THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) I. N,N'-Bis-(acetylacetone) ethylenediimine and N,N'-Bis-(1,1,1-trifluoroacetylacetone) ethylenediimine

Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)₂], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)₂], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)₂], g_z =2.183 ± 0.003, g_x =2.047 ± 0.004, g_y =2.048 ± 0.004, A_z =204.8 × 10^?4cm^?1, A_x =31.5 × 10^?4cm^?1, A_y =27.1 × 10^?4 cm^?1, A_zN= 12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.3 × 10^?4 cm^?1: Cu[en(tfacac)₂], g_z =2.192 ± 0.002, g_x =2.048 ± 0.004, g_y =2.046 ± 0.004, A_z =200.8 × 10^?4 cm^?1, A_x =31.1 × 10^?4 cm^?1, A_y =28.3 × 10^?4 cm^?1, A_zN =12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.6 × 10^?4 cm^?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp².     

Pulse radiolysis and voltammetry of bis(diamine)dioxorhenium(V) complexes

The Re(V) complexes [Re(L)₂O₂]⁺ [L = en (1,2-diaminoethane) or pn (1,3-diaminopropane)] are reduced irreversibly near −1.5 V (SCE) in a neutral or basic aqueous solution, but protonation causes a significant anodic shift of ≈ + 1 V. No oxidation is observed in aqueous solution before the solvent limit (≈ + 1 V) at solid electrodes but oxidation of [Re(en)₂O₂]⁺ with OH in pulse radiolysis experiments generates a Re(VI) intermediate which decays by first-order kinetics (k_d 2.5 × 10⁴ s⁻¹), apparently by rate-determining ligand loss. Reduction with e⁻_aq likewise forms transient d³-Re(IV) complexes which show first-order decay (6 × 10³ s⁻¹ for en, 9 × 10³ s⁻ for pn), ultimately to ReO₂. Transient intermediates were characterized by their electronic spectra, which for d³-Re(IV) complexes are qualitatively similar to Cr(III) and known octahedral Re(IV) complexes with different donor ligands.     

High resolution Fourier transform spectroscopy of the PbO molecule from investigation of the O2(1Δg)—Pb reaction

From the reaction of Pb with metastable oxygen O₂(¹Δ_g) in a Broida type oven we have analysed at high resolution some vibrational levels of the X0⁺, a1, A0⁺ and B1 states of the ²⁰⁸PbO molecule. The rotational parameters determined allowed us to recalculate the position of the various isotope lines to within 0.01 cm⁻¹. We have found a negative value of ω_eχ_e (−0.123 (25) cm⁻¹) in A0⁺, contrary to previous observations. The Ω type doubling in a1 varies from +1.8 × 10⁻⁴ cm⁻¹ (υ′ = 2) to +2.3 × 10⁻⁴ cm⁻¹ (υ′ = 9) and in B1 from −1.17 × 10⁻⁴ cm⁻¹ (υ′ = 0) to −0.97 × 10⁻⁴ cm⁻¹ (υ′ = 2).     

THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) II. N,N'-bis(salicylidene)ethylenediimine and 7-methyl-N,N'-bis (salicylidene)ethylenediimine

