V2O2F4(H2O)2·H2O: a new V4+ layer structure related to VOF3

V^IV oxyfluorides are of interest as frustrated magnets. The successful synthesis of two‐dimensionally connected vanadium(IV) oxyfluoride structures generally requires the use of ionic liquids as solvents. During solvothermal synthesis experiments aimed at producing two‐ and three‐dimensional vanadium(IV) selenites with triangular lattices, the title compound, diaquatetra‐μ‐fluorido‐dioxidodivanadium(IV) monohydrate, V₂O₂F₄(H₂O)₂·H₂O, was discovered and features a new infinite V⁴⁺‐containing two‐dimensional layer comprised of fluorine‐bridged corner‐ and edge‐sharing VOF₄(H₂O) octahedral building units. The synthesis was carried out under solvothermal conditions. The V⁴⁺ centre exhibits a typical off‐centring, with a short V=O bond and an elongated trans‐V—F bond. Hydrogen‐bonded water molecules occur between the layers. The structure is related to previously reported vanadium oxyfluoride structures, in particular, the same layer topology is seen in VOF₃.     

Quantum chemical calculation of exchange interactions in supramolecularly arranged N,N′‐dioxy‐2,6‐diazaadamantane organic biradical

Quantum mechanical exchange effects in purely organic N,N′‐dioxy‐2,6‐diazaadamantane biradical derivatives with promesogenic substituents have been studied. To determine intermolecular exchange energies, packing conditions of the radical core units in layered liquid crystalline phases are simulated using the Gaussian 09 program. The broken symmetry approach gives J ≈ 7 cm^?1 for intramolecular ferromagnetic exchange interactions between nitroxyl radical centers in one molecule. Both ferromagnetic and antiferromagnetic intermolecular interactions are possible in this kind of systems according to the obtained calculation results. Depending on the mutual positioning and orientation of molecules, the intermolecular antiferromagnetic exchange constant can reach a value of ?50 cm^?1, and the intermolecular ferromagnetic constant a value of 10 cm^?1. The simultaneous presence of intramolecular and intermolecular exchange between spin‐carrying centers in this kind of supramolecularly ordered multispin systems is favorable for the formation of magnetically interacting chains and two‐dimensional networks. © 2016 Wiley Periodicals, Inc.     

An Experimental and Theoretical Investigation on Pentacoordinated Cobalt(III) Complexes with an Intermediate S=1 Spin State: How Halide Ligands Affect their Magnetic Anisotropy

Understanding the factors that control the magnitude and symmetry of magnetic anisotropy should facilitate the rational design of mononuclear metal complexes in the quest for single‐molecule magnets (SMMs), based on a single metal ion, with high blocking temperatures and large energy barriers. The best strategy is to define magnetostructural correlations through the investigation of a series of metal complexes. It has been demonstrated that the main contribution to the magnetic anisotropy arises from the spin‐orbit coupling (SOC) effect in metal‐ion‐based systems, so current studies focus particularly on the use of both ligands and metal ions possessing a large SOC. In this context, we report a unique series of halide Co^III complexes, [CoL(X)], with X=Cl, Br, I ( CoX ) and L=2,2′‐(2,2′‐bipyridine‐6,6′‐diyl)bis(1,1‐diphenylethanethiolate), which possess a rare intermediate S=1 spin ground state. The S=1 Co^III complexes are attractive species because they possess a remarkably large axial zero‐field splitting (defined by D from the following Hamiltonian: H =DS_z²), as well as the halide ligands inducing large SOC constants. The single‐crystal X‐ray structures reveal that the CoBr and CoI complexes are isostructural with the previously described CoCl complex. Their coordination sphere displays a distorted pentacoordinated square pyramidal geometry, with the halide located in the Co^III axial position. Large positive D values of 35, 26, and 18 cm^?1 are found for CoCl , CoBr , and CoI , respectively, through analysis of the magnetic susceptibility data as a function of temperature. To rationalize this trend, theoretical calculations based on both density functional theory (DFT) and complete active space self‐consistent field (CASSCF) methods are performed successfully. Both the sign and magnitude of D are predicted remarkably well by these theoretical approaches. The DFT calculations also show that the resulting D values originate from a balance of several contributions, and that many factors, including differences in their structural properties and in the contribution of the halide, should be taken into account to explain the trend of D in this series of complexes.     

Self-assembly and photoelectric properties of cerium complexes with 3,4,9,10-perylenetetracarboxylic acid on nanocrystalline TiO_2 films

Self-assembled (SA) films (PMP, M = Ce3+ or Ce4+) of 3,4,9,10-perylenetetracarboxylic acid (PTA) on nanocrystalline TiO2 films with Ce3+ or Ce4+ as a bridge were fabricated and characterized with UV-Vis, IR, and XPS synchrotron radiation photoelectron spectroscopy (SRPES) which gave the HOMO energy levels for the SA films. It was shown that thin-layer sandwich-type solar cells based on these SA films possess good properties for photoelectric conversion. While PTA-loaded TiO2 electrode (P) generated 26.9% of incident monochromatic photon-to-electron conversion efficiency (IPCE), PMP-sensitized Ti02 electrodes yielded 55.8% and 39.1% for Ce4+ and Ce3+ respectively. PMP films can be considered as a kind of complexes whose HOMO energy levels were proved to be higher than that of film P, which is one of the major reasons for the increase in IPCE from film P to film PMP.     

