Surface composition of Pt25Ni75(111) investigated by ISS and STM

Summary Ion scattering spectroscopy results show Pt enrichment in the topmost atomic layers of a Pt₂₅Ni₇₅(111) single crystal due to preferential sputtering. The increased lattice constant caused thereby leads to subsurface lattice mismatch dislocations, which have been studied by scanning tunneling microscopy. Agreement is found for the Pt concentration estimated from the density of dislocations and the results obtained by ISS. Thermal annealing induces further segregation of Pt in the topmost atomic layer. The composition of the subsurface layers has been studied and a strong dependence on the annealing temperature has been found. The observed Pt enrichment in the first monolayer for the thermodynamic equilibrium state agrees well with a thermodynamic theory.     

Competitive segregation of Si and P on Fe96.5Si3.5 (100) and (110)

Annealing an Fe_96.5Si_3.5 (100)/(110) bicrystal, containing 90 ppm P, leads immediately to a strong segregation of silicon. The Si atoms, however, desegregate subsequently and are displaced by P, whose segregation enthalpy is larger than that of silicon. The corresponding surface structures formed on both faces have been studied using complementary methods: Scanning tunneling microscopy (STM) to obtain atomically resolved geometrical information and Auger electron spectroscopy (AES) for the determination of the surface composition. Si substitutes surface Fe atoms on both faces and forms ordered surface alloys, whereas P occupies hollow sites on the surface. Si and P form c(2 × 2) superstructures on the (100) surface, whereby each segregated phosphorus atom blocks in the average one silicon segregation site. The (110) surface, on the other hand, is characterized by a c(1 × 3) Si superstructure. Due to the anisotropy of this surface the P/Si exchange proceeds by the formation of silicon coverage decreasing domain boundaries within the silicon structure, which are simultaneously occupied by P atoms. Furthermore the comparison of the AES and STM derived phosphorus coverages indicates a P multilayer segregation on the (110) surface.     

On the crystal chemistry of Tm2Ni1.896(4)In, Tm2.22(2)Ni1.81(1)In0.78(2), Tm4.83(3)Ni2In1.17(3), and Er5Ni2In

The rare earth-nickel-indides Tm₂Ni_1.896(4)In, Tm_2.22(2)Ni_1.81(1)In_0.78(2), Tm_4.83(3)Ni₂In_1.17(3), and Er₅Ni₂In were synthesized from the elements by arc-melting and subsequent annealing for the latter three compounds. Three indides were investigated by X-ray powder and single crystal diffraction: Mo₂FeB₂ type, P4/mbm, Z=2, a=731.08(4), c=358.80(3) pm, wR₂=0.0201, 178 F² values, 13 variables for Tm₂Ni_1.896(4)In, a=734.37(7), c=358.6(1) pm, wR₂=0.0539, 262 F² values, 14 variables for Tm_2.22(2)Ni_1.81(1)In_0.78(2), and Mo₅SiB₂ type, I4/mcm, a=751.0(2), c=1317.1(3) pm, wR₂=0.0751, 317 F² values, 17 variables for Tm_4.83(3)Ni₂In_1.17(3). X-ray powder data for Er₅Ni₂In revealed a=754.6(2) and c=1323.3(5) pm. The Mo₂FeB₂ type structures of Tm₂Ni_1.896(4)In and Tm_2.22(2)Ni_1.81(1)In_0.78(2) are intergrowths of slightly distorted CsCl and AlB₂ related slabs, however, with different crystal chemical features. The nickel sites within the AlB₂ slabs are not fully occupied in both indides. Additionally In/Tm mixing is possible at the center of the CsCl slab, as is evident from the structure refinement of Tm_2.22(2)Ni_1.81(1)In_0.78(2). The Mo₅SiB₂ type structures of Tm_4.83(3)Ni₂In_1.17(3) and Er₅Ni₂In can be considered as an intergrowth of distorted CuAl₂ and U₃Si₂ related slabs in an ABA′B′ stacking sequence along the c-axis. Again, one thulium site shows Tm/In mixing. The U₃Si₂ related slab has great structural similarities with the Mo₂FeB₂ type structure of Tm₂Ni_1.896(4)In and Tm_2.22(2)Ni_1.81(1)In_0.78(2). The crystal chemical peculiarities and chemical bonding in these intermetallics are briefly discussed.     

