Ab initio chemical kinetics for the unimolecular decomposition of Si2H5 radical and related reverse bimolecular reactions

For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat‐CVD) processes using small silanes as precursors, disilanyl radical (Si₂H₅) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a‐Si:H film growth on large‐area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si₂H₅ producing smaller silicon hydrides including SiH, SiH₂, SiH_3, and Si₂H₄, and the related reverse reactions involving these species by using ab initio molecular‐orbital calculations. The results show that the lowest energy path is the production of SiH + SiH₄ that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si₂H₅. Additionally, the dissociation energies for breaking the Si? Si and H? SiH₂ bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH₂, HSiSiH₂, and Si₂H₄(C_2h) at 0 K by using the isodesmic reactions, such as ²HSiSiH₂ + ¹C₂H₆→¹Si₂H₆ + ²HCCH₂ and ¹Si₂H₄(C_2h) + ¹C₂H₆ → ¹Si₂H₆ + ¹C₂H₄. The results of SiH (87.2 kcal/mol), SiH₂ (64.9 kcal/mol), HSiSiH₂ (98.0 kcal/mol), and Si₂H₄ (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si₂H₅ and the related bimolecular reverse reactions have been predicted and tabulated for different T, P‐conditions with variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH + SiH₄ product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH₂ + SiH₃, HSiSiH₂ + H₂, and Si₂H₄(C_2h) + H under T, P‐conditions typically used in PECVD and Cat‐CVD. © 2013 Wiley Periodicals, Inc.     

Ab initio chemical kinetics for reactions of H atoms with SiHx (x = 1–3) radicals and related unimolecular decomposition processes

Hydrogen atoms and SiH_x (x = 1–3) radicals coexist during the chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a‐Si:H) thin films for Si‐solar cell fabrication, a technology necessitated recently by the need for energy and material conservation. The kinetics and mechanisms for H‐atom reactions with SiH_x radicals and the thermal decomposition of their intermediates have been investigated by using a high high‐level ab initio molecular‐orbital CCSD (Coupled Cluster with Single and Double)(T)/CBS (complete basis set extrapolation) method. These reactions occurring primarily by association producing excited intermediates, ¹SiH₂, ³SiH₂, SiH₃, and SiH₄, with no intrinsic barriers were computed to have 75.6, 55.0, 68.5, and 90.2 kcal/mol association energies for x = 1–3, respectively, based on the computed heats of formation of these radicals. The excited intermediates can further fragment by H₂ elimination with 62.5, 44.3, 47.5, and 56.7 kcal/mol barriers giving ¹Si, ³Si, SiH, and ¹SiH₂ from the above respective intermediates. The predicted heats of reaction and enthalpies of formation of the radicals at 0 K, including the latter evaluated by the isodesmic reactions, SiH_x + CH₄ = SiH₄ + CH_x, are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and unimolecular reactions have been predicted with tunneling corrections using transition state theory (for direct abstraction) and variational Rice–Ramsperger–Kassel–Marcus theory (for association/decomposition) by solving the master equation covering the P,T‐conditions commonly employed used in industrial CVD processes. The predicted results compare well experimental and/or computational data available in the literature. © 2013 Wiley Periodicals, Inc.     

Bildung siliciumorganischer Verbindungen. 111. Die Hydrierung Si-chlorierter,C-spiroverbrückter 2,4-Disilacyclobutane mit LiAlH4 und iBu2AlH. Der Zugang zum Si8C3H20

