Uncommon hydrogen bonds between a non-classical ethyl cation and π hydrocarbons: a preliminary study

This study undertakes a theoretical investigation into uncommon hydrogen bonds between the ethyl cation (C₂H₅ ⁺) and π hydrocarbons. Firstly, it considers the hyperconjugation effect of the ethyl cation, in which the non-localized hydrogen (H⁺) is taken to be a pseudoatom bound to the carbons of the methyl groups. The goal of the research is to use this electronic phenomenon to gain a better understanding of the (H⁺···π) and (H⁺···p-π) hydrogen bonds, which are considered uncommon because they are formed through the interaction of the H⁺ of the ethyl cation with the π bonds of the acetylene (C₂H₂) and ethene (C₂H₄), as well as with the pseudo-π bond of the cyclopropane (C₃H₆). In view of this, B3LYP/6-311++G(d,p) calculations were used to determine the geometries of the C₂H₅ ⁺···C₂H₂, C₂H₅ ⁺···C₂H₄, and C₂H₅ ⁺···C₃H₆ hydrogen-bonded complexes. Deformations of the bond lengths and bond angles of these systems were analyzed geometrically. Examination of the stretch frequencies and absorption intensities of the (H⁺···π) and (H⁺···p-π) hydrogen bonds has revealed red-shifts in π and p-π bonds. After structural modeling and vibrational characterization, analysis of the charge transfer following the ChelpG approach and subsequently quantification of the hydrogen bond energies (basis sets superpostition error and zero point vibrational energies being considered) were used to predict the strength of the (H⁺···π) and (H⁺···p-π) hydrogen bonds. In addition, the molecular topography was estimated using the quantum theory of atoms in molecules (QTAIM). QTAIM was chosen because of a desire to understand the (H⁺···π) and (H⁺···p-π) hydrogen bonds chemically on the basis of the quantity of charge density and interpretation of Laplacian fields. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Theoretical studies on Ru(fppz)2(CO)L (L = N -heterocyclic ligand): Electronic structure, absorption, phosphorescence, and solvatochromism

A series of ruthenium(II) complexes Ru(fppz)₂(CO)L [fppz = 3-trifluoromethyl-5(2-pyridyl)pyrazole; L = pyridine (1), 4-dimethylaminopyridine (2), 4-cyanopyridine (3)] were designed and investigated theoretically to explore their electronic structures, absorption, and emissions as well as the solvatochromism. The singlet ground state and triplet excited state geometries were fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO of 1–3 is composed of d_yz(Ru) atom and π(fppz). The LUMO of 1 and 2 is dominantly contributed by π*(fppz) orbital, but that of 3 is contribute by π*(L). Absorption and phosphorescence in vacuo, C₆H₁₂, and CH₃CN media were calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest-lying absorption of 1 and 2 at 387 and 391 nm is attributed to {[d_yz(Ru) + π(fppz)] → [π*(fppz)]} transition, but that of 3 at 479 nm is assigned to {[d_yz(Ru) + π(fppz)] → [π*(L)]} transition. The phosphorescence of 1 and 2 at 436 and 438 nm originates from ³{[d_yz(Ru) + π(fppz)] [π*(fppz)]} excited state, while that of 3 at 606 nm is from ³{[d_yz(Ru) + π(fppz)] [π*(L)]} excited state. The calculation results showed that the absorption and emission transition character can be changed from MLCT/ILCT to MLCT/LLCT transition by altering the substituent on the L ligand. The phosphorescence of 1 and 2 does not have solvatochromism, but that of 3 at 606 nm (vacuo), 584 nm (C₆H₁₂), and 541 nm (CH₃CN) is strongly dependent on the solvent polarity, so introducing electron-withdrawing group on ligand L will induce remarkable solvatochromism. Supported by the National Natural Science Foundation of China (Grant Nos. 20573042, 20703015, and 20333050)     

A Thermal And Structural Study on Lanthanum Hexacyanocobaltate(III) Pentahydrate. Part II

