Reaktionen von Pentafulven‐Komplexen des Titans mit Nitrilen und iso‐Nitrilen — Synthese und Isomerisierungen von σ, π‐Chelatkomplexen mit Cp∼N‐Liganden

Reactions of Pentafulvene Complexes of Titanium with Nitriles and iso‐Nitriles — Synthesis and Isomerizations of σ, π‐Chelat Complexes with Cp∼N‐Ligands The reactions of fulvene complexes Cp*Ti{η⁶—C₅H₄=C(R)(R')}Cl (R = H, R' = tBu ( 1 ); R = Me, R' = iPr ( 4 )) with nitriles and iso‐nitriles, leading to σ, π‐chelat complexes with Cp∼N‐ligands, have been examined and the formed products characterized. Whereas in the reactions of 1 and 4 , respectively, with nitriles a 1, 2‐mono‐insertion of the CN‐group in the Ti—C(R)(R') (Fv) bond is observed, the reaction with iso‐nitrils leads to the insertion of two molecules iso‐nitrile. The nitrile insertion product of 1 is characterized by an imine‐enamine tautomerization. Whereas the primary built meta stable imine species ( 3 ) was only identified by NMR measurements in solution, the enamine tautomer ( 2 ) crystallized from n‐hexane, so that the crystal structure could be determined. The primary formed iminoacyl complex ( 7 ) rearranges due to the electrophilicity of the titanium centre and builds a Ti—N bond with significant N(pπ) → Ti(dπ) bonding character.     

Multi‐channel coupling effects for electronic excitations leading to the b3∑, a3∑, and c3∏u states of H2

In this work we use the unitarized distorted wave method to study the effect of multi‐channel coupling on the calculated electronic excitation cross sections in H₂. Specifically, such an effect for electronic excitations leading to the excited states b³∑, a³∑, and c³∏_u for incident energies varying from 15 to 60 eV is studied. Our results have shown that converged cross sections can be obtained with the inclusion of only triplet intermediate states, except for energies near the excitation thresholds, where the inclusion of singlet intermediate states is important. Also, convergence improves with increasing energies for all excitations considered. Comparison of our calculated cross sections with available experimental and other theoretical results is encouraging. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

A cyano‐bridged dinuclear 4f–3d array

A cyano‐bridged bimetallic 4f–3d complex, tri­aqua‐1κ³O‐μ‐cyano‐1:2κ²N:C‐penta­cyano‐2κ⁵C‐tetrakis(2‐pyrrolidone‐1κO)­chromium(III)­dysprosium(III) dihydrate, [CrDy(C₄H₇NO)₄(CN)₆(H₂O)₃]·2H₂O, has been prepared and characterized by X‐ray crystallographic analysis. The structure consists of a neutral cyano‐bridged Dy–Cr dimer. A hydrogen‐bonded three‐dimensional architecture is formed through N—H?O, O—H?N and O—H?O hydrogen bonds.     

Energy and density analysis on the H2 molecule from the united atom to dissociation: The Σ, Π, Δ, ϕ, and Γ manifolds

We present 140 accurate potential energy curves, PECs, for the Σ, Π, Δ, ?, and Γ manifolds for the H₂ molecule, mapping all the states with energy below the H ground state. The full configuration interaction, nonrelativistic Born–Oppenheimer computations are performed with large and optimized basis sets of Slater‐type and spherical Gaussian functions; these new basis sets are somewhat larger than those used in recent published studies on the 60 Σ state PECs. The full CI computations are performed twice, with Hartree–Fock and with Heitler–London‐type functions, allowing the identification of the ionic component in the total energy. The computed energies are within 10^?5 hartree from the most accurate PECs in literature. We aim (a) at the evaluation of the PECs starting at very short and unexplored internuclear distances (0.01 bohrs) and ending at full dissociation, (b) at the systematic prediction of high excited state PECs dissociating as 1s + 4l and 1s + 5l, and (c) at the characterization of the evolution of the 140 PEC electronic densities from united atom to dissociation. With this work we fill a gap in today literature, which has dealt mainly with low excited states, generally excluding short internuclear distances. The electronic configuration at the united atom persists as dominant configuration well beyond the equilibrium separation, and it switches to that at dissociation often with energy patterns seemingly irregular, in particular when the values of the principal quantum number at dissociation and at the united atom differ by one or more unit. The Hund's singlet‐triplet splitting, which propagates from the united atom to the molecule, is discussed. The singlet and triplet states are rather close in energy in the Π manifolds, and approach degeneracy in the Δ and ? manifolds, to become fully degenerate in the Γ manifolds. Discussions on the correlation energy correction, adiabatic correction, spectroscopic constants and on general features of the H₂ excited states are presented. The H₂ molecule is a system, which—to be understood—needs consideration of both the very short internuclear distances in approaching the united atom and of the very high excited states below H. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Stereo‐dynamics of the F + HCl → HF + Cl reaction

