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

Abstract

Engaging the nominally terminal oxo atoms of the linear uranyl (UO ) cation in non-covalent interactions represents both a significant challenge and opportunity within the field of actinide hybrid materials. An approach has been developed for promoting oxo atom participation in a range of non-covalent interactions, through judicious choice of electron donating equatorial ligands and appropriately polarizable halogen-donor atoms. As such, a family of uranyl hybrid materials was generated based on a combination of 2,5-dihalobenzoic acid and aromatic, chelating N-donor ligands. Delineation of criteria for oxo participation in halogen bonding interactions has been achieved by preparing materials containing 2,5-dichloro- (25diClBA) and 2,5-dibromobenzoic acid (25diBrBA) coupled with 2,2'-bipyridine (bipy) (1 and 2), 1,10-phenanthroline (phen) (3-5), 2,2':6',2''-terpyridine (terpy) (6-8), or 4'-chloro-2,2':6',2''-terpyridine (Cl-terpy) (9-10), which have been characterized through single crystal X-ray diffraction, Raman, Infrared (IR), and luminescence spectroscopy, as well as through density functional calculations of electrostatic potentials. Looking comprehensively, these results are compared with recently published analogues featuring 2,5-diiodobenzoic acid which indicate that although inclusion of a capping ligand in the uranyl first coordination sphere is important, it is the polarizability of the selected halogen atom that ultimately drives halogen bonding interactions with the uranyl oxo atoms.

Probing hydrogen and halogen-oxo interactions in uranyl coordination polymers: a combined crystallographic and computational study

“…[1][2][3][4][5][6][7][8][9][10][11] This approach is predicated upon the directed assembly of tectons into crystalline architectures via attractive, noncovalent synthons, and utilization within uranyl hybrid materials has necessitated the development of a hierarchy of acceptordonor pairing preferences based on a detailed knowledge of the relationship between intra-and intermolecular interactions. 12 Recently, our group has been investigating the potential for crystal engineering to support engagement of the nominally terminal uranyl oxo groups, [13][14][15][16][17] and here we continue these efforts, employing hydrogen and halogen bonding for assembly and then describing uranyl oxo atom behavior as a synthon acceptor site. Development of a hierarchy of uranyl acceptor-donor pairing preferences requires a metric for adjudicating interaction strengths, which can then be qualitatively applied to judging which synthon acceptor and donor sites are 'best'.…”

Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions

“…Although the range of polynuclear uranyl‐based architectures is very broad, which is perfectly highlighted in a recent review, most of them are built with polytopic ligands featuring diverse coordination sites and modes. Even in the case of monotopic ligands such as halogenated benzoic acids, which at first view have only one obvious metal binding site (the carboxylate group), while the halogen sites are usually considered terminal binding sites, a great effort has been done to discover that the halogen sites can serve as supramolecular synthons or even as sites for covalent bonding in actinide systems. On the other hand, there are rare examples of compounds of uranyl ions with anions of aliphatic monocarboxylic acids L , which are constructed of large heteronuclear clusters (Figure ).…”

Restricted Speciation and Supramolecular Assembly in the 5f Block

“…Moreover, electrostatic potential maps of selected uranyl tectons confirmed and quantified the importance of halogen polarizability on oxo atom engagement. Sigma hole energies were found to be negative for chlorine, small and positive for bromine, and a factor or ten greater in magnitude (than bromine) for the more polarizable iodine atoms (Figure ), whereas sigma hole energies for oxo atoms stayed nearly constant, independent of chelating N‐donor and amount of equatorial electron donation …”

“… Representative UO 2 ‐2,5‐dihalobenzoic‐Cl‐terpy complexes and corresponding calculated electrostatic potentials, adapted from ref. (K. P. Carter, M. Kalaj, R. G. Surbella III, L. C. Ducati, J. Autschbach, C. L. Cahill, Chem. Eur.…”

“…Sigma hole energies were found to be negative for chlorine, small and positive for bromine, and af actor or ten greater in magnitude (than bromine) for the more polarizable iodine atoms ( Figure 12), whereas sigma hole energies for oxo atoms stayed nearly constant, independento fc helating N-donor and amount of equatorial electron donation. [30] More recently,t he 'cap-and-link' strategy has been used to probe the extent to which electron donationf rom chelating Ndonorl igandsc an foster oxo atom engagement in halogen bondingi nteractions. Using two sets of isomorphous complexes, differing only in halogena tom at the periphery of the tectons, means of assembly were evaluated and results indicated that inclusiono fm ore electron donating N-donorl igand (i.e.…”