First-Principles Calculations of Magnetism in Nanoscale Carbon Materials Confining Metal with <Emphasis Type="Italic">f</Emphasis> Valence Electrons

The f electrons in the unfilled shell of actinide and lanthanide display complex bonding behavior and the hybridized sp electrons in carbon could show spin polarization in finite nanostructures. Correspondingly, materials combining these two features exhibit abundant magnetic properties. In this paper, we outline our first-principles calculations on various nanoscale carbon materials confining U and Gd which are representative actinide and lanthanide, respectively. The complex interaction between f electrons and sp electrons make the induced magnetic property sensitive to metal specie and carbon confinement. Specially, (1) The magnetism could be suppressed by stronger adsorption with vacancy sites on graphene and adjusted by varying the valence state of some endohedral metallofullerenes (EMFs). (2) The magnetic coupling between metal and carbon structures could be promoted by large curvature when confinement site is carbon nanotubes and altered by the adatom defect on fullerene cages. (3) Untrivial magnetic property with large net spin and asymmetric spin distribution is obtained by confining U atom and Gd atom in one fullerene as a heteronuclear EMF. These results contribute to a systematic understanding of the magnetism in nanoscale carbon materials confining metal with f valence electrons.     

Sensitizing activity of metal tetraphenylporphines toward diethylaminobenzaldehyde <Emphasis Type="Italic">N,N</Emphasis>-diphenylhydrazone and its dependence on the central metal atom

The sensitizing activity of metal (Cu, Co, Ni, Zn, and Ag) tetraphenylporhines (TPPs) toward N,N-diphenylhydrazone of diethylaminobenzaldehyde was studied. It was found that the sensitized photosensitivity essentially depends on the electronic structure of the central metal atom in the TPP molecule: porphyrin complexes with metals that have vacant d or f shells or unpaired electrons (Co, Cu, Ni, and Ag TPPs) do not act as spectral sensitizers for diethylaminobenzaldehyde N,N-diphenylhydrazone.     

Use of the bond-projected superposition principle in determining the conditional probabilities of orbital events in molecular fragments

The problem of defining and determining the multi-conditional probabilities of many-orbital events in the chemical bond system of a molecule is addressed anew within theoretical framework of the one-determinantal orbital representation of molecular electronic structure. Its solution is vital for determining the information-theoretic indices of bond couplings between molecular fragments or the reactant/product subsystems in chemical reactions. The superposition principle of quantum mechanics, appropriately projected into the occupied subspace of molecular orbitals, is used to condition the atomic orbitals or general basis functions of the self-consistent-field calculations. The conditional probabilities between the subspaces of basis functions (atomic orbitals) are derived from an appropriate generalization of the bond-projected superposition principle. They are then used to define the triply-conditional probabilities, relating one conditional event to another. The resulting expression is shown to satisfy the relevant non-negativity and symmetry requirements. It is applied to probe the π-bond coupling in butadiene and benzene.     

Quantum-chemical study of donor-acceptor interactions in chelate dicarbonyl complexes of rhodium(I)

DFT calculations were used to analyze the electronic structures of 15 mono- and dicarbonyl rhodium(I) complexes with bidentate O,O-, N,N-, and N,O-donor ligands. The characteristics describing the metal-CO bond (bond length and spin-spin coupling constant J(CRh)) were found to depend on which of the donor atoms (N or O) is trans to the carbonyl group. Because of this, the trans-effect transmitted along the σ-bonds can be judged from the values of these characteristics. The characteristics whose values are determined by the populations of the π-antibonding orbitals of the CO groups primarily depend on the cis-partners in the coordination sphere.     

Tautomerism in the Sulfonamide Moiety: Synthesis,Experimental and Theoretical Characterizations

Following our previous work, we synthesized N-(7-methyl-5,6-diphenyl-2-m-tolyl-7H-pyrrolo[2,3-d]pyrimidin-4-yl)benzensulfonamides to study the sulfonylimine-sulfonamide tautomerism. This goal is performed using the density functional theory (DFT). Four plausible isomers including the keto and enol sulfonamide as well as Z and E sulfonimide are considered for each of compounds. The DFT calculations are carried out at the B3LYP/6-31+G(d,p) level of theory. The optimized geometric parameters such as bond lengths and bond angles are calculated. The computed IR vibrational frequencies and ¹H NMR chemical shifts are in good agreement with the experimental data. The structure of all compounds is confirmed on the basis of their full spectral data. In all three compounds, the Z-sulfonimide form is more stable than the other isomers. A high energy gap between the frontier orbitals confirms the stability of the compounds.     