Comparative analysis of some thermo-physical properties of Se90Zn10 and Te90Zn10 alloys

The present paper reports a comparative study of some thermo-physical properties (thermal conductivity, diffusivity and specific heat per unit volume) of Se₉₀Zn₁₀ and Te₉₀Zn₁₀ alloys. Simultaneous measurements of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) of twin pellets of Se₉₀Zn₁₀ and Te₉₀Zn₁₀ alloys using transient plane source (TPS) technique have been made at room temperature. From the measured values of λ_e and χ_e, the specific heat per unit volume (C_v) has been calculated. The results indicate that the measured values of these parameters are higher for Te₉₀Zn₁₀ alloy as compared to Se₉₀Zn₁₀ alloy. This is explained in terms of thermal conductivity of chalcogen elements Se and Te.     

Interactions magnetiques intra- et interclusters dans les perovskites hexagonales Cs4Ni3CdF12(12R) et Cs5Ni4CdF15(10H)

The magnetic properties of Cs₄Ni₃CdF₁₂(12R) and Cs₅Ni₄CdF₁₅(10H) have been interpreted in terms of isolated entities in a large temperature range (T > 20 K). The model is based on a Heisenberg-Dirac-Van Vleck Hamiltonian. The intracluster magnetic interactions are ferromagnetic. At low temperature one has to take account of the intercluster interactions and of the zero-field splitting of Ni²⁺ to give a more satisfying interpretation of the magnetic behavior.     

Yb5Ni4Sn10 and Yb7Ni4Sn13: New polar intermetallics with 3D framework structures

The title compounds have been obtained by solid state reactions of the corresponding pure elements at high temperature, and structurally characterized by single-crystal X-ray diffraction studies. Yb₅Ni₄Sn₁₀ adopts the Sc₅Co₄Si₁₀ structure type and crystallizes in the tetragonal space group P4/mbm (No. 127) with cell parameters of a=13.785(4) Å, c=4.492 (2) Å, V=853.7(5) Å³, and Z=2. Yb₇Ni₄Sn₁₃ is isostructural with Yb₇Co₄InGe₁₂ and crystallizes in the tetragonal space group P4/m (No. 83) with cell parameters of a=11.1429(6) Å, c=4.5318(4) Å, V=562.69(7) Å³, and Z=1. Both structures feature three-dimensional (3D) frameworks based on three different types of one-dimensional (1D) channels, which are occupied by the Yb atoms. Electronic structure calculations based on density functional theory (DFT) indicate that both compounds are metallic. These results are in agreement with those from temperature-dependent resistivity and magnetic susceptibility measurements.     

Crystal structure and magnetic properties of Ba2Ni3F10

Ba₂Ni₃F₁₀ is monoclinic (space group $\text{C2}\text{m}$), a = 18.542(7) Å, b = 5.958(2) Å, c = 7.821(3) Å, β = 111°92(10). Ba₂Co₃F₁₀ and Ba₂Zn₃F₁₀ are isostructural. The structure has been refined from 995 reflections by full-matrix least-squares refinement to a weighted R value of 0.048 (unweighted R, 0.047). The three-dimensional network can be described either by complex chains connected to each other by octahedra sharing corners or with an 18L dense-packing sequence. The basic unit (Ni₃F₁₀)^4? is discussed and compared to the different unit existing in Cs₄Mg₃F₁₀. Antiferromagnetic properties of Ba₂Ni₃F₁₀ (T_N = 50 K are described.     