We present a quasi‐classical trajectory (QCT) study on product polarization for the reaction F(²P) + HCl(v = 0, j = 0) → HF + Cl(²P) on a recently computed 1² A′ ground‐state surface reported by Deskevich et al. J Chem Phys, 2006, 124, 224303. Four polarization dependent generalized differential cross‐sections (2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t), (2π/σ)(dσ₂₂₊/dω_t), and (2π/σ)(dσ_21?/dω_t) were calculated in the center‐of‐mass frame at four different collision energies. The obtained P(θ_r), P(?_r), and P(θ_r, ?_r), which denote respectively the distribution of angles between k and j′, the distribution of dihedral angle denoting k‐k′‐j′ correlation and the angular distribution of product rotational vectors in the form of polar plots, indicate that the degree of rotational alignment of the product HF molecule is strong and the degree of the rotational alignment decreases as collision energy increases. The product rotational angular momentum vector j′ is not only aligned, but also oriented along the y‐axis, and the molecular rotation of the product prefers an in‐plane reaction mechanism rather than the out‐of‐plane mechanism. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The nickel-group IV molecules NiC,NiSi, and NiGe

All electron ab initio calculations have been applied to elucidate the electronic states and the nature of the chemical bonds in the molecules NiC, NiSi, and NiGe. The calculations have revealed that the ground states of all three molecules are¹Σ⁺, but due to the open 3d shell of the Ni atom the molecules have many low-lying electronic states. The NiC molecule is strongly polar, and the low-lying electronic states have been identified as those arising when the angular momenta of the³F_g Ni⁺ ion are coupled to the angular momenta of the⁴S_uC^? anion. The chemical bond in the NiC molecule has triple bond character due to the valence bond couplings between the Ni 4s and 3dπ electrons and theC 2p electrons. The chemical bonds in the molecules NiSi and NiGe are very much alike; they are double bonds composed of oneσ and oneπ bond. Theσ bond is due to the doubly occupied delocalized molecular orbital composed of the Ni 4s orbital and the Si 3pσ or the Ge 4pσ orbital. Theπ bond originates from the valence bond coupling between the localized hole in the Ni 3dπ orbital and the valencepπ electron of Si or Ge.     

Structure determination of three furan‐substituted benzimidazoles and calculation of π–π and C—H...π interaction energies

The synthesis and structural characterization of 2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazole [C₁₆H₁₂N₂O₂, (I)], 2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazol‐3‐ium chloride monohydrate [C₁₆H₁₃N₂O₂⁺·Cl⁻·H₂O, (II)] and the hydrobromide salt 5,6‐dimethyl‐2‐(furan‐2‐yl)‐1‐(furan‐2‐ylmethyl)‐1H‐benzimidazol‐3‐ium bromide [C₁₈H₁₇N₂O₂⁺·Br⁻, (III)] are described. Benzimidazole (I) displays two sets of aromatic interactions, each of which involves pairs of molecules in a head‐to‐tail arrangement. The first, denoted set (Ia), exhibits both intermolecular C—H...π interactions between the 2‐(furan‐2‐yl) (abbreviated as Fn) and 1‐(furan‐2‐ylmethyl) (abbreviated as MeFn) substituents, and π–π interactions involving the Fn substituents between inversion‐center‐related molecules. The second, denoted set (Ib), involves π–π interactions involving both the benzene ring (Bz) and the imidazole ring (Im) of benzimidazole. Hydrated salt (II) exhibits N—H...OH₂...Cl hydrogen bonding that results in chains of molecules parallel to the a axis. There is also a head‐to‐head aromatic stacking of the protonated benzimidazole cations in which the Bz and Im rings of one molecule interact with the Im and Fn rings of adjacent molecules in the chain. Salt (III) displays N—H...Br hydrogen bonding and π–π interactions involving inversion‐center‐related benzimidazole rings in a head‐to‐tail arrangement. In all of the π–π interactions observed, the interacting moieties are shifted with respect to each other along the major molecular axis. Basis set superposition energy‐corrected (counterpoise method) interaction energies were calculated for each interaction [DFT, M06‐2X/6‐31+G(d)] employing atomic coordinates obtained in the crystallographic analyses for heavy atoms and optimized H‐atom coordinates. The calculated interaction energies are −43.0, −39.8, −48.5, and −55.0 kJ mol⁻¹ for (Ia), (Ib), (II), and (III), respectively. For (Ia), the analysis was used to partition the interaction energies into the C—H...π and π–π components, which are 9.4 and 24.1 kJ mol⁻¹, respectively. Energy‐minimized structures were used to determine the optimal interplanar spacing, the slip distance along the major molecular axis, and the slip distance along the minor molecular axis for 2‐(furan‐2‐yl)‐1H‐benzimidazole.     

