Row Of Periodic Table Research Articles

A rapid screening platform for catalyst discovery in azide–alkyne cycloaddition by ICP-MS/MS

We developed a rapid high-throughput screening platform using a modified ICP-MS/MS system for monovalence metal ions catalysts discovery in azide–alkyne cycloaddition. Among the ten monovalence metal ions in the first row of periodic table containing Sc+, Ti+, V+, Cr+, Mn+, Fe+, Co+, Ni+, Cu+, and Zn+, five monovalence metal ions of Sc+, Co+, Ni+, Cu+ and Zn+ ions show relatively stronger catalytic activities than others. The catalytic mechanism of Sc+, Co+ and Ni+ ions is similar to the Cu+ ions, but Zn+ ions take a different catalytic route. A yields range of 77–98% for azide-alkyne cycloaddition was achieved with Sc+, Co+, Ni+, Cu+ and Zn+ ions as catalyst, respectively by using a UV laser ablation reactor in 20min, notable that the yields of Co+ and Sc+ ions were even higher than the common catalyst of Cu+ ions. The proposed platform would be used not only for catalyst discovery in azide-alkyne cycloaddition, but also for the discovery of single atom/ion catalysts in other organic reactions.

The 4s and 3d subshells: Which one fills first in progressing through the periodic table and which one fills first in any particular atom?

In this paper, first we discuss an old problem in teaching electron configuration of transition metals and the order in which the orbitals are filled. Then we propose two simple computational experiments, in order to show that in the case of first row transition metals and the main group elements after them, the electrons occupy the 3d subshell before the 4s. It is shown that if we begin with the bare nucleus of above elements in the vacuum and then continue with adding the electrons the 19th electron firstly occupies the 3d subshell and not the 4s. Indeed, the 4s subshell in the third row of periodic table only fills first in the case of K and Ca atoms. However, the 3d subshell in transition metals and the main group elements after them is more stable than 4s and so fills first. Thus there is no scientific reason to write the electron configuration of transition elements as [Ar] 4s 3d and the correct form is [Ar] 3d 4s.

Bond length estimates for oxide crystals with a molecular power law expression

A molecular power law bond length regression expression, R(M–O) = 1.39(s/r)−0.22, defined in terms of the quotient, s/r, where s is the averaged Pauling bond strength for the bonded interaction comprising a given molecular coordination polyhedron and r is the periodic table row number for the M atom, serves to replicate the bulk of the 470 individual experimental M–O average bond lengths estimated with Shannon’s (Acta Crystallogr A 32(5):751–767, 1976) crystal radii for oxides to within 0.10 A. The success of the molecular expression is ascribed to a one-to-one deep-seated connection that obtains between the electron density accumulated between bonded pairs of atoms and the average Pauling bond strength. It also implies that the bonded interactions that constitute oxide crystals are governed in large part by local forces. Although the expression reproduces the bond lengths involving rare earth atoms typically to within ~0.05 A, it does not reproduce the lanthanide ionic radius contraction. It also fails to reproduce the experimental bond lengths for selected transition cations like Cu1+, Ag1+ and VILSFe2+ and for cations like IVK+, VIBa2+ and IIU6+.

High‐temperature mass spectrometric determinations of relative ionization cross‐sections of gaseous TiO, TiO2, VO, VO2, YO, HfO and GeO molecules

Accurate values of electron ionization cross-sections of high-temperature vapor species are of importance in mass spectrometric investigations as well as in a variety of other fields. However, the present experimental techniques are subject to many inherent difficulties or are limited in applicability and so far have yielded relatively few reliable values. Theoretical calculations are not sufficiently accurate. So the need for experimental ionization cross-section data for these species is very important. Measurements were performed by high-temperature Knudsen effusion mass spectrometry with a MS-1301 mass spectrometer. Vaporization was carried out using molybdenum effusion cells containing samples of pure Au, V2O3, Ti3O5, GeO2 and Y2O3-HfO2 systems. The VO, VO2, TiO, TiO2, YO, HfO and GeO vapor species were identified over the samples studied. The partial pressures of Au and the oxides were measured by a complete isothermal vaporization method. The relative ionization cross-sections σ(Au)/σ(i) were determined for the gaseous oxides studied. The results were compared with the literature data. The inapplicability of the 'additivity rule' is shown. This finding is in good agreement with a tendency to changing ionization cross-sections in the Periodic Table row of gaseous M, МО and МО2 species.

A comparison of two-component and four-component approaches for calculations of spin-spin coupling constants and NMR shielding constants of transition metal cyanides

Relativistic density functional theory (DFT) calculations of nuclear spin-spin coupling constants and shielding constants have been performed for selected transition metal (11th and 12th group of periodic table) and thallium cyanides. The calculations have been carried out using zeroth-order regular approximation (ZORA) Hamiltonian and four-component Dirac-Kohn-Sham (DKS) theory with different nonrelativistic exchange-correlation functionals. Two recent approaches for representing the magnetic balance (MB) between the large and small components of four-component spinors, namely, mDKS-RMB and sMB, have been employed for shielding tensor calculations and their results have been compared. Relativistic effects have also been analysed in terms of scalar and spin-orbit contributions at the two-component level of theory, including discussion of heavy-atom-on-light-atom effects for (1)J(CN), σ(C), and σ(N). The results for molecules containing metals from 4th row of periodic table show that relativistic effects for them are small (especially for spin-spin coupling constants). The biggest effects are observed for the 6th row where nonrelativistic theory reproduces only about 50%-70% of the two-component ZORA results for (1)J(MeC) and about 75% for heavy metal shielding constants. It is important to employ a full Dirac picture for calculations of heavy metal shielding constants, since ZORA reproduces only 75%-90% of the DKS results. Smaller discrepancies between ZORA-DFT and DKS are observed for nuclear spin-spin coupling constants. No significant differences are observed between the results obtained using mDKS-RMB and sMB approaches for magnetic balance in four-component calculations of the shielding constants.