Abstract

The EPR spectra of single crystals of ⁶³Cu(II) doped N, N'-bis(salicylidene)ethylenediimine Ni(II), [Ni(sal)₂en] and 7-methyl-N, N'-bis(salicylidene)ethylenediimine Ni(II), [Ni(7-me sal)₂en] have been studied. The usual doublet spin-Hamiltonian parameters for the complexes have been found to be: Cu(II)[(sal)₂en]; g _z =2.192 ± 0.002; g _x =2.046 ± 0.004; g _y =2.049 ± 0.004; A _z =201.0 × 10^?4 cm^?1; A _x =29.3 × 10^?4 cm^?1; A _y =31.3 × 10^?4 cm^?1; A^N _z =12.6 × 10^?4 cm^?1; A ^N _x =14.5 × 10^?4 cm^?1; A ^N _y =15.7 × 10^?4 cm^?1; A ^H _z =6.3 × 10^?4 cm^?1; A ^H _x =7.3 × 10^?4 cm^?1; A ^H _y =7.9 × 10^?4 cm^?1; Cu(II)[(7-me sal)₂en]; g _z =2.189 ± 0.002; g _x =2.037 ± 0.004; g _y =2.046 ± 0.004; A _z =203.0 × 10^?4 cm^?1; A _x =36.9 × 10^?4 cm^?1; A _y =22.7 × 10^?4 cm^?1; A ^N _z =12.6 × 10^?4 cm^?1; A ^N _x =13.3 × 10^?4 cm^?1; A ^N _y =14.0 × 10^?4 cm^?1. Values of molecular orbital coefficients calculated for these complexes show that their bonding properties are similar to those of other compounds of this type. There is considerable covalency in the metal-ligand [sgrave]-bonds, and significant in-plane pi-bonding is present.     

Synthesis,formation constants and reactions of cationic rhodium(I) complexes of nitriles

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with nitriles produce new cationic rhodium(I) complexes, [RhL(CO)(PPh₃)₂]ClO₄ [L = CH₃CN (1), CH₃CH₂CH₂CN (2) or C₆H₅CN (3)], whose spectral data suggest that the nitriles are coordinated through the nitrogen atom. Formation constants for the reaction Rh(ClO₄)(CO)(PPh₃)₂ + L ⇋ [RhL(CO)(PPh₃)₂]ClO₄, have been measured to be 1.01 × 10⁵ M⁻¹ (CH₃CN), 1.07 × 10⁵ M⁻¹ (CH₃CH₂CH₂CN) and 2.59 × 10⁴ M⁻¹ (C₆H₅CN) at 25°C in monochlorobenzene. The differences in the formation constants for the different nitriles seem to be predominantly due to differences in ΔH (not to differences in ΔS). The nitriles in 1–3 are readily replaced with nitrogen base ligands (unsaturated nitriles and pyridine) and PPh₃.     

Synthesis,structure and fluxional behaviour of isomeric bis(trimethylstannyl)dihydropentalenes

Interaction of dihydropentalene (IV) with trimethylstannyldiethylamide in molar ratios of 1:1 or 1:2 leads to mono- or bis-organotin derivatives of IV, respectively. X-ray analysis of trans(E)-bis(trimethylstannyl)dihydropentalene (Va) has been carried out, R = 3.4%. Molecules of Va are centrosyommetric. The parmeters of monoclinic cell: a 8.680(1), b 7.322(1), c 13.073(2) Å, β 97.74(1)°, space group P2₁/c, Z = 2. Geometrical parameters of Va have been determined and their values are discussed in comparison with the same parameters for η¹-cyclopentadienyl compounds of elements. Chemical shifts ¹³C, ¹H and ¹¹⁹Sn and coupling constants ¹³C-¹¹⁹Sn and ¹¹⁷Sn-¹¹⁹Sn of bis- and tris-organotin derivatives of IV have been determined. Rapid intramolecular suprafacial metallotropic rearrangement, proceeding as a [1,5]-sigmatropic shift of SnMe₃ group, has been found in Va and cis-(Z)-bis(trimethylstannyl)dihydropentalene (Vb). Activation parameters have been evaluated by the analysis of temperature dependence of ¹³C NMR spectra within the framework of degenerate two-site exchange in the isomers Va and Vb, E_A: 42.2±0.9 and 31.2±0.6 kJ · mole⁻¹; ΔH^≠₂₉₈: 39.8±0.9 and 27.7±0.6 kJ · mole⁻¹; ΔS^≠₂₉₈: −6.2±4.0 and −87.0±3.1 J · mole⁻¹ · K⁻¹ and ΔG^≠₂₉₈: 41.6±1.5 and 54.6±1.1. kJ δ mole⁻¹, respectively.     

