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.     

TM7TM'6B8 (TM = Ta, Nb; TM' = Ru, Rh, Ir): new compounds with [B6] ring polyanions

The ternary boron compounds TM(7)TM'(6)B(8) (TM = Ta, Nb; TM' = Ru, Rh, Ir) were prepared by high-temperature thermal treatment of mixtures of the elements. An analysis of the chemical bonding by the electron density/electron localizability approach reveals formation of covalently bonded polyanions [B(6)] and [TM'(6)B(2)]. The cationic part of the structure contains separated TM cations. In agreement with the chemical bonding analysis and band structure calculations, all TM(7)TM'(6)B(8) compounds are metallic Pauli-paramagnets (TM' = Ru, Rh) or diamagnets (TM' = Ir).     

Observation of Confinement-Free Neutral Group Three Transition Metal Carbonyls Sc(CO)7 and TM(CO)8 (TM=Y,La)

Spectroscopic characterization of neutral highly-coordinated compounds is essential in fundamental and applied research, but has been proven to be a challenging experimental target because of the difficulty in mass selection. Here, we report the preparation and size-specific infrared-vacuum ultraviolet (IR-VUV) spectroscopic identification of group-3 transition metal carbonyls Sc(CO)₇ and TM(CO)₈ (TM=Y, La) in the gas phase, which are the first confinement-free neutral heptacarbonyl and octacarbonyl complexes. The results indicate that Sc(CO)₇ has a C_2v structure and TM(CO)₈ (TM=Y, La) have a D_4h structure. Theoretical calculations predict that the formation of Sc(CO)₇ and TM(CO)₈ (TM=Y, La) is both thermodynamically exothermic and kinetically facile in the gas phase. These highly-coordinated carbonyls are 17-electron complexes when only those valence electrons that occupy metal−CO bonding orbitals are considered, in which the ligand-only 4b_1u molecular orbital is ignored. This work opens new avenues toward the design and chemical control of a large variety of compounds with unique structures and properties.     

X-ray,structural assignment and molecular docking study of dihydrogeodin from Aspergillus Terreus TM8

A re-cultivation of the thermophilic fungus Aspergillus terreus TM8, and working up of its extract afforded the dichloro-benzophenone derivative, dihydrogeodin (1) in addition to the butyrolactones I (2), V (3) and VI (4). A literature surveying revealed one recent structural assignment trial for dihydrogeodin (1), however, with some inaccuracies. We report herein a full assignment of dihydrogeodin (1) using extensive study of 1D, 2D NMR and ESI HR mass data. For the first time as well, we report the planar structure of 1 using X-ray crystallography. Docking and molecular dynamic simulation of dihydrogeodin (1) on the isomerase cyclophilin A has revealed its significant potential activity as an antiviral and immunosuppressive agent.     

Solvothermal Synthesis and Characterization of [TM(1,2-dap)_3]HgSb_2Se_5(TM = Co,Fe)with a Chain Structure

One organic-decorated quanternaery [TM(1,2-dap)3]Hg Sb2Se5(1,2-dap = 1,2-dianinopropane, TM = Co(1), Fe(2)) compound has been solvothermally synthesized. The compounds crystallize in triclinic space group P 1, with a = 11.248(6), b = 11.542(7), c = 12.180(12) ?, V =1268.7(16) ?~3, Z = 2, F(000) = 1010 for 1 and a = 11.311(5), b = 11.558(5), c = 12.180(9) ?, V =1276.5(12) ?~3, Z = 2, F(000) = 1008 for 2. The crystal structure consists of one-dimensional anionics chains composed of Hg Se4 tetrahedra and SbSe_3 trigonal pyramids sharing corners and[TM(dap)_3]~(2+) cations. The [HgSb_2Se+5~(2-)]∞ anionic chains run along the [001] direction, and are surrounded by the [TM(dap)_3]~(2+) cations. Meanwhile, 8-ring [Hg_2Sb_2Se_4] and 6-ring [HgSb_2Se_2] are alternately found. The compounds were structurally characterized by elemental analysis,thermogravimetric analysis, infrared spectroscopy and UV-Vis diffuse reflectance spectroscopy.     

