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Chemistry	83%

Selected Abstracts

A New Trinuclear Linear Copper(II) Complex: Unusual Crystal Structure with Semi-Coordinated Thiophene Moieties and Weak Antiferromagnetic Coupling Through the Bridging Imidazolate Rings

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2004
Yufei F. Song
Abstract A trinuclear copper(II) complex, [Cu3(imthio)2(NO3)4(MeOH)2] [where Himthio is 1,1-bis(imidazol-2-yl)-3-(thiophen-2-yl)-2-azapropane], has been synthesized by the reaction of Himthio with Cu(NO3)2·3H2O in MeOH. The structure of the copper complex is centrosymmetric and contains a linear trinuclear array of copper atoms. The central copper(II) ion, Cu1, which lies on an inversion centre, is equatorially coordinated by four nitrogen atoms from two anionic imthio ligands and axially by two semicoordinated thiophene sulfur atoms to give an octahedral environment (Cu1,S1 3.136 Å). The Himthio ligand bridges Cu1 and the terminal copper(II) ions through imidazole nitrogen atoms. The coordination around the external ions is completed by the oxygen atoms from two nitrate groups and by a methanol molecule in a distorted square-pyramidal geometry. The two terminal copper(II) complexes can be considered to be chelating ligands for the central CuII ion. The EPR spectrum of the complex in MeOH at 77 K shows two mononuclear species, as is fully confirmed by EPR simulation. Magnetic susceptibility of the complex shows weak antiferromagnetic behaviour (J = ,71.37 cm,1) caused by the overlapping of the magnetic orbitals of the copper atoms and the bridging imidazolate rings. (© Wiley-VCH Verlag GmbH & Co.. KGaA, 69451 Weinheim, Germany, 2004) [source]

Dynamic Behavior of an N -Metalated ,-Enaminoimine Complex , Preparation of N -Phosphanylenamine and ,-Enaminoimine Derivatives

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2003
Alexandrine Maraval
Abstract Variable-temperature NMR spectroscopy of the ,-enaminoimine complex 2 showed a dynamic process which was attributed to an internal fluxional aldimido N -zirconated ,-linear/,-bent structure. Such an internal rearrangement has been previously proposed to occur in these systems but never observed. We have prepared a variety of (N -phosphanyl-,-enamino)imine ligands using the hydrozirconation/transmetalation reaction of malonodinitrile compounds RCH(CN)2 (R = H, PPh2). In addition to their potential uses in coordination chemistry, these systems are good tools for the study of intramolecular hydrogen bonding. The X-ray crystal structure of 14 at 180 K shows an unsymmetrical system with the N(H) proton localized on one of the two chelating nitrogen atoms, consistent with the existence in solution of a low barrier proton transfer process with a double-well potential. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

An Ab Initio Molecular Dynamics Study of Bioactive Phosphate Glasses,

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
Emilia Tang
First principles molecular dynamics simulations of ternary phosphate-based glasses P2O5CaONa2O (PBGs) have been carried out in order to provide an accurate description of the local structure and properties of these important materials for biomedical applications. The structures of PBGs with compositions (P2O5)0.45(CaO)x(Na2O)0.55,,,x (x,=,0.30, 0.35, and 0.40) were generated using a full ab initio molecular dynamics melt-and-quench procedure. The analysis of the structure of the glasses at 300,K shows the prevalence of the metaphosphate Q2 and pyrophosphate Q1 species, whereas the number of Q3 units, which constitute the three-dimensional phosphate network, significantly decreases with the increase in calcium content in the glass. Calculation of the pair and angular distribution functions suggests that the rigidity of the phosphate tetrahedral glass network increases with the concentration of calcium, an observation which is interpreted in terms of the tendency of Ca2+ to be a stronger coordinator than sodium. [source]

An ordered low-temperature phase of barium nitroprusside trihydrate studied by neutron diffraction

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2003
G. Chevrier
Crystals of barium pentacyanonitrosylferrate trihydrate (barium nitroprusside trihydrate), Ba[Fe(CN)5(NO)]·3H2O, have been studied by neutron diffraction in order to examine the structural behaviour of the compound in the 20,120,K temperature range and to determine the structure at 105,K. The results show the existence of a new crystal phase of the compound at 80,K (with a duplicated a parameter), which still exists at 20,K. The crystal structure at 105,K shows a rearrangement of the water molecules, which results in an ordered structure with P1 symmetry. Two of the four independent nitroprusside cations are rotated by 4.5° around the [100] direction. [source]

To scavenge or not to scavenge: that is the question

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009
Elzbieta Nowak
Analysis of a series of diffraction data sets measured from four native as well as four nicotinic acid-soaked crystals of trypsin at 100,K shows a high variability in radiation-sensitivity among individual crystals for both nicotinic acid-soaked and native crystals. The level of radiation-sensitivity and the extent of its variability is statistically indistinguishable between the two conditions. This suggests that this potential scavenger does not have any statistically significant effect on the amount of radiation damage incurred in the crystals on X-ray irradiation. This is in contrast to previous results [Kauffmann et al. (2006), Structure, 14, 1099,1105] where only one crystal specimen was used for each condition (native and nicotinic acid-soaked). [source]

Muon Implantation of Metallocenes: Ferrocene

CHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007
Upali
Abstract Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17,T, for the low-temperature phase at 18,K. The high-temperature phase at 295,K shows that only the last feature shifted down to about 0.49,T and a muon spin relaxation peak at about 0.106,T which approaches zero field when reaching the phase transition temperature of 164,K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe,Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the ,SR spectra of ferrocene was estimated to be 584,K. Correlation time for the ring rotation dynamics of the Fe,Mu radical at this temperature is 3.2,ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported. [source]