Formation of Organosilicon Compounds. 111. The Hydrogenation of Si-chlorinated, C-spiro-linked 2,4-Disilacyclobutanes with LiAlH₄ or iBu₂AlH. The Access to Si₈C₃H₂₀ The hydrogenation of Si-chlorinated, C-spiro-linked 2,4-disilacyclobutanes containing C(SiCl₃)₂ terminal groups with LiAlH₄ in Et₂O proceeds under complete cleavage of the fourmembered rings and under elimination of one SiH₃ group. Such, Si₈C₃Cl₂₀ 4 forms (H₃Si)₂CH? SiH₂? CH(SiH₃)? SiH₂? CH(SiH₃)₂ 4 α, and even Si₈C₃H₂₀ 4a with LiAlH₄ forms 4 α. The hydrogenation of related compounds containing however CH(SiCl₃) terminal groups similarly proceeds under ring cleavage but no SiH₃ groups are eliminated. Such, (Cl₃Si)CH(SiCl₂)₂CH(SiCl₃) 41 forms (H₃Si)₂CH? SiH₂? CH₂(SiH₃) 41 α. However, in reactions with iBu₂AlH in pentane neither the disilacyclobutane rings are cleaved nor are SiH₃ groups eliminated. Only by this method Si₈C₃H₂₀ is accessible from 4 , Si₆C₂H₁₆ 3a from Si₆C₂Cl₁₆ 3 and Si₄C₂H₁₂ 41a from 41 . C(SiCl₃)₄ cleanly produces C(SiH₃)₄. Based on the knowledge about the different properties of LiAlH₄ and iBu₂AlH in hydrogenation reactions of disilacyclo-butanes it was possible to elucidate the composition and the structures of the hydrogenated derivatives of the product mixture from the reaction of MeCl₂Si? CCl₂? SiCl₃ with Si(Cu) [1] and to trace them back to the initially formed Si chlorinated disilacyclobutanes Si₆C₂Cl₁₅Me 34 , Si₆C₂Cl₁₄Me₂ 35 , Si₈C₃Cl₁₉Me 36 and Si₈C₃Cl₁₈Me₂ 37 . Compound 4a forms colourless crystals of space group P1 with a = 799.7(6), b = 1263.6(12), c = 1758.7(14) pm, α = 103.33(7)°, β = 95.28(6)°, γ = 105.57(7)° and Z = 4.     

The structures,thermochemistry, and electron affinities of hydrogenated silicon clusters Si6Hn/Si6H (n = 3–14)

The hydrogenated silicon clusters structures, electron affinities, and dissociation energies of the Si₆H_n/Si₆H (n = 3?14) species have been systematically investigated by means of three density functional theory (DFT) methods. The basis set used in this work is of double‐ζ plus polarization quality with additional diffuse s‐ and p‐type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. Three different types of energy separations presented in this work are the adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert), and the vertical detachment energy (VDE). The first Si? H dissociation energies D_e (Si₆H_n→ Si₆H_n?1+H) for the neutral Si₆H_n and D_e (Si₆H→Si₆H+H) for the anionic Si₆H species have also been reported. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Unexpected Silaazetidine Formation in the Thermolysis of thf‐Supported Silanimine Et2Si=N–SitBu3·thf

The silyl amide Et₂SiCl‐NLi‐SitBu₃ can be cleanly prepared from precursor silylamine Et₂SiCl‐NH‐SitBu₃ and Li[nBu]. The CF₃SO₃SiMe₃ induced LiCl elimination of Et₂SiCl‐NLi‐SitBu₃ in thf afforded a 2‐silaazetidine derivative by [2+2] cycloaddition of Et₂Si=N–SitBu₃ with Et₂Si(OCH=CH₂)–NH–SitBu₃. X‐ray quality crystals of this 2‐silaazetidine derivative (triclinic, space group P$\bar{1}$ ) were grown from benzene at room temperature. The starting material for this approach, Et₂SiCl–NH–SitBu₃, is water‐sensitive. Hydrolysis of Et₂SiCl‐NH‐SitBu₃ gave [tBu₃SiNH₃]Cl along with (Et₂SiO)_n oligomers. The hydro chloride [tBu₃SiNH₃]Cl could be isolated and was characterized by X‐ray crystallography (trigonal, space group P$\bar{3}$ ).     