Probing Structure,Thermochemistry, Electron Affinity and Magnetic Moment of Erbium-Doped Silicon Clusters ErSi<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 3–10) and Their Anions with Density Functional Theory

The lowest energy structures and electronic properties of ErSi _n (n = 3–10) and their anions were probed using the ABCluster global search technique combined with the PBE, TPSSh and B3LYP schemes. The lowest energy energies of neutral ErSi _n (n = 3–10) can be regarded as substituting a Si atom of the lowest energy structure of Si_n+1 with a Er atom. The additional electron effects on the geometries are very strong, resulting the lowest energy structures of ErSi _n ^? with n > 6 are different from their neutral counterparts. Starting from n = 7, the potential energy surfaces of ErSi _n ^? are very flat, resulting isomeric arrangements occur and functional dependence of the predicted most stable structures exist. The AEAs, VDEs and simulated PES of ErSi _n (n = 3–10) are reported. Introducing Er to Si cluster can significantly improve photochemical reactivity of the cluster. The 4f electron of Er atom in ErSi₄, ErSi _n ^? (n = 4, 7–10) prefers to take part in bonding. The total magnetic moments of ErSi _n and their anions are mainly provided by the 4f electrons of Er atom. The dissociation energies of Er from ErSi _n and their anions were evaluated to inspect relative stability.     

Ab initio calculations of group IVA tetrachloride complexes: V. Dynamics of the formation of the complex of SiCl<Subscript>4</Subscript> with tetramethylurea

Quantum-chemical calculations of the system SiCl₄←OC[N(CH₃)₂]₂ were fulfilled by the RHF/6-31G(d) method with full geometry optimization and at varied Si←O distances. The calculation with full geometry optimization does not lead to the unusual trigonalbipyramidal structure of the complex, found experimentally, and this structure is reproduced when the right angles between axial Si-Cl bonds and the coordination Si←O bond were set. Complex formation results in electron density transfer from the carbonyl C atom and from the H atoms of the electron donor, as well as from the Si atom is transferred mainly on axial Cl atoms [basically, on their p _z (p _σ) orbitals]. The total energy of such complex is higher by 0.936 eV than that of the most energetically favorable form of the studied system.     

Interpretation of the Parameters of the EPR Spectra of Transition Metal Complexes

The calculated parameters of the EPR spectra of complexes of d¹ and d⁹ ions were presented. The covalent bond parameters used in the calculations were determined from EPR and experimental optical data (inverse problem of EPR spectroscopy). Various contributions to the expressions for the EPR parameters were compared. The observed abnormal values of the EPR parameters were discussed. The effects of charge-transfer states and the vibronic coupling on the components of g, A, and A^L tensors were considered. Mechanisms of spin density transfer to ligands in paramagnetic complexes were proposed.     

A quantum-chemical study of the structure and conformational dynamics of the acrolein molecule in the ground electronic state

The geometric parameters (including vibrationally averaged parameters), energy differences (ΔE) between the s-cis and s-trans conformers, and barrier to internal rotation (V _t ) were calculated for the acrolein molecule CH₂=CHCHO by various quantum-chemical methods (MP2, DFT, CASSCF, QCISD, CCSD(T), and MR-AQCC). The MP2 and B3LYP methods were used to calculate internal rotation potential functions and vibrational frequencies; the calculations were performed in various anharmonic approximations. To refine the ΔE and V _t values, two-dimensional (using a basis set of atomic orbitals) VFPA extrapolation procedure was applied, which allowed the results to be estimated in the FCI/CBS approximation taking into account nonadiabaticity, core correlation effects, and changes in the difference between zero point energies.     

Dipole moments and structure of <Emphasis Type="Italic">ortho</Emphasis>-diphenyl(diethyl)phosphinoyl-substituted benzyl alcohols,phenols, and their derivatives

The method of dipole moments and DFT B3LYP/6-31G* quantum-chemical calculations were used to study the structures of ortho-substituted aryl-and arylmethyldiphenyl(diethyl)phosphine oxides. It was established that methyl ethers of phosphorus-containing benzyl alcohols and phenols exist as equilibrium mixtures of several conformers with prevalence of forms with the weakest steric interactions. Preferred conformers of o-[(diethylphosphinoyl)methyl]benzyl alcohol and i-[(diphenylphosphinoyl)methyl]phenol contain an intramolecular hydrogen bond between the hydroxyl hydrogen atom and phosphinoyl oxygen atom.     

