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1.
Volker Jonas Gernot Frenking Manfred T. Reetz 《Journal of computational chemistry》1992,13(8):935-943
The performance of effective core potentials (ECP) for the main group elements of group IV has been studied by calculating the geometries and reaction energies of isodesmic reactions for the molecules M(CH3)nCl4 ? n (M = C, Si, Ge, Sn, Pb; n = 0–4) at the Hartree–Fock level of theory. The results are compared with data from all electron calculations and experimental results as far as available. The all electron calculations were performed with a 3-21G(d) and a 6-31G(d) basis set for Si, a (43321/4321/41) basis set for Ge, and a (433321/43321/431) basis set for Sn. For the ECP calculations the potentials developed by Hay and Wadt with a configuration (n)sa(n)pb and the valence basis set (21/21), extended by a set of d functions, are employed. © 1992 by John Wiley & Sons, Inc. 相似文献
2.
H.A. Hyman 《Chemical physics letters》1975,31(3):593-595
The long-range, van der Waals interaction is considered for the system M*(nsnp 1,3P1)/noble gas (1S0), where M* is any atom with two valence electrons outside closed shells. An important “correlation” effect is shown to arise due to the different symmetry properties of the spatial parts of the singlet and triplet wavefunctions; this is the direct analogue of the effect of angular correlation in the ground-state problem. Detailed calculations are carried out for Hg*(6s6p 1,3P1) interacting with the noble gases. 相似文献
3.
4.
The significant similarity between MF3, MF4–, and M2F7– (M = Au, Br) is studied using quantum chemical methods. It is expected that compounds containing Au3F10– anions are likely to be stable. A theoretical background for the ongoing attempts of their synthesis is provided by calculations on the stabilities and molecular structures of various bromine and gold anions with the general composition of MnF3n+1– (n = 1, 2, 3, 4). The anions show unexpected differences and peculiarities in their energetically preferable molecular structures. Different chain‐like structures are predicted as the global minima for the hypothetical Au3F10– and Br4F13– anions. 相似文献
5.
Konrad Schubert 《Monatshefte für Chemie / Chemical Monthly》1982,113(6-7):651-667
The two-correlations model for the binding in alloy phases is applied to carbides. The model considers a valence electron spatial correlation (namedb correlation) and a core electron spatial correlation (namedc correlation) and assumes that they are in good commensurability with the crystal cella and with one another; the types of the correlations together with the commensurability are named a binding. The well known concept of interstitial structures of carbides is extended by the assumption that the valence electrons of the C atoms and the peripheral d electrons of the transition metal atoms (T atoms) take part in thec correlation while the valence electrons of the T atoms form ab correlation which lies in good commensurability with thec correlation and contributes thus to the stability of a phase. This model explains the high melting temperature of TiC, it gives the sequence of structures for increasing C mole fraction in a mixture like WC
M
(M=undetermined mole number) and it affords a simple interpretation of the martensite phenomenon. Only in B
n
atom carbides, like Al4C3 or SiC, the valence electrons of B
n
and of C appear to form ab correlation, so that the core electrons of the C and of the B
n
atoms form thec correlation. By these assumptions becomes clear why great atoms like Tl, Pb, Bi do not form interstitial compounds with C, or why in the SiC compound and in Al4C3(AlN)
M
there are many homeotypic phases (polytypes). In three component carbides also, the occurrence of certain structural types is better understood by the analysis of the binding.
