Observation of Transition-Metal–Boron Triple Bonds in IrB2O− and ReB2O−

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π→BR back-donation, despite the electron deficiency of boron. An electron-precise metal–boron triple bond was first observed in BiB₂O⁻ [Bi≡B−B≡O]⁻ in which both boron atoms can be viewed as sp-hybridized and the [B−BO]⁻ fragment is isoelectronic to a carbyne (CR). To search for the first electron-precise transition-metal-boron triple-bond species, we have produced IrB₂O⁻ and ReB₂O⁻ and investigated them by photoelectron spectroscopy and quantum-chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂O⁻ has a closed-shell bent structure (C_s, ¹A′) with BO⁻ coordinated to an Ir≡B unit, (⁻OB)Ir≡B, whereas ReB₂O⁻ is linear (C_∞v, ³Σ⁻) with an electron-precise Re≡B triple bond, [Re≡B−B≡O]⁻. The results suggest the intriguing possibility of synthesizing compounds with electron-precise M≡B triple bonds analogous to classical carbyne systems.     

Observation of Transition‐Metal–Boron Triple Bonds in IrB2O− and ReB2O−

Multiple bonds between boron and transition metals are known in many borylene (:BR) complexes via metal d_π→BR back‐donation, despite the electron deficiency of boron. An electron‐precise metal–boron triple bond was first observed in BiB₂O^? [Bi≡B?B≡O]^? in which both boron atoms can be viewed as sp‐hybridized and the [B?BO]^? fragment is isoelectronic to a carbyne (CR). To search for the first electron‐precise transition‐metal‐boron triple‐bond species, we have produced IrB₂O^? and ReB₂O^? and investigated them by photoelectron spectroscopy and quantum‐chemical calculations. The results allow to elucidate the structures and bonding in the two clusters. We find IrB₂O^? has a closed‐shell bent structure (C_s, ¹A′) with BO^? coordinated to an Ir≡B unit, (^?OB)Ir≡B, whereas ReB₂O^? is linear (C_∞v, ³Σ^?) with an electron‐precise Re≡B triple bond, [Re≡B?B≡O]^?. The results suggest the intriguing possibility of synthesizing compounds with electron‐precise M≡B triple bonds analogous to classical carbyne systems.     

Enhanced lithium electrochromism of atmospheric pressure plasma jet-synthesized tungsten/molybdenum oxide films for flexible electrochromic devices

Enhanced lithium electrochromic performances of mixed organo-tungsten oxide (W _x O _y C _z )/organo-molybdenum oxide (Mo _x O _y C _z ) films by a rapid codeposition onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at a short exposed duration of 23 s using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of hexacarbonyl precursors [W(CO)₆ and Mo(CO)₆] are investigated. The flexible organo-tungsten–molybdenum oxide (WMo _x O _y C _z ) films demonstrated noteworthy electrochromic performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄–propylene carbonate electrolyte by the switching measurements of potential sweep from ?1 to 1 V at a scan rate of 50 mV/s and the potential step at ?1 and 1 V, even after being bent 360^o around a 2.5-cm diameter rod for 1,000 cycles. The optical modulation (ΔT) of 61.3 % for MoO _y C _z films at a wavelength of 795.6 nm was significantly improved up to 72.5 % for WMo _x O _y C _z films cosynthesized with an APPJ.     

A novel boron-rich quaternary scandium borocarbosilicide Sc3.67−xB41.4−y−zC0.67+zSi0.33−w

A novel quaternary scandium borocarbosilicide Sc_3.67−xB_41.4−y−zC_0.67+zSi_0.33−w was found. Single crystallites were obtained as an intergrowth phase in the float-zoned single crystal of Sc_0.83−xB_10.0−yC_0.17+ySi_0.083−z that has a face-centered cubic crystal structure. Single crystal structure analysis revealed that the compound has a hexagonal structure with lattice constants a = b = 1.43055(8) nm and c = 2.37477(13) nm and space group (No. 187). The crystal composition calculated from the structure analysis for the crystal with x = 0.52, y = 1.42, z = 1.17, and w = 0.02 was ScB_12.3C_0.58Si_0.10 and that agreed rather well with the composition of ScB_11.5C_0.61Si_0.04 measured by EPMA. In the crystal structure that is a new structure type of boron-rich borides, there are 79 structurally independent atomic sites, 69 boron and/or carbon sites, two silicon sites and eight scandium sites. Boron and carbon form seven structurally independent B₁₂ icosahedra, one B₉ polyhedron, one B₁₀ polyhedron, one irregularly shaped B₁₆ polyhedron in which only 10.7 boron atoms are available because of partial occupancies and 10 bridging sites. All polyhedron units and bridging site atoms interconnect each other forming a three-dimensional boron framework structure. Sc atoms reside in the open spaces in the boron framework structure.     

