Structures and stability of N9, N9 − and N9 + clusters

 Ab initio molecular orbital calculations for N₉, N⁻ ₉ and N⁺ ₉ isomers were carried out at the HF/ 6-31G*, B3PW91/6-31G*, B3LYP/6-31G* and MP2/ 6-31G* levels of theory. Stable equilibrium geometric structures were determined by harmonic vibrational frequency analyses at the HF/6-31G*, B3PW91/6-31G* and B3LYP/6-31G* levels of theory. The most stable free-radical N₉ cluster is structure 1 with C _{2 v} symmetry and that of anion N⁻ ₉ is structure 3 with C _s symmetry. Only one stable structure of the N⁺ ₉ cation with C _{2 v} symmetry was predicted. Their potential application as high-energy-density materials has been examined. Received: 15 June 1999 / Accepted: 11 October 1999 / Published online: 14 March 2000     

Improved Syntheses of N‐Desmethylcitalopram and N,N‐Didesmethylcitalopram

An improved and efficient synthesis of N‐desmethylcitalopram (2) and N,N‐didesmethylcitalopram (3) is presented. The method involved N‐demethylation of citalopram (1) using 1‐chloroethyl chloroformate to give 2 in 87% yield. Synthesis of 3 was accomplished by alkylation of 8 with 1‐(3‐bromopropyl)‐2,2,5,5‐tetramethyl‐1‐aza‐2,5‐disilacyclopentane (9).     

Thermal and FTIR spectral studies of N,N′-diphenylguanidine

Thermal decomposition of N,N??-diphenylguanidine (DPG) was investigated by simultaneous TG/DSC-FTIR techniques under nonisothermal conditions. Online FTIR measurements illustrate that aniline is a major product of DPG decomposition. The observation that the activation energy depends on the extent of conversion indicates that the DPG decomposition kinetics features multiple processes. The initial elimination of aniline from DPG involves two pathways because of the isomerization of DPG. Mass spectrometry and thin film chromatography suggest that there are two major intermediate products with the major one of C₂₁N₃H₁₇. The most probable kinetic model deduced through multivariate nonlinear regression method agrees well with the experimental data with a correlation coefficient of 0.9998. The temperature-independent function of conversion f(??), activation energy E and the pre-exponential factor A of DPG decomposition was also established through model-fitting method in this research.     

Physicochemical studies of the structure of N,N′-dinitrourea and its salts

The properties and behavior of dinitrourea and its potassium and dipotassium salts in different solvents have been studied by IR and UV spectroscopy. In different media, dinitrourea can exist in several tautomeric forms. An XRD study of the potassium and dipotassium salts of dinitrourea revealed a tendency toward equalization of the bond lengths of the C-N⁻-NO₂ fragments compared with those of C-NH-NO₂, which agrees with the results of quantum-chemical calculations.     

The structure effect of N,N,N′,N′-alkylamide in the extraction of uranium and thorium

In this paper, nine N,N,N,N-tetraalkyldiamides have been synthesized and the extracting ability for uranium and thorium under different conditions has been studied. All results were compared with those obtained by using tributyl phosphate (TBP) under exactly the same conditions. The extracting ability of thorium and uranium for different N,N,N,N-tetraalkyldiamides is discussed.     

2,7-Dibromonaphthalene and 4,4′-dibromobiphenyl in the synthesis of oxadiamine N,N, N′, N′-tetraaryl derivatives and studies of formation of bismacrocyclic compounds from them

Russian Chemical Bulletin - The Pd-catalyzed tetraarylation of diamines and oxadiamines with 2,7-dibromonaphthalenes and 4,4′-dibromobiphenyl was studied. These reactions gave the...     

The effect of structure and phase transformation on the mechanical properties of Re₂N and the stability of Mn₂N

First‐principles calculations were carried out on recently synthesized Re₂ and Re₃ as well as hypothetical Tc and Mn nitrides. It is found that structure and covalent bonds play an important role in determining mechanical properties. Under a large strain along (0001)〈101 0〉direction, Re₂N undergoes a phase transformation with a slight increase in ideal shear strength. On the other hand, it is transformed into a phase with weaker mechanical properties, if the strain is along Re₂〈1 21 0〉 direction. Mn₂N can be synthesized under moderate conditions due to its more negative formation energy. Re₂N, Re₃N, and Mn₂N show structure‐related mechanical property under larger strains to ReB₂ but exhibit much lower ideal strengths, which is attributed to the larger ionicity of cation–anion bond. Three‐dimensional framework of strong covalent bonds is thus highly recommended to design superhard materials. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Reactions of N-Allyl- and N-Propargyltriflimides with N,N′-Disubstituted Carbodiimides

The alkylating activity of N-allyl- and N-propargyltriflimides toward N,N′-dicyclohexyl- and N,N′-diphenylcarbodiimides has been studied. Activation of the nitrogen atom by two electron-withdrawing trifluoromethanesulfonyl groups favors cleavage of the C–N bond in the absence of a catalyst with the formation of N-substituted unsaturated ureas.

     

Synthetic Studies of N‐demethylossamine and Elaboration of its Glycosylation

An amino‐sugar, N‐demethylossamine, was efficiently synthesized from D‐threonine, two stereogenic centers of which were directly used as those at the C‐4 and 5 positions of the target sugar. In addition, the glycosylation study indicated that reaction of the acetate 7 with cyclopentanol under Lewis acid conditions, provided the desired α‐L‐glycoside 9α.      