Über die Bindungstypen in Carbiden
Zusammenfassung Das Zweikorrelationenmodell für die Bindung in Legierungsphasen wird auf Carbide angewandt. Das Modell betrachtet eine Ortskorrelation der Valenzelektronen (genanntb-Korrelation) und eine Ortskorrelation der peripheren Rumpfelektronen (genanntc-Korrelation) und nimmt an, daß diese in guter Kommensurabilität mit der Kristallzellea und miteinander stehen; die Typen der Korrelationen zusammen mit der Kommensurabilität zwischen ihnen kennzeichnen den Bindungstyp. Der bekannte Begriff der Einlagerungsstrukturen der Carbide wird erweitert durch die Annahme, daß die Valenzelektronen der C-Atome und die peripheren d-Elektronen der Übergangsmetallatome (T-Atome) an derc-Korrelation teilnehmen, während die Valenzelektronen der T-Atome eineb-Korrelation bilden, die in guter Kommensurabilität zurc-Korrelation steht und so zur Stabilität der Phase beiträgt. Das Modell erklärt die hohe Schmelztemperatur von TiC, es gibt die Abfolge der Strukturen für steigenden C-Molenbruch in einer Mischung wie WC M (M=unbestimmte Molenzahl) und es liefert eine einfache Deutung des Martensit-Phänomens. Lediglich in B n -Carbiden wie Al4C3 oder SiC scheinen die Valenzelektronen der B n - und der C-Atome dieb-Korrelation zu bilden, so daß die Rumpfelektronen der C- und B n -Atome diec-Korrelation bilden. Durch diese Annahmen wird klar, warum große Atome wie Tl, Pb, Bi keine Einlagerungsverbindungen mit C bilden oder warum in der Verbindung SiC oder in Al4C3(AlN) M viele homöotypische Phasen (Polytype) auftreten. Auch in dreikomponentigen Carbiden wird das Auftreten bestimmter Strukturtypen besser verständlich durch die Analyse des Bindungstyps.相似文献
6.
Reza Ghiasi 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(12):2148-2155
The nature of H2B=NH2...M
n+, HB=NH...M
n+, and Borazine...M
n+ interactions were studied with ab-initio calculations. The interaction energies were calculated at B3LYP/6-31G(d, p) level. The calculations suggest that the size and charge of cation are two influential factors that affect the nature of
interaction. The theory of atoms in molecules (AIM) and natural bond orbital (NBO) analysis of complexes indicate that the
variation of densities and the extent of charge shifts upon complexation correlate well with the obtained interaction energies. 相似文献
7.
Toshikatsu Koga Shigeyoshi Yamamoto Tsuyoshi Shimazaki Hiroshi Tatewaki 《Theoretical chemistry accounts》2002,108(1):41-45
We report minimal-type contracted Gaussian-type function (GTF) sets, #n=(n3333/n33/n3) with n=5 and 6, #7= (74333/743/74), and #8= (84333/843/75), for the fourth-row atoms from Rb to Xe. Test calculations are performed
on the Ag2 molecule. Spectroscopic constants given by split valence sets derived from #5 and #6 are a little contaminated by basis set
superposition error. However, we find that the fully valence split #8 set, (8433111/84111/711111), yields essentially the
same results as a large GTF set, (22s15p12d), with a general contraction, when p-, d-, and f-type polarization functions are
augmented. The present #7 and #8 CGTF sets are recommended for ab initio molecular calculations including fourth-row atoms.
Received: 15 January 2002 / Accepted: 16 April 2002 / Published online: 24 June 2002 相似文献
8.
The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform a crystal-chemical analysis of compounds whose structures contain Os atoms surrounded by chalcogen atoms. Depending on the valence state, Os atoms bind four to seven X atoms (X = O, S, Se, Te) forming OsX
n
coordination polyhedra which can be tetrahedra (n = 4), trigonal bipyramids or square pyramids (n = 5), octahedra (n = 6), or pentagonal bipyramids (n = 7). In some compounds, pairs of OsO6 octahedra share edges to form Os–Os bonds. The influence of the Os valence state and the nature of the chalcogen atom on the composition and structure of the [Os
a
X
b
] groups is discussed. On the basis of analysis of the crystal-structural data from the standpoint of the 18-electron rule, dependences of the Os–O and Os–Os bond orders on the bond lengths are proposed. 相似文献
9.
Is it True That the Normal Valence‐Length Correlation Is Irrelevant for Metal–Metal Bonds?
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Dr. Vijay Singh Dr. Mudit Dixit Dr. Monica Kosa Prof. Dan Thomas Major Prof. Elena Levi Prof. Dr. Doron Aurbach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(15):5269-5276
The most intriguing feature of metal–metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal–metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation. 相似文献
10.