Approach to thermal properties and electronic polarizability from average single bond strength in ZnOBi2O3B2O3 glasses

The glass transition temperature (T_g), density, refractive index, Raman scattering spectra, and X-ray photoelectron spectra (XPS) for xZnO-yBi₂O₃-zB₂O₃ glasses (x=10-65, y=10-50, z=25-60 mol%) are measured to clarify the bonding and structure features of the glasses with large amounts of ZnO. The average electronic polarizability of oxide ions (α_O2−) and optical basicity (Λ) of the glasses estimated using Lorentz-Lorenz equation increase with increasing ZnO or Bi₂O₃ content, giving the values of α_O2−=1.963 Å³ and Λ=0.819 for 60ZnO-10Bi₂O₃-30B₂O₃ glass. The formation of BOBi and BOZn bridging bonds in the glass structure is suggested from Raman and XPS spectra. The average single bond strength (B_MO) proposed by Dimitrov and Komatsu is applied to the glasses and is calculated using single bond strengths of 150.6 kJ/mol for ZnO bonds in ZnO₄ groups, 102.5 kJ/mol for BiO bonds in BiO₆ groups, 498 kJ/mol for BO bonds in BO₃ groups, and 373 kJ/mol for BO bonds in BO₄ groups. Good correlations are observed between T_g and B_MO, Λ and B_MO, and T_g and Λ, proposing that the average single bond strength is a good parameter for understanding thermal and optical properties of ZnOBi₂O₃B₂O₃ glasses.     

Fluorination of dimethylmercury,tetramethylsilane and tetramethylgermanium. Synthesis and characterization of polyfluorotetramethylsilanes,polyfluorotetramethylgermanes,bis(trifluoromethyl)mercury and tetrakis(trifluoromethyl)germanium

It has been found possible to preserve metal—carbon and metalloid—carbon bonds during direct fluorination. The reaction of dimethylmercury with fluorine gives bis(trifluoromethyl)mercury in 6.5% yield. Fluorination of tetramethylsilane has led to the isolation of the new polyfluorotetramethylsilanes of the following type, Si(CH₃)_x(CH₂F)_y(CHF₂)_z, x + y + z = 4. Also characterized were compounds containing SiCF₃. It has been possible to synthesize tetrakis(trifluoromethyl)germanium in 63.5% yield from the reaction of fluorine with tetramethylgermanium. Also characterized were many polyfluorotetramethylgermanes of the following type, Ge(CF₃)_x(CF₂H)_y(CFH₂)_z (x + y + z = 4).     

Theoretical study of the strong intramolecular hydrogen bond and metal-ligand interactions in group 10 (Ni, Pd, Pt) bis(dimethylglyoximato) complexes

The structural and bonding characteristics of the bis(dimethylglyoximato) complexes of group 10 transition metals ([M(dmg)₂], where M = Ni, Pd and Pt) were investigated by means of quantum chemical computations. The equilibrium geometries, energetic and bonding properties were computed using the B3P86 exchange-correlation density functional in conjunction with a 6-311+(+)G^∗∗ basis set. The computations revealed that the strong O⁻?H-O hydrogen bond exists only in the presence of the metal cations. The free (dmg)₂²⁻ ligand has significantly different geometry in which the O⁻?H-O interaction is replaced by N?O-H bonds. The characteristics of the metal-ligand interactions were determined by natural bond orbital analysis.     

Multiple Bonding Between Group 3 Metals and Fe(CO)3−

Heteronuclear Group 3 metal/iron carbonyl anion complexes ScFe(CO)₃^?, YFe(CO)₃^?, and LaFe(CO)₃^? are prepared in the gas phase and studied by mass‐selective infrared (IR) photodissociation spectroscopy as well as quantum‐chemical calculations. All three anion complexes are characterized to have a metal–metal‐bonded C_3v equilibrium geometry with all three carbonyl ligands bonded to the iron center and a closed‐shell singlet electronic ground state. Bonding analyses reveal that there are multiple bonding interactions between the bare group‐3 elements and the Fe(CO)₃^? fragment. Besides one covalent electron‐sharing metal–metal σ bond and two dative π bonds from Fe to the Group 3 metal, there is additional multicenter covalent bonding with the Group 3 atom bonded to Fe and the carbon atoms.     

