Theoretical study of the substituent effects of the equatorial ligands on penta-coordinated trigonal bipyramidal compounds.(Natural Sciences)

論文(Article)We have studied the substituent effect of equatorial ligands of some penta-coordinated trigonal bipyramidal compounds (MX_3Y_2: M=N, P and As; X=H, F, CH_3 and CN; Y=H and F) by using the ab initio molecular orbital method. We divided the whole molecule into two parts i.e. the equatorial part and the apical part, and discussed the stabilization of apical orbitals by drawing the orbital energy correlation diagram. The apical bond stabilization energy is considerably affected through the change of the symmetric apical orbital interaction for fluorine compounds. The substituent effect on HOMO of the equatorial part comes from the antibonding σ-donating interaction between ligand orbital and the lone-pair orbital of the central atom, while LUMO is affected through the σ-type attractive interaction between ligand and ndz^2 orbital of the central atom. The strong substituent effect on LUMO is induced by F through the σ-type interaction. On the other hand π-type effect on HOMO becomes important when CH_3 is introduced to the equatorial part. As the number of CN increases, the antibonding π-type interaction between ligands and the central atom decreases and HOMO of the equatorial part is stabilized. The energy gaps between HOMO and LUMO of nitrogenous compounds are much wider than those of phosphorous and arsenious compounds.departmental bulletin pape

分子軌道法計算プログラムGaussian 03 - その7 -

2007-11departmental bulletin pape

分子軌道法計算プログラムGaussian 03 ―その10―

2008-08-29departmental bulletin pape

The Institutional Presidency from a Comparative Perspective: Argentina and Brazil since the 1980s

This paper focuses on the evolution of the institutional presidency - meaning the cluster of agencies that directly support the chief of the executive - in Argentina and Brazil since their redemocratization in the 1980s. It investigates what explains the changes that have come about regarding the size of the institutional presidency and the types of agency that form it. Following the specialized literature, we argue that the growth of the institutional presidency is connected to developments occurring in the larger political system - that is, to the political challenges that the various presidents of the two countries have faced. Presidents adjust the format and mandate of the different agencies under their authority so as to better manage their relations with the political environment. In particular, we argue that the type of government (coalition or single-party) has had consequences for the structure of the presidency or, in other words, that different cabinet structures pose different challenges to presidents. This factor has not played a significant role in presidency-related studies until now, which have hitherto mostly been based on the case of the United States. Our empirical references, the presidencies of Argentina and Brazil, typical cases of coalitional as well as single-party presidentialism respectively allow us to show the impact of the type of government on the number and type of presidential agencies

X-ray molecular orbital analysis. II. Application to diformohydrazide, (NHCHO)₂

The molecular orbitals (MOs) of diformohydrazide have been determined from the electron density measured by X-ray diffraction. The experimental and refinement procedures are explained in detail and the validity of the obtained MOs is assessed from the crystallographic point of view. The X-ray structure factors were measured at 100 K by a four-circle diffractometer avoiding multiple diffraction, the effect of which on the structure factors is comparable to two-centre structure factors. There remained no significant peaks on the residual density map and the R factors reduced significantly. Among the 788 MO coefficients, 731 converged, of which 694 were statistically significant. The C—H and N—H bond distances are 1.032 (2) and 1.033 (3) Å, respectively. The electron densities of theoretical and experimental MOs and the differences between them are illustrated. The overall features of the electron density obtained by X-ray molecular orbital (XMO) analysis are in good agreement with the canonical orbitals calculated by the restricted Hartree Fock (RHF) method. The bonding-electron distribution around the middle of each bond is well represented and the relative phase relationships of the π orbitals are reflected clearly in the electron densities on the plane perpendicular to the molecular plane. However, differences are noticeable around the O atom on the molecular plane. The orbital energies obtained by XMO analysis are about 0.3 a.u. higher than the corresponding canonical orbitals, except for MO10 to MO14 which are about 0.7 a.u. higher. These exceptions are attributed to the N—H...O′′ intermolecular hydrogen bond, which is neglected in the MO models of the present study. The hydrogen bond is supported by significant electron densities at the saddle points between the H(N) and O′′ atoms in MO7, 8, 14 and 17, and by that of O′′-p extended over H(N) in MO21 and 22, while no peaks were found in MO10, 11, 13 and 15. The electron density of each MO clearly exhibits its role in the molecule. Consequently, the MOs obtained by XMO analysis give a fundamental quantum mechanical insight into the real properties of molecules.</jats:p

Ab Initio Study of Proton Affinities of Three Crown Ethers

Ab initio calculations of 12-crown-4, 15-crown-5, and 18-crown-6 and their protonated species have been performed. As a reference molecule, 1-(2‘-methoxy)ethoxy-2-methoxyethane (glyme-2) is also examined. Three protonated crown ethers are found to have quite similar moieties to that of glyme-2H+. The ring strain due to formation of intramolecular hydrogen bonds is a measure of proton affinity (PA) values. The present computational result supports Meot-Ner's and Kebarle's PA values of 12-crown-4. Those of 15-crown-5 and 18-crown-6 reported by Kebarle were very close to the present theoretical values

Preparation, Characterization, and Reactivity of Dinitrogen Molybdenum Complexes with Bis(diphenylphosphino)amine Derivative Ligands that Form a Unique 4‑Membered P–N–P Chelate Ring

Five dinitrogen–molybdenum complexes bearing bis­(diphenylphosphino)­amine derivative ligands (LR) that form a unique 4-membered P–N–P chelate ring, trans-[Mo­(N2)2(LR)2] (2R: R = Ph, Xy, p-MeOPh, 3,5-iPr2Ph, iPr), were prepared for the purpose of binding a dinitrogen molecule. The corresponding two dichloride-molybdenum complexes, trans-[MoCl2(LR)2] (1R: R = Ph, Xy), were also prepared as comparisons. FT-IR spectra of 2R were measured and compared the ν­(NN) values. Moreover, X-ray crystal structure determination of 1R (R = Ph, Xy) and 2R (R = Xy, 3,5-iPr2Ph) is performed. These experimental results indicated that the coordinated dinitrogen molecule gets easily influenced by the N-substitutent of diphosphinoamine ligand. In addition, to investigate the effect of the properties of the diphosphinoamine ligand for the dinitrogen molybdenum complexes, we performed DFT calculations that focused on the difference of N-substituent, the dihedral angle between P–N–P plane and N-substituent aryl group, and the P–N–P bite angle. This calculation revealed that the competition between the back-donation from metal to dinitrogen and that from metal to ligand was affected by P–N–P bite angle and the dihedral angle of N-substituent of ligand. In order to examine the reactivity with respect to conversion of dinitrogen to ammonia, protonation and trimethylsilylation reactions of the coordinated dinitrogens were carried out for 2R