Ground electronic state and geometry of SF3

Ab initio LCAO MO SCF calculations with DZ + 3d(S) basis functions show that the sulphur trifluoride radical is a planar π-radical having a ²B₁ ground state. Like ClF₃, it has an umbrella-structure. However, it becomes Y-shaped in its first ²A₁ excited state which has been calculated to lie only ≈ 2.4 eV above the ²B₁ ground state.     

Calculations on 1,8-naphthoquinone predict that the ground state of this diradical is a singlet

(12/12)CASPT2, (16/14)CASPT2, B3LYP, and CCSD(T) calculations have been carried out on 1,8-Naphthoquinone (1,8- NQ ), to predict the low-lying electronic states and their relative energies in this non-Kekulé quinone diradical. CASPT2 predicts a ¹A₁ ground state, with three other electronic states—³B₂, ³B₁, and ¹B₁—within about 10 kcal/mol of the ground state in energy. On the basis of the results of these calculations, it is predicted that NIPES experiments on 1,8- NQ ^•– will find that 1,8- NQ is a diradical with a singlet ground state. © 2018 Wiley Periodicals, Inc.     

Does He2 Exist?

For the electronic ground state X ¹Σ⁺_g, the potential-energy function of He₂ reported by Aziz et al. has been transformed into the form V(z), containing only eight parameters, which is more suitable for the investigation of the existence of states of discrete energy. We found no evidence that a bound vibration-rotational state of the stable diatomic molecule ³He₂ or ⁴He₂, even if rotating, can exist in the electronic ground state.     

Magnetic Multistability in an Anion-Radical Pimer

Radical pimers are the simplest and most important models for studying charge-transfer processes and provide deep insight into π-stacked organic materials. Notably, radical pimer systems with magnetic bi- or multistability may have important applications in switchable materials, thermal sensors, and information-storage media. However, no such systems have been reported. Herein, we describe a new pimer consisting of neutral N-(n-propyl) benzene triimide ([BTI-3C]) and its anionic radical ([BTI-3C]^−.) that exhibits rare magnetic multistability. The crystalline pimer was readily synthesized by reduction of BTI-3C with cobaltocene (CoCp₂). The transition occurred with a thermal hysteresis loop that was 27 K wide in the range of 170–220 K, accompanied by a smaller loop with a width of 25 K at 220–242 K. The magnetic multistability was attributed to slippage of the π-stacked BTI structures and entropy-driven conformational isomerization of the side propyl chains in the crystalline state during temperature variation.     

Tetracyanide-bridged divanadium complexes: redox switching between strong antiferromagnetic and strong ferromagnetic coupling

Reaction of [(Me3tacn)V(CF3SO3)3] (Me3tacn = N,N',N'-trimethyl-1,4,7-triazacyclononane) with LiCN in DMF results in oligomerization of cyanide to form [(Me3tacn)2V2(CN)4(mu-C4N4)]. The structure of this binuclear complex features a planar tetracyanide unit bridging two VIV centers via imido type linkages. The conjugated pathway provided by the bridging ligand leads to strong antiferromagnetic coupling (J = -112 cm-1) and an S = 0 ground state. Reduction of the complex with cobaltocene generates the Class III mixed-valence anion [(Me3tacn)2V2(CN)4(mu-C4N4)]1-, wherein resonance exchange induces strong ferromagnetic coupling to give a well-isolated S = 3/2 ground state.     

Construction and applications of symmetrized valence bond wave functions

A method constructing symmetry-adapted bonded Young tableau bases is proposed, based on the symmetry properties of bonded tableaus and the projection operator associated with a point group. Several examples including the ground states and π excited states of O₃⁻, O₃, O₃⁺, and C₃⁻ are shown for instruction to construct the symmetrized valence bond (VB) wave function. Excitation energies of transitions from the ground states to π excited states of O₃⁻, C₃H₅, and C₃⁻ are calculated with an optimized symmetrized valence bond wave function in the σ–π separation approximation. Good agreement between the VB and experimental excitation energies is observed. The bonding features of the ground state and the first π excited singlet and triplet states for S₃ are discussed according to bonding populations from VB calculations. Both the singlet-biradical and the dipole structures have significant contributions to the ground state X ¹A₁ of S₃, while the excited state 1 ¹B₂ is essentially composed of the dipole structures, and the 1 ³B₂ excited state is comprised from a triplet-biradical structure. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 1–7, 1998     

Interaction of chromocene with MgO and reactivity of the adsorbed species towards CO: An IR study

