New organogermanium cations [RGe(OCH2CH2NME2)2]+ with intramolecular N→Ge coordination bonds

New organohalogermanes RGe(OCH₂CH₂NMe₂)₂X (R = Ph, X = I (5); R = Me, X = Cl (6) or I (7)) with an intramolecular N→Ge coordination bond were synthesized. According to the ¹H and ¹³C NMR spectroscopic data, iodides 5 and 7 exist in solution as ionic compounds with the pentacoordinated germanium atom. In solution of compound 4 (R = Ph, X = Cl), there is an equilibrium between the ionic and covalent forms. The equilibrium shifts toward the ionic form with increasing solvent polarity or temperature. In solution, chloride 6 is a covalent compound. The structures and relative stabilities of different isomers of compounds 4–7 were studied by quantum chemical calculations at the density functional level of theory. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 892–900, May, 2007.     

Electronic structures of 4d transition metal monoxides by density functional theory

Bond distances, dissociation energies, ionization potentials and electron affinities of 4d transition metal monoxides from YO to CdO and their positive and negative ions were studied by use of density functional methods B3LYP, BLYP, B3PW91, BPW91, B3P86, BP86, SVWN, MPW1PW91 and PBE1PBE. It was found that calculated properties are highly dependent on the functionals employed, especially for dissociation energy. For most neutral species, pure density functionals BLYP, BPW91 and BP86 have good performance in predicting dissociation energy than hybrid density functionals B3LYP, B3PW91 and B3P86. In addition, BLYP gives the largest bond distance compared with other density functional methods, while SVWN gives shortest bond distance, largest dissociation energy and electron affinity. For the ground state, the spin multiplicity of the charged species can be obtained by ± 1 of their corresponding neutral species.     

Chemical bond in alkali metal sulfates

In the context of the density functional theory of the local electron density the valence and differential density distribution in crystalline sulfates of M₂SO₄ (M is Li, Rb, and Cs) and double sulfates of MLiSO₄ were calculated using the pseudopotential method in the basis set of numerical atomic pseudo-orbitals. It is shown that in lithium sulfate crystallographically inequivalent oxygen atoms are in different charge states and have a different force of chemical bonding with sulfur. Anions are bonded to each other through lithium atoms that form tetrahedral complexes with oxygen. In rubidium sulfates the electron clouds of the anions overlap and chain structures form. Chemical bonding between the anion and the cation has an ionic nature. These features of the electron structure manifest themselves in double sulfates, where LiO₄ complexes that link the anionic chains also form, and heavy metals serve as cations.     

Non planar silylium, germylium and stannylium ions

Quantum mechanical calculations at the B3LYP/6-311+G(d,p) and MP2/6-311+G(d,p) level of theory reveal that higher congeners of the aromatic imidazolium ion, e.g. 2-E-imidazolium ions (E = Si, Ge, Sn), adopt either planar or pyramidal structures, depending on the substituent R ² attached to the element and on the group 14 element itsself. In the case of 2-silaimidazolium ions chemically significant energy differences in favour of non-planar cations are predicted only for strongly σ-electron withdrawing substituents R ² such as F or CF₃. The pyramidalization computed for the germanium and tin analogues are however significant for all investigated substituents R ² and are accompanied by a substantial stabilization compared to the corresponding planar structures. A detailed bonding analysis reveals that the non-planar cations are best described as complexes of monovalent group 14 element cations R ²E⁺ with the diazabutadiene ligand.     

Elucidating the mechanism for the reduction of nitrite by copper nitrite reductase--a contribution from quantum chemical studies

Density functional methods have been applied to investigate the properties of the active site of copper-containing nitrite reductases and possible reaction mechanisms for the enzyme catalysis. The results for a model of the active site indicate that a hydroxyl intermediate is not formed during the catalytic cycle, but rather a state with a protonated nitrite bound to the reduced copper. Electron affinity calculations indicate that reduction of the T2 copper site does not occur immediately after nitrite binding. Proton affinity calculations are indicative of substantial pK(a) differences between different states of the T2 site. The calculations further suggest that the reaction does not proceed until uptake of a second proton from the bulk solution. They also indicate that Asp-92 may play both a key role as a proton donor to the substrate, and a structural role in promoting catalysis. In the D92N mutant another base, presumably a nearby histidine (His-249) may take the role as the proton donor. On the basis of these model calculations and available experimental evidence, an ordered reaction mechanism for the reduction of nitrite is suggested. An investigation of the binding modes of the nitric oxide product and the nitrite substrate to the model site has also been made, indicating that nitric oxide prefers to bind in an end-on fashion to the reduced T2 site.     

