Anion−π Interactions as Controlling Elements in Self-Assembly Reactions of Ag(I) Complexes with π-Acidic Aromatic Rings

Abstract

Reactions of 3,6-bis(2'-pyridyl)-1,2,4,5-tetrazine (bptz) and 3,6-bis(2'-pyridyl)-1,2-pyridazine (bppn) with the AgX salts (X = [PF6]-, [AsF6]-, [SbF6]-, and [BF4]-) afford complexes of different structural motifs depending on the pi-acidity of the ligand central ring and the outer-sphere anion. The bptz reactions lead to the polymeric [[Ag(bptz)][PF6]]infinity (1) and the dinuclear compounds [Ag2(bptz)2(CH3CN)2][PF6]2 (2) and [Ag2(bptz)2(CH3CN)2][AsF6]2 (3), as well as the propeller-type species [Ag2(bptz)3][AsF6]2 (4) and [Ag2(bptz)3][SbF6]2 (5a and 5b). Reactions of bppn with AgX produce the grid-type structures [Ag4(bppn)4][X]4 (6-9), regardless of the anion present. In 6-9, pi-pi stacking interactions are maximized, whereas multiple and shorter (therefore stronger) anion-pi interactions between the anions and the tetrazine rings are established in 1-5b. These differences reflect the more electron-rich character of the bppn pyridazine ring as compared to the bptz tetrazine ring. The evidence gleaned from the solid-state structures was corroborated by density functional theory calculations. In the electrostatic potential maps of the free ligands, a higher positive charge is present in the bptz as compared to the bppn central ring. Furthermore, the electrostatic potential maps of 3, 4, and 5b indicate an electron density transfer from the anions to the pi-acidic rings. Conversely, upon addition of the [AsF6]- ions to the cation of 7, there is negligible change in the electron density of the central pyridazine ring, which supports the presence of weaker anion-pi interactions in the bppn as compared to the bptz complexes. From the systems studied herein, it is concluded that anion-pi interactions play an important role in the outcome of self-assembly reactions.

A Structural Investigation of Anion–Triazole Interactions: Observation of “π‐Pockets” and “π‐Sandwiches”

“…While this is the intuitively expected result: a close (and hence strong [32] ) anion-π interaction would be expected to involve an anion positioned close to the "ideal" location directly above the ring centroid, it disagrees with the general trend found by Reedijk et al [8] in their survey of the CSD. [7] In that survey it seems that the size of the mean plane-centroid-X angle has very little effect on the X···centroid distance, if anything shorter distances being weakly associated with smaller (further from 90°) angles.…”

“…For example, a number of metal complexes of 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (dptz) or 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazine (dpztz) have been prepared by the groups of Dunbar [9,32,33] and Champness [34] that contain an anion-tetrazine-anion arrangement with centroid-anion distances as short as 2.75 Å for both anions. It is worth noting, however, that in most structures there is an "excess" of anion, when compared with π-deficient aromatic rings, particularly given that one anion may be involved in interactions with a number of π-rings.…”

Anion‐π‐Wechselwirkungen ins rechte Licht gerückt

“…Dieser Schluss wurde durch den Umstand untermauert, dass die Reaktion eines ähnlichen Liganden (bppn, bei dem der zentrale Tetrazinring durch ein Pyridazin ersetzt ist) mit AgX-Salzen (X = PF 6 À , AsF 6 À , SbF 6 À , BF 4 À ) im Verhältnis 1:1 nur gitterartige Strukturen liefert, unabhängig davon, welches Anion vorhanden ist. [136] Ein weiteres Beispiel der Selbstorganisation von Ag IKoordinationsnetzwerken über Anion-p-Wechselwirkungen stammt von Zhou et al [137] Bei ihrer Untersuchung von Ag IMetall-Komplexen mit 2,4,6-Tri(2-pyridyl)-1,3,5-trazin (tpt) fanden sie, dass die Selbstorganisation der Ag-tpt-Koordination durch polyatomare Anionen (ClO 4 À , BF 4 À und PF 6 À ) über Anion-p-Wechselwirkungen gelenkt wird (Abbildung 24). Die Umsetzung von AgX mit tpt ergab hochsymmetrische, isostrukturelle Koordinationsnetzwerke, bei denen in den Rçntgenkristallstrukturen Anion-p-Wechselwirkungen zwischen den Anionen und den tpt-Liganden zu beobachten waren.…”

“…In den Hçhlungen dieses offenen Netzwerks eingebettete Anionen werden von vier komplementären p-Anion-p-SandwichAbbildung 23. Kristallstrukturfragmente mehrerer bptz-Komplexe mit verschiedenen Strukturtypen [136] zusammen mit den CSD-Referenzcodes.…”

Intra-/Intermolecular Bifurcated Chalcogen Bonding in Crystal Structure of Thiazole/Thiadiazole Derived Binuclear (Diaminocarbene)PdII Complexes

“…CB is usually defined as non-covalent interactions between localized positive regions on a chalcogen atom in the extension of the covalent bonds (σ-holes) and electron donor species serving as CB acceptors [11][12][13][14][15][46][47][48][49][50]. Unlike halogens a chalcogen atom possess two σ-holes at the same time and is prone to the formation of bifurcated chalcogen bonding (BCB) (Figure 1) [51][52][53][54][55][56][57]. In the continuation of our projects focused on metal-mediated reactions of isocyanides [15,[58][59][60][61][62][63][64][65][66][67][68] and on non-covalent interactions [15,58,[69][70][71][72][73][74][75][76][77], we recently reported on the coupling between cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H4) and various thiazol-and thiadiazol-2-amines that leads to a mixture of two regioisomeric binuclear diaminocarbene complexes corresponding to kinetically (3a-d) or thermodynamically (4a-d) controlled regioisomers (Scheme 1).…”