Untersuchungen an Metallchelaten mit Liganden des Cuproin- und Ferrointyps. XXI. Struktur und Bindung der Dinitrato-mono(cuproin)- und Dinitrato-mono(ferroin)kupfer(II)-Chelate

Studies on Metal Chelates with Ligands of the Cuproin and Ferroin Type. XXI. Structure and Bonding of Dinitrato-mono(cuproin)- and Dinitrato-mono(ferroin)-copper(II) Chelates Chelates of the type Cu(N? N)(NO₃)₂ (N? N = bipy, phen, dmp, dmch, dpch, and bich) are characterized by means of e.s.r., u.v.-vis, i.r., and conductivity measurements. On the basis of these results the possible structures of these chelates both in solution and in the solid state are discussed. The MO coefficients, which could be obtained by e.s.r. measurements, are indicating a high covalency of the out-of-plane π-bonding, but only low covalency of the σ-bonding and the in-plane π-bonding.     

The determination of a π-sigma constant for substituents attached to silicon

The proton, ¹³C, and ²⁹Si chemical shifts and the ¹³C¹H coupling constants of a series of compounds of the type (CH₃)₃SiX were measured and correlated with inductive and resonance σ constants. In order to provide a comparison with a homologous series in which π-bonding is absent, shifts and coupling constants were obtained for the t-butyl series, (CH₃)₃CX. Only the coupling constants gave significant correlations with σ_I. A series of σ constants, presumably reflective of the amount of π-bonding, were obtained from the deviations from the J vs. σ_I plot. The magnitudes of these values indicate that oxygen is a better π-donor than nitrogen and chlorine.     

Die Kristallstruktur einer triklinen Modifikation von Uranpentachlorid

The Crystal Structure of a Triclinic Modification of Uranium Pentachloride From solution uranium pentachloride crystallizes at room temperature in a triclinic modification belonging to the space group P1 . The unit cell contains one formula unit (UCl₅)₂ and has the dimensions a = 707, b = 965, c = 635 pm and α = 0.495 π, β = 0.652 π, γ = 0.603 π rad. The crystal structure was solved with the aid of X-ray diffraction data and was refined to a reliability index of R = 0.082. The structure consists of (UCl₅)₂ molecules having the point symmetry mmm in which the uranium atoms are linked with one another via two chlorine atoms. The crystal lattice can be derived from a hexagonal closest packing of chlorine atoms in which 1/5 of all octahedral holes are occupied by uranium atoms.     

Die Kristall- und Molekülstruktur von Dicäsium- μ-Oxodekafluorodiarsenat

Crystal and Molecular Structure of Dicaesium-μ-Oxodecafluorodiarsenate, Cs₂(As₂F₁₀O) The crystal structure of Cs₂(As₂F₁₀O) has been determined from three-dimensional data. The compound crystallizes in the monoclinic space group P2₁/m, the lattice constants being a = 9.175(4), b = 10.690(5), c = 5.619(3)(Å); β = 105,50(5)°. The anion (As₂F₁₀O)^2– with the point symmetry C_s contains a As? O? As-bridge, whose partial π-bonding is to be discussed. The bond lengths and angles are: As? O: 1.77(2) and 1.68(2) Å, resp., As? O? As: 139(1)°; As…As: 3.225(4) Å, the numbers in parantheses being the standard deviation of the last figure.     

Studies of the substituent effect in aromatic systems by 35 Cl-NQR. Chloroacetanilides ClxC6H5−x NHCOCH3−y Cly

The ³⁵Cl-NQR spectra of 45 chlorosubsitituted acetanilides, Cl_xC₆H_5?xNHCOCH_3?yCl_y, were investigated and the temperature dependence of some spectra, especially of monochloroacetic acid derivatives, was measured. A preliminary assignment of the NQR frequencies is given. A correlation between NQR frequencies and substituent parameters permits the study of the substituent effect of the acetamido group, ? NHCOCH_3?yCl_y. The chloro-substitution in the side chain of the acetanilides seems to have no noticeable influence on the ³⁵Cl-NQR frequencies of the chlorine atoms at the benzene ring. The NQR frequencies of the chlorine atoms in the chloroacetamido group are, on the other hand, insensitive to substitutions at the benzene nucleus. The possibility of steric influences on the NQR spectrum of ortho-chloro-substituted acetanilides is discussed. The investigation further confirms that a crystal field effect of about ±500 kHz must be considered in the interpretation of NQR spectra of chlorobenzene derivatives.     

