Molecular orbital description of the ligand-field spectra of some tetrahalogeno anions

A MO-based model [1] has been used to describe the ligand-field spectra of the tetrahedral ions MX₄ ^2- (M = Ni, Co, Fe, Mn and X = Cl, Br, I). Independent assignments of the ligand-field spectra of the latter ions are obtained from published work [1–8]. The energies of the spin-orbit baricentres of the ligand-field transitions are calculated as functions of two orbital population parameters and the energy separations between the e and t ₂ MO's. From the least-squares analysis of the independently assigned experimental spectra, empirical values of these three parameters are extracted.     

The origins of tetrahedral coordination in molten and glassy ZnCl2 and other group-2B metal dihalides

We report the results of first-principles calculations carried out within a relativistic density-functional method, on the molecular trimers of the MX₂ compounds (with M = Zn or Cd and X = Cl, Br, or I), showing how a distorted tetrahedral coordination of a group-2B metal atom by halogens first arises. The trimers of HgX₂ are also discussed, both in unstable and in stable configurations.     

Hydrogen bonding involved with superhalogen MX2NY: its influence on the structure and stability of the superhalogen

The hydrogen-bonded complexes formed of superhalogen MX₂NY (M?=?Li, Na; N?=?Be, Mg; X, Y?=?F, Cl, Br) and hydrogen fluoride have been investigated with quantum chemical calculations at the MP2/aug-cc-pVDZ and M06-2X/aug-cc-pVDZ levels of theory. It was shown that the M06-2X method presents similar results with the MP2 method. The strength of hydrogen bonding is related with the nature of metal and halogen atoms. The metal with greater electron-donating ability leads to a stronger hydrogen bond, whereas the halogen with bigger electron-withdrawing ability also results in the stronger hydrogen bond. The presence of hydrogen bond has a small effect on the structures of the superhalogen and contributes to the stability of the superhalogen.     

Positron annihilation from excited states of [X-e+] systems

The relative probabilities for the radiative de-excitation 2p₊ → ls₊ versus 2γ-annihilation for the hdot; ns²np⁶2p₊, ²P state of the [X^-e⁺] system with X = F, Cl, Br, and I are presented. It is shown that a positron captured into a 2p₊ orbital undergoes annihilation with electrons of the system instead of radiative transition to the ground state of the [X^-e⁺] system.     

Photoelectron spectra of fluorotribromomethane and fluorotrichloromethane

High resolution He(I) photoelectron spectra are reported for fluorotribromomethane CFBr₃ and fluorotrichloromethane CFCl₃. The assignments are based on CNDO/2 calculations, symmetry arguments, the fine structures of the bands, and comparison with the photoelectron spectra of related compounds. Linear relationships have been found between the Pauling electronegativity values for the halogen atoms and the observed vertical ionization energies corresponding to a₂ of a₂′ orbitals of CFX₃ and related compounds CHX₃, OPX₃, BX₃ and PX₃ (X = F, Cl, Br, I).     

Ultraviolet photoelectron spectra of gas phase and condensed tin and lead dihalides (MX2 ; M = Sn,Pb; X = Cl,Br, I)

The photoelectron spectra and electronic structures of the methylene dihalides, CH₂X₂ (X = F, Cl, Br and I), have been calculated by the overtapping-spheres SCF-Xα-MS method. The results are in good agreement with experimental data. Calculated assignments of the spectra are also presented and interpreted by assuming interaction between lone-pair and bonding orbitals.     

The photoelectron spectrum and valence shell structure of (CuX) 3 and (AgCl) 3

Gas-phase He(I) and He(II) spectra have been obtained of CuX and AgCl, where X = Cl, Br, and I. Spectra have been interpreted in terms of a cyclic trimer and shown to be markedly similar to those of the molecules in the solid state. Frequency-dependence of band intensity has been used to deduce the contribution of Cu 3 d and X valence p orbitals to molecular orbitals associated with the various regions of the spectrum.     

