Mehrkernige Kobaltkomplexe. V. Präparative Herstellung von Tetrakis (äthylendiamin)-μ-peroxo-μ-amido- und μ-peroxo-μ-thiocyanatodikobalt (III)-Komplexen ausgehend von Tetrakis (äthylendiamin)bis-(ammin)-μ-peroxo-dikobalt (III)-tetraperchlorat

Polynuclear Cobalt Complexes. V. Preparation of tetrakis (ethylenediamine)-μ-peroxo-μ-amido and μ-peroxo-μ-thiocyanato-dicobalt (III) complexes starting from tetrakis (ethylenediamine)bis-(ammine)-μ-peroxo-dicobalt (III)-tetraperchlorate Racemic tetrakis (ethylenediamine)-μ-peroxo-μ-amido-dicobalt (III) thiocyanate and its corresponding hydroperoxo- and superoxo-complexes have been isolated from [(en)₂(NH₃)Co(O₂)(NH₃)(en)₂](ClO₄)₄. A new binuclear peroxo complex containing thiocyanate as bridging ligand was prepared by the same method. The stretching frequencies of the CN- and CS-group as well as the NCS-bending frequence in the IR. spectrum of [(en)₂Co(O₂, SCN)Co(en)₂](NO₃)₃ suggest that the μ-thiocyanato group is N-bonded (2050, 750, 475 cm^?1). A comparison of IR. spectra of known singly and doubly bridged μ-peroxo complexes is made. Characteristic absorption bands, assignable to ν(O? O) and ν(Co? O) are given.     

Synthesis and characterisation of saturated and unsaturated triruthenium clusters containing electronically symmetrical and asymmetrical alkynes

The synthesis and characterisation of μ₃-η²-alkynyl triruthenium clusters, [Ru₃(μ₃-η²-R¹-4-C₆H₄CCR²)(μ-dppm)(μ-CO)(CO)₇] (1, saturated), [Ru₃(μ₃-η²-R¹-4-C₆H₄CCR²)(μ-dppm)(CO)₇] (2, unsaturated) and [Ru₃(μ₃-η²-R¹-4-C₆H₄CCR²)(μ-dppm)(PPh₃)(CO)₇] (3, saturated) containing symmetrical and asymmetrical alkynes in which R¹ and R² are electron donor or electron withdrawing groups in the para position of the aromatic ring(s) or R² is ferrocenyl, are reported. Clusters 1 were obtained from the reactions of [PPN][Ru₃(μ-Cl)(CO)₁₀] with R¹-4-C₆H₄CCR² and dppm. Clusters 1 were successfully decarbonylated to give unsturated clusters 2, with the exception of the FcCCC₆H₄-4-NO₂ containing cluster, which is stable. Novel adducts 3 were obtained in high yields by addition of PPh₃ to unsaturated clusters 2. Clusters 1-3 were characterised by analytical and spectroscopic data, and structures were proposed on the basis of systematic ³¹P NMR studies and correlations with X-ray structural data of related compounds available in the literature. Saturated compounds 1 contain a CO and a dppm ligands bridging the same edge, which is also parallel to the μ₃-η²-alkyne, as opposed to the structure previously proposed for the PhCCPh and other derivatives, and established by X-ray crystallography for the PhCCCCPh cluster derivative, in which the dppm ligand bridges a different edge. Unsaturated compounds 2 exhibit the same structure established for the PhCCPh derivative in the solid state, with the alkyne bonded in the μ₃-η²-mode perpendicular to the Ru₂ edge supported by the dppm ligand. Because the dppm phosphorus chemical shifts were sensitive to the alkyne electronic asymmetry, it was possible to show that clusters containing electronically asymmetrical alkynes exist in two inseparable isomeric forms, which differ with respect to the alkyne orientation. Similarly to their osmium analogues, saturated compounds 3 exist as inseparable mixtures of isomers that differ with respect to the position of the bridging CO and dppm ligands, and in the cases of asymmetrical alkyne derivatives, also with respect to the orientation of the alkyne. This work has established, therefore, that μ-CO and dppm ligand positions respective to the μ₃-η²-alkyne in saturated clusters 1 and 3 are sensitive both to the nature of the coordinated alkyne and to the presence of a PPh₃ in place of a CO ligand on the metal frame.     

