In continuation of our previous brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes by Aghabozorg et al. [1], we briefly surveyed the current research in the field of proton transfer compounds supramolecular synthons and their self-assembled metallic complexes from the points of view of Crystal Engineering and Density Functional Theory (DFT) since 2008. Our research groups have recently focused on the proton delivery from acids, which are considered to be suitable proton donors, to amines as proton acceptors. The results were the production of several proton transfer ion pairs possessing some remaining donor sites applied for coordination to metal centers in the preparation of metal-organic compounds. Some of the complexes showed contributions of both cationic and anionic fragments of the starting ion pair, while some others contained only one of these species as ligand. Our review and investigation of compounds revealed that they mainly focused on the concept of supramolecular systems, co-crystallization, stereochemically active lone pairs, coordination polyhedron, mainly on the various interactions involved, including van der Waals, ion pairing, hydrogen bondings, face to face ν-β stackings and edge to face C-Hπ, C-Oπ, N-H3π and SS. These interactions were the most commonly used strategies in the extension of supramolecular structures.

A brief review of structural concepts of novel supramolecular proton transfer compounds and their metal complexes (part II)

HIV-1 integrase (IN) is one of three enzymes encoded by the HIV genome and is essential for viral replication. Recently, HIV-1 IN inhibitors have emerged as a new promising class of therapeutics. Herein, we report the discovery of azaindole carboxylic acids and azaindole hydroxamic acids as potent inhibitors of the HIV-1 IN enzyme and their structure−activity relationships. Several 4-fluorobenzyl substituted azaindole hydroxamic acids showed potent antiviral activities in cell-based assays and offered a structurally simple scaffold for the development of novel HIV-1 IN inhibitors.

Azaindole hydroxamic acids are potent HIV-1 integrase inhibitors.

(H9a-Acr)2[Ni(hypydc)2]·4H2O (1), (H9a-Acr)2[Co(hypydc)2]·3H2O (2), (H9a-Acr) [Cr(hypydc)2]·3H2O (3), and (H9a-Acr)2[Cd(hypydc)2]·3H2O (4) compounds (H2hypydc = 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 hypydc2− 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 three-dimensional 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 Mn+–H2hypydc–9a-Acr in aqueous solution.

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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

The Cr(III) and Ca(II) complexes (dmpH)[Cr(pydc)2]•H2O (1) and [Ca2(pydc)2(H2O)6].2pydcH2 (2) were synthesized by reaction of 2,9-dimethyl-1,10-phenanthroline (dmp) and pyridine-2,6-dicarboxylic acid (pydcH2) with Cr(NO3)3 and Ca(NO3)2, respectively, and characterized using IR spectroscopy, single crystal X-ray diffraction method and solution studies. The space group and crystal system of these two compounds are P2
 1/c and monoclinic. The crystal dimensions are a = 9.785(3) A, b = 25.671(4) A, c = 9.3402(16) A, β = 90.790(17)° for (1) and a = 9.1319(4) A, b = 14.8430(8) A, c = 12.2449(7) A, β = 98.227(5)° for (2). In complex (1), a water molecule presents in the crystal packing, linking the anionic and cationic fragments together by hydrogen bonding and thus increases the stabilization of crystal lattices. In complex (2), the coordinated water molecules relate each dimer to adjacent dimers forming infinite molecular ribbons by strong hydrogen bondings. Hydrogen bonding and ion pairing play an important role in stabilizing these crystals. The complexation reactions of pydc, dmp and pydc+dmp with Cr3+ and Ca2+ ions in aqueous solution were investigated by potentiometric pH titrations and the equilibrium constants for all major complexes formed were evaluated.

Chromium(III) and Calcium(II) complexes obtained from dipicolinic acid: Synthesis, characterization, X-Ray crystal structure and solution studies

Structural variation within uraniumVI heterocyclic carboxylates: Solid and solution states studies

A polymeric self-assembled complex, [Pb(pydc)]n was prepared from the complexation of a novel pyridine containing a self-assembleing system, [pnH2][pydc] (pydcH2 = pyridine-2,6-dicarboxylic acid and pn=propane-1,3-diammine) with lead(II) nitrate. The crystal system is monoclinic with space group P21/n and four molecules per unit-cell. The unit cell dimensions are: a = 9.7599(7)A, b = 5.5482(4)A, c = 14.1954(10)A, β = 104.5790(10)°. The final R value was 0.0192 for 2088 measured reflections. The main structure of this self-assembling compound is formed along the 21 screw axis.