EPR- und Ligandenfeld-Spektren von Chlorovanadaten(IV). Die Kristallstruktur von PPh4[VxTi2–xCl9] (x = 0,15)

E.P.R. and Ligand Field Spectra of Chlorovanadates(IV). The Crystal Structure of PPh₄[V_xTi_2–xCl₉] (x = 0.15) Black, moisture-sensitive crystals of PPh₄[V_xTi_2–xCl₉] (x = 0.15) are formed by the reaction of titanium tetrachloride and PPh₄[VCl₅] in dichloromethane. Its EPR and ligand field spectra as well as those of PPh₄[VCl₅] and (PPh₄)₂[V₂Cl₉][VCl₅] · CH₂Cl₂ were recorded. In the mixed crystals of PPh₄[V_0.15Ti_1.85Cl₉], the existence of [VTiCl₉]^? ions consisting of trigonally distorted, face sharing octahedra can be proven by the spectra. The spectra of the compounds with [VCl₅]^? ions can only be explained when a significant Jahn-Teller distortion of the trigonal bipyramids is assumed; this distortion was not detected in the crystal structure determination of (PPh₄)₂[V₂Cl₉][VCl₅] · CH₂Cl₂. The crystal structure of PPh₄[V_0.15Ti_1.85Cl₉] was determined by X-ray diffraction (2588 independent observed reflexions, R = 0.044). Crystal data: triclinic, space group P1 , a = 1090.4, b = 1217.4, c = 1287.7 pm, α = 73.19°, β = 69.87°, γ = 82.15°, Z = 2. The compound consists of PPh₄^⊕ and [V_0.15Ti_1.85Cl₉]^? ions. In the anions, Ti and V atoms are distributed statistically in the two face sharing octahedra.     

Synthesis and characterization of cyclometallated palladium(II) and platinum(II) complexes with amide-thiolate ligands

The redox reaction of bis(2-benzamidophenyl) disulfide (H₂L-LH₂) with [Pd(PPh₃)₄] in a 1:1 ratio gave mononuclear and dinuclear palladium(II) complexes with 2-benzamidobenzenethiolate (H₂L⁻), [Pd(H₂L-S)₂(PPh₃)₂] (1) and [Pd₂(H₂L-S)₂ (μ-H₂L-S)₂(PPh₃)₂] (2). A similar reaction with [Pt(PPh₃)₄] produced only the corresponding mononuclear platinum(II) complex, [Pt(H₂L-S)₂(PPh₃)₂] (3). Treatment of these complexes with KOH led to the formation of cyclometallated palladium(II) and platinum(II) complexes, [Pd(L-C,N,S)(PPh₃)]⁻ ([4]⁻) and [Pt(L-C,N,S) (PPh₃)]⁻ ([5]⁻). The molecular structures of 2, 3 and [4]⁻ were determined by X-ray crystallography.     

Gold clusters: synthesis and characterization of [Au8(PPh3)7(CNR)]2+, [Au9(PPh36(CNR2]3+ and [Au11(PPH37(CNR)2O]2+ and their reactivity towards amines. The crystal structure of [Au11(PPh3)7(CN-i-Pr)2I](PF6)2

In the reactions of [Au₈(PPh₃)₇]²⁺, [Au₈(PPh₃)₈]²⁺ and [Au₉(PPh₃)₈]³⁺ with RNC (R = isopropyl and t-butyl) in dichloromethane [Au₈(PPh₃)₇CNR]²⁺ is initially, and is then converted into [Au₉(PPh₃)₆(CNR)₂]³⁺ via various intermediates. [Au₉(PPh₃)₆(CNR)₂]³⁺ reacts with I⁻ at low temperature (−78°C) in methanol to yield [Au₁₁(PPh₃)₇(CNR)₂I]²⁺, but when the reaction is carried out at room temperature Au₁₁ (PPh₃)₆(CNR)I₃ is formed. The cluster compounds have been characterised by elemental analysis, ³¹P{¹H} NMR, conductivity measurements, IR and ¹⁹⁷Au Mössbauer spectroscopy. The reactions of the clusters with amines to form carbene clusters are very slow, and the reasons for this are considered.The structure of [Au₁₁C₁₃₄H₁₁₂IN₂P₇](PF₆ was determined by X-ray diffraction. M_r = 3796.39 cubic, space group 143_d, a 37.955(12) Å, V 54677.2 ų, Z = 16, D_c = 2.21 Mg m⁻³, Mo-K_α radiation (graphite crystal monochromator, λ 0.71069 Å), μ(Mo-K_α) 125.2 cm⁻¹, F(000) = 33510.3, T 293 K. Final conventional R-factor = 0.048, R_w = 0.062 ofr 1867 unique reflections and 198 variables. The Au-skeleton is the same as in Au₁₁(PPh₃)₈I₃ having C_3v symmetry with one central and 10 peripheral Au atoms.     