A Double-Band Emitter with Ultranarrow-Band Blue and Narrow-Band Green Luminescence

Understanding the origin and mechanisms of luminescence is a crucial point when it comes to the development of new phosphors with targeted luminescence properties. Herein, a new phosphor belonging to the substance class of alkali metal lithosilicates with the generalized sum formula Cs_{4−x−y−z}Rb_xNa_yLi_z[Li₃SiO₄]₄:Eu²⁺ is reported. Single crystals of the cyan-emitting UCr₄C₄-type phosphor show a peculiar double-band luminescence with one ultranarrow emission band at 473 nm and a narrow emission band at 531 nm under excitation with UV light (λ_exc=408 nm). Regarding occupation of the channels by the light metal ions, investigations of single-crystal XRD data led to the assumption that domain formation with distinct lithium- and sodium-filled channels occurs. Depending on which of these channels hosts the activator ion Eu²⁺, a green or blue emission results. The herein-presented results shed new light on the luminescence process in the well-studied UCr₄C₄-type alkali metal lithosilicate phosphors.     

Paramagnetic resonance of interstitial mo5+ in a tio2 lattice

Paramagnetic absorption of Mo⁵⁺ has been studied in a polycrystalline TiO₂ rutile lattice, The g tensor (g_x = 1.897, g_y = 1.920, g_z = 1.857) and the hyperfine tensor (A_x = 32.7, (A_y = 51.2, (A_z = 58.5 (in 10^?4 cm^?1)) are in agreement with those expected for an nd¹ ion in an interstitial position.     

NMR study of the order-disorder phase transitions of KHCO3 and KDCO3 single crystals

KHCO₃ and its deuterated analogue KDCO₃ are typical materials that undergo order-disorder phase transitions at 318 and 353 K, respectively. The spin-lattice relaxation times, T₁, spin-spin relaxation times, T₂, and the number of resonance lines for the ¹H, ²D, and ³⁹K nuclei of these crystals were investigated using NMR spectrometer. These materials are known to exhibit anomalous decreases in T₁ near T_C, which have been attributed to a structural phase transition. Additionally, changes in the symmetry of the (HCO₃)₂²⁻ (or (DCO₃)₂²⁻) dimers in these materials are associated with large changes in T₁, T₂, and the number of resonance lines. Here we found that the resonance lines for ¹H, ²D, and ³⁹K nuclei decrease in number as the temperature is increased up to T_C, indicating that the orientations of the (HCO₃)₂²⁻ (or (DCO₃)₂²⁻) dimers and the environments of the K ions change at T_C. Moreover, based on number of resonance lines, the results further indicate that the (HCO₃)₂²⁻ (or (DCO₃)₂²⁻) dimers reorientate to approximately parallel to the directions of the hydrogen bonds (or deuteron bonds) and the direction of the a-axis. The transitions at 318 and 345 K of the two crystals are of the order-disorder type. The present results therefore indicate that the orientations of the (HCO₃)₂²⁻ and (DCO₃)₂²⁻ dimers and the environment of the K ion play a significant role in these phase transitions.     

Nature of α,β-CCC agostic bonding in metallacyclobutanes

The α,β-CCC agostic bonding in metallacyclobutanes is examined on the basis of structural, bonding, energetics, and electron density features. The structural features such as C_α–C_β, M–C_α, and M–C_β distances and C_αC_βC_α and MC_αC_β angles of the agostic metallacyclobutanes were distinctly different from those of the corresponding non-agostic complexes. Two different orbital interactions characteristic of the agostic complex, causing the deformation of the propane-1,4-diyl unit of the metallacyclobutane were identified. The energy difference between the propane-1,4-diyl unit of metallacyclobutane in an agostic complex to that in a non-agostic complex is proposed as a good measure for the strength of α,β-CCC agostic interaction (E_agostic). E_agostic values of 37.0, 36.2, 13.7, 28.6, and 23.9 kcal/mol were obtained for the Grubb’s first generation Ru, Grubb’s second generation Ru, Ti, W, and Ta metallacyclobutane complexes and these values showed a linear correlation with the electron density at the ring CPs. The QTAIM features of the agostic complexes viz. the smaller ρ value at the C_α–C_β BCPs, larger ellipticity of the C_α–C_β BCPs, and diminished covalent character of C_α–C_β bonds as seen in their Laplacian of the electron density (∇²ρ) at the BCPs, when compared with the non-agostic systems, fully supported the agostic bonding interactions. The α,β-CCC bonding is considered as the first example of a π type orbital formed between a metal atom and a carbon atom, where there is no σ bond connectivity and this type of bonding is anticipated with all transition metals provided that the metal center is highly electron deficient.     

