Photoelectron Spectra of Unsaturated Oxides. I. 1,4-Dioxin and related systems

The He (Iα) photoelectron spectra of the four unsaturated oxides 3,4-dihydropyran ( 6 ), γ-pyran ( 7 ), 2, 3-dihydro-1, 4-dioxin ( 9 ) and 1, 4-dioxin ( 10 ) are reported and analysed. Band assignments are based on ab-initio calculations, using the STO-3G basis set. The proposed orbital sequences (with reference to the coordinate systems given in Table 1) are, for the top three orbitals: 6 , π, nσ, nπ; 7 , 3b₁(π), 1a₂(π), 11a₁(σ); 9 , 11b(π), 12a(σ), 11a(π); 10 , 2b_3u(π), 1b_1g(π), 6a_g(σ). Finally the (almost) localized π-orbitals have been computed by the Foster-Boys localization procedure.     

The electronic structure of molecules by a many-body approach: V. Ionization potentials and one-electron properties of cyclopentadiene and 1-sila-cyclopentadiene-(2,4)

The valence ionization potentials (IP's) of cyclopentadiene and 1-sila-cyclopentadiene-(2,4) are studied by an ab initio many-body approach which includes the effect of electron correlation and reorganization beyond the Hartree-Fock approximation. The Hartree-Fock approximation gives the correct ordering of the IP's for cyclopentadiene but this ordering does not agree with the results of the previous experimental and theoretical studies. The ordering is 1a₂(π), 2b₁(π), 4b₂, 6a₁, 5a₁, 3b₂, 1b₁ (π), 4a₁, 2b₂, 3a₁. For sila-cyclopentadiene the ordering of the IP's is: 1a₂(π), 4b₂, 2b₁(π), 6a₁, 1b₁(π), 5a₁, 3b₂, 4a₁, 3a₁, 2b₂. The Hartree-Fock approximation is found to be incorrect with respect to the ordering of the 4b₂ and 2b₁(π) IP's. A number of one-electron properties are calculated in the one-particle approximation and compared with the available experimental data.     

Trans-N2F2 and cis-N2F2: A green's function calculation on their photoelectron spectra

The vertical valence ionization potentials of trans-N₂F₂ and cis-N₂F₂ have been computed by a many-body Green function method. For trans-N₂F₂ the agreement with experiment is very satisfactory in general and the calculations permit an analysis and assignment of the experimental photoelectron spectrum. The ionization potentials of cis-N₂F₂ are predictions. The ordering of the ionization potential is for trans-N₂F₂ 5ag(n₊), 2a_u(π), 4b_u(n_?), 4ag, 1b_g(π), 1a_u(π), 3b_u, 3a_g, 2b_u and for cis-N₂F₂ 4b₂ (n_?), 2b₁ (π) + 5a₁(n+), 3b₂, 1a₂ (π), 1b₁(π), 4a₁, 3a₁, 2b2, n₊ and n_? denote lone pairs on the N atoms except for the 4b_u(n_?) orbital which has the largest contribution from the F atoms.     

Photoelectron spectroscopy of heterocycles. Azaindenes and azaindolizines

The HeI photoelectron (PE) spectra of indole ( 1 ), benzimidazole ( 2 ), indazole ( 3 ), 3-chloro-indazole ( 4 ), imidazo[1,2-b]pyridazine ( 5 ), 6-chloroimidazo[1,2-b]pyridazine ( 6 ), 2-phenyl-imidazo[1,2-b]pyridazine ( 7 ), 2-phenyl-6-chloroimidazo[1,2-b]pyridazine ( 8 ), tetrazolo[1,2-a]-pyridine ( 9 ) and 8-cyanotetrazolo[1,5-a]pyridine ( 10 ) have been recorded. The spectra of 2–10 are of special interest for studying lone pair interactions. The assignment of the PE spectra submitted here, conjointly with the electronic structure of the studied compounds is discussed on the basis of molecular orbital calculations.     

