Crystal Structure of Zeolite X Exchanged with Pb(H) at pH 6.0 and Dehydrated : ((Pb^4+)_14(Pb^2+)_18(Pb_4O_4)_8Si_100Al_92O_384)

다국어 초록 (Multilingual Abstract)

A single crystal of zeolite X was 39% overexchanged with aqueous Pb^2+ at pH 6 0 After dehydration at 420℃ and 2 × 10^-6 Torr, its crystal structure was determined by X-ray diffraction techniques in the cubic space group Fd3- at 21℃ (a = 25 238(5) Å). The structure, Pb_61O_32-Si_100Al_92O_384 per unit cell, was freinde to the final error indices R_1 = 0.080 and R_2 = 0.070 withe 486 reflections for which I > 3σ(Ⅰ) Pb^4+ formed upon evacation at elevated temperature by a reaction which may be written, per unit cell, as 64 Pb^2+ + 36 OH^- → 18 Pb^2+ + 8 Pb_4O_4 + 14 Pb^4+ + 14 H_2 + 4 H_2O. Pb ions occupy three nonequivalent sites. Each of 14 lead ions at site Ⅱis nearly in a six-ring plane where it coordinates to three framework oxygens at 2 32(2) Å and to a nonframework oxygen at 2 24(2) Å, these short distances indicate that these are Pb^4+. Eighteen Pb^2+ ions, also at site Ⅱ, are 2 54(2) Å from three framework oxygens and 2 95(2) Å from a nonframework oxygen. Each sodalite cage is filled by a nearly cubic Pb_4O_4 cluster with Pb^2+ and O^2- ions alternating, the four Pb^2?? ions (32 per unit cell) are at site I', each is 2.67(2) Å from three framwork oxygens and 2 59(3) Å from three nonframework oxygens. Each Pb_4O_4 cube bonds radially via its oxygens through six-rings to four additional lead ions (Pb^2+ and Pb^4+) to give larger cationic clusters, perhaps predominantly of formula [Pb_8O_4]^12+ The 18 Pb^2+ ions which are external to the Pb_4O_4 cubes appear to have axial nonbonding lone pairs which extend into the supercage

목차 (Table of Contents)

• 1.Introduction
• 2.Experimental Section
• 3.Discussion
• 3.References and Notes