The thermal dehydration of La[Co(CN)₆]⋅5H₂O proceeded through at least three stages from the temperature range of30~230°C, and an abrupt mass loss occurred around 350°C and the perovskite type oxide,LaCoO₃ was obtained at 1000°C. After dehydration, the color of the anhydride changed from white to pale blue around 230°C and furthermore, the color changed to blue around 290°C. These color changes were discussed on the basis of the changes of coordination structures around Co ions. In La[Co(CN)₆]⋅5H₂O, Co³⁺ ions lie at the center of the O_h crystal field consisted of six CN^– ions. However, in the pale blue specimen, Co³⁺ ions were situated in the center of D_4h crystal field which was distorted the O_h one by lengthening of the trans CN^– ions along z-axis. In the blue specimen, Co³⁺ ions were reduced to Co²⁺ ions which were situated in the T_d crystal field formed by four CN^–ions as [Co(CN)₄]^2–. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reactions of [Cp*Ru(H<Subscript>2</Subscript>O)(NBD)]<Superscript>+</Superscript> with diynes

Abstract  Formal [2 + 2 + 2] addition reaction of [Cp*Ru(H₂O)(NBD)][BF₄] (NBD = norbornadiene) with 4,4′-Diethynylbiphenyl generates [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂. The reaction of [Cp*Ru(H₂O)(NBD)][BF₄] with 1,4-diphenylbutadiyne generates the unusual [2 + 2 + 2] additional organic compound Ph–C≡C–C₉H₈–Ph in addition to the organometallic compound [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄]. [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BPh₄]₂ is generated after the reaction of compound [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂ with Na[BPh₄]. The structure of this compound was confirmed by X-ray diffraction. A possible approach to form Ph–C≡C–C₉H₈–Ph and [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄] is suggested. Graphical Abstract  Formal [2 + 2 + 2] addition reaction of [Cp*Ru(H₂O)(NBD)]BF₄ (NBD = norbornadiene) with 4,4′-Diethynylbiphenyl generates [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂. The reaction of [Cp*Ru(H₂O)(NBD)][BF₄] with 1,4-diphenylbutadiyne simply generates unusual [2 + 2 + 2] additional organic compound Ph–C≡C–C₉H₈–Ph in addition to the organometallic compound [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄]. [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BPh₄]₂ is generated after the reaction of compound [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂ with Na[BPh₄]. The structure of this compound was confirmed by X-ray diffraction. And the possible approach to form Ph–C≡C–C₉H₈–Ph and [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄] was suggested. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sandwich complexes of Si, Ge, Sn, and Pb with cyclopentadienyl type derivatives of corannulene and fullerene C60: stability estimates and molecular and electronic structure prediction by the MNDO/PM3 method

The ability of cyclopentadienyl type derivatives of corannulene C₂₀H₁₀ and fullereneI _h -C₆₀ to form η⁵-π-complexes and the problem of their existence is discussed. MNDO/PM3 calculations of half-sandwich complexes η⁵-π-MC₂₀H₁₅, η⁵-π-MC₂₀H ₁₅ ⁺ , η⁵-π-MC₆₀H₅, η⁵-π-MC₆₀H₅ and sandwich complexes 2η⁵-π-M(C₂₀H₁₅)₂, 2η⁵-π-M(C₂₀H₁₅)₂, 2η⁵-π-M(C₆₀H₅)₂ (M=Si, Ge, Sn, Pb) were performed. For all systems studied, local minima were found on corresponding potential energy surfaces and the heats of formation, geometric parameters, and distributions of effective atomic charges were calculated. Sandwich complexes are most likely to exist with M=Si and Ge. The energy and geometric characteristics of η⁵-π-complexes of corannulene were compared with those of η⁵-π-complexes of fullereneI _h -C₆₀. It was concluded that the results of quantum-chemical calculations of sandwich type corannulene derivatives can be used for simulation of the geometry and electronic structure of analogous complexes of fullereneI _h -C₆₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1649–1656, September, 1999.     

