Open-framework and microporous vanadium silicates

A series of novel vanadium silicates with open-framework and microporous structures has been synthesized under mild hydrothermal conditions. Ten distinct framework types have been identified that all have structures based on cross-linking single silicate sheets with square pyramidal V(IV)O(5) units to give compounds with the general formula A(r)[(VO)(s)(Si(2)O(5))(p)(SiO(2))(q)].tH(2)O, where A is Na, K, Rb, Cs, or a combination. The vanadosilicate (VSH-n) structures have free channel diameters up to 6.5 A and show good thermal stability, absorption, and ion-exchange properties, suggesting their potential for technological applications as molecular sieves or in catalysis.     

Synthesis, structure and properties of CsHSi3O7, a layered silicate with a chiral structure

The chiral layered silicate CsHSi₃O₇ has been synthesized by hydrothermal techniques, and its structure determined by single crystal X-ray diffraction. The compound crystallizes in the space group P2₁2₁2₁. The silicate single layer consists of both four- and three-connected SiO₄ tetrahedra and may be considered as a member of a series of layer structures with the general formula (Si₄O₉)_m(Si₂O₅)_n. Strong hydrogen bonds occur between the terminal OH⁻ and O²⁻ ions of neighboring layers. The Cs⁺ cations can be ion-exchanged by protons to give a phase of composition H₂Si₃O₇·H₂O with a water molecule occupying the original Cs position, as confirmed by single crystal X-ray diffraction data. The water molecule in H₂Si₃O₇·H₂O can be readily removed without collapse of the crystal structure. Both CsHSi₃O₇ and H₂Si₃O₇·H₂O show SHG (second harmonic generation) efficiencies comparable to that of quartz, and both are not phase-matchable materials.     

双氮桥式配体双核铑(d7—d7)络合物与氯代烃光化学氧化反应的研究

本文首次报导了双氮桥式配体双铑(d~-—d~7)络合物Rh_2L_4在可见光辐照下与氯代烃发生光化学反应。四种络合物的量子产率皆具有波长依赖性并与溶剂和轴向配体的性质有关。光化学反应产物经快速原子质谱和闪光光解法鉴定。另外, 将光化学反应产物和电解产物进行了ESR和循环伏安法的对比测定。结果表明, 标题络合物与氯代烃发生不可逆的一电子光诱导转移反应, 生成Rh_2L_4Cl。     

Hydrothermal synthesis and structures of the novel niobium phosphates [NbOF(PO4)](N2C5H7) and [(Nb0.9V1.1)O2(PO4)2(H2PO4)](N2C2H10)

Two new niobium phosphates were synthesized and their crystal structures determined from single-crystal X-ray data. [NbOF(PO₄)](N₂C₅H₇) (1) (monoclinic, space group P2₁/c, a=11.442(1), b=9.1983(7), c=9.1696(8) Å, β=109.94(1)°) has a layered structure and is the first example of a negatively charged NbOF(PO₄) layer analogous to the MO(H₂O)PO₄ (M=V, Nb) layers. The layer charge is compensated by interlayer 4-aminopyridnium cations that adopt an unusual arrangement as a consequence of H-bonding and π-π interactions. The interlayer aminopyridnium cations can be exchanged with alkylammonium ions which form bilayers inclined at ∼65° to the NbOF(PO₄) layer. [(Nb_0.9V_1.1)O₂(PO₄)₂(H₂PO₄)] (N₂C₂H₁₀) (2) (orthorhombic, space group Pbca, a=15.821(2),b=9.0295(9),c=18.301(2) Å) has a disordered three-dimensional structure based on NbO(PO₄) layers cross-linked by phosphate tetrahedra, and has a similar structure to the known vanadium analog [V₂O₂(PO₄)₂(H₂PO₄)] (N₂C₂H₁₀).     

周期律的“不规则性”

本文对周期律的“不规则性”及其理论阐释进行了探讨。