The Vibrational Spectra of Complexes with Planar Monothiooxamides. IV. The Copper(II) and Copper(I) Complexes of Neutral Monothiooxamides

The new complexes CuX₂(LH₂), CuX₂ (SH₃) (X = Cl, Br), CuX(LH₂), CuX(SH₃) (X = Cl, Br, I), CuX(H₄MTO)₂ (X = Cl, Br), Cul(H₄MTO) and CuX(H₃MMTO)₂ (X = Cl, Br, I), where LH₂ = N.N′-dimethyl-monothiooxamide, SH₃ = N(s)-methylmonothiooxamide, H₄MTO = monothiooxamide and H₃MMTO = N_(o)-methylmonothiooxamide, have been prepared. The complexes were characterized by elemental analyses, conductivity measurements, magnetic moments and spectroscopic (UV/VIS, FT-IR, Laser-Raman) studies. The vibrational analysis of the complexes has been given using NH/ND, CH₃/CD₃ and ⁶³cu/⁶⁵cu isotopic substitutions. The neutral monothiooxamides behave as monodentate ligands in the Cu(I) complexes coordinating through their thioamide sulfur atom. The ligands LH2 and SH₃ act as bidentate chelating agents in the Cu(II) complexes with ligated atoms being the thioamide sulfur and the amide oxygen.     

Regium bonds formed by MX (M═Cu,Ag, Au; X═F,Cl, Br) with phosphine-oxide/phosphinous acid: comparisons between oxygen-shared and phosphine-shared complexes

ABSTRACT

Regium bonds interaction between phosphine oxide (H₃PO), the trans phosphinuous acid (T-PH₂OH), the cis phosphinuous acid (C-PH₂OH) and MX (M═Cu, Ag, Au; X═F, Cl, Br) complexes were investigated by means of ab initio MP2/aug-cc-pVTZ method. For phosphinuous acid and MX complexes, two types of regium bonded interaction (trans and cis complexes) are observed and the two types of structures are very easily transformed from one type to another due to a low energy barrier. The molecular interaction energies are in the order of Au?>?Cu?>?Ag, F?>?Cl?>?Br and increase with the decrease of intermolecular distance R_int. Two resonance-type structures of P:M-X (ωI) ? P–M:X (ωII), O:M-X (ωI) ? O–M:X (ωII) are recognised by the natural resonance theory (NRT) and the natural bond orbitals (NBOs) analysis. The competition between ωI ? ωII resonance structures mainly arises from hyperconjugation interactions, in all phosphor-shared complexes, P–M:X resonance accounts for a larger proportion which leads to the covalent characters. All of complexes have been described in terms of their electron density properties.     

Halogen bond between hypervalent halogens YF3/YF5 (Y=Cl,Br, I) and H2X (X= O,S, Se)

ABSTRACT

The complexes of H₂X (X?=?O, S, Se) with hypervalent halogens YF₃ and YF₅ (Y?=?Cl, Br, I) have been studied. The σ-hole on the Y atom participates in a halogen bond with the lone pair on the chalcogen atom. In addition, some secondary interactions coexist with the halogen bond in most complexes. The interaction energy correlates with the nature of both X and Y atoms. In most cases, the complex is more stable for the heavier Y atom and the lighter X atom. Of course, there are some exceptions in H₂X···YF₃. YF₃ forms a more stable complex with H₂X than does YF₅. These complexes are dominated by electrostatic interaction and the halogen bond involving H₂S and H₂Se exhibits some covalent character.

Halogen bond plays an important role in chemical reactions and multivalent halogens can regulate chemical reactions by participating in a halogen bond. Thus we compare the effect of the chalcogen electron donor on the strength and nature of halogen bonding involving multivalent halogens.     

99Ru Mössbauer spectroscopic study on salts of ruthenocene with halogens

⁹⁹Ru Mössbauer spectra at 5 K have been measured on samples of salts of ruthenocene with halogens, expressed as [Ru(C₅H₅)₂X]Y (X=Cl, Br, Y=PF₆, and X=1, Y=13). The values of both the isomer shift and the quadrupole splitting of these salts with halogens are larger compared to those of ruthenocene. It is concluded that ruthenocene gives salts having direct chemical bonding between Ru and Cl, Br, or I, and that the Ru atom in each salt is in a higher oxidation state than 2+ in ruthenocene.     

