Synthesis,X-ray structure and spectroscopy of Cu(II) complexes derived from diacetylazine dioxime

Complexes of Cu(II) with the polydentate diacetylazine dioxime ligand C₈H₁₄N₄O₂ have been synthesized by template and non-template reactions. The crystal structure of [Cu(C₈H₁₃N₄O₂)]₂[ClO₄]₂(C₂H₅OH)₂ has been determined to establish the conformation of the ligand and the coordination of the oxime function. The structural analysis shows that the nearly planar [C₈H₁₃N₄O₂]^? group behaves as a bridging tetradentate ligand. The distorted square-pyramidal coordination about each Cu atom includes three N donors from two oxime and azine and one O donor from the other oxime, the ethanol molecule occupying the apical position. A perchlorate anion is loosely bonded to Cu. The intramolecular Cu…Cu separation is 3.725(2) Å. The compound crystallizes in the centrosymmetric space group P$\text{1}$ triclinic lattice with refined lattice parameters of a = 11.963(8) Å, b = 9.784(7) Å, c = 7.501(6) Å, α = 90.69(4)°, β = 104.53(4)°, γ = 90.83(4)°, V = 849.7 ų and Z = 2. Full-matrix least-squares refinement of 1490 independent reflexions led to final discrepancy indices, R = 0.059, and R_w = 0.065. The Cu centres are highly coupled as indicated by the ESR spectrum. There is no evidence that the C₈H₁₄N₄O₂ ligand stabilizes unusual oxidation states of Cu.     

Electronic structure and reactivity of ylidic systems : V. Ylid structure information form NMR data

Bond systems in triphenylphosphorus ylids, methylenetrimethylphosphorane and their tricarbonylnickel salts are discussed by interpretation of ¹³C NMR results.     

Rotational isomerism in divinylether studied by gas phase electron diffraction, microwave spectroscopy, infrared band profile simulation and ab initio calculations

The conformational behaviour of divinyl ether in the gas phase was explored by infrared band profile simulations and joint analysis of electron diffraction and microwave data. At 300 K the rotameric mixture contains 80% [sp, ac] and 20% [ap, ap] forms. Geometries have been studied using constraints taken from ab initio 4-21G gradient geometry and force field calculations. Differences between some unresolved bond distances and angles were constrained to the calculated values. Scale factors for the ab initio force field were refined from the diffraction data. In addition the transferability of scale factors from methyl vinyl ether to divinyl ether was tested. The investigation demonstrates that molecular orbital constrained models are consistent with and rationalize all experimental gas phase results. Subject to the ab initio constraints, the analysis yields the following model (r_g-distances, r-angles; numbers in parentheses are 6 times the least-squares ESDs): (C---H) = 1.103(12) A, (C---C) = 1.337(2) A, (C---O) = 1.389(2) A. Torsion angles for the [sp, ac] form are −13(6)° and 145(4)°.     

Organometallic complexes containing the bridging group N,N′-o-phenylenebis(salicylideneimine); crystal and molecular structure of μ-N,N′-o-phenylenebis(salicylideneiminato)bis(2-C,N-acetophenoneoximepalladium(II))

The reactions of the conjugate base of (methylmethoxycarbene)pentacarbonylchromium(0) with epoxides and with methyl bromoacetate give alkylated carbene complexes which cannot be obtained by previous synthetic routes.     

The isolation and X-ray structure of a complex between lithium picrate and dibenzo-36-crown-12

The crystal structure of 2Li picrate.dibenzo-36-crown-12.2H₂O was determined by X-ray diffraction methods. The 2:1 (metal:ligand) complex crystalli     

Synthesis and crystal structure of [N,N′-bis(2,3,5,6-tetrafluorophenyl)-ethane-1,2-diaminato(2-)]dipyridineplatinum(II)

The reaction of PtCl₂en (en = ethane-1,2-diamine) with TlO₂CC₆F₅ in boiling pyridine unexpectedly yielded a polyfluorophenyl-stabilized ethane-1,2-diaminatoplatinum(II) complex, Pt[N(p-HC₆F₄)CH₂]₂(py)₂, 1a, the structure of which has been established by X-ray crystallography.     

Ethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic) acid as complexing agent

Metal derivatives of ethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic) acid (EDTMP, H₈L) with some bivalent ions—Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) have been isolated in various stoichiometric ratios from aqueous medium. Electronic spectra indicate them to be six-coordinated. EPR studies of Cu(II) complexes show that they are tetragonally elongated. Magnetic moments of M₄L derivatives are very low due to antiferromagnetic exchange interactions, but the moments go on increasing for M₃Na₂L and M₂Na₄L and are normal for MNa₆L derivatives, due to isolation of paramagnetic centres by diamagnetic sodium ions. IR spectra and thermal stability of the complexes have also been studied.     

The preparation and X-ray crystal and molecular structure of (α,1,2-η-6-methylbenzyl) bis(triphenylphosphine)rhodium(I)

Reaction of [RhCl(PPh₃)₃] with [o-MeC₆H₄CH₂MgBr] affords high yields of the non-fluxional complex, [Rh(CH₂C₆H₄Me)(PPh₃)₂] which has been shown crystallographically to contain a 1-3-η-benzyl group bound through the phenyl carbon atom that is not substituted with the methyl group. Crystals of this compound are triclinic, space group P$\text{1}$, with a = 10.561(6). b = 17.705(3), c = 10.934(4) Å, α = 80.69(3), β = 116.86(4), γ = 102.30(4)° and Z = 2. The structure was solved via the heavy-atom method and refined to R = 0.032 using 5379 diffractometer data with I > 1.56(I). Attempts to prepare π-bonded xylylene complexes from this compound by reaction with base have been unsuccessful, but protonation followed by recrystallisation from acetone gives [Rh{(CH₃)₂CO}₂(PPh₃)₂]BF₄.     

The calculation of electron density and temperature in Ar spectroscopic plasmas from continuum and line spectra

The measurement of electron temperature and electron density from line and continuum radiation in Ar plasmas used for spectroscopic purposes is discussed. The correct equations for the calculation of these parameters from experimentally observable quantities are identified. Such expressions yield the theoretical spectral irradiance expected from line and continuum radiation. To aid calculations, grouped constants from these equations are calculated using SI units of measure. The sources of accurate values for the parameters and correction factors appearing in the irradiance equations are listed. In addition the approximations made in order to simplify electron temperature and electron density determinations are reviewed. Practical aspects of making accurate measurements of these parameters in Ar plasmas are considered. Theoretical plots of line to continuum emission ratio vs electron temperature and of continuum irradiance vs electron density are presented as an illustration using parameters appropriate for Ar emission at 430 nm and the spectrally adjacent continuum.     

The enantiomers of N,N-dimethylthiobenzamides: Chromatographic behaviour and rotational barriers

N,N-Dimethylthiobenzamides bearing hydrogen atoms in both orthopositions were shown by ¹H NMR in the presence of an optically active alcohol to have non-coplanar π-systems. The barrier to rotation about the C(sp²-C(sp²) bond amounts to 43 ± 2 kJ/mol. Liquid chromatography on triacetylcellulose served for the enrichment of enantiomers of 2-substituted thiobenzamides. In several cases considerable enantioselectivity (relative retention up to 8.7) was observed. The barriers to enantiomerization (Tables 3, 4 and 5), determined by thermal racemization, were discussed in terms of non-bonding interactions, electrostatic repulsions and buttressing effects in the transition state of rotation.     

Absorption and emission spectroscopy and magnetic susceptibility of sodium β-alumina doped with Mn,Co, and Ni

The absorption spectrum and magnetic susceptibility vs temperature have been measured for β-alumina doped with Mn, Co, and Ni. In addition, the emission spectra of Mn-doped samples have been measured. Mn and Co are shown to occupy tetrahedral sites and to be in the +2 oxidation state in β-alumina, in agreement with the results of previous investigators. Nickel is shown to occupy both octahedral and tetrahedral sites in β-alumina. Evidence indicates that nickel on octahedral sites is in the +3 oxidation state while that occupying tetrahedral symmetry sites is in the +2 oxidation state. The bands in the absorption spectrum for each metal are assigned and Dq, B, and C are calculated where possible.     

