B–B(N‐Me2)–B(NMe2) Br to give a tub‐shaped seven‐membered C2B3P2 ring system with the P atoms in a pyramidal and the B atoms in a planar environment.
Geminal di(hypersilyl) Compounds — the Synthesis and Structure of Bis[tris(trimethylsilyl)silyl]methanol
Authors: Gross Thoralf , Oehme Hartmut , Kempe Rhett
Published: July 2007

Tris(trimethylsilyl)silyllithium (1) reacts with methyl formate in diethyl ether (molar ratio 2:1) to give 1,2‐di(hypersilyl)‐ ethylene 13. The formation of 13 proceeds through the intermediates formyl tris(trimethylsilyl)silane (4) and lithium bis‐[tris(trimethylsilyl)silyl]methoxide (5). In diethyl ether, the alkoxide 5 spontaneously eliminates lithium trimethylsilanolate thereby generating 1,1‐bis(trimethylsilyl)−2‐[tris(trimethylsilyl)silyl]silene (9), which undergoes a formal [2+2] cycloaddition with the carbonyl compound 4 to afford 13. This was verified by crossover experiments. In Pentane, the alkoxide 5 is moderately stable. Thus, the intermediate 5, prepared by reaction fo 1 with tert‐butyl formate in pentane. was protonated with water to give the di(hypersilyl)methanol 6 in good yield. The structure of 6 in good yield. The structure of 6 was elucidated by an X‐ray crystal structure analysis, which expectedly revealed tremendous distortions of the molecular skeleton. Thus, the spatial demand of the two extended hemispherical (Me3Si)3Si groups forces a widening of the Si–C–Si angle at the central sp3 carbon atom to a value of 135.5°.
A Monomeric Bis(arena)lead(II) Complex with a Plumbocene‐like Bent Sandwich Structural Unit — Structure of [Pb(1,2‐C6H4Me2)2(AlCl4)2
Authors: Frank Walter , Wittmer Franz‐Georg
Published: July 2007

Bis(o‐xylene)lead(II) bis(tetrachloroaluminate), obtained from lead(II) chloride and aluminium trichloride in o‐xylene, has been shown by X‐ray crystallography to be a mononuclear lead complex with point group symmetry C2 The two aromatic ligands are arranged similarly to those in monomeric plumbocene. The coordination sphere is completed by two bidentate AlCl4−ions. The lead center uses about a quarter of its bonding capability for each of the four ligands
Titanium and Zirconium Complexes Containing a Novel Dianionic Trifunctional Amido Ligand
Authors: Friedrich Stefan , Schubart Martin , Gade Lutz H. , Scowen Ian J. , Edwards Andrew J. , McPartlin Mary
Published: July 2007

The novel tridentate diamidoamine ligands [RC(2C5H4N)(CH2NSiMe3)2)2− (R = H, CH3) have been synthesized and coordinated to TiIV giving the pentacoordinate complexes [MX2(RC(2‐C5H4N)(CH2NSiMe3)2}] (M = Ti, Zr; X = Cl, Br). The crystal structure analysis of [TiBr2{HC(2‐C5H4N)(CH2)2}] (M = Ti, Zr; X = Cl, Br). The crystal structure analysis of [TiBr2{HC(2‐C5H4N)(CH2NSiMe3))] (10b) confirmed the involvement of the pyridyl function in the coordination to the meta centre occupying an apical position in the trigonal bipyramidal ligand polyhedron. alkylation of [TiCl2{H3CC(2‐C5H4N)(CH2NSiMe3)2)] (12a) with one or two molar equivalents of [RMgCl](R = PhCH2, Me3SiC2) yielded the mono‐ and dialkyl complexes [TiClR{H3CC(2‐C5H4N)(CH2NSiMe3)2)] and [TiR2(H3CC(2‐C5H4N)(CH2NSiMe3)2)] and [TiR2(H3CC(2‐C5H4N)(CH2NSiMe3)2}] in good yields. Depending on the steric demand of the alkyl group coordination or decoordination of the pyridyl group leads to four‐ or five‐coordinate species. A crystal structure analysis of the pentacoordinate complex [TiCl(CH2SiMe3){H3CC(2‐C5H4N)(CH2NSiMe3)2}] (16) was carried out.
Phosphanyl‐Substituted Phosphaferrocenes as p,p‐Chelate Ligands
Authors: Ganter Christian , Brassat Lutz , Ganter Beate
Published: July 2007

