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排序方式: 共有274条查询结果,搜索用时 31 毫秒
1.
Minna GünesÛ Jussi Valkonen 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):i119-i120
Caesium tetrasilver dizinc nonathiocyanate, Cs[Ag4Zn2(SCN)9], forms a continuous structure, where the Ag atoms and the S atoms of the thiocyanate groups form chains which run along [101]. These chains are bonded together through the Cs and Zn atoms. It is not possible to distinguish between space groups P1 and P, but, if the latter space group is correct, the structure contains a thiocyanate group disordered across a centre of inversion. The structure is described in space group P, in which the Cs atom also lies on a centre of inversion. 相似文献
2.
3.
Medical grade PVC plasticised with polycaprolactone–polycarbonate (PCL–PC) was subjected to aqueous environments at different temperatures. The release profile during ageing was determined by solid phase microextraction (SPME) and GC–MS. At the same time changes in the surface composition due to, for example, migration of PCL–PC from the blend were followed by FTIR. Almost no changes in the material or its surface composition were observed during 98 days at 37 °C in water or phosphate buffer. Only trace amount of 6-hydroxyhexanoic acid the final hydrolysis product of PCL–PC was detected in the GC–MS chromatograms and the weight loss was negligible. Even when the ageing temperature was raised to 70 °C only minor increase in the amount of 6-hydroxyhexanoic acid was observed and the weight loss after 98 days was under 1%. Changes in the FTIR spectra indicating migration of PCL–PC towards the surface of the PVC/PCL–PC tubing were observed first after 70 days at 70 °C. Large increase in the hydrolysis rate of PCL–PC and almost complete depletion of PCL–PC from the blend was observed when the ageing temperature was raised to 100 °C. 相似文献
4.
Virve A. Karttunen Mikko Linnolahti Tapani A. Pakkanen Janne Maaranen Päivi Pitkänen 《Theoretical chemistry accounts》2007,118(5-6):899-913
The performance of quantum chemical methods for geometry prediction of hafnocenes was evaluated. HF, B3LYP and MP2 in combination
with nonrelativistic (MHF) and relativistic (MWB and LANL2DZ) basis sets for hafnium together with standard basis sets 3-21G*,
6-31G* and 6-311G** for other elements were applied. Five basic structural parameters of the optimized structures of the hafnocenes
were compared with experimental crystal structures obtained from the Cambridge structural database. Altogether 80 hafnocenes
were included in the analysis. The results show that relativistic corrections are necessary for Hf atom. However, even the
Hartree–Fock (HF) method, when combined with relativistic pseudopotentials, reproduces the experimental crystal structures
with significant accuracy. The good performance of the HF method can be understood to originate from the absence of significant
near-degeneracy correlations for hafnium. On average, the B3LYP and MP2 methods provide structural parameters somewhat closer
to the experimental ones. 相似文献
5.
Summary Translational symmetry has been shown to be useful in the calculation of electronic structures of large lattice models. The number of unique integrals has been derived for cases of different dimensionality. For the unique integrals zero screening and approximation methods are described. The method has been applied to arrays of hydrogen atoms and to a zincblende surface model. When the size of the system is increased the translationally unique integrals are shown to become either zero or they can be calculated by simple coulombic approximations. 相似文献
6.
Tuula T. Pakkanen Tapani A. Pakkanen Kimmo Smolander 《Journal of Molecular Structure》1987,162(3-4):313-320
The structures of two glycinohydroxamoto (GHA) complexes of Ni(II) and Co(III) have been determined by single-crystal X-ray diffraction methods. The crystals of Ni(GHA)2 are monoclinic with a = 5.360(1), b = 7.315(4), c = 10.194(4) Å, β = 96.57(3), Z = 2, and space group P21/c. The crystals of Co(GHA)3•1/2 H2O are monoclinic with a = 22.467(19), b = 8.041(4), c = 13.700(11) Å, β = 116.01(7), Z = 8, and space group C2/c. The values of the final residuals R for Ni(GHA)2 and Co(GHA)3•1/2 H2O are 0.0275 and 0.032, respectvely. The molecular structures of Ni(GHA)2 and Co(GHA)3 consist of a square planar and an octahedral coordination, respectively, with the glycinohydroxamato (NH2CH2CONOH−) ligands coordinating to the metal ion via the N (amino) and the N (NOH−). These two complexes are the first well-established cases of coordination of the NHO− group of a hydroxamic acid to a transition metal via the nitrogen atom. 相似文献
7.
