A microporous potassium vanadyl phosphate analogue of mahnertite: hydrothermal synthesis and crystal structureстатья
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Дата последнего поиска статьи во внешних источниках: 19 октября 2015 г.
Аннотация:The novel phase K 2.5 Cu 5 Cl(PO 4 ) 4 (OH) 0.5 (VO 2 ) · H 2 O was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using low-temperature (100 K)single-crystal synchrotron diffraction data and refined against F 2 to R = 0.035. The compound crystallizes in the tetragonal space group I 4/ mmm , with unit-cell parameters
a = 9.8120(8), c = 19.954(1) Å , V = 1921.1(2) Å 3 , and Z = 4. Both symmetrically independent Cu 2+ sites show elongated square-pyramidal coordination. The V 5+ ions reside
in strongly distorted five-vertex VO 5 polyhedra with 50% occupancy. The structure is based on a 3 D anionic framework built from Cu- and V-centered five-vertex polyhedra
and PO 4 tetrahedra. Channels in the [100] and [010] directions accommodate large K atoms and H 2 O molecules. The compound is a new structural representative of the topology
shown by the lavendulan group of copper arsenate and phosphate minerals. Their tetragonal or pseudotetragonal crystal structures are characterized by two types of 2 D slabs alternating along one axis of their unit cells. One slab, described by the formula [Cu 4 X ( T O 4 ) 4 ] ∞ (where X = Cl, O and T = As, P), is common to all phases, whereas
the slab content of the other set differs among the group members. We suggest interpreting this family of compounds in terms of the modular concept and also consider
the synthetic phase Ba(VO)Cu 4 (PO 4 ) 4 as a simplest member of this polysomatic series.