Dicyclohexyl‐acid diphenylphosphanyl‐substituted phosphaferrocenes 2 and 3 were synthesized by substitution of the amino group in 2‐dimethylaminomethyl‐3,4,‐dimethylphosphaferrocene 1 · Homologization of 2‐formyl‐3,4‐dimethylphosphaferrocene 4 by one CH2 unit via Wittig olefination provided access to the phosphanylethyl derivative 9. Ligands 2, 3 and 9 formed P, P‐chelate complexes with tetracarbonyl metal fragments in good yield. X‐ray crystal structure determinations were carried out for the five‐ring chelate complex 2. Mo(CO)4 (≡ l0), and the six‐ring chelate complex 9 . Mo(CO)4, (≡ 13).
Cyclic Diynes with Silicon in the Bridges: Structural and Photoelectron Spectroscopic Investigations
Authors: Stahr Helmut , Gleiter Rolf , Haberhauer Gebhard , Irngartinger Hermann , Oeser Thomas
Published: July 2007

The structures of 6‐isopropylidene‐1,1‐dimethyl‐1‐silacyclodeca‐3,8‐diyne (2), 1,6‐dimethyl‐1,6‐disilabicyclo[4.4.4]tetradeca‐3,8,12‐tryine (4), and 1,1,2,2,3,3‐hexamethyl‐1,2,3‐trisilacyclodeca‐4,9‐diyne (6) have been investigated by means of X‐ray crystallography. In 2 and 6 a chair conformation is adopted in the solid solid state. In 4 the three butyne groups are twisted around the SiSi axis against one another. The torsion along the triple bond axis (Si‐CH2‐CH2,/Si) amounts to 29.0(1). The He(I) photoelectron (PE) spectra of 2 and 6 together with those of 1,1‐dimethyl‐1‐silacyclodeca‐3,8‐diyne (1), 1,1,6,6‐tetramethyl‐1,6‐disilacyclodeca‐3,8‐diyne (3),1,12,2,3,3‐hexamethyl‐1,2,3‐trisilacycloundeca‐4,10‐diyne (7) have also been recorded. The PE spectra were interpreted on the basis of results from SCF MO calculations (3–21G*). They reveal a smaller splitting of the π‐bands in 1–3 as compared to cyclodeca‐1,6‐diyne. In the PE spectra of 5–7 we encountered a strong interaction between the silicon chain and the in‐plane π‐orbitals.
Dynamic Modeling and Simulation of Steam Cracking Furnaces
Authors: Ghashghaee M. , Karimzadeh R.
Published: July 2007

The transient modeling of thermal cracking furnaces is developed. This representation is capable of describing and predicting the unsteady‐state behavior of cracking furnaces during start‐up. To accurately predict the heat transfer to the reactor tube, the fireside conditions are coupled with the process side. The mutual interaction of these two sections is found to be very stiff in terms of convergence of the computations. The two‐dimensional transient zone model is developed for the radiative heat exchange calculation. A simplified model for the convection section is also used to predict the crossover temperature at each time increment. The main simulation outputs are the flue gas properties as well as the distributions of heat flux, refractory wall and coil skin temperatures versus time. The dynamic simulation is implemented for a conventional procedure used in the start‐up run of the olefin furnaces.
An Analysis of Pressure Drop and Holdup for Liquid‐Liquid Upflow through Vertical Pipes
Authors: Jana A. K. , Ghoshal P. , Das G. , Das P. K.
Published: July 2007