Electron paramagnetic resonance and spin-lattice relaxation in two-dimensional systems

The anisotropies of the EPR linewidth andg-factor were investigated in two-dimensional molecular composites of the type [NH₃?R?NH₃]MX₄. Measurements were performed both in single crystals and powders over the temperature range 4.2–290 K. The spin-lattice relaxation timeT ₁ was measured using the modulation method, as a function of temperature. The samples exhibit different structures and coupling interactions, according to the nature of the halogen X, the metal M and the organic radical R. We have analysed the influence of these parameters on spin behavior by studying the samples [NH₃?(CH) _n ?NH₃]MX₄ with M=Mn, Cu; X=Cl, Br, andn=2, 3, 4, 5. When R is constituted by molecules with unsaturated bonds, these materials can be considered as excellent matrices for selective polymerisation reactions by irradiation or thermal processing. We have performed EPR measurements on the heated complex of propargylamine and cadmium chloride [HC∈C?CH₂?NH₃]₂CdCl₄. The obtained data are interpreted taking into account the strong exchange interaction and the various coupling interactions in the samples. The thermal dependences ofT ₁ are explained by means of the Bloembergen and Wang three-reservoir model. The data whow spin diffusion when the metal is manganese, and an antisymmetric exchange interaction modulated by phonons in the case of copper. The nature of the halogen plays an important role in spin dynamics and namely in spin-lattice relaxation. The results obtained on [HC∈C?CH₂?NH₃]₂CdCl₄ after heating under vaccum show the creation of many paramagnetic centers due to the vanishing of triple bonds and the occurrence of a strong exchange interaction.     

Strain effects on phase transitions in transition metal dichalcogenides

We perform density functional theory calculation to investigate the structural and electronic properties of various two-dimensional transition metal dichalcogenides, MX₂ (M=Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, or W, and X=S or Se), and their strain-induced phase transitions. We evaluate the relative stability and the activation barrier between the octahedral-T and the trigonal-H phases of each MX₂. It is found that the equilibrium and phase transition characteristics of MX₂ can be classified by the group to which its metal element M belongs in the periodic table. MX₂ with M in the group 4 (Ti, Zr, or Hf), forms an octahedral-T phase, while that with an M in the group 6 (Cr, Mo, or W) does a trigonal-H phase. On the other hand, MX₂ with M in the group 5 (V, Nb, or Ta), which is in-between the groups 4 and 6, may form either phase with a similar stability. It is also found that their electronic structures are strongly correlated to the structural configurations: mostly metallic in the T phase, while semiconducting in the H phase, although there are some exceptions. We also explore the effects of an applied stress and find for some MX₂ materials that the resultant strain, either tensile or compressive, may induce a structural phase transition by reducing the transition energy barrier, which is, in some cases, accompanied by its metal-insulator transition.     

一类金属卤化物中孤对电子立体化学活性 及其对双折射率的影响机制研究

双折射材料广泛应用在激光通讯等工程和研究领域。本文使用第一性原理方法研究了后过渡金属卤化物PbX2和BiX3(X=Cl, Br, I)的电子结构与双折射率。计算结果表明,PbX2和BiX3(X=Cl,Br,I)中阳离子孤对电子立体化学程度自X=Cl至X=I逐渐减弱。原子轨道计算分析表明M s-X p (M为阳离子,X为卤素)轨道能级差值决定阳离子孤对电子立体化学活性程度;能级差值越大,孤对电子立体化学活性程度越弱。费米面附M p轨道极大影响材料双折射率的大小,因而使得这些材料的双折射率从X=Cl至X=I逐渐增强。     

Fourier Transform Infrared and Raman Spectra of Metal Halide Complexes of 3,5-Lutedine in Relation to Their Structures

Abstract

Fourier transform infrared (4000-200 cm¹) and Raman (3500-50 cm^?1) spectra are reported for metal(II) halide 3,5-lutidine (3,5-dimethylpyridine) complexes of the following stoichiometries: M(3,5L)₄X₂ M=Co or Ni, X=C1 or Br; M=Mn or Cu, X=Br; M=Cd, X=I; M(3,5L)₃X₂ M=Fe, X=C1; M=Cu, X=Br; Hg(3,5L) X₂ X=C1 or Br.

