Molecular dynamics study of the thermal entropy in mixed zinc chalcogenides

Molecular dynamics (MD) calculations were performed to determine the vibrational contribution to the entropy of mixing and its importance for the mixing of ZnO/ZnS and ZnS/Zn3P2. These systems were modeled by cyclic clusters Zn48O48, Zn32S32, and Zn48P32. The mixed cyclic clusters considered were Zn48O47S, Zn32S31O, Zn33S30P2, and Zn47S2P30. For each of the clusters, the entropy was calculated in the range of the experimental temperature of the mixing process. The convergence of the entropy with respect to the number of MD steps was studied. Finally, the thermal part of the entropy of mixing was determined, and its dependence on the number of MD steps was investigated. It was found that the thermal entropy is important for the Gibbs free energy of mixing near the miscibility gaps.     

Small, nonstoichiometric zinc sulfide clusters

Recent experiments indicated that the formation of small, nonstoichiometric clusters Zn(n)S(m) and Zn(n)S(m)+ was possible. In this work, the ground states of these clusters, where 1 < or = n, m < or = 4, were studied using density functional theory. Global minima were found to be primarily cyclic structures in which the S-Zn-S preference for large bond angles was preserved. Ionization was shown to lead to structural relaxation and occasionally major changes in conformation. Cohesive energies are reported as a function of cluster composition. Qualitative comparisons were extracted from the energetics resulting from structural optimizations, and such comparisons appear to be consistent with the experiment. The computational data for the ZnS(n) and Zn(n)S(m) (where m > n) clusters indicated that sulfur-sulfur bonding in larger ZnS clusters could be feasible without significant energetic cost and that such structures should at least be considered.     

XAFS analysis of coprecipitation of zinc by sulfide ions in an acidic solution

The fluorescence XAFS (X–ray absorption fine structure) technique using synchrotron radiation was applied to characterize zinc in the Hg–Zn, Cd–Zn, and Bi–Zn coprecipitates, and to elucidate the reaction mechanism of the coprecipitation of zinc from a strong acidic solution. Hg L_II–, Cd K–, and Bi L_III–edge XAFS spectra suggested that the respective host materials of the coprecipitates listed above are metacinnabar (HgS), greenockite (CdS), and bismuthinite (Bi₂S₃) and that existence of zinc has not affected the local structure of the host metal sulfides in each system. On the other hand, the Zn K–edge XAFS spectra of each coprecipitate indicated that the chemical forms of zinc compounds are controlled by the crystal structure of the host sulfides.The shapes of the Zn K–XAFS spectra of the Hg–Zn and Cd–Zn coprecipitates showed a strong resemblance to those of crystalline standards ZnS, wurtzite and spharelite. It was suggested that the two coprecipitated phases (HgS, ZnS) and (CdS, ZnS) may form a solid solution in the Hg–Zn and Cd–Zn coprecipitates. The local structure around the zinc(II) ion in the Bi–Zn coprecipitate is the same as that around hexaaqua–zinc(II) ions, and adsorption of soluble ions or mechanical occlusion from the mother liquor is regarded as a driving force of coprecipitation in the Bi–Zn system.     

Modeling the photoelectron spectra of the valence O2p-band of zinc oxide by the Xα-scattered wave method

The photoelectron spectra (PES) of the valence O2p-band of zinc oxide are modeled by Xα-scattered wave cluster calculations in a wide range of incident quantum energies hv (from 30 to 150 eV and 1253.6 eV). For the Zn₁₀O₁₀ cluster, the calculated intensities of PES reproduce well the specific features of the experimental spectra. It is shown that Zn3d-electrons participate in covalent binding of zinc and oxygen. The admixture of the Zn3d-states in the hybrid orbitals of the valence band is ≈7%. Deceased. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 5, pp. 877–886, September-October, 1997.     

