Variable dimensionality in the uranium fluoride / 2- methyl-piperazine system: syntheses and structures of ufo-5, 6, and 7; zero, one, and two dimensional materials with unprecedented topologies

摘要

The hydrothermal syntheses and structure of a new series of organically templated U~(1V) materials are presented. The materials, UFO-5 (C_5N_2H_(14))_2(H_3O)U_2F_(13), UFO-6 (C_5N_2H_(14))_2U_2F_(12)H_2O and UFO-7 (C_5N_2H_(14))(H_3O)U_2F_(11), exhibit unprecedented topologies as well as represent 0-D (UFO-5), 1-D (UFO-6), and 2-D (UFO-7) phases. By systematic experimentation and utilizing a composition prism, wherein the reagents including H_2O are dgraphically depicted, we have determined stability regions in which UFO-5, 6, and 7 can be synthesized as phase pure products. In addition, through pH measurements we observe a direct relationship between the acidity of the reaction and the dimensionality of the product. We suggest that the increased acidity facilitates condensation of the molecular uranium units in UFO-5, to produce the 1-D UFO-6 and at higher acidity the 2-D UFO-7.