The π-Orbital Sequence in Norbornadiene and Related Hydrocarbons

A method outlined previously [1] is used to show that in norbornadiene ( 3 ) the b ₂(π) orbital lies above a ₁(π), as predicted by theory. This indicates that in 3 through-space interaction between the two basis π-orbitals π_a and π_b is more important than through-bond interaction. Analysis of the PE.-spectra of 8-isopropylidene-tricyclo[3.2.1.0^2,4]-octane ( 13 ) and the corresponding octene ( 15 ) confirms that the π-orbital π_c of the exocyclic double bond conjugates more strongly with the symmetric Walsh-orbital e _s of the cyclopropano moiety than with the π-orbital π_a of a double bond in the same position.     

Photoelectron-Spectroscopic Evidence for the Orbital Sequence in Fulvene and 3, 4-Dimethylene-cyclobutene

The photoelectron spectra of fulvene (II) and of 3,4-dimethylene-cyclobutene (III) have been recorded. The PE. bands are correlated, in order of increasing ionisation potentials, with the following orbitals: II: 1 a ₂(π), 2 b ₁(π), 7 b ₂(π), 1 b ₁(π); III: 2 b ₁(ω), 1 a ₂(π), 10 a ₁(ω), 8 b ₂(ω), 1 b ₁(π). This assignment is based on a semi-quantitative perturbation MO-model and on the SCF-LCAO-MO calculations reported by Praud, Millie & Berthier [5] for benzene, II and III.     

2‐(4‐Bromophenyl)‐1,2‐dihydropyrimido[1,2‐a]benzimidazol‐4(3H)‐one and 4‐(4‐methylphenyl)‐3,4‐dihydropyrimido[1,2‐a]benzimidazol‐2(1H)‐one form hydrogen‐bonded base‐paired dimers

The title compounds, 2‐(4‐bromo­phenyl)‐1,2‐di­hydro­pyrimido­[1,2‐a]­benzimidazol‐4‐(3H)‐one, C₁₆H₁₂Br­N₃O, (IVa), and 4‐(4‐methylphenyl)‐3,4‐dihydropyrimido[1,2‐a]benzimidazol‐2‐(1H)‐one, C₁₇H₁₅N₃O, (Vb), both form R(8) centrosymmetric dimers via N—H?N hydrogen bonds. The N?N distance is 2.943 (3) Å for (IVa) and 2.8481 (16) Å for (Vb), with the corresponding N—H?N angles being 129 and 167°, respectively. However, in other respects, the supra­molecular structures of the two compounds differ. Both compounds contain different C—H?π interactions, in which the C—H?π(centroid) distances are 2.59 and 2.47 Å for (IVa) and (Vb), respectively (the latter being a short distance), with C—H?π(centroid) angles of 158 and 159°, respectively. The supramolecular structures also differ, with a short Br?O distance of 3.117 (2) Å in bromo derivative (IVa), and a C—H?O interaction with a C?O distance of 3.2561 (19) Å and a C—H?O angle of 127° in tolyl system (Vb). The di­hydro­pyrimido part of (Vb) is disordered, with a ratio of the major and minor components of 0.9:0.1. The disorder consists of two non‐interchangeable envelope conformers, each with an equatorial tolyl group and an axial methine H atom.     

The n-orbital sequence in 1,3 diazaadamantane

The photoelectron spectra of 1,3-diazaadamantane (1) and 1,3-diaza-6-methyleneadamantane (2) have been measured. An analysis of the spectra based on a ZDO model indicates that the ordering of the n-orbitals in 1 is b₂(n?λσ) above a₁(n₊?λσ). The splitting of b₂ and a₁ in 1 is dominated by the through space interaction. These results are confirmed by semiempirical calculations of the Extended Hückel and MINDO/3 type. An analysis of the PE spectrum of 1,3-diazaadamantanone(6) (5) indicates that in 5 the inductive effect of the CO group is dominant.     

Three closely related thienyl‐substituted 1,4‐epoxynaphtho[1,2‐b]azepines: hydrogen‐bonded assembly in one,two and three dimensions