Synchrotron radiation studies of mass-selected Fe nanoclusters deposited in situ

A portable UHV-compatible gas aggregation cluster source, capable of depositing clean mass-selected nanoclusters in situ, has been used at synchrotron radiation facilities to study the magnetic behaviour of exposed and Co-coated Fe clusters in the size range 250 to 540 atoms. X-ray magnetic circular dichroism (XMCD) studies of isolated and exposed 250-atom clusters show a 10% enhancement in the spin magnetic moment and a 75% enhancement in the orbital magnetic moment relative to bulk Fe. The spin moment monotonically approaches the bulk value with increasing cluster size but the orbital moment does not measurably decay till the cluster size is above ∼ 400 atoms. The total magnetic moments for the supported particles though higher than the bulk value are less than those measured in free clusters. Coating the deposited particles with Co in situ increases the spin moment by a further 10% producing a total moment per atom close to the free cluster value. At low coverages the deposited clusters are super-paramagnetic at temperatures above 10 K but a magnetic remanence at higher temperature emerges as the cluster density increases and for cluster films with a thickness greater than 50 ?(i.e. 2-3 layers of clusters) the remanence becomes greater than that of an Fe film of the same thickness produced by a conventional deposition source. Thick cluster-assembled film show a strong in-plane anisotropy. Received 14 December 2000     

Ground-state geometries and stability of NaMg clusters using ab initio molecular dynamics method

The ground-state geometries, energetics and the stability of ( n =1-12) clusters are studied using ab initio molecular dynamics method. Our results indicate that the ground-state geometries of large clusters () are different from those of clusters where a trivalent impurity Al is added to the same monovalent host Na. Other features observed are an early appearance of 3-dimensional structure and a pentagonal growth path from n =6 up to n =11. As expected, the ground-state geometry of is not an icosahedron but can be viewed as a distorted form of one of the low lying geometries of cluster. In the energetically favored structures impurity atom Mg is never located at the center of the cluster. The stability analysis based on the energetics shows (8 valence electrons) to be the most stable. In addition there is a remarkable even-odd pattern observed in the dissociation energy and the second difference in energy which is absent in earlier studies of and clusters. Received: 16 September 1998 / Received in final form: 15 February 1999     

Imaging and tunneling spectroscopy of gold nanocrystals and nanocrystal arrays

Scanning tunneling microscopy (STM) and spectroscopy (STS) have been used to determine the structural and electronic properties of thiol-passivated 29000 amu gold nanocrystals, both individually and in spontaneously formed quasi-two-dimensional arrays. Experiments were performed at temperatures of 300 K, 77 K, and 8 K. Even at room temperature, tunneling through these 1.7 nm nanocrystals is shown to give rise to a Coulomb blockade. At cryogenic temperatures, the spectroscopy of the nanocrystals in arrays and in isolation shows an incremental charging effect (the Coulomb staircase) and evidence is found for quantization of the electronic states. Received: 10 September 1998 / Received in final form: 16 February 1999     

Spatial and angular distributions of third harmonic generation from metal surfaces

Third harmonic generation from planar and spherical metal surfaces is studied theoretically through the standard Green function method, so that the results are not affected by the uncertainty associated with previous simplified models. In general the pattern of the non-linear scattering loosely resembles the pattern of Mie scattering. The strong backward scattering is uniquely related to the non-linear process. These results differ significantly from the predictions of the surface charge model. Received: 20 May 1998 / Received in final form: 25 August 1998 / Accepted: 1st September 1998     

燃烧法制备La_2O_3纳米晶的研究

以硝酸镧作为氧化剂,柠檬酸铵作为燃料,用少量尿素作引发剂,采用燃烧法制备了La_2O_3纳米晶.并研究了煅烧温度、原料计量比和释放气体等因素对样品的影响.室温固相反应法制得的粘稠膏状络合物LaCit,当加热至150 ℃时立即引起燃烧,得到灰色前驱物,前驱物经700 ℃煅烧2 h得到单晶纳米La_2O_3样品.利用XRD、TEM和SEM测试方法对样品表征,结果表明:样品形貌为透明矩形片状单晶,平均长度为100~150 nm,宽度为40~80 nm,厚度约为20 nm,产率为85;~87;,粒度分布均匀,具有良好的分散性.     

高速电弧喷涂NiCrBMoFe/BaF2·CaF2涂层的摩擦磨损性能研究

利用高速电弧喷涂技术制备了NiCrBMoFe和NiCrBMoFe/BaF₂·CaF₂两种复合涂层.两种涂层均含非晶相与纳米晶相,非晶相质量百分数分别达45%和33%.NiCrBMoFe涂层中纳米晶相弥散分布在非晶母相中;NiCrBMoFe/BaF₂·CaF₂涂层纳米晶相以团聚形态存在.检测了两种涂层的摩擦磨损性能.在常温下,NiCrBMoFe和NiCrBMoFe/BaF₂·CaF₂两种涂层的摩擦系数分别为0.5和0.375,后者比基体18Cr₂Ni₄WA的摩擦系数下降了25%,耐磨性能优异.在高温摩擦磨损条件下,NiCrBMoFe/BaF₂·CaF₂涂层也具有良好的耐磨性能.在450 ℃左右,涂层中BaF₂·CaF₂固体润滑相会析出涂层表面,形成一层低摩擦系数的润滑转化膜,使涂层具有良好的减摩润滑作用.