Electron localizability indicators ELI–D and ELIA for highly correlated wavefunctions of homonuclear dimers. I. Li2, Be2, B2, and C2

Electron localizability indicators based on the parallel‐spin electron pair density (ELI–D) and the antiparallel‐spin electron pair density (ELIA) are studied for the correlated ground‐state wavefunctions of Li₂, Be₂, B₂, and C₂ diatomic molecules. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations to investigate the local effect of electron correlation on the extent of electron localizability in position space determined by the two functionals. The results are complemented by calculations of effective bond order, vibrational frequency, and Laplacian of the electron density at the bond midpoint. It turns out that for Li₂, B₂, and C₂ the reliable topology of ELI–D is obtained only at the correlated level of theory. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Electron localizability indicators ELI and ELIA: the case of highly correlated wavefunctions for the argon atom

Electron localizability indicators based on the same-spin electron pair density and the opposite-spin electron pair density are studied for correlated wavefunctions of the argon atom. Different basis sets and reference spaces are used for the multireference configuration interaction method following the complete active space calculations aiming at the understanding of the effect of local electron correlation when approaching the exact wavefunction. The populations of the three atomic shells of Ar atom in real space are calculated for each case.     

Electron localizability indicator for correlated wavefunctions. II Antiparallel-spin pairs

The electron localizability indicator for anti parallel-spin pairs is closely associated with the correlation of the motion of opposite-spin electrons. At the Hartree–Fock level this functional is constant throughout the whole space, whereas for correlated wavefunctions structures resembling atomic shells and the bonding situation emerges.     

Electron localizability indicator for correlated wavefunctions. III: singlet and triplet pairs

The electron pair density can be decomposed into the symmetric and antisymmetric parts. The antisymmetric component is connected with the probability that two electrons are coupled to a triplet. On the basis of triplet-coupled electrons the electron localizability indicator is defined, describing the correlation of motion of electrons forming a triplet pair. In case of spin-polarized systems the electron localizability indicator for triplet pairs combines the two spin channels together into a single functional.     

A 3d‐4f Complex Constructed by the Assembly of a Cationic Template, [Cu(en)2]2+, and a 3D Anionic Coordination Polymer, [Sm2(C2O4)3(C5O5)(H2O)2]2–

A three‐dimensional (3D) 3d‐4f complex, [Cu(en)₂][Sm₂(C₅O₅)(C₂O₄)₃(H₂O)₂] · 8H₂O ( 1 ) (en = ethylenediamine, C₅O₅^2– = dianion of 4,5‐dihydroxycyclopent‐4‐ene‐1,2,3‐trione), were prepared via the in‐situ ring‐opening oxidation reaction of croconate in the presence of the template‐directed complex, [Cu(en)₂]²⁺ cation. The structural characterization determined by X‐ray diffraction determination reveals that the 3D anionic coordination polymer of [Sm₂(C₂O₄)₃(C₅O₅)(H₂O)₂]^2– in 1 can be describe in terms of in‐plane 2D honeycomb‐like [Sm₂(C₂O₄)₃] layered frameworks bridged by oxalate with bis‐chelating mode, being mutually interlinked via the bridge of μ_1,2,3,4‐croconate ligands with bis‐chelating coordination mode to complete the 3D open framework, which gives rise to 1D channels with pore size of 14.023 × 11.893 Å (longest atom–atom contact distances) along the b axis. The structure‐directing complex, [Cu(en)₂]²⁺, and solvated water molecules are resided into these honeycomb‐type hexagonal channels. The thermal stability of 1 was further studied by TGA and in‐situ powder X‐ray diffraction measurement.     

Study on Pair Correlation Energies of Isoelectronic Systems F^－, HF and H2F^＋

The intrapair and interpair correlation energies of F-, HF and H2F^ systems are calculated and analyzed using MP2-OPT2 method of MELD program with cc-PVSZ^* basis set. From the analysis of pair correlation energies of these isoelectronlc sysoterns, it is found that the 1sF^2 pair correlation energy is trans-ferable in these three isociectronic systems. According to the definition of pair correlation contribution of one electron pair to a system, the pair correlation contribution values of these three systems are calculated. The correlation contribution values of inner electron pairs and H—F bonding electron pair in HF molecule with those in H2F^ system are compared. The results indicate that the bonding effect of a molecule is one of the im-portant factors to influence electron correlation energy of the system. The comparison of correlation energy contributions in-cluding triple and quadruple excitations with those only includ-ing singles and doubles calculated with 6-311 G(d) basis set shows that the higher.excitation correlation energy contribution gives more than 2 % of the total correlation energy for these sys-tems.     

Crystallographic report: Diazido[bis(2‐pyridyl)amine]zinc(II) hydrate, [Zn(C10H9N3)2(N3)2]·H2O

In mononuclear [Zn(C₁₀H₉N₃)₂(N₃)₂]·H₂O, the zinc atom has an approximate octahedral geometry, coordinated with four pyridyl nitrogen atoms derived from two bis(2‐pyridyl)amine molecules and two terminal nitrogen donors of the azide anions. Hydrogen‐bonding interactions extend this structure to form a double‐layer architecture. Copyright © 2004 John Wiley & Sons, Ltd.     