https://www.jstage.jst.go.jp/article/analscix/23/0/23_0_x99/_pdf

Crystal Structure of a Polymeric Self-Assembled Lead(II) Complex

The title proton-transfer compound, C3H12N22+·2C7H4NO4−·2C7H5NO4·8H2O or (pnH2)(pydcH)2.2(pydcH2)·8H2O, was obtained by the reaction of pyridine-2,6-dicarboxylic acid (pydcH2) and propane-1,3-diamine (pn) in aqueous solution. Both neutral and monoanionic forms of the diacid are observed in the crystal structure. The negative charge of two monoanions is balanced by the dicationic propane-1,3-diaminium species. In addition, considerable π–π stacking inter­actions between the aromatic rings of the (pydcH)− and (pydcH2) fragments [with centroid–centroid distances of 3.5108 (11)–3.5949 (11) A] are observed. The most important feature of this crystal structure is the presence of a large number of O—H⋯O, O—H⋯N, N—H⋯O, N—H⋯N, C—H⋯O and C—H⋯N hydrogen bonds, with D⋯A ranging from 2.445 (2) to 3.485 (3) A. These inter­actions as well as ion pairing and π–π stacking connect the various fragments into a supra­molecular structure.

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Propane-1,3-diaminium-2-carboxy-pyridine-6-carboxyl-ate-pyridine-2,6-dicarboxylic acid-water (1/2/2/8).

The title polymeric compound, {(C3H12N2)[Co(C10H2O8)(H2O)2]·0.5H2O}n, was obtained by the reaction of cobalt(II) nitrate hexa­hydrate with the proton-transfer compound (pnH2)2(btc)·2H2O (pn = propane-1,3-diamine and btcH4 = benzene-1,2,4,5-tetra­carboxylic acid) in aqueous solution. Each Co2+ ion is situated on a crystallographic twofold rotation axis and is coordinated in a distorted octa­hedral geometry by six O atoms [Co—O = 2.0650 (9)–2.1107 (8) A] from two coordinated water mol­ecules and four (btc)4− ligands which also act as bridging ligands between Co2+ ions. In the crystal structure, a wide range of non-covalent inter­actions consisting of O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, as well as ion pairing, van der Waals forces and C—H⋯π stacking between the propane-1,3-diammonium ions and the aromatic rings of benzene-1,2,4,5-tetra­carboxyl­ate ligands, connect the various fragments, forming a three-dimensional supra­molecular structure. The crystal studied was an inversion twin.

Poly[propane‐1,3‐diammonium [diaqua(μ4‐4‐benzene‐1,2,4,5‐tetracarboxylato)cobaltate(II)] hemihydrate]

Faculty of Chemistry, Tarbiat Moallem University, 49 Mofateh Ave., 15614 Tehran, Iran, Department of Chemistry, Islamic Azad University, North Tehran Branch, Tehran, Iran, Department of Chemistry, Faculty of Science, Payame Noor University, Qom Center, Qom, Iran, Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran, and Faculty of Chemistry, Iran University of Science and Technology, Tehran, Iran Correspondence e-mail: haghabozorg@yahoo.com

Guanidinium (aqua-2jO)(4-hydroxy-6- carboxypyridine-2-carboxylato- 2jO,N,O)(l-4-hydroxypyridine-2,6- dicarboxylato-1:2jO,N,O:O)- (4-hydroxypyridine-2,6-dicarboxylato- 1jO,N,O)dizincate(II) dihydrate

Elham Motyeian

Papers

Crystal Structure of a Polymeric Self-Assembled Lead(II) Complex

Propane-1,3-diaminium-2-carboxy-pyridine-6-carboxyl-ate-pyridine-2,6-dicarboxylic acid-water (1/2/2/8).

Poly[propane‐1,3‐diammonium [diaqua(μ4‐4‐benzene‐1,2,4,5‐tetracarboxylato)cobaltate(II)] hemihydrate]

Guanidinium (aqua-2jO)(4-hydroxy-6- carboxypyridine-2-carboxylato- 2jO,N,O)(l-4-hydroxypyridine-2,6- dicarboxylato-1:2jO,N,O:O)- (4-hydroxypyridine-2,6-dicarboxylato- 1jO,N,O)dizincate(II) dihydrate