EPR and optical absorption studies of Cu2+ doped bis (glycinato) Mg (II) monohydrate single crystals

Electron paramagnetic resonance (EPR) study of Cu²⁺ doped bis (glycinato) Mg (II) monohydrate single crystals is carried out at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the parameters: Cu²⁺ (I), g_x = 2.1577 ± 0.0002, g_y = 2.2018 ± 0.0002, g_z = 2.3259 ± 0.0002, A_x = (87 ± 2) × 10^?4 cm^?1, A_y = (107 ± 2) × 10^?4 cm^?1, A_z = (141 ± 2) × 10^?4 cm^?1; Cu ²⁺ (II), g_x = 2.1108 ± 0.0002, g_y = 2.1622 ± 0.0002, g_z = 2.2971 ± 0.0002, A_x = (69 ± 2) × 10^?4 cm^?1, A_y = (117 ± 2) × 10^?4 cm^?1and A_z = (134 ± 2) × 10^?4 cm^?1. The ground state wave function of the Cu²⁺ ion in this lattice is evaluated to be predominantly |x² ? y². The g-factor anisotropy is also calculated and compared with the experimental value. With the help of the optical absorption study, the nature of bonding in the complex is discussed.     

Kinetic study of some reactions related to the Mn(II)-catalyzed bromate-saccharide oscillating reactions

In the stirred batch experiment, the Mn(II)-catalyzed bromate-saccharide reaction in aqueous H₂SO₄ or HClO₄ solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second-order rate constants of the Mn(III)-saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M⁻¹ s⁻¹ in 1.00 M H₂SO₄ and (4.69, 7.51, 10.2, 13.5, and 36.2) M⁻¹ s⁻¹ in (2.00–4.00) M HClO₄ for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo-first-order rate constant of the Mn(III)-Br⁻ reaction is k_obs = (0.2 ± 0.1) [Br⁻] + (130 ± 5)[Br⁻]² + (2.6 ± 0.1) × 10³[Br⁻]³ + (1.2 ± 0.2) × 10⁴[Br⁻]⁴ s⁻¹ and the rate constant of the Br₂ Mn(II) reaction is less than 1 × 10⁻⁴ M⁻¹ s⁻¹. The second-order rate constants of the Br₂-saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10⁻⁴ M⁻¹ s⁻¹ at 25°C for glucose, galactose, xylose, arabinose, and ribose, respectively.     

Thermodynamic properties of potassium metasilicate (K2SiO3)

The standard enthalpy of formation of potassium metasilicate (K₂SiO₃), determined by hydrofluoric acid solution calorimetry, was found to be ΔH^o_f,298 = −363.866±0.421 kcal mol⁻¹ (−1522.415±1.762 kj mol⁻¹). The standard enthalpy of formation from the oxides was found to beΔH^o₂₉₈ = −64.786±0.559 kcal mol⁻¹ (−271.065±2.339 kJ mol⁻¹).These experimentally determined data were combined with data from the literature to calculate the Gibbs energies of formation and equilibrium constants of formation over the temperature range of the literature data. The standard enthalpies of formation and Gibbs energies of formation are given as functions of temperature. The standard Gibbs energy of formation is ΔG_f,298.15⁰ = −341.705 kcal mol⁻¹ (−1429.694 kJ mol⁻¹).     

