Firas F. Awwadi

Strong rail spin 1/2 antiferromagnetic ladder systems: (dimethylammonium)(3,5-dimethylpyridinium)CuX4, X = Cl, Br.

The mixed cation salts, (dimethylammonium)(3,5-dimethylpyridinium)CuX4 (X = Cl, Br), henceforth (DMA)(35DMP)CuX4, are new examples of spin-ladders based on nonbonded halide...halide interactions between CuX4(2-) anions. In these structures, double rows of the CuX4(2-) anions are sheathed by the 35DMP(+) cations, while the edges are capped by the DMA(+) cations. For the Br salt, the Br...Br contacts that define the rungs of the ladder are 4.017 A in length, while those that define the rails are 3.983 A. For the Cl salt, the corresponding lengths are 3.967 and 4.045 A. The susceptibility data for the Br salt exhibits a maximum at approximately 5.5 K, and fitting the data to the spin 1/2 antiferromagnetic ladder model yields 2J(rail)/k = -7.95 K and 2J(rung)/k = -4.07 K. The exchange coupling is much weaker in the Cl salt, no maximum in chi is observed down to 1.8 K, and the corresponding exchange constants are -1.59 and -1.25 K, respectively. An analysis is made of the structural factors involved in the J(rung) pathway.

Transition metal halide salts and complexes of 2-aminopyrimidine: manganese(II) compounds – crystal structures of (2-aminopyrimidinium)4 [MnCl4(H2O)]2, [(2-aminopyrimidine)2MnBr2(H2O)2·2H2O and (2-aminopyrimidinium)2+[MnBr2(H2O)4]Br2

The reaction of MnX2 (X = Cl, Br) with 2-aminopyrimidine (L) in neutral or acidic solution yields compounds of the forms [MnCl2L] n (1), (LH)4[MnCl4(H2O)]2 (2), [MnBr2L2(H2O)2]·2H2O (4) and (LH2)[MnBr2(H2O)4]-Br2 (5). The single-crystal X-ray structures of compounds 2, 4, 5 and the ligand salt, 2-aminopyrimidinium bromide, 3, are reported. Compound 1 is proposed to form a two-dimensional coordination polymer. Compound 2 adopts a dimer structure with the Mn(II) ions bridged by two chloride ions. The dimers are linked into a ladder motif via hydrogen bonding between coordinated water molecules and adjacent chloride ions. Compound 4 is a neutral, octahedral Mn(II) complex that is linked into chains via π-stacking interactions. Compound 5 is a co-crystal of [MnBr2(H2O)4] and 2-aminopyrimidine dihydrobromide. Crystal data: For (2): monoclinic, P21/c, a = 7.5011(15), b = 16.6411(12), c = 12.4462(14) Å; β = 91.092(13)°, V = 1533.3(4) Å3, Z = 4, D calc = 1.740 Mg m−3, μ = 1.541 mm−1, R = 0.0262 for [|I| ≥ 2σ(I)]. For (3): monoclinic, P21/c, a = 4.2934(5), b = 8.1959(9), c = 17.439(2) Å; β = 92.054(2)°, V = 613.25(12) Å3, Z = 4, D calc = 1.907 Mg m−3, μ = 6.593 mm−1, R = 0.0303 for [|I| ≥ 2σ(I)]. For (4): triclinic, P-1, a = 7.5312(18), b = 7.7139(15), c = 8.7044(14) Å; α = 67.482(8)°, β = 84.834(13)°, γ = 63.659(13)°, V = 406.71(14) Å3, Z = 1, D calc = 1.948 Mg m−3, μ = 5.746 mm−1, R = 0.0447 for [|I| ≥ 2σ(I)]. For (5): orthorhombic, Pnma, a = 17.1866(18), b = 12.0498(12), c = 7.1260(8) Å; V = 1475.8(3) Å3, Z = 4, D calc = 2.447 Mg m−3, μ = 11.727 mm−1, R = 0.0550 for [|I| ≥ 2σ(I)].