Syntheses, crystal structures, and properties of three new metal selenites Na2Co2(SeO3)3, Na2Co1.67Ni0.33(SeO3)3, and Na2Ni2(SeO3)3

Three new sodium cobalt (nickel) selenite compounds, namely, Na₂Co₂(SeO₃)₃, Na₂Co_1.67Ni_0.33(SeO₃)₃, and Na₂Ni₂(SeO₃)₃ have been hydro-/solvothermally synthesized in the mixed solvents of acetonitrile and water. Single-crystal X-ray diffraction analyses reveal that these isostructural compounds belong to the orthorhombic Cmcm space group and their structures feature three-dimensional open frameworks constructed by the two-dimensional layers of [MSeO₃] pillared by the [SeO₃]²⁻ groups. The two different types of Na⁺ ions reside in the intersecting two-dimensional channels parallel to the a- and c-axes, respectively. Their thermal properties have been investigated via TGA-DSC. The magnetic measurements indicate the existence of the antiferromagnetic interactions in these compounds.     

The molecular structures of H2Os3(CO)10, H(SC2H5)Os3(CO)10 and (OCH3)2Os3(CO)10

X-ray crystallographic analyses of H₂Os₃(CO)₁₀, H(SC₂H₅)Os₃(CO)₁₀ and (OCH₃)₂Os₃(CO)₁₀ are reported. Although hydrogen atom positions have not been located, the essential isostructural nature of the three commplexes establishes the hydride ligands as bridging two metal atoms, separated by 2.670 Å, with a formal bond order of two; the bridging hydrido- and thiolato-ligands span an osmium---osmium bond of length 2.863 Å and formal bond order one; the two μ-methoxy ligands bridge two metal atoms separated by 3.078 Å which, by simple 18 electron rule counting, has a metal---metal bond order of zero. Some general comments are made on the structures of polynuclear transition metal carbonyls.     

A combined experimental and theoretical study of resonance emission spectra of SO2( B2)

Experimental and theoretical resonance emission spectra are obtained for a number of vibrational states of SO₂( ¹B₂). The experimental emission spectra are dominated by (n₁ν₁, n₂ν₂, 0) bands, but some weak activity in the anti-symmetric stretch (ν₃) is observed. The calculated emission spectra based on an empirical near-equilibrium potential energy surface agree reasonably well with experiment for two lowest states investigated here, but fail to reproduce higher ones. Resonance Raman spectra are also calculated and agree well with an earlier experiment.     

Tuning the sulfur-heterometal interaction in organolead(IV) complexes of [Pt2(μ-S)2(PPh3)4]

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with Ph₃PbCl, Ph₂PbI₂, Ph₂PbBr₂ and Me₃PbOAc result in the formation of bright yellow to orange solutions containing the cations [Pt₂(μ-S)₂(PPh₃)₄PbR₃]⁺ (R₃ = Ph₃, Ph₂I, Ph₂Br, Me₃) isolated as PF₆⁻ or BPh₄⁻ salts. In the case of the Me₃Pb and Et₃Pb systems, a prolonged reaction time results in formation of the alkylated species [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (R = Me, Et). X-ray structure determinations on [Pt₂(μ-S)₂(PPh₃)₄PbMe₃]PF₆ and [Pt₂(μ-S)₂(PPh₃)₄PbPh₂I]PF₆ have been carried out, revealing different coordination modes. In the Me₃Pb complex, the (four-coordinate) lead atom binds to a single sulfur atom, while in the Ph₂PbI adduct coordination of both sulfurs results in a five-coordinate lead centre. These differences are related to the electron density on the lead centre, and indicate that the interaction of the heterometal centre with the {Pt₂S₂} metalloligand core can be tuned by variation of the heteroatom substituents. The species [Pt₂(μ-S)₂(PPh₃)₄PbR₃]⁺ display differing fragmentation pathways in their ESI mass spectra, following initial loss of PPh₃ in all cases; for R = Ph, loss of PbPh₂ occurs, yielding [Pt₂(μ-S)₂(PPh₃)₃Ph]⁺, while for R = Me, reductive elimination of ethane gives [Pt₂(μ-S)₂(PPh₃)₃PbMe]⁺, which is followed by loss of CH₄.     