New octahedral bis(diphenylphosphino)methanide derivatives and heterometallic species from mixed ligand isocyanide-dppm iron(II) complexes

The cationic [FeL(dppm)(CNPh)₃]ⁿ⁺ (1a: L = I, n = 1; 1b: L = CNPh, n = 2) are readily deprotonated by KOH to give [FeL(dppm-H)(CNPh)₃]ⁿ⁻¹ (2a and 2b). 2a reacts with [thtAuPPh₃]PF₆ to give mer-[FeI((PPh₂)₂C(H)(AuPPh₃))-(CNPh)₃]PF₆ (3). The new heterotrimetallic species [FeL((PPh₂)₂C(AuPPh₃)₂)-(CNPh)₃]ⁿ⁺ (4a and 4b) have been obtained from 1a and 1b by treatment with ClAuPPh₃ in the presence of KOH.     

Kalium-Hexacyanomanganat(IV): Präparation und Spektren

Potassium Hexacyano-mianganate(IV): Preparation and Spectra K₂[Mn(CN)₆] and so far not described K₂[Mn(CN)₆] · 3DMF were prepared in analytical purity. IR, Raman and UV spectra of both compounds are given and discussed. The spin-forbidden ²E_g, ²T_1g — ⁴A_2g transition proves the Racah parameter B₅₅ and the nephelauxetic ratio β₅₅ to be 651 em^?l and 0.61 respectively.     

Radiation-chemical processes as disclosure of electronic states in a bis(dinitrogen) molybdenum complex

On the basis of experimental data the energy levels of the central-atom orbitals in the complex [Mo(N₂)₂(dppe)₂] [dppe = 1,2-bis(diphenylphosphine)ethane] were calculated. Using the diagram thus obtained the eletronic configuration of the irradiation-generated ion, [Mo(N₂)₂(dppe)₂]⁻, was determined to be as follows: (b_2g)² (e_g)⁴ (b_1g)¹ or (b_2g)² (e_g)⁴ (e_u). The yields from the decomposition of [Mo(N₂)₂(dppe)₂] in the solid phase in a hydrogen atmosphere were determined on the basis of the decrease in band intensities at 306 and 377 nm: G(− MoN₂)_306nm = 0.01, and G(− MoP)_377nm = 0.1 (molecules per 100 eV). In toluene solution it was found that G(− MoN₂) > G(− MoP). The yields observed were in accordance with the calculated levels. Using a mass spectrometer the volatile products of [Mo(N₂)₂(dppe)₂] radiolysis in H₂ and O₂ atmospheres were identified as H₃N, H₄N₂, NO and N₂O. In the light of the results mentioned above (as well as the IR results) a mechanism for the radiolysis of [Mo(N₂)₂(dppe)₂] in the solid phase was proposed.     

Intensities of lines in the band a 1Δg (v′= 0) − X3Σ−g (v″ = 0) of 16O2 in absorption

Line-strengths in the band a¹Δ_g (v′= 0) − X³Σ⁻_g (v″ = 0) of gaseous ¹⁶O₂ in absorption near 7.9 × 10⁵ m⁻¹ have been remeasured in the laboratory under conditions of pressure less than 101,000 Pa and temperature near 300 K. The band-strength is estimated to be (2.1 ± 0.3) × 10⁻²⁶ m, and the coefficient for self-broadening of individual lines near the band centre is (10 ± 1) m⁻¹ bar⁻¹. No evidence of an underlying continuum was found.     

Azide ligand substitution reaction in zinc bis(diethyldithiocarbamate)

The azide ligand substitution reaction in tetrahedral zinc bis(diethyldithiocarbamate) has been studied by extraction. The reaction has been shown to proceed by both solvent and azide ion interactions with k₀ = 5.0 × 10⁻⁴ s⁻¹ and k₁ = 1.9 × 10⁻³ M⁻¹ s⁻¹. A general discussion of the reaction mechanism is provided.     