Vibrational assignments are given for all the observed bands. Some structure- spectra correlations are found. For a given series of isomorphous complexes the sum of the difference between the liquid and ligand values of the vibrational modes of 3,5-lutidine is found to increase in the order of the second ionization potentials of the metals. The frequency shifts are also found to depend on the halogen.     

A comparative study of model halogen-bonded, π-hole-bonded and cationic complexes involving NCX AND H2O (X = F,Cl, Br)

A MP2/6-311+ +G(d,p) study of NCX (X = F, Cl, Br) has shown that it is possible to attach an electrophile (H⁺, Be²⁺) to the positive halogen X surface of NCX. The stability and properties of model halogen-bonded and π-hole carbon-bonded NCX/H₂O complexes were found to be significantly affected by H⁺ or Be²⁺ cationic attachment at the N atom. The halogen-bonded complexes are destabilised by binding at the N, while an attached proton enhances the binding in the π-hole bonded dimers. For the attached Be²⁺, an unusual complex was obtained with the NCF subunit, whereas the complexes containing Cl and Br were destabilised by the interaction.     

The vapor phase Raman spectra,Raman band contour analyses,Coriolis constants,force constants,and values for thermodynamic functions of the trihalides of group V

The vapor phase Raman spectra have been recorded of the molecules PX₃ (X = F, Cl, or Br), AsX₃ (X = F, Cl, Br, or I), and SbX₃ (X = Cl, Br, or I) in sealed tubes at 22–365°C as appropriate. Attempts to record the vapor phase Raman spectra of the molecules PI₃, SbF₃, and BiX₃ (X = F, Cl, Br, or I) were unsuccessful. The infrared and Raman rotational branch separations of the a₁ species fundamentals for these molecules are in agreement with the theoretically calculated values. The Raman band contours of the e-species fundamentals have been analyzed to yield, in favorable cases, values for the corresponding Coriolis constants which have been compared with those obtained from infrared band contour analyses, and which have been employed to constrain the e-species force constants. It is concluded that the Raman contour method for defining Coriolis and thus force constants should be regarded as further, but not necessarily the best, experimental method with which to help to constrain the field. Values for various thermodynamic functions of the molecules have been calculated from the new values for the fundamental frequencies and from the most recent structural data.     

Orbital contributions to relativistic corrections of the NMR nuclear magnetic shielding tensor originated in scalar field-dependent operators

In this work relativistic corrections to the magnetic shielding constant (σM), which arise from scalar field-dependent operators (both linear and bilinear), are calculated and decomposed into contributions from molecular orbitals (MOs). Numerical results for the magnetic shielding constant of the heavy nucleus X in closed shell atomic ions X^? and HX compounds (X = F, Cl, Br, I) are presented. The relative importance of inner-shell and valence electrons in the definition of each one of these terms is thus assessed and its relation with their sensitivity to changes in a chemical environment is discussed.     

The Vibrational Spectra of Complexes with Planar Monothiooxamides. III. The Palladium(II) Complexes of Neutral Monothiooxamides

The new complexes trans-[PdX₂(H₄MTO)2] (X = Cl, Br, I), trans-[PdX₂(H₃MMTO)2] (X = Cl, Br, I), trans-[PdX₂(SH₃)2] (X = Cl, Br), [Pd(H₄MTO)₄]CI₂ and [Pd(H₃MMTO)₄]CI₂, where H₄MTO = monothiooxamide, H₃MMTO = N(o)-methylmonothiooxamide and SH₃ = N(s)-methylmonothiooxamide, have been prepared. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods and spectroscopic (UV/VIS, FT-IR, Laser-Raman) studies. The vibrational analysis of the complexes is given using NH/ND and CH₃/CD₃ isotopic substitutions. Monomeric square planar structures are assigned for the complexes in the solid state. The neutral monothiooxamides behave as monodentate ligands coordinating through their thioamide sulfur atom. The complex [Pd(SH2)2] was isolated during the thermal decomposition of trans-[PdCl₂(SH₃)₂].