Exact spin-pairing energies at the crossovers in octahedral d 4, d 5, d 6, and d 7 transition metal complexes

Exact spin-pairing energies are calculated by direct diagonalization of the relevant ligand field plus interelectronic repulsion matrices for the configurations d ⁴, d ⁵, d ⁶, and d ⁷ of octahedral transition metal ions. The results are presented in terms of /B as function of = C/B for the range of values =3.0 to 8.0. Comparison with the quantity resulting from a simplified approach in which configuration interaction is neglected or considered on an approximate basis only reveals significant differences. Useful estimates of spin-pairing energies are provided, in addition, on the basis of empirical magnetic and electronic spectral data.

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Zusammenfassung Exakte Spinpaarungsenergien für die Konfigurationen d ⁴, d ⁵, d ⁶ und d ⁷ oktaedrischer Übergangsmetallionen werden durch direkte Diagonalisierung der entsprechenden Matrizen des Ligandenfeldes sowie der Elektronenwechselwirkung berechnet. Die Ergebnisse für /B werden in Abhängigkeit von = C/B für den Wertebereich =3.0 bis 8.0 angegeben. Ein Vergleich mit der Größe , die bei einer vereinfachten Behandlung unter Vernachlässigung oder näherungsweiser Berücksichtigung der Konfigurationswechselwirkung erhalten wird, zeigt auffallende Unterschiede. Nützliche Abschätzungen der Spinpaarungsenergie werden außerdem unter Benutzung empirischer magnetischer und elektronenspektroskopischer Daten erhalten.

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Résumé Les énergies exactes de couplage de spin sont calculées par diagonalisation directe du champ de ligand correspondant en plus des matrices de répulsion électronique pour les configurations d ⁴, d ⁵, d ⁶ et d ⁷ des ions octaédriques des métaux de transition. Les résultats sont présentés en termes de /B en fonction de = C/B dan l'intervalle =3,0 à 8,0. On trouve des différences significatives par comparaison de avec les valeurs résultant d'une approche simplifiée sans interaction de configuration ou avec interaction de configuration approchée. De plus, des estimations des énergies de couplage de spin sont obtenues à partir de données empiriques magnétiques et spectrales.

     

First principle study of AlX (X=3d, 4d, 5d elements and Lu) dimer

The ground state equilibrium bond length, harmonic vibrational frequency, and dissociation energy of AlX (X=3d,4d,5d elements and Lu) dimers are investigated by density functional method B3LYP. The present results are in good agreement with the available experimental and other theoretical values except the dissociation energy of AlCr. The present calculations show that the late transition metal can combine strongly with aluminum compared with the former transition metal. The present calculation also indicates that it is more reasonable to replace La with Lu in the Periodic Table and that the bonding strengths of zinc, cadmium, and mercury with aluminum are very weak.     

Selective Complexation of Hydrazone Based Ketimine with 3d, 4d,and 5d Metals: Synthesis,Characterization, and Biological Activity

Russian Journal of General Chemistry - The hydrazone derived ketimine of dehydroacetic acid and its metal {Cu(II), Ni(II), Zn(II), Fe(III), Cd(II), Pd(II), La(III), Nd(III), Ce(III)} complexes are...     

2a,4a-Diazacyclopenta[c,d]Azulenes

A method of preparing 5-aryl-1,2-pentaniethyleneimidazoles from O-methylcaprolactim and -aminoacetophenone hydrochlorides is described. It is shown that 1, 2-tri-, -tetra-, and -pentamethyleneirrüdazoles and phenacyl bromide give the corresponding quaternary imidazolium salts, cyclization of which in the presence of base gives the previously unknown 5,6, 78-tetrahydro-2a, 4a-diazacyclopenta(c,dJazulenes (IVa-i).T. G. Shevchenko National Unkiversity, Kiev 254017. T. G. Shevchenko Educational Institute, Chernigov 250037. Translated from Khimiya Geterotskilicheskikh Soedinenii, No. 8, pp. 1072–1077, August, 1996. Original article submitted February 27, 1996; revision submitted June 27, 1996.     