Auf dem Wege zu einem Disilin –Si≡Si–: Bildung von RHSi=SiHR und Hinweise auf die intermediäre Bildung von RSi≡SiR (R = SiH(SitBu3)2)

Compounds of Silicon. 146. Unsaturated Silicon Compounds. 59. On the Way to a Disilyne –Si≡Si–: Formation of RHSi=SiHR and Indication of the Intermediate Formation of RSi≡SiR (R = SiH(Si t Bu₃)₂) Reaction of R*₂HSi–SiHBr–SiHBr–SiHR*₂ with an equimolar amount of NaR* × 2 THF in THF at –78 °C (R* = supersilyl = SitBu₃) or reaction of R*₂ClSi–SiHBr–SiHBr–SiClR*₂ with a two‐molar amount of NaR* × 2 THF in C₆D₆ at room temperature leads in the first case to the yellow disilene (R*₂HSi)HSi=SiH(SiHR*₂) ( 1 ) and to the red cyclotetrasilene [–R*HSi–R*Si=SiR*–SiHR*–] ( 3 ), respectively, in the latter case to the colorless bicyclotetrasilane R*₄H₂Si₄ ( 4 ). The disilene 1 (for > Si= in ²⁹Si‐NMR: d of d at 141.32 ppm with ¹J_SiH = 149.9 Hz, ²J_SiH = 0.9 Hz) slowly isomerizes at room temperature (τ_1/2 ca. 3 h) under formation of the colorless trisilacyclopentane [–CH₂–SiH(SiH₂SiHR*₂)–SiHR*–SitBu₂–CMe₂–] ( 2 ) and adds methanole under formation of the colorless compound R*₂HSi–SiH₂–SiH(OMe)–SiHR*₂. As initial stage of 3 the disilyne R*₂HSi–Si≡Si–SiHR*₂ is in consideration, which by way of R*HSi=SiR*–SiR*=SiHR* may transform into 3 . The characterization of 2 and 3 results among others from X‐ray structure analyses, whereby for 3 an unexpectable long double bond (2.36 Å) has been found. The identification of 4 results from comparison with an authentic sample (formed from R*HBrSi–SiBr₂R* and NaR* × 2 THF).     

Sterically Tuned P‐Phosphanylamino Phosphaalkenes (Me3Si)2C=PN(R)PPh2 and (iPrMe2Si)2C=PN(R)PPh2

Deprotonation of the aminophosphanes Ph₂PN(H)R 1a – 1h [R = tBu ( 1a ), 1‐adamantyl ( 1b ), iPr ( 1c ), CPh₃ ( 1d ), Ph ( 1e ), 2,4,6‐Me₃C₆H₂ (Mes) ( 1f ), 2,4,6‐tBu₃C₆H₂ (Mes*) ( 1g ), 2,6‐iPr₂C₆H₃ (DIPP) ( 1h )], followed by reactions of the phosphanylamide salts Li[Ph₂PNR] 2a , 2b , 2g , and 2h with the P‐chlorophosphaalkene (Me₃Si)₂C=PCl, and of 2a – 2g with (iPrMe₂Si)₂C=PCl, gave the isolable P‐phosphanylamino phosphaalkenes (Me₃Si)₂C=PN(R)PPh₂ 3a , 3b , 3g , and (iPrMe₂Si)₂C=PN(R)PPh₂ 4a – 4g . ³¹P NMR spectra, supported by X‐ray structure determinations, reveal that in compounds 2a , 2b , 3a , and 3b , with bulky N‐alkyl groups the Si₂C=P–N–P skeleton is non‐planar (orthogonal conformation), whereas 3g , 3h , and 4g with bulky N‐aryl groups exhibit planar conformations of the Si₂C=P–N–P skeleton. Solid 3g and 4g exhibit cisoid orientation of the planar C=P–N–C units (planar I) but in solid 3h the transoid rotamer is present (planar II). From 3g , 4d , and 4g mixtures of rotamers were detected in solution by pairs of ³¹P NMR patterns ( 3h : line broadening).     

