Coordination Polymers and Cage-Containing Frameworks in Uranyl Ion Complexes with rac- and (1R,2R)-trans-1,2-Cyclohexanedicarboxylates: Consequences of Chirality

Abstract

Racemic and enantiopure (1R,2R) forms of trans-1,2-cyclohexanedicarboxylic acid (Hchdc and R-Hchdc, respectively) have been used in the synthesis of a series of 13 uranyl ion complexes, all obtained under solvo-hydrothermal conditions and in the presence of additional metal cations and/or N-donor ligands. While the homometallic complex [UO(R-chdc)] (1) was only obtained with the enantiopure ligand, complexes [UO(chdc)(THF)] (2), [UO(chdc)(DMF)] (3), and [UO(chdc)(NMP)] (4), with a coordinated solvent molecule, were obtained from the racemic form only; all crystallize as two-dimensional (2D) assemblies. The two complexes [UO(chdc)(bipy)](5) and [UO(R-chdc)(bipy)] (6), where bipy is 2,2'-bipyridine, are isomorphous since 5 crystallizes as a racemic conglomerate; they are both one-dimensional (1D) homochiral, helical polymers. The heterometallic complexes [UOCu(chdc)(bipy)(HO)]·HO (7) and [UOCu(R-chdc)(bipy)]·3HO (8) crystallize as a 1D or a 2D species, respectively, while [UOCd(R-chdc)(HO)]·HO (9) displays a 2D arrangement with the unusual Cairo pentagonal tiling topology. The four complexes [(UO)Na(chdc)(HO)] (10), [(UO)Ag(chdc)(HO)] (11), [(UO)Na(R-chdc)(HO)] (12), and [(UO)Pb(R-chdc)(HO)] (13) are closely related, all of them containing tetranuclear, pseudotetrahedral [(UO)(chdc/R-chdc)] cage motifs, that are assembled into a three-dimensional (3D) framework by bridging counterions (Na, Ag, or Pb). These cages define a new pathway to assembly of such species based on the unique coordination geometry of uranyl ion, differing from the widely exploited use of octahedral metal ions.

[Ni(cyclam)]2+ and [Ni(R,S-Me6cyclam)]2+ as Linkers or Counterions In Uranyl–Organic Species with cis- and trans-1,2-Cyclohexanedicarboxylate Ligands

“…isolated from both racemic and resolved t-1,2-chdcH2, 12,13 it appears that the ligand stereochemistry is not an important influence on the form of the complex. Here also, an oxo anion is present, and the two independent uranium cations and their image through inversion form a bis-(µ3-oxo)-bridged cluster analogous to that found in 4 ( Figure 6).…”

“…6 Greater opportunities, however, are offered by the use of transition metal ions, not only because of their varied spectroscopic, magnetic and redox properties but also because of the extensive nature of their known coordination chemistry with macrocyclic ligands, [7][8][9][10][11] (R,S-Me6cyclam (meso isomer) = 7(R),14(S) -5,5,7,12,12,14-hexamethylcyclam) on the crystal structures adopted by uranyl ion complexes of both cis-and trans-1,2-cyclohexanedicarboxylate, ligands known otherwise to give rise to a number of novel uranyl ion complexes. [12][13][14] With the quadridentate macrocycles forming a square-planar N4…”

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

“…36,37 In all six uranyl complexes reported here, obtained from media incorporating crown ethers, oxalate is found as a coligand, although not initially present. Given that the cyclohexanedicarboxylate ligands have been used in solvo-hydrothermal syntheses of their uranyl ion complexes in the absence of crown ethers and have not been found to form complexes also incorporating oxalate, 15,22,23 an obvious implication from this work is that crown ethers, over a long reaction period under hydrothermal conditions and in the presence of uranyl nitrate, can be converted to oxalate. This was somewhat unexpected given that one of the first demonstrations of the unique properties of crown ethers was that of the solubilisation of as powerful an oxidant as KMnO4 in apolar solvents 38 and that crown ethers have been used as phase-transfer catalysts in a wide variety of oxidations.…”

“…Uranyl complexes with this isomer appear to be generally much less amenable to crystallization than those of the trans isomer, either in its racemic or pure enantiomeric (1R,2R form). 22,23 The asymmetric unit in 2 contains four uranyl ions, two c-1,2-chdc 2-ligands in the chiral chair conformation with one carboxylate group equatorial and the other axial, four oxalate anions, two of which are centrosymmetric, and two Na(15C5) moieties (Figure 2). Atoms U1 and U3 are both chelated between the two carboxylate groups of one c-1,2-chdc 2-ligand, bound to one more respectively, and Na1 is also coordinated to the uranyl oxo atom O1 with a bond length of 2.502 (11) Å, a value within the usual range for these rather common bonds.…”

“…Previous experience 22,23 of the synthesis of uranyl ion complexes of both racemic and enantiomerically pure t-1,2-chdc 2-suggests that any difference between complexes 4 and 5 should be expected to be quite subtle, and indeed this appears to be so. Luminescence properties.…”