Rapid Evaluation of Individual Hydrogen Bonding Energies in Linear Water Chains

A model is proposed to rapidly evaluate the individual hydrogen bonding energies in linear water chains. We regarded the two O--H bonds of a water molecule as two dipoles. The magnitude of the O--H bond dipole mo- ment can be varied due to the other water molecules＇ presence. An analytic potential energy function, which explicitly contains the permanent dipole-dipole interactions, the polarization interactions, the van der Waals interactions and the covalent interactions, was therefore established. The individual hydrogen bonding energies in a series of linear water chains were evaluated via the analytic potential energy function and compared with those obtained from the CP-corrected MP2/aug-cc-pVTZ calculations. The results show that the analytic potential energy function not only can produce the individual hydrogen bonding energies as accurately as the CP-corrected MP2/aug-cc-pVTZ method, but is very efficient as well, demonstrating the model proposed is reasonable and useful. Based on the individual hy- drogen bonding energies obtained, the hydrogen bonding cooperativity in the linear water chains was explored and the natures of the hydrogen bonding in these water chains were discussed.     

Tb3+离子4f75d组态能级的电子云扩大效应

研究了电子云扩大效应对Tb3+离子5d能级的影响. 利用光谱理论, 将电子云扩大效应比率β同Tb3+离子4f75d组态的自旋允许和禁阻跃迁能级的能级差联系起来, 通过复杂晶体化学键理论确定了化学键的共价性、 相应键体积极化率以及配体离子的有效电荷与β的线性关系, 同时得到了对β有影响并与Tb3+离子自身相关的因子.     

共价和极化对119Sn、129I穆斯堡尔谱位移的影响

利用化学键的介电理论研究了119Sn、 129I穆斯堡尔谱同质异能位移,发现由共价性fcμ和极化率αLμ定义的化学环境因子h与穆斯堡尔谱同质异能位移δ存在线性关系：δ=δ0+bh, h=(μαLμfcμ）1/2。     

Spectroscopic and antimicrobial studies of La, Pr, Nd and Gd complexes of a dipodal [N,N,N] chelating ligand

The lanthanide complexes of bis(benzimidazole-2′-yl-methyl)amine (BImz) having molecular formula [M(BImz)X₃H₂O]·nH₂O (M = La, Pr, Nd, or Gd; X = Cl or ClO₄ and n = 1, 2 or 3) were prepared and characterized spectroscopically through IR, ¹H and ¹³C NMR, FAB-mass, UV–visible and luminescence spectroscopy. TGA data suggested presence of coordinated and the lattice water. The oscillator strengths of the f–f transitions and the covalency parameters (β, b^1/2 and δ) have been evaluated from the electronic spectral data. The proposed hepta-coordinate geometry for the complexes has been ascertained from the molecular model computations. CV studies indicate formation of a stable quasi-reversible redox couple Gd^III/IV in the solution. The in vivo antimicrobial activities of the complexes have been evaluated against gram +ve and gram −ve bacteria and fungi.     

Correlation in the lanthanide series

Summary The correlations lgK vs. lgK,V vs.V (K - stability constant of the complex,V - unit cell volume of compound) within the lanthanide tetrads were reviewed. Ligands with -C = N-group were found to show a positive deviation from the lgK vs. lgK plot.

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Korrelation in der Lanthanidenserie

Zusammenfassung Es wurden die Korrelationen lgK gegen lgK undV gegenV (wobeiK die Stabilitätskonstante des Komplexes ist undV das Einheitszellenvolumen) innerhalb der Lanthanidentetraden untersucht. Bei Liganden mit -C = N-Gruppen wurde eine positive Abweichung von von der lgK - lgK-Geraden festgestellt.

     

Comparison of optical properties and crystal structures of the praseodymium and europium chloroderivatives of acetates

The praseodymium and europium dichloroacetates were obtained in the form of monocrystals. Crystal structures of the Ln(HCl₂CCOO)₃·2H₂O (Ln=Pr, Eu) compounds were determined by X-ray analysis. Both crystals proved to be isomorphous. They are monoclinic, space group P2₁/n with: a=9.747(6), b=13.857(7), and c=23.595(9) Å, β=95.03(4)°, U=3175(3) Å³, Z=8 for C₆H₇Cl₆O₈Pr and a=9.634(7), b=13.757(11), and c=23.524(14) Å, β=94.84(4)°, U=3107(4) Å³, Z=8 for C₆H₇Cl₆O₈Eu. There are two symmetry independent lanthanide cations, which adopt a nine-coordinate geometry with seven oxygen atoms from carboxylate groups and two oxygen atoms from water molecules. Absorption (Pr³⁺, Eu³⁺), emission and emission excitation (Eu³⁺) spectra of single crystals of Ln(HCl₂CCOO)₃·2H₂O were recorded at room temperature and low temperatures down to 4.2 K. Spectral intensities of the investigated systems are parametrized in terms of the Judd–Ofelt theory and compared to those of lanthanide trichloroacetates and acetates crystals. The relationship between the hypersensitivity and covalency is discussed. The nephelauxetic ratio β and Sinha's parameter δ are calculated based on the absorption spectra. The variation of these parameters and their correlation with the nature of metal–ligand bond is discussed. The bond polarity and bond strength of coordination complex determine the activity and stereospecifity of the catalyst thus the study of these properties are very important because of the application of lanthanide carboxylates as precursors of catalysts. The spectroscopic results are correlated with those from the crystal structure studies, especially with Ln–O distances and the co-ordinating forms of the carboxylate ions. The vibronic coupling in the f–f transitions were analysed. In order to determine the vibronic coupling quantitatively, calculations of the R=I_VIB./I_0-phonon rates were performed from the low temperature absorption spectra. The correlation between the vibronic coupling and covalency is analysed.     

EMR and optical study of Mn2+ doped potassium trihydrogen selenite

The EMR study of Mn2+ doped potassium trihydrogen selenite is performed and the site of Mn2+ in the lattice is discussed. The zero field parameters providing good fit to the observed EMR spectra are estimated. The spin-Hamiltonian parameters g, A, B, D, and a are (2.0003 +/- 0.0002), (31 +/- 2) x 10(-4), (20 +/- 2) x 10(-4), (87 +/- 2) x 10(-4), and (-9 +/- 1) x 10(-4) cm(-1), respectively. The percentage of covalency of the metal-ligand bond is also determined. The optical absorption study suggests the lattice distortion in the crystal. The electron repulsion and crystal field parameters having good fit to the observed optical spectra are evaluated. The band positions are fitted with the Racah parameters (B and C), the cubic crystal field splitting parameters (Dq), and the Trees correction (alpha). The values of B, C, Dq, and alpha are 871, 2967, 670, and 76 cm(-1), respectively.