The thermal decomposition reactions of [Co(en)n(phen)m]Cl3 complexes

The thermal behaviour of [Co(en)_n(phen)_m]Cl₃ complexes has been studied using thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA) in air, nitrogen and oxygen atmospheres. The effect of the stoichiometry of the complexes and that of the gas atmosphere in the furnace chamber on the thermal decomposition reaction is evidenced and discussed. The following thermal stability order has been found [Co(en)₃]Cl₃ [Co(en)₂(phen)]Cl₃ > [Co(en)(phen)₂]Cl₃ [Co(phen)₃]Cl₃     

Ca0.8-2x(YbxTb0.1Na0.1+x)2xWO4近红外下转换荧光粉水热合成及发光性质

一种在近红外光谱(NIR)区域高效的量子剪裁现象已在Ca_0.8-2x(Yb_xTb_0.1Na_0.1+x)_2xWO₄(x=0~0.2)荧光粉中得到证实,该量子剪裁通过吸收紫外线光子发射近红外光子,能量传递包括两个协同过程,分别是WO₄^2-基团到Yb³⁺离子和WO₄^2-基团到Tb³⁺离子再到Yb³⁺离子,Yb³⁺离子的掺杂浓度对荧光粉在可见光和近红外光谱的发光,荧光寿命和量子效率的影响已进行了详细得研究。经计算,量子效率最大达到135.7%。铽与镱共掺钨酸钙的近红外量子剪裁,通过吸收太阳光谱的1个紫外光到2个1000nm光子(2倍光子数增加)的下转化机制实现高效率硅太阳能电池的途径。     

Global minima of (C60)nCa, (C60)nF and (C60)nI clusters

Likely candidates for the lowest potential energy minima of (C₆₀)_nCa²⁺, (C₆₀)_nF⁻ and (C₆₀)_nI⁻ clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C₆₀ intermolecular interaction, an averaged Lennard–Jones C₆₀–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C₆₀ multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C₆₀)_n cluster, the coordination shell being tetrahedral for Ca²⁺ and F⁻. The I⁻ ion has an octahedral coordination shell in the global minimum for (C₆₀)₆I⁻, however for 12  n  8 the preferred coordination geometry is trigonal prismatic.     

The metastable Ni7±xS6, and mixed Ni6±x(S1−ySey)5, phases

The closely related, narrowly non-stoichiometric, metastable as well as thermodynamically stable “phases” in the metal-rich part of the Ni–S phase diagram near the nominal composition Ni_7±xS₆ have been carefully re-investigated via electron diffraction and transmission electron microscope imaging. Two quite distinct polymorphs have been identified, a minority incommensurate interface-modulated polymorph and a (heavily twinned) majority I1a1, a=2a_p, b=2b_p, c=−a_p+c_p superstructure (of an underlying Bmmb, a_p3.3, b_p16.4, c_p11.3 Å parent structure) polymorph. The incommensurate polymorph is shown to be very closely related to the only known polymorph of Ni_6±xSe₅ and is rapidly stabilized to room temperature upon doping of the sulfide compounds with selenium.     

Ca0.8-2x(YbxTb0.1Na0.1+x)2xWO4近红外下转换荧光粉水热合成及发光性质

一种在近红外光谱(NIR)区域高效的量子剪裁现象已在Ca0.8-2x(Ybx Tb0.1Na0.1+x)2x WO4(x=0～0.2)荧光粉中得到证实,该量子剪裁通过吸收紫外线光子发射近红外光子,能量传递包括两个协同过程,分别是WO42-基团到Yb3+离子和WO42-基团到Tb3+离子再到Yb3+离子,Yb3+离子的掺杂浓度对荧光粉在可见光和近红外光谱的发光,荧光寿命和量子效率的影响已进行了详细的研究。经计算,量子效率最大达到135.7%。铽与镱共掺钨酸钙的近红外量子剪裁,通过吸收太阳光谱的1个紫外光子到2个1 000 nm光子(2倍光子数增加)的下转化机制实现高效率硅太阳能电池的途径。     