Bonding properties of bicyclopropylidene: gas phase electron diffraction study and X-ray crystal structure analysis

The C=C double bond length in bicyclopropylidene (1) was found to be 131.4(1) and 130.4(8) pm by electron diffraction at 20° and X-ray diffraction at −40°C respectively. This value is in remarkable agreement with that obtained by molecular mechanics calculations; it is significantly shorter than the double bond in normal olefins.     

Adduct formation of some tris(N,N dialkyldithiocarbamato)Cr(III) complexes with iodine

Spectrophotometric studies of dichloromethane solutions containing iodine and some Cr(S₂CNR₂)₃ complexes (where R₂NCS^?₂ are: OC₄H₈NCS^?₂ = modtc; (C₂H₅)₂NCS^?₂ = Et₂dtc; (C₆H₅CH₂)₂NCS^?₂ = Bz₂dtc) have shown the formation of 1:1 adducts whose spectral features were studied and which suggested that charge-transfer interaction involving iodine and a sulphur atom of a coordinated dithiocarbamato ligand occurred.A new BASIC non-linear least-squares program which performs an optimization of the absorbance data taken at several wavelengths was devised to evaluate reliable formation constants.The thermodynamic parameters have been calculated and compared with those obtained in the same conditions as above by a reinvestigation of the known 1:1 complex formation of iodine with the corresponding tetraalkylthiuram-disulphides, where the donor site is also the sulphur atom of the thiocarbonyl group. The ?ΔH° values related to the Cr(dtc)₃ · I₂ complexes are about 2 kcal lower than those of thiuram disulphides, showing a lowering of the donor strength of the thiocarbonyl sulphur as a consequence of the coordination to the metal.     

Synthesis of two dibenzo-3, 2, 3-tetramines and their Ni(II), Zn(II) and Cd(II) complexes. The X-ray structure of diiodo-[2, 3:10, 11-dibenzo-1, 5, 8, 12-tetraazadodecane]cadmium(II)

Convenient syntheses of the tetramines 2, 3:10, 11-dibenzo-1, 5, 8, 12-tetraazadodecane, (L1, and 3, 4:9, 10-dibenzo-1, 5, 8, 12-tetraazadodecane (L2), are described. Both ligands form complexes with Ni(II), Zn(II) and Cd(II). The X-ray structure of [Cd(L1)I₂), confirms a five coordinate geometry for the Cd atom, where the two iodines are bonded to the metal and (L1) acts as a tridentate ligand. The complex crystallises in the monoclinic space group P2₁/c with a = 19.741(4) Å, b = 8.726(3) Å, c = 12.221(4) Å, and β = 104.55(3)°. The structure was refined to R = 0.062 for 1051 reflections.     

Synthesis of tert-butyl mercapto complexes of titanium(IV). X-ray crystal structure of Ti(diars)Cl2 (tBuS)2

The new class of tert-butyl mercapto compounds, Ti(L)Cl₂(^tBuS)₂ (L = diars, dmpe, dppe), has been synthesized and characterized. The X-ray crystal structure of Ti(diars)Cl₂(^tBuS)₂ (1) shows that the Ti(IV) atom has a distorted octahedral geometry with trans chlorides and cis tert-butyl mercapto units. The structures of the other complexes are similar based on spectroscopic (NMR, IR) evidence. Crystal data for (1): C₁₈H₃₄As₂Cl₂S₂Ti, M = 583.24, trigonal space group P3₁21 (No. 152), a = b = 16.892(5) Å, c = 8.492(2) Å, U = 2098.4 ų, Z = 3, D_c = 1.389 gcm^?3, μ = 29.841 cm^?1, λ(MoK_α) = 0.71069 Å (graphite monochromator). Refinement of 948 observed (1371 unique measured; I > 3σ(I) reflections gave a final R = 0.0462 and R_w = 0.0597.     