Zirconium titanate ceramic pigments: Crystal structure, optical spectroscopy and technological properties

Srilankite-type zirconium titanate, a promising structure for ceramic pigments, was synthesized at 1400 °C following three main doping strategies: (a) ZrTi_1−xA_xO₄, (b) ZrTi_1−x−yA_xB_yO₄ and (c) Zr_1−xC_xTiO₄ where A=Co, Cr, Fe, Mn, Ni or V (chromophores), B=Sb or W (counterions) and C=Pr (chromophore); x=y=0.05. Powders were characterized by XRD with Rietveld refinements and DRS in the UV-visible-NIR range; technological properties were appraised in several ceramic matrices (frits, glazes and body). Zirconium titanate can be usefully coloured with first row transition elements, giving green and greenish yellow (Co and Ni); orange-buff (Cr and V); tan-brown hues (Mn and Fe). In industrial-like synthesis conditions, a disordered structure as (Zr,Ti)O₂, with both Zr and Ti randomly distributed in the octahedral site, is achieved. Doping with chromophores and counterions induces unit cell dimensions variation and causes an oversaturation in zirconium oxide. Optical spectroscopy reveals the occurrence of Co²⁺, Cr³⁺, Fe³⁺, Mn²⁺, Mn³⁺, Ni²⁺, V³⁺ and V⁴⁺. The zirconium titanate pigments fulfil current technological requirements for low-temperature applications, but exhibit a limited chemico-physical stability for higher firing temperature and in chemically aggressive media.     

Formation of scandium carbides and scandium oxycarbide from the elements at high-(P, T) conditions

Synchrotron diffraction experiments with in situ laser heated diamond anvil cells and multi-anvil press synthesis experiments have been performed in order to investigate the reaction of scandium and carbon from the elements at high-(P,T) conditions. It is shown that the reaction is very sensitive to the presence of oxygen. In an oxygen-rich environment the most stable phase is ScO_xC_y, where for these experiments x=0.39 and y=0.50-0.56. If only a small oxygen contamination is present, we have observed the formation of Sc₃C₄, Sc₄C₃ and a new orthorhombic ScC_x phase. All the phases formed at high pressures and temperatures are quenchable. Experimentally determined elastic properties of the scandium carbides are compared to values obtained by density functional theory based calculations.     

Synthesis of new molybdenum-tungsten, vanadium-tungsten and vanadium-molybdenum-tungsten oxynitrides from freeze-dried precursors

Interstitial molybdenum-tungsten, vanadium-tungsten and vanadium-molybdenum-tungsten oxynitrides in the solid solution series Mo_1−zW_z(O_xN_y) and V_1−zW_z(O_xN_y) (z=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1), and V_1−u−zMo_uW_z(O_xN_y) (u, z=0.2, 0.33, 0.4, 0.6; u+z<1), have been obtained by ammonolysis of precursors resulting from the freeze-drying of aqueous solutions of the metal salts (NH₄VO₃, (NH₄)₆Mo₇O₂₄·4H₂O and (NH₄)₆W₁₂O₃₉·18H₂O). A study of the influence of the preparative variables on the outcomes of this procedure is presented. Compounds in the Mo_1−zW_z(O_xN_y) series are prepared as single phases by ammonolysis of the respective freeze-dried precursors (during 2 h) at different temperatures between 973 and 1023 K, optimised for each composition, followed by slow cooling of the samples (except for the Mo-only containing phase, in which fast cooling has been used). Compounds in the V_1−zW_z(O_xN_y) and V_1−u−zMo_uW_z(O_xN_y) series are prepared as single phases by ammonolysis (during 2 h) of crystalline precursors (as resulting from thermal treatment in air at 873 K, during 12 h, of the freeze-dried precursors) at 1073 K, followed by slow cooling of the samples. All the compounds in these series have the rock-salt crystal structure, in which the metal atoms are in an fcc arrangement, with non-metal atoms occupying octahedral interstitial positions. The materials have been characterized by X-ray powder diffraction, elemental analysis, scanning electron microscopy and magnetic measurements.     

