The thermochemistry of carbonyl complexes of Cr,Mo and W with pyridine and acetonitrile

Microcalorimetric measurements at elevated temperatures of the heats of thermal decomposition and of iodination of a number of [M(CO)_nL_6-n] complexes (M = Cr, Mo, W; n = 3, 4; L = py, MeCN) have led to values for the standard enthalpies of formation of the following crystalline compounds (values given in kJ mol^?) at 25°C: fac-[Mo(CO)₃py₃](275 ± 12), fac-[Mo(CO)₃(NCCH₃)₃]  (410 ± 12), fac-[W(CO)₃py₃](250 ± 12), fac-[W(CO)₃(NCCH₃)₃](405 ± 12) and cis-[Cr(CO)₄py₂](505 ± 20). From these and other data, including estimated heats of sublimation, the bond enthalpy contributions of the various metalligand bonds in the gaseous metal complexes were evaluated as follows (values in kJ mol^?): D(Crpy) 102, D(Mopy) 146, DWPy) 173, D(Mo7z.sbnd;NCMe) 135 and D(WNCMe) 169. For a given metal the bond enthalpy contribution decreased in the order D(MCO) > D(Mpy) > D(Mz.sbnd;NCMe). This order is related to the σ- and π-bonding character of the ligand.     

EPR study of dithiophosphate,dithiocarbamate, and xanthate complexes of Cr(V), Mo(V), and W(V)

Liquid and frozen solutions of diethyl dithiophosphate, diethyl dithiocarbamate, and butyl xanthate complexes of Cr(V), Mo(V) and W(V) were studied by the EPR method in the temperature range from 293–77dg K. The spin-Hamiltonian parameters were determined. Conclusions were drawn about the structure of these complexes and about the bond character within the complexes. A multiplicity of the hyperfine splitting constants from Cr⁵³, Mo^95,97, and W¹⁸³ to the constant of additional hyperfine splitting from the p³¹ isotope is observed in diethyl phosphate complexes.     

Synthesis and spectroscopic studies of europium chelate complexes

The synthesis of the mixed complexes of the europium ion with 2-pyridylcarbinol-N-oxide, and 2,2′-dipyridyl and 1,10-phenanthroline were prepared. The compounds, were characterized by means of chemical analyses, vibrational spectra, molar conductivities, and electronic spectra. The emission of the [EuL₃, phen] complex at 10 K is very intense and an assignment of the point symmetry of the Eu(III) ion has been made.     

Radiation reduction of Cr, Mo and W isopolymetalates in aqueous system

The radiation-chemical processes in aqueous solutions of dichromates, isopolymolybdates and isopolytungstates have been studied. The radiation reduction of Cr(VI) to Cr(III), Mo(VI) to Mo(V) and W(VI) to W(V) takes place. Molybdenum and tungsten blues are the products of the last two processes in acid solutions. The yields of reduction decrease significantly with the increase of pH. The mechanisms of the processes have been discussed. The photochemical reduction of Mo(VI) and W(VI) for the production of corresponding 5-valent states have been used to the study of their electron scavenging efficiencies. It has been shown that these efficiencies decrease in the order: Mo(V)>W(V)>Cr(VI)>Mo(VI)>W(VI).     

Synthesis,characterization, electrochemical and theoretical study of substituted phenyl-terpyridine and pyridine-quinoline based mixed chelate ruthenium complexes

