Host-guest structural architectures in hydrous alkaline (Li, K) uranyl chromates and dichromates

Abstract

Two new (Cr2O7)2− and/or (CrO4)2− containing uranyl compounds with K and Li: [K10(Cr2O7)2(H2O)2]|(UO2)(CrO4)4| (1) and |Li2(H2O)5|[(UO2)(CrO4)2] (2) were obtained via two various synthesis routes in the K2Cr2O7–CrO3–(UO2)(NO3)2·6H2O–H2O (1) and LiCl–CrO3–(UO2)(NO3)2·6H2O (2) systems. The key feature of the crystal structure of 1 is the formation of hydrous potassium dichromate [K10(Cr2O7)2(H2O)2]6+ 2D units acting as hosts for guest |(UO2)(CrO4)4|6− clusters. (Cr2O7)2− groups are not bonded via common oxygen atoms to (UO2)2+ in 1 which is the first example of such structural architecture in uranyl oxysalts with tetrahedral TO4 (T=Si4+, As5+, P5+, Cr6+, etc.) anions. In the structure of 2, UrO5 and CrO4 coordination polyhedra share corners to produce [(UO2)(CrO4)2]2− layers with |Li2(H2O)5|2+ tetramers guest species in the interlayer.