Kinetics of Si2H2 produced by the 193 nm photolysis of disilane

Si₂H₂ species were produced through the 193 nm excimer laser photolysis of Si₂H₆. Time‐resolved photoionization mass spectrometry was employed to study the reaction kinetics of Si₂H₂. The lower limit of self‐reaction of Si₂H₂ was estimated, k(Si₂H₂ + Si₂H₂) ≥ (1.7 ± 0.5) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, through analysis of the decay traces. This rate constant was independent of a total pressure on the entire pressure range (p_total = 1–7 Torr). No reaction of Si₂H₂ with H₂, CH₄, SiH₄, and Si₂H₆ was confirmed. The decay rates of Si₂H₂ reacting with O₂, NO, and HCl exhibit negative dependence on the total pressure. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 136–141, 2001     

Gas‐phase reactions of SiHn+ (n = 1,2) with NF3: A computational investigation on the detailed mechanistic aspects

The mechanism of the gas‐phase reactions of SiH_n⁺ (n = 1,2) with NF₃ were investigated by ab initio calculations at the MP2 and CAS‐MCSCF level of theory. In the reaction of SiH⁺, the kinetically relevant intermediates are the two isomeric forms of fluorine‐coordinated intermediate HSi‐F‐NF₂⁺. These species arise from the exoergic attack of SiH⁺ to one of the F atoms of NF₃ and undergo two competitive processes, namely an isomerization and subsequent dissociation into SiF⁺ + HNF₂, and a singlet‐triplet crossing so to form the spin‐forbidden products HSiF⁺ + NF₂. The reaction of SiH₂⁺ with NF₃ involves instead the concomitant formation of the nitrogen‐coordinated complex H₂Si‐NF₃⁺ and of the fluorine‐coordinated complex H₂Si‐F‐NF₂⁺. The latter isomer directly dissociates into NF₂⁺ + H₂SiF, whereas the former species preferably undergoes the passage through a conical intersection point so to form a H₂SiF‐NF₂⁺ isomer, which eventually dissociates into H₂SiF⁺ and NF₂. © 2012 Wiley Periodicals, Inc.     

Ion—molecule reactions in GeH4/SiH4 systems studied by ion trap mass spectrometry

Gas phase ion—molecule reactions occurring in GeH₄/SiH₄ systems under different partial pressures and their mechanisms have been investigated by ion trap mass spectrometry (ITMS). SiH⁺_n (n=0–3) and GeH⁺_n (n = 0–3) are the main ionic species at zero reaction time when the GeH₄: SiH₄ ratio is in the range 1:1 to 1:12. Self-condensation sequences are observed at increasing reaction times. Moreover, formation of ions containing GeSi bonds, such as GeSiH⁺_n (in = 2–5) and GeSi₂H⁺_n (n = 4, 5), occurs by reactions of Si₂H⁺_n (n = 2–5) and Si₃H⁺_n (n = 4, 5) with GeH₄. At longer reaction times, further substitution of silicon with germanium in GeSiH⁺_n (n = 2–5) ions has been observed, to give Ge₂H⁺_n (n = 2–5).     

Infrared Spectrum of the Si3H8+ Cation: Evidence for a Bridged Isomer with an Asymmetric Three‐Center Two‐Electron Si?H?Si Bond