In the present work, we report two methoxy-substituted phenyl-terpyridine ruthenium complexes with pyridine carboxyquinoline and NCS as ancillary ligands, [Ru(OMePhtpy)(pcqH)(NCS)](PF₆) (1) and [Ru(triOMePhtpy)(pcqH)(NCS)](PF₆) (2) (where OMePhtpy = (4′-(4-methoxy)phenyl-2,2′:6′,2″-terpyridine, triOMePhtpy = (4′-(3,4,5-trimethoxy)phenyl-2,2′:6′,2″-terpyridine and pcqH = pyridine-carboxyquinoline). Both complexes have been characterized by spectroscopic techniques e.g., mass, ¹H-NMR and FTIR. UV–vis spectrophotometric and electrochemical studies for both complexes have been performed. The substitution pattern of the –OMe groups have been successfully utilized to tune the redox potential of the metal complexes. On the anodic side of cyclic voltammogram, 1 and 2 show an irreversible wave corresponding to Ru^II/III couple at 0.95 and 0.85 V, respectively. The lower Ru^II/III oxidation potential for 2 may be attributed to increased electron density on ruthenium due to three (+R) methoxy–groups appended to the phenyl moiety of triOMePhtpy. DFT optimization of structure and energy calculation reveals that in both complexes, HOMO is metal- and thiocyanate-based, whereas the LUMO is based on pcqH. Correlation of TDDFT results with experimental electronic spectrum indicates that bands at 502 nm (1) and 528 nm (2) are of MLLCT character from ruthenium-thiocyanate to pcqH.     

Pulsed-field ionization electron spectroscopy of group 6 metal (Cr, Mo, and W) bis(benzene) sandwich complexes

Group 6 metal bis(benzene) sandwich complexes (M-bz(2): M=Cr, Mo, and W and bz=C(6)H(6)) were produced with laser vaporization molecular beam techniques and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and density functional theory calculations. Each sandwich complex is in a D(6h) eclipsed configuration with (1)A(1g) and (2)A(1g) as the neutral and cationic ground electronic states, respectively. The adiabatic ionization energies for Cr-, Mo-, and W-bz(2) are measured to be 44,081(7), 44,581(10), and 43,634(7) cm(-1), respectively. The metal-benzene stretch and benzene torsion frequencies of the ion are measured to be 264, 277, and 370 cm(-1) and 11, 21, and 45 cm(-1) for Cr-, Mo-, and W-bz(2), respectively. In addition, a C-H out-of-plane bending mode is measured to be 787 cm(-1) for the Cr(+)-bz(2) complex, while a C-C in-plane bending mode is measured to be 614 cm(-1) for the W(+)-bz(2) complex. The unusual trend in the ionization energy and metal-benzene stretch frequency indicates strong relativistic effects on tungsten binding.     

Four-membered chelate aminoalkenyl complexes of platinum(II). Synthesis,carbonylation and oxidation to aminoacidato complexes

Amination of Pt^II-allene complexes of the type cis[PtCl₂(Me₂CCCHR)(PPh₃)] gives the new four-membered C, N chelate aminoalkenyl complexes [$\text{PtC(CMe}{}_2\text{)CHRN}$Me₂(PPh₃)Cl]. These undergo ready insertion of carbon monoxide into the CPt σ-bond; the resulting acyl complexes are oxidized by hydrogen peroxide to aminoacidato complexes, and the free unsaturated β-aminoacids can be recovered in good yield by ligand displacement.     

Synthesis,spectral characterization,and antidiabetic study of new furan-based vanadium(IV) complexes

We have synthesized furan-based vanadium complexes, bis(5-nitrofuran-2-carboxylato)oxovanadium(IV) – [VO(5NF)₂], bis(1-furan-2-yl-ethanonato)oxovanadium(IV) sulfate – [VO(2AF)₂]SO₄, and bis(5-methyl-2-furalato)oxovanadium(IV) sulfate – [VO(MFFA)₂]SO₄ possessing [VO(O₄)] coordination mode. These complexes are characterized by physico-chemical and spectroscopic methods. Based on electron paramagnetic resonance parameters, the proposed geometry is close to a distorted square pyramid. Animal study was carried out using standard protocol and the complete profile of glucose, protein, and total cholesterol levels were analyzed followed by an oral glucose tolerance test.     