Two Hexagonal Series of Lanthanoid(III) Oxide Fluoride Selenides: M6O2F8Se3 (M = La – Nd) and M2OF2Se (M = Nd,Sm, Gd – Ho)
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Dirk D. Zimmermann Hagen Grossholz Sarah Wolf Oliver Janka Alexander C. Müller Thomas Schleid 《无机化学与普通化学杂志》2015,641(11):1926-1933
Two hexagonal series of lanthanoid(III) oxide fluoride selenides with similar structure types can be obtained by the reaction of the components MF3, M2O3, M, and Se in sealed niobium tubes at 850 °C using CsI as fluxing agent. The compounds with the lighter and larger representatives (M = La – Nd) occur with the formula M6O2F8Se3, whereas with the heavier and smaller ones (M = Nd, Sm, Gd – Ho) their composition is M2OF2Se. For both systems single‐crystal determinations were used in all cases. The compounds crystallize in the hexagonal crystal system (space group: P63/m) with lattice parameters of a = 1394–1331 pm and c = 403–372 pm (Z = 2 for M6O2F8Se3 and Z = 6 for M2OF2Se). The (M1)3+ cations show different square antiprismatic coordination spheres with or without an extra capping fluoride anion. All (M2)3+ cations exhibit a ninefold coordination environment shaped as tricapped trigonal prism. In both structure types the Se2– anions are sixfold coordinated as trigonal prisms of M3+ cations, being first condensed by edges to generate trimeric units and then via faces to form strands running along [001]. The light anions reside either in threefold triangular or in fourfold tetrahedral cationic coordination. For charge compensation, both structures have to contain a certain amount of oxide besides fluoride anions. Since F– and O2– can not be distinguished by X‐ray diffraction, bond‐valence calculations were used to address the problem of their adjunction to the available crystallographic sites. 相似文献
11.
Dr. Lenka Pallova Dr. Etienne S. Gauthier Dr. Laura Abella Marion Jean Dr. Nicolas Vanthuyne Dr. Vincent Dorcet Dr. Laure Vendier Prof. Jochen Autschbach Dr. Jeanne Crassous Dr. Stéphanie Bastin Dr. Vincent César 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(28):7722-7730
The straightforward, multigram-scale synthesis of the partially saturated H6-fluoreno[n]helicenes (n=5 or 7) featuring a central, overcrowded alkene is described. The key cyclization step was based on an intramolecular McMurry reaction from the corresponding 1,5-diketones. Chiral stationary phase HPLC analysis and isomer separation indicate that each helicenic compound is constituted of three diastereoisomers at room temperature, i. e. the configurationally stable (R,R,P)/(S,S,M) pair of enantiomers and an apparently achiral compound resulting from the rapid interconversion between the (R,S,P) and (S,R,M) enantiomers. The partially saturated H6-fluoreno[n]helicenes are oxidatively aromatized to give an efficient access to the corresponding fluoreno[n]helicenes. The chiroptical properties (vibrational and electronic circular dichroism) of the chiral, enantiopure compounds have been measured and analyzed by quantum-chemical calculations, confirming their helicoidal nature. 相似文献
12.
Dr. Qing-Dou Xu Dr. Xiao Ma Chen Zeng Dr. Shao-Dong Su Sheng-Min Hu Ying-Ying Huang Prof. Xin-Tao Wu Prof. Tian-Lu Sheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(34):e202104486
To investigate the effects of cis/trans-configuration of the cyanidometal bridge and the electron donating ability of the auxiliary ligand on the cyanidometal bridge on metal to metal charge transfer (MMCT) in cyanidometal-bridged mixed valence compounds, two groups of trinuclear cyanidometal-bridged compounds cis/trans-[Cp(dppe)Fe(μ-NC)Ru(4,4’-dmbpy)2(μ-CN)Fe(dppe)Cp][PF6]n (n=2 ( cis/trans - 1[PF6]2 ), 3 ( cis/trans - 1[PF6]3 ), 4 ( cis/trans - 1[PF6]4 )) and cis/trans-[Cp(dppe)Fe(μ-NC)Ru(bpy)2(μ-CN)Fe(dppe)Cp][PF6]3 ( cis/trans - 2[PF6]3 ) were synthesized and fully characterized. The experimental results indicate that for these one- and two-electron oxidation mixed valence compounds, the trans-configuration compounds are more beneficial for MMCT than the cis-configuration compounds, and increasing the electron donating ability of the auxiliary ligand on the cyanidometal bridge is also conductive to MMCT. Moreover, compounds cis/trans - 1[PF6]n (n=3, 4) and cis/trans - 2[PF6]3 belong to localized compounds by analyzing the experimental characterization results, supported by the TDDFT calculations. 相似文献
13.