Theoretical studies of structure,stability, and chemical bonding in oxohydride OM4H6 complexes

The results of ab initio RHF/3-21G, RHF/6-31G*, and MP2/6-31G** / / HF/6-31G* calculations for 10 possible configurations of OM₄H₆ molecules (MO · 3MH₂, M = Be, Mg) are reported. Five isomers of OBe₄H₆ and three isomers of OMg₄H₆ have been found within an energy range of ã 15 kcal mol⁻¹. The “lanternlike” C_3v structure is the most favorable one for both complexes. Both molecules OM₄H₆ are stable to decomposition through all of the studied pathways. Chemical bonding in the OM_k polyhedra containing two-, three-and four-coordinated oxygen atoms is discussed. © 1996 John Wiley & Sons, Inc.     

Bridge‐Localized HOMO‐Binding Character of Divinylanthracene‐Bridged Dinuclear Ruthenium Carbonyl Complexes: Spectroscopic,Spectroelectrochemical, and Computational Studies

The electronic properties of four divinylanthracene‐bridged diruthenium carbonyl complexes [{RuCl(CO)(PMe₃)₃}₂(μ? CH?CHArCH?CH)] (Ar=9,10‐anthracene ( 1 ), 1,5‐anthracene ( 2 ), 2,6‐anthracene ( 3 ), 1,8‐anthracene ( 4 )) obtained by molecular spectroscopic methods (IR, UV/Vis/near‐IR, and EPR spectroscopy) and DFT calculations are reported. IR spectroelectrochemical studies have revealed that these complexes are first oxidized at the noninnocent bridging ligand, which is in line with the very small ν(C?O) wavenumber shift that accompanies this process and also supported by DFT calculations. Because of poor conjugation in complex 1 , except oxidized 1⁺ , the electronic absorption spectra of complexes 2⁺ , 3⁺ , and 4⁺ all display the characteristic near‐IR band envelopes that have been deconvoluted into three Gaussian sub‐bands. Two of the sub‐bands belong mainly to metal‐to‐ligand charge‐transfer (MLCT) transitions according to results from time‐dependent DFT calculations. EPR spectroscopy of chemically generated 1⁺ – 4⁺ proves largely ligand‐centered spin density, again in accordance with IR spectra and DFT calculations results.     

Synthesis, spectroscopic characterization and X-ray studies of two novel double open cubane-like cadmium(II) complexes

Two novel azide cadmium(II) compounds [Cd₄(dafone)₄Cl₂(μ_1,1-N₃)₄(μ_1,1,1-N₃)₂] (1) and [Cd₄(dafone)₄(N₃)₂(μ_1,1-N₃)₄(μ_1,1,1-N₃)₂] (2) were synthesized and characterized by spectroscopic and crystallographic methods. They are first cadmium(II) complexes adopting double open cubane-like structure. The fluorescence properties of the complexes 1 and 2 were examined both in solid state and solution, and compared with the free ligand. Additionally, the electronic spectra of 4,5-diazafluoren-9-one and 1 were investigated at the TDDFT level.     

Structural Diversity in Cyclometalated Diiridium(III) Complexes with Bridging syn and anti μ2-Oxamidato and μ2-Dithioxamidato Ligands

Six new diiridium complexes containing 2-methyl-6-phenylpyridyl as the cyclometalating ligand with a μ₂-oxamidato or a μ₂-dithioxamidato ligand as the bridge have been synthesized in 60–73 % yields. These complexes were revealed by multinuclear NMR spectroscopy to contain inseparable mixtures of diastereomers (rac, ΔΔ/ΛΛ and meso, ΔΛ) with bridges in anti and syn configurations. The remarkable variety of isomers present was confirmed by X-ray crystallography on single crystals grown from mixtures of each complex. In one complex with a N,N’-bis(4-trifluoromethylphenyl)-μ₂-oxamidato bridge, two single crystals of anti and syn isomers were structurally determined. Two single crystals of the μ₂-dithioxamidato bridge complex were found to contain rac and meso forms of the syn isomer. Hybrid DFT computations on the four isomers of each diiridium complex revealed negligible energetic preferences for one isomer despite the methyl groups in the 2-methyl-6-phenylpyridyl cyclometalating ligands being close to the neighboring methyl groups and the bridge, thus supporting the experimental findings of isomer mixtures. Two distinct broad emissions with maxima at 522–529 nm and at 689–701 nm observed in these complexes in dichloromethane are attributed to mixed metal-ligand to ligand charge transfer (MLLCT) excited states involving the pyridyl and bridge moieties respectively with the aid of electronic structure computations.     