Synthesis and characterisation of HRuRh3(CO)12. Crystal structures of HRuRh3(CO)12, HRuRh3(CO)10(PPh3)2 and HRuCo3(CO)10(PPh3)2

A new ruthenium-rhodium mixed-metal cluster HRuRh₃(CO)₁₂ and its derivatives HRuRh₃(CO)₁₀(PPh₃)₂ and HRuCo₃(CO)₁₀(PPh₃)₂ have been synthesized and characterized. The following crystal and molecular structures are reported: HRuRh₃(CO)₁₂: monoclinic, space group P2₁/c, a 9.230(4), b 11.790(5), c 17.124(9) Å, β 91.29(4)°, Z = 4; HRuRh₃(CO)₁₀(PPh₃)₂·C₆H₁₄: triclinic, space group P$\text{1}$, a 11.777(2), b 14.079(2), c 17.010(2) Å, α 86.99(1), β 76.91(1), γ 72.49(1)°, Z = 2; HRuCo₃(CO)₁₀(PPh₃)₂·CH₂Cl₂: triclinic, space group P$\text{1}$, a 11.577(7), b 13.729(7), c 16.777(10) Å, α 81.39(4), β 77.84(5), γ 65.56°, Z = 2. The reaction between Rh(CO)₄^? and (Ru(CO)₃Cl₂)₂ tetrahydrofuran followed by acid treatment yields HRuRh₃(CO)₁₂ in high yield. Its structural analysis was complicated by a 80–20% packing disorder. More detailed structural data were obtained from the fully ordered structure of HRuRh₃(CO)₁₀(PPh₃)₂, which is closely related to HRuCo₃(CO)₁₀(PPh₃)₂ and HFeCo₃(CO)₁₀(PPh₃)₂. The phosphines are axially coordinated.     

Synthesis and structure of the cadmium(II) complex [Cd2(Ph(NH2)2)5(DMFA)4](B10H10)2

A new binuclear cadmium(II) complex with neutral ligands, 1,2-diaminobenzene (DMB) and dimethylformamide (DMF), [Cd₂(Ph(NH₂)₂)₅(DMFA)₄](B₁₀H₁₀)₂, was synthesized and studied by IR spectroscopy and X-ray diffraction. The crystals are monoclinic, a = 26.198(3) ?, b = 12.742(3) ?, c = 21.658(3) ?, β = 119.985(10)°, Z = 8, space group C2/c. The distorted octahedral environment of Cd is formed by four nitrogen atoms of three DAB molecules and two oxygen atoms of DMF molecules. Three independent DAB molecules perform different functions: one chelates the Cd atom, another is linked to cadmium as a monodentate ligand, and the third one bridges two Cd atoms, thus forming the dimer. The amino groups of the DAB molecules are involved in the N-H⋯O and N-H⋯N hydrogen bonds and in N-H⋯B and N-H⋯H-B specific interactions with the cluster boron anion. Original Russian Text ? E.A. Malinina, V.V. Drozdova, L.V. Goeva, I.N. Polyakova, N.T. Kuznetsov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 6, pp. 922–926.     