The interaction of chromocene with partially and totally dehydroxylated MgO and the reactivity of the adsorbed species towards CO have been studied by IR spectroscopy. Cp₂Cr is weakly adsorbed on residual surface MgOH groups, forming hydrogen bonded species and, on the extended (100) faces, forming clustered (Cp₂Cr)_n species. A stronger interaction is observed with the highly unsaturated ions located on the edges and corners of the MgO microcrystals. Upon dosage of CO at room temperature, Cp₂CrCO complexes are formed which are stabilized by interaction with the Mg²⁺ and O²⁻ ions of the surface. The occurrence of an activated process leading to [Cp₂Cr]⁺ and [CpCr(CO)₃]⁻ charged reaction products is also observed.     

Electrochemical Behavior of Cobaltocene in Ionic Liquids

The electrochemical behavior of cobaltocenium has been studied in a number of room temperature aprotic ionic liquids. Well defined, diffusion controlled, anodic and cathodic peaks were found for the Cc⁺/Cc (cobaltocenium/cobaltocene) reduction/oxidation on gold, platinum and glassy carbon electrodes. Values of the peak separation parameters suggest quasireversibility or even irreversibility for the redox process. The difference between the ferrocene/ferrocenium and cobaltocenium/cobaltocene couples has been evaluated as equal to (1.350 ± 0.020) V. Values of the cobaltocenium (Cc⁺) diffusion coefficients D have been calculated on the basis of the Randles–Sevcik equation.     

Molecular fragmentations: Part IV. The mass spectral fragmentation of carbon tetrachloride

MINDO/3 calculations have been made of the molecular structures and energies of seven isomeric forms of the molecular cation (CCl₄)⁺, of the mass spectral fragment pairs:

and also of a number of neutral fragment pairs. Reaction energy profiles have been calculated for two fragmentations of (CCl₄)⁺, into [(CCl₂)⁺ + Cl₂], and into [(CCl₃)⁺ + Cl^?], in the latter of which the reaction proceeds via a rather stable intermediate; for the fragmentation of three electronic states of (CCl₃)⁺ into [(CCl₂)⁺ + Cl^?], where the ground singlet state and first triplet state of (CCl₃⁺ yield the ground doublet state of (CCl₂)⁺, but the first excited singlet of (CCl₃)⁺ yields the first excited doublet of (CCl₂)⁺ ; and for the fragmentation of the ground state of (CCl₃)⁺ into [(CCl)⁺ + Cl₂].     

Crossed-beám chemiluminescence. II. Kinetics and mechanisms for reactions of group IIA Metals in ground and metastable states with fluorine

Visible chemiluminescence technique under crossed-beam conditions has been applied to the study of the reactions of the group IIA metal atoms Mg, Ca, Sr and Ba in their ground state (¹S₀) or in an excited metastable state (³P_i, ³D_i or ¹D₂) with F₂. The monofluoride emission bands are the most prominent features in the chemiluminescence spectrum. Using higher fluorine densities radiation is observed from excited alkaline earth difluorides, which are shown to principally originate from secondary reactions. Formations of MF* are determined to be first order with respect to both the metal atom and the fluorine molecule. Total cross sections for removal of ground state metal atoms from the beam by F₂ are 115 ± 15Ų for Ca, 125 ± 15Ų for Sr, and 160 ± 15Ų for Ba, which is consistent with an electron jump model. Chemiluminescence cross sections are reported for the reactions involving electronically excited reactants M*. Photon yields of 12 ± 3% for Mg*, 18 ± 5% for Ca*, 20 ± 5% for Sr*, and 15 ± 8% for Ba* reacting with F₂ are measured. These high photon yields are remarkable when compared with absolute photon yields for the ground state reactions which indicate that less than 2% of the products are MF* molecules. It was possible to obtain vibrational state distributions for some of the excited monofluorides which are found to be populated in a non-thermal manner. This strongly suggests that the dynamics of the reactions are governed by a direct mechanism. From the crossed-beam chemiluminescence spectra the dissociation energies of the ground state monofluorides are estimated. In addition, improved spectroscopic constants, dissociation energies and dissociation products of some of the excited electronic states of MF are given.     