Theoretical study on the intramolecular proton transfer reactions of 3-methyl-5-hydroxyisoxazole and its water complexes

The optimized structures and proton transfer reactions of 3-methyl-5-hydroxyisoxazole and its water complexes (3-M-5-HIO · (H₂O)_n · (n = 0–3)) were computed at B3LYP and MP2 theoretical level. The results indicates that 3-M-5-HIO has four isomers (Ecis, Etrans, K1 and K2), and the keto tautomer, and K2 is the most stable isomer in the gas phase. Hydrogen bonding between 3-M-5-HIO and the water molecules can dramatically lower the barrier by the concerted transfer mechanism. Ecis · (H₂O)₃ → K1 · (H₂O)₃ and Ecis · (H₂O)₂ → K2 · (H₂O)₂ is found to be very efficient. Comparing with the proton transfer mechanism of 5-HIO shows that the methyl substitution prevents the intramolecular proton transfer.     

Methyl hydrogen peroxide dimer: A structural study

Methyl hydrogen peroxide (MHP) exhibits a tendency to form a stable dimer by hydrogen-bonding. Ab initio theoretical investigations on methyl hydrogen peroxide dimer (MHPD) carried out herein lead to several energetically stable structures that have a direct bearing on the reactivity of the monomer in terms of its molecular electrostatic potential (MESP). To gauge the role played by the electron-correlation in lending stability to MHP and its dimer, we employ the density functional theory (DFT) (as implemented by B3LYP-functional), and subsequently second order Møller-Plesset (MP2) perturbation theory, using the basis sets 6-31G(d, p) and 6-311++G(2d, 2p). Simulated infra-red vibrational spectra lead to spectral intensity redistribution upon dimerization. Energetically the lowest MHPD is endowed with inversion symmetry and has two hydrogen bonds, while three other structures emerge: one energetically very close with two H-bonds, and the two others, with three H-bonds each, yet higher by about 2 kcal mol⁻¹.     

电子亲和势法判断负离子聚合单体的活性

提出了利用不同取代基烯类单体的电子亲和势来判断其负离子聚合反应活性的方法.采用密度泛函理论的B3LYP/6-31G(d)方法优化了不同取代基烯类单体几何构型,在B3LYP/6-311++G(3df,2p)水平上计算了其电子亲和势.通过电子亲和势计算值与文献报道实验数据比较,表明本文采用的计算方法是比较可靠的.结合不同取代基烯类单体的电子亲和势的计算结果,通过与Q-e关系及取代基常数σ数据进行比较表明,电子亲和势可以用来判断不同单体负离子聚合反应的活性高低.     

INVERSE OPALINE STRUCTURE TITANIA PHOTONIC CRYSTALS BY FUNCTIONALLY MODIFIED COLLOIDAL CRYSTALS TEMPLATING

Ordered macroporous titania photonic crystals （PCs） and photonic balls were fabricated by functional modified polymer colloidal crystals. The TiO2 PCs and balls formed through this method exhibit no cracks and lacunae in large areas on their surface and their inner structures.     

基于交叉共轭结构的功能材料

近年来,人们对交叉共轭体系的制备、性能以及理论研究方面产生了极大的兴趣。本文综述了近期国内外在交叉共轭体系研究方面取得的一些最新进展,重点介绍了其在自组装、有机电致发光和离子检测等方面的最新发展动态。最后还对本课题组在交叉型p-n双嵌段寡聚物方面的研究作了详细的介绍,并对一些热点问题作了展望。