Iodine Chemisorption, Interpenetration and Polycatenation: Cationic MOFs and CPs from Group 13 Metal Halides and Dipyridyl Linkers.

Invited for the cover of this issue are Klaus Müller-Buschbaum and co-workers at Giessen University. The image depicts an aluminium-based MOF as a novel material for the capture of iodine radioisotopes from a potential gas atmosphere exposure. Read the full text of the article at 10.1002/chem.202104171.

Iodine-Chemisorption, Interpenetration and Polycatenation: Cationic MOFs and CPs from Group 13 Metal Halides and Di-Pyridyl-Linkers.

Eight cationic, two-dimensional metal-organic frameworks (MOFs) were synthesized in reactions of the group 13 metal halides AlBr3 , AlI3 , GaBr3 , InBr3 and InI3 with the dipyridyl ligands 1,2-di(4-pyridyl)ethylene (bpe), 1,2-di(4-pyridyl)ethane (bpa) and 4,4'-bipyridine (bipy). Seven of them follow the general formula 2 ∞ [MX2 (L)2 ]A, M=Al, In, X=Br, I, A- =[MX4 ]- , I- , I3 - , L=bipy, bpa, bpe. Thereby, the porosity of the cationic frameworks can be utilized to take up the heavy molecule iodine in gas-phase chemisorption vital for the capture of iodine radioisotopes. This is achieved by switching between I- and the polyiodide I3 - in the cavities at room temperature, including single-crystal-to-single-crystal transformation. The MOFs are 2D networks that exhibit (4,4)-topology in general or (6,3)-topology for 2 ∞ [(GaBr2 )2 (bpa)5 ][GaBr4 ]2 ⋅bpa. The two-dimensional networks can either be arranged to an inclined interpenetration of the cationic two-dimensional networks, or to stacked networks without interpenetration. Interpenetration is accompanied by polycatenation. Due to the cationic character, the MOFs require the counter ions [MX4 ]- , I- or I3 - counter ions in their pores. Whereas the [MX4 ]- , ions are immobile, iodide allows for chemisorption. Furthermore, eight additional coordination polymers and complexes were identified and isolated that elaborate the reaction space of the herein reported syntheses.

Properties of perhalogenated {closo-B10} and {closo-B11} multiply charged anions and a critical comparison with {closo-B12} in the gas and the condensed phase.

closo-Borate anions [closo-BnXn]2- are part of the most famous textbook examples of polyhedral compounds. Substantial differences in their reactivity and interactions with other compounds depending on the substituent X and cluster size n have been recognized, which favor specific closo-borates for different applications in cancer treatment, chemical synthesis, and materials science. Surprisingly, a fundamental understanding of the molecular properties underlying these differences is lacking. Here, we report our study comparing the electronic structure and reactivity of closo-borate anions [closo-BnXn]2- (X = Cl, Br, I, n = 10, 11, 12 in all combinations) in the gas phase and in solution. We investigated the free dianions and the ion pairs [nBu4N]+[closo-BnXn]2- by gas phase anion photoelectron spectroscopy accompanied by theoretical investigations. Strong similarities in electronic structures for n = 10 and 11 were observed, while n = 12 clusters were different. A systematic picture of the development in electronic stability along the dimension X is derived. Collision induced dissociation shows that fragmentation of the free dianions is mainly dependent on the substituent X and gives access to a large variety of boron-rich molecular ions. Fragmentation of the ion pair depends strongly on n. The results reflect the high chemical stability of clusters with n = 10 and 12, while those with n = 11 are much more prone to dissociation. We bridge our study to the condensed phase by performing comparative electrochemistry and reactivity studies on closo-borates in solution. The trends found at the molecular level are also reflected in the condensed-phase properties. We discuss how the gas phase values allow evaluation of the influence of the condensed phase on the electronic stability of closo-borates. A synthetic method via an oxidation/chlorination reaction yielding [closo-B10Cl10]2- from highly chlorinated {closo-B11} clusters is introduced, which underlines the intrinsically high reactivity of the {closo-B11} cage.

Unprecedented Efficient Structure Controlled Phosphorescence of Silver(I) Clusters Stabilized by Carba-closo-dodecaboranylethynyl Ligands.

{Ag2 (12-C≡C-closo-1-CB11 H11 )}n and selected pyridine ligands have been used for the synthesis of photostable Ag(I) clusters that, with one exception, exhibit for Ag(I) compounds unusual room-temperature phosphorescence. Extraordinarily intense phosphorescence was observed for a distorted pentagonal bipyramidal Ag(I) 7 cluster that shows an unprecedented quantum yield of Φ=0.76 for Ag(I) clusters. The luminescence properties correlate with the structures of the central Ag(I) n motifs as shown by comparison of the emission properties of the clusters with different numbers of Ag(I) ions, different charges, and electronically different pyridine ligands.

Sb- and Bi-based coordination polymers with N-donor ligands with and without lone-pair effects and their photoluminescence properties.

Fifteen new sublimable Sb- and Bi-based chlorido, bromido and iodido coordination polymers (CPs) with linear bispyridyl ligands are presented in this work and compared in terms of their crystal structures and photoluminescence properties. The Sb-CPs occur in two structural motifs: 1∞[Sb2X6(L)2] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (1), 1,2-bis(4-pyridyl)ethane (bpa) (2), 4,4'-bipyridine (bipy) (X: Br, I; 3)) with two polymorphs showing negligible stereochemical demand of the lone-pair and 1∞[SbCl3(bipy)] (3a) featuring a stereochemically active lone pair with significant 5p-contribution at SbIII. This is accompanied by differences in the coordination polyhedra being octahedral for high s-character, whereas a high p-character of the lone pair results in a square pyramid as the coordination sphere. The Bi-CPs are represented by the general formula 1∞[Bi2X6(L)2] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (4), 1,2-bis(4-pyridyl)ethane (bpa) (5)) and thus show no significant 6p-character of the lone pairs. For examining the parallels and differences between the SbIII- and BiIII-CPs, both are compared in terms of structures and luminescence properties, as well as with related literature known CPs. Altogether, this comparison of structures and properties allows for gaining new insights into the photoluminescence mechanisms of the Sb and Bi-containing CPs. For the first time, distinct hints on the participation of inter-valence charge transfer transitions in E3+-pairs (E: Sb, Bi) were observed for the Sb- and Bi-containing coordination polymers constructed from N-donor ligands.