Rare earth-nickel-indides Dy5Ni2In4 and RE4Ni11In20 (RE=Gd, Tb, Dy)

The new rare earth metal (RE)-nickel-indides Dy₅Ni₂In₄ and RE₄Ni₁₁In₂₀ (RE=Gd, Tb, Dy) were synthesized from the elements by arc-melting. Well-shaped single crystals were obtained by special annealing sequences. The four indides were investigated by X-ray diffraction on powders and single crystals: Lu₅Ni₂In₄ type, Pbam, Z=2, a=1784.2(8), b=787.7(3), c=359.9(1) pm, wR₂=0.0458, 891 F² values, 36 variables for Dy₅Ni₂In₄, U₄Ni₁₁Ga₂₀ type, C2/m, a=2254.0(9), b=433.8(3), c=1658.5(8) pm, β=124.59(2)°, wR₂=0.0794, 2154 F² values, 108 variables for Gd₄Ni₁₁In₂₀, a=2249.9(8), b=432.2(1), c=1657.9(5) pm, β=124.59(2)°, wR₂=0.0417, 2147 F² values, 108 variables for Tb₄Ni₁₁In₂₀, and a=2252.2(5), b=430.6(1), c=1659.7(5) pm, β=124.58(2)°, wR₂=0.0550, 2003 F² values, 109 variables for Dy₄Ni_10.80In_20.20. The 2d site in the dysprosium compound shows mixed Ni/In occupancy. Most nickel atoms in both series of compounds exhibit trigonal prismatic coordination by indium and rare earth atoms. Additionally, in the RE₄Ni₁₁In₂₀ compounds one observes one-dimensional nickel clusters (259 pm Ni₁-Ni₆ in Dy₄Ni_10.80In_20.20) that are embedded in an indium matrix. While only one short In₁-In₂ contact at 324 pm is observed in Dy₅Ni₂In₄, the more indium-rich Dy₄Ni_10.80In_20.20 structure exhibits a broader range in In-In interactions (291-364 pm). Together the nickel and indium atoms build up polyanionic networks, a two-dimensional one in Dy₅Ni₂In₄ and a complex three-dimensional network in Dy₄Ni_10.80In_20.20. These features have a clear consequence on the dysprosium coordination, i.e. a variety of short Dy-Dy contacts (338-379 pm) in Dy₅Ni₂In₄, while the dysprosium atoms are well separated (430 pm shortest Dy-Dy distance) within the distorted hexagonal channels of the [Ni_10.80In_20.20] polyanion of Dy₄Ni_10.80In_20.20. The crystal chemistry of both structure types is comparatively discussed.     

Ligand Dynamics in H2Os3(CO)10 and H2Os3(CO)10L

The variable temperature ¹³C NMR spectra of H₂Os₃(CO)₁₀ and H₂Os₃(CO)₁₀L (L P(C₆H₅)₃, P(O-i_C₃H₇)s3) and P(i_C₃H₇)₃) have been recorded and the results interpreted in terms of a localized exchange process involving concerted motion of the hydride and the carbonyl ligands. Taken along with previously reported variable temperature ¹H NMR data the results provide a complete picture of the ligand dynamics in these systems.     

The new ternary pnictides Er12Ni30P21 and Er13Ni25As19: Crystal structures and magnetic properties

The new ternary pnictides Er₁₂Ni₃₀P₂₁ and Er₁₃Ni₂₅As₁₉ have been synthesized from the elements. They crystallize with hexagonal structures determined from single-crystal X-ray data for Er₁₂Ni₃₀P₂₁ (space group P6₃/m, a=1.63900(3) nm, c=0.37573(1) nm, Z=1, R_F=0.062 for 1574 F-values and 74 variable parameters), and for Er₁₃Ni₂₅As₁₉ (Tm₁₃Ni₂₅As₁₉-type structure, space group P6?, a=1.6208(1) nm, c=0.38847(2) nm, Z=1, R_F=0.026 for 1549 F-values and 116 variable parameters). These compounds belong to a large family of hexagonal structures with a metal-metalloid ratio of 2:1. HRTEM investigations were conducted to probe for local ordering of the disordered structure at the nanoscale. The magnetic properties of the phosphide Er₁₂Ni₃₀P₂₁ have been studied in the temperature of range 2<T<300 K and with applied fields up to 5 T. The magnetic susceptibility follows the Curie-Weiss law from 4 to 300 K. The measured value of μ_eff=9.59 μ_B corresponds to the theoretical value of Er³⁺.