Triplet‐State Aromaticity of 4nπ‐Electron Monocycles: Analysis of Bifurcation in the π Contribution to the Electron Localization Function

The π contribution to the electron localization function (ELF) is used to compare 4nπ‐ and (4n+2)π‐electron annulenes, with particular focus on the aromaticity of 4nπ‐electron annulenes in their lowest triplet state. The analysis is performed on the electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all‐carbon annulenes are set up: the span in the bifurcation values ΔBV(ELF_π) should be small, ideally zero, and the bifurcation value for ring closure of the π basin RCBV(ELF_π) should be high (≥ 0.7). On the basis of these criteria, nearly all 4nπ‐electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)π‐electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D_4h and D_8h symmetry, respectively, the RCBV(ELF_π) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of α‐ and β‐electrons.     

All‐electron relativistic computations on the low‐lying electronic states,bond length,and vibrational frequency of CeF diatomic molecule with spin–orbit coupling effects

Ab initio all‐electron computations have been carried out for Ce⁺ and CeF, including the electron correlation, scalar relativistic, and spin–orbit coupling effects in a quantitative manner. First, the n‐electron valence state second‐order multireference perturbation theory (NEVPT2) and spin–orbit configuration interaction (SOCI) based on the state‐averaged restricted active space multiconfigurational self‐consistent field (SA‐RASSCF) and state‐averaged complete active space multiconfigurational self‐consistent field (SA‐CASSCF) wavefunctions have been applied to evaluations of the low‐lying energy levels of Ce⁺ with [Xe]4f¹5d¹6s¹ and [Xe]4f¹5d² configurations, to test the accuracy of several all‐electron relativistic basis sets. It is shown that the mixing of quartet and doublet states is essential to reproduce the excitation energies. Then, SA‐RASSCF(CASSCF)/NEVPT2 + SOCI computations with the Sapporo(‐DKH3)‐2012‐QZP basis set were carried out to determine the energy levels of the low‐lying electronic states of CeF. The calculated excitation energies, bond length, and vibrational frequency are shown to be in good agreement with the available experimental data. © 2018 Wiley Periodicals, Inc.     

Electron-ion coincidence study of photofragmentation of the CdCl(2) molecule

In this work, the photofragmentation subsequent to valence and Cd4d photoionization of cadmium dichloride (CdCl₂) were studied using He I and synchrotron excitation. The measurements were performed with a photoelectron‐photoion coincidence (PEPICO) setup, and the connection between the singly ionized electronic states and cationic fragments was investigated. The valence‐ionized states were found to lead to , Cd⁺ and CdCl⁺. The Cd4d^{? 1} states were found to lead only to Cl⁺ ions. The observed charge transfer effect between Cd and Cl was concluded to take place due to internal conversion or fluorescence decay to dissociating valence states either directly or through consecutive fragmentation. The fragmentation energetics were investigated with molecular ab initio calculations, and the calculated energies were found to agree with the detected fragment appearances. Copyright © 2011 John Wiley & Sons, Ltd.     