Effect of intermolecular interactions on the molecular structure; theoretical study and crystal structures of 4-bromopyridinium tetrafluoroborate and diaqua(3-bromopyridine)difluorocopper(II)

The role of C–Br⋯F interactions in two crystal structures (4BP)BF4 (I) and Cu(H2O)2(3bp)F2 (II), (where 4BP is the 4-bromopyridinium cation and 3bp is 3-bromopyridine) is investigated. Crystal structure analysis indicates that the supramolecular assembly of I is based on symmetrical bifurcated C–Br⋯F halogen bonding and the bifurcated N–H⋯F hydrogen bonding, while that of II is based on O–H⋯F hydrogen bonding interactions. The Br⋯F distance in I is 0.13 A less than the sum of van der Waals radii. In contrast, the Br⋯F distance in II is 0.04 A longer than the sum of van der Waals radii, indicating that the C–Br⋯F interaction plays a minor role in developing the supramolecular structure of II. The structure of I is the first reported with perfect symmetrical bifurcated C–Br⋯F halogen bonding. II is the first reported crystal structure with C–Br⋯F–tM interactions, tM = transition metal. Theoretical calculations have shown that a charge assisted symmetrical bifurcated C–Br⋯F interaction is stronger than the corresponding linear one, whereas in the normal (not charge assisted) C–Br⋯F halogen bonding both linear and bifurcated interactions have comparable strength. This conclusion is supported by structure analysis of reported structures in this work and the published data in Cambridge Structural Database (CSD).

Copper–halide bonds as magnetic tunnels; structural, magnetic and theoretical studies of trans-bis(2,5-dibromopyridine)dihalo copper(II) and trans-bis(2-bromopyridine)dibromo copper(II)

The magneto-structural correlations in Cu(25dbp)2X2 and Cu(2bp)2Br2, where 25dbp = 2,5-dibromopyridine, X = Cl or Br, and 2bp = 2-bromopyridine have been investigated. The supramolecular structures of Cu(25dbp)2X2 are based on C–Br⋯X–Cu halogen bonding interactions. The temperature dependence of the susceptibility of Cu(25dbp)2Cl2 is best represented by an antiferromagnetic chain model. This agrees with the supramolecular structure; Cu(25dbp)2Cl2 molecules form linear chains of Cu–Cl⋯Cl–Cu structural units. In contrast, the magnetic susceptibility of Cu(25dbp)2Br2 is best represented by a ferromagnetic chain model; Cu(25dbp)2Br2 molecules form a chain structure based on Cu⋯Br2⋯Br–Cu where Br2 is the bromine atom on position 2 of the 2,5-dibromopyridine ligand. The susceptibilities of Cu(2bp)2Br2 indicate that the magnetic exchange interaction is very weak, even though Cu(2bp)2Br2 forms an isostructural chain structure similar to that observed in Cu(25dbp)2Br2. This paramagnetic behavior might be due to the presence of competitive antiferromagnetic and ferromagnetic exchange pathways. The shortest Cu–Br⋯Br–Cu distance is 4.5 A in Cu(2bp)2Br2, where Br is the bromide ligand, whereas the shortest inter-bromide ligand distance is 5.4 A in Cu(25dbp)2Br2. The two-bromide exchange pathway is known to be antiferromagnetic. This analysis is supported by DFT/B3LYP calculations. Calculations show that there is a significant spin density on the halide ligands, whereas, only a small spin density resides on Br2 (organic bromine). Also, the calculated spin density surface shows the presence of a spin end-cap along the Cu–X bond, which can rationalize the two-halide exchange pathway. In addition, theoretical calculations reveal that the two-halide exchange pathway in CuX2L2 compounds is stronger than the corresponding interaction in [CuX42−] compounds.

Trans/cis isomerization of [RuCl2{H2CC(CH2PPh2)2)}(diamine)] complexes: Synthesis, spectral, crystal structure and DFT calculations and catalytic activity in the hydrogenation of α,β-unsaturated ketones

Three complexes of the general formula trans/cis-[Ru((II))(dppme)(N-N)Cl2] {dppme is H2C=C(CH2PPh2)2 and N-N is 1,2-diaminocyclohexane (trans/cis-(1)) and 1-methyl-1,2-diaminopropane (trans-(2)} were obtained by reacting trans-[RuCl2(dppme)2] with an excess amount of corresponding diamine in CH2Cl2 as a solvent. The complexes were characterized by an elemental analysis, IR, (1)H, (13)C and (31)P{1H} NMR, FAB-MS and UV-visible. The trans-(1) (kinetic product) readily isomerizes to the cis-(1) (thermodynamic product) and this process was followed by using (31)P{(1)H} NMR, cