Rotational excitation of ions produced by the He(2 S) Penning ionization of CO and N2

Rotational-state distributions of the CO⁺ (A–X, B–X) and N₂⁺(B–X) emissions produced by the collisions of He(2 ³S) with CO and N₂ were studied in the collision energy (E_R range 100–200 meV. The rotational populations of the emitting states can be fitte by single Boltzmann temperatures (T_R. The T_R (320 ± 30 K) for the ν′ = 3 and 4 levels of the CO⁺ (A²Π) state are nearly independent of, or slightly increase with, E_R, while T_R for the CO⁺(B²Σ⁺, ν′ = 0) state increases rapidly with E_R.The T_R (430 ± 20 K) for the N₂⁺(B²Σ⁺, ν′ = 0) state is nearly independent or slightly decreases with increasing E_R. Interactions providing these trends are discussed.     

Molecular structure and electrochemical properties of the Pt complex of 1,1′-bis(methylthio)ferrocene and the Pd complexes of 1,4,7-trithia[7]- and 1,5,9-trithia[9] (1,1′)ferrocenophanes

Molecular structures of (triphenylphosphine) [1,1′-bis-(methylthio)ferrocene-S,S′,Fe]Pt(BF₄)₂ (1), (1,5,9-trithia[9]ferrocenophane-S,S′,S″,Fe)Pd(BF₄)₂ (2), and (acetonitrile)(1,4,7-trithia[7]ferrocenophane-S,S′,S″,Fe)Pd(BF₄)₂ (3) were determined by X-ray analyses. The Pt in 1 and the Pd atom in 2 have a somewhat distorted square-planar geometry including the Fe atom of the ferrocene moiety, while the Pd atom in 3 is coordinated by one equivalent of acetonitrile and takes a distorted tetragonal-pyramidal geometry. The distances of the Fe---M bond (M = Pd, Pt) in 1–3 are 2.851(2), 2.827(2), and 3.0962(8) Å, respectively. Cyclic voltammetry of 1–3 gave no reversible wave, but afforded some information supporting the presence of a dative bond.     

Vibrational population inversion in CS(A) through the dissociative excitation of CS2 by Ar(P2)

The CS(A ¹Π → X ¹Σ⁺) emission spectra resulting from the energy transfer reaction of Ar(³P₂) + CS₂ under single collision condition have been obtained. The relative vibrational populations of the nascent product CS(A ¹Π, υ′) have been determined by means of spectral simulation. A population inversion is found at υ′ = 1. The population data are approximately represented by a distribution predicted from the impulsive half collision model. The dynamics and energetics of CS(A) formation has been discussed in detail.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

Syntheses of mixed ligands complexes of Ru(II) with 4,4′-dicarboxy-2,2′-bipyridine and substituted pteridinedione and the use of these complexes in electrochemical photovoltaic cells

The synthesis, spectral and photoelectrochemical studies of mixed ligand complexes of [Ru(dcbpy)₂(LL)]Cl₂, where LL=2,4-(1,3-N,N′-dimethyl)pteridinedione (DMP), 6,7-dimethyl-2,4-(1,3-N,N′-dimethyl)pteridinedione (MDMP), 6,7-diphenyl-2,4-(1,3-N,N′-dimethyl)pteridinedione (PhDMP), dibenzo[h,j]-(1,3-N,N′-dimethyl)isoalloxazine (BIAlo), 6,7-bis(pyrid-2-yl)-2,4-(1,3-N,N′-dimethyl) pteridinedione (PyDMP) were carried out. These complexes were attached to sol–gel processed TiO₂ electrodes and the photocells fabricated were illuminated with polychromatic radiation in the presence of I₂/I₃⁻ as redox electrolyte. The incident photon to current conversion efficiency determined was found to be 20–48%.     