The IR spectrum of Si₃H₈⁺ ions produced in a supersonic plasma molecular beam expansion of SiH₄, He, and Ar is inferred from photodissociation of cold Si₃H₈⁺–Ar complexes. Vibrational analysis of the spectrum is consistent with a Si₃H₈⁺ structure ( 2⁺ ) obtained by a barrierless addition reaction of SiH₄ to the disilene ion (H₂Si?SiH₂⁺) in the silane plasma. In this structure, one of the electronegative H atoms of SiH₄ donates electron density into the partially filled electrophilic π orbital of the disilene cation. The resulting asymmetric Si? H? Si bridge of the 2⁺ isomer with a bond energy of approximately 60 kJ mol^?1 is characteristic for a weak three‐center two‐electron bond, which is identified by its strongly IR active asymmetric Si? H? Si stretching fundamental at about 1765 cm^?1. The observed 2⁺ isomer is calculated to be only a few kJ mol^?1 less stable than the global minimum structure of Si₃H₈⁺ ( 1⁺ ), which is derived from vertical ionization of trisilane. Although more stable, 1⁺ is not detected in the measured IR spectrum of Si₃H₈⁺–Ar, and its lower abundance in the supersonic plasma is rationalized by the production mechanism of Si₃H₈⁺ in the silane plasma, in which a high barrier between 2⁺ and 1⁺ prevents the efficient formation of 1⁺ . The potential energy surface of Si₃H₈⁺ is characterized in some detail by quantum chemical calculations. The structural, vibrational, electronic and energetic properties as well as the chemical bonding mechanism are investigated for a variety of low‐energy Si₃H₈⁺ isomers and their fragments. The weak intermolecular bonds of the Ar ligands in the Si₃H₈⁺–Ar isomers arise from dispersion and induction forces and induce only a minor perturbation of the bare Si₃H₈⁺ ions. Comparison with the potential energy surface of C₃H₈⁺ reveals the differences between the silicon and carbon species.     

Synthese von verbrückend substituierten sekundären Phosphanen sowie deren Reaktionen mit Triisopropylindium

In this work we report the synthesis and characterisation of the 1.5‐diphosphanyldiethylether O{C₂H₄PH(SiiPr₃)}₂ ( 2 ) in which two silyl‐substituted phosphine groups are linked by an ether bridge as well as the compound O(SiiPr₂PHEt)₂ ( 3 ) where two ethyl substitute phosphine groups are connected by a siloxane bridge. In addition, we describe the metalation of 2 and 3 with triisopropylindium. These reactions lead to the compounds [O{C₂H₄P(SiiPr₃)IniPr₂}₂] ( 4 ) and [O{SiiPr₂P(Et)IniPr₂}₂] ( 5 ) with In₂P₂ ring structures.     

Theoretical Investigation on the Reactions of H with (CH3)4‐nSiHn (n = 1–4)

The abstractions of H with (CH₃)_4‐nSiH_n (n = 1–4) have been investigated at high levels of ab initio molecule orbital theory. Geometries have been optimized at the MP‐2 level with 6–31G(d) basis set, and G2MP2 level has been used for the final energy calculations. Theoretical analysis provided conclusive evidence that the main process occurring in each case is the abstraction of H from the Si? H bond leading to the formation of the H₂ and silyl radicals; the abstraction of H from C? H bond has higher barrier and is difficult to react in each case. The kinetics of the title reactions have been calculated with variational transition state theory over the temperature range 200–1000 K, and the theoretical rate constants match well with the experimental values.     

Transition‐Metal‐Mediated Cleavage of a SiSi Double Bond

Reaction of carbene‐stabilized disilicon ( 1 ) with Fe(CO)₅ gives the 1:1 adduct L:Si?Si[Fe(CO)₄]:L (L:=C{N(2,6‐Prⁱ₂C₆H₃)CH}₂) ( 2 ) at room temperature. At raised temperature, however, 2 may react with another equivalent of Fe(CO)₅ to give L:Si[μ‐Fe₂(CO)₆](μ‐CO)Si:L ( 3 ) through insertion of both CO and Fe₂(CO)₆ into the Si₂ core, which represents the first experimental realization of transition metal‐carbonyl‐mediated cleavage of a Si?Si double bond. The structures and bonding of both 2 and 3 have been investigated by spectroscopic, crystallographic, and computational methods.     