Reactivity of tetrathiometalates with alkynes. Synthesis and characterisation of dithiolene complexes of Mo,W, and V by ESMS and XRD

The reaction of DMA (C₂(CO₂Me)₂) with MoS₄²⁻, WS₄²⁻, and VS₄³⁻ led to six dithiolene compounds. (NEt₄)₂[Mo₂(X)₂(μ-S) ₂(η²-S₂C₂(CO₂Me)₂)₂] 1, (X = O or S), (NEt₄)₂[V(η²-S₂C₂(CO₂Me)₂)₃] 2a, (NEt₄)₂[V(O)(η²-S₂C₂(CO₂Me)₂)₂] 2b, (NEt₄)₂[W₂(S)₂(μ-S)₂(η²-S₂C₂(CO₂Me)₂)₂] 3, (NEt₄)₂[W(O)(η²-S₂C₂(CO₂Me)₂)₂] 4 and (NEt₄)₂[W₂(μ-S)₂(η² -S₂C₂(CO₂Me)₂)₄] 5 were isolated in the solid state. The structures of 2a, 3, 4 and 5 were determined by single crystal X-ray diffraction study. The compounds 1 and 2b were characterised in solution by ESMS (Electrospray Mass Spectrometry) and in the solid state by IR spectroscopy. ESMS data also allowed proposal of a reaction scheme which rationalizes the formation of the different species present in solution.     

Electronic structure and bonding in heteronuclear dimers of V, Cr, Mo, and W: a CASSCF/CASPT2 study

Heteronuclear dimers like CrMo, CrW, MoW, VCr, VMo, VW, and their anions have been investigated by means of multiconfigurational quantum chemistry methods, using the complete active space self-consistent field followed by second-order perturbation theory, CASSCF/CASPT2. We explored in great detail several spectroscopic properties such as bond length, potential energy surfaces, dissociation energies, ionization potentials, electron affinities, low-lying excited states, vibrational frequencies, and dipole moments. All proposed dimers show ground states with a pronounced multireference character. The group VI heterodimers have a (1)Σ(+) ground state, while the mixed group V-group VI heterodimers show a (2)Δ ground state. Among all dimers, only VCr presents a potential energy profile with a deep minimum in the d-d region and a shelf-like potential in the s-s region. All the remaining dimers show only the short-range minimum. The largest effective bond order is obtained for the MoW, with a value of 5.2, that is, a weak sextuple bond. Most of the obtained results are valuable tools to drive future experimental investigations.     

A radical pathway to synthesise Mo and W dithiolene complexes

A new method has been developed to synthesise bis η(5)-cyclopentadienyl dithiolene complexes of molybdenum and tungsten. This procedure involves the in situ thermolysis of the azo compounds, 2,2'-azobisisobutyronitrile (AIBN) or 1,1'-azobiscyclohexanecarbonitrile (ACCN) (R'(2)N(2), R' = CMe(2)CN or C(6)H(10)CN, respectively), which initiates a reaction between [Cp(2)M(S(4))] (M = Mo or W) and an alkyne (HC(2)R, R = Ph, 2-pyridyl or 2-quinoxalinyl) and produce the corresponding [Cp(2)M(S(2)C(2)RR')] compound.     

Preparation of Al,Cr, Nb,Mo, and W Monophosphides from a Lithium Metaphosphate Melt

Synthesis of a series of phosphides (AlP, CrP, NbP, MoP, and WP) by reactions of powdered metals with a melt of lithium metaphosphate LiPO₃ was studied. Thermodynamic parameters (H ⁰ _{2 9 8}, S ⁰ _{2 9 8}, G ⁰ _{2 9 8}, and G ⁰ _{1 2 7 3}) of the reactions were calculated and their temperature modes were optimized on the basis of the standard thermodynamic characteristics of the initial substances and the reaction products. X-ray patterns of the powders of the obtained compounds are presented.     

