Crystal engineering with coordination compounds of 2,6-dicarboxy-4-hydroxypyridine and 9-aminoacridine fragments driven by different nature of the face-to-face π⋯π stacking

Abstract

H9a-Acr) 2 [Ni(hypydc) 2 ]•4H 2 O (1), (H9a-Acr) 2 [Co(hypydc) 2 ]•3H 2 O (2), (H9a-Acr) [Cr(hypydc) 2 ]•3H 2 O (3), and (H9a-Acr) 2 [Cd(hypydc) 2 ]•3H 2 O ( 4) compounds (H 2 hypydc = 2,6-dicarboxy-4-hydroxypyridine or chelidamic acid; 9a-Acr = 9-aminoacridine) were synthesized via proton transfer and characterised by elemental analysis, IR spectroscopy, and single crystal X-ray diffraction techniques. Thermogravimetric analysis (TGA) was carried out on compounds 1 and 2. Compounds 1-4 have distorted octahedral geometries with two hypydc 2− ions coordinated as tridentate ligands to each metal ion through one oxygen atom of each carboxylate group and the nitrogen atom of the pyridine ring. In the compounds, strong hydrogen bonds between anionic, cationic, and water fragments and especially the different natures of the π + ⋯π − and π − ⋯π − stacking interactions play important roles in the construction of threedimensional supramolecular frameworks which have been analysed in detail. The smaller trans N-M-N angle observed in 3 as compared with the others has been analysed using DFT calculations. Solution studies have also been performed to understand the behaviour of the ternary systems M n+ -H 2 hypydc-9a-Acr in aqueous solution.

Syntheses and X-ray crystal structure studies of four new coordination complexes and salts based on proton-transferred pyridine-2,6-dicarboxylic acid N-oxide

“…Logically, protonated 9-aminoacridine molecules are arranged in an antiparallel stacking mode [40]. The geometry, bond distances and angles of 3 are comparable with similar compounds reported in the literature [41][42][43].…”

Synthesis, X‐ray characterization and density functional theory studies of N6‐benzyl‐N6‐methyladenine–M(II) complexes (M = Zn, Cd): The prominent role of π–π, C–H···π and anion–π interactions

“…Each dicationic moiety is hydrogen‐bonded to the anionic trinuclear Cd complex via two strong hydrogen bonds (red dashed lines). Several previous works have been devoted to the analysis of the so‐called π + –π + interactions, which are similar in nature to the conventional π‐stacking interaction and the anionic counterions are needed to thermodynamically stabilize the assembly.…”

Two new copper and nickel complexes of pyridine-2,6-dicarboxylic acid N-oxide and their proton transferred salts: Solid state and DFT insights

“…According to Table 2, the M−O mean distances for four N-oxide complexes decreased in the following order Co > Ni > Cu which parallels the decreasing metallic radius while the sudden increase in the average distances for Zn is due to the d 10 electron configuration. Furthermore, it is clear that a Jahn-Teller distortion is exhibited for Cu 2+ which appears as an elongation of the M−O Water distance in compound 2.In order to better investigate the effects of the N-oxidation, some compounds were selected withH 2 pydcandchelidamic acid (H 2 hpydc) as acidic ligands and 9a-acr as the base and with Co, Ni, Cu and Zn as transition metals [24][25].These exhibit a similar layered structure in the solid state, all of them arranged in the form of alternating cationic and anionic layers.The essential difference between these and 2 and 3is the coordination mode of(pydco) 2− and (hpydc) 2− which act as tridentate ligands with O 4 N 2 metal environments. Dihedral angles between the least squares planes of the two coordinated acidic ligandsare 83−86°,thus these ligands are almost perpendicular to each other.…”