A Novel Niobium Cluster Aqua Ion with Capping μ4‐Se Ligand

The aqueous solution chemistry of niobium is underexplored, and well characterized aqua complexes are scarce. In this contribution, a new niobium aqua complex was obtained by treatment of Zn‐reduced ethanolic solution of NbCl₅ with HCl in the presence of a selenide source (ZnSe). This is the first example of selenium containing aqua complex of niobium. The yellow‐green aqua complex was isolated by cation‐exchange chromatography and transformed into corresponding isothiocyanate complex by ligand exchange, which was crystallized as (PyH)_4.5[H_1.5Nb₄SeO₅(NCS)₁₀] · 0.5H₂O. X‐ray structural analysis revealed a metal‐metal bonded tetranuclear {Nb₄(μ₄‐Se)(μ₂‐O)₅}⁴⁺ core with a capping μ₄‐Se ligand.     

Electronic spectra and electrochemical properties of bis(dimethylglyoximato)iron(II) complexes containing axialN-heterocyclic ligands

Gaussian analysis of the electronic spectra of 25 bis(dimethylglyoximato)iron(II) complexes containing axialN-heterocyclic ligands are discussed and comparisons made with the spectra of the corresponding [Fe(CN)₅L]^3– complexes. The energies of the metal-to-axial and metal-to-equatorial ligand charge-transfer transitions exhibit opposite trends, correlating with the electronic properties of the axial ligands, and with the redox potentials of the Fe^II/Fe^III couple.     

Synthesis,structures, and property studies on Zn(II), Ni(II), and Cu(II) complexes with a Schiff base ligand containing thiocarbamide group

A Schiff base ligand containing thiocarbamide group of 4-phenyl-1-(4-methoxyl-1-phenylethylidene)thiosemicarbazide (HL) and its three mononuclear metal complexes of ZnL₂ (1), NiL₂ (2), and CuL₂ (3) have been synthesized. Elemental analysis, IR, and X-ray single crystal diffraction characterizations for the ligand and the three complexes have been carried out. In the three complexes, the central metallic ions of Zn²⁺, Ni²⁺, and Cu²⁺ coordinate with two deprotonated ligands of L⁻, respectively. In 1, Zn²⁺ ion adopts a distorted tetrahedral geometry, while in 2 and 3, both the Ni²⁺ and Cu²⁺ ions possess distorted square planar configurations. For the four compounds, UV–Vis spectra have been measured and DFT calculations at B3LYP/LANL2DZ level of theory prove that the electronic spectra of HL and 1 are corresponding with electronic transitions of n → π* and π → π* in the ligand itself and the electronic spectra of 2 and 3 are attributed to intraligand electronic transitions as well as d–d electronic transitions. Electrochemical investigations reveal that the different metal–ligand interactions have changed the peak shapes and peak locations, which are corresponding with the DFT-B3LYP/LANL2DZ calculational results. Fluorescence spectra measurements indicate that the ligand emits purple fluorescence and the complex 1 emits stronger blue fluorescence, while the complexes 2 and 3 quench fluorescence. The thermal analyses result show that the three complexes undergo two similar decomposition processes because of their similar geometric configurations.     

