Toward the control of the magnetic anisotropy of Fe(II) cubes: a DFT study

We present the results of our all-electron density-functional calculations on the magnetic anisotropy of the [Fe4(sap)4(MeOH)4] and [Fe4(sae)4(MeOH)4] polynuclear complexes. Our calculations, which predict that only the second complex is a single-molecule magnet (with a magnetic anisotropy energy barrier of 5.6 K), are in qualitative agreement with the experimental data. The analysis of the projected anisotropies of each Fe(II) ion, together with a study of the variation of the D value as a function of several geometrical parameters, allows us to qualitatively understand the different magnetic behaviors of both complexes. In addition to this, we also present a simple rule based on the analysis of the molecular orbitals of the system that allows us to predict how to enhance (by a factor of 6, approximately) the magnetic anisotropy barrier of these systems. Specifically, we will show that, for high-spin Fe(II) ions, the local easy axis of magnetization is perpendicular to the plane defined by the Fe(II)-d orbital which is doubly occupied. If similar rules were found for other metal ions, rational synthetic strategies to control magnetic anisotropy could be established.     

Kadomtsev-Petviashvili (KP) Burgers Equation in Dusty Negative Ion Plasmas: Evolution of Dust-Ion Acoustic Shocks

We study the nonlinear propagation of dust-ion acoustic (DIA) shock waves in an un-magnetized dusty plasma which consists of electrons, both positive and negative ions and negatively charged immobile dust grains. Starting from a set of hydrodynamic equations with the ion thermal pressures and ion kinematic viscosities included, and using a standard reductive perturbation method, the Kadomtsev-Petviashivili-Burgers (K-P-Burgers) equation is derived, which governs the evolution of DIA shocks. A stationary solution of the K-P-Burgers equation is obtained and its properties are analysed with different plasma number densities, ion temperatures and masses. It is shown that a transition from shocks with negative potential to positive one occurs depending on the negative ion concentration in the plasma and the obliqueness of propagation of DIA waves.     

Evolutions of Longitudinal Structure Function F L upto Next-to-Next-to-Leading Orders at Small-x

We compute the longitudinal structure function F _L of proton from its QCD (Quantum Chromodynamics) evolution equation in next-to-next-to-leading order (NNLO) approximation at small-x. Here we use Taylor series expansion method to solve the evolution equation for small-x and the obtained simple analytical expressions for F _L provide t- and x-evolution equations for the computation of the longitudinal structure function. Finally, we compare our results with the recent H1, ZEUS experimental data and results of MSTW, CT10 parameterizations and Block, Donnachie-Landshoff (DL) models. Our results are in good agreement with the data and the related fittings and parameterizations, which can also be described within the framework of perturbative QCD.     

Nitric oxide reactivity of copper(II) complexes of bidentate amine ligands: effect of chelate ring size on the stability of a [Cu(II)-NO] intermediate

Three copper(II) complexes, 1, 2, and 3 with L(1), L(2) and L(3) [L(1) = 2-(2-aminoethyl)-pyridine; L(2) = 2-(N-ethyl-2-aminoethyl)-pyridine; L(3) = 3,3'-iminobis(N,N-dimethylpropylamine)], respectively, were synthesized and characterized. Addition of nitric oxide gas to the degassed acetonitrile solution of the complexes were found to result in the reduction of the copper(II) center to copper(I). In cases of complexes 1 and 2, the formation of the [Cu(II)-NO] intermediate prior to the reduction of Cu(II) was evidenced by UV-visible, solution FT-IR and X-band EPR spectroscopic studies. However, for complex 3, the formation of [Cu(II)-NO] has not been observed. DFT calculations on the [Cu(II)-NO] intermediate generated from complex 1 suggest a distorted square pyramidal geometry with the NO ligand coordinated to the Cu(II) center at an equatorial site in a bent geometry. In the case of complex 1, the reduction of the copper(II) center by nitric oxide afforded ligand transformation through diazotization at the primary amine site in acetonitrile solution; whereas, in an acetonitrile-water mixture, it resulted in 2-(pyridine-2-yl)ethanol. On the other hand, in cases of complexes 2 and 3, it was found to yield N-nitrosation at the secondary amine site in the ligand frameworks. The final organic products, in each case, were isolated and characterized by various spectroscopic studies.     

