Metal–organic frameworks exhibiting strong anion–π interactions

Abstract

Coordination polymers offer a significant potential for applications in adsorption, guest and anion recognition and sensing. Their structure commonly provides binding sites for such specific interactions as pi-pi stacking and XH...pi hydrogen bonding. The latter reflects the ability of the pi-cloud to interact with positively polarized atoms. An electrostatic interaction between anionic species and electron deficient heterocycles, which parallels the above binding scheme, is also possible and very recently the existence of anion-pi interactions was proved in the solid state and in solution. This effect may be significant also for biomolecule/solution interfaces, as it occurs in protein structures. In fact, such interactions could be especially relevant for host-guest chemistry of coordination polymers, particularly for functionalization of hydrophobic crystal cavities and for the design of geometrically rigid anion receptors. However, typical electron deficient heterocycles such as 1,3,5-triazines and 1,2,4,5-tetrazines are very weak donors and they are hardly suitable for bridging metal ions and the generation of coordination frameworks. As a system that combines efficient donor properties towards transition metal ions and a pronounced ability for anion-pi interactions we have developed unsubstituted pyridazino[4,5-d]pyridazine, which was readily accessible by a novel one-pot synthesis involving inverse electron demand Diels-Alder cycloaddition (Scheme 1). Unusual anion binding properties of the ligand may be clearly related to its electron-deficiency (LUMO energy -1.591 vs. -0.288 eV for the parent pyridazine), influenced also by N-coordination to such Lewis acids as metal ions.

Construction of Supramolecular Assemblies Based on Anion–π Interactions

“…11.5) based on 1,4,5,8,9, 12-hexaazatriphenylene (HAT) substituted with cyano groups that is able to interact with three anions by one side of the polycyclic ring and with one anion by the opposite site [93]. Moreover, it is easily available by a one-pot syn thesis involving inverse electron demanding Diels-Alder cycloaddition [95]. It was concluded that the formation of typical anion-π non-covalent complexes, charge transfer complexes, or electron transfer adducts strongly depends on the type of anion.…”

“…The pyridazino [4,5-d]pyridazine ligand (L pp ) has been utilized by Gural'skiy et al [95] to investigate the ability of this ring to establish anion-π interactions providing an attractive structural synthon and an unique π-bifunctional building block for novel polymeric and molecular anion receptors. Two examples are represented in Figure 11.7.…”

“…FIgURE 11.5 X-ray structure of [HAT(CN) 6 ] 2 [Br − ]3 . Interaction energies of Cl − -π complexes of pyridazino[4,5-d]pyridazine and related rings [Fragments of the X-ray crystal structures containing μ 2 -and μ 4 -coordination of pyridazino[4,5-d]pyridazine[95]. Interaction energies of Cl − -π complexes of pyridazino[4,5-d]pyridazine and related rings [Fragments of the X-ray crystal structures containing μ 2 -and μ 4 -coordination of pyridazino[4,5-d]pyridazine[95].…”

The solid-state structures of two photoluminescent 2D silver(I) arenedisulfonate incorporating aminopyrimidyl ligands: Substituents influence on π⋯π interaction

“…Although Ag(I) ion is a particularly good candidate for the flexible coordinative tendencies of sulfonate anion, there is limited structures about arenedisulfonate complexes involving the Ag(I) ion and such complexes modified by N-donor ligands [16,17]. On the other hand, 2-aminopyrimidine-type ligands possessing potential hydrogen bond and p-electron donors usually form diverse nonvalent interactions such as hydrogen-bonding, pÁ Á Áp stacking, C-HÁ Á Áp and anionÁ Á Áp interactions [18][19][20][21], and are widely used in designing coordination polymers (CPs) by us [22][23][24][25][26][27][28][29] and others [30,31]. As extended work, we introduced 1,5-naphthalenedisulfonic acid (H2nds) as an auxiliary ligand into our previous systems and successfully obtained two new 2D CPs, namely [Ag(apym)(nds) 0.5 ] n (1) and [Ag(dmapym)(nds) 0.5 ] n (2) (apym = 2-aminopyrimidine, dmapym = 2-amino-4,6-dimethylpyrimidine, H2nds = 1,5-naphthalenedisulfonic acid).…”

Multiple anion···π interactions with a soft selenium atom: Accommodation of NCSe− anions inside hydrophobic pockets of adamantane/1,2,4-triazole coordination framework

“…Since coordination of the heterocycle to the metal ions enhances the ability for the anion···π interactions [4], this phenomenon is relevant for the solid-state coordination chemistry as an important factor governing disposition of counter anions, their recognition and selective binding [5]. It was considered as a design tool for the generation of supramolecular structures involving different types of π···anion···π and anion···π···anion sandwiches [6,7], double interactions with polycyclic receptors [8], anion···π and hydrogen bonding [7] and combined anion···π, lone pair···π and π/π interactions [9]. The cooperative effect of these forces is particularly prevalent for the anions located in the predefined cages with π-acidic surface [10] and therefore such systems themselves provide a useful probe for studying the weaker anion···π and lone pair···π bonding.…”