The electronic quenching rates of NO(AΣ, v=0–2)

The electronic quenching rates of NO(A²Σ⁺, v^′=0–2) are measured for the gases He, Ar, Xe, N₂, O₂, CO₂, N₂O, and SF₆. The variations of the fluorescence intensity were measured for the (0,0), (1,0), and (2,0) bands of the γ band system when the quencher gases were added. The quenching rates were determined by using the Stern–Volmer plots with the known radiative lifetimes of the excited states. The electronic quenching rate constants are fast for the group of gases of O₂, CO₂, N₂O, and SF₆, whose quenching rate constants are in the order of 10⁻¹⁰ cm³/s. The quenching rate constants are slow for the group of gases including He, Ar, Xe, and N₂ whose rate constants are in the order of 10⁻¹⁴ cm³/s. For the slow group, the quenching rate constants increase rapidly for v^′=2 compared with those of v^′=0 and 1.

The charge transfer model and collision complex model are used to understand the quenching mechanism. For the fast group which mainly consists of gases with positive electron affinities, the charge transfer model adequately describes the mechanism. For the slow quenching group, a theoretical background is provided by consider the coupling of initial and final states in the complex potential surfaces.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Ethylene oligomerization by diimine iron(II) complexes/EAO

The catalytic properties of a series of Fe(II) diimine complexes (diimine=N,N′-o-phenylenebis(salicylideneaminato), N,N′-ethylenebis(salicylideneaminato), N,N′-o-phenylenebisbenzal, N,N′-ethylenebisbenzal) in combination with ethylaluminoxane (EAO) for ethylene oligomerization have been investigated. Treatment of the iron(II) complexes with EAO in toluene generates active catalytic systems in situ that oligomerize ethylene to low-carbon olefins. The effects of reaction temperature, ratios of Al/Fe and reaction periods on catalytic activity and product distribution have been studied. The activity of complex FeCl₂(PhCH=o-NC₆H₄N=CHPh) with EAO at 200°C is 1.35×10⁵ g oligomers/mol Fe·h, and the selectivity of C_4–10 olefins is 84.8%.     

Cyano-bridged bimetallic complexes of copper(II) with tetracyanonickelate(II). Crystal structure of [Cu(dpt)Ni(CN)4]

Five new complexes of composition [Cu(dpt)Ni(CN)₄] (1) (dpt=dipropylenetriamine), [Cu(dien)Ni(CN)₄]·2H₂O (2) (dien=diethylenetriamine), [Cu(N,N′-dimeen)Ni(CN)₄]·H₂O (3) (N,N′-dimeen=N,N′-dimethylethylenediamine), [Cu(N,N-dimeen)Ni(CN)₄]·H₂O (4) (N,N-dimeen=N,N-dimethylethylenediamine) and [Cu(trimeen)Ni(CN)₄] (5) (trimeen=N,N,N′-trimethylethylenediamine) have been obtained by the reactions of the mixture of Cu(ClO₄)₂·6H₂O, appropriate amine and K₂[Ni(CN)₄] in water and have been characterized by IR and UV–Vis spectroscopies and magnetic measurements. The crystal structure of [Cu(dpt)Ni(CN)₄] (1) has been determined by single-crystal X-ray analysis. The structure of 1 consists of a one-dimensional polymeric chain ---Cu(dpt)---NC---Ni(CN)₂---CN---Cu(dpt)--- in which the Cu(II) and Ni(II) atoms are linked by CN groups. The nickel atom is four coordinate with four cyanide-carbon atoms (two cyano groups are terminal and two cyano groups (in cis fashion) are bridged) in a square-planar arrangement and the copper atom is five coordinate with two cyanide-nitrogen and three dpt-nitrogen atoms, in a distorted square-pyramidal arrangement. The temperature dependence of magnetic susceptibility (2–300 K) was measured for compound 1. The magnetic investigation showed the presence of a very weak antiferromagnetic interaction (J=−0.16 cm⁻¹) between the copper atoms within each chain through the diamagnetic Ni(CN)₄ ²⁻ ions.     