Octacarbonyl Anion Complexes of Group Three Transition Metals [TM(CO)8]− (TM=Sc,Y, La) and the 18‐Electron Rule

We report the gas‐phase synthesis of stable 20‐electron carbonyl anion complexes of group 3 transition metals, TM(CO)₈⁻ (TM=Sc, Y, La), which are studied by mass‐selected infrared (IR) photodissociation spectroscopy. The experimentally observed species, which are the first octacarbonyl anionic complexes of a TM, are identified by comparison of the measured and calculated IR spectra. Quantum chemical calculations show that the molecules have a cubic (O_h) equilibrium geometry and a singlet (¹A_1g) electronic ground state. The 20‐electron systems TM(CO)₈⁻ are energetically stable toward loss of one CO ligand, yielding the 18‐electron complexes TM(CO)₇⁻ in the ¹A₁ electronic ground state; these exhibit a capped octahedral structure with C_3v symmetry. Analysis of the electronic structure of TM(CO)₈⁻ reveals that there is one occupied valence molecular orbital with a_2u symmetry, which is formed only by ligand orbitals without a contribution from the metal atomic orbitals. The adducts of TM(CO)₈⁻ fulfill the 18‐electron rule when only those valence electrons that occupy metal–ligand bonding orbitals are considered.     

Octacarbonyl Anion Complexes of Group Three Transition Metals [TM(CO)8]− (TM=Sc,Y, La) and the 18‐Electron Rule

We report the gas‐phase synthesis of stable 20‐electron carbonyl anion complexes of group 3 transition metals, TM(CO)₈^? (TM=Sc, Y, La), which are studied by mass‐selected infrared (IR) photodissociation spectroscopy. The experimentally observed species, which are the first octacarbonyl anionic complexes of a TM, are identified by comparison of the measured and calculated IR spectra. Quantum chemical calculations show that the molecules have a cubic (O_h) equilibrium geometry and a singlet (¹A_1g) electronic ground state. The 20‐electron systems TM(CO)₈^? are energetically stable toward loss of one CO ligand, yielding the 18‐electron complexes TM(CO)₇^? in the ¹A₁ electronic ground state; these exhibit a capped octahedral structure with C_3v symmetry. Analysis of the electronic structure of TM(CO)₈^? reveals that there is one occupied valence molecular orbital with a_2u symmetry, which is formed only by ligand orbitals without a contribution from the metal atomic orbitals. The adducts of TM(CO)₈^? fulfill the 18‐electron rule when only those valence electrons that occupy metal–ligand bonding orbitals are considered.     

Hydroxide oxidation and peroxide formation at embedded binuclear transition metal sites; TM = Cr, Mn, Fe, Co

Key steps in electro-catalytic water oxidation on binuclear Transition Metal (TM) sites are addressed. These comprise (a) two one-electron oxidation steps of TM-OH moieties to form the corresponding two TM=O oxy-groups, and (b) a chemical step whereby the two oxy-species form a TM-O-O-TM peroxy-bridge. A test rig representing a generic low crystal field oxide support is described and employed. The energetics for homo-nuclear Cr(III-V), Mn(III-V), Fe(II-IV) and Co(II-IV) sites are compared. The uniqueness of the tyrosine/tyrosyl-radical (TyrOH/TyrO˙) reference potential for driving the oxidation steps is demonstrated. The oxidation of adsorbed TM-OH moieties on binuclear Mn and Co candidates requires an overpotential of approximately 0.5 V relative to the chosen reference potential. Correspondingly, the subsequent O-O bond formation becomes strongly exothermic, of the order of 1 eV. The hydroxide oxidation steps on binuclear CrCr and FeFe systems are, in total, exothermic by 1.21 and 0.61 eV, respectively, relative to the TyrOH/TyrO˙ reference potential. Consequently, the chemical step for transforming the TM=O moieties to the peroxo species is found to be endothermic by the order of 0.7 eV. Based on these findings, a catalyst containing one TM from each class is suggested. The validity of this concept is demonstrated for the FeCo binuclear site. The results are discussed in the context of experimental observations, which display a preference for mixed oxide systems.     