Electrocatalytic Water Oxidation Activity-Stability Maps for Perovskite Oxides Containing 3d, 4d and 5d Transition Metals

Improving catalytic activity without loss of catalytic stability is one of the core goals in search of low-iridium-content oxygen evolution electrocatalysts under acidic conditions. Here, we synthesize a family of 66 SrBO₃ perovskite oxides (B=Ti, Ru, Ir) with different Ti : Ru : Ir atomic ratios and construct catalytic activity-stability maps over composition variation. The maps classify the multicomponent perovskites into chemical groups with distinct catalytic activity and stability for acidic oxygen evolution reaction, and highlights a chemical region where high catalytic activity and stability are achieved simultaneously at a relatively low iridium level. By quantifying the extent of hybridization of mixed transition metal 3d-4d-5d and oxygen 2p orbitals for multicomponent perovskites, we demonstrate this complex interplay between 3d-4d-5d metals and oxygen atoms in governing the trends in both activity and stability as well as in determining the catalytic mechanism involving lattice oxygen or not.     

Electronic structures and chemical bonding in transition metal monosilicides MSi (M = 3d, 4d, 5d elements)

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using the density functional method. Ground state was assigned for each species. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides an ionic component, covalent bonds are formed between the metal s,d orbitals and the silicon 3p orbital. The covalent character increases from ScSi (YSi) to NiSi (PdSi) for 3d (4d) metal monosilicides, then decreases. For 5d metal monosilicides, the covalent character increases from LaSi to OsSi, then decreases. For the dissociation of cations, the dissociation channel depends on the magnitude of the ionization potential between metal and silicon. If the ionization potential of the metal is smaller than that of silicon, channel MSi+ --> M+ + Si is favored. Otherwise, MSi+ --> M + Si+ will be favored. A similar behavior was observed for anions, in which the dissociation channel depends on the magnitude of electron affinity.     

Emission of secondary ions from 3d, 4d, and 5d transition metals under chloro-trifluoro-methane CClF3 as reactant gas

Surface interactions of CClF₃ with polycrystalline samples of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Rh, Pd, Ag, Ta, W, Re, Ir, and Pt were investigated by means of moderate dynamic SIMS. As observed with other reactant gases these transition metals in most cases appear to be discernible into “dissociative” and (partial) “molecular” adsorbents. Small signals of oxidic secondary ions which are detectable for residual gas conditions vanished under the action of CClF₃. However, due to strong polarization by either of the halogens, the emission of Me²⁺ ions is enhanced for Ti, V, and Nb. Received: 6 August 1997 / Revised: 22 December 1997 / Accepted: 29 December 1997     

Emission of secondary ions from 3d, 4d, and 5d transition metals under chloro-trifluoro-methane CClF3 as reactant gas

Surface interactions of CClF₃ with polycrystalline samples of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Rh, Pd, Ag, Ta, W, Re, Ir, and Pt were investigated by means of moderate dynamic SIMS. As observed with other reactant gases these transition metals in most cases appear to be discernible into “dissociative” and (partial) “molecular” adsorbents. Small signals of oxidic secondary ions which are detectable for residual gas conditions vanished under the action of CClF₃. However, due to strong polarization by either of the halogens, the emission of Me²⁺ ions is enhanced for Ti, V, and Nb.     

Synthesis of Unprecedented 4d/4f-Polypnictogens

A series of 4d/4f-polyarsenides, -polyarsines and -polystibines was obtained by reduction of the Mo-pnictide precursor complexes [{Cp^tMo(CO)₂}₂(μ,η^2:2-E₂)] (E=As, Sb; Cp^t=tBu substituted cyclopentadienyl) with two different divalent samarocenes [Cp*₂Sm] and [(Cp^Me4nPr)₂Sm]. For the reductive conversion of the Mo-stibide only one product was isolated, featuring a planar tetrastibacyclobutadiene moiety as an unprecedented ligand for organometallic compounds. For the corresponding Mo-arsenide a tetraarsacyclobutadiene and a second species with a side-on coordinated As₂²⁻ anion was isolated. The latter can be considered as reaction intermediate for the formation of the tetraarsacyclobutadiene.     