The present study has attempted to investigate pressure drop and holdup during simultaneous flow of two liquids through a vertical pipe. The liquids selected were kerosene and water. The measurements were made for phase velocities varying from 0.05–1.2 m/s for both liquids. The pressure drop was measured with a differential pressure transducer while the quick closing valve (QCV) technique was adopted for the measurement of liquid holdup. The measured holdup and pressure drop were analyzed with suitable theoretical models according to the existing flow patterns. The analysis reveals that the homogeneous model is suitable for dispersed bubbly flow whereas bubbly and churn‐turbulent flow pattern is better predicted by the drift flux model. On the other hand, the two fluid flow model accurately predicts the pressure drop in core annular flow.
Enhanced Boiling of Methanol on Copper Coated Surface
Authors: Prasad L. , Siraj Alam M. , Gupta S. C. , Agarwal V. K.
Published: July 2007

This paper presents an experimental investigation on nucleate pool boiling of saturated methanol on uncoated as well as copper‐coated mild steel heating tubes of various thicknesses at atmospheric and subatmospheric pressures. It also includes the effect of heat flux, pressure and coating thickness on the boiling heat transfer coefficient of coated tube surfaces. Heat flux was progressively increased from 15,670.20 to 43,151.57 W/m2 in six steps and pressure from 23.02 to 98.68 kN/m2 in five steps. Boiling characteristics on such surfaces are compared with those on uncoated ones. Also, a criterion for enhanced boiling of methanol on copper‐coated tubes is described.
Photocatalytic Oxidation of Isopropanol in Aqueous Solution Using Perovskite‐Structured La2Ti2O7
Authors: Ku Y. , Wang L.‐C. , Ma C.‐M.
Published: July 2007

This study is focused on the application of a highly‐doped layered perovskite, La2Ti2O7, as the photocatalyst for the photocatalytic decomposition of isopropanol (IPA). The La2Ti2O7 powder prepared by solid state reaction was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), UV‐Vis diffuse reflectance spectrophotometry (UV‐DRS), X‐ray photoelectron spectroscopy (XPS), and zeta potential. The temporal behavior of the photocatalytic decomposition of IPA in aqueous solution by the UV/La2Ti2O7, with a photoreactor operated in a recirculation mode, was studied under various conditions including solution pH, light intensity, and La2Ti2O7 loading. The decomposition of IPA in aqueous solution by La2Ti2O7 photocatalytic processes was found to be technically feasible. A kinetic equation was developed for modeling the photocatalytic decomposition of IPA by the UV/La2Ti2O7 photocatalytic processes.
Exploration of the Binding Mode of Indanesulfonamides as Selective Inhibitors of Human Carbonic Anhydrase Type VII by Targeting Lys 91
Authors: Thiry Anne , Masereel Bernard , Dogné Jean‐Michel , Supuran Claudiu T. , Wouters Johan , Michaux Catherine
Published: July 2007

Convulsions are common neurological disorders in clinical medicine and are triggered by several mechanisms. The enhancement of neuronal excitability can be related, among other factors, to GABAergic depolarization. Carbonic anhydrase (CA) VII contributes to this electrophysiological behavior by providing bicarbonate anion, which can mediate current through channels coupled to GABAA receptors. Among the cytosolic CAs, the mechanism of action and inhibition of CA VII is less understood. We present herein the pharmacological evaluation of both enantiomers of an indanesulfonamide compound substituted by a pentafluorophenyl moiety against CA VII and five other human CA isoforms to evaluate their selectivity. The investigated compounds are powerful inhibitors of hCA VII, with Ki values in the range of 1.7–3.3 nM, but their selectivity needs to be improved. A molecular modeling study was conducted to rationalize the structure–activity relationships and provide useful insight into the future design of selective hCA VII inhibitors.
Global existence for three‐dimensional incompressible isotropic elastodynamics
Authors: Sideris Thomas C. , Thomases Becca
Published: July 2007