Specific fragmentation of the K‐shell excited/ionized pyridine derivatives studied by electron impact: 2‐, 3‐ and 4‐methylpyridine

Fragmentation of the pyridine ring upon K‐shell excitation/ionization has been studied with gaseous 2‐, 3‐ and 4‐methylpyridine by the electron‐impact method. Ab initio molecular orbital (MO) calculations were also carried out to explore electronic states correlating with specific fragments. Some specific fragmentation channels were identified from the ionic fragments enhanced characteristically at the N 1s edge. Yields of the C₂HN⁺ and C₅H₅⁺/C₅H₆⁺ ions show that the fission of the N? C2 and C4? C5/C5? C6 bonds of the ring is likely to occur after the N 1s excitation and ionization. Ab initio MO calculations for the 2‐methylpyridine molecule indicate that the dissociation channels to produce these ions are only accessible through the excited states of the parent molecular dication, which can be formed by Auger decays after the N 1s ionization. Fragment ions via hydrogen rearrangement are produced as well, but the rearrangement is not a phenomenon specific to the K‐shell excitation/ionization. Copyright © 2010 John Wiley & Sons, Ltd.     

Using (FH)2 and (FH)3 to Bridge the σ‐Hole and the Lone Pair at P in Complexes with H2XP,for X=CH3, OH,H, CCH,F, Cl,NC, and CN

Ab initio MP2/aug′‐cc‐pVTZ calculations are used to investigate the binary complexes H₂XP:HF, the ternary complexes H₂XP:(FH)₂, and the quaternary complexes H₂XP:(FH)₃, for X=CH₃, OH, H, CCH, F, Cl, NC, and CN. Hydrogen‐bonded (HB) binary complexes are formed between all H₂XP molecules and FH, but only H₂FP, H₂ClP, and H₂(NC)P form pnicogen‐bonded (ZB) complexes with FH. Ternary complexes with (FH)₂ are stabilized by F?H???P and F?H???F hydrogen bonds and F???P pnicogen bonds, except for H₂(CH₃)P:(FH)₂ and H₃P:(FH)₂, which do not have pnicogen bonds. All quaternary complexes H₂XP:(FH)₃ are stabilized by both F?H???P and F?H???F hydrogen bonds and P???F pnicogen bonds. Thus, (FH)₂ with two exceptions, and (FH)₃ can bridge the σ‐hole and the lone pair at P in these complexes. The binding energies of H₂XP:(FH)₃ complexes are significantly greater than the binding energies of H₂XP:(FH)₂ complexes, and nonadditivities are synergistic in both series. Charge transfer occurs across all intermolecular bonds from the lone‐pair donor atom to an antibonding σ* orbital of the acceptor molecule, and stabilizes these complexes. Charge‐transfer energies across the pnicogen bond correlate with the intermolecular P?F distance, while charge‐transfer energies across F?H???P and F?H???F hydrogen bonds correlate with the distance between the lone‐pair donor atom and the hydrogen‐bonded H atom. In binary and quaternary complexes, charge transfer energies also correlate with the distance between the electron‐donor atom and the hydrogen‐bonded F atom. EOM‐CCSD spin‐spin coupling constants ^2hJ(F–P) across F?H???P hydrogen bonds, and ^1pJ(P–F) across pnicogen bonds in binary, ternary, and quaternary complexes exhibit strong correlations with the corresponding intermolecular distances. Hydrogen bonds are better transmitters of F–P coupling data than pnicogen bonds, despite the longer F???P distances in F?H???P hydrogen bonds compared to P???F pnicogen bonds. There is a correlation between the two bond coupling constants ^2hJ(F–F) in the quaternary complexes and the corresponding intermolecular distances, but not in the ternary complexes, a reflection of the distorted geometries of the bridging dimers in ternary complexes.     

Oxygen Quenching of nπ* Triplet Phenyl Ketones: Local Excitation and Local Deactivation

We have studied the charge‐transfer‐induced deactivation of nπ* excited triplet states of benzophenone derivatives by O₂(³Σ), and the charge‐transfer‐induced deactivation of O₂(¹Δ_g) by ground‐state benzophenone derivatives in CH₂Cl₂ and CCl₄. The rate constants for both processes are described by Marcus electron‐transfer theory, and are compared with the respective data for a series of biphenyl and naphthalene derivatives, the triplet states of which have ππ* configuration. The results demonstrate that deactivation of the locally excited nπ* triplets occurs by local charge‐transfer and non‐charge‐transfer interactions of the oxygen molecule with the ketone carbonyl group. Relatively large intramolecular reorganization energies show that this quenching process involves large geometry changes in the benzophenone molecule, which are related to favorable Franck‐Condon factors for the deactivation of ketone‐oxygen complexes to the ground‐state molecules. This leads to large rate constants in the triplet channel, which are responsible for the low efficiencies of O₂(¹Δ_g) formation observed with nπ* excited ketones. Compared with the deactivation of ππ* triplets, the non‐charge‐transfer process is largely enhanced, and charge‐transfer interactions are less important. The deactivation of singlet oxygen by ground‐state benzophenone derivatives proceeds via interactions of O₂(¹Δ_g) with the Ph rings.     