Pressure dependence of secondary ion emission from selected 3d, 4d, and 5d transition metals under N2O, NO, and NO2

The reactant gas pressure dependence of secondary ion emission from surfaces of polycrystalline Cr, Fe, Co, Mo, Rh, W, Re, and Ir under the action of N₂O, NO and NO₂ was observed by means of moderate dynamic SIMS. The mass spectra for constant reactant gas pressure indicate the existence of two different groups of transition metals showing either dissociative or partial molecular adsorption behavior. This is confirmed at least above some suitable reactant gas pressure. Besides some special details (Fe/NO; Co/NO) several of the relative secondary ion intensities vs. reactant gas pressure exhibit similar curvature as for O₂, thus indicating the NO_x gases to be modified sources of oxygen. At higher pressures molecular secondary ions with and without metal atoms come to be appreciable. Received: 28 May 1997 / Revised: 2 February 1998 / Accepted: 4 February 1998     

Pressure dependence of secondary ion emission from selected 3d, 4d, and 5d transition metals under N2O, NO, and NO2

The reactant gas pressure dependence of secondary ion emission from surfaces of polycrystalline Cr, Fe, Co, Mo, Rh, W, Re, and Ir under the action of N₂O, NO and NO₂ was observed by means of moderate dynamic SIMS. The mass spectra for constant reactant gas pressure indicate the existence of two different groups of transition metals showing either dissociative or partial molecular adsorption behavior. This is confirmed at least above some suitable reactant gas pressure. Besides some special details (Fe/NO; Co/NO) several of the relative secondary ion intensities vs. reactant gas pressure exhibit similar curvature as for O₂, thus indicating the NO_x gases to be modified sources of oxygen. At higher pressures molecular secondary ions with and without metal atoms come to be appreciable.     

Molecular structures,bond energies,and bonding analysis of group 11 cyanides TM(CN) and isocyanides TM(NC) (TM = Cu,Ag, Au)

We report on quantum chemical calculations at the DFT (BP86/TZP) and ab initio (CCSD(T)/III+) levels of the title compounds. The geometries, vibrational spectra, heats of formation, and homolytic and heterolytic bond dissociation energies are given. The calculated bond length of Cu-CN is in reasonable agreement with experiment. The theoretical geometries for CuNC and the other group 11 cyanides and isocyanides which have not been measured as isolated species provide a good estimate for the exact values. The theoretical bond dissociation energies and heats of formation should be accurate with an error limit of +/-5 kcal/mol. The calculation of the vibrational spectra shows that the C-N stretching mode of the cyanides, which lies between 2170 and 2180 cm(-)(1), is IR inactive. The omega(1)(C-N) vibrations of the isocyanides are shifted by approximately 100 cm(-)(1) to lower wavenumbers. They are predicted to have a very large IR intensity. The nature of the metal-ligand interactions was investigated with the help of an energy partitioning analysis in two different ways using the charged fragments TM(+) + CN(-) (TM = transition metal) and the neutral fragments TM(*) + CN(*) as bonding partners. The calculations suggest that covalent interactions are the driving force for the formation of the TM-CN and TM-NC bonds, but the finally formed bonds are better described in terms of interactions between TM(+) and CN(-), which have between 73% and 80% electrostatic character. The contribution of the pi bonding is rather small. The lower energy of the metal cyanides than that of the isocyanides comes from the stronger electrostatic interaction between the more diffuse electron density at the carbon atom of the cyano ligand and the positively charged nucleus of the metal.     

Electrophilic substitution reactions in 4H-benzo[d,e,f]carbazole

The behavior of 4H-benzo[d,e,f]earbazole and its N-aeetyl derivative in various electrophilic substitution reactions (e.g. nitration, nitrosation, bromination, Friedel-Crafts acylations) has been investigated, and a number of new derivatives of this heterocycle (some of which are to be tested as potential carcinogens and enzyme-inducers) have been synthesized.     