Kinetics of Depletion of Electronically Excited Ti Atom by CH4, C2H2, C2H4 and C2H6

The kinetics of depletion of ground state Ti(a³F) and electronically excited state Ti(a⁵F) upon interactions with CH₄, C₂H₂, C₂H₄, and C₂H₆ are studied in a fast-flow reactor at a He pressure of 0.70 Torr. No depletion of ground state Ti(a³F) was observed upon interaction with all hydrocarbons studied here. Two alkanes, CH₄ and C₂H₆, were also quite inert for depletion of the excited state Ti(a⁵F), On the other hand, C₂H₂ and C₂H₄ deplete the excited state Ti(a⁵F) very efficiently. Rate constants were determined to be (266 ± 86) and (476 ± 88) × 10^?12 cm³s^?1 for Ti(a⁵F) + C₂H₄ and Ti(a⁵F) + C₂H₂, respectively. These large rate constants compared with the ground state Ti were explained by an electron donor-acceptor interaction model that works in the interaction between C₂H₄ or C₂H₂ and the excited state with unfilled 4s orbital.     

High-Spin Iron(VI), Low-Spin Ruthenium(VI), and Magnetically Bistable Osmium(VI) in Molecular Group 8 Nitrido Trifluorides NMF3

Pseudo-tetrahedral nitrido trifluorides N≡MF₃ (M=Fe, Ru, Os) and square pyramidal nitrido tetrafluorides N≡MF₄ (M=Ru, Os) were formed by free-metal-atom reactions with NF₃ and subsequently isolated in solid neon at 5 K. Their IR spectra were recorded and analyzed aided by quantum-chemical calculations. For a d² electron configuration of the N≡MF₃ compounds in C_3v symmetry, Hund's rule predict a high-spin ³A₂ ground state with two parallel spin electrons and two degenerate metal d(δ)-orbitals. The corresponding high-spin ³A₂ ground state was, however, only found for N≡FeF₃, the first experimentally verified neutral nitrido Fe^VI species. The valence-isoelectronic N≡RuF₃ and N≡OsF₃ adopt different angular distorted singlet structures. For N≡RuF₃, the triplet ³A₂ state is only 5 kJ mol⁻¹ higher in energy than the singlet ¹A′ ground state, and the magnetically bistable molecular N≡OsF₃ with two distorted near degenerate ¹A′ and ³A“ electronic states were experimentally detected at 5 K in solid neon.     

Potential energy surfaces for OsH2

Summary We compute the potential energy surfaces of 12 electronic states of OsH₂ (four quintet, four triplet, and four singlet) arising from⁵ D ground state of the Os atom as well as triplet and singlet excited states using the complete active space multiconfiguration self-consistent field (CAS-MCSCF) followed by multireference configuration interaction (MRCI) and relativistic CI (RCI) calculation which include up to 430,000 configurations. We find that the⁵ D ground state of Os atom does not insert into H₂ while the excited³ F state of Os does. The³ B ₁ ground state of OsH₂ (there are two other nearly degenerate states) in the absence of spin-orbit coupling was found to be 22 kcal/mol more stable than Os(⁵ D)+H₂. The spin-orbit mixing of³ B ₁,³ B ₂,³ A ₂, and¹ A ₁ states was so strong that it induces significant change in bond angles (up to 10°) for OsH₂.Dedicated to Prof. Klaus RuedenbergCamille and Henry Dreyfus Teacher-Scholar     

Maximum Spin Polarization in Chromium Dimer Cations as Demonstrated by X‐ray Magnetic Circular Dichroism Spectroscopy

X‐ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr₂⁺. Our results indicate that the removal of a single electron from the 4sσ_g bonding orbital of Cr₂ drastically changes the preferred coupling of the 3d electronic spins. While the neutral molecule has a zero‐spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of S=11/2, and almost twice the bond length of the neutral molecule. This spin configuration can be interpreted as a result of indirect exchange coupling between the 3d electrons of the two atoms that is mediated by the single 4s electron through a strong intraatomic 3d‐4s exchange interaction. Our finding allows an estimate of the relative energies of two states that are often discussed as ground‐state candidates, the ferromagnetically coupled ¹²Σ and the low‐spin ²Σ state.     