Structure,chemical bonding and electrochemical behavior of heteroatom-substituted carbons prepared by arc discharge and chemical vapor deposition

The structural characteristics, chemical bonding and electrochemical properties of the heteroatom-substituted carbons synthesized by arc discharge and chemical vapor deposition have been investigated. C_xN was prepared only as a soot by arc discharge in nitrogen atmosphere; BC_x and B_xC_yN_z were obtained both as soot and cathode deposits by arc discharge of graphite rods having B₄C and boron nitride (BN) in argon and nitrogen atmospheres, respectively. Transmission electron microscopic study showed that C_xN, BC_x and B_xC_yN_z soots were composed of nanoparticles with diameters of 20–100 nm, while cathode deposits contained nanotubes with diameters of ca. 20 nm or less and nanoparticles with diameters less than 100 nm. It was found from XPS study that C_xN contained a large amount of pyridine type nitrogen atoms at the edge of graphene layer; the BBC₂ structure was dominant in BC_x; and B₃N, B₂NC and BNC₂ structures might exist in B_xC_yN_z. Carbon- and C_xN-coated graphite were prepared by deposition of carbon and C_xN onto natural graphite powder, respectively. The concentrations of coated C_xN layers were between C₂₁N and C₆₂N. Charge–discharge profiles of C_xN, BC_x and B_xC_yN_z soots prepared by arc discharge were similar to each other, giving linearly increasing potential with lithium ion deintercalation. C_xN soot heat-treated at 3000°C showed a similar profile for charge–discharge curves to that of graphite with a charge capacity of 334 mAh g⁻¹. On the other hand, C_xN-coated graphite exhibited as high as 397 mAh g⁻¹ larger than ∼365 mAh g⁻¹ for carbon-coated graphite and that of heat-treated C_xN soot.     

Electron Capture Dissociation of Trivalent Metal Ion-Peptide Complexes

With electrospray ionization from aqueous solutions, trivalent metal ions readily adduct to small peptides resulting in formation of predominantly (peptide + M_T ? H)²⁺, where M_T = La, Tm, Lu, Sm, Ho, Yb, Pm, Tb, or Eu, for peptides with molecular weights below ~1000 Da, and predominantly (peptide + M_T)³⁺ for larger peptides. ECD of (peptide + M_T ? H)²⁺ results in extensive fragmentation from which nearly complete sequence information can be obtained, even for peptides for which only singly protonated ions are formed in the absence of the metal ions. ECD of these doubly charged complexes containing M_T results in significantly higher electron capture efficiency and sequence coverage than peptide-divalent metal ion complexes that have the same net charge. Formation of salt-bridge structures in which the metal ion coordinates to a carboxylate group are favored even for (peptide + M_T)³⁺. ECD of these latter complexes for large peptides results in electron capture by the protonation site located remotely from the metal ion and predominantly c/z fragments for all metals, except Eu³⁺, which undergoes a one electron reduction and only loss of small neutral molecules and b/y fragments are formed. These results indicate that solvation of the metal ion in these complexes is extensive, which results in the electrochemical properties of these metal ions being similar in both the peptide environment and in bulk water.      

The Liquid Junction Potential in Potentiometric Titrations. IX. The Calculation of Potentials Across Liquid Junctions of the Type, AY|AY+BY z(B)+HY+ A y L, for Emf Cells where Strong or Weak Complexes are Formed, Respectively, at [Y−] = C mol⋅L−1, Constant and −log 10[H+]≤ 7

In the present part, potential functions are derived for the calculation of the total potential anomalies, Δ E _B and Δ E _H, for Emf cells where strong or weak complexes are formed, respectively. A weak or strong electrolyte is considered to be used as complexing agent (A _y L), respectively, at the experimental condition, [Y^?] = C mol?L^?1, constant. The cells have indicator electrodes reversible to B ^z(B)+ (cell B) and H⁺ ions (cell H), respectively. The system, HY–BY _z(B)-A _Y L-AY and the protolysis of the acids HL and H₂L in the ionic medium (A⁺, Y^?) are studied. Here, y = |z _L |. Moreover, some useful Emf titrations are suggested for the experimental determination of the slope functions SL(H, L^?), SL (H, L^2?) and SL(H, HL^?). The usefulness of the derived potential functions is established using the H⁺-acetate^? (CH₃COO^?) system as an example.     

Spin-orbit perturbation of the anion states by a heavy cation in NaNO2:Ag+

Optical and ODMR studies of NaNO₂: Ag⁺ crystals at T < 4.2 K have shown very selective spin-orbit perturbations on the properties of the nitrite triplet state T₁, by the heavy cation dopant. The perturbed T₁ — S₀ transition shows mainly z-axis polarization associated with the τ_y spin state (z- and y-axes in-plane with the z-axis bisecting the ONO angle). The fine structure splitting constants for the perturbed T₁ state are D = -3Y/2 = ± 15.508 GHz and E = (Z - X)/2 = 3 .643 GHz.