One-dimensional structures of zinc(II) and cobalt(II) coordination complexes [Zn(NCS)2(PPz)]n and [CoCl2(PPz)]n (PPz=piperazine)

The reaction of Zn(NO₃)₂·6H₂O with PPz hexahydrate (PPz=piperazine) and NH₄SCN in CH₃OH afforded the complex [Zn(NCS)₂(PPz)]_n (1). The reaction of CoCl₂·6H₂O with PPz in CH₃OH afforded the complex [CoCl₂(PPz)]_n (2). The PPz ligand in 1 is coordinated to the metal centers through both nitrogen atoms to form a 1-D zigzag-chain structure and the distorted tetrahedral coordination geometry at each zinc center is completed by a pair of N-bonded thiocyanate ligands. Compound 2 has an analogous 1-D zigzag-chain structure containing terminal chloro ligands. Important NCSH---N hydrogen-bonding interactions in compound 1 and N---HCl---M and C---HCl---M hydrogen-bonding interactions in compound 2 play a significant role in aligning the polymer strands in the crystalline solid.     

Evidence for Pdx(CO)y compound formation on an alumina substrate

Although stable binary Pd carbonyls are unknown in the gas phase, we found strong evidence for a stable carbonyl-like Pd compound on an oxide surface: by in situ vapour deposition of Pd at a rate of 2 × 10¹³ atoms s⁻¹ cm⁻² onto an alumina substrate (90 K) at a pressure of 2 × 10⁻⁶ mbar CO, a binary compound of Pd and CO is formed which is stable up to 190 K. As substrate serves a well-ordered aluminium oxide film grown on a NiAl(110) single crystal surface. The system was characterized under UHV (ultrahigh vacuum) conditions by means of TDS, LEED, UPS and XPS in a coverage range between 1.4 × 10¹⁴ Pd atoms cm⁻² and 1.4 × 10¹⁶ Pd atoms cm⁻². The decomposition at 190 K results in the formation of metallic Pd particles and is accompanied by a sharp and dominant feature in the thermal desorption spectra.     

Structural and magnetic properties of the solid solution () YMn1−x(Cu3/4Mo1/4)xO3

Recently, the ferroelectromagnet YMnO₃ has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn_1−xM_xO₃ solid solutions in which substitution of the foreign M cation preserves the hexagonal P6₃cm structure. In contrast there exist several homeotypic phases with the general formula, Ln_1+nCu_nMO_3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn_1−x(Cu_3/4Mo_1/4)_xO₃ compounds have been synthesized. The solid solution, from YMnO₃ (x=0) to YCu_3/4Mo_1/4O₃ (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P6₃cm, of YMnO₃. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu³⁺/Mo⁶⁺ cationic ordering. Dilution of the Mn³⁺ magnetic array by the paramagnetic (Cu²⁺) and diamagnetic (Mo⁶⁺) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions.     

Ammonia deposition in fullerene: (NH3)n@C60

Deposition of ammonia molecules in fullerene has been investigated theoretically by performing semi-empirical molecular orbital calculation at PM3 level within RHF formalism. C₆₀ cluster has been doped endohedrally by ammonia molecules. Structural and electronic properties of the systems considered have been studied. It has been found that C₆₀ cluster can store at most six ammonia molecules. The ammoniacal endofullerenes, (NH₃)_n@C₆₀, have been found stable but endothermic.     

Interconverting WW Triple Bonds and W4 Clusters: Structures of W4(OPrn)16 and [Li2W2(OPrn)8(DME)]2*

