Analysis of NMR and FT-IR spectra on the bis(substituted cyclopentadienyl)dichlorides of titanium and zirconium
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Electronegativity
Cyclopentadienyl complex
Electronegativity
Formal charge
Effective nuclear charge
Atomic radius
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In this work, we propose a new representative electronegativity scale χDC based on a statistical analysis of 11 electronegativity scales associated with electric ionic resonance energy, ionization potential, electron affinity, polarizability, electric force, average orbital energy, chemical potential, electrochemical reduction potential, and electric potential energy. Among these scales, it is the new PE° electronegativity scale, which relates the reduction potential E° to Pauling's electronegativity scale. The scale χDC gives more weight to the physicochemical factors, which influence the electronegativity, but this scale is not necessarily the best electronegativity scale for the element. This scale is based on (1) the average of the experimental electronegativity values; (2) the proximity of an experimental value to the average given by the difference and the ratio to this average; (3) in critical cases, the periodicity network of the periods and the groups; and (4) the periodicity of the sequence of the ratios of the experimental electronegativity values to the best-selected electronegativity value. We have also taken as probe scales Nagle's, Allred and Rochow's, Allen's (Hoffman's and Politzer's), PE°, Gordy's, and Ghosh's electronegativity scales in order to investigate the trend of the physicochemical factors which influence the electronegativity. With this trend, we have determined zones where a physicochemical property influences the electronegativity more. We have also found that physicochemical perturbations such as the orbital overlap, the stable configurations, the nephelauxetic effect, the width of the band gap, the ligand field stabilization energy, the penetration of the orbitals, and the lattice energy influence the electronegativity. Besides, we have analyzed the exactness of the electronegativity of the scales through the periodical ranking, the chemical tripartite separation among ionic, covalent, or metallic bond (taking into account the amplitude of the metalloid band), and the physicochemical property of bond force. The representative χDC electronegativity scale is the best in periodicity, followed by Batsanov's and Pauling's scales. In the type of chemical bond, the ranking depends on the number and kind of compounds in the sample, but in general, Pauling's, the ARS, and Batsanov's electronegativity scales are the best with a confidence interval of 95%. On the other hand, in the physical bond force, Batsanov's, Pauling's, Mulliken's, Nagle's, Allen's, the ARS, and the χDC electronegativity scales are the best scales. Also, we have considered the free atom and the in situ hypotheses of electronegativity and used the low and high oxidation states to verify these hypotheses. Besides, as an example of the utility of this ranking of scales, we have analyzed the relation of lanthanum La and lutetium Lu to Group 3, lanthanides, and hafnium Hf. We also analyze the vertical, horizontal, Knight's move, and isodiagonal periodicity of the electronegativity and associate this periodicity to a similar chemical-physical behavior of elements or ions.
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Electronegativity values derived from various methods are compared, and a complete electronegativity scale is arranged for all the elements. A chart is given which shows a systematic relation of electronegativity to the periodic system of the elements. A linear relationship is found between electronegativity and the work function of metals.
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The experimental approaches to estimation of comparative electronegativity and chemical hardness of organometallic groups have been proposed. Qualitative data on the electronegativity of L nM groups were obtained from 19F NMR study of model systems 4-FC6H4QMLn (Q = CC, N(R), O, C(O)O, S), (4-FC6H4)3 SnML n and (4-FC6H4)3SnQML n (Q = O, S), containing a great variety of different organometallic groups containing transition or heavy main-group metals. The data on chemical hardness of L nM groups were obtained from NMR study of distribution of different L nM groups between hard and soft anions. The following basic results have been obtained. (1) The relative electronegativity and chemical hardness of L nM groups can change in parallel or not with the electronegativity and hardness of the central metal atom. (2) The substituents in Ar can substantially modify electronegativity and hardness of Ar nM groups; the influence of Ar groups has an inductive nature; the increase in electron-donating ability of aryl ligands enhances the hardness of Ar nM cations. (3) The relative electronegativity and hardness of L nM groups in L nMX are invariant and do not depend on X.
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Cyclopentadienyl complex
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According to the principle of electronegativity equilibrium,we revised the formula for gradual sum even way to calculate electronegativities of groups,and calculated some often-used electronegativities of groups by the revised formula in this paper.The calculated results not only conform very much to the several scales of group electronegativities which are widely accepted,but also can distinguish electronegativities of symmetrical groups(-XY and-YX),indicating regular changes.
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Although for most elements the Pauling electronegativity varies only slightly from one compound to another (assuming constant oxidation number), for oxygen there is enormous variation. For binary oxides, MyOz, where the oxidation number of M corresponds to a noble-gas electronic configuration, e.g. as in Na2O, MgO or P2O5 but not As2O3 or MnO, the electronegativity of oxygen, xo, depends upon the electronegativity of M, xM, according to: xo= 4.1 –xM–0.25//0.86. This relationship is shown to be in accordance with electronegativity, xo, decreasing as the negative charge on oxygen increases. It also accounts for smaller than expected electronegativity differences, xo–xM, when M is a highly electropositive element such as an alkali metal.
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Infrared spectroscopy has been used to study a series of synthetic agardite minerals. Four OH stretching bands are observed at around 3568, 3482, 3362, and 3296 cm −1 . The first band is assigned to zeolitic, non-hydrogen-bonded water. The band at 3296 cm −1 is assigned to strongly hydrogen-bonded water with an H bond distance of 2.72 A. The water in agardites is better described as structured water and not as zeolitic water. Two bands at around 999 and 975 cm −1 are assigned to OH deformation modes. Two sets of AsO symmetric stretching vibrations were found and assigned to the vibrational modes of AsO 4 and HAsO 4 units. Linear relationships between positions of infrared bands associated with bonding to the OH units and the electronegativity of the rare earth elements were derived, with correlation coefficients >0.92. These linear functions were then used to calculate the electronegativity of Eu, for which a value of 1.1808 on the Pauling scale was found.
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A new scale of electronegativity is designed on the basis of the environment independent absolute radii of atoms. In this scale, the electronegativity is an intrinsic free-atom property and the basis of assumption is quantum mechanically viable. The qualitative relation between the size and electronegativity is relied upon and a quantitative general formula of evaluation of electronegativity in terms of the absolute radii of atoms is suggested as χ = a × (1/R)+ b, where χ is electronegativity and R is absolute radius of atoms, a and b are two constants determined by least square fitting for each period of elements separately. A number known as electronegativity is computed for each 103 elements of periodic table through the above formula and the unit assigned to χ is energy. The new scale of electronegativity is found to observe the simple rules that all the scales of electronegativity must obey. The evaluated scale reproduces the silicon rule where the electronegativities of the eight elements of metalloid group are very close to each other and the electronegativity of silicon atom is smallest of the group. A striking feature of the new scale is that the electronegativity of N atom is greater than that of Cl atom. The characteristic properties of chalcogens and transition metal atoms have been nicely correlated in terms of the computed values of χ of such elements. The evaluated electronegativities of the elements beautifully exhibit the periodic behaviour of periods and groups of the Periodic Table. The revealed internal consistencies suggest that the present effort of introducing a scale of electronegativity based on absolute radius of atoms is largely successful.
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