The directed synthesis and the spectral and magnetic characteristics of a new multispin (S=7/2,T=292 K) trinuclear complex

The new trinuclear complex K{(CoTp^t-Bu)[Fe(CN)₆](CoTp^t-Bu)}, in which the initial structural fragments are linked by CN⁻ bridges, was synthesized by the directed stitching of mononuclear complexes, one of which was [Fe(CN)₆]³⁻ while the other was cobalt(II) tris(3-tert-butyl-l-pyrazolyl)borate ([(CoTp^t-Bu)]⁺). The magnetic moment of K{(CoTp^t-Bu)[Fe(CN)₆](CoTp^t-Bu)} at 292 K was 8.07 μ_β (S=7/2), indicating the absence of antiferromagnetic exchange interactions in the trinuclear complex. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 6, pp. 351–354, November–December, 1998.     

Temperature dependence of the ratios of the rate constants of hydroxylation of the cycloalkanes C6H12/C6D12 and C5H10/C6H12 in sulfuric acid

The temperature dependence of the ratios of the rate constants k(C₅H₁₀)/k(C₆H₁₂) and k(C₆H₁₂)/k(C₆D₁₂) for the reaction of the cycloalkanes C₅H₁₀, C₆H₁₂, and C₆D₁₂ with OH⁺ cations in the system (NH₄)₂S₂O₈ (0.1 mol/kg)-H₂SO₄ (94.4 mass %) in the 6–50 °C range has been studied. The activation energies found E(C₆H₁₂) − E(C₅H₁₀) = − 5.3 ± 0.3 and E(C₆D₁₂) − E(C₆H₁₂) = 7.9 ± 0.7 (kJ/mol) permits the comparison of OH⁺ to a group of reagents (NO₊², Pd²⁺, HSO₊³) which interact with the C-H bond via an electrophilic substitution mechanism. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 354–358, November–December, 2008.     

Electronic structure of the 3,3′-bis-[η5-π-1,2-dicarba-3-nickel(III)-closododecaborate](1-) anion, {NiIII[η5-π-(3)-1,2-B,C2H11]2}, in salts with different cations,in salts with different cations

The results of the spectral and magnetochemical studies of some salts of the “sandwich-like” paramagnetic anion {Ni^III[η⁵-π-(3)-1,2-B⁹C₂H₁₁]₂}^– (I) with the Cs⁺, (CH₃)₄N⁺, and (C₆H₅)₄P⁺ cations and the cation complex of Fe(II) and 1,10-phenanthroline, [Fe^IIPhen₃]²⁺, are reported. The solid-phase IR, Raman, and X-ray photoelectron spectroscopy methods and optical spectroscopy of solutions were used. The effective magnetic moments (μ_eff) of Ni(III) in anion (I) were measured by the Faraday technique and corrected for the diamagnetism of the aromatic cluster ligands 1,2-B₉C₂H ₁₁ ²⁻ (II). It is established that μ_eff is weakly dependent on the nature of the cation. The problems concerned with the nature of the metal-ligand bonds in metal-carborane systems like (I) are discussed. The hypothesis of the charge transfer from ligands (II) to the transition metal atoms is validated, the donor ability rows of the π-ligands are introduced, and the cluster structure of the systems under study is attested. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1060–1071, November–December, 1996. Translated by I. Izvekova     

A novel porous supramolecular complex constructed by the co-crystallization of melamine and sulfate via hydrogen bonds and aromatic π-π interaction

Co-crystallization of melamine(MA) and sulfate results in crystalline product [(C₃H₇N₆⁺)₂(SO₄²⁻)] · 2H₂O. The novel supramolecular complex has been characterized by elemental analysis, thermal analysis (TGA and DSC), nuclear magnetic resonance (NMR), and single crystal X-ray diffraction. X-ray crystallographic studies of the complex reveal that the title complex has a 3-D microporous structure which is linked by intense intermolecular hydrogen-bonding interactions (N–H······O, N–H······N, O–H······O) and aromatic π-π interaction, which stabilize the whole crystal framework. The TGA curve shows that the complex is stable up to 500 °C, above which its structure begins to collapse.     