Hydrogen complexes of <Emphasis Type="Italic">O</Emphasis>-vinylacetoxime with trifluoroacetic acid

According to B3LYP/6-31G** calculations, the stable antiperi-, antiperiperiplanar and antiperi-, synperiperiplanar conformers of O-vinylacetoxime (1) form with trifluoroacetic acid strong H complexes of two types: with N···H-O and O···H-O hydrogen bonds. The former are more stable. Complexation changes N-O and C-O bond lengths in molecule 1, as well as mutual orientation of its vinyl and azomethine groups. The structural effect depends on the orientation of the H bond, which, in its turn, is determined by the nature of the electron-donor center. When the nitrogen atom of oxime 1 is involved in complex formation, the H bond lies in the molecular plane, whereas the H bond involving the oxygen atom is directed in parallel with its lone electron pair.     

Splitting of the <Emphasis Type="Italic">d</Emphasis><Superscript><Emphasis Type="Italic">N</Emphasis></Superscript> atomic states in icosahedral 3<Emphasis Type="Italic">d</Emphasis> metal endofullerenes M@C<Subscript>60</Subscript>

Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C₆₀ (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d ^N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d ^N atomic states in the icosahedral field generated by fullerene C60 (I _h ) on a metal atom (ion) remain non-split for different charged states of the metal and C₆₀. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d ^N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures.     

<Emphasis Type="Italic">N</Emphasis>-allyl and <Emphasis Type="Italic">N</Emphasis>-propargyl trifluoromethanesulfonimides. Theoretical analysis

Tautomers of N-allyl- and N-propargyl-substituted trifluoromethanesulfonimides (CF₃SO₂)₂NR (R = CH₂CH=CH₂, Z/E-CH=CHMe, CH₂C≡CH, CH=CH=CH₂, C≡CCH₂) were calculated by the DFT (B3LYP, wB97XD, PBE1PBE), MP2, and CBS-QB3 methods. The results were compared with the theoretical data for the corresponding amines and amides NHRR¹ (R¹ = H, CF₃SO₂). It was shown that there is no conjugation between the nitrogen atom and C=C bond and that conjugation exists with the C≡C bond with electron density displacement toward the nitrogen atom. The calculations of anions derived from N-allyl- and N-propargyl-trifluoromethanesulfonimides revealed the possibility of their rearrangement with elimination of trifluoromethanesulfinate anion and formation of its H-complex with N-(prop-2-en-1-ylidene)trifluoromethanesulfonamide or N-(prop-2-yn-1-ylidene)trifluoromethanesulfonamide.     

Molecular structure of ErCl<Subscript>3</Subscript> and YbCl<Subscript>3</Subscript> according to the data of the simultaneous electron diffraction and mass spectrometric experiment

The saturated vapors of ErCl₃ and YbCl₃ were studied in a simultaneous electron diffraction and mass spectrometric experiment at 1165 K and 1170 K, respectively. In the vapors of these compounds, we found up to 3 mol.% dimers along with the monomers. The parameters of the r _g effective configuration of the monomer molecules were determined. For ErCl₃ and YbCl₃, the internuclear distances r _g(Ln-Cl) were 2.436(5) Å and 2.416(5) Å, and the bond angles ∠_g(Cl-Ln-Cl) were 117.0(10)° and 117.2(10)°, respectively. The equilibrium configurations and vibration frequencies of the monomer and dimer molecules were calculated by the HF, B3LYP, and MP2 methods using the combination of the ECP_D energy-consistent quasirelativistic core potential, including 4f electrons [Kr4d ¹⁰4f ⁿ ], and the contracted [5s4p3d] valence basis set for Er and Yb atoms and the MIDIX [4s3p1d] basis set for Cl atoms. The parameters of the effective r _g configuration of the monomer molecules corresponding to the temperature of the experiment were calculated. The difference between the calculated equilibrium r _e(Ln-Cl) and temperature-averaged r _g(Ln-Cl) distances was found to be 0.001–0.002 Å and did not exceed the error of the r _g(Ln-Cl) parameter determined in the electron diffraction experiment. The experimental parameters of the r _g structure were shown to be consistent with the idea about the planar equilibrium geometrical configuration of ErCl₃ and YbCl₃ molecules.     