Electronic Properties of Mono‐Substituted Tetraferrocenyl Porphyrins in Solution and on a Gold Surface: Assessment of the Influencing Factors for Photoelectrochemical Applications
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Dr. Andrea Vecchi Nathan R. Erickson Jared R. Sabin Prof. Barbara Floris Prof. Valeria Conte Prof. Mariano Venanzi Dr. Pierluca Galloni Prof. Victor N. Nemykin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):269-279
Two unsymmetric meso‐tetraferrocenyl‐containing porphyrins of general formula Fc3(FcCOR)Por (Fc=ferrocenyl, R=CH3 or (CH2)5Br, Por=porphyrin) were prepared and characterized by a variety of spectroscopic methods, whereas their redox properties were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) approaches. The mixed‐valence [Fc3(FcCOR)Por]n+ (n=1,3) were investigated using spectroelectrochemical as well as chemical oxidation methods and corroborated with density functional theory (DFT) calculations. Inter‐valence charge‐transfer (IVCT) transitions in [Fc3(FcCOR)Por]+ were analyzed, and the resulting data matched closely previously reported complexes and were assigned as Robin–Day class II mixed‐valence compounds. Self‐assembled monolayers (SAMs) of a thioacetyl derivative (Fc3(FcCO(CH2)5SCOCH3)Por) were also prepared and characterized. Photoelectrochemical properties of SAMs in different electrolyte systems were investigated by electrochemical techniques and photocurrent generation experiments, showing that the choice of electrolyte is critical for efficiency of redox‐active SAMs. 相似文献
14.
Olga Martin Ana Sanchez-Camacho Francisco Mendicuti Wayne L. Mattice 《Journal of Polymer Science.Polymer Physics》1997,35(7):1127-1133
Steady-state fluorescence measurements and molecular dynamics simulations have been used to study the intramolecular formation of excimers in five model compounds for polyesters containing naphthalene groups separated by flexible spacers. The model compounds are derived from 2-hydroxynaphthalene and HOOC (CH2)n COOH, n = 2–6. The ratio of the intensity of excimer and monomer emissions, ID/IM, is nearly independent of the viscosity of the medium, η, over the range covered in dilute solution. Although ID/IM is always very small, it shows an odd–even effect for the first four members of the series, with maxima when n is odd. Molecular dynamics simulations provide an explanation for the small values of ID/IM, their weak dependence on η, and the trend of ID/IM with n. The results for the present series of model compounds are compared with previous work, which reported larger values of ID/IM, and a stronger dependence of ID/IM on η, for bichromophoric compounds derived from 2-naphthoic acid and aliphatic glycols, where the direction of the ester groups is reversed. The origin of the difference in the behavior of ID/IM in the two series is identified. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1127–1133, 1997 相似文献
15.
Thermodynamic calculations predict the formation of hydrochloric acid gas and alkali tungstates during hydrogen reduction
of WO3 doped with alkali chlorides MCl (M=Li, Na, K). The formation of HCl was proved experimentally by simultaneously coupled TG-MS
measurements from RT to 1200°C. The formation of HCl is the result of the reaction between MCl, WO3 and water. Ubiquitous traces of moisture in the gas are sufficient for reaction according to WO3+(2+2n)MCl +(1+n)H2O→M2+2nWO4+n+(2+2n)HCl (n=0, 1, 2). Laboratory reduction tests showed that the formed tungstates differ. NaCl and KCl form monotungstates (n=0), while LiCl produces more lithium-rich compounds (n=1, 2). Temperature and humidity, among other process factors, control subsequent reduction of the tungstates to metals.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
Alon Gal Michael Cais David H. Kohn 《Journal of polymer science. Part A, Polymer chemistry》1971,9(7):1853-1863
The self-condensation of α-ferrocenylmethylcarbonium ion in nitroethane yielded polymers of Mn up to 20,000. The change of [η] and Mn with the reaction time indicated that the process consisted of a rapid primary growth stage, an induction period, a second growth stage, and a crosslinking stage. The [η]–Mn correlation for a series of polymeric fractions in the Mn = 0.1–7.2 × 104 range points to a highly branched structure. 相似文献
17.