Anion substitution in zinc chalcogenides

Anion substitution effects on the structure and energy of zinc chalcogenides were studied with the semiempirical molecular orbital method MSINDO. Cyclic clusters of different sizes were chosen as model systems. The convergence of the bulk properties of the perfect clusters with increasing cluster size was tested. Single and multiple substitution of oxygen atoms in zinc oxide by sulfur and of sulfur atoms in zinc sulfide by oxygen served to determine the energetics of substitution for these two cases. It was found that the substitution of oxygen by sulfur in ZnO is easier than the substitution of sulfur by oxygen in ZnS in agreement with experimental results. The interaction between two oxygen atoms vs. two selenium atoms in zinc sulfide was investigated. Oscillations of the cluster energy in dependence of the distance between the two doping atoms were observed. These are explained by the relative sites of the doping atoms in the crystal lattice. The magnitude of the oscillations is smaller in ZnS:Se than in ZnS:O, because the difference between the anion radii of S2- and Se2- is smaller than between S2- and O2-. This is also reflected in the band gap.     

Syntheses and properties of zinc and calcium complexes of valinate and isovalinate: metal alpha-amino acidates as possible constituents of the early Earth's chemical inventory

We have studied the ligand behavior of racemic isovalinate (iva) and valinate (val) towards zinc(II) and calcium(II). The following solid metal amino acidates were obtained from aqueous solutions: Zn3Cl2(iva)4 (1), Zn3Cl2(val)4 (2). Zn(val)2 (3), Zn(iva)2 x 2H2O (4), Zn(iva)2 x 3.25H2O (5), Zn(iva)2 (6), Ca(iva)2x xH2O (7), and Ca(val)2 x H2O (8). Except for complex 3, these were hitherto unknown compounds. The conditions under which they formed, together with current ideas of the conditions on early Earth, support the assumption that alpha-amino acidate complexes of zinc and calcium might have belonged to early Earth's prebiotic chemical inventory. The zinc isovalinates 1, 4, and 5 were characterized by X-ray crystal structure analyses. Complex 1 forms a layer structure containing four- and five-coordinate metal atoms, whereas the zinc atoms in 4 and 5 are five-coordinate. Compound 5 possesses an unprecedented nonpolymeric structure built from cyclic [Zn6(iva)12] complexes, which are separated by water molecules. The thermolyses of solids 1. 3, and 8 at 320 degrees C in an N2 atmosphere yielded numerous organic products, including the cyclic dipeptide of valine from 3 and 8. Condensation, C-C bond breaking and bond formation, aromatization, decarboxylation, and deamination reactions occurred during the thermolyses. Such reactions of metal-bound a-amino acidates that are abiotically formed could already have contributed to an organic-geochemical diversity before life appeared on Earth.     

Spectrophotometric determination of zinc in copper-base alloys with TAN

TAN reacts with zinc(II) forming a red complex with composition 1:2 Zn(II)-TAN and absorption maximum at 582 nm. Zinc can be determined with this reagent in the presence of Triton X-100, in the pH range 6.20-8.00 with a molar absorptivity of 4.5×10⁴ l/mol/cm Beer's Law was obeyed up to least 1.55 g/ml. Copper interference was eliminated with a mixture of thiosulfate and ascorbic acid and nickel separated by precipitation with dimethylglyoxime. The proposed method was used for zinc determination in several copper-base alloys and the results of analysis in comparison with certified values indicated that the procedure was accurate and precise. A derivative procedure is also proposed, allowing zinc determination with high sensitivity (5-400 ng/ml).     

Three novel zinc(II) sulfonate-phosphonates with tetranuclear or hexanuclear cluster units

Hydrothermal reactions of zinc(II) carbonate with m-sulfophenylphosphonic acid (m-HO3S-Ph-PO3H2) and 1,10-phenanthroline (phen) or 4,4'-bipyridine (bipy) lead to three novel zinc(II) sulfonate-phosphonates, namely, [Zn(phen)3]2[Zn4(m-O3S-Ph-PO3)4(phen)4].20H2O (1), [Zn6(m-O3S-Ph-PO3)4(phen)8].11H2O (2), and [Zn6(m-O3S-Ph-PO3)4(bipy)6(H2O)4].18H2O (3). Compound 1 contains a tetranuclear zinc(II) cluster anion in which four Zn(II) ions are bridged by two tetradentate and two bidentate phosphonate groups, and the four negative charges of the cluster are compensated by two [Zn(phen)3]2+ cations. Compound 2 features a hexanuclear zinc(II) cluster in which the same tetranuclear cluster of 1 is bridged with two additional Zn(II) ions. The structure of 3 features a porous 3D network based on hexanuclear zinc(II) units of [Zn6(m-O3S-Ph-PO3)4] interconnected by 4,4'-bipy ligands. The hexanuclear cluster in 3 is different from that in 2 in that all four phosphonate groups in 3 are tridentate bridging. Compounds 1, 2, and 3 exhibit broad blue fluorescent emission bands at 378, 409, and 381 nm, respectively.     

