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

Abstract

Four new supramolecular coordination complexes and salts based on proton-transferred pyridine-2,6-dicarboxylic acid N-oxide formulated as (Htata) (Hpydco)ÁH 2 O (1), (Htata) 2 (pydco)Á2H 2 O (2), (H9a-acr) 2 [Zn(pydco) 2 (H 2 O) 2 ]Á4H 2 O (3), and (H9a-acr) 2 [Co(pydco) 2 (H 2 O) 2 ]Á4H 2 O (4) (where H 2 pydco = pyridine-2,6-dicarboxylic acid N-oxide, tata = 2,4,6-triamino-1,3,5-triazine (melamine) and 9a-acr = 9-aminoacridine) have been synthesized by proton transfer from H 2 pydco as ligand and to tata and 9a-acr. The structures of 1-4 were characterized by elemental analysis, infrared spectroscopy, and single crystal X-ray diffraction methods. Compounds 1 and 2 are salts of proton-transferred H 2 pydco and melamine with two separate formulas. There is a difference between the anionic fragment in 1 and 2, the anionic part of 1 retains one acid proton (Hpydco -) which is involved in a strong, intramolecular hydrogen bonding with the oxygen attached to nitrogen, while the acid units in 2 are fully deprotonated (pydco 2-). The linear chains of melaminium cations with an anionic motif and water molecules lead to 2-D zipper layers in 1 and 2-D zigzag layers in 2. These layers are held together via an extensive network of hydrogen bonds, p ? -p 1 stacking, N ? -H_p ? , and lp_p ? interactions to extend the structures into the 3-D supramolecular framework. Single-crystal studies revealed that 3 and 4 are isostructural with distorted octahedral geometry about the metal consisting of two pydco 2-ligands acting in bidentate fashion and two transdisposed water molecules. They also adopt alternating cationic and anionic layers with 9-aminoacridinium cations and transition metal complex anions which are linked to each other by a variety of noncovalent interactions such as ion pairing, hydrogen bonding and p-p stacking.

Recurrent Supramolecular Motifs in a Series of Acid–Base Adducts Based on Pyridine-2,5-Dicarboxylic Acid N-Oxide and Organic Bases: Inter- and Intramolecular Hydrogen Bonding

“…We recognize several cyclic synthons in this layer described by R 4 2 (8), R 2 2 (8), R 3 2 (8), and R 4 4 (26) graph sets (Figure S2 in the Supporting Information). The three-dimensional (3D) network is built by several weak, but distinct, interactions: (i) π interactions between anionic parts (Hpydco – ) (3.484 Å), (ii) π interactions between cationic parts (Htata + ) (3.992 Å), (iii) C–O···π interactions between oxygen of the 5-carboxylate group from Hpydco – and the triazine ring of Htata + (3.112 Å), and (iv) N–H···π interactions between nitrogen of the amino group from Htata + and the pyridine ring of Hpydco – (3.627 Å) (Figure S3 in the Supporting Information). ,, …”

“…At least half of the marketed active pharmaceutical ingredients (APIs) are administered as salts. In general, a salt is formed via proton transfer from an acid to a base, leading to the formation of a conjugate acid (protonated base) and conjugate base (deprotonated acid). − Over the past decade, Mirzaei et al have focused on the synthesis and structural characterization of novel supramolecular proton-transferred compounds − and coordination complexes , based on derivatives of pyridinedicarboxylic acids, owing to their remarkable applications such as anticancer properties, anti-HIV agent, gas adsorbent, etc. − …”

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

“…As mentioned above, two complexes containing zinc and cobalt which are isostructural with 2 and 3 have been synthesized recently [12]. Average bond distances for all four compounds show that M−O mean (aqua)> M−O mean (N-oxide)> M−O mean (carboxylate), and the torsion angle for the free carboxylate group is near 90°.…”

“…O-donor ligands are of particular interest because they have significant medical properties especially when they are connected to biologically important metals [10].Some applications of this class of ligands can involve the reduction in unwanted responses to drugs, improved anti-microbial activities and improved antiulcerous, anti-tumor and anti-bacterial activities [11]. Recently, our research group has been interested in the synthesis, determination of structural features and coordination behavior ofOdonor ligands based onpyridine-2,6-dicarboxylic acid N-oxide (H 2 pydco) with metal ions [12] and, in particular, to investigate the influence of the N-oxide moiety on the coordination mode(s)in the crystal lattice as compared with those of theparentpyridine-2,6-dicarboxylic acid (H 2 pydc). Both carboxylate groups in H 2 pydcoare structurally symmetrical and the N-oxide group of H 2 pydcois a considerably better electron donor than the ring nitrogen atom ofH 2 pydc [13].ACSD searchof structures containing H 2 pydco showed that most of the compounds are polynuclear, contain additional neutral ligands as "spacers" and were synthesized under hydro(solvo)thermal conditions.…”

“…1) [14].Following our previous work with the H 2 pydco ligand as anO-donor ligand and two different metal centers (zinc and cobalt as biologically relevant metals) [12],we continue the study with two different first-row transition metals, copper and nickel to analyze their effect on the crystal lattice as well as their proton transfer salts.From these studies, the anionic [M(pydco) 2 ] 2-salts with [H9a-acr] + cationsare found to be isostructural and the M II ionshave distorted octahedral geometry with two (pydco) 2-ions coordinated as chelating bidentate ligands. This suggested that the hydrogen-bonded network of organic ligands would serve as a host lattice in which one metal could be replaced by another metal without disturbing the lattice [16].…”