Alcoholysis of W₂(NMe₂)₆ with excess n-propanol in hexane yields the tetranuclear cluster, W₄(OPrⁿ, I. Reduction of I with two equivalents of Li₂COT in THF gives a small yield of Li₂W₂(OPrⁿ)₈. Single crystals were isolated by cooling the product mixture in DME and were shown to be [Li₂W₂(OPrⁿ)₈(DME)]₂, II, which consists of a unique “dimer of dimers” structure. In this reaction sequence, W₄¹⁶⁺ cluster formation is followed by four electron reduction to reform the (W≡W)⁶⁺ unit. Better yields of the lithium salt can be obtained by the addition of LiOPrⁿ/HOPrⁿ solutions to W₂(OBu^t)₆ in which case Li₂W₂(OPrⁿ)₈ has been obtained as a 1:1 adduct with LiOPr. This identity of this salt was confirmed by solution NMR spectroscopy. In the alternative reaction, the (W≡W)⁶⁺ center remains intact from reactant to product. No attempt has been made to separate the product from excess LiOPr. DFT (ADF 2004.01) molecular orbital calculations on the model cluster W₄(OH)₁₆ are used to help elucidate the disruption of the W₄ cluster upon four electron reduction. The molecular structures of compounds I and II are reported.*Dedicated to Professor F. A Cotton on the occasion of his 75th birthday.     

Au10(TBBT)10: the Begining and the End of Aun(TBBT)m Nanoclusters

Gold(I) thiolate compounds (i.e. Au^I-SR) are important precursors for the synthesis of atomically precise Au_n(SR)_m nanoclusters. However, the nature of the Au^I-SR precursor remains elusive. Here, we report that the Au₁₀(TBBT)₁₀ complex is a universal precursor for the synthesis of Au_n(TBBT)_m nanoclusters (where TBBT=4-tertbutylbenzenethiol/thiolate). Interestingly, the Au₁₀(TBBT)₁₀ complex is also found to be re-generated through extended etching of the Au_n(SR)_m nanoclusters with excess of TBBT thiol and O₂. The formation of well-defined Au₁₀(TBBT)₁₀ complex, instead of polymeric Au^I-SR, is attributed to the bulkiness of the TBBT thiol. Through 1D and 2D NMR characterization, the structure of Au₁₀(TBBT)₁₀ is correlated with the previously reported X-ray structure, which contains two inter-penetrated Au₅(TBBT)₅ rings. The photophysical property of Au₁₀(TBBT)₁₀ complex is further probed by femtosecond transient absorption spectroscopy. The accessibility of the precise Au₁₀(TBBT)₁₀ precursor improves the efficiency of the synthesis of the Au_n(TBBT)_m nanoclusters and is expected to further facilitate excellent control and understanding of the reaction mechanisms of nanocluster synthesis.     

Luminescent properties of the potassium zinc phosphates of composition K1−xTlxZn(PO3)3

Crystalline and glassy K_1−xTl_xZn(PO₃)₃ polyphosphates have been synthesized and characterized. UV–visible spectroscopy was systematically used in order to analyze the optical properties of Tl⁺ ions both in crystalline and glassy forms with the similar compositions. The investigated polyphosphates can be considered as a model system since the spectroscopic properties of Tl⁺ ions in the glasses could be deduced by comparison with those in crystals. From structural point of view, in the crystalline forms the thallium ions are six-fold coordinated in a dissymmetrical oxygenated sites. Three luminescences (α, A_X, A_T) have been then observed and were attributed to the isolated Tl⁺ ions. In the glassy forms, an additional luminescence (D) has been detected in the low-energy range and was assigned to the Tl⁺ pairs formation. The relationship between the Tl⁺ site symmetry and its optical properties is discussed in the context of the Fukuda's model.     

Experimental evidence of structural transition from fcc to bulk bcc in nanophase metal clusters of (Fe)n, (Cr)n, (Mo)n and (W)n produced by CO2 laser multiphoton decomposition of metal carbonyls

We have produced nanophase metal clusters, (Fe)_n, (Cr)_n, (Mo)_n and (W)_n, by multiphoton decomposition of the corresponding metal carbonyls with a 10.6 μm CO₂ laser in the presence of Ar and SF₆. The size distribution was narrow and the average diameter was 6, 3.5, 2 and 1 nm for Fe, Cr, Mo and W clusters, respectively. The structure was found to be bcc for both Fe and Cr clusters, fcc for Mo clusters, and amorphous for W clusters (note that all the bulk metals have bcc structure). Considering the cluster sizes (9630, 1870, 230 and 30 for Fe, Cr, Mo and W clusters, respectively) estimated from their average diameters, it is likely that there exists a structural transition from fcc to bulk bcc with increasing cluster size in these metal clusters.     