The existence of global‐in‐time classical solutions to the Cauchy problem for incompressible, nonlinear, isotropic elastodynamics for small initial displacements is proved. The generalized energy method is used to obtain strong dispersive estimates that are needed for long‐time stability. This requires the use of weighted local decay estimates for the linearized equations, which are obtained as a special case of a new general result for certain isotropic symmetric hyperbolic systems. In addition, the pressure that arises as a Lagrange multiplier to enforce the incompressibility constraint is estimated as a nonlinear term. The incompressible elasticity equations are inherently linearly degenerate in the isotropic case; i.e., the equations satisfy a null condition necessary for global existence in three dimensions. © 2007 Wiley Periodicals, Inc.
Hodge genera of algebraic varieties I
Authors: Cappell Sylvain E. , Maxim Laurentiu G. , Shaneson Julius L.
Published: July 2007

The aim of this paper is to study the behavior of Hodge‐theoretic (intersection homology) genera and their associated characteristic classes under proper morphisms of complex algebraic varieties. We obtain formulae that relate (parametrized families of) global invariants of a complex algebraic variety X to such invariants of singularities of proper algebraic maps defined on X. Such formulae severely constrain, both topologically and analytically, the singularities of complex maps, even between smooth varieties. Similar results were announced by the first and third author in [13, 32]. © 2007 Wiley Periodicals, Inc.
Spectroscopic Fingerprints of Amine and Imide Functional Groups in Self‐Assembled Monolayers
Authors: Ruiz‐Osés Miguel , Kampen Thorsten , González‐Lakunza Nora , Silanes Iñaki , Schmidt‐Weber Philipp M. , Gourdon André , Arnau Andrés , Horn Karsten , Ortega J. Enrique
Published: July 2007

The electronic structures of naphthalene tetracarboxylic diimide (NTCDI) and 1,4‐bis(4,6‐diamino‐1,3,5‐triazin‐2‐yl)benzene (BDG) monolayer assemblies grown on Au(111) are investigated by photoemission spectroscopy, X‐ray absorption, and density functional theory. The different spectroscopic features in the absorption and core‐level photoemission spectra are understood in terms of contributions from different core and molecular levels at N‐ and O‐atom sites. This study provides clear spectroscopic fingerprints for amine and imide functional end groups, which drive the self‐organization process in a number of planar, π‐conjugated molecular structures.
Symbolic Analysis of Linear Non‐Reciprocal Circuits
Authors: Nitescu Miruna , Constantinescu Florin
Published: July 2007

A symbolic expression of a transfer function in a linear non‐reciprocal circuit is proved; the symbolic parameters may be proper immittances and controlled source parameters. the effectiveness of computation of symbol product coefficients is improved by using a generation‐and‐test algorithm of symbol combinations. A comparison between the most efficient symbolic analysis methods and the proposed method is performed. It is concluded that the proposed method is competitive with these methods.
Higher‐order modelling of the diffusion dynamics in a bipolar transistor
Authors: Lehtinen Kari , Sipila Markku , Porra Veikko
Published: July 2007

A higher‐order diffusion model for a bipolar transistor has been developed. This model is based on the Padé approximation of the quasi‐static expansions of the base and collector currents and gives improved accuracy for the simulation of fast transients and periodic operation at high frequencies. the effect of higher‐order circuit elements on accuracy is demonstrated by calculating the transient response to a step excitation and by determining the scattering parameters of a transistor model with higher‐order elements linearized about an operating point. the higher‐order model is replaced by an equivalent circuit including only conventional elements, and the transient behaviour of these two models is compared.
Noise and sensitivity optimization in the design of second‐order single‐amplifier filters
Authors: Bowron P. , Mezher K. A.
Published: July 2007

Simultaneous optimization of the sensitivity and noise performance of second‐order single‐amplifier RC filter sections resolves a long‐standing discrepancy and reveals practical trade‐offs. the influences of controlled gain, component spread and design choice are elucidated for both bandpass and lowpass complementarily symmetrical circuits.
On Improved Representation Theorems For Multidimensional Lossless Bounded Matrices
Authors: Fettweis A. , Basu Sankar
Published: July 2007

An improved form of representation of multidimensional (k‐D) discrete lossless two‐ports in a form similar to the well‐known Belevitch canonical form of classical one‐dimensional network theory is presented. Representations of the transfer function matrix, chain matrix and hybrid matrix associated with discrete lossless multidimensional twoports are derived on the basis of our earlier result.