GC-MS determination and optimization of extraction of N,N′-dimethyl-N,N′-diphenylcarbamide from building materials

N,N’-dimethyl-N,N’-diphenylcarbamide (centralite) extracted from building materials was quantitated using ion trap GC-MS detection technique. Both linearity and standard deviation of the calibration curve were dependent on the conditions of the mass spectral detection. The most precise calibration has been achieved by quantification of a mass ion not participating in secondary reactions and which is produced via single fragmentation. The best recovery of centralite was obtained after either 30 min of normal extraction with toluene at 60 °C or 10 min of ultrasonic extraction with chloroform at room temperature. Using the latter method resorption processes might cause decrease in efficiency of the recovery at longer extraction time. Received: 3 July 1998 / Revised: 5 November 1998 / Accepted: 26 January 1999     

Calorimetric study of the solubilization of ethylenediamine,N,N-dimethylaminoethylamine and N,N,N′,N′-tetramethylethylenediamine by reversed AOT micelles

Distribution constants and standard enthalpies of transfer of ethylenediamine (en), N,N-dimethylaminoethylamine (dmen) and N,N,N,N-tetramethylethylenediamine (tmen) partitioned between n-heptane and water containing reversed sodium bis(2-ethylhexyl) sulfosuccinate (AOT) micelles as a function of the molar concentration ratio R (R=[water]/[AOT]) were evaluated by a calorimetric method. The results show that en, dmen and tmen molecules, solubilized in the reversed micelles, are distributed between the micellar aqueous core and the micellar palisade layer. An analysis of the thermodynamic parameters of the partition process demonstrates the peculiar solvent properties of the water containing reversed AOT micelles.     

Crystal Structure and Fluorescence Spectra of A Complex of Europium Picrate with N,N,N′,N′-tetraphenyl-3,6,9-trioxaundecanediamide

The title complex Eu(Pic)₃(TTD) crystallizes in space group Pcab with a = 23.714(4), b = 29.245(6), c = 32.035(8)Å, V = 22216(7)ų, Z = 16, D_c = 1.63 g cm^-1, w = 12.5 cm^-1, F(000) = 10976 and its structure was solved and refined to R = 0.083. Two crystallographically different Eu(Pic)₃(TTD) units, in which the coordination numbers of two central ions (Eu1 and Eu2) are nine and ten, respectively, are present in the asymmetric unit. In the ⁷F₀ → ⁵D₀ excitation spectrum of the complex, there are two sharp peaks at 578.5 and 579.0 nm indicating that the complex has two Eu(III) sites. Two different patterns in the ⁵D₀ → ⁷F_j (j = 1-4) luminescence spectrum have been observed (selectively excited ⁵D₀), which further reveals the existence of two Eu(III) sites compatible with the result of the structure determination.     

Synthesis and Crystal Structure of N,N′-4-aminomethyl-pyromellitic diimide

1 INTRODUCTION N,N?-4-aminomethyl-pyromellitic diimide (4-pmpmdwas firstly obtained[1] in 1989 as one of the bypro-ducts by refluxing equimolar quantities of pyrome-llitic anhydride, n-hexylamine and 4-aminomethyl py-ridine in dry DMF to assemble electronic donor-spa-cer-acceptor systems, but its structure and coordina-tion chemistry did not receive attention at that time.For 4-pmpmd, the entity of two methylene groups(-CH2-) between the rigid pyromellitic diimide (PMDcore and two fre…     

Synthesis and Crystal Structure of N,N′-4-aminomethyl-pyromellitic diimide

The title compound N,N′-4-aminomethyl-pyromellitic diimide (4-pmpmd) crystallizes in monoclinic, space group P21/c with a = 4.785(1), b = 6.200(1), c = 29.907(2) (A), β =93.583(11)°, V= 885.5(2) (A)3, Dc = 1.494 g/cm3, Z = 2, C22H14N4O4, Mr = 398.37,μ(MoKα) = 0.106mm-1 and F(000) = 412, and its structure was refined to R = 0.0469 and wR = 0.1017 for 1194observed reflections (Fo ＞ 4σ(Fo)). The X-ray diffraction shows the existence of the staggered multi-dimensional supramolecular network based on the Z-mode conformation of the title compound.     

Syntheses and Characterization of Metal Complexes of L－Lysine－N，N，N＇，N＇－tetraacetic Acid and L－Lysine－N，N，N＇，N＇－tetramethylenepho sphonic Acid

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Synthesis and Characterization of N‐methylenephenyl Phosphonic Chitosan

Chitosan is a natural based polymer obtained by alkaline deacetylation of chitin, exhibiting excellent properties such as non‐toxicity, biocompatibility and biodegradability. N‐Methylenephenyl phosphonic chitosan (NMPPC) is synthesized from chitosan by reacting with phenyl phosphonic acid using formaldehyde. The NMPPC was characterized by FTIR, ³¹P‐NMR, X‐ray diffraction, scanning electron microscopy, thermogravimeteric analysis and solubility studies. A significant decrease of molecular weight was observed in the NMPPC. The TGA studies suggested that NMPPC has less thermal stability than chitosan. The X‐ray diffraction analysis showed that NMPPC was amorphous in nature. The solubility property of the polymer was improved after the incorporation of a phenyl phosphonic group.