The interpretation of the crystal field parameters for fn-electron systems by the angular overlap model. Rare-earth ions in LaCl3

The crystal field parameters of trivalent rare-earth ions subsituted in LaCl₃ are interpreted by the angular overlap model, where σ and π-bonding has been considered.     

Silicon-29 and carbon-13 NMR studies of organosilicon chemistry. II—The Methylethoxysilanes MenSi(OEt)4−n

Silicon-29, carbon-13 and oxygen-17 NMR data are reported for the methylethoxysilanes, Me_nSi(OEt)_4?n with n = C to 3. The values of ¹J(SiC) vary greatly, in a manner which appears to be inconsistent with an effect of s-character variation alone. The chemical shifts are discussed in terms of possible π-bonding. Silicon-29 and carbon-13 spin-lattice relaxation times and nuclear Overhauser effects are also reported and discussed.     

Quantification of the trans influence in d8 square planar and d6 octahedral complexes: a database study

A systematic search of the Cambridge structural database was undertaken to quantify the trans influence in square planar and octahedral transition metal compounds. For square planar geometry, d⁸ metal centers were studied, while octahedral searches focused on low-spin d⁶ complexes. Two probe ligands (PL) were used to measure the effect of the trans ligand (TL), chloride, and triphenylphosphine (PPh₃). For the TLs O=CX₂, NR₃, pyridine, and Cl^? (X?=?any non-metal, R?=?H or hydrocarbon), the effects on the metal–probe ligand (M–PL) distance were statistically equal and were taken as essentially no trans influence. The other ligands studied showed significant decrease in the mean M–PL bond order, relative to the above ligands: SR₂?=?0.941; S=CX₂?=?0.887; PPh₃?=?0.825; phenyl?=?0.743; CR₃?=?0.719; hydride?=?0.685. Some variation in the trans influence is observed, based on the geometry of the metal center and the PL. In general, electron-donating, σ-bonding ligands lead to a larger trans influence, but π-bonding effects can also be important, particularly when the probe ligand also has π-bonding properties.     

The preparation and properties of cationic dicarbonylcyclopentadienyliron complexes of organic carbonyl compounds: molecular structure of dicarbonylcyclopentadienyliron(3-methylcyclohexenone) hexafluorophosphate

A number of complexes CpFe(CO)₂(L) (L = aldehyde, ketone, ester, amide) have been prepared either by treatment of [CpFe(CO)₂]₂ or CpFe(Co)₂Br with AgPF₆ in the presence of L or by a ligand exchange reaction employing CpFe(CO)₂(isobutylene)BF₄. NMR spectral data suggest that these complexes involve iron—oxygen σ-bonding rather than π-bonding to the carbonyl group. This is confirmed by an X-ray structure determination of the 3-methylcyclohexenone complex. The exchange stability of these complexes parallels their basicity.     

Transition Metal Complexation of σ Bonds

The first σ complexes were found in the 1960s and 1970s, but they did not attract more than passing attention. Only now are we beginning to recognize their key role in the chemical reactions of σ bonds, and this has encouraged more detailed study. In contrast with the more familiar π-donor complexes such as M? (CH₂?CH₂) and complexes like M? NH₃, in which the one pair of electrons on the N atom is bound to the metal atom, in a σ complex an X? H group binds to the transition metal atom; the X? H σ-bonding electron pair acts as a 2e donor to give an (X-H)-M type complex. Dihydrogen complexes (X = H) are one important group of σ complexes. C-H-M complexes (X = R₃C) with an agostic C-H-M interaction have not only been found in the ground state but also implicated in the transition states of many important organometallic transformations such as Ziegler–Natta catalysis and sigma bond metathesis. The importance of X? H bond activation will encourage continued growth in this field.     