(2R,4S)‐2‐(3‐Methylthiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxynaphtho[1,2‐b]azepine, C₁₉H₁₇NOS, (I), crystallizes with a single enantiomer in each crystal, whereas its geometrical isomer (2RS,4SR)‐2‐(5‐methylthiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxy‐naphtho[1,2‐b]azepine, (II), and (2RS,4SR)‐2‐(5‐bromothiophen‐2‐yl)‐2,3,4,5‐tetrahydro‐1,4‐epoxynaphtho[1,2‐b]azepine, C₁₈H₁₄BrNOS, (III), both crystallize as racemic mixtures. A combination of one C—H...O hydrogen bond and two C—H...π(arene) hydrogen bonds links the molecules of (I) into a three‐dimensional framework; the molecules of (II) are linked into a C(4)C(4)[R₂²(7)] chain of rings by a combination of C—H...N and C—H...O hydrogen bonds; and in (III), where Z′ = 2, a combination of four C—H...π(arene) hydrogen bonds and two C—H...π(thienyl) hydrogen bonds links the molecules into complex sheets. Comparisons are made with the assembly patterns in some aryl‐substituted 1,4‐epoxynaphtho[1,2‐b]azepines.     

The Photoelectron Spectra of Ni,Pd, Pt-Diallyl

The He (I) photoelectron (PE.) spectra of bis (π-allyl)palladium (2a) , bis (π-allyl)platinum (3a) , bis (π-methallyl)palladium (2b) and bis (π-methallyl)-platinum (3b) have been recorded and compared with the PE. spectra of bis (π-allyl)nickel (1a) and bis (π-methallyl)nickel (1b) . By use of the He (II) PE. spectra 2a, 2b and 3b and correlations between the PE. spectra of 1–3 it is possible to assign the first seven to eight transitions in the PE. spectra of 1–3 . In contrast to previous assignments it is shown that the first band in the PE. spectrum of 1a corresponds to the ejection of an electron from 7a_u, a pure ligand orbital. The assignment proposed is supported by semiempirical calculations of the INDO-type by considering the relaxation effects explicitly using the ΔSCF and transition operator method.     

Synthesis and structure of some group VII 1,2-diacyl cyclopentadiene complexes and their pyridazine derivatives

A series of 1,2-diacyl cyclopentadienyl tricarbonyl manganese and rhenium complexes, [M(CO)₃{η⁵-1,2-C₅H₃(CO-(R)₂}] (3a–c and 4a–b), were isolated utilizing a straightforward, 3-step route. The synthetic pathway began with a 1,2-diacyl cyclopentadiene (fulvene), followed by the formation of its corresponding thallium salt and transmetallation with the appropriate pentacarbonyl metal bromide. X-ray crystallographic analysis and high-accuracy mass spectrometry confirmed the structures of the both the 4-methoxyphenyl and 4-chlorophenyl diacyl rhenium complexes, [Re(CO)₃{η⁵-1,2-C₅H₃(CO-(4-OCH₃)C₆H₄)₂}] (4a) and [Re(CO)₃{η⁵-1,2-C₅H₃(CO-(4-Cl)C₆H₄)₂}] (4b). Diacyl complexes 3a–c and 4a–b were then ring-closed with hydrazine hydrate to form their corresponding pyridazine complexes, [M(CO)₃{η⁵-1,2-C₅H₃(1,4-(R)₂N₂C₂}] (5a–c and 6a–b), in good yields (60–83%). The pyridazyl ligands were found to be relatively labile, and recrystallization of the target complexes 5a–c and 6a–b afforded only the free pyridazine ligands.     

Binuclear iridium complexes containing bridging 1,2-dicarba-closo-dodecaborane-1,2-dichalocogenolato ligands: Molecular structures of the complexes [(CODIr)2(μ2-S2C2(B10H10))] and [(CpIr)2(μ2-Se2C2(B10H10))]

Four binuclear iridium complexes with a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligands [Ir₂(COD)₂(μ₂-E₂C₂B₁₀H₁₀)] [E = S (3a), Se (3b)] [(Cp^∗Ir)₂(μ₂- E₂C₂B₁₀H₁₀)] [E = S (5a), Se (5b)] have been synthesized through different method. The formal oxidation state of iridium in complexes 3 and 5 are I and II, respectively, due to the different electron donor coordinated to the iridium center. All four complexes 3a-5b are characterized by IR, ¹H, ¹³C, ¹¹B NMR spectra and elemental analyses. The molecular structures of complex 3a and 5b have been determined by X-ray crystallographic analysis, only 5b shows the metal-metal interaction between the two iridium atoms.     