Electrochemical approach to direct homogeneous chemical cyanation of ferricenium salts: The complexing of system components

An unusual homogeneous chemical reaction of a direct cyanation of ferricenium salts by hydrocyanic acid is analyzed on the basis of an electrochemical approach and the notions of the chemistry of coordination compounds about an inner-sphere electron transfer. The complexing between a ferricenium cation and cyanide anion is confirmed experimentally using a potentiometric titration of aqueous solutions of ferricenium tetrafluoroborate by hydrocyanic acid. Variations of the mechanism of a rebound substitution of the CN group in the cyclopentadienyl ring for the hydrogen atom are considered. The mechanism is based on the notion about an inner-sphere redox reaction between the Fe(III) atom of a ferricenium cation and the CN^- anion. The magnitude and sign of the difference between standard potentials of systems [(C₅H₅)₂M)]⁺/(C₅H₅)₂M and CN⁺/CN^- are found to represent a thermodynamic criterion indicating whether cations of metallocenes [(C₅H₅)₂M]⁺ may be directly cyanated by hydrocyanic acid. Dedicated to the memory of Academician A.N. Nesmeyanov, in connection with his centennial.     

Vibrational spectroscopy of intermediates in benzene-to-pheno conversion by FeO<Superscript>+</Superscript>

Gas-phase FeO⁺ can convert benzene to phenol under thermal conditions. Two key intermediates of this reaction are the [HO-Fe-C₆H₅]⁺ insertion intermediate and Fe⁺(C₆H₅OH) exit channel complex. These intermediates are selectively formed by reaction of laser ablated Fe⁺ with specific organic precursors and are cooled in a supersonic expansion. Vibrational spectra of the sextet and quartet states of the intermediates in the O-H stretching region are measured by infrared multiphoton dissociation (IRMPD). For Fe⁺(C₆H₅OH), the O-H stretch is observed at 3598 cm⁻¹. Photodissociation primarily produces Fe⁺+C₆H₅OH; Fe⁺(C₆H₄)+H₂O is also observed. IRMPD of [HO-Fe-C₆H₅]⁺ mainly produces FeOH⁺+C₆H₅ and the O-H stretch spectrum consists of a peak at ∼3700 cm⁻¹ with a shoulder at ∼3670 cm⁻¹. Analysis of the experimental results is aided by comparison with hybrid density functional theory computed frequencies. Also, an improved potential energy surface for the FeO⁺+C₆H₆ reaction is developed based on CBS-QB3 calculations for the reactants, intermediates, transition states, and products.     

Ion—molecule reactions of CH+3 with acetonitrile at thermal translational energies

The 0.1 eV translational energy reactions of CH⁺₃ and CD⁺₃ with acetonitrile were studied in a tandem Dempster-ion cyclotron resonance mass spectrometer. Channels leading to CH₃CNH⁺ (7%), H₂CN⁺ (58%), and C₂H⁺₅ (35%) were observed. For CD⁺₃ reactant ions the H₂CN⁺ and C₂H⁺₅ products show evidence of complete H, D isotopic scrambling, suggesting an intermediate complex.     

Impact of Transition Metal Substituents on Polysilane Properties: Iron versus Ruthenium

Summary. The previously unknown ruthenio disilanes Rp–Si₂Me₄–C₆H₄X (Rp = η⁵-C₅H₅Ru(CO)₂; X = H, Br, –CHO, CH=C(CN)₂) were synthesized from ClSi₂Me₄C₆H₄X (X = H, Br) and Rp⁻ using conventional chemical methods. Trends in the UV/Vis absorption spectra indicate strong electronic coupling within the Rp–Si–Si–C_aryl fragment and, therefore, closely resemble the ones observed for the corresponding iron complexes. The four compounds however, were shown to be less sensitive towards UV irradiation. The crystal structure of Rp–Si₂Me₄–C₆H₄CH=C(CN)₂ was determined by X-ray diffraction and exhibits an all-trans-array of the Ru–Si–Si–C_aryl moiety, what is a basic requirement for optimal through-bond interaction.     