A study on copper(II)-Schiff base-azide coordination complexes: Synthesis, X-ray structure and luminescence properties of [Cu(L)(N3)]X (L = Schiff bases; X = ClO4, PF6)

Two Schiff bases N,N′-(bis(pyridin-2-yl)benzylidene)propane-1,3-diamine (pbpd) and N,N′-(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (pfbd) have been prepared and used to synthesize copper(II) complexes. Four complexes of the type [Cu(L)(N₃)]X (1–4) [L = pbpd; X = ClO₄ (1); L = pbpd; X = PF₆ (2); L = pfbd; X = ClO₄ (3); L = pfbd; X = PF₆ (4)] have been synthesized and characterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical, luminescence and other physicochemical properties. Two representative complexes of the series, 2 and 3, have been characterized by single crystal X-ray diffraction measurements which reveal that in each complex the copper(II) ion assumes a distorted trigonal bipyramidal environment through coordination of the metal centre by two pyridine N atoms and two imine N atoms of the Schiff base with the fifth position occupied by a N atom of a terminal . They display intraligand ¹(π–π^*) fluorescence at room temperature and intraligand ³(π–π^*) phosphorescence in glassy solutions (MeOH at 77 K). A band (492 nm) observed for the complexes in their solid-state emission spectra is an excimeric emission arising due to an aromatic π–π interaction. Electrochemical electron transfer study reveals Cu^II–Cu^I reduction in methanolic solutions.     

Conformational and structural analysis of N-N′-bis(4-methoxybenzylidene)ethylenediamine

The Schiff base compound, N-N′-bis(4-methoxybenzylidene)ethylenediamine (C₁₈H₂₀N₂O₂) has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space group P2₁/n with a=10.190(1), b=7.954(1), c=10.636(1) Å, β=111.68(1)°, V=801.1(1) ų, Z=2 and D_cal=1.229 Mgm⁻³. The title structure was solved by direct methods and refined to R=0.056 for 2414 reflections [I>3.0σ(I)] by full-matrix anisotropic least-squares methods. The energy profile of the compound was calculated by PM3 method as a function of θ[N1′–C9′–C9–N1]. The most stable molecular structure of the title compound is the anti conformation, which is different in energy by 5.0 and 1.0 kcal mol⁻¹ from the eclipsed conformation I and gauche conformations, (III and V), respectively.     

Evaluation of the immobilized artificial membrane phosphatidylcholine: Drug discovery column for high-performance liquid chromatographic screening of drug–membrane interactions

Chromatographic retention factors (k′) of a series of eight β-adrenoceptor antagonist compounds (β-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k′ values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The β-adrenolytic drug's log k′_IAM values obtained with an IAM.PC.DD column were compared to an ^esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k′_IAM and the logarithm of the n-octanol–water partition coefficients (r_IAM.PC.DD=0.8710 vs. r_IAM.PC.MG=0.9538), the C₁₈ HPLC retention factors (r_IAM.PC.DD=0.8408 vs. r_IAM.PC.MG=0.9380), the liposome partition coefficients (r_IAM.PC.DD=0.8887 vs. r_IAM.PC.MG=0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the ^esterIAM.PC.MG column than the IAM.PC.DD column.     

High-order torsional couplings in the infrared spectrum of 3,3,3-trifluoropropene

A 2 MHz resolution electric-resonance optothermal spectrometer and a microwave-sideband CO₂ laser have been used with microwave-infrared double resonance to investigate high-order torsional couplings in the 10 μm infrared spectrum of 3,3,3-trifluoropropene. Three normal mode vibrations are studied with band origins at 963.4, 980.2 and 1025.2 cm⁻¹. The 963.4 cm⁻¹ band is well characterized by an asymmetric-top Hamiltonian, except for the presence of a weak perturbation for J′ = 7, K_a′ = 2 affecting only the A-symmetry internal-rotor state. Microwave-infrared double resonance is used to study the microwave spectrum of the perturbing or ‘dark’ state. The observed dark-state K-doublet asymmetry splittings and rotational-state selection rules indicate that the perturbing state has five quanta of excitation in the torsional mode (ν₂₁) built upon the A″ ν₁₉ fundamental. The precise frequency determined for 5 β₂₁ of 421(2) cm⁻¹ leads to the first accurate determination of the barrier to CF₃ internal rotation as 641(5) cm⁻¹. In contrast to the 963.4 cm⁻¹ vibration, the 980.2 and 1025.2 cm⁻¹ modes show a large number of J′ and K_a′ perturbations which differentially affect the A and E symmetry internal-rotor states. The magnitude of the perturbation-induced A/E splittings indicate that the perturbing states must have at least four quanta of torsional excitation. The present results suggest that high-order vibrational interactions are important in the vibrational dynamics of molecules at low levels of overall vibrational excitation.     

