Colorimetric response to anions by a "robust" copper(II) complex of a [9]aneN3 pendant arm derivative: CN- and I- selective sensing

The 1 : 1 complex [Cu(L)](BF(4))(2)·MeCN (1) of the tetradentate ligand 1-(2-quinolinylmethyl)-1,4,7-triazacyclononane (L) selectively changes its colour in the presence of CN(-) in H(2)O and MeCN (without undergoing decomplexation from the macrocyclic ligand). The same complex in MeCN assumes different colours in the presence of CN(-) or I(-).     

Unprecedented eta3-M3 coordination mode in a terpyridine ligand

The gold(I) complex [Au3(C6F5)3(eta3-Fcterpy)](Fcterpy = 4'-ferrocenyl-2,2'ratio6',2'-terpyridine) represents the first example of a terpyridine ligand bonded to three different metals. The aurophilic interactions present in the molecule may contribute to the overall stability of the system, as was shown by DFT calculations. The positive Mayer indices (0.152 and 0.138), as well as the magnitude of the binding interaction between terpy and the Au(I)L fragments, support this interpretation.     

Paper-Based Probes with Visual Response to Vapors from Nitroaromatic Explosives: Polyfluorenes and Tertiary Amines

Although it is well-known that nitroaromatic compounds quench the fluorescence of different conjugated polymers and form colored Meisenheimer complexes with proper nucleophiles, the potential of paper as a substrate for those macromolecules can be further developed. This work undertakes this task, impregnating paper strips with a fluorene-phenylene copolymer with quaternary ammonium groups, a bisfluorene-based cationic polyelectrolyte, and poly(2-(dimethylamino)ethyl methacrylate) (polyDMAEMA). Cationic groups make the aforementioned polyfluorenes attachable to paper, whose surface possesses a slightly negative charge and avoid interference from cationic quenchers. While conjugated polymers had their fluorescence quenched with nitroaromatic vapors in a non-selective way, polyDMAEMA-coated papers had a visual response that was selective to 2,4,6-trinitrotoluene (TNT), and that could be easily identified, and even quantified, under natural light. Far from implying that polyfluorenes should be ruled out, it must be taken into account that TNT-filled mines emit vapors from 2,4-dinitrotoluene (DNT) and dinitrobenzene isomers, which are more volatile than TNT itself. Atmospheres with only 790 ppbv TNT or 277 ppbv DNT were enough to trigger a distinguishable response, although the requirement for certain exposure times is an important limitation.     

Synthesis and molecular structure of the all-trans- and the trans–cis-[UO2Br2(OAsPh3)2] isomers

The all-trans and the trans–cis isomers of [UO₂Br₂(OAsPh₃)₂] have been prepared by reacting UO₂Br₂·xH₂O with OAsPh₃. The molecular structures for both isomers have been established by X-ray diffraction analysis. The all-trans isomer is singular as the two U---OAsPh₃ bonds are very different.     

Method of achieving phase delay with wide optical bandwidth in multimode interference devices

A completely passive method of achieving phase delays inside multimode interference devices is presented. The desired relative phase is obtained by adjustment of the width of the waveguides in conjunction with the tapers to avoid interference inside the multimode section. One can generally apply the delay lines to avoid the use of active elements, and they are less sensitive to changes in wavelength than the traditional method with bends. Using this method, we have designed and analyzed a zero-to-one mode converter. The converter exhibits minimum excess loss of 0.100 and 0.102 for TE and TM polarization, respectively. A very large 1-dB bandwidth exceeding 350 nm is achieved.     

Binuclear oxomolybdenum(V) chlorides: Molecular structure of Mo2O4Cl2(DMF)4 and Mo2O4Cl2(bipy)2 · DMF

Reduction of MoO₂Cl₂(DMF)₂ (DMF = dimethylformamide) with PPh₃ in mild conditions afforded the dinuclear species Mo₂O₃Cl₄(DMF)₄. Related compounds could be prepared by substitution of DMF with stronger bases. While attempting to grow crystals of these compounds new complexes with the syn-[Mo₂O₄]²⁺ core were obtained. The molecular structures of Mo₂O₄Cl₂(DMF)₄, and Mo₂O₄Cl₂(bipy)₂ (bipy = 2,2′-bipyridine) have been established by X-ray diffraction analysis.     

Dinuclear oxomolybdenum(VI) acetylacetonates: Crystal and molecular structure of Mo2O5(acac)2L2 (L = D2O,DMF)

The behavior of MoO₂(acac)₂ (acac = acetylacetonate) towards representative amines, amides, sulfoxides and phosphine oxides in common solvents has been examined. Compounds of the composition Mo₂O₅(acac)₂L₂ [L = H₂O, D₂O, dimethylformamide (DMF), dimethylacetamide (DMA), dimethylbenzamide (DMBA), tetramethylurea (TMU), dimethylsulfoxide (DMSO), dibutylsulfoxide (Bu₂SO), p-tolylsulfoxide (p-Tol₂SO), tributylphosphine oxide (OPBu₃), triphenylphosphine oxide (OPPh₃), hexamethylphosphoramide (HMPA)], derived from partial hydrolysis of MoO₂(acac)₂ followed by condensation and coordination of L, can readily be isolated. The crystal and molecular structures of Mo₂O₅(acac)₂L₂ (L = D₂O, DMF) have been established by X-ray diffraction analysis.     

Sand attrition in conical spouted beds

A study was carried out on the attrition in conical spouted beds using two sands with different properties for several bed heights and gas flow rates. Furthermore, the influence of a draft tube was studied at ambient and high temperatures. The main objective was to acquire knowledge on the attrition of sand beds for biomass pyrolysis in a pilot plant provided with a conical spouted bed reactor. A first-order kinetic equation is proposed for sand attrition in a conical spouted bed at room temperature. The predicted attrition rate constant depends exponentially on excess air velocity over that for minimum spouting. Both the draft tube and temperature increase contribute to reduction of attrition.     

Melting behavior of large disordered sodium clusters

The melting-like transition in disordered sodium clusters Na₉₂ and Na₁₄₂ is studied by performing density functional constant-energy molecular dynamics simulations. The orbital-free version of the density functional formalism is used. In Na₁₄₂ the atoms are distributed in two distinct shells (surface and inner shells) and this cluster melts in two steps: the first one, at ≈130 K, is characterized by the development of a high intrashell atomic mobility, and the second, homogeneous melting at ≈270 K, involves diffusive motion of all the atoms across the whole cluster volume. On the contrary, the melting of Na₉₂ proceeds smoothly over a very broad temperature interval, without any abrupt change in the thermal or structural indicators. The occurrence of two steps in the melting transition is suggested to be related to the existence of a grouping of the atoms in radial shells, even if those shells present a large degree of internal disorder. It then appears that a cluster can be considered fully amorphous (totally disordered) only when there are no radial regions of low atomic density separating shells. The isomer of Na₉₂ studied here fulfills this criterion and its thermal behavior can be considered as representative of that expected for fully amorphous clusters. Disordered Na₁₄₂, on the other hand, that has a discernible structure of an inner and a surface shell, should be considered as not fully disordered. The thermal behavior of these two clusters is also compared to that of icosahedral (totally ordered) sodium clusters of the same sizes. Received 5 February 2001 and Received in final form 21 May 2001