Dimere low-spin Eisen(III)-Phthalocyanine: Synthese und Eigenschaften ferromagnetisch gekoppelter μ-Oxodi(acidophthalocyaninatoferrate(III))

Dimeric Low-Spin Iron(III) Phthalocyanines: Synthesis and Properties of Ferromagnetically Coupled μ-Oxodi(acidophthalocyaninatoferrates(III)) μ-Oxodi(phthalocyaninatoiron(III)) ([(FePc^2?)₂O]) dissolved in pyridine reacts with different Tetra(n-butyl)ammonium salts yielding partly solvated Di(tetra(n-butyl)ammonium)-μ-oxodi(acidophthalocyaninatoferrates(III)) ((ⁿBu₄N)₂[(Fe(X)Pc^2?)₂O]; X^? = CN^?, Im^?, NCO^?, NCS^?, NO₂^?). The uv-vis. spectra show the typical B, Q, N and L regions of the Pc^2? ligand scarcely influenced by the axial ligands X. In comparison with [(FePc^2?)₂O] mainly the B region is hypsochromically shifted due to strong excitonic coupling (> 3 kK). Two regions of weak absorbance at ca. 7.6–8.7 and 11.4–13.0 kK are assigned to trip-doublet transitions. The m.i.r. and resonance Raman spectra are dominated by the fundamental vibrations of the Pc^2? ligand being characteristic for hexa-coordinated low-spin Fe^III phthalocyanines. Internal vibrations of the ambident axial ligands X are in accordance with the proposed Fe? X bond. The i.r. active asym. (Fe? O? Fe) stretching vibration is observed in the region 631–690 cm^?1. Fe? X stretching vibrations are only present in the f.i.r. spectra. The magnetic properties and Mößbauer spectra are interpreted in terms of an electronic model which assumes that a S′ = 1 ground state arises from strong ferromagnetic coupling of the low-spin Fe^III centres. Both spin-Hamiltonian and ligand-field models have been employed to fit the variable temperature susceptibility data. These low-spin μ-oxo Fe^III dimers are rare compared to the many known examples of coupled high-spin species including the parent, [(FePc^2?)₂O].     

Synthesis of new mixed ligand complexes of copper(II) dithiocarbamates

New mixed ligand complexes of copper(II) dithiocarbamates of the general formula, [CuCl(R₂dtc)L] or [CuCi(R′ dtc)L] (RCH₃ or C₂H₅, R′ = (CH₂)₅, dtc =-NCSS^? and L = Pyridine, 3-picoline or 4-picoline), have been prepared by the reaction of bis(dithiocarbamato)di-μ-chloro-dicopper(II) complexes with pyridine or picolines. The complexes are found to be non-electrolytes in nitrobenzene. Magnetic susceptibilities, i.r. and electronic spectra of the complexes are reported. A psuedo-tetrahedral structure is suggested for these complexes.     

Synthesis,characterization and photochemistry of some monometallic and bimetallic 2,2′-bipyrimidine complexes of chromium and tungsten carbonyls

Synthesis, electronic absorption spectra, ¹³C NMR and photochemistry are reported for the complexes M(CO)₄bpym (M = Cr or W) and [W(CO)₄]₂bpym. The electronic absorption spectra indicate, for these complexes, that the lowest lying metal-to-ligand (L) charge transfer (MLCT) excited state is lower in energy than the ligand field (LF) excited states. The ¹³C NMR spectra showed that the chemical shifts of C(5) and C(6) for the M-bpym complexes move downfield with respect to that of the free ligand, bpym, while C(4) moves upfield upon complexation. Small, wavelength-dependent quantum yields for loss of CO were obtained upon irradiation. These quantum yields were an order of magnitude larger for the Cr-bpym complex than for the W complexes (Φ = 2.4 x 10^?2 quanta/min for Cr-bpym, 2.5 x 10^?3 quanta/min for W-bpym and 1.1 x 10^?3 quanta/min for W-bpym-W, λ_irr = 366 nm).     

Spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-Methylpyridine and 4-Methylpyridine Cu4OBrnCl(6−n)L4 complexes

The tetranuclear Cu₄OBr_nCl_(6-n)L₄ complexes, where L = 3-methylpyridine (3-Mepy), 4-methylpyridine (4-Mepy) and n=0–6 with trigonal bipyramidal coordination of copper(II) were prepared and their infrared and electronic absorption spectra as well as cyclic voltammograms in nitromethane solutions were measured. The polyhedra in Cu₄OBr_nCl_(6−n) (3-Mepy)₄ molecules are less distorted comparing with those of 4-Mepy analogues as indicated by infrared Cu₄O absorptions, far infrared Cu—Br, Cu—Cl, and Cu—N absorptions, d—d bands in electronic spectra and potentials, measured by cyclic voltammetry. The 3-Mepy complexes exhibit strong single infrared Cu₄O absorptions, while for related 4-Mepy complexes doubly split Cu₄O bands were observed. Two strongly overlapped d—d bands in electronic absorption spectra of the 3-and 4-Mepy complexes in nitromethane were resolved by Gaussian fitting. The 4-Mepy ligand produces slightly stronger ligand field than its 3-Mepy analogue. The maxima of high-energy d—d bands are in a linear correlation with the number of bromide ligands. The correlations for corresponding low-energy bands are considerably deviated from linearity. The halfwave potentials of the complexes in nitromethane correlate with both the number of bromides and the data of electronic absorption spectra suggesting that the reducing electron at the electrode process enters the half-filled d _{z 2} orbital of the copper(II) atom. The origin of a difference between the 3-and 4-Mepy complexes in their spectral and electrochemical properties is also discussed.     

Electronic structure,UV spectra and reactivity of non-benzenoid systems by the INDO/S-CI method: Part II. Methylenecyclopropene and its derivatives

The electronic spectra, frontier molecular orbitals, charge distribution and dipole moments of nine compounds containing the cyclopropenyl ring have been studied by the all-valence-electrons INDO/S-CI method. The theoretical results agree fairly well with the experimental indications, where available. The σ-contribution to the net charge density on the ring as well as the μ_σ and s—p polarization contributions to the dipole moments are higher than in the fulvene derivatives, indicating greater participation of the smaller-ring system. The UV spectra of compounds containing two coupled rings correlate with those of the component frameworks, in agreement with previous semi-empirical calculations.     

Structural effect of ligand chirality and its spectroscopic consequences

Two series of pure and diluted lanthanide crystals with l and dl-isoleucine of formula [Ln(Ile)₂(H₂O)₄]₂(ClO₄)₆ (Ln=Eu, Nd) isomorphic for Eu and Nd ions were synthesised. The europium complex with l-isoleucine (1) and the neodymium one with the dl form (2) have been studied by single-crystal X-ray diffraction. The space groups are monoclinic C2 and triclinic P1̄ for l and dl isoleucine, respectively, and Z=2 and 1. The crystal structures consist of non-centrosymmetric and centrosymmetric dimer units for the l and dl ligand forms, respectively. Thus, the structural effect of ligand chirality was found and its spectroscopic consequences are reported. An attempt has been made to show the relation between the symmetry of the dimeric units and splitting of the electronic transitions. Well resolved absorption spectra down to 5 K are measured. Concentration effects on the intensities of electronic transition are examined. The vibronic coupling and cooperative interaction are analysed and confronted for complexes with l-handed and racemic ligand form. Following the vibrational analysis of the Raman spectra the assignment of [Nd(Ile)₂(H₂O)₄]₂(ClO₄)₆ vibronics are given. The nature of observed phenomena is briefly discussed.     

Synthesis and characterization of tungsten carbonyl complexes containing N-methyl substituted urea and thiourea ligands

Six new mixed-ligand tungsten carbonyl complexes containing N-methyl substituted urea and thiourea of the type W(CO)₄[RCH₂N-(C=X)NH₂] where X?=?O or S and R?=?morpholine, piperidine and diphenylamine are reported. These have been prepared by refluxing hexacarbonyl tungsten(0) with corresponding ligands in THF to produce cis-disubstituted products, [(L-L)W(CO)₄] where L-L?=?a chelating bidentate ligand, morpholinomethyl urea (MMU), morpholinomethyl thiourea (MMTU), piperidinomethyl urea (PMU), piperidinomethyl thiourea (PMTU), diphenylaminomethyl urea (DAMU) and diphenylaminomethyl thiourea (DAMTU). The compounds have been characterized by elemental analysis, IR, electronic and ¹³C NMR spectra, magnetic moments and conductivity measurements. The IR spectra suggests that in all the complexes, the ligands are bidentate chelating, coordinating the metal through carbonyl oxygen or thiocarbonyl sulphur and the ring nitrogen or tert-nitrogen of diphenylamine. The CO force constants and CO–CO interaction constants for these derivatives have also been calculated using Cotton–Kraihanzel secular equations, which indicate poor π-bonding ability of the ligands. ¹³C NMR and electronic spectra reveal loss of cis-carbonyl ligands to produce cis-disubstituted tetracarbonyl derivatives. Molecular modeling studies have been carried out using Hyperchem release 7.52 which suggest a distorted octahedral geometry for these complexes.     