Simulation of molecular and electronic structure of η5-π-complexes of fullereneI h -C 60 with half-sandwich XCp species (X=Si, Ge, Sn)

The molecular and electronic structure of hypothetical complexes of unsubstituted fullerene C₆₀ withI _h symmetry and its cyclopentadienyl type derivatives were simulated by the MNDO/PM3 method taking the C₆₀(XC[) _n molecules (n=1, 2, 10, 12; X=Si, Ge, Sn) and η⁵-C₆₀H₅XCp (X=Ge, Sn), respectively, as example. The complexes 12η⁵-πC₆₀(XCp)₁₂ and η⁵-πC₆₀XCp withI _h andC _5v symmetry, respectively, were found to be the most stable compounds. The energies of the X−C₆₀ bonds in these complexes are close to those of X−Cp bonds in bis(cyclopentadienyl) complexes XCp₂ and are substantially higher than the energies of similar bonds in complexes of unsubstituted fullerene η¹-πC₆₀(XCp)⁻ and η⁵-πC₆₀(XCp)⁺. Geometric parameters and spin densities in radicals C₆₀XCp and biradicals C₆₀(XCp)₂ and C₆₀H₁₀ were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2155–2165, November, 1998.     

Synthesis, characterization and properties of β-octamolybdate-supported transition metal complexes with mixed ligands: [Cu(2,2′-bipy)(C6H5NO2)(H2O)]2[Mo8O26]·5H2O

A novel organic–inorganic hybrid compound [Cu(2,2′-bipy)(C₆H₅NO₂)(H₂O)]₂[Mo₈O₂₆]·5H₂O (1), (2,2′-bipy = 2,2′-bipyridine; C₆H₅NO₂ = pyridine-4-carboxylic acid) has been prepared and characterized by elemental analyses, IR spectrum, thermal stability analysis, and single-crystal X-ray diffraction. Compound 1 is a discrete cluster, constructed from β-[Mo₈O₂₆]⁴⁻ subunits covalently bonded to two [Cu(2,2′- bipy)(C₆H₅NO₂)(H₂O)]₂⁴⁺ coordination cations via terminal oxo groups that connect one molybdenum site. A 3D supramolecular network is further formed by extensive hydrogen bonding interactions and π–π interactions of the 2,2′-bipy and pyridine-4-carboxylic acid ligands. EPR and magnetic susceptibility studies have been used to elucidate the electronic properties of the Cu²⁺ centres, and the results are in good agreement with the structural features of the compound.     

Crystal structure and spectral characteristics of {[(C6H5)NH]2C=NH(C6H5)}[B(C6H5)4]·C2H5OH

A novel compound of {[(C₆H₅)NH]₂C=NH(C₆H₅)}[B(C₆H₅)₄]·C₂H₅OH is prepared and examined by single crystal X-ray diffraction. Crystal data: C₄₅H₄₄BN₃O, M = 653.64, monoclinic, space group P2₁/c, unit cell parameters: a = 24.375(2) Å, b = 17.5829(15) Å, c = 18.090(1) Å, β = 105.277(2)°, V = 7479.0(11) ų, Z = 8, d _calc = 1.161 g/cm³, T = 293 K, R ₁ = 0.064. The structure contains two crystallographically independent cations, two anions, and two solvate ethanol molecules. Three types of interactions occur between them: interionic N-H(N)⋯π and N(H)⋯π⋯H(C), π-delocalized system of Ph rings of the anions, and interaction of ions with ethanol molecules N-H⋯O-H(O)⋯π. The compound is characterized by IR and luminescence spectra. At room temperature, the emission intensity grows with time of exposure to UV irradiation. Original Russian Text Copyright ? 2008 by T. M. Polyanskaya, E. A. Il’inchik, V. V. Volkov, M. K. Drozdova, O. P. Yur’eva, and G. V. Romanenko __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 49, No. 3, pp. 512–521, May–June, 2008.     

Dimerization and Coordination Properties of Zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine in Relation to DABCO in <Emphasis Type="Italic">o</Emphasis>-Xylene and Chloroform

For the first time the interactions between zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in o-xylene and chloroform have been studied by calorimetric titration and NMR and electron absorption spectroscopic methods. It has been found that in o-xylene at concentrations of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc higher than 6×10⁻⁴ mol⋅L⁻¹ π–π dimers species are formed (λ _max= 685 nm). Additions of DABCO to the solution up to mole ratio 1 : 8 (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc : DABCO) lead to a shift of the aggregation equilibrium towards monomer species due to formation of monoligand axial complexes. Further increasing the DABCO concentration results in formation of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc—DABCO—Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc sandwich dimers (λ _max= 675 nm).     