Ferromagnetic vs. nonmagnetic phases of 2‐D Wigner electron crystal

The ferromagnetic and nonmagnetic phases of 2‐D Wigner electron crystal are investigated using a localized representation for the electrons. The ground‐state energies of ferromagnetic and nonmagnetic phases of 2‐D Wigner electron crystal are computed in the range of r_s = 10–200. The low density favorable for Wigner crystallization is found to be 2.85 × 10¹³ e cm^?2 for ferromagnetic phase and 5.07 × 10¹³ e cm^?2 for the nonmagnetic phase of 2‐D Wigner electron crystal. For the given structure, the ground‐state energies of ferromagnetic and nonmagnetic phases are compared. It is found that the energy of the ferromagnetic phase is less than that of the nonmagnetic phase of the 2‐D Wigner electron crystal. Also, the results are compared with various experimental and theoretical works and it is found that our results are in good agreement with the experimental and other theoretical results for the 2‐D Wigner electron crystal. The structure‐dependent Wannier functions, which give proper localized representation for Wigner electrons, are employed in the calculation. The role of correlation energy is suitably taken into account. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Interpreting 2hJ(F,N), 1hJ(H,N) and 1J(F,H) in the hydrogen‐bonded FH–collidine complex

Ab initio EOM‐CCSD calculations were performed to determine ¹⁹F,¹H, ¹⁹F,¹⁵N and ¹H,¹⁵N spin–spin coupling constants in model complexes FH–NH₃ and FH–pyridine as a function of the F—H and F—N distances. The absolute value of ¹J(F,H) decreases and that of ^1hJ(H,N) increases rapidly along the proton‐transfer coordinate, even in the region of the proton‐shared F—H—N hydrogen bond. In contrast, ^2hJ(F,N) remains essentially constant in this region. These results are consistent with the recently reported experimental NMR spectra of FH–collidine which show that ^1hJ(H,N) increases and ¹J(F,H) decreases, while ^2hJ(F,N) remains constant as the temperature of the solution decreases. They suggest that the FH–collidine complex is stabilized by a proton‐shared hydrogen bond over the range of experimental temperatures investigated, being on the traditional side of quasi‐symmetric at high temperatures, and on the ion‐pair side at low temperatures. Copyright © 2002 John Wiley & Sons, Ltd.     

Change of the favored routes of EI MS fragmentation when proceeding from N1, N1‐dimethyl‐N2‐arylformamidines to 1,1,3,3‐tetraalkyl‐2‐arylguanidines: substituent effects

Although series of N¹, N¹‐dimethyl‐N²‐arylformamidines and of 1,1,3,3‐tetraalkyl‐2‐arylguanidines are structurally analogous and similar electron‐ionization mass spectral fragmentation may be expected, they display important differences in the favored routes of fragmentation and consequently in substituent effects on ion abundances. In the case of formamidines, the cyclization‐elimination process (initiated by nucleophilic attack of the N‐amino atom on the 2‐position of the phenyl ring) and formation of the cyclic benzimidazolium [M‐H]⁺ ions dominates, whereas the loss of the NR₂ group is more favored for guanidines. In order to gain information on the most probable structures of the principal fragments, quantum‐chemical calculations were performed on a selected set. A good linear relation between log{I[M‐H]⁺I [M]^+?} and σ_R⁺ constants of substituent at para position in the phenyl ring occurs solely for formamidines (r = 0.989). In the case of guanidines, this relation is not significant (r = 0.659). A good linear relation is found between log{I[M‐NMe₂]⁺/I [M]^+?} and σ_p⁺ constants (r = 0.993). Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of 11C, 18F, 15O, and 13N radiolabels for positron emission tomography

Positron emission tomography (PET) is a powerful and rapidly developing area of molecular imaging that is used to study and visualize human physiology by the detection of positron-emitting radiopharmaceuticals. Information about metabolism, receptor/enzyme function, and biochemical mechanisms in living tissue can be obtained directly from PET experiments. Unlike magnetic resonance imaging (MRI) or computerized tomography (CT), which mainly provide detailed anatomical images, PET can measure chemical changes that occur before macroscopic anatomical signs of a disease are observed. PET is emerging as a revolutionary method for measuring body function and tailoring disease treatment in living subjects. The development of synthetic strategies for the synthesis of new positron-emitting molecules is, however, not trivial. This Review highlights key aspects of the synthesis of PET radiotracers with the short-lived positron-emitting radionuclides (11)C, (18)F, (15)O, and (13)N, with emphasis on the most recent strategies.     

Natural bond orbital‐based energy density analysis for correlated methods: Second‐order Møller–Plesset perturbation and coupled‐cluster singles and doubles

Natural bond orbital‐based energy density analysis (NBO‐EDA), which split energies into atomic and bonding contributions, is proposed for correlated methods such as coupled‐cluster singles and doubles (CCSD) and second‐order Møller–Plesset (MP2) perturbation. Applying NBO‐EDA for CCSD and MP2 to ethylene and the Diels–Alder reaction, we are successful in obtaining useful knowledge regarding electron correlation of π‐ and σ‐type orbitals, and clarifying the difference of the reaction barriers and heat of reaction calculated by CCSD and MP2. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

A simple and efficient 2N2O–Cu(II) complex as a catalyst for N‐arylation of imidazoles in water

Four inexpensive and air‐ and moisture‐stable 2N2O–Cu complexes were synthesized, one of which proved to exhibit good catalytic activity for the N‐arylation of imidazoles in water. A variety of aryl iodides and aryl bromides underwent coupling with imidazoles promoted by the catalytic system with moderate to excellent yields. Copyright © 2015 John Wiley & Sons, Ltd.