8.
Koshevoy IO Grachova EV Tunik SP Haukka M Pakkanen TA Heaton BT Iggo JA Podkorytov IS 《Dalton transactions (Cambridge, England : 2003)》2004,(22):3893-3899
Two novel heterometallic octahedral clusters [Rh(4)Pt(2)(CO)(11)(dppm)(2)](1) and [Ru(2)Rh(2)Pt(2)(CO)(12)(dppm)(2)](2) were synthesized by the reaction of [Rh(2)Pt(2)(CO)(6)(dppm)(2)] with [Rh(6)(CO)(14)(NCMe)(2)] and Ru(3)(CO)(12), respectively. Solid state structures of 1 and 2 have been established by a single crystal X-ray diffraction study. Two dppm ligands in 1 are bonded to one platinum and three rhodium atoms, which form an equatorial plane of the Rh(4)Pt(2) octahedron. Two rhodium and two platinum atoms bound to the diphosphine ligands in 2 are nonplanar to give an octahedral C2 symmetric Ru(2)Rh(2)Pt(2)(dppm)2 framework. The (31)P NMR investigation of and (1D, (31)P COSY, (31)P-[(103)Rh] HMQC) and simulation of 1D spectral patterns showed that in both clusters the structures of the M(6)(PP)(2) fragments found in the solid state are maintained in solution. 相似文献
9.
报道了深圳市南山区714名0 ̄6岁儿童头发中6种必需微量和宏量元素的水平,分析了不同年龄、性别儿童6种元素的异常状况,研究结果表明,儿童头发中锌、铜、铁、钙和锰元素缺乏状况相当严重总缺乏率占89.9%。 相似文献
10.
Ligand substitution of the mixed-metal clusters FeRu2(CO)12 and Fe2Ru(CO)12 with triphenylphosphine and trimethylphosphite has been studied. Mono- and di-substituted derivatives have been synthesized and characterized structurally. The following crystal and molecular structures are reported: Fe2Ru(CO)11PPh3: triclinic, space group P, a 9.203(2), b 11.903(3), c 15.117(4) Å, α 81.54(2), β 87.28(2), γ 66.72(2)°, Z = 2; Fe2Ru(CO)11P(OMe)3: orthorhombic, space group Pna21, a 17.220(5), b 14.572(4), c 8.708(6) Å, Z = 4, FeRu2(CO)11PPh3: monoclinic, space group P21/n, a 11.435(3), b 16.034(5), c 16.642(4) Å, β 93.35(2)°, Z = 4; FeRu2(CO)10(PPh3)2: orthorhombic, space group Pccm, a 14.854(4), b 17.180(7), c 16.786(12) Å, Z = 4.Ligand substitution is found to occur preferentially at the ruthenium centers of the FeRu2 and Fe2Ru clusters. Monosubstitution causes expansion of both of the clusters while the overall geometry is practically unchanged. Disubstitution of FeRu2(CO)12 causes contraction of the cluster and leads to a formation of carbonyl bridges. The structural trends have been interpreted in terms of electronic and packing effects of ligand substitution. The X-ray structures of Fe2Ru(CO)12 and FeRu2(CO)12 are not known; the ligand substitution studies indicate that Fe2Ru(CO)12 has the same structure as Fe3(CO)12, and that FeRu3(CO)12 does not have a Ru3(CO)12 structure as postulated previously from the IR studies. 相似文献