Die Kristallstrukturen von [Cu2Cl2(AA · H+)2](NO3)2 und [AA · H+]Pikr− (AA · H+ = Allylammonium; Pikr− = Pikrat)

The Crystal Structures of [Cu₂Cl₂(AA · H⁺)₂](NO₃)₂ and [AA · H⁺]Picr^? (AA · H⁺ = Allylammonium; Picr^? = Picrat) By an alternating current electro synthesis the crystal-line π-complex [Cu₂Cl₂(AA · H⁺)₂](NO₃)₂ has been obtained from CuCl₂ · 2H₂O, allylamine (AA), and HNO₃ in ethanolic solution. X-ray structure analysis revealed that the compound crystallized in the monoclinic system, space group P2₁/a, a = 7.229(3), b = 7.824(3), c = 26.098(6) Å, γ = 94.46(5)°, Z = 4, R = 0.025 for 2 023 reflections. The crystal structure is built up of Cu_nCl_n chains which are connected by π-bonding bidentate AA · H⁺ …? ON(O)O …? H⁺ · AA units. For comparision with the above complex the structure of [AA · H⁺]Picr^? (Picr^? = picrate anion) is also reported.     

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.     

An electron diffraction determination of the molecular structures of silyl- and germyl-manganese pentacarbonyl in the gas phase

The molecular structures of the title compounds have been determined by gas phase electron diffraction methods. The SiMn and GeMn bond lengths are 240.7 ? 0.5 and 248.7 ? 0.2 pm respectively and the CMnC angles in the silyl and germyl cases are 94.5 ± 2° and 97 ± 2° respectively. Comparisons are made with the reported structure of CH₃Mn(CO)₅ and He^I photoelectron spectra of these compounds in an attempt to determine the extent of d → d π-bonding in the SiMn or GeMn bonds.     

THE EPR SPECTRUM OF COPPER-DOPED SINGLE CRYSTALS OF GLYCYLGLYCINE

Abstract

The EPR Spectrum of Cu(II)-doped into a single crystal of α-glycylglycine is reported. The results show that there are several magnetically non-equivalent sites, only two of which were strong enough to be analysed. The values parameters in the spin Hamiltonian deduced from the data are: g _z =2.242 ± 0.003, g _x =2.062 ± 0.005, g _y =2.044 ± 0.005, A _z =162.8 ± G, A _x =32.6 ± 2.0 G, A _y =21.6 ± 2.0 G. The Cu(II) environment seems to be square planar and involving four ligand molecules, each molecule forming one bond with the copper. The nitrogens are located in the trans position. The bonding is chiefly in-plane [sgrave]-bonding.     

Substituent effects in second row molecules : Silicon-containing compounds

Substituent interaction energies are calculated by ab initio molecular orbital methods for the two series SiH₂X^- and SiH₃X for the directly bound substituents X = BH₂, CH₃, NH₂, OH, F and the results compared with those for the corresponding first row species. Interactions with the groups NH₂, OH, F are as large in the neutral as in the anionic series and this is attributed to the presence of important π-bonding interactions, supplementing the effects of inductive withdrawal of σ-electrons. The restoration of charge neutrality by π-donation to silicon is more important in the neutral molecules, σ-electron transfer from silicon in the anions. π-Bonding with the π-acceptor substitutent BH₂ is favourable, as it is in the CH₃X and CH₂X^- systems, but with π-donor substituents the interactions are always destabilizing.     

ESR-Spektren von CuN4-Chromophoren II: Komplexe mit Ammoniak, Äthylendiamin,Biguanid, N-Trifluoracetimidoyl-trifluoracetamidin,N-Trichloracetimidoyl-trichloracetamidin,Tetraaza-undecan,Hexamethyl-tetraaza-cyclotetradecan und -cyclotetra decadien in Einkristallen

The ESR spectra of eight copper complexes with two groups of nitrogen ligands have been measured in the solid state. The first group includes the σ-bonding ligands ammonia, ethylenediamine, 1,4,8,11-tetraaza-undecane, and the macrocyclic hexamethyl-1,4,8,11-tetraazacyclotetradecane of CURTIS . Ligands of the second group are biguanide, the CF₃ and CCl₃ derivatives of acetimidoyl-acetamidine, and hexamethyl-1, 4,8,11-tetraazacyclotetradecadiene. Single crystals of the parent Pt^II, Ni^II, or Zn^II compounds were used as host lattices and magnetic diluents. The spectra of the chromophores CuN₄, showing resolved hyperfine structure due to copper and nitrogen nuclear spins, are fitting a Spin-Hamiltonian on the basis of virtual site symmetry D_4h. The parameters g∥, g?, A∥, and A? were used to derive delocalization coefficients in terms of the LCAO-MO model introduced by MAKI and MC GARVEY . The comparative study clearly reveals that no reliable information on π-bonding is provided by application of this model. The results on σ-bonding ligands are particularly valuable in showing that the simple LCAO-MO model cannot account for the attenuation of spin orbit coupling due to σ-bonding in a physically meaningful way. Our results are qualitatively in agreement with AMMETER'S explanation of this phenomenon in terms of a virtual expansion of the d-shell in antibonding orbitals.     