过渡金属铁配合物Fe(CO)_(5-x)(PR_3)_x的结构与性质的理论研究

采用密度泛函理论(DFT)对一系列低价铁化合物Fe(CO)_(5-x)(PR_3)_x(x=1~3,R=H,F,Me)的几何结构、电子结构、成键特点以及热力学性质进行了理论研究。结果表明引入膦配体后不会造成Fe(CO)x(PR_3)_(5-x)的几何结构畸变,为略扭曲的三角双锥形。自然键轨道(NBO)分析显示,膦配体与羰基铁基团间存在电荷转移,有效增强Fe-CO之间的共价作用。多数稳定结构Fe(CO)x(PR_3)_(5-x)的第一膦配体解离能要比第一羰基解离能低,预示Fe(CO)_(5-x)(PR_3)_x的反应活性比Fe(CO)5有明显提高。     

过渡金属铁配合物Fe(CO)5-x(PR3)x的结构与性质的理论研究

采用密度泛函理论（DFT）对一系列低价铁化合物Fe（CO）_5-x（PR₃）_x（x=1~3,R=H,F,Me）的几何结构、电子结构、成键特点以及热力学性质进行了理论研究。结果表明引入膦配体后不会造成Fe（CO）_x（PR₃）_5-x的几何结构畸变,为略扭曲的三角双锥形。自然键轨道（NBO）分析显示,膦配体与羰基铁基团间存在电荷转移,有效增强Fe-CO之间的共价作用。多数稳定结构Fe（CO）_x（PR₃）_5-x的第一膦配体解离能要比第一羰基解离能低,预示Fe（CO）_5-x（PR₃）_x的反应活性比Fe（CO）₅有明显提高。     

Negative hyperconjugation in methyl and silyl anions and its effect on the acidities of CH(4-n)Fn CH(4-n)C1n SiH(4-n)Fn and SiH(4-n)Cln

Group separation reactions calculated using an ab intio molecular orbital calculation at the MP4/6-31 + + G(d,p) level of theory, show the negative hyperconjugation between fluorine atoms to be larger in methanes than in silanes. Stabilisation due to negative hyperconjugation is larger in anions than in identically substituted neutral molecules, e.g. 43.1 kcal mol⁻¹ in CF₃⁻ compared with 26.7 kcal mol⁻¹ in CHF₃. By contrast, in chloro-substituted methanes, silanes, methyl anions and silyl anions, group separation energies are approximately zero, indicating no appreciable negative hyperconjugation. An -chloro substituent is more effective than an -fluoro one at delocalising the negative charge of an anion and, as a consequence, the chloromethanes and chlorosilanes are all more acidic than the identically substitued fluoromethanes and fluorosilanes. For chloro-substituted molecules the acidity is linearly dependent on the number of chlorine atoms; for fluoro-substituted molecules stabilisation by negative hyperconjugation results in each additional fluorine atom increasing the acidity by larger increments.     

Excess properties of the (Ln2−2xCaxThx)(PO4)2 (Ln = La, Ce) solid solutions

X-ray powder diffraction at room temperature and drop calorimetry at T = 1005 K were performed on LnPO₄–CaTh(PO₄)₂ (Ln = La, Ce) solid solutions. The results show excess molar volume and excess enthalpy indicating deviations from ideal behaviour that have been interpreted in terms of lattice strains resulting from the ion size effects of substitution of the Ln³⁺ with (Ca²⁺ + Th⁴⁺).     