Theoretical prediction on HBeN− and HNBe− anions using multiconfiguration second‐order perturbation theory

The HBeN^? and HNBe^? anions have been investigated for the first time using the CASSCF, CASPT2, and DFT/B3LYP methods with the contracted atomic natural orbital (ANO) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and B3LYP/cc‐pVTZ levels. The ground and the first excited states of HBeN^? are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HNBe^? is X²Σ⁺ state. The A²Π state of HNBe^? has unique imaginary frequency. A bend local minimum M1 was found along the 1²A″ potential energy surface and the A²Π state of HNBe^? should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HBeN bond angle. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical investigation of Wulf and Chappuis bands in the spectrum of ozone

The ground state and some lowest excited states of ozone are calculated by the semiempirical MNDO method using configuration interaction to explain the Wulf absorption band and photodissociation of ozone. The results of calculations show that³A₂(1³A′’) is the lowest excited triplet state of O₃; a transition to this state from the ground X¹ A₁ state is responsible for the weak Wulf absorption. The oscillator strength (f = 3.2·10^-7) and the radiative lifetime of the A₂ state (Τ = 0.01 s) are in agreement with recent ab initio calculations. Translated fromZhumal Struktumoi Khimii, Vol. 38, No. 6, pp. 1067–1073, November–December, 1997.     

Ab initio calculations on the three lowest states of HO+2

Ab initio calculations were performed for the three lowest lying states of HO⁺₂. The ground state was found to be a bend ³A″ state. The first excited ¹A′ state cannot appropriately be described by a single determinant, therefore a MC SCF calculation was employed.     

Ab initio investigation of the HCO and COH molecule-ions: Structure and potential surfaces for dissociation in ground and excited states

Ab initio SCF calculations are reported for the potential surfaces of the HCO⁺ and COH⁺ molecular ions in both ground and low-lying excited states. An analysis of the bonding characteristics of the two systems is undertaken, from which it is noted that the 5σ and 1π orbital energy levels in HCO⁺ are inverted relative to the order found in both COH⁺ and also in CO itself. This fact leads to a situation in which the (1π, 2π) excited states of HCO⁺ as well as the ground state are more stable than their COH⁺ counterparts, whereas the opposite relationship is observed for (5σ, 2π) species. In addition it is pointed out that those states which populate the 7a' in-plane component of the 2π MO in either molecule-ion are characterized both by bent equilibrium structures and also by dissociation into CO⁺ + H, whereas all other low-lying species, including the ground state, prefer linear structures which dissociate via a CO + H⁺ channel.     

Tetra-hydrides of the third-row transition elements: spin–orbit coupling effects on geometrical deformation in WH4 and OsH4

The dissociation energies of MH₄ (M =  La, Hf–Hg) were computed using full optimized reaction space (FORS) multi-configuration self-consistent field (MCSCF) and second-order multi-reference Møller–Plesset perturbation methods with the SBKJC basis sets augmented by a set of polarization functions (SBKJC(f,p)). It was shown that of the molecules examined, only four tetra-hydrides HfH₄, TaH₄, WH₄, and OsH₄ with T_d symmetry are lower in energy than the corresponding dissociation limits. For WH₄ and OsH₄, the potential energy surfaces from the D_4h to the T_d structure were explored from both theoretical calculations and symmetry arguments based on the pseudo-Jahn- Teller effect. As for WH₄, it is found that the ground state could be ³E_g, ³A_2g, or ³B_2g at the D_4h structure. The present calculations suggest that the ground state is ³E_g, and that this state is stabilized by the e_u deformation into a C_2v structure (³B₁) and then sequentially to the most stable T_d structure (³A₂). If the molecular system is promoted to the lowest ³B_2g state, the D_4h structure can directly deform into the most stable T_d structure along the b_2u vibrational mode. For OsH₄, the ground state (⁵B_1g) at the D_4h structure deforms into a D_2d structure and the resulting ⁵B₂ state strongly interacts with the lowest ³E and ¹A₁ states due to the spin-orbit couplings (SOCs). As a result, it was shown that the relativistic potential energy of the lowest spin-mixed state (ground state) monotonically decreases along the D_2d deformation path from the D_4h to the T_d structure.     

Synthesis and characterization of chromocenes containing bulky cyclopentadienyl ligands

Two equivalents of K[Cp′] (Cp′=C₅(i-Pr)₃H₂, C₅(i-Pr)₄H, C₅(t-Bu)₂H₃) react with CrCl₂ in THF to give the corresponding chromocenes, Cp′₂Cr, in good yield. Despite the presence of bulky substituents on the rings that could affect their properties, the complexes are extremely air- and moisture-sensitive, and possess a low-spin ground state. The low-spin paramagnetic nature of each chromocene was confirmed by magnetic susceptibility measurements. The solid-state structure of [C₅(i-Pr)₃H₂]₂Cr was obtained using single crystal X-ray analysis. It displays rigorously parallel rings, with an average Cr–C(ring) distance of 2.17(1)Å; the chromium resides on a crystallographically imposed inversion center. The orientation of the isopropyl groups minimizes unfavorable steric interactions between the rings.