Aziz Ibragimov

Conformational dimorphism in o-nitrobenzoic acid: alternative ways to avoid the O...O clash.

Polymorphism is a challenging phenomenon and the competitive packing alternatives which are characteristic for polymorphs may be encountered for essentially rigid molecules. A second crystal form of the well known compound o-nitrobenzoic acid, C7H5NO4, an important intermediate in the production of dyes, pharmaceuticals and agrochemicals, is described. Although obtained serendipitously, its intra- and intermolecular features match expectations from database searches and theoretical calculations. O-H...O hydrogen-bonded carboxylic acid dimers represent the building blocks in both polymorphs. For steric reasons and in agreement with a calculated potential energy surface, the carboxylic acid and nitro groups cannot simultaneously be coplanar with the benzene ring but have to tilt. In the well established crystal form, this out-of-plane torsion is more pronounced for the nitro substituent. In contrast, the new polymorph is characterized by a major tilt of the carboxylic acid group. The molecules in both alternative crystal forms achieve a similar compromise with respect to acceptable intramolecular O...O contacts.

X-Ray Structures of Three Polymeric and Two Mononuclear Metal Complexes on the Base of p-Aminobenzoic Acid

Crystals of five coordination compounds have been grown from solutions containing p-aminobenzoic acid (PABA), diethanolamine (DEA) and salt of the definite metal. The X-ray crystallography attests that complexes [Co(PABA)2(H2O)2]n·H2O (1), [Ni(PABA)2(H2O)2]n·H2O (1′) and [Zn(PABA)2(H2O)]n·H2O (2) are polymeric, while Mn(DEA)2·2(PABA)·2(H2O) (3) and Cr(DEA)2·2(PABA) (4) are mononuclear coordination compounds. In the isomorphic polymers 1 and 1′ metal ions are bridged to infinite columns by coordination bonds of the two antiparallel PABA molecules (bimolecular association). The complex 2 is 2-D polymer repeating units of which are hexagons generated by combination of mono- and bimolecular associations. All six coordination sites of Mn2+- and Cr2+-ions in 3 and 4 are occupied by two DEA molecules retaining PABA anions in outer sphere. The CSD analysis shows that there are five types of coordination polymers bridged by O and N atoms of the PABA-molecules. As a result of this research two new type motif polymers have been added to the existing list.Graphical Abstract

Crystal structure of trans-bis­(di­ethano­lamine-κ3O,N,O′)manganese(II) bis­(3-amino­benzoate)

The title salt, [Mn(C4H11NO2)2](C7H6NO2)2, contains a centrosymmetric cation with the Mn2+ ion coordinated octahedrally by two tridentate diethanolamine (DEA) ligands. The cations are connected to the anions through O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network structure.

Charge density of the biologically active molecule (2-oxo-1,3-benzoxazol-3(2H)-yl)acetic acid

(2-Oxo-1,3-benzoxazol-3(2H)-yl)acetic acid is a member of a biologically active class of compounds. Its molecular structure in the crystal has been determined by X-ray diffraction, and its gas phase structure was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory. In order to understand the dynamics of the molecule, two presumably soft degrees of freedom associated with the relative orientation of the planar benzoxazolone system and its substituent at the N atom were varied systematically. Five conformers have been identified as local minima on the resulting two-dimensional potential energy surface within an energy window of 27 kJ mol(-1). The energetically most favourable minimum closely matches the conformation observed in the crystal. Based on high-resolution diffraction data collected at low temperature, the experimental electron density of the compound was determined. Comparison with the electron density established by theory for the isolated molecule allowed the effect of intermolecular interactions to be addressed, in particular a moderately strong O-H...O hydrogen bond with a donor...acceptor distance of 2.6177 (9) Å: the oxygen acceptor is clearly polarized in the extended solid. The hydrogen bond connects consecutive molecules to chains, and the pronounced charge separation leads to stacking between neighburs with antiparallel dipole moments perpendicular to the chain direction.

Dimorphism of Hexaaquanickel(Ii) Bis(p-Nitrobenzoate) Dihydrate Salt: A New Triclinic Crystal Form

Room temperature crystallization from a water/ethanol solution of NiSO4, p-nitrobenzoic acid (HPNBA), and thiourea yields single crystals of [Ni(H2O)6](PNBA)2·2H2O. Crystal data are: a = 5.9626(8), b = 7.3552(11), c = 12.3459(17) Å, α = 97.885(12), β = 96.714(11), γ = 91.158(11)°, V = 532.28(13) Å3, space group Pī, Z = 1. An alternative monoclinic crystal form of the same compound with a slightly lower packing efficiency was previously obtained. The Ni(II) cation is located on a crystallographic inversion center and octahedrally coordinated by six water molecules. The PNBA moieties occupy an outer coordination sphere acting as counter-anions. An intricate system of H bonds between the complex cation, the PNBA anions, and the co-crystallized water molecules results in a three-dimensional network.

Two supramolecular complexes based on 4-hydroxybenzoic acid and triethanolamine: Synthesis and structure

Two new copper and nickel complexes with triethanolamine (TEA) and 4-hydroxybenzoic acid (L) have been synthesized within the framework of systematic studies into the formation of mixed-ligand metal complexes on the basis of commercially available compounds with the simplest structure, such as ethanolamines and benzoic acid monoderivatives (hydroxy-, amino-, and nitrobenzoic acids). According to X-ray diffraction data, the complexes have the compositions [Cu2(L)2(TEA)2] · [Cu(TEA)2] · 2H2O (I) and [Ni(TEA)2] · 2L (II). Compound I is a mixed-ligand complex, while complex II is a supramolecular compound consisting of a nickel–TEA monoligand complex anion and non-coordinated L. TEA molecules in complex I are coordinated in both tetradentate and tridentate mode, while only tridentate coordination is typical for complex II. The coordination polyhedra of metal atoms are tetragonal bipyramids elongated due to the Jahn–Teller effect in complex I and octahedra in complex II. In both crystals, structural units are linked into 2D associates via hydrogen bonds.