Ligand‐to‐Ligand Charge‐Transfer Transitions of Platinum(II) Complexes with Arylacetylide Ligands with Different Chain Lengths: Spectroscopic Characterization,Effect of Molecular Conformations,and Density Functional Theory Calculations

The complexes [Pt(tBu₃tpy){C?C(C₆H₄C?C)_n?1R}]⁺ (n=1: R=alkyl and aryl (Ar); n=1–3: R=phenyl (Ph) or Ph‐N(CH₃)₂‐4; n=1 and 2, R=Ph‐NH₂‐4; tBu₃tpy=4,4’,4’’‐tri‐tert‐butyl‐2,2’:6’,2’’‐terpyridine) and [Pt(Cl₃tpy)(C?CR)]⁺ (R=tert‐butyl (tBu), Ph, 9,9’‐dibutylfluorene, 9,9’‐dibutyl‐7‐dimethyl‐amine‐fluorene; Cl₃tpy=4,4’,4’’‐trichloro‐2,2’:6’,2’’‐terpyridine) were prepared. The effects of substituent(s) on the terpyridine (tpy) and acetylide ligands and chain length of arylacetylide ligands on the absorption and emission spectra were examined. Resonance Raman (RR) spectra of [Pt(tBu₃tpy)(C?CR)]⁺ (R=n‐butyl, Ph, and C₆H₄‐OCH₃‐4) obtained in acetonitrile at 298 K reveal that the structural distortion of the C?C bond in the electronic excited state obtained by 502.9 nm excitation is substantially larger than that obtained by 416 nm excitation. Density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations on [Pt(H₃tpy)(C?CR)]⁺ (R= n‐propyl (nPr), 2‐pyridyl (Py)), [Pt(H₃tpy){C?C(C₆H₄C?C)_n?1Ph}]⁺ (n=1–3), and [Pt(H₃tpy){C?C(C₆H₄C?C)_n?1C₆H₄‐N(CH₃)₂‐4}]⁺/+H⁺ (n=1–3; H₃tpy=nonsubstituted terpyridine) at two different conformations were performed, namely, with the phenyl rings of the arylacetylide ligands coplanar (“cop”) with and perpendicular (“per”) to the H₃tpy ligand. Combining the experimental data and calculated results, the two lowest energy absorption peak maxima, λ₁ and λ₂, of [Pt(Y₃tpy)(C?CR)]⁺ (Y=tBu or Cl, R=aryl) are attributed to ¹[π(C?CR)→π*(Y₃tpy)] in the “cop” conformation and mixed ¹[d_π(Pt)→π*(Y₃tpy)]/¹[π(C?CR)→π*(Y₃tpy)] transitions in the “per” conformation. The lowest energy absorption peak λ₁ for [Pt(tBu₃tpy){C?C(C₆H₄C?C)_n?1C₆H₄‐H‐4}]⁺ (n=1–3) shows a redshift with increasing chain length. However, for [Pt(tBu₃tpy){C?C(C6H4C?C)_n?1C₆H₄‐N(CH₃)₂‐4}]⁺ (n=1–3), λ₁ shows a blueshift with increasing chain length n, but shows a redshift after the addition of acid. The emissions of [Pt(Y₃tpy)(C?CR)]⁺ (Y=tBu or Cl) at 524–642 nm measured in dichloromethane at 298 K are assigned to the ³[π(C?CAr)→π*(Y₃tpy)] excited states and mixed ³[d_π(Pt)→π*(Y₃tpy)]/³[π(C?C)→π*(Y₃tpy)] excited states for R=aryl and alkyl groups, respectively. [Pt(tBu₃tpy){C?C(C₆H₄C?C)_n?1C₆H₄‐N(CH₃)₂‐4}]⁺ (n=1 and 2) are nonemissive, and this is attributed to the small energy gap between the singlet ground state (S₀) and the lowest triplet excited state (T₁).     