Observation and rovibrational analysis of the ν2 band of HCN–HCl

The high-resolution infrared absorption spectrum of an equilibrium mixture of HCN and HCl in a static gas long-path absorption cell is recorded in the 2500–2900 cm⁻¹ spectral region at 205 K. The spectrum shows rovibrational structure which has the typical appearance of a parallel band of a linear molecule and is assigned to the intramolecular H–Cl stretching vibration band ν₂ of the linear HCN–H³⁵Cl heterodimer. The rovibrational analysis of the band yield a band origin ν₀ of 2779.0968(12) cm⁻¹ together with a value for the upper-state rotational constant B′ of 0.067722(2) cm⁻¹. The observed red shift of 107 cm⁻¹ for the ν₂ band of HCN–H³⁵Cl relative to the H–Cl stretching vibration band of monomer H³⁵Cl is in excellent agreement with results from the MP2/6−311++G** level of theory. The value of the upper-state rotational constant shows that the intermolecular hydrogen bond shortens by 0.022 Å upon intramolecular vibrational excitation of the ν₂ mode.     

Synthesis, characterization and catalytic activity in Heck-type reactions of orthometallated Pd and Pt complexes derived from (1R,2R)-1,2-diaminocyclohexane

The chiral bis-imine (1R,2R)-C₆H₁₀-[E---N=CH---C₆H₃---3,4-(OMe)₂]₂ 1 (LH) reacts with [Pd(OAc)₂] (1:1 molar ratio; OAc=acetate) giving the orthometallated [Pd(OAc)(C₆H₂---4,5-(OMe)₂---2-CH=N-(1R,2R)-C₆H₁₀---N=CH---C₆H₃-3′,4′-(OMe)₂-κ-C,N,N)] 2 (abbreviated as [Pd(OAc)(L-κ-C,N,N)]), through C---H bond activation on only one of the aryl rings and N,N-coordination of the two iminic N atoms. 2 reacts with an excess of LiCl to give [Pd(Cl)(L-κ-C,N,N)] 3. The reaction of 3 with AgClO₄ and neutral or anionic ligands L′ (1:1:1 molar ratio) affords [Pd(L-κ-C,N,N)(L′)](ClO₄) (L′=PPh₃ 4a, NCMe 5, pyridine 6, p-nitroaniline 7) or [Pd(I)(L-κ-C,N,N)] 8. Complex 4a reacts with wet CDCl₃ giving [Pd(C₆H₂---4,5-(OMe)₂---2-CH=N-(1R,2R)---C₆H₁₀---NH₂-κ-C,N,N)(PPh₃)](ClO₄) 4b as a result of the hydrolysis of the C=N bond not involved in the orthometallated ring. The molecular structure of 4b·CH₂Cl₂ has been determined by X-ray diffraction methods. Cleavage of the Pd---N bond trans to the C_aryl atom can be accomplished by coordination of strongly chelating ligands, such as acetylacetonate (acac) or bis(diphenylphosphino)ethane (dppe), forming [Pd(acac-O,O′)(L-κ-C,N)] 9 and [Pd(L-κ-C,N)(dppe-P,P′)](ClO₄) 12, while classical N,N′-chelating ligands such as 1,10-phenantroline (phen) or 2,2′-bipyridyl (bipy) behave as monodentate N-donor ligands yielding [Pd(L-κ-C,N,N)(κ¹-N-phen)](ClO₄) 10 and [Pd(L-κ-C,N,N)(κ¹-N-bipy)](ClO₄) 11. Treatment of 1 with PtCl₂(DMSO)₂ (1:1 molar ratio) in refluxing 2-methoxyethanol gives Cl₂Pt[(NH₂)₂C₆H₁₀---N,N′] 13a and [Pt(Cl)(C₆H₂---4,5-(OMe)₂---2-CH=N-(1R,2R)---C₆H₁₀---NH₂-κ-C,N,N)] 13b, while [Pt(Cl)(L-κ-C,N,N)] 14 can be obtained by reaction of [Pt(μ-Cl)(η³-2-Me---C₃H₄)]₂ with 1 in refluxing CHCl₃. Complexes 2 and 3 catalyzed the arylation of methyl acrylate giving good yields of the corresponding methyl cinnamates and TON up to 847 000. Complex 3 also catalyzes the hydroarylation of 2-norbornene, but with lower yields and without enantioselectivity.     