Synthesis, structure, and fungicidal activity of mono- and binuclear mixed-ligand copper complex with p-nitrobenzoic acid and monoethanolamine

Mixed-ligand metal complexes based on ethanolamines and simple monosubstituted benzoic acids, in particular, mono- and binuclear copper complexes with monoethanolamine (MEA) and p-nitrobenzoic acid (PNBA), [Cu2+((PNBA)2-(MEA)2)] (I) and [2Cu2+((PNBA)4-(MEA)2(H2O)2)] (II), were prepared for the first time. The structures of the complexes were characterized by FT IR spectroscopy and X-ray diffraction (CIF files CCDC no. 1497849 (I) and no. 1497848 (II)). The doubly charged copper ions are coordinated at the vertices of octahedra, which are highly distorted due to the Jahn–Teller effect. In the crystals of the mononuclear complex I, the molecules are joined into columns, whereas in the binuclear compound II, a three-dimensional framework is formed owing to intermolecular H-bonds involving the nitro group. Fungicidal activities were found for compounds I, II, MEA, PNBA, previously obtained single-ligand copper complexes with MEA and PNBA, and MEA- and PNBA-based organic salt. The biological activity gradually increases in the series: ligand, single-ligand metal complex, organic salt, mono- and binuclear mixed-ligand complex, i.e., some ligands and copper ions show a synergistic effect.

Molecular and crystal structure of a mixed-ligand cadmium complex with p-hydroxybenzoic acid and monoethanolamine

Single crystals of a mixed-ligand cadmium complex of the composition Cd(PHBA)2(MEA) 2 are grown from the solution of Cd(CH3OO)2, p-hydroxybenzoic acid (PHBA) and monoethanolamine (MEA) in aqueous ethanol. The crystallographic data are as follows: a = 11.6400(2) Å, b = 10.1363(1) Å, c = 16.6296(2) Å, β = 93.937(1)°, space group I2/a, V = 1957.44(5) Å3, Z = 4. In the complex molecule located on the twofold axis, ligands of both types are bidentately bound to the cadmium ion having the coordination number 8. In the crystal structure, two H bonds of the O–H•••O type combine complex molecules into layers parallel to the ab plane.

X-ray structure characterization of metal–benzoic acid organic complexes

An increasing interest has been sustained in the chemistry of metal-organic frameworks owing to their unique unusual properties and potential biological activities. Mono-substituted derivatives of benzoic acid such as hydroxybenzoic and nitrobenzoic acids demonstrate a low antimicrobial and moderate growth stimulating actions. Ethanolamines also show the same types of the biological action. In mixed-ligand metal complexes on the base of these substances an enhancement of biological activity may be more pronounced. The title compounds, mixed-ligand Ni-complex of o-nitrobenzoic acid (ONBA) with diethanolamine (DEA) and Cd-complex of p-hydroxybenzoic acid (PHBA) with monoethanolamine (MEA) we prepared and exhibit antimicrobial activity of these complexes against fungi Fusarium oxysporum and Candida albicans. Because of these activities, the X-ray crystal structures shown below are of great interest to our continuing investigations. An inner coordination sphere of the Ni-complex consists of 2 ONBA and 2 DEA molecules. In the Cd-complex a metal ion coordinates 2 PHBA and 2 MEA molecules: former molecules are linked bidentately throw oxygen atoms O1 and O2 of carboxylate groups while latter molecules are chelated throw nitrogen N1 and oxygen O4. Coordination polyhedron is difficult to describe with known polyhedr but it is near to bicapped trigonal prism. In order to assess enhancement of the biological action monoligand metal complexes and organic salts between ligands also were prepared. They will be discussed in detail. This work is funding in the framework of fundamental grants for Uzbekistan. [1] Aziz B. Ibragimov et al. (2016) J. Chem. Crystallogr. 46-8, 352-363. [2] A. B. Ibragimov et al. (2017) J. Inorg. Chem. 62-4, 439-445.

Synthesis and structure of mono- and polynuclear Cu(II) complexes with α-(N-benzoxazolin-2-one)acetic acid

Two compounds with the α-(N-benzoxazolin-2-one)acetic acid ligand (L) were synthesized: [Cu(L)2(NH2C2H4OH)2] (I) and [Cu(L)2(H2O)2]n (II), viz., mono- and polynuclear complexes, respectively. According to X-ray diffraction data (CIF files CCDC no. 1008795 (I) and 1008794 (II)), the coordination polyhedron of the metal atom in I is an extended tetragonal bipyramid with four heteroatoms of two monoethanolamine molecules in the equatorial plane. The carboxyl oxygen atoms of two ligands L occupy the apical positions. In complex II, a tetragonal bipyramid is also formed, having two O atoms of the carboxyl groups of the L molecule and two water O atoms in the equatorial plane. Two oxygen atoms of the carboxyl groups of the L molecule occupy apical positions. Complex II is a 2D polymer (polymerization involves four O atoms of the carboxyl group) with the [CuL2(H2O)2] unit.