Synthesis and characterization of new quaternary polyselenide Ba4TMSbSe12 (TM = Nb,Ta)

Two new quaternary polyselenides, Ba₄TMSbSe₁₂ (TM = Nb, Ta), are synthesized using a solid state reaction. They crystallize in a new structural type with a P‐1 triclinic space group, characterized according to single‐crystal X‐ray diffraction. The structure is alternately stacked using isolated NbSe₉^5? and SbSe₃^3?, which are separated by Ba²⁺. The structure contains the NbSe₉^5? unit with a bipentagonal pyramidal shape coordinated with Se^2? and Se₂^2? in monodenteate and bidentate modes. The vibrational property of the diselenide Se₂^2? unit was studied using Raman spectrum analysis. ultraviolet–visible diffused reflectance and temperature‐dependent resistivity measurements indicate semiconductor behaviors. Calculations of electronic structures indicate the presence of a band gap and strong Se‐Se interactions in the diselenide group, which experimentally supports the measured physical properties.     

Molecular magnetic materials based on 4d and 5d transition metals

The study of paramagnetic compounds based on 4d and 5d transition metals is an emerging research topic in the field of molecular magnetism. An essential driving force for the interest in this area is the fact that heavier metal ions introduce important attributes to the physical properties of paramagnetic compounds. Among the attractive characteristics of heavier elements vis-à-vis magnetism are the diffuse nature of their d orbitals, their strong magnetic anisotropy owing to enhanced spin-orbit coupling, and their diverse structural and redox properties. This critical review is intended to introduce readers to the topic and to report recent progress in this area. It is not fully comprehensive in scope although we strived to include all relevant topics and a large subset of references in the area. Herein we provide a survey of the history and current status of research that has been conducted on the topic of second and third row transition metal molecular magnetism. The article is organized according to the nature of the precursor building blocks with special topics being highlighted as illustrations of the special role of heavier transition metal ions in the field. This paper is addressed to readers who are interested in molecular magnetism and the application of coordination chemistry principles to materials synthesis (231 references).     

Density functional investigation of metal-metal interactions in mixed-valence d2d3 (Cr, Mo, W) and d3d4 (Mn, Tc, Re) face-shared [M2Cl9]2- systems

The molecular and electronic structures of mixed-valence face-shared (Cr, Mo, W) d(2)d(3) and (Mn, Tc, Re) d(3)d(4) [M(2)Cl(9)](2-) dimers have been calculated by density functional methods in order to investigate metal-metal bonding in this series. The electronic structures of these systems have been analyzed using potential energy curves for the broken-symmetry and other spin states arising from the d(2)d(3) and d(3)d(4) coupling modes. In (d(2)d(3)) [Mo(2)Cl(9)](2-) and [W(2)Cl(9)](2-), the global minimum has been found to be a spin-doublet state characterized by delocalization of the metal-based electrons in a multiple metal-metal bond (with a formal bond order of 2.5). In contrast, weak coupling between the metal centers and electron localization are favored in (d(2)d(3)) [Cr(2)Cl(9)](2-), the global minimum for this species being a ferromagnetic S = 5/2 state with a relatively long Cr-Cr separation. The (d(3)d(4)) [Re(2)Cl(9)](2-) system also exhibits a global minimum corresponding to a metal-metal bonded spin-doublet state with a formal bond order of 2.5, reflecting the electron-hole equivalence between d(2)d(3) and d(3)d(4) configurations. Double minima behavior is predicted for (d(3)d(4)) [Tc(2)Cl(9)](2-) and [Mn(2)Cl(9)](2-) due to two energetically close low-lying states (these being S = 3/2 and S = 5/2 states for the former, and S = 5/2 and S = 7/2 states for the latter). A comparison of computational results for the d(2)d(2), d(2)d(3), and d(3)d(3) [W(2)Cl(9)](z-) series and the d(3)d(3), d(3)d(4), and d(4)d(4) [Re(2)Cl(9)](z-) series indicates that the observed trends in metal-metal distances can only be rationalized if changes in both the strength of sigma bonding and metal-metal bond order are taken into consideration. These two factors act conjointly in the W series but in opposition to one another in the Re series. In the case of the [Cr(2)Cl(9)](z-) and [Mn(2)Cl(9)](z-) dimers, the metal-metal bond lengths are significantly shorter for mixed-valence (d(2)d(3) or d(3)d(4)) than d(3)d(3) systems. This result is consistent with the fact that some degree of metal-metal bonding exists in the former (due to partial delocalization of a single sigma electron) but not in the latter (where all metal-based electrons are completely localized).