Preparation, composition and structure of some nickel and zinc ferrocyanides: Experimental results

Several methods have been used for preparation of nickel and zinc ferrocyanides: precipitation, growth in a gel and a new method based on growth on a solid alkali-metal ferrocyanide. The granulometry, morphology, composition and structure of the compounds were studied. Only the last method of preparation gives products suitable for use as ion fixators in columns on a large scale. The nickel ferrocyanide compositions can be written as M(I)(2x)Ni(2-x)Fe(CN)(6).yH(2)O with M(I) Na, K, Cs, H and 0 < x < 0.8. They have a cubic lattice with a partial occupancy of iron sites. For zinc ferrocyanides, rhombohedral M(I)(2)Zn(3)[Fe(CN)(6)](2).xH(2)O, trigonal Zn(2)Fe(Cn)(6).2H(2)O and other cubic compounds were found. Products resulting from the fixation of caesium by ion-exchange were also studied.     

Complexation of the vulcanization accelerator tetramethylthiuram disulfide and related molecules with zinc compounds including zinc oxide clusters (Zn4O4)

Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn(2+), ZnMe(2), Zn(OMe)(2), Zn(OOCMe)(2), and the heterocubane cluster Zn(4)O(4) with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me(2)NCS(2)(*), Me(2)NCS(3)(*), Me(2)NCS(2)(-), and Me(2)NCS(3)(-) have been studied by quantum chemical methods at the MP2/6-31+G(2df,p)//B3LYP/6-31+G* level of theory. More than 35 zinc complexes have been structurally characterized and the energies of formation from their components calculated for the first time. The binding energy of TMTD as a bidendate ligand increases in the order ZnMe(2)相似文献   

Low Temperature Preparation of 3D Solid and Hollow ZnS Nanosphere Self-Assembled from Nanoparticles by Varying Sulfur Source

In this work, we report a facile hydrothermal method for the preparation of three dimensional hollow ZnS nanostructures, using Zinc bis(salicyle aldehitato), Zn(Sal)₂, thioacetamide (TAA) and thioglycolic acid (TGA) as Zn²⁺, sulfur source and capping agent, respectively. The ZnS solid and hollow sphere was produced from the self-assembly of nanoparticles with diameters of 11 ± 2 nm with TGA and TGA, TAA, respectively. Furthermore, with changing zinc precursor from Zn(Sal)₂ to zinc acetate [Zn(OAC)₂], ZnS nanorods were obtained. The products were characterized by XRD, SEM, TEM, selected area electron diffraction, and FT-IR spectra. The influence of surfactant (Polyethylene glycol) on the morphology of the products was also investigated. Possible formation mechanism and optical properties of these architectures were also reported.     

Crystal structure of the complex Zn(2,2′-Bipy)(C2H5OCS2)2 with mono- and bidentate ethylxanthate ligands

While seeking molecular precursors for ZnS films obtained by gas phase chemical deposition [1, 2] we synthesized mixed-ligand compounds ZnL(ROCS₂)₂ [R = i-Pr. /-Bu; L = 2,2′-bipyridyl (2,2′-Bipy), 1,10-phenanthroline (Phen)] [3]. The volatile complex Zn(2,2′-Bipy)(i-PrOCS₂)₂ was used as a precursor to obtain electroluminescent ZnS:Mn films [4]. According to XRD data, the compound Zn(Phen)(i-BuOCS₂)₂ is monomeric. The c.n. of zinc is six. The Phen and 1-B11OCS₂ ions behave as cyclic bidentate ligands [3, 5]. It was assumed that other mixed-ligand complexes with Phen and 2,2′-Bipy have an analogous structure [3]. Here we report on the structure of the known mixed-ligand complex of zinc(II) ethylxanthate with 2,2′-bipyridyl [6, 7]. It was found that the behavior of alkylxanthate ligands in mixed-ligand complexes of zinc(II) is more complex. Translated from Zhumal Stmktumoi Khimii, Vol. 41, No. 1, pp. 196-201, January–February, 2000.     

