Uranyl complexes as scaffolding or spacers for cucurbit[6]uril molecules in homo- and heterometallic species, including a uranyl-lanthanide complex

The reaction of uranyl nitrate with cucurbit[6]uril (CB6) and carboxylic or sulfonic ligands under hydrothermal conditions and in the presence of additional metal cations (K^I or Ce^III) or cosolvents provided four complexes, which were crystallographically characterized. The compound [(UO₂)₂K₂(CB6)(adc)₂(NO₃)₂(H₂O)₂].5H₂O (1), where H₂adc is 1,3-adamantanedicarboxylic acid, crystallizes in the form of a central K₂(CB6)²⁺ column surrounded by two one-dimensional (1D) polymeric UO₂(adc)(NO₃)^- chains attached to the column by nitrate bridges, with a perfect match of the repeat lengths in the two subunits. The longer 1,3-adamantanediacetic acid (H₂adac) gives the complex [(UO₂)₂(adac)₂(HCOOH)₂].CB6.6H₂O (2), in which the 1D uranyl-containing polymer and columns of CB6 molecules form a layered arrangement held by weak CH..O hydrogen bonds. The complex formed with the dipotassium salt of methanedisulfonic acid (K₂mds), [(UO₂)₂K₂(CB6)(mds)₂(OH)₂(H₂O)₈].4H₂O (3), is a 1D polymer, in which K₂(CB6)²⁺ units are connected to one another by doubly hydroxide-bridged uranyl dimers in which the disulfonates are terminal, chelating ligands; connection between the two subunits is solely through potassium oxo-bonding to uranyl. The complex [(UO₂)₂Ce₂(CB6)(C₂O₄)₃(NO₃)₄(H₂O)₆].2H₂O (4) is a 1D polymer containing bridging oxalate ligands formed in situ, in which CB6 is coordinated to the lanthanide cations only; one nitrate ligand and one water ligand, hydrogen-bonded to each other, are included in the CB6 cavity, with the possible occurrence of interactions between nitrate oxygen atoms and ureido carbon atoms. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)