Photoisomerisation in single molecules of nitroprusside embedded in mesopores of xerogels

Photoswitchable hybrid materials are successfully prepared by embedding guanidinium nitroprussides (GuNP, (CN₃H₆)₂[Fe(CN)₅NO]) into mesopores of transparent xerogel monoliths. The such prepared hybrid materials exhibit a higher photostability than the corresponding GuNP solutions, whereby the chemical stability of the [Fe(CN)₅NO]²⁻-anion in titania gel is nearly infinite. By irradiation with light in the blue-green spectral range one nitrosyl isomer is formed by a 180° rotation of the NO ligand changing the Fe–NO into a Fe–ON coordination (SI), which is detected by the shift of the ν(NO) stretching vibration from 1945 cm⁻¹ (Fe–NO) to 1820  cm⁻¹ (Fe–ON). Consequently there is enough space around the NO-ligand for such movement in xerogel mesopores. The embedding in silica xerogels increases the achievable population of the isomeric nitrosyl configuration to about 15% with respect to a single crystalline powder where only 9% are reached.     

Multiple-layer heterometallic MnII–AgI coordination polymers constructed from [Ag 2I (CN)3]? and [AgI(CN)2]? units

Two multiple-layer heterometallic Mn^II–Ag^I coordination polymers, {Mn^II(ampyz)(H₂O)[Ag₂^I(CN)₃][Ag^I(CN)₂]·ampyz} _n (1) and {[Mn^II(benzim)₂[Ag^I(CN)₂]₂][(benzim)Ag^I(CN)]·H₂O} _n (2) where ampyz = 2-aminopyrazine and benzim = benzimidazole, have been prepared and structurally characterized. Compound 1 reveals a multiple-layer two-dimensional network with strong hexanuclear argentophilic interactions leading to an infinite three-dimensional framework. Compound 2 has an unprecedented double-layer two-dimensional squared grid-type network with (4,4) topology through Ag^I···Ag^I and π–π interactions between two adjacent squared layers. These double-layer networks of 2 are linked to others by π–π interactions, leading to a three-dimensional framework.     

Ab initio MO LCAO SCF simulation of molecular and electronic structure of η5-π-C60H5XCp (X=Fe, Si) complexes

The problem of existence of η⁵-π-complexes of unsubstituted fullereneI _h -C₆₀ and its cyclopentadienyl type derivative C₆₀H₅ ^. is discussed.Ab initio MO LCAO SCF calculations of hypothetical sandwich systems η⁵-π-C₆₀H₅XCp (X=Fe (1a), Si (1b)), the cationic complex C₆₀FeCp⁺ of unsubstituted C₆₀, and the C₆₀H₅ ^. radical were performed in the STO-3G and 3-21G basis sets. In the1a, 1b, and C₆₀H₅ ^. systems, hydrogen atoms are attached to carbon atoms of fullerenei _h -C₆₀ at α-positions relative to the same pentagonal face (pent ^*). In η⁵-complexes, XCp species are also coordinated to this face. According to calculations in the 3-21G basis set, the Fe-pent ^* bond energy in complex1a is much higher than those of similar bonds in1b and in the η⁵-π-C₆₀FECp⁺ cation (117 kcal mol⁻¹ vs. 37 and 64 kcal mol⁻¹, respectively) and is 7 kcal mol⁻¹ higher than the Fe−Cp bond energy in the classical sandwich system FeCp₂. The Fe…C _pent* and Fe…C_Cp distances in complex1a are slightly shorter than the Fe…C distance in the ferrocene molecule. The spin populations in the C₆₀H₅ ^. radical are almost completely localized on the atoms of thepent ^* face, which must favor the formation of η⁵-π-complexes of this radical. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1657–1662, September, 1999.