The intramolecular dynamics of allene in the region around 6000 cm via eigenstate resolved IR spectroscopy

We have recorded and analyzed the molecular beam spectra of allene in the regions of the ν₁ + ν₅ and 2 ν₈ bands around 5947.5 and 6135.5 cm⁻¹, respectively. The ν₁ + ν₅ band only shows minor perturbations and we suspect the presence of a doorway state that causes parallel Coriolis coupling to the bath states. Perpendicular Coriolis interactions do not seem to play an important role since the size of the matrix elements does not increase systematically with J′. The spectrum in the region of the 2 ν₈ band is more complicated; a total of six sub-bands has been identified with K = 0–2. Based on the lack of any systematic dependence on J′ and an inverse dependence of the coupling on K, we expect that neither parallel nor perpendicular Coriolis coupling is present in this band. The effective lifetime for both bands is calculated to be about 200 ps, which is very similar to the lifetimes of an acetylenic C---H stretch overtone.     

Synthesis, crystal structures and magnetic properties of Cu(II) compounds bridged by the terephthalate ligand and hydrogen bonds

A 3D network [Cu(tmen)(tp)(H₂O)₂]_n (1) (tmen = N,N,N′,N′-tetramethylethylenediamine; tp = terephthalate) and a 2D sheet [Cu(pyrazole)₂(tp)]_n (2), featuring 1D chains interwoven by hydrogen bonds, have been prepared and characterized by means of X-ray analyses and magnetic measurements. For 1, coordinative zigzag chains contain Cu(II) centers capped by the chelate ligand tmen, in which the tetragonal structure is elongated due to Jahn–Teller distortion. Coordinated water molecules are hydrogen-bonded to two free carboxylate oxygens of tp bridges, leading to the observed 3D structure. The use of the non-chelating capping ligand pyrazole produced the covalent-bonded 1D linear compound 2 with hydrogen bonds. A severe octahedral distortion of the Cu(II) center arises from a small bite angle (52.3(1)°) of two carboxylate oxygen atoms of tp, which are in turn hydrogen-bonded to the N–H groups of pyrazole ligands coordinated to Cu(II) atoms in neighboring chains. Magnetic data were fitted with the high-temperature series expansion for the Heisenberg chain spin Hamiltonian H = −J∑_iS_i · S_i + 1 together with consideration of the molecular field approximation (zJ′). Both compounds interestingly exhibit ferromagnetic interactions with g = 2.17, J = 4.08 cm⁻¹, zJ′ = −0.28 cm⁻¹ for 1 and g = 2.09, J = 1.47 cm⁻¹, zJ′ = −0.04 cm⁻¹ for 2. By taking into account structural parameters of distances between Cu atoms, it is reasonably assigned that the ferromagnetic couplings (J > 0) in these systems originate from the hydrogen bonds. The spin density of the d_x²-y² orbital on a Cu(II) atom in a chain is propagated and induced over the d_z² orbital of another Cu(II) atom in an adjacent chain. This orbital orthogonality gives rise to such interactions. The negative zJ′ term suggests that the tp bridges communicate only tiny antiferromagnetic interactions.     