An improved form of representation of multidimensional (k‐D) discrete lossless two‐ports in a form similar to the well‐known Belevitch canonical polynomial associated with the system. This fact is true for both discrete and continuous systems and apparently has remained unnoticed even in ID.
Neural network for non‐linear programming with linear equality constraints
Authors: Osowski Stanisłsaw
Published: July 2007

This paper presents a simplified approach to neural optimization in the presence of linear equality constraints. In contrast to the standard Lagrangian approach, the constraints simplify the final neural circuit instead of complicating it. the number of elements used is also significantly reduced. Instead of n + t integrators we need only n – t. There is also a similar saving in the number of preprocessing non‐linear devices. Elimination of the constraints allows a large speed‐up of the solution.
A collocation algorithm for calculating the periodic solutions of non‐linear oscillators
Authors: Buonomo A.
Published: July 2007

An approximation method is given for calculating the periodic solutions of non‐linear oscillators based upon the well‐known method of collocation, which belongs to the class of projection methods. Unlike available techniques, the method leads to a simple and efficient algorithmic procedure which consists of solving a system of non‐linear equations given in a simple explicit form.

To demonstrate the effectiveness of the proposed algorithm, the results of some typical oscillator circuits are provided.
Perfect pairs of trees in graphs
Authors: Novak Ladislav , Gibbons Alan
Published: July 2007

We introduce the concept of perfect pairs of trees of a graph as a natural generalization of so‐called maximally distant pairs of trees. Several propositions and remarks are presented to display the properties of this new notion. Lemma 1, which plays a central role, gives five equivalent statements characterizing the relation ‘to be maximally distant from’ between pairs of trees. Symmetrization of this relation leads to our concept of a perfect pair of trees, the properties of which are given in Theorem 1. Remark 4 shows how naturally our new concept arises. Additionally, certain examples are provided to illustrate perfect pair structures in a graph.
Existence and stability of periodic solutions in weakly non‐linear electrical circuits via averaging and functional analytical methods
Authors: Ulmet D. E.
Published: July 2007

The method of averaging has been extensively used to detect invariant manifolds for non‐linear dynamical systems. In this paper we combine the averaging analysis with some functional analytical methods to prove the existence and stability of periodic solutions for a class of weakly non‐linear electrical circuits. We also prove a specific averaging theorem for these circuits using Gronwall estimates and the Sanchez‐Palencia summation trick. These results are applied to the model equations of a system of coupled Van der Pol oscillators to obtain the existence of orbitally asymptotically stable periodic solutions. Finally we construct asymptotic approximations of these solutions and perform a numerical simulation of the flow.
Programmable analogue vlsi cnn chip with local digital logic
Authors: Halonen K. , Porra V. , Roska T. , Chua L.
Published: July 2007

A new integrated circuit cellular neural network implementation with digitally or continuously selectable template coefficients is presented. Local logic and memory are added into each cell, providing a simple dual (analogue and digital) computing structure. Variable gain OTAs are used as the voltage‐controlled current sources to programme the template element values. the cells have local switched feedback (both analogue and digital) to feed from the output to the input or state capacitor. Therefore this analogue array processor can be applied to solve problems with a sequence of different templates. A 4 × 4 CNN circuit is realized using the 2 μm analogue CMOS process.
Stability analysis of generalized cellular neural networks
Authors: Guzelis Cuneyt , Chua Leon O.
Published: July 2007