Electrochemical behaviour of zinc gluconate complexes

Voltammetric studies revealed that under transient conditions in the pH range 3.7 to 5.0, the deposition of zinc from ZnSO₄ solutions involves the formation of adsorbed monovalent zinc. The conversion of divalent zinc to monovalent is a slow step. In the presence of gluconate, the reduction of divalent complex involves the monovalent zinc complex and the second electron transfer is slow. In the pH range 10 to 12.5, the zinc complex may be [(Zn(GH₄)₄]2^- and is found to vary with gluconate and OH^- ions. The conversion of [Zn(GH₄)(OH)_abs ^-] to Zn(OH)₂ or Zn(GH₄)₂ is the slow step in the reduction of the complexes. In strong alkali solutions sodium gluconate forms zinc hydroxy gluconate complexes. [Zn(OH)₃(GH₄)]^2- to adsorbed [Zn(OH)(GH₄)]^- is the slow step in the reduction.     

Functionalized manganese-doped zinc sulfide quantum dot-based fluorescent probe for zinc ion

We report on a simple strategy for the determination of zinc ion by using surface-modified quantum dots. The probe consists of manganese-doped quantum dots made from zinc sulfide and capped N-acetyl-L-cysteine. The particles exhibit bright yellow-orange emission with a peak at 598?nm which can be attributed to the ⁴T₁→⁶A₁ transition of Mn(II). This bright fluorescence is effectively quenched by modifying the sulfur anion which suppresses the radiative recombination process. The emission of the probe can then be restored by adding Zn(II) which causes the formation of a ZnS passivation layer around the QDs. The fluorescence enhancement caused is linear in the 1.25 to 30?μM zinc concentration range, and the limit of detection is 0.67?μM.

Zn7{(2-C5H4N)CH(OH)PO3}6 (H2O)6]SO4 x 4H2O: a zinc phosphonate cluster with a drum-like cage structure

Direct reaction of hydroxy(2-pyridyl)methylphosphonic acid with zinc sulfate under hydrothermal conditions results in the formation of the novel heptanuclear cluster compound [Zn7{(2-C5H4N)CH(OH)PO3}6 (H2O)6]SO4 x 4H2O (1). The inorganic core of the cluster can be described as a cylindrical drum made up of six Zn atoms bridged by six {CPO3} units that is centered by a seventh Zn atom. Crystal data: monoclinic, C2/c, a = 22.690(2) A, b = 16.675(2) A, c = 18.151(2) A, beta = 93.390(2) degrees.     

Adsorption kinetics of zinc in multicomponent ionic systems

Using commercial activated carbon as an adsorbent, the kinetics of adsorption of zinc from multicomponent ionic systems having cadmium and mercury has been studied and reported. The variables investigated have been the chemical nature, ionic strength, and pH of the adsorptive (Zn2+) solution. The adsorption of Zn2+ is speeded up by the presence of Cd2+ and Hg2+ ions provided that the concentration of these two ions is high as compared to the concentration of Zn2+. When the ionic strength of the solution in relative terms is high (i.e., > 3 x 10(-4) M), however, the adsorption of Zn2+ decelerates. Also, the adsorption process is greatly accelerated at pH 12, whereas at pH 2 it does not occur at all.     

In situ STM study of zinc electrodeposition on Au(111) from the ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate

The electrodeposition of Zn on Au(111) was investigated with cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) in the air and water stable ionic liquid 1-ethyl-3-methylimidazolium trifluoromethylsulfonate ([EMIm]TfO) with a Zn(TfO)₂ concentration of 0.2 M. It has been found that the structure [EMIm]TfO/Au(111) is very complex. Furthermore, the addition of Zn(TfO)₂ changes the interfacial structure significantly. The first STM-probed Zn islands appear at +0.3 V, and their growth leads to the formation of a thin zinc layer. A bulk deposition of Zn is obtained with in situ STM at ?0.1 V. Furthermore, in situ STM reveals that the deposition of Zn is accompanied by the formation of Au-Zn surface alloys.     