Synthesis,spectral characterization and crystal structure of copper(II) complexes of 2-hydroxyacetophenone-N(4)-phenyl semicarbazone

Six new copper(II) complexes of 2-hydroxyacetophenone-N(4)-phenyl semicarbazone have been synthesized and physico-chemically characterized. The tridentate character of the semicarbazone is inferred from IR spectra. Based on EPR studies, the spin Hamiltonian and bonding parameters have been calculated. The g   values, calculated for all the complexes in frozen DMF, indicate the presence of the unpaired electron in the d_x2-y2${\text{d}}_{x^2-y^2}$ orbital. The metal–ligand bonding parameters evaluated showed strong in-plane σ and in-plane π-bonding. The structure of the compound, CuLphen has been resolved using single crystal X-ray diffraction studies. The crystal structure revealed a monoclinic lattice with space group symmetry P2₁/c. The compound adopts a distorted square pyramidal geometry with a N₂O₂ core as the base.     

Synthesis and X-Ray Crystal Structure of the TiMgCl6(CH3COOC2H5)4 Adduct

The molecular and crystal structure of TiMgCl₆(CH₃COOC₂H₅)₄, obtained by reacting TiCl₄ with a solution of MgCl₂ in dry CH₃COOC₂H₅, have been determined by x-ray diffraction. The structure was solved by direct and Fourier methods and refined by least-squares techniques to R = 0.052 for 2722 independent observed reflections. Unit-cell dimensions are a = 17.122(7), b = 9.833(3), c = 9.646(3) Å, α = 111.10(7)°, β = 107.22(6)°, γ = 103.11(6)° with Z = 2 for P1 . The titanium(IV) atom is octahedrally coordinated by six chlorine atoms (Ti? Cl_t = 2.293(2) Å, Ti? Cl_b = 2.480(2) Å) and magnesium by two chlorine atoms (Mg? Cl_b = 2.528(2) Å) and the carbonyl oxygen atoms of the four CH₃COOC₂H₅ residues (Mg? O = 2.038(5) Å). The octahedra share an edge by a double chlorine bridge between the magnesium and titanium atoms. Changes in the configurations and dimensions of the free acceptor and donor molecules on adduct formation are discussed. One of the ethylacetate residues shows positional disorder, eventually with Bonding through its ethereal oxygen.     

Bis-Phosphaketenes LM(PCO)2 (M=Ga,In): A New Class of Reactive Group 13 Metal-Phosphorus Compounds

Phosphaketenes are versatile reagents in organophosphorus chemistry. We herein report on the synthesis of novel bis-phosphaketenes, LM(PCO)₂ (M=Ga 2 a , In 2 b ; L=HC[C(Me)N(Ar)]₂; Ar=2,6-i-Pr₂C₆H₃) by salt metathesis reactions and their reactions with LGa to metallaphosphenes LGa(OCP)PML (M=Ga 3 a , In 3 b ). 3 b represents the first compound with significant In−P π-bonding contribution as was confirmed by DFT calculations. Compounds 3 a and 3 b selectively activate the N−H and O−H bonds of aniline and phenol at the Ga−P bond and both reactions proceed with a rearrangement of the phosphaethynolate group from Ga−OCP to M−PCO bonding. Compounds 2–5 are fully characterized by heteronuclear (¹H, ¹³C{¹H}, ³¹P{¹H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).     

The assessment of the crystal-field parameters for fn-electron systems by the angular overlap model rare-earth ions m3+ in limf 4 and substituted in liyf4

Experimental crystal-field parameters of trivalent rare-earth ions (M³⁺) in LiMF₄ or substituted in LiYF₄ are fitted in terms of tile angular overlap model accounting for σ- and π-bonding.