ThSi2 Type Ytterbium Disilicide and its Analogues YbTxSi2–x (T = Cr,Fe, Co)

YbSi₂ and the derivatives YbT_xSi_2–x (T = Cr, Fe, Co) crystallizing in the α‐ThSi₂ structure type were obtained as single crystals from reactions run in liquid indium. All silicides were investigated by single‐crystal X‐ray diffraction, I4₁/amd space group and the lattice constants are: a = 3.9868(6) Å and c = 13.541(3) Å for YbSi₂, a = 4.0123(6) Å and c = 13.542(3) Å for YbCr_0.27Si_1.73, a = 4.0142(6) Å and c = 13.830(3) Å for YbCr_0.71Si_1.29, a = 4.0080(6) Å and c = 13.751(3) Å for YbFe_0.34Si_1.66, and a = 4.0036(6) Å, c = 13.707(3) Å for YbCo_0.21Si_1.79. YbSi₂ and YbT_xSi_2–x compounds are polar intermetallics with three‐dimensional Si and M (T+Si) polyanion sub‐networks, respectively, filled with ytterbium atoms. The degree of substitution of transition metal at the silicon site is signficant and leads to changes in the average bond lengths and bond angles substantially.     

The mechanism of plasma-induced deposition of amorphous silicon from silane

Time-resolved mass spectrometric data show that the concentration of di- and trisilane, which are formed from monosilane under discharge conditions typical for the deposition of high electronic quality amorphous silicon, correlate with the measured deposition rate of a-Si. The data can be quantitatively and self-consistently described by a simple set of consecutive reactions:

1. SiH₄ →-SiH₂ + H₂
2. SiH₂ + SiH₄ → Si₂H₆
3. SiH₂ + Si₂H₆ → Si₃H₈
4. Si _n H_{2(n + 1)} →n ·a-Si:H+(n+1)H₂,n=2,3

The only fitting parameter necessary for an excellent fit of the measured data over a wide range of experimental parameters is the value of the reactive sticking coefficient .for the decomposition of di- and trisilane (reaction 3). The resultant value agrees well with the published data of other authors and with those calculated from the measured deposition rate and Si₂H₆, concentration. We did not find and physically meaningful way to lit the measured data with the various “SiH₃ models” proposed by other authors who assumed that the dominant species responsiblefor the deposition of a-Si: H is the SiH₃, radical. For this and some additional reasons mentioned in the present paper. the SiH₃ model is in disagreement with available experimental data.     

Reduction of Disilane (tBu3Si)Br2Si‐SiBr2(SitBu3) in Presence of C2H4: A Mechanistic Approach

The reduction of R*–SiBr₂–SiBr₂–R* ( 2 ) with NaR* (R* = supersilyl = SitBu₃) in presence of C₂H₄ provides a white crystalline solid (η²‐C₂H₄)R*Si–SiR*(Br)(CH₂–CH₂–R*) ( 3 ) characterized by X‐ray diffraction analysis. Compound 3 is accompanied with an impurity of R*(Br)₂Si–Si(Br)(R*)(CH₂–CH₂–R*) ( 4 ). The formation of 3 and 4 runs complicated because of several reactive partners. However, reduction of 2 with sodium naphthalenide in presence of ethene runs straightforward with formation of a mixture of tetrahedrane R*₄Si₄ ( 1 ) and bis(silirane) R*(η²‐C₂H₄)Si–Si(η²‐C₂H₄)R* ( 5 ). The latter is formed by [1+2]‐cycloaddition reaction of intermediate disilyne R*Si≡SiR* with ethene. Compound 5 has been characterized by X‐ray structure determination. The ¹H NMR spectrum of the silacyclopropane ring protons shows AA′BB′ complex spectrum comprising of 2 sets each of 12 transitions.     

The Sialons MLn[Si4−xAlxOxN7−x] with M = Eu,Sr, Ba and Ln = Ho‐Yb – Twelve Substitution Variants with the MYb[Si4N7] Structure Type