Diagnosis of magnetoresponsive aromatic and antiaromatic zones in three‐membered rings of d‐ and f‐block elements

Magnetoresponsive three‐membered rings of d‐ and f‐block elements have been thoroughly investigated with the help of electronic structure calculation methods. The magnetic response of the clusters was evaluated by the Nucleus Independent Chemical Shifts (NICS)_zz‐scan curves, which in conjunction with symmetry‐based selection rules for the most significant translationally and rotationally allowed transitions helped rationalize and predict the orbital‐type of aromaticity/antiaromaticity of the clusters. The magnetoresponsive early (Groups 3, 4, and 5) transition metal M₃ rings exhibit successive aromatic and antiaromatic zones separated by a nodal plane. The magnetoresponsive late (Groups 11 and 12) transition metal M₃ rings exhibit long‐range aromatic zone with the NICS_zz(R) values decaying rapidly and monotonically with respect to R. The magnetic response of Group 10 transition metal M₃ rings is similar to that of the early transition metal M₃ rings, but it is long‐range antiaromatic only for the [c‐Ni₃] cluster. The NICS_zz‐scan curve of the [(H_tLa)₃(μ₂‐H)₆] cluster is indicative of weak pure σ‐aromaticity due to the induced diatropic ring current from the translationally allowed a → e′ and e′ → a transitions. The aromatic–antiaromatic behavior of the [(H_tCe)₃(μ₂‐H)₆]⁺ and [(H_tTm)₃(μ₂‐H)₆]²⁻ clusters is similar to that of the early d‐block elements. The magnetic response of [(H_tYb)₃(μ₂‐H)₆]³⁻ is similar to that of [c‐Hg₃]²⁻. The [(H_tLu)₃(μ₂‐H)₆] cluster can be considered as a doubly (σ + π) aromatic system, with the σ‐aromatic component being much stronger than the π‐aromatic one. Finally, the [(X_tRe)₃(μ₂‐X)₆] and [(X_tRu)₃(μ₂‐X)₆]⁺ (X = Cl, Br, I) clusters exhibit significant aromatic character with the greatest contribution to the induced diatropic ring currents coming from π‐type transitions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Ionic bonding of lanthanides,as influenced by d‐ and f‐atomic orbitals,by core–shells and by relativity

Lanthanide trihalide molecules LnX₃ (X = F, Cl, Br, I) were quantum chemically investigated, in particular detail for Ln = Lu (lutetium). We applied density functional theory (DFT) at the nonrelativistic and scalar and SO‐coupled relativistic levels, and also the ab initio coupled cluster approach. The chemically active electron shells of the lanthanide atoms comprise the 5d and 6s (and 6p) valence atomic orbitals (AO) and also the filled inner 4f semivalence and outer 5p semicore shells. Four different frozen‐core approximations for Lu were compared: the (1s²–4d¹⁰) [Pd] medium core, the [Pd+5s²5p⁶ = Xe] and [Pd+4f¹⁴] large cores, and the [Pd+4f¹⁴+5s²5p⁶] very large core. The errors of Lu? X bonding are more serious on freezing the 5p⁶ shell than the 4f¹⁴ shell, more serious upon core‐freezing than on the effective‐core‐potential approximation. The Ln? X distances correlate linearly with the AO radii of the ionic outer shells, Ln³⁺‐5p⁶ and X^?‐np⁶, characteristic for dominantly ionic Ln³⁺‐X^? binding. The heavier halogen atoms also bind covalently with the Ln‐5d shell. Scalar relativistic effects contract and destabilize the Lu? X bonds, spin orbit coupling hardly affects the geometries but the bond energies, owing to SO effects in the free atoms. The relativistic changes of bond energy BE, bond length R_e, bond force k, and bond stretching frequency v_s do not follow the simple rules of Badger and Gordy (R_e～BE～k～v_s). The so‐called degeneracy‐driven covalence, meaning strong mixing of accidentally near‐degenerate, nearly nonoverlapping AOs without BE contribution is critically discussed. © 2015 Wiley Periodicals, Inc.     

