Probing the Influence of N‐Donor Capping Ligands on Supramolecular Assembly in Molecular Uranyl Materials

Abstract

The syntheses and crystal structures of six new compounds containing the UO 2 2+ cation, 3,5-dichlorobenzoic acid, and a chelating N-donor [2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (dimethylphen), 2,2′:6′,2′′-terpyridine (terpy), 4′-chloro-2,2′:6′,2′′-terpyridine (Cl-terpy), or 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ)] are reported. Single-crystal X-ray diffraction analysis of these materials enabled the exploration of the structural relationship between the benzoic acids and the chelating N-donor as well as providing a platform to evaluate the effects of ligand choice on uranyl hydrolysis and subsequent oligomerization. At an unadjusted pH (ca. 3), a mix of uranyl monomers and dimers are [a] All organic materials, 3,5-dichlorobenzoic acid (Alfa Aesar, 99 %) and the chelating N-donors [2,2′-bipyridine (Sigma Aldrich, 99+%), 1,10-Eur. J. Inorg. Chem. 2016, 126-137 www.eurjic.org Eur. J. Inorg. Chem. 2016, 126-137 www.eurjic.org136 order to increase the sample concentration and enhance the resulting luminescence spectra. The solid material was then allowed to air-dry for approximately ten minutes, allowing for the evaporation of the cyclohexane, and then a cover slide was placed on top of the sample and secured with adhesive tape.Supporting Information (see footnote on the first page of this article): ORTEP figures of all compounds, PXRD spectra of all compounds, IR spectra of complexes 1, 4, and 5, and tables of selected supramolecular interaction distances and bond lengths are all available. Note:The authors declare no competing financial interest.

Engaging the Terminal: Promoting Halogen Bonding Interactions with Uranyl Oxo Atoms

“…Complexes 1 , [UO 2 (bipy)(25diClBA) 2 ], and 2 , [UO 2 (bipy)(25diBrBA) 2 ], crystallize in the space groups C 2/ c and P , respectively, and are isostructural with UO 2 ‐3,5‐dichlorobenzoic acid‐bipy and UO 2 ‐2,5‐diiodobenzoic acid‐bipy materials we have described previously . Looking at the global structure of 1 (Figure ), the uranyl tectons are assembled to form a 2 D sheet in the (0 1 0) plane through a combination of hydrogen‐bonding and halogen‐halogen interactions.…”

“…Looking at the global structure of 1 (Figure ), the uranyl tectons are assembled to form a 2 D sheet in the (0 1 0) plane through a combination of hydrogen‐bonding and halogen‐halogen interactions. Bifurcated hydrogen‐bonding interactions with the uranyl oxo atom (O1), which stem from hydrogen atoms on the chelating bipy ligand and the 2,5‐dichlorobenzoic acid, link the tectons of 1 into a 1 D chain and this assembly motif mirrors what we have observed previously in similar uranyl hybrid materials . These 1 D chains are further linked into a 2 D sheet through Type I halogen–halogen interactions between chlorine atoms at the 5‐position of 2,5‐dichlorobenzoic acid ligands on neighboring 1 D chains (Figure ).…”

“…Single crystal X‐ray crystallographic analyses of complexes 1 – 10, which feature either 2,5‐dichloro‐ (25diClBA) or 2,5‐dibromobenzoic acid (25diBrBA) ligands along with chelating N ‐donor ligands of varying size (bipy, phen, terpy, and Cl‐terpy) (Scheme ), revealed two dominant tectons: monomers ( 1 – 3 , 7 – 10 ) and dimers ( 4 – 6 ). Local structures are not described as each complex has analogues in our previous studies,, yet modes of supramolecular assembly are described in detail for all complexes ( 1 – 10 ) as they highlight how changing the halogen atoms at the periphery of a tecton can change the synthon(s) utilized for assembly.…”

“…Our group has focused on this problem primarily through the synthesis of [UO 2 ] 2+ materials in highly acidic and high halide media, yet herein we continue our recent efforts focused on hydrothermally generating discrete, reproducible tectons through the use of a polypyridyl N ‐donor capping ligands in the first coordination sphere, to promote a single uranyl species with a specific coordination geometry . N ‐donor capping ligands are paired with halogen functionalized benzoic acids such that tecton assembly occurs by way of halogen or hydrogen bonding interactions, π–π stacking, or a combination thereof ,. We recently used this same approach to systematically engage the typically terminal uranyl oxo groups in halogen bonding interactions through the selection of a range of electron‐donating, chelating N ‐donors along with 2,5‐diiodobenzoic acid .…”

Restricted Speciation and Supramolecular Assembly in the 5f Block

“…In a family of twelve complexes featuring various bromobenzoic acids with chelating ligands such as 1,10‐phenanthroline, 2,2′:6′,2′′‐terpyridine, and 4′‐chloro‐2,2′:6′,2′′‐terpyridine, four were found to feature halogen bonding interactions involving the uranyl oxo atoms (Figure ) . As this study did not elucidate the mechanisms that led to oxo atom engagement in supramolecular assembly, and as materials featured variations in both benzoic acid and chelating N‐donor ligands, a follow‐up study using 3,5‐diclorobenzoic acid and the same chelating ligands was conducted, which yielded six complexes, none of which featured oxo atom participation in halogen bonding interactions …”