Low frequency infrared spectra of metallophthalocyanines and their chloroderivatives

The solid state spectra(650-50 cm⁻¹) of Cr, Fe, Co, Zn and Cd phthalocyanines are reported and discussed in comparison with the spectra of their mono and/or bis-chloro derivatives. The frequency and relative intensity of the absorption bands are related to structural (deviation from D_4h symmetry) or electronic population (oxidation of the aromatic ligand) variations in the series.     

Reaktionen von Nitrosylkomplexes: VII. Bildung von μ-Amido-Liganden Durch Carbanion-Addition an oder katalytische Hydrierung von μ-Nitrosyl-Liganden

Reactions of [CpCo(μ₂-NO)]₂ (I) (Cp = η⁵-C₅H₅) with lithiumorganyls LiR (R = C₆H₅, t-C₄H₉) at room temperature yield very complex product mixtures, whereas at low temperature nucleophilic attack of the carbanions at the nitrogen atom of only one μ-NO ligand predominates. After hydrolysis Cp₂Co₂(μ₂-NO)(μ₂-NHR) is obtained. In the case of R = t-C₄H₉ two isomers are formed, one of which was characterized by X-ray diffraction analysis. Catalytic hydrogenation (Raney nickel, 1 atm of H₂) of I, leads to Cp₂Co₂(μ₂-NO)(μ₂-NH₂), which, after further interaction with hydrogen decomposes liberating ammonia. The IR, ¹H NMR, and mass spectra of the new complexes are discussed.     

Electronic Excitation of [(μ4‐η2‐alkyne)Rh4(CO)8(μ‐CO)2]: An In Situ UV/Vis Spectroscopy,Spectral Reconstruction and DFT Study

Reactions of three alkynes, namely, 1‐heptyne, 3‐hexyne and 1‐phenyl‐1‐butyne, with [Rh₄(CO)₉(μ‐CO)₃] are performed in anhydrous hexane under argon atmosphere with multiple perturbations of alkynes and [Rh₄(CO)₉(μ‐CO)₃]. The reactions are monitored by in situ UV/Vis spectroscopy, and the collected electronic spectra are further analyzed with the band‐target entropy minimization (BTEM) family of algorithms to reconstruct the pure component spectra. Three BTEM estimates of [(μ₄‐η²‐alkyne)Rh₄(CO)₈(μ‐CO)₂], in addition to that of [Rh₄(CO)₉(μ‐CO)₃], are successfully reconstructed from the experimental spectra. Time‐dependent density functional theory (TD‐DFT) predicted spectra at the PBE0/DGDZVP level are consistent with the corresponding BTEM estimates. The present study demonstrates that: 1) the BTEM family of algorithms is successful in analyzing multi‐component UV/Vis spectra and results in good spectral estimates of the trace organometallics present; and 2) the subsequent DFT/TD‐DFT methods provide an interpretation of the nature of the electronic excitation and can be used to predict the electronic spectra of similar transition organometallic complexes.     

Heteropolytungstates with Transition Metal Ions (Ni,Fe). Solution Electronic Spectra

Solution electronic spectra (λ = 400–1350 mμ) of the [H₃NiFeW₁₁O₄₀]^6? heteropolyanion as compared with those of the [Ni(H₂O)₆]²⁺ aquo-ion were recorded. On the basis of the ligand field parameter, of the effective magnetic moment and of the molar extinction as well as of the characteristics of the spectra, the octahedral environment of Ni²⁺ in the 11-tungstonickeloferric anion was demonstrated.