Experimental and theoretical study of X-ray <Emphasis Type="Italic">K</Emphasis> edges absorption spectra of carbon and nitrogen in the phthalocyanine H<Subscript>2</Subscript>Pc molecule

The study of the electronic structure of H₂Pc was carried out to examine the structure of the lowest unoccupied molecular orbitals (LUMO) of molecule phthalocyanine by X-ray absorption spectroscopy using quantum-chemical calculations. The theoretical calculations were performed on the stationary theory (frozen orbital approximation, Z+1 model) and time-dependent density functional theory (TDDFT). A consideration of K edges absorption spectra of carbon and nitrogen in the common scale of binding energies allows estimating the contributions of AO of all phthalocyanine atoms to the LUMO, defining the sequence of levels, the binding energies of the corresponding levels, and also the character of electronic interactions between individual atoms. It was shown that the best agreement between the experimental and theoretical pre-edge structures of the absorption spectra of nitrogen and carbon for H₂Pc is observed in the case of the application of stationary density functional theory in Z+1 model to account for an X-ray hole. In this case the 2p _π AO of the Nα_(1,2) and Сα atoms make a predominant contribution to the LUMO. The 2p _π AO of the Nα_(1,2) atoms mainly contribute to the boundary LUMO with the energy ~–2.3 eV.     

Post-synthetic modification of divalent nickel acetate cubanes with carboxylates

Starting from nickel(II) cubane [Ni^II₄(HL)₄(OAc)₄] (2a), five different tetranuclear cubic complexes [Ni^II₄(HL)₄(O₂CR)₄] (3) were generated simply by applying a post-synthetic cubane modification strategy via a complete acetate-to-carboxylate co-ligand exchange. This was achieved by stirring the parent complex 2a with a large excess of the corresponding sodium carboxylate salt 4 for three days in THF. Single-crystal X-ray structure analyses of Ni^II cubanes 3a·2 Et₂O and 3b·0.5 CH₂Cl₂·0.5 Et₂O reveal unequivocally that both are isostructural in terms of the [Ni₄(μ₃-O₄]⁴⁺ core and crystallize in the triclinic space group P-1 with two molecules in the unit cell. In the solid state, the cubic centers of 3a,b differ only slightly in bond lengths and angles mainly due to the different substituents in the carboxylate co-ligand and packing in the unit cell. The orientation of 3a,b and the formation of supramolecular aggregates in the crystal packing were controlled by π–π interactions as well as intra- and intermolecular O–H?O hydrogen bonds. Variable-temperature magnetic susceptibility measurements reveal that 3a–c show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for all investigated complexes.     

Near Cancellation of Through Space and Through Bond Interaction in bicyclo[3.2.2]nona-6,8-diene

The photoelectron spectra of bicyclo[3.2.2]nonane and its five dehydrogenated analogues are reported. Analysis of the π-bands reveals that the unsymmetrical diene 5 retains the ‘natural order’ of the π-orbitals present in the lower homologues, i. e. the in-phase below the out-of-phase combination of the basis π-orbitals π_a and π_c. The isomeric diene 4 is the first member of the symmetrical homologous series (I), which inverts this order, so that a ₁(π) (in phase!) lies above b ₂(π) (out-of-phase!).     

Photoelectron spectrum and ground state electronic structure of chromyl chloride vapor

The electronic structure of chromyl chloride CrO₂Cl₂ has been investigated by ultraviolet (HeI) photoelectron spectroscopy. Mulliken-Wolfsberg-Helmholtz molecular orbital calculations have been performed in order to provide a model for interpretation of the photoelectron spectra and to assist in assigning the low-energy optical absorption and emission transitions. The first ionization potential of CrO₂Cl₂ at 11.8 eV is due to ionization of the near-degenerate oxygen and chlorine nonbonding 2a₂, 4b₁, and 4b₂ MO's. The first unoccupied orbital is basically a chromium dπ^* orbital. The excitations (2a₂, 4b₁, 4b₂)→ 7a₁^* correlate well with the three low energy absorption transitions observed.     

