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Free keywords:
Palladium, Lead, Oxide hydroxides, Crystal structure, Inert electron pair
Abstract:
New Pb2PdO2(OH)2 and Pb2PdO(OH)4(H2O) were synthesized at ambient conditions from respective KOH alkaline and metal nitrate aqueous feed stocks in high purity and as coarse crystals. The constitutions of the two lead palladates were determined by combined powder neutron and single-crystal X-ray diffraction studies. Both crystal structures exhibit a distinct pseudo symmetry, and settling the true lattice symmetry [Pb2PdO2(OH)2: a = 5.9512(3) Å, b = 5.9479(3) Å, c = 7.9480(2) Å, α = 90.256(4)°, β = 90.392(4)°, γ = 119.694(1)°; Pb2PdO(OH)4(H2O): a = 10.706(2) Å, b = 10.32(1) Å, c = 5.7813(3) Å, α = β = γ = 90°] required to employ high resolution synchrotron powder diffraction data. The combined use of neutron and X-ray diffraction measurement has enabled solving the crystal structure of Pb2PdO2(OH)2 including hydrogen positions. For Pb2PdO(OH)4(H2O) only a high symmetry, heavy atoms (Pb, Pd, O) average structure was determined, since the background in the neutron data was strongly enhanced due to the high amount of incoherently scattering hydrogen atoms and considerable disorder present. The crystal structures feature unprecedent connectivities, however, as expected square-planar coordination of palladium(II) and typical crooked surroundings of lead(II) with the 6s2 lone pair acting as a virtual ligand.
