The interpretation of the crystal field parameters for f-electron systems by the angular overlap model. The rare-earth hydroxides

The crystal field parameters of some rare-earth hydroxide systems are interpreted by the angular overlap model, where σ- and π-bonding has been considered.     

PHI: A powerful new program for the analysis of anisotropic monomeric and exchange‐coupled polynuclear d‐ and f‐block complexes

A new program, PHI, with the ability to calculate the magnetic properties of large spin systems and complex orbitally degenerate systems, such as clusters of d‐block and f‐block ions, is presented. The program can intuitively fit experimental data from multiple sources, such as magnetic and spectroscopic data, simultaneously. PHI is extensively parallelized and can operate under the symmetric multiprocessing, single process multiple data, or GPU paradigms using a threaded, MPI or GPU model, respectively. For a given problem PHI is been shown to be almost 12 times faster than the well‐known program MAGPACK, limited only by available hardware. © 2013 Wiley Periodicals, Inc.     

Facile Synthesis Method for the Preparation of Large‐scale Ultra‐small GdPO4:Tb and GdPO4:Tb@LaPO4 Nanowires

A simple and efficient method is presented for the large‐scale synthesis of ultra‐small, wired‐shaped GdPO₄:Tb nanostructured phosphor material with an average diameter of 2–5 nm and typical average length of 100 nm. X‐ray diffraction (X RD), transmission electron microscopy (TEM), energy dispersive X‐ray (EDX) analysis, as well as FTIR, UV–vis, emission, and excitation spectral techniques were employed to examine the crystal phase, purity, morphology, surface chemistry, and optical and photoluminescence properties of the as‐prepared nanoproducts. The TEM image clearly revealed the single‐phase, highly crystalline, narrow‐size‐distributed, ultra‐small, wire‐shaped nanostructures, which was confirmed from the XRD pattern. Optical absorption spectra in the ultraviolet region show high absorbance because of the high solubility and colloidal stability in aqueous solvents. Surface coating of an undoped LaPO₄ shell remarkably enhanced the crystallinity and photoluminescence properties of the nanowires (NWs). Core/shell NWs represent high emission and excitation intensity regardless of the core NWs because of a decrease in multiphoton relaxation pathways. It could be a highly suitable nanomaterial for optical bioprobes, biodetectors, and so on.     

The interpretation of the crystal field parameters for fn-electron systems by the angular overlap model. Rare-earth ions in LaCl3

The crystal field parameters of trivalent rare-earth ions subsituted in LaCl₃ are interpreted by the angular overlap model, where σ and π-bonding has been considered.     

Study of influence of additives of tyloxapol on the chromatographic characteristics of the model compounds: the comparative characterization of micellar mobile phases of tyloxapol and Triton X‐100

The chromatographic behavior of model compounds of biomedical significance (organic acids, amino acids, drugs) was investigated using mobile phases modified with tyloxapol. The influence of factors such as concentration of tyloxapol, content of organic modifier and pH of mobile phase on the retention factor of solutes was studied. The results were compared with the data obtained by elution with mobile phases containing Triton X‐100 additives, since units of Triton X‐100 are repeated in the structure of tyloxapol. Divergence in chromatographic behavior of model compounds was explained by the difference in physico‐chemical characteristics (microviscosity, polarity, critical micelle concentration, shape of micelles, etc.) of tyloxapol and Triton X‐100 micelles. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of a genomic model for high‐dimensional chemometric analysis

The rapid development of new technologies for large‐scale analysis of genetic variation in the genomes of individuals and populations has presented statistical geneticists with a grand challenge to develop efficient methods for identifying the small proportion of all identified genetic polymorphisms that have effects on traits of interest. To address such a “large p small n” problem, we have developed a heteroscedastic effects model (HEM) that has been shown to be powerful in high‐throughput genetic analyses. Here, we describe how this whole‐genome model can also be utilized in chemometric analysis. As a proof of concept, we use HEM to predict analyte concentrations in silage using Fourier transform infrared spectroscopy signals. The results show that HEM often outperforms the classic methods and in addition to this presents a substantial computational advantage in the analyses of such high‐dimensional data. The results thus show the value of taking an interdisciplinary approach to chemometric analysis and indicate that large‐scale genomic models can be a promising new approach for chemometric analysis that deserve to be evaluated more by experts in the field. The software used for our analyses is freely available as an R package at http://cran.r‐project.org/web/packages/bigRR/ . Copyright © 2014 John Wiley & Sons, Ltd.     