Density functional investigations of endohedral metallofullerenes TM@C24 (TM = Mn,Fe, Co,Ni, Cu,and Zn)

The theoretical investigations on TM@C₂₄ (TM = Mn, Fe, Co, Ni, Cu, and Zn) with different spin configurations have been performed by using the hybrid DFT‐B3PW91 functional in conjunction with 6‐31G(d) basis sets. The results show that the ground states of Fe@C₂₄ and Ni@C₂₄ are their spin triplet states, whereas the ground state of Co@C₂₄ is spin quartet state. Moreover, three Fe@C₂₄ isomers are favorable in energy. The HOMO and LUMO of Zn@C₂₄ indicates that there is no hybridization between Zn atomic orbitals and the C₂₄ cage orbitals. Natural population analysis shows that the charges always transfer from the TM atoms to the C₂₄ cage. In going from isolated TM atom to TM@C₂₄, the occupation of the 4s orbital is strongly reduced. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Nuclear techniques characterization of short-range order in Zr-TM-Cu-Al-Ni (TM=Hf,Ti, Fe) bulk metallic glasses

In this paper an overview of recent and new perturbed angular correlation (PAC), Mössbauer (MS) and positron annihilation (PAS) experiments on Zr- and Hf-based bulk metallic glasses is presented. PAC results showed that all samples in their as-prepared amorphous state, irrespective of the preparation method used, are well described by a dense random packing of ions (DRP). Hf-based samples showed a greater electric field gradient (EFG) value than Zr-based ones for same composition. A general observation is that the relaxed amorphous and supercooled liquid has the same local arrangements than the initial amorphous state. The crystallization behaviour is not preparation-method dependant but composition and impurities have a major influence on it. Preliminary positron annihilation lifetime measurements on amorphous samples yielded one characteristic lifetime, with a value intermediate between those for the well-annealed and defected metallic constituents of the alloys. Mössbauer spectra of as-prepared amorphous alloys consist of a broad asymmetric doublet, originating from a distribution of electric field gradients characteristic for amorphous samples.     

The relationship between thermodynamic properties and local atomic structure of Al-TM (TM = Mn,Fe, Co,Ni, Cu) melts

The relationship between structure and thermodynamic properties of Al- transition metal (TM) (TM = Mn, Fe, Co, Ni, Cu) melts had been studied by using the results of X-ray diffraction experiments, reverse Monte Carlo simulations and the model of ideal associated solution (MIAS). It was considered that local atomic structure of melts is determined by dense non-crystalline atomic packing and energy of interatomic interactions. This allowed to choose the types of associates for the MIAS. It is shown that the prominent role of the atomic packing factor in the Al-Mn, Al-Fe melts leads to correlation between the local atomic ordering of melts and the one of relevant polytetrahedral phases and defines a set of associates. Strengthening of heteroatomic interactions in the Al-Co, Al-Ni melts leads to an increase of the energy factor role in determining their structure and properties that reduces the number of associates from three for the Al-Mn melts to one for the Al-Ni.     

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.     

Determination of Anti-Tumor Agent TM208, 4-Methyl-piperazine-1-carbodithioc Acid 3-Cyano-3,3-diphenylpropyl Ester Hydrochloride, in Rats by LC

A new, specific and sensitive high performance liquid chromatography analytical procedure was developed and validated for the determination of TM208 in rat primary solid organs/tissues and plasma. TM208 was extracted from the appropriate matrix using methanol followed by centrifugation at 11,255×g for 20 min and injection of a 30 μL aliquot. Separation was carried out under gradient conditions using an ODS C18 column equipped with a guard column. The mobile phase consisted of methanol and water and retention times of TM208 and plunarizine (IS) were 17.658 and 26.175 min, respectively. The analytical procedure provided acceptable precision, accuracy, recoveries and linearity. Stability studies showed that TM208 was stable in organs/tissues homogenates for three freeze–thaw cycles, at room temperature for at least 24 h 3 weeks at ?20 °C. The validated method was successfully applied to the determination of TM208 in SD rats following oral administration at a dose of 250 mg kg^?1.     