Synthesis and interface structures of zinc sulfide sheathed zinc-cadmium nanowire heterojunctions

Zinc sulfide (ZnS) sheathed zinc (Zn)-cadmium (Cd) nanowire heterojunctions have been prepared by thermal evaporating of ZnS and CdS powders in a vertical induction furnace at 1200 degrees C. Studies found that both the Zn and Cd subnanowires, within a single nanoheterojunction, are single-crystallines with the growth directions perpendicular to the [210] plane, whereas the sheathed ZnS is polycrystalline with a thickness of ca. 5 nm. The Zn/Cd interface structure in the ZnS sheathed Zn-Cd nanowire heterojunctions was thoroughly experimentally studied by high-resolution transmission electron microscopy and theoretically studied using a near-coincidence site lattice (NCSL) concept. The results show that the Cd and Zn have a crystalline orientation relationship as [0001]Zn//[0001]Cd, (10(-)10)Zn//(10(-)10)Cd, (01(-)10)Zn//(01(-)10)Cd, and ((-)1100)Zn//((-)1100)Cd.     

Modulation of the intercalation properties of copper-zinc mixed-metal phosphonate materials

New layered mixed divalent metal vinylphosphonates Cu(II) (1-x)Zn(II) (x)(O(3)PC(2)H(3)).H(2)O have been prepared from a range of pre-formed copper-zinc oxides Cu(II) (1-x)Zn(II) (x)O obtained by isomorphous substitution of zinc into the tenorite-type structure of Cu(II)O. The corresponding mixed divalent copper-zinc vinylphosphonates have been characterised by powder X-ray diffraction, elemental analysis, infrared spectroscopy and thermogravimetric analysis. All compounds have been shown to consist of a single-phase solid solution that crystallises in an monoclinic unit cell, space group P2(1)/c with a=9.86-9.90, b=7.61-7.64, c=7.32-7.35 A and beta=95.9-96 degrees, with the exception of the pure zinc vinylphosphonate (x=1), the structure of which is comparable to other Zn(II)(O(3)PR).H(2)O materials. Studies of the intercalation of n-butylamine into the range of copper-zinc vinylphosphonates have demonstrated that significant modulation of the adsorption properties occurs; whereas one mole of amine is intercalated into the pure zinc vinylphosphonate to give Zn(II)(O(3)PC(2)H(3)).(C(4)H(9)NH(2)), for all other members of the series two moles of amine are coordinated to give intercalated compounds of composition Cu(II) (1-x)Zn(II) (x)(O(3)PC(2)H(3)).[(C(4)H(9)NH(2))(1-x)(C(4)H(9)NH(2))(x)](2) from which the amine can be sequentially removed from the different metal sites; this opens up possibilities for further applications of these materials.     

Low temperature synthesis of cubic phase zinc sulfide quantum dots

In this study, we report on a new method for the synthesis of ZnS quantum dots (QDs). The synthesis was carried out at low temperature by a chemical reaction between zinc ions and freshly reduced sulfide ions in ethanol as reaction medium. Zinc chloride and elemental sulfur were used as zinc and sulfur sources, respectively and hydrazine hydrate was used as a strong reducing agent to convert elemental sulfur (S₈) into highly reactive sulfide ions (S²⁻) which react spontaneously with zinc ions. This facile, less toxic, inexpensive route has a high yield for the synthesis of high quality metal sulfide QDs. Transmission electron microscopy (TEM) image analysis and selected area electron diffraction (SAED) reveal that ZnS QDs are less than 3 nm in diameter and are of cubic crystalline phase. The UV-Vis absorption spectrum shows an absorption peak at 253 nm corresponding to a band gap of 4.9 eV, which is high when compared to the bulk value of 3.68 eV revealing strong quantum confinement. PL emission transitions are observed at 314 nm and 439 nm and related to point defects in ZnS QDs.