Study on the Geometric and Electronic Structures of Al<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>Si<Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> (n = 3, 4, 5; m = 1, 2, 3, 4) Clusters

Genetic algorithm combined with the semi-empirical Hamitonian AM1/PM3 is used to search the low energy isomers of Al _n Si _m (n = 3, 5, m ≤ 3 and n = 4, m ≤ 4) and the charged clusters with 20 and 28 valence electrons. The candidate structures were optimized by the density functional theory PBE0 and B3LYP models with the triply split basis sets including polarization functions. The electronic structures show that Al–Si binary clusters behave like metal clusters. The molecular orbitals accord with that predicted by the jellium model, and the electron localization function shows the valence electrons are delocalized over the entire clusters. The clusters having 20 and 28 valence electrons exhibit pronounced stabilities and large energy gaps. The 20 valence electrons of Al₄Si₂ and Al₃Si₃ ⁺, Al₅Si^? form closed shells 1S ²1P ⁶2S ²1D ¹⁰. Al₄Si₄ and Al₅Si₃ ^? have oblate structures and the P, D, F levels spilt considerably in these clusters. The electron density distributions suggest that doping silicon in the aluminum clusters enhances the stability considerably.     

Benzoid–Quinoid tautomerism of schiff bases and their structural analogs: LVII. 2-[(3-oxo-5-phenylpyrazolidin-1-yl)methylidene]-1<Emphasis Type="Italic">H</Emphasis>-indene-1,3(2<Emphasis Type="Italic">H</Emphasis>)-dione

Potentially tautomeric azomethine imide, 2-[(3-oxo-5-phenylpyrazolidin-1-yl)methylidene]-1H-indene- 1,3(2H)-dione, has been synthesized by condensation of 5-phenylpyrazolidin-3-one with 2-(hydroxymethylidene)-1H-indene-1,3(2H)-dione. According to the IR, ¹H and ¹³C NMR, and electronic absorption spectroscopy data and DFT B3LYP/6-311++G(d,p) quantum chemical calculations, the title compound in solution exists as planar tricarbonyl tautomer stabilized by intramolecular hydrogen bond between the NH proton of the pyrazolidine fragment and carbonyl oxygen atom of the indene fragment. Its crystal structure was determined by X-ray analysis.     

Sorption of adamantane phenylamide derivatives on hyper-cross-linked polystyrene from water–acetonitrile eluents

Study of the main physicochemical features of the sorption of phenylamide adamantane derivatives on hyper-cross-linked polystyrene from water–acetonitrile solutions shows that both hydrophobic and electronic interactions make a large contribution to retention, especially for a chlorine-containing derivative in which there are π–p and π–d interactions between the outer-shell electrons of the chlorine atom in addition to π–π interactions between aromatic fragments of the sorbate and sorbent.     

Linear versus bent bonding in metal-phosphinidene complexes: Theoretical studies of the electrophilic phosphinidene complexes [(Cp)(CO)2MPMe)], [(Cp)(CO)3MPMe)] (M = Cr, Mo, W)

Density functional theory calculations have been performed for the title phosphinidene complexes using the exchange correlation functionals BP86 and B3LYP. The optimized bond lengths and angles of the model compounds are in excellent agreement with experiment. The M-P bond lengths in linear phosphinidene complexes correspond to a Pauling bond order of ∼ 3. The bent geometries at phosphorus in the bent metal phosphinidene complexes are consistent with the presence of a trivalent phosphorus(III) center which is singly bonded to carbon and doubly bonded to transition metal. The analysis of the delocalized Kohn-Sham orbitals shows the polarization of the M-P σ bonding orbitals towards the phosphorus atom in the MPMe bonds, while in the MPMe bond, the contributions of metal and phosphorus are almost the same. In the linear phosphinidene complexes the contributions of the covalent bonding ΔE_orb are more than the electrostatic interaction ΔE_elstat. The bent phosphinidene complexes have a lower degree of covalent bonding than the linear phosphinidene complexes. The major differences between the linear and bent phosphinidene complexes are found in the degree of π-bonding. The MPMe bonds show a true M-P π bond and a deviated π bond due to slight bent M-P-C bond angles. The MPMe bonds show a true M-P π bond and a lone-pair on phosphorus.