Crystal structure of partially Pd2+-exchanged zeolite X dehydrated in oxygen at 400 °C.: Formation of linear Pd2O3 clusters proposed to be HO-PdIV-O-PdIV-OH in (Pd2+)14(HOPdOPdOH4+)8(Na+)32-Si100Al92O384

The crystal structure of partially Pd2+-exchanged zeolite X, dehydrated at 400 degrees C in a flowing O-2 stream (a = 24.982(4) Angstrom), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd (3) over bar at 21(1) degrees C. The crystal was first Pd2+-exchanged in a flowing stream of 0.05 M aqueous Pd(NH3)(4)Cl-2 for 3 days. After dehydration at 400 degrees C in flowing oxygen, the crystal was evacuated at 21(1) degrees C and 2 x 10(-6) Torr for 2 h. The structure was refined to the final error indices R-1 = 0.070 and R-2 = 0.051 for the 196 reflections for which I > 2 sigma(I). In this structure, Pd2+ ions are found at four crystallographic sites: Na+ ions fill just one, and nonframework oxygens are found at two. Eight pd(2+) ions and eight O2- 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 Pd2+ ions is octahedrally coordinated by framework oxygens. Sixteen Pd4+ ions at site I' (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 teriminal, 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-IV-O-Pd-IV-OH](4+) clusters with O-Pd-O-Pd-O Linear. Thirty-two Na+ 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 Pd2+ ions at another site I' (Pd-O = 2.371(11) Angstrom) are displaced 1.11 Angstrom from six-ring plane into sodalite cages. About four Pd2+ ions lie at site III' in the supercage (Pd-O = 2.16(5) Angstrom).