Mixed-ligand coordination of the (UO2)2+ cation and apophyllite topology of uranyl chlorochromate layer in the structure of ((CH3)2CHNH3)[(UO2)(CrO4)Cl(H2O)]

Addition of the Cl- anions to the synthesis mixture stabilizes specific structures of uranyl complexes which results in new compounds with the unprecedented structural topologies. ((CH3)(2)CHNH3)[(UO2)(CrO4) center dot Cl(H2O)] is a new member of the small family of compounds based upon the Ur(XmOn)(5) (X = Cl, Br, I) bipyramids. The structure is based upon uranyl chloride chromate layers that alternate with the layers of protonated amine molecules. The layers contain UrClO(4) pentagonal bipyramids that share three of its equatorial corners with CrO4 tetrahedra. Topological analysis shows that the [(UO2)(CrO4)Cl(H2O)](-) layer belongs to the same topology of interpolyhedral linkage as in alpha-UO2MoO4(H2O)(2). This type of topology (linkage of 4-membered rings creating 8-membered rings) is known in silicate crystal chemistry as the topology of the [Si4O10] layers in the minerals of the apophyllite group. Their linkage via various intermediate units results in a large family of open-framework and pillared silicates.