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Crown Ethers and Their Alkali Metal Ion Complexes as Assembler Groups in Uranyl–Organic Coordination Polymers with cis-1,3‑, cis-1,2‑, and trans-1,2-Cyclohexanedicarboxylates

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journal contribution
posted on 2018-03-26, 00:00 authored by Pierre Thuéry, Youssef Atoini, Jack Harrowfield
Alkali metal cations (Na+, K+) and crown ether molecules (12C4, 15C5, 18C6) were used as additional reactants during the hydrothermal synthesis of uranyl ion complexes with cis/trans-1,3-, cis-1,2- and trans-1,2-cyclohexanedicarboxylic acids (c/t-1,3-chdcH2, c-1,2-chdcH2, and t-1,2-chdcH2, respectively, the latter as racemic or pure (1R,2R) enantiomer). Oxalate anions generated in situ are present in all the six complexes isolated and crystallographically characterized, [(UO2)2(c-1,3-chdc)2(C2O4)]­[UO2(H2O)5]·(12C4)·2H2O (1), [(UO2)4Na2(c-1,2-chdc)2(C2O4)3(15C5)2] (2), [(UO2)4K2(c-1,2-chdc)2(C2O4)3(18C6)1.5(H2O)1.5] (3), [(UO2)12K5(R-t-1,2-chdc)4(C2O4)10(18C6)5(OH)­(H2O)3]·4H2O (4), [(UO2)12K5(rac-t-1,2-chdc)4(C2O4)10(18C6)5(OH)­(H2O)3]·4H2O (5), and [(UO2)8K4(rac-t-1,2-chdc)4(C2O4)6(18C6)3(H2O)2] (6). In complex 1, the [UO2(H2O)5]2+ counterions link the ladderlike uranyl-containing one-dimensional polymers and the uncomplexed crown ether molecules through hydrogen bonds. In all the other complexes, two-dimensional uranyl/chdc/oxalate subunits are formed, with topologies depending on the stoichiometry, in which the 1,2-chdc2– ligands are bound to three uranium atoms, one of them chelated by the two carboxylate groups, and the oxalate ligands are bis-chelating. In complex 2, the Na­(15C5)+ cations are bound to one layer through double Na-carboxylate or Na-oxo cis-bonding and they are thus mere decorating groups. In contrast, the quasi-planar K­(18C6)+ groups in 36, partially affected by disorder, are generally trans-coordinated to two uranyl oxo groups pertaining to different layers, thus uniting the latter into a three-dimensional framework.

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