Crystal structure of xenon encapsulate within Na-A zeolite

The positions of Xe atoms encapsulated in the molecular-dimensioned cavitie s of fully dehydrated Na-A have been determined. Na-A was exposed to 1050 a tm of xenon gas at 400 degrees C for seven days, followed by cooling at pre ssure to encapsulate Xe atoms. The resulting crystal structure of Na-A(7Xe) (a = 12.249(1) Angstrom, R-1 = 0.065, and R-2 = 0.066) were determined by single-crystal X-ray diffraction techniques in the cubic space group Pm (3) over bar m at 21(1) degrees C and 1 atm. In the crystal structure of Na-A( 7Xe), seven Xe atoms per unit cell are distributed over four crystallograph ically distinct positions: one Xe atom at Xe(1) lies at the center of the s odalite unit, two Xe atoms at Xe(4) are found opposite four-rings in the la rge cavity, and four Xe atoms, two at Xe(2) and others at Xe(3), respective ly, occupy positions opposite and between eight- and six-rings in the large cavity. Relatively strong interactions of Xe atoms at Xe(2) and Xe(3) with Na+ ions of four-, eight-, and six-rings are observed: Na(1)-Xe(2) = 3.09( 6), Na(2)-Xe(3) = 3.11(2), and Na(3)-Xe(2)= 3.37(8) Angstrom. In each sodal ite unit, one Xe atom is located at its center. In each large cavity, six X e atoms are found, forming a distorted octahedral arrangement with four Xe atoms, at equatorial positions teach two at Xe(2) and Xe(3) and the ether t wo at axial positions (at Xe(4)). With various reasonable distances and ang les, the existence of (Xe)6 cluster is proposed (Xe(2)Xe(3) = 4.78(6) and 4 .94(7), Xe(2)-Xe(4) = 4.71(6) and 5.06(6), Xe(3)-Xe(4) = 4.11(3) and 5.32(4 ) Angstrom, Xe(2)Xe(3)-Xe(2)= 93(1), Xe(3)-Xe(2)-Xe(3)= 87(1), Xe(2)-Xe(4)- Xe(2)= 91(4), Xe(2)-Xe(4)-Xe(3) = 55(2), 59(1), 61(1), and 68(1), and Xe(3) -Xe(4)-Xe(3) = 89(1)degrees). These arrangements of the encapsulated Xe ato ms in the large cavity are stabilized by alternating dipoles induced on Xe( 2), Xe(3), and Xe(4) by eight- and six-ring Na+ ions as well as four-ring o xygens, respectively.