Kristallstrukturen,Normalkoordinatenanalysen und 15N‐NMRund 77Se‐NMR‐Verschiebungen von trans‐[OsO2(NCO)4]2–, trans‐[OsO2(NCS)4]2– und trans‐[OsO2(SeCN)4]2–

Crystal Structures, Normal Coordinate Analyses, and ¹⁵N NMR and ⁷⁷Se NMR Chemical Shifts of trans ‐[OsO₂(NCO)₄]^2–, trans ‐[OsO₂(NCS)₄]^2–, and trans ‐[OsO₂(SeCN)₄]^2– The crystal structures of trans‐(Ph₃PNPPh₃)₂[OsO₂(NCO)₄] ( 1 ) (orthorhombic, space group Pbca, a = 19.278(3), b = 16.674(4), c = 19.982(2) Å, Z = 4), trans(n‐Bu₄N)₂[OsO₂(NCS)₄] ( 2 ) (triclinic, space group P1, a = 12.728(3), b = 12.953(3), c = 16.255(6) Å, α = 97.39(4), β = 105.62(2), γ = 95.25(3)°, Z = 2) and trans‐(n‐Bu₄N)₂[OsO₂(SeCN)₄] ( 3 ) (tetragonal, space group I4/m, a = 13.406(2), c = 12.871(1) Å, Z = 2) have been determined by single‐crystal X‐ray diffraction analysis, showing the bonding of NCO and NCS via the N atom but the coordination of SeCN via the Se atom to osmium. Based on the molecular parameters of the X‐ray determinations the vibrational spectra have been assigned by normal coordinate analyses. The valence force constants are for 1 f_d(OsO) = 6.43, f_d(OsN) = 3.32, f_d(NC) = 14.50, f_d(CO) = 12.80, for 2 f_d(OsO) = 6.56, f_d(OsN) = 1.75, f_d(NC) = 15.00, f_d(CS) = 5.50, and for 3 f_d(OsO) = 6.75, f_d(OsSe) = 0.99, f_d(SeC) = 3.23, f_d(CN) = 15.95 mdyn/Å. The observed NMR shifts are δ(¹⁵N) = –386.6 ( 1 ), δ(¹⁵N) = –294.7 ( 2 ) and δ(⁷⁷Se) = 108.8 ppm ( 3 ).     

Ab initio study of 4-monosubstituted pyrimidines in ground and excited n → π* states

Ab initio SCF and SCF -CI calculations have been performed to investigate substituent effects on ground- and excited-state properties of 4-R-pyrimidines, and to compare these with substituent effects in 2- and 4-R-pyridines, with R including the π donating and σ withdrawing groups CH₃, NH₂, OH, F, and C₂H₃ and the σ and π electron-withdrawing groups CHO and CN. Substitution leads to significant changes in the internal angles of the pyrimidine ring, which are independent of the nature of the substituent. The geometry of the pyrimidine ring is more sensitive to substitution in the 4 position than the pyridine ring geometry is to substitution in either the 2 or the 4 position. The isodesmic reaction energies for substituent transfer from the 4 position of pyrimidine to the 2 or 4 position of pyridine indicate that all R groups except CN have a relative stabilizing effect in pyrimidine. The presence of a π donating group leads to an increase in the n→π* transition energy of 4-R-pyrimidines, while the π withdrawing group CN leads to a decrease in the transition energy relative to pyrimidine. Orbital energy differences and virtual excitation energies tend to correlate with n→π* transition energies of 4-R-pyrimidines with saturated R groups, but such correlations are masked by π conjugation, n orbital interaction, and configurational mixing when the unsaturated groups C₂H₃, CHO, and CN are present. The electronic effects of a π donating group are stronger when the group is bonded to pyrimidine than to pyridine, but those of a π withdrawing group are weaker when the group is bonded to pyrimidine.     

Theoretical Study of the Reactions M++CH3F (M=Ge,As, Se,Sb)

CASSCF–MRMP2 calculations have been carried out to analyze the reactions of the methyl fluoride molecule with the atomic ions Ge⁺, As⁺, Se⁺ and Sb⁺. For these interactions, potential energy curves for the low‐lying electronic states were calculated for different approaching modes of the fragments. Particularly, those channels leading to C? H and C? F oxidative addition products, H₂FC? M? H⁺ and H₃C? M? F⁺, respectively were explored, as well as the paths which evolve to the abstraction (M? F⁺+CH₃) and the elimination (CH₂M⁺+HF) asymptotes. For the reaction Ge⁺+CH₃F the only favorable channel leads to fluorine abstraction by the ion. As⁺ and Sb⁺ can react with CH₃F along pathways yielding stable addition products. However, a viable path joining the oxidative addition product H₃C? M? F⁺ with the elimination asymptote CH₂M⁺+HF was found for the reaction of the fluorocarbon compound with As⁺. No favorable channels were detected for the interaction of fluoromethane with Se⁺. The results discussed herein allow rationalizing some of the experimental data found for these interactions through gas‐phase mass spectrometry.