Varied role of organic carboxylate dizwitterions and anionic donors in mixed-ligand uranyl ion coordination polymers

Abstract

The dizwitterionic dicarboxylate ligands 1,1′-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-4-carboxylate) (pL) and 1,1′-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-3-carboxylate) (mL) have been reacted with uranyl cations under solvo-hydrothermal conditions to generate a series of five complexes containing also additional anionic donors....

Flexible Aliphatic Diammonioacetates as Zwitterionic Ligands in UO22+ Complexes: Diverse Topologies and Interpenetrated Structures

“…We have reported the synthesis and crystal structure of a series of 12 uranyl ion complexes involving the diammonioacetate zwitterionic ligands L1 and L2 associated with diverse coordinating anions, mainly anionic polycarboxylates, and also oxo, hydroxo and chlorido donors. As previously found in families of complexes involving different zwitterions, − combining zwitterionic and anionic polycarboxylates most often gives the desired mixed-ligand species. There are however some anomalies here, with the protonated zwitterion being a simple counterion in 1 , the terephthalate being completely absent in 10 , and, more interestingly, the tendency of 2,5-thiophenedicarboxylate to counteract mixed-ligand behavior through self-sorting, resulting in the remarkably complicated heterointerpenetrated structure seen in complex 11 .…”

“…Overall, the number of complexes involving L1 (9) is much larger than that with L2 (3), which genuinely reflects the more amenable character of the complexes of the former to crystallization, since the same attempts were performed with both. Compared with the zwitterionic dicarboxylates previously used in similar studies, − enhanced flexibility could be expected from L1 and L2, and indeed several conformations have been found for both ligands. Three main geometries are found for L1, extended as in complexes 1 or 4 , kinked and S-shaped as in 3 , 5 and 7 – 9 , and C-shaped as in 11 , the molecule being centrosymmetric in the two former cases (the exceptions being found in 10 and 11 , two complexes containing several inequivalent molecules in different conformations).…”

“…However, we have found recently that one way to obtain the desired mixed-ligand uranyl ion coordination polymers is to use a mixture of anionic and zwitterionic polycarboxylates, in part possibly as a result of a decrease of electrostatic repulsions in the metal coordination sphere compared with the case in which all ligands are anionic, but also as a consequence of limiting the number of anionic carboxylate donors in the reaction mixtures to less than that required for [UO 2 (RCO 2 ) 3 ] − species. This has been demonstrated in the case of several anionic polycarboxylates of different size, shape, and denticity with either the metal-containing zwitterionic carboxylate Ni­(tpyc) 2 (tpyc – = 2,2′;6′,2″-terpyridine-4′-carboxylate) , or the aromatic derivatives 1,1′-[(2,3,5,6-tetramethylbenzene-1,4-diyl)­bis­(methylene)]­bis­(pyridin-1-ium- n -carboxylate) ( n = 3 or 4), and 1,1′,1″-[(2,4,6-trimethylbenzene-1,3,5-triyl)­tris­(methylene)]­tris­(pyridin-1-ium-4-carboxylate). , This strategy consisting of combining ligands very different in terms of size, geometry, and flexibility, but of similar donor strength, has generated some original structures, such as polynuclear rings , and entangled polymers, and thus has induced attempts to extend this investigation to other zwitterionic dicarboxylates. We report herein our results with two flexible diammonioacetates, N,N,N ′ ,N ′-tetramethylethane-1,2-diammonioacetate (L1) and N,N,N ′ ,N ′-tetramethylpropane-1,3-diammonioacetate (L2), represented in Scheme .…”

“…This has been demonstrated in the case of several anionic polycarboxylates of different size, shape, and denticity with either the metalcontaining zwitterionic carboxylate Ni(tpyc) 2 (tpyc − = 2,2′;6′,2″-terpyridine-4′-carboxylate) 14,15 or the aromatic derivatives 1,1′-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis-(methylene)]bis(pyridin-1-ium-n-carboxylate) (n = 3 or 4), and 1,1′,1″-[(2,4,6-trimethylbenzene-1,3,5-triyl)tris-(methylene)]tris(pyridin-1-ium-4-carboxylate). 16,17 This strategy consisting of combining ligands very different in terms of size, geometry, and flexibility, but of similar donor strength, 17 has generated some original structures, such as polynuclear rings 15,16 and entangled polymers, 16 and thus has induced attempts to extend this investigation to other zwitterionic dicarboxylates. We report herein our results with two flexible diammonioacetates, N,N,N′,N′-tetramethylethane-1,2-diammonioacetate (L1) and N,N,N′,N′-tetramethylpropane-1,3diammonioacetate (L2), represented in Scheme 1.…”

Oligozwitterions in coordination polymers and frameworks – a structural view

“…Although as yet unexplored in regard to any possible applications, it has been demonstrated 17,82,101–104 that carboxylate di- or tri-zwitterions and anionic polycarboxylates can form mixed ligand coordination polymers in which both ligands act as bridges, seemingly consistent with the different donor species having almost identical bonding interactions. Bond lengths to zwitterion carboxylate-O and anionic carboxylate-O are similar but the common adoption of a bis or tris(κ 1 O ) mode of bonding by the zwitterions may indicate that they have a weaker structural influence and in the particular case of thiophene-2,5-dicarboxylate as the anion, 103 the isolated crystals have the composition of a mixed-ligand species but the structure in fact involves independent polymer networks of the two ligands (Fig.…”