The reactions between K5Bi4, [(C6H6)Cr(CO)3] or [(C7H8)Mo(CO)3], and [2.2.2]crypt in liquid ammonia yielded the compounds [K([2.2.2]crypt)]3(η3‐Bi3)M(CO)3 · 10NH3 (M = Cr, Mo), which crystallize isostructurally in P21/n. Both contain an 18 valence electron piano‐stool complex with a η3‐coordinated Bi3‐ring ligand. The Bi–Bi distances range from 2.9560(5) to 2.9867(3) Å and are slightly shorter than known Bi–Bi single bonds but longer than Bi–Bi double bonds. The newly found compounds complete the family of similar complexes with E3‐ring ligands (E = P‐Bi). 相似文献
18.
We develop a simple semiempirical model that correlates the Auger parameter to the ground state valence charge of the core-ionized atom with closed shell electron configuration. Until now, the Auger parameter was employed to separate initial and final state effects that influence the core electron binding energy. The model is applied to Cu(I) and Cu (II) compounds with the Auger parameter defined as α' = EbFL (2p3/2) + EkFL (L3M45M45;1G). The Auger parameter shift for Cu(I) ion in CuI, CuBr, CuFeS2, Cu2S, and Cu2O compounds—with respect to the copper free atom—increases with the electronic polarizability of the nearest-neighbour ligands suggesting a nonlocal screening mechanism. This relaxation process is interpreted as due to an electron transfer from the nearest-neighbour ligands toward the spatially extended 4sp valence orbitals of the core-ionized Cu(I) ion. In agreement with our model, a linear relationship is found between the Auger parameter shift and the ground state Bader valence charge obtained by density functional theory calculations. The Auger parameter shift for the Cu (II) ion in CuF2, CuCl2, CuBr2, CuSO4, Cu (NO3)2•3H2O, Cu3(PO4)2, Cu (OH)2, and CuO compounds is very close to the Auger parameter of metallic copper, and therefore, it is not related to the calculated ground state Bader valence charge. The relaxation process in the final state is dominated by the local screening mechanism, which involves an electron transfer from the nearest-neighbour ligands toward the spatially contracted 3d orbitals of the core-ionized Cu (II) ion. 相似文献
19.
Simion Coca Krzysztof Matyjaszewski 《Journal of polymer science. Part A, Polymer chemistry》1997,35(16):3595-3601
A general method for the transformation of “living” carbocationic into “living” radical polymerization, without any modification of chain ends, is reported for the preparation of ABA block copolymers. For example, α,ω-difunctional polyisobutene, capped with several units of styrene, Cl-St-PIB-St-Cl, prepared cationically (Mn = 7800, Mw/Mn = 1.31) was used as an efficient difunctional macroinitiator for homogeneous “living” atom transfer radical polymerization to prepare triblock copolymers with styrene, PSt-PIB-PSt (Mn = 28,800, Mw/Mn = 1.14), methyl acrylate, PMA-PIB-PMA (Mn = 31,810, Mw/Mn = 1.42), isobornyl acrylate, PIBA-PIB-PIBA (Mn = 33,500, Mw/Mn = 1.21), and methyl methacrylate, PMMA-PIB-PMMA (Mn = 33,500, Mw/Mn = 1.47). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3595–3601, 1997 相似文献
20.
Dr. Israel Fernández Dr. Nicole Holzmann Prof. Gernot Frenking 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14194-14210
Quantum chemical calculations of the alkaline-earth oxides, imides and dihydrides of the alkaline-earth atoms (Ae=Be, Mg, Ca, Sr, Ba) and the calcium cluster Ca6H9[N(SiMe3)2]3(pmdta)3 (pmdta=N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) have been carried out by using density functional theory. Analysis of the electronic structures by charge and energy partitioning methods suggests that the valence orbitals of the lighter atoms Be and Mg are the (n)s and (n)p orbitals. In contrast, the valence orbitals of the heavier atoms Ca, Sr and Ba comprise the (n)s and (n−1)d orbitals. The alkaline-earth metals Be and Mg build covalent bonds like typical main-group elements, whereas Ca, Sr and Ba covalently bind like transition metals. The results not only shed new light on the covalent bonds of the heavier alkaline-earth metals, but are also very important for understanding and designing experimental studies. 相似文献