Molecular and Crystal Structures of CpSmX2(THF)3 (X = Br,I)

The reaction of Cp₂Sm(THF) with 1,2-dibromoethane or 1,2-diiodoethane leads to an equimolar mixture of Cp₃Sm(THF) and CpSmX₂(THF)₃ (X = Br, I). CpSmBr₂(THF)₃ crystallizes in the monoclinic system (P2₁, Z = 2, a = 804.6(1), b = 1507.6(2), c = 913.8(1) pm, β = 107.36(1)°, R₁ = 0.0327, wR₂ = 0.0578), while CpSmI₂(THF)₃ is orthorhombic (Pna2₁, Z = 4, a = 1950.6(3), b = 1377.1(2), c = 831.93(9) pm, R₁ = 0.0438, wR₂ = 0.0412). The ligand arrangement around the formally eight coordinate Sm atom is a distorted octahedron with the centroid of the Cp-ring and one THF-molecule in the apical positions, whilst the halides are transoid in the equatorial plane.     

Synthesis of 1,2-Disubstituted Ferrocene Containing a Heteroaryl Group

A convenient synthesis of [C₅H₅Fe(1,2-C₅H₃(CH₂R)(Heteroaryl)], (R=NMe₂, Heteroaryl=5-benzoylthien-2-yl(3a), 2-nitropyrid-5-yl(3b), 5-nitrothien-2-yl(3c), 6-methoxy-8-nitroquino-3-yl(3d); R=MeO, Heteroaryl=5-benzoylthien-2-yl(6a), 2-nitropyrid-5-yl)(6b) from [C₅H₅Fe(1,2-C₅H₃(CH₂R)(SnBu₃)], (R=NMe₂, OMe), via Stille coupling reaction is described.     

The ionization energies of bridged [14]annulenes and of dicyclohepta[cd,gh] pentalene

The ionization energies J_J, of 1,6;8,13-alkanediylidene-[14]annulenes ( 2 to 5 ) and of dicyclohepta[cd,gh]pentalene ( 1 ) have been determined by photoelectron spectroscopy, using HeI radiation. The data are interpreted in terms of Koopmans' theorem (J_J = ?ε_J) on the basis of correlation diagrams and with the help of simple molecular orbital models. If the bridge is an ethane-, propane- or butane-diylidene group, the π-orbital sequence, in descending order of orbital energies, is (in C_2v): b₁, b₂, a₂, a₁. The sequence is due to a complicated and not uniquely definable interplay of inductive, conjugative and homoconjugative effects. A detailed analysis of these effects suggests that the effective angle of twist between two consecutive basis-AOs 2p_μ, 2p_ν of the peripheral π-system should be smaller than the twist angles θ_μν determined by X-ray analysis, i.e. that the pi;-ribbon adjusts elastically and is no longer locally orthogonal to the σ-frame. In the non-alternant hydrocarbon 1 of symmetry D_2h, the sequence is 2b_2g, 3b_1u, 2b_3g, 1a_u, 2b_1u. The sequence 3b_1u above 2b_3g, _i.e. the reverse of b₂ above a₁ in the bridged [14]annulenes, is explained as being due to the interaction of the semilocalized perimeter orbitals b_1u and b_3g with the bonding (π(B_1u))and antibonding (π*(B_3g)) orbital of the central double bond. In 2 the replacement of the two latter orbitals by the Walsh-orbitals of the cyclopropane moiety leads to the sequence b₁, b₂, a₁, a₂. From the data observed for 1 to 5 and for 1,6-methano-[10]annulene [11], a crude estimate for the orbital energies of the hypothetical all-cis D_10h-[10]- and D_14h-[14]annulenes can be derived.     

两个含[MS4Cu4]簇核的一维配位聚合物{[MS4Cu4(bpe)2(ani)2I2]·3.5ani}n (M=Mo, W; ani=苯胺)的组装及其晶体结构

前驱团簇[Et₄N]₄[MS₄Cu₄I₆](M=Mo (1a); W (1b))与双齿桥连配体1, 2-双(4-吡啶基)乙烷(bpe)在苯胺溶液中反应, 生成2个结构相似的一维[MS₄Cu₄]团簇基配位聚合物{[MS₄Cu₄(bpe)₂(ani)₂I₂]·3.5ani}_n (M=Mo (2), W (3); ani=苯胺)。通过元素分析、红外光谱和X-射线单晶衍射对2和3进行了表征。晶体结构分析表明前驱团簇1a和1b中五核马鞍形[MS₄Cu₄]簇核分别在2和3中得以保留, 2个桥连配体bpe连接相邻的簇核, 在[111]方向延伸形成一维“Z”字形链结构。