The oxonitridoalumosilicates (so‐called sialons) MLn[Si_4?xAl_xO_xN_7?x] with M = Eu, Sr, Ba and Ln =Ho, Er, Tm, Yb were obtained by the reaction of the respective lanthanoid metal, the alkaline earth carbonates or europium carbonate, resp., AlN, “Si(NH)₂” and MCl₂ as a flux in a radiofrequency furnace at temperatures around 2100 °C. The compounds MLn[Si_4?xAl_xO_xN_7?x] are relevant for the investigation of substitutional effects on the materials properties due to their ability of tolerating a comparatively large phase width up to x ≈ 2.0(5). The crystal structures of the twelve compounds were refined from X‐ray single crystal data and X‐ray powder data and are found to be isotypic to the MYb[Si₄N₇] structure type. The compounds crystallize in space group P6₃mc (no. 186, hexagonal) and are made up of chains of so‐called starlike units [N^[4](SiN₃)₄] or [N^[4]((Si,Al)(O,N)₃)₄], respectively. These units are formed by four (Si,Al)(N/O)₄ tetrahedra sharing a common central nitrogen atom. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on the four‐fold bridging site and nitrogen and oxygen were distributed equally on both of the two‐fold bridging sites, resulting in charge neutrality of the compound. The Si and Al atoms were distributed equally on their two crystallographic sites, referring to their elemental proportion in the compound, due to being poorly distinguishable by X‐ray methods. The chemical compositions of the compounds were derived from electron probe micro analyses (EPMA).     

Cyano-bridged Ln^3＋-Cr^3＋ Binuclear Complexes [Ln（L）x（H2O）y^- Cr（CN）6]·mL·nH2O （Ln=La-Nd,x=5, y=2, m=1 or 2, n=2 or 2.5; Ln-Sm-Dy,Er, x=4, y=3, m=0, n=1.5 or 2.0; L= 2-pyrrolidinone）： Structure,Magnetism and Spin Density Map

In order to shed light upon the nature and mechanism of 4f-3d magnetic exchange interactions, a series of binuclear complexes of lanthanide（3＋） and chromium（3＋） with the general formula [Ln（L）5（H2O）2Cr（CN）6]·mL· nH2O （Ln=La （1）, Ce （2）, Pr （3）, Nd （4）; x=5, y=2, m=1 or 2, n=2 or 2.5; L=2-pyrrolidinone） and [Ln（L）4（H2O）3Cr（CN）6] ·nH2O （Ln=Sm （5）, Eu （6）, Gd （7）, Tb （8）, Dy （9）, Er （10）; x=4, y=3, m=0, n= 1.5 or 2.0; L=2-pyrrolidinone） were prepared and the X-ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln-CN-Cr unit, in which Ln^3＋ in a square antiprism environment is bridged to an octahedral coordinated Cr^3＋ ion through a cyano group. The magnetic properties of the complexes 3 and 6-10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g= 1.98, J=0.40 cm^-1, zJ＇= -0.21 cm^-1 on the basis of a binuclear spin system （Scd=7/2, Scr=3/2）, revealing an intra-molecular Gd^3＋-Cr^3＋ ferromagnetic interaction and an inter-molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory （DFT）, combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm^-1, supporting the observation of weak ferromagnetic intra-molecular interaction in 7. The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd^3＋ and Cr^3＋ was discussed.     

Computational investigation of the adsorption and reactions of SiHx (x = 0–4) on TiO2 anatase (101) and rutile (110) surfaces

The adsorption and reactions of the SiH_x (x = 0–4) on Titanium dioxide (TiO₂) anatase (101) and rutile (110) surfaces have been studied by using periodic density functional theory in conjunction with the projected augmented wave approach. It is found that SiH_x (x = 0–4) can form the monodentate, bidentate, or tridentate adsorbates, depending on the value of x. H coadsorption is found to reduce the stability of SiH_x adsorption. Hydrogen migration on the TiO₂ surfaces is also discussed for elucidation of the SiH_x decomposition mechanism. Comparing adsorption energies, energy barriers, and potential energy profiles on the two TiO₂ surfaces, the SiH_x decomposition can occur more readily on the rutile (110) surface than on the anatase (101) surface. The results may be used for kinetic simulation of Si thin‐film deposition and quantum dot preparation on titania by chemical vapor deposition (CVD), plasma enhanced CVD, or catalytically enhanced CVD. © 2013 Wiley Periodicals, Inc.