Highly Kinked Uranyl Chromate Nitrate Layers in the Crystal Structures of A[(UO₂)(CrO₄)(NO₃)] (A = K, Rb)

Abstract

Two first uranyl chromate nitrates, K[(UO 2 )(CrO 4 )(NO 3 )] (1) and Rb[(UO 2 )(CrO 4 )(NO 3 )] (2), were prepared by solid-state reactions and characterized by electron microprobe analysis and singlecrystal X-ray diffraction. The compounds are isotypic [1: monoclinic, P2 1 /c, a = 9.881(5), b = 7.215(4), c = 14.226(6) Å, β = 124.85(3)°, V = 832.3(7) Å 3 ; 2: monoclinic, P2 1 /c, a = 9.804(1), b = 7.359(1), c = 14.269(1) Å, β = 122.048(4), V = 872.6(1) Å 3 ]. The structures of 1

Complex Uranyl Dichromates Templated by Aza-Crowns

“…Each of the eight Cr atoms is tetrahedrally coordinated by four O atoms. CrO4 tetrahedra are distorted with the Cr-O bond lengths varying from 1.562(12) to 1.793 (12) Å. This feature is typical for all previously reported uranyl polychromates [19,20].…”

“…Some strong distortions in several bond-lengths values are due to the instability of grown crystal under X-ray beam. (12) Cr8B-O17 1.682(15) Cr1-O1 1.621(11) Cr5-O20 1.642 (12) Cr8B-O32 1.729 (14) The monoclinic structure of 2 contains two symmetrically independent U 6+ cations also forming linear UO2 2+ ion each coordinated by five oxygen atoms at the equatorial vertices of pentagonal The monoclinic structure of 2 contains two symmetrically independent U 6+ cations also forming linear UO 2 2+ ion each coordinated by five oxygen atoms at the equatorial vertices of pentagonal bipyramids similar to those observed in 1. Water molecules are absent in the coordination sphere of U1 atom in 2, whereas U2 coordination environments are similar to those in 1 with the formation of UO 6 (H 2 O) pentagonal bipyramids ( There are three symmetrically independent U atoms in the triclinic structure of 3 (Table 4), all forming linear uranyl cations equatorially coordinated by five O atoms to form pentagonal bipyramids.…”

“…Uranyl molybdates tend to form framework structures [5] due to the flexibility and broad variation of U-O-Mo bond angles. Uranyl chromates constitute a particularly versatile class among the compounds considered as they exhibit all the features listed above: both mono- [6][7][8][9][10][11][12][13][14][15][16] and bidentate [17][18][19] linkage modes of CrO 4 tetrahedra to UO 7 uranyl bipyramids, formation of corner-sharing tetrahedral chromate polyanions [19][20][21], flexibility and variation of U-O-Cr angles similar to those in uranyl molybdates and formation of framework structures [22], and variability of coordination environments [23][24][25]. The tendency of the CrO 4 2− to form isopolyanions in acidic media leads to formation of structures involving simultaneously several polychromate moieties such as Cr 2 O 7 2− dimers, Cr 3 O 10 2− trimers and Cr 4 O 13 2− tetramers [26].…”

Novel [(UO 2 )O 6 (NO 3 ) n ] ( n = 1, 2) based units in organically templated uranyl compounds

“…However some exceptional examples are known [16]. Crystal chemistry of uranyl nitrates is generally structurally restricted to 0-dimensional finite clusters with some known exceptions [17].…”

Microporous uranyl chromates successively formed by evaporation from acidic solution

“…[23]) framework structures are also known. Uranyl chromates show a great diversity of different 0D, 1D and 2D structures [24][25][26][27][28][29][30][31], but 3D framework structural architectures have remained unknown to date. From a practical point of view, uranyl oxysalt structures with large open spaces possessing channels and cavities are believed to have some potential as materials for sorption, separation or catalysis processes in the actinide industry, or for the management of spent nuclear fuel [32].…”