Magnetic susceptibility of 1,1′,2,2′-tetramethylcobaltocene and 1,1′-diethylcobaltocene: Evidence for the dynamic Jahn-Teller effect

The magnetic susceptibility of 1,1′,2,2′-tetramethylcobaltocene, Co[C₅H₃(CH₃)₂]₂, and 1,1′-diethylcobaltocene, Co(C₅H₄C₂H₅)₂, has been studied between 0.99 and 296 K. The data are well reproduced by a calculation of the dynamic Jahn-Teller effect for the ²E_1g(a_1g²e_2g⁴e_1g) ground state of D_5d symmetry. A suitable set of parameter values is given by ζ = 100 cm⁻¹, δ = 150 cm⁻¹, k_JT = 0.40, κ = 0.70. The magnetism of cobaltocene, Co(C₅H₅)₂, may be described by parameter values of comparable magnitude. The results imply a significantly larger reduction of the spin-orbit coupling parameter ζ due to covalency than of the orbital reduction factor κ.     

Intervalence electron transfer through a thiolate bridge ligand: a Fe–S–R–Fe mixed valence complex

The reaction of Cp(dppe)FeI with the ligands 2,2′- and 4,4′-dithiobispyridine (S₂(Py)₂) give the mononuclear or binuclear complexes of the type [Cp(dppe)Fe-S₂(Py)₂]PF₆, [Cp(dppe)Fe---SPy]PF₆ or [{Cp(dppe)Fe}₂-μ-SPy](PF₆)₂ depending on the reaction condition. Reaction of Cp(dppe)FeI with dithiobispyridines in presence of TlPF₆ as halide abstractor and using CH₂Cl₂ as a solvent gives the complexes [Cp(dppe)Fe-4,4′-S₂(Py)₂)₂]PF₆ (1) and [CpFe(dppe)-2,2′-S₂(Py)₂]PF₆ (2) whereas the same reaction using CH₃OH as a solvent and NH₄PF₆ as the halide abstractor leads to the formation of the Fe^III–thiolate complex [Cp(dppe)Fe-2,2′-SPy]PF₆ (3) and the mixed-valence complex [Cp(dppe)Fe^III-μSPy-Fe^II(dppe)Cp](PF₆)₂ (4). Magnetic and ESR measurements are in agreement with one unpaired electron delocalized between them. Mössbauer data indicate clearly the presence of two different iron sites, each one of the N-bonded and S-bonded iron atoms, with intermediate oxidation state Fe^II---Fe^III. An electron transfer intervalence absorption was observed for this complex at 780 nm (in CH₂Cl₂). By applying the Hush theory the intervalence parameters were obtained; =0.028, H_ab=361 cm⁻¹ which indicate Class II Robin–Day. Estimation of the rate electron transfer affords a value k_th=6.5×10⁶ s⁻¹. Solvent effect on the intervalence transition follow the Hush prediction for high dielectric constants solvents which permit the evaluation of the outer and inner-sphere reorganizational parameters, which were analyzed and discussed. The electronic interaction parameters compare well with those found for electron transfer in metalloproteins.     

Photodissociation spectroscopy of Mg—Ar

Mg⁺—Ar ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. The complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as X ²Σ⁺ → ²Π is observed with an origin at 31387 cm⁻¹ (vac) for ²⁴Mg⁺—Ar. The ²⁴Mg⁺—Ar spectrum is characterized by a 15 member progression with a frequency (ω′_e) of 272 cm⁻¹. An extrapolation of this progression fixes the excited state dissociation energy (D′_o) at 5552 cm⁻¹. The corresponding ground-state value (D″_o) is 1270 cm⁻¹ (3.6 kcal/mol). The ²Π _, spin—orbit splitting is 76 cm⁻.