Theoretical study on H2 elimination pathways of silylenoid H2SiLiF with CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl

Ab initio molecular orbital calculations have been performed to explore the reaction potential energy surfaces of silylenoid H2SiLiF with XH n hydrides, where XH n = CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H2SiLiF + H-XH n − 1 → H n XSiLiF + H2, which involves H2 elimination following the initial formation of an association complex via a four-membered ring transition state to form the substituted three-membered ring silylenoid H n XSiLiF and a H2 molecule. This theoretical calculations suggest that (i) for H2 eliminations there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in periodic table, and (ii) for the second-row hydrides, the H2 elimination reactions are less exothermic than for the first-row hydrides and the reaction barriers are lower for X–S and Cl. Compared to the insertions of H2SiLiF into XH n , the H2 elimination pathways should be unfavorable with higher barrier and lower exothermic.

Optimum valence bond scheme: theoretical study of small clusters of elements in the second and third row of periodic table

Using optimum valence bond scheme which reduces the computation effort, we study systematically the properties of the critical structures (critical points) of small clusters (up to four atoms) of elements in the second and third row of the periodic table. We also show the evolution process of the clusters from two atoms to four atoms. By examining the electronic structures of all clusters, we can understand why the four-atom clusters for specific elements can have three-dimensional structures with Td symmetry. More interestingly, comparing the variation of the binding energy of such small clusters with the melting points and boiling points of corresponding pure element materials, we can understand the effect of the critical structures in the melting and boiling processes.

A physical basis for Pauling's definition of bond strength

The average strength, s, of the bonded interactions comprising a cation containing oxide anion coordination polyhedron and the value of the electron density, ρ(r c ), at the bond-critical points are inversely correlated with bond length. In each case, the observed bond lengths, R, were modeled with power-law expressions defined in terms of s/r and ρ(r c )/r, respectively, where r is the Periodic Table row number of the cation involved in the bonded interaction. On the basis of the close connection between bond strength and the value of the electron density at the bond-critical point, we conclude that bond strength is a direct measure of bond type; the greater its value, the greater the localization of electron density in the binding region and the greater the shared–electron covalent character of the bonded interaction.

Quantification of the various contributors to rate enhancement in nucleophilic strain releasing reactions.

Since cyclopropanes are much more reactive than cyclobutanes despite their nearly identical strain energy, it has become clear that rate enhancement in cyclopropanes is partly due to strain release but also partly due to an additional factor about whose nature there is no consensus. Activation and equilibrium energies for a series of nucleophilic reactions of MeO-, MeS-, MeNH-, Me2N-, and MePH- with strained rings ranging from epoxide to aza-cubane were computed at the HF/631 + G* level. Using the Marcus equation, in combination with the computed intrinsic barrier for the identity reactions of the same nucleophiles with the strain free reference compounds (e.g., MeO- with Me-O-Me and Me2N- with Me3N), enabled a quantitative determination of the individual contributions of the partial strain release and the additional factor to the overall lowering of the transition state energy. Analysis of the data reveals the following: (a) There is no contribution of the additional factor to rate enhancement in four membered rings for first row elements (O and N) and only a small contribution (approximately 2 kcal) for second row elements (S and P). This is to be compared with a contribution of 7-17 kcal for three membered rings. (b) A significant synergistic effect is observed. Thus, in housane, for example, the additional factor amounts to 12.7 kcal which is more (by nearly 5 kcal) than the sum of the individual contributions of the isolated three and four membered rings. (c) The magnitude of the additional factor was found to be Periodic Table row dependent.

Electronic structure of dilute Fe1-xPxalloys

New experimental data of lattice constants, residual resistivities and magnetic properties (magnetisations and hyperfine fields at phosphorus and iron atoms) are presented and discussed in relation with the electronic structure of phosphorus as dilute impurity in an iron matrix; most of them are in agreement with the appearance of '3sp' virtual bound states near the Fermi level. The iron hyperfine field values compared with those measured in more concentrated amorphous alloys show in both systems a typical dependence with the number of phosphorus atoms as nearest neighbours. A comparison of the whole data with those obtained for other 'sp' substitutional impurities of the same periodic table row (Al, Si) or column (As, Sb) points out the role played by the valence and the period of impurity on the investigated properties.

Effet de période dans les alliages à base de métaux de transition

The electronic screening around an impurity does not depend only on the impurity excess change but also on the impurity periodic table row. We study this period effect in the transitional alloys ; its origin can be understood by taking into account the stability and the spatial extension of the impurity and matrix «d» atomic orbitals. We extend the classical tight binding calculation for a dilute alloy taking into account these parameters and we calculate the electronic screening around an impurity by a self consistent perturbation method. We show that this period