Self‐consistent field for fragmented quantum mechanical model of large molecular systems

Fragment‐based linear scaling quantum chemistry methods are a promising tool for the accurate simulation of chemical and biomolecular systems. Because of the coupled inter‐fragment electrostatic interactions, a dual‐layer iterative scheme is often employed to compute the fragment electronic structure and the total energy. In the dual‐layer scheme, the self‐consistent field (SCF) of the electronic structure of a fragment must be solved first, then followed by the updating of the inter‐fragment electrostatic interactions. The two steps are sequentially carried out and repeated; as such a significant total number of fragment SCF iterations is required to converge the total energy and becomes the computational bottleneck in many fragment quantum chemistry methods. To reduce the number of fragment SCF iterations and speed up the convergence of the total energy, we develop here a new SCF scheme in which the inter‐fragment interactions can be updated concurrently without converging the fragment electronic structure. By constructing the global, block‐wise Fock matrix and density matrix, we prove that the commutation between the two global matrices guarantees the commutation of the corresponding matrices in each fragment. Therefore, many highly efficient numerical techniques such as the direct inversion of the iterative subspace method can be employed to converge simultaneously the electronic structure of all fragments, reducing significantly the computational cost. Numerical examples for water clusters of different sizes suggest that the method shall be very useful in improving the scalability of fragment quantum chemistry methods. © 2015 Wiley Periodicals, Inc.     

On the calculation of arbitrary multielectron molecular integrals over Slater‐type orbitals using recurrence relations for overlap integrals I. Single‐center expansion method

The multicenter charge‐density expansion coefficients [I. I. Guseinov, J Mol Struct (Theochem) 417 , 117 (1997)] appearing in the molecular integrals with an arbitrary multielectron operator were calculated for extremely large quantum numbers of Slater‐type orbitals (STOs). As an example, using computer programs written for these coefficients, with the help of single‐center expansion method, some of two‐electron two‐center Coulomb and four‐center exchange electron repulsion integrals of Hartree–Fock–Roothaan (HFR) equations for molecules were also calculated. Accuracy of the results is quite high for the quantum numbers, screening constants, and location of STOs. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 146–152, 2000     

Syntheses,Structures, and Properties of the Complexes [Ag(N∧S)n](X), N∧S = 1‐Methyl‐2‐(alkylthiomethyl)‐1H‐benzimidazoles,X = PF6 (n = 2) or PO2F2 (n = 1)

The complexes [Ag(η²‐N∧S)₂](PF₆), N∧S = 1‐methyl‐2‐(methylthiomethyl)‐1H‐benzimidazole, mmb (complex 1 ) or 1‐methyl‐2‐(tert‐butylthiomethyl)‐1H‐benzimidazole, mtb (complex 2 ), and [Ag(μ,η²‐mmb)(μ,η²‐O₂PF₂)] (complex 3 ) were synthesized and characterized by X‐ray crystallography. Long Ag–S (ca. 2.70 Å) and shorter Ag–N bonds (ca. 2.23 Å) are part of characteristically distorted tetrahedral coordination arrangements at the silver(I) ions in 1 and 2 . Unexpectedly, the comparison with the copper analogue [Cu(η²‐mmb)₂](PF₆) reveals a more tetrahedral and less linear coordination arrangement for the corresponding silver species. Compound 3 as obtained by hydrolysis of the PF₆ ion or by the use of AgPO₂F₂ exhibits bridging mmb and η²‐difluorophosphate ligands in a chain‐type structure.     

1H NMR analysis of O‐methyl‐inositol isomers: a joint experimental and theoretical study

Density functional theory (DFT) calculations of ¹H NMR chemical shifts for l ‐quebrachitol isomers were performed using the B3LYP functional employing the 6‐31G(d,p) and 6‐311 + G(2d,p) basis sets. The effect of the solvent on the B3LYP‐calculated NMR spectrum was accounted for using the polarizable continuum model. Comparison is made with experimental ¹H NMR spectroscopic data, which shed light on the average uncertainty present in DFT calculations of chemical shifts and showed that the best match between experimental and theoretical B3LYP ¹H NMR profiles is a good strategy to assign the molecular structure present in the sample handled in the experimental measurements. Among four plausible O‐methyl‐inositol isomers, the l ‐quebrachitol 2a structure was unambiguously assigned based only on the comparative analysis of experimental and theoretical ¹H NMR chemical shift data. The B3LYP infrared (IR) spectrum was also calculated for the four isomers and compared with the experimental data, with analysis of the theoretical IR profiles corroborating assignment of the 2a structure. Therefore, it is confirmed in this study that a combined experimental/DFT spectroscopic investigation is a powerful tool in structural/conformational analysis studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Revisiting the Fundamental Nature of Metal-Ligand Bonding: An Impartial and Automated Fitting Procedure for Angular Overlap Model Parameters