Conformational isomers and isomerization of group 6 (Cr, Mo, and W) metal-bis(toluene) sandwich complexes probed by variable-temperature electron spectroscopy

Group 6 metal (Cr, Mo, and W)-bis(toluene) sandwich complexes are synthesized in a laser-vaporization molecular beam source. Conformational isomers and isomerization of these complexes are studied by variable-temperature pulsed-field-ionization zero-electron-kinetic-energy spectroscopy and density functional theory. For Cr-bis(toluene), four rotational conformers are identified with methyl-group dihedral angles of 0, 60, 120, and 180°. The ground electronic states of these conformers are (1)A(1) (C(2v), 0°), (1)A (C(2), 60 and 120°), and (1)A(g) (C(2h), 180°) in the neutral form and (2)A(1) (C(2v), 0°), (2)A (C(2), 60 and 120°), and (2)A(g) (C(2h), 180°) in the singly charged cationic form. For Mo- and W-bis(toluene), the four rotamers are resolved into three (0, 60/120, and 180°) and two (0 and 60/120/180°) groups, respectively. For all three metal sandwiches, the most stable conformer is in the complete eclipsed configuration (0°) and has the highest ionization energy. The conversion from 60/120/180° to 0° rotamer is observed from helium to argon supersonic expansions and is more efficient for the heavier Mo and W species.     

Quantum chemical study of the structures and dynamic behavior of tricarbonyl complexes of Group 6 metals (Cr,Mo, W) with polyaromatic hydrocarbons using the density functional theory

The quantum chemical study of the mechanism was performed for tricarbonyl η⁶-complexes of coronene I-M and kekulene II-M (M = Cr, Mo, W) by the density functional method. The activation barriers of η⁶,η⁶-interring haptotropic rearrangements (IHR), being the migration of the metaltricarbonyl group M(CO)₃ from one six-membered aromatic ring to another, were determined. The processes of η⁶,η⁶-IHR in the metal tricarbonyl complexes with relatively high polycyclic aromatic hydrocarbons (PAH) I and II occur with close energy barriers (ΔG^≠ ≈ 20—25 kcal mol^–1), which are lower than the barriers (ΔG^≠ ~ 30 kcal mol^–1) of similar transformations measured or calculated earlier for the chromium tricarbonyl complexes of naphthalene and its derivatives and other PAH. For the molybdenum tricarbonyl complexes the activation barriers of η⁶,η⁶-IHR decrease additionally by ~ 5 kcal mol^–1 compared to those for the chromium tricarbonyl complexes, whereas for the tungsten tricarbonyl complexes they increase again and become approximately equal to the activation barriers of similar chromium tricarbonyl complexes. All stationary states on the potential energy surface determining the mechanism of η⁶,η⁶-IHR are characterized by a decrease in hapticity compared to the initial and final complexes.     

Synthesis,spectral, bioactivity,and NLO properties of chalcone metal complexes

A series of metal(II) complexes ML and ML₂ [where M?=?Cu(II), Co(II), Ni(II), Zn(II), Mn(II), Cd(II), and VO(II); L?=?2-hydroxyphenyl-3-(1H-indol-3-yl)-prop-2-en-1-one (HPIP)] have been prepared and characterized by elemental analysis, magnetic susceptibility, molar conductance, IR, UV-Vis, NMR, Mass, and ESR spectral studies. Conductivity measurements reveal that the complexes are non-electrolytes, except VO(II) complex. Spectroscopy and other data show square pyramidal geometry for oxovanadium and octahedral geometry for the other complexes. Redox behavior of the copper(II) and vanadyl complexes has been studied with cyclic voltammetry. Antimicrobial activities against several microorganisms indicate that a few complexes exhibit considerable activity. The nuclease activity shows that the complexes cleave DNA. All synthesized compounds can serve as potential photoactive materials as indicated from their characteristic fluorescence properties. The second harmonic generation efficiency of the ligand is higher than that of urea and KDP.     

Zur Abtrennung kleiner Mobmengen aus Erzen, die Ti, W, Mo und Cr enthalten

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