(SrTiO_3)_(1-x)(SrTaO_2N)_x固溶体的制备及光催化性能研究(英文)

通过高温固相反应合成了N掺杂的SrTiO3和(SrTiO3)1-x(SrTaO2N)x固溶体,对其进行了X射线衍射,紫外可见吸收光谱,X射线光电子能谱分析和比表面积的表征。随x由0增大至0.4,固溶体带隙变窄,由3.2eV降至2.3eV,吸收光谱由紫外光区扩展到可见光区。在甲醇溶液(50mLCH3OH+220mLH2O)中进行了光催化分解水产生氢气的反应,在硝酸银溶液(270mL,0.01mol·L-1)中进行了光催化分解水产生氧气的反应,在可见光(λ420nm)照射下,实现了可见光响应的光催化分解水。     

Thermal decomposition of polymeric aminoborane (H2BNH2)x under hydrogen release

Polymeric aminoborane (H₂BNH₂)_x has been isolated during the thermal decomposition of solid borazane H₃BNH₃ at temperatures below 370 K. Polymeric aminoborane is a white noncrystalline solid, stable at room temperature and up to 380 K. In the temperature range of 380–500 K polymeric aminoborane undergoes a thermal decomposition, which was studied by differential scanning calorimetry (DSC), by thermogravimetry (TG) and by volumetric measurements. The solid residue was characterized by IR spectroscopy, by powder X-ray diffraction (XRD) analysis and by solid state ¹¹B NMR spectroscopy.

The thermal decomposition of polymeric aminoborane (H₂BNH₂)_x is an exothermic process accompanied by evolution of nearly 1 mol hydrogen per mole H₂BNH₂ unit corresponding to the volumetric measurements. The detected mass loss of the solid phase indicates the formation of further gaseous products beside hydrogen. The final mass loss increases with rising heating rate, in contrast to the final amount of evolved hydrogen, which still remains constant.     

Diffraction and DAFS Studies of a Ba4(BaxPt1−x)Pt2O9Twinned Crystal, a Member of the Bap(BaxPt1−x)Ptp−2O3p−3Series

Crystallographic studies of the Ba–Pt–O system have been undertaken using X-ray and electron diffraction techniques. The system is described by means of a Ba_p(Ba_xPt²⁺_1−x)Pt⁴⁺_p−2O_3p−3formula which corresponds to a BaO₃hexagonal based framework with Pt chains, whereprepresents the oxygen deficiency and the presence of both Pt⁴⁺and Pt²⁺cations in the compounds, andxa possible substitution of Pt²⁺by Ba²⁺in trigonal prismatic sites. The structure of a Ba₄(Ba_0.04Pt²⁺_0.96)Pt⁴⁺₂O₉crystal has been solved by using 5548 X-ray difraction reflections collected on a twinned crystal. Refinements were performed with two distinct models: an “average”P321 space group and an “orthorhombic”C2 space group with cell parametersa=17.460(4) Å,b=10.085(2) Å,c=8.614(3) Å. In this structure, two Pt⁴⁺and one Pt²⁺cations are distributed over four Ba planes and form chains along thecaxis, consisting of two face-sharing Pt⁴⁺O₆octahedra connected with one Pt²⁺O₆trigonal prism. A lattice misfit occurs between the rigid barium lattice and the PtO₃chains, giving rise to a composite structure. Twinning and domain configurations are described and taken into account in the refinement. This twinning is related to the presence of Pt²⁺cations, whose positions break the threefold axis symmetry. A diffraction anomalous fine structure (DAFS) study was also performed on this twinned single crystal. Anomalous scattering factorsf′ andf″ for platinum in this crystal were refined near the L_IIIPt absorption edge. They confirm the weak barium occupancy of the trigonal prismataic site and the Pt⁴⁺valence of the octahedral sites. Reflection overlaps, due to twinning, flatten the DAFS sensitivity to Pt atoms in the prismatic sites and did not allow their clear valence determination, but Pt–O bond lengths agree with the presence of Pt²⁺cations at the center of prismatic faces. Electron diffraction patterns of powders having slightly different composition show a continuous evolution of incommensurate Bragg peaks and a weak correlation between the PtO₃chains. They also confirm the composite nature and the one-dimensionality of the Ba_p(Ba_xPt²⁺_1−x)Pt⁴⁺_p−2O_3p−3series, which can produce highly anisotropic physical properties.