Sulfur-containing carbene-metal compounds: General route from carbon disulfide manganese complexes; X-ray structure of 1,3-dithiol-2-ylidenemanganese(I) derivative

Chiral carbene-manganese(I) complexes have been synthesized by the cyclo-addition of dimethyl acetylenedicarboxylate to the coordinated CS₂ ligand in Mn(η²-CS₂)(CO)(L)C₅H₄R (L = P(OMe)₃; PMe₂Ph; PMe₃). Irrespective of the nature of the ligand L, these 1,3-dithiol-2-ylidenemanganese(I) complexes are stable towards isomerisation into heterometallocycles and exhibit low frequency carbonyl absorption bands in the infrared consistent with a strong electron releasing effect of the carbene ligand. The structure of Mn(CS₂C₂(CO₂Me)₂)(CO)(P(OMe)₃)(C₅H₅) has been determined by X-ray analysis of a suitable crystal. The molecule shows a carbene carbonmanganese bond C(7)Mn of length 1.876 Å and a planar carbene which does not adopt the 1,3-dithiolium aromatic-ring geometry but contains a carboncarbon double bond, C(8)C(9), of length of 1.341 Å. The CO₂Me groups are out of the plane of the carbene ligand and two positions with equal occupancy are found for each oxygen atom O(3) and O(5) belonging to the CO groups.     

A diphosphide adduct of ditungsten-hexaisopropoxide: X-ray crystal structure of W2(OPri)6(py)(μ-P2)

From the reaction between W₂(OPrⁱ)₆(py)₂ and CO₂(μ-P₂)(CO)₆ in hexane at room temperature a black crystalline product has been shown to be W₂(OPrⁱ)₆(py)(μ-P₂) by a single crystal X-ray determination. There is a central pseudo tetrahedral W₂P₂ moiety with WW = 2.695(1) Å, PP = 2.154(4) Å and WP = 2.45(2) Å (averaged) corresponding to essentially single bond distances. This new compound is an analogue of the ethyne adducts W₂(OR)₆(py)(μ-C₂H₂), where R = Bu^t and CH₂Bu^t, and these in turn are related to CO₂(CO)₆(μ-X) compounds (X = P₂, C₂R₂) by isolobal relationships.     

Mechanism of fluoride loss from fluoropolytungstates possessing the keggin structure

The fluoropolytungstates [H₂W₁₂F₂O₃₈]^4? and [HW₁₂F₃O₃₇]^4?, which are of the metatungstate type with the fluoride ions occupying inner sites, lose fluoride ion and form more higly charged species [H₂W₁₂FO₃₉]^5? and [HW₁₂F₂O₃₈]^5? in aqueous solution about pH 3 in media of suitable ionic strength. Kinetic results are presented here consistent with a mechanism involving less condensed species containing 11 tungsten and 1, 2 or 3 fluoride atoms. Involvement of such species is supported by the isolation of the aluminotungstates [HW₁₁AlF₃O₃₆(H₂O)] (TMA)₅², 30H₂O and [H₂W₁₁AlF₂O₃₇(H₂O)](TMA)₅, 17H₂O.     

Formation constant and stoichiometry of the acetonitrile:18-crown-6 complex by nuclear magnetic resonance, raman and infrared spectroscopy

Crown ethers are increasingly used in a variety of chemical applications. While crown ether complexes with alkali-metal cations have been extensively studied, relatively little is known about their complexes with neutral molecules to form so-called host: guest complexes. The use of NMR is reported for the determination of the formation constant (2.1 +/- 0.1) for the acetonitrile: 18-crown-6 complex. The suitability of Raman spectroscopy for studies of the solid-phase complex is demonstrated and limitations in the use of infrared spectroscopy are discussed.