Crystal structure of partially Pd{sup 2+}-exchanged zeolite X dehydrated in oxygen at 400 C. Formation of linear Pd{sub 2}O{sub 3} clusters proposed to be HO-Pd{sup IV}-O-Pd{sup IV}-OH in (Pd{sup 2+}){sub 14}(HOPdOPdOH{sup 4+}){sub 8}(Na{sup +}){sub 32}-Si{sub 100}Al{sub 92}O{sub 384}
The crystal structure of partially Pd{sup 2+}-exchanged zeolite X, dehydrated at 400 C in a flowing O{sub 2} stream (a = 24.982(4){angstrom}), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd{bar 3} at 21(1) C. The crystal was first Pd{sup 2+}-exchanged in a flowing stream of 0.05 M aqueous Pd(NH{sub 3}){sub 4}Cl{sub 2} for 3 days. After dehydration at 400 C in flowing oxygen, the crystal was evacuated at 21(1) C and 2 x 10{sup {minus}6} Torr for 2 h. The structure was refined to the final error indices R{sub 1} = 0.070 and R{sub 2} = 0.051 for the 196 reflections for which I > 2{sigma}(I). In this structure, Pd{sup 2+} ions are found at four crystallographic sites: Na{sup +} ions fill just one, and nonframework oxygens are found at two. Eight Pd{sup 2+} ions and eight O{sup 2{minus}} ions fill the 16 double six-oxygen ring (D6R) centers (site I) per unit cell; this interpretation of the electron density at site I behaves well in least-squares refinement. Each of these Pd{sup 2+} ions is octahedrally coordinated by framework oxygens. Sixteen Pd{sup 4+} ions at site I{prime} (Pd-O = 2.103(13){angstrom}) lie in six-ring planes. With the eight oxide ions at site I at central positions and 16 more terminal, they form eight linear O-Pd-O-Pd-O clusters along 3-fold axes per unit cell. Each passes through the center of a D6R and extends into its two adjacent sodalite cavities. Considering bond lengths and charge balance, it is proposed that they are [HO-Pd{sup IV}-O-Pd{sup IV}-OH]{sup 4+} clusters with O-Pd-O-Pd-O linear. Thirty-two Na{sup +} ions fill site II and are recessed 1.03(1){angstrom} into the supercage from the single six-ring plane (Na-O = 2.258(11){angstrom}). About two Pd{sup 2+} ions at another site I{prime} (Pd-O = 2.371(11){angstrom}) are displaced 1.11 {angstrom} from six-ring plane into sodalite cages. About four Pd{sup 2+} ions lie at site III{prime} in the supercage (Pd-O = 2.16(5){angstrom}).
- Research Organization:
- Pusan National Univ. (KR)
- OSTI ID:
- 20026922
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 11; Other Information: PBD: 23 Mar 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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