초록
The structure of partially $Ag^+$-exchanged zeolite 4A, $Ag_{7.6}Na_{4.4}-A$, vacuum dehydrated at $370^{\circ}C$, has been determined by single-crystal x-ray diffraction techniques in the cubic space group, Pm3m (a = 12.311(1)${\AA}$) at $24(1)^{\circ}}C$. The structure was refined to the final error indices $R_1$ = $R_2$ (weighted) = 0.064 using 266 independent reflections for which $I_0$>$3{\sigma}(I_0)$. Three $Na^+$ ions occupy the 3 8-ring sites, and the remaining ions, 1.4 $Na^+$ and 6.6 $Ag^+$, fill the 8 6-ring sites; each $Ag^+$ ion is nearly in the [111] plane of its 3 O(3) ligands, and each $Na^+$ ion is 0.9${\AA}$ from its corresponding plane, on the large-cavity side. One reduced silver atom per unit cell was found inside the sodalite unit. It was presumably formed from the reduction of a $Ag^+$ ion by an oxide ion of a residual water molecule or of the zeolite framework. It may be present as a hexasilver cluster in 1/6 of the sodalite units, or, most attractively among several alternatives, as an isolated Ag atom coordinated to 4 Ag ions in each sodalite unit to give $(Ag_5)^{4+}$, symmetry 4mm.