A rather general class of neural networks, called generalized cellular neural networks (CNNs), is introduced. the new model covers most of the known neural network architectures, including cellular neural networks, Hopfield networks and multilayer perceptrons. Several sets of conditions ensuring the input‐output stability and global asymptotic stability of generalized CNNs have been obtained. the conditions for the stability of individual cells are checked in the frequency domain, while the stability of the overall network is analysed in terms of the stability of individual cells and the connectivity characteristics. the results on the global asymptotic stability are useful for the design of a generalized CNN such that the orbit of each state converges to a globally asymptotically stable equilibrium point which depends only on the input and not on the initial state. Such a network defines an algebraic map from the space of external inputs to the space of steady state values of the outputs and hence can accomplish cognitive and computational tasks.
An accurate reference‐generating circuit for successive approximation current mode A/D converters
Authors: Krishnan Shoba , Wey Chin‐Long
Published: July 2007

As pressures increase on VLSI designers to use a lower supply voltage of 3.3 V rather than the present 5 V, current mode signal‐processing techniques will surely become increasingly important and attractive. This paper presents the design of a reference‐generating (RG) circuit which employs a current mode divide‐by‐two circuit. Current dividers are usually implemented by using resistor networks or weighted transistors. the division accuracy of such solutions is limited by resistor or transistor mismatch. In this study the proposed divide‐by‐two circuit does not rely on well‐matched components and high‐gain op amps to achieve high accuracy. This paper also addresses the relationship among the operation and accuracy of the division process, the transistor mismatch and the resolution of a converter which employs the RG circuit. the proposed RG circuit can be implemented not only for medium‐speed successive approximation current mode A/D converters but also for A/D converter arrays achieving a high conversion rate.
Uncountable transfinite graphs and electrical networks
Authors: Zemanian A. H.
Published: July 2007

Up to now the theory of infinite and transfinite graphs and electrical networks has been established only for the case where the branch sets are countable. This work extends that prior theory to graphs and networks with uncountable branch sets, a structure that arises quite naturally in the theory of transfinite graphs. Moreover, conditions on the local structure of the transfinite graph are given which insure the countability of the branch set. Finally, it is shown that only countably many of the branches in an uncountable electrical network can have non‐zero voltages and currents, and therefore the restriction to countability in the prior theory is not essentially restrictive.
A PWL ladder circuit which exhibits hysteresis
Authors: Parodi Mauro , Storace Marco , Cincotti Silvano
Published: July 2007

A circuit model for static hysteresis is presented. the circuit has a ladder structure with linear capacitors and piece wise linear resistors. the model behaviour shows all basic characteristics of static hysteresis phenomena. the model is put into relation with others proposed in the literature. an analysis of the model properties and a detailed comparison with the static Preisach model are made.
Optimality condition for truncated generalized laguerre networks
Authors: Belt H. J. W. , Brinker A. C. Den
Published: July 2007

The optimality condition for the free parameter in a truncated Laguerre network in both continuous‐time and discrete‐time has recently been established. This condition is of a very simple form and is independent of the power spectrum of the input signal, which makes it attractive for system identification purposes. the simple form of the optimality condition stems from the following property. the derivative of a basis function in the Laguerre series w.r.t. to the free parameter can be expressed in the previous and next basis functions. This property not only applies to the basis functions in a Laguerre series but also to those in specific generalizations of the Laguerre series. In particular we consider the generalized Laguerre functions and what will be called the Meixner‐like functions. For these generalizations the same optimality condition as for a Laguerre series holds.
Models for transmission lines with connecting transistors based on wave digital filters
Authors: Erbar Maximilian , Horneber Ernst‐Helmut
Published: July 2007

Based on the theory of wave digital filters (WDFs), models are derived to simulate interconnection circuits. They contain lumped transmission line models and transmission line models derived from their partial differential equations (distributed models). Both kinds of models are implemented in the transmission line simulator ALWX in order to calculate the signal wave‐forms on transmission lines and the cross‐talk behaviour between them. Additional MOS transistor models extend the possible applications. Compared with other simulators, ALWX shows significant advantages in CPU time while producing results with high accuracy.