The properties and reactivities of transition metal complexes are often discussed in terms of Ligand Field Theory (LFT), and with ab initio LFT a direct connection to quantum chemical wavefunctions was recently established. The Angular Overlap Model (AOM) is a widely used, ligand-specific parameterization scheme of the ligand field splitting that has, however, been restricted by the availability and resolution of experimental data. Using ab initio LFT, we present here a generalised, symmetry-independent and automated fitting procedure for AOM parameters that is even applicable to formally underdetermined or experimentally inaccessible systems. This method allows quantitative evaluations of assumptions commonly made in AOM applications, for example, transferability or the relative magnitudes of AOM parameters, and the response of the ligand field to structural or electronic changes. A two-dimensional spectrochemical series of tetrahedral halido metalates ([M^IIX₄]²⁻, M=Mn−Cu) served as a case study. A previously unknown linear relationship between the halide ligands’ chemical hardness and their AOM parameters was found. The impartial and automated procedure for identifying AOM parameters introduced here can be used to systematically improve our understanding of ligand–metal interactions in coordination complexes.     

On the calculation of arbitrary multielectron molecular integrals over Slater‐type orbitals using recurrence relations for overlap integrals. II. Two‐center expansion method

Using expansion formulas for the charge‐density over Slater‐type orbitals (STOs) obtained by the one of authors [I. I. Guseinov, J Mol Struct (Theochem) 1997, 417, 117] the multicenter molecular integrals with an arbitrary multielectron operator are expressed in terms of the overlap integrals with the same screening parameters of STOs and the basic multielectron two‐center Coulomb or hybrid integrals with the same operator. In the special case of two‐electron electron‐repulsion operator appearing in the Hartree–Fock–Roothaan (HFR) equations for molecules the new auxiliary functions are introduced by means of which basic two‐center Coulomb and hybrid integrals are expressed. Using recurrence relations for auxiliary functions the multicenter electron‐repulsion integrals are calculated for extremely large quantum numbers. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 117–125, 2001     

Similar Coordination – Different Dimensionality: Synthesis,Single Crystal Structures,and Theoretical Studies of Hydrogen‐bonded {[Ca(H2O)2L4]I2}n/∞ (1: L = CH3COOC2H5, n = 1; 2: L = OC4H8, n = 2)

CaI₂(H₂O)₂ reacts with O‐donor ligands L to yield coordination compounds of the type {[Ca(H₂O)₂L₄]I₂}_n/∞, ( 1 : L = CH₃COOC₂H₅, n = 1; 2 : L = THF, n = 2). Both compounds feature a coordination number of six around the calcium atom with two water molecules in axial positions and four ligands L in equatorial positions of a tetragonal bipyramid. Due to only a slight variation in the arrangement of the cationic units [Ca(H₂O)₂L₄]²⁺, hydrogen bonds can be built up between them and the iodide anions in different ways in order to lead to a one‐dimensional polymer for 1 and a two‐dimensional polymer for 2 . Density functional theory calculations provide useful informations on the involved orbitals on the μ₂‐bridging iodide and on the structure of the systems, leading to a small H–I–H angle of 71.2° in 1 compared to a large H–I–H angle of 121.8° in 2 .     

Nature of the near‐IR band in the electronic absorption spectra of neutral bis(tetrapyrrole) rare earth(III) complexes: Time‐dependent density functional theory calculations

The nature of the near‐IR band in the electronic absorption spectra of bis(tetrapyrrole) rare earth(III) complexes Y(Pc)₂ (1), La(Pc)₂ (2), Y(Pc)(Por) (3), Y(Pc)[Pc(α‐OCH₃)₄] (4), Y(Pc)[Pc(α‐OCH₃)₈] (5), and Y(Pc)[Pc(β‐OCH₃)₈] (6) was studied on the basis of time‐dependent density functional theory (TD‐DFT) calculations. The electronic dipole moment along the z‐axis in the electronic transition of the near‐IR band in all the studied neutral bis(tetrapyrrole) yttrium(III) and lanthanum(III) double‐deckers is well explained on the basis of the composition analysis of the orbitals involved. The electronic transition in the near‐IR band causes the reversion of the orbital orientation of one tetrapyrrole ring in both homoleptic and heteroleptic bis(tetrapyrrole) rare earth complexes and induces electron transfer from the tetrapyrrole ring with lower orbital energy to the other ring in the heteroleptic bis(tetrapyrrole) rare earth(III) complexes. The near‐IR band can work as an ideal characteristic absorption band to reflect the π–π interaction between the two tetrapyrrole rings in bis(tetrapyrrole) rare earth(III) double‐decker complexes because of its peculiar electronic transition nature. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010