Synthesis of 5-alkylated barbituric acids and 3-alkylated indoles via microwave-assisted three-component reactions in solvent-free conditions using Hantzsch 1,4-dihydropyridines as reducing agents

Reaction of barbituric acids with aldehydes and dihydropyridines in one pot under microwave (MW) irradiation in the absence of solvent, affords 55–82% of the 5-benzylated barbituric acids. Use of alkyl nitriles or barbituric acids with indole-3-aldehyde and dihydropyridine (DHP) afforded 3-alkylated indoles in 57–76 % yield. In each case DHPs are converted to pyridines.     

First example of a Cu(I)-(η2-O,O)nitrite complex derived from Cu(II)-nitrosyl

Copper(II) complex, 1, of the bidentate ligand, L [L = bis(2-ethyl-4-methyl-imidazol-5yl)methane] has been synthesized and structurally characterized. Addition of nitric oxide gas to a degassed acetonitrile solution of 1 yielded the corresponding copper(ii)-nitrosyl complex, 2. In acetonitrile, complex 2 on reaction with water afforded the corresponding copper(I)-nitrite complex, 3. Single crystal structure of complex 3 reveals the bidentate nitrite (η(2)-O,O) bonding. This is the first example of a structurally characterized Cu(I)-(η(2)-O,O)nitrite complex with N-donor ligand. The sequence of the formation of these complexes is just the reverse of the key steps of the postulated nitrite reduction cycle by CuNiRs.     

Charge transfer excitations in cofacial fullerene-porphyrin complexes

Porphyrin and fullerene donor-acceptor complexes have been extensively studied for their photo-induced charge transfer characteristics. We present the electronic structure of ground states and a few charge transfer excited states of four cofacial porphyrin-fullerene molecular constructs studied using density functional theory at the all-electron level using large polarized basis sets. The donors are base and Zn-tetraphenyl porphyrins and the acceptor molecules are C(60) and C(70). The complexes reported here are non-bonded with a face-to-face distance between the porphyrin and the fullerene of 2.7 to 3.0 A?. The energies of the low lying excited states including charge transfer states calculated using our recent excited state method are in good agreement with available experimental values. We find that replacing C(60) by C(70) in a given dyad may increase the lowest charge transfer excitation energy by about 0.27 eV. Variation of donor in these complexes has marginal effect on the lowest charge transfer excitation energy. The interfacial dipole moments and lowest charge transfer states are studied as a function of face-to-face distance.     

A Few Theta-Function Identities and Some of Ramanujan's Modular Equations

We prove three modular equations of Ramanujan using theta-function identities. Proofs via methods known to Ramanujan were not available hitherto. One had previously been proved by classical methods, and two had been proved using the theory of modular forms.     

Silicon-mediated C-isoprenylation of phenols

C-isoprenylation of phenols has been effected using a combination of isoprene and in situ generated iodotrimethylsilane or hydrogen iodide.     

Plasma-maser instability of the ion acoustics wave in the presence of lower hybrid wave turbulence in inhomogeneous plasma

A theoretical study is made on the generation mechanism of ion acoustics wave in the presence of lower hybrid wave turbulence field in inhomogeneous plasma on the basis of plasma-maser interaction. The lower hybrid wave turbulence field is taken as the low-frequency turbulence field. The growth rate of test high frequency ion acoustics wave is obtained with the involvement of spatial density gradient parameter. A comparative study of the role of density gradient for the generation of ion acoustics wave on the basis of plasma-maser effect is presented. It is found that the density gradient influences the growth rate of ion acoustics wave.