The structural,mechanical, and thermodynamic properties of B2-type TMZr (TM = Ru,Mo, Rh,Os, and Re) compounds from first-principles calculations

The B2-type cubic Zr-based compounds are attractive advanced high-temperature materials because of the strong and symmetrical bonds. However, the mechanical and thermodynamic properties of the B2-type cubic Zr-based compounds are not well understood. Here, we use the first-principles calculations to investigate the structural, elastic modulus, ductility, and thermodynamic properties of TMZr (TM = Ru, Mo, Rh, Os, and Re) compounds. Two novel TMZr compounds, MoZr and ReZr, are first predicted by using the phonon dispersion and formation enthalpy, respectively. The results show that the B2-type TMZr compounds not only exhibit high elastic modulus but also show better ductility due to the symmetrical TM-Zr metallic bonds. In particular, the calculated elastic modulus of OsZr is larger than that of the other four TMZr compounds, indicating that the OsZr shows the strongest deformation resistance in five TMZr compounds. The calculated Θ _D of RuZr is 328 K, which is larger than that of the other four TMZr compounds. The calculated phonon density of state shows that the high-temperature thermodynamic properties of TMZr derive from the vibration of Zr atom. Therefore, our work predicts that the B2-type OsZr is an attractive high-temperature structural material.     

Determination of Anti-Tumor Agent TM208, 4-Methyl-piperazine-1-carbodithioc Acid 3-Cyano-3,3-diphenylpropyl Ester Hydrochloride,in Rats by LC

A new, specific and sensitive high performance liquid chromatography analytical procedure was developed and validated for the determination of TM208 in rat primary solid organs/tissues and plasma. TM208 was extracted from the appropriate matrix using methanol followed by centrifugation at 11,255×g for 20 min and injection of a 30 μL aliquot. Separation was carried out under gradient conditions using an ODS C18 column equipped with a guard column. The mobile phase consisted of methanol and water and retention times of TM208 and plunarizine (IS) were 17.658 and 26.175 min, respectively. The analytical procedure provided acceptable precision, accuracy, recoveries and linearity. Stability studies showed that TM208 was stable in organs/tissues homogenates for three freeze–thaw cycles, at room temperature for at least 24 h 3 weeks at −20 °C. The validated method was successfully applied to the determination of TM208 in SD rats following oral administration at a dose of 250 mg kg⁻¹.

     

Disordered structures of the TM-Mg-Zn 1/1 quasicrystal approximants (TM = Hf, Zr, or Ti) and chemical intergrowth

The structures of three quasicrystal approximant phases in the TM-Mg-Zn (TM = Hf, Zr, Ti) systems with the analyzed compositions Hf5Mg18Zn77, Zr5Mg18Zn77, and Ti5.5Mg17.5Zn77 have been synthesized, and their structures have been analyzed by single-crystal X-ray diffraction. The structure analyses revealed that these cubic phases with the space group Pm3 contain two different rhombic-triacontahedral clusters. These clusters are so-called Bergman-type atomic clusters and previously known approximants of face-centered icosahedral (F-type) quasicrystals are composed only of Mackay-type clusters, thus these compounds are seen as new prototype structures. Electron density maps calculated by the maximum entropy method (MEM) show that one of the atomic clusters displays characteristic structural disorder. The disorder in these phases is related to the chemical intergrowth of different Friauf polyhedra, and the prospects of new guide lines for finding quasicrystals composed of such polyhedra are discussed.