Cation directed formation of uranyl phosphonocarboxylates frameworks comprised of cross-linked chains

Three new uranyl phosphonate frameworks with barium or lead were hydrothermally synthesized using phosphonoacetate and phosphonopropionate ligands. The first two frameworks are made up of cross-linked chains that are comprised of uranyl pentagonal bipyramids connected by the three oxygen atoms of the phosphonate tetrahedra. The carboxylates of the ligands bond to the uranyl ions of other chains to form the perpendicular rows that comprise the framework. The third framework is similar to the first, being comprised of interpenetrating chains. However, the longer carbon chain of the phosphonopropionate allows for a less strained packing of the chains. The crystallization of the barium uranyl phosphonate framework was investigated as a function of iron concentration using scanning electron microscopy. The use of iron to grow larger crystals of the phosphonoacetate lead framework is also described. The barium containing framework was found to disassociate in water with the chains disassociating from each other. The top shows scanning electron microscopy images highlighting how the use of Fe(III) as a modulator results in better quality crystals. The bottom shows the chains that comprise the barium framework and how they interweave to make the framework. It is also shown down the channels of the [001] direction. [Display omitted] •Three new M2+ uranyl phosphonate frameworks (M ​= ​Ba, Pb) were synthesized.•The frameworks are made up of interwoven chains connected through the phosphonate.•Iron was used to aid in crystallization of the barium framework.