A proton magnetic resonance study of ligand exchange on hexakis(1,1,3,3-tetramethylurea) thulium(III)

A ¹H NMR study of the rate of exchange of 1,1,3,3-tetramethylurea (tmu) on [Tm(tmu)₆]³⁺ is found to be independent of [tmu] over a five-fold variation in CD₃CN solution, and to be characterized by k(298.2 K) = 145 ± 1 s⁻¹, ΔH^# = 29.3±0.3 kJ mol⁻¹, and ΔS^# = 105±1 J K⁻¹ mol⁻¹. These data are discussed in conjunction with data from related lanthanide and pseudo-lanthanide systems and the mechanistic implications are considered.     

Analysis of torsional spectra of molecules with two internal C3ν, rotors—XXVI. A far infrared study of 1,1-dimethylhydrazine

The infrared spectra of 1,1-dimethylhydrazine, (CH₃)₂NNH₂, and two isotopomers, (CD₃)₂NNH₂ and (CH₃)₂NND₂, have been recorded in the region between 600 and 100 cm⁻¹. Very rich and complex spectra were obtained and analysis of the data has been carried out. The interpretation of the spectra arising from the two methyl torsional modes of the −d₀ compound was carried out using a semi-rigid model, and the resulting potential function obtained is V₃₀ = 1685 ± 12 cm⁻¹ (4.82 ± 0.04 kcal mol⁻¹); V₀₃ = 1827 ± 16 cm⁻¹ (5.22 ± 0.05 kcal mol⁻¹); V₆₀ = −92±5cm⁻¹ (−0.26 ± 0.02 kcal mol⁻¹); V₀₆ = −41 ± 6cm⁻¹ (−0.12 ± 0.02 kcal mol⁻¹) and V^′₃₃ = −51 ± 5 cm⁻¹ (−0.15 ± 0.01 kcal mol⁻¹). Ab initio gradient calculations were carried out employing the 3–21G and 6–31G* basis sets, as well as the 6–31G* basis set with electron correlation at the MP2 level. The structural parameters, conformational stability, and three-fold barriers to internal rotation have been determined and the gauche conformer is calculated to be more stable than the trans form by 783 cm⁻¹ (2.24 kcal mol⁻¹) with the MP2/6–31G* basis set. These calculations were also used to re-evaluate the previously reported assignment of the fundamental modes, and to obtain a potential function for the asymmetric torsion. All of these results are discussed and compared with corresponding quantities for some similar compounds.     

Zero-phonon and vibronic structure of [Os(bpy)32+ doped into single-crystal [Ru(bpy)3](ClO4)2

Highly resolved emission and absorption spectra of [Os(bpy)₃]²⁺, doped into single-crystal [Ru(bpy)₃](ClO₄)₂, are reported. Our investigations, at low temperatures (2⩽T⩽50 K) and high magnetic fields ( 0⩽H⩽6 T ), lead to the following results: The three lowest excited states of [Os(bpy)₃]²⁺ in this matrix are identified from zero-phonon transitions lying at 14169 ± cm⁻¹ (line I), 14230± cm⁻¹ (line II), and 14380 ± 2 cm⁻¹ (line III). These transitions are found at the same energies (within the experimental error of ± 2 cm⁻¹) in absorption and emission. The extinction coefficients of II and III are ≈ 10³ XXX mol⁻¹ cm⁻¹ while the transition |0>→ |I> (line I) is strongly forbidden. However, under high magnetic fields this absorption line grows in due to a mixing of |I> with |II>. A large number of vibronic peaks is identified in the emission spectra. The corresponding vibrational modes are compared to Raman and IR data of [Ru(bpy)₃]²⁺ and [Os(bpy)₃]²⁺. Several distinct modes couple more strongly to the transition from the lowest excited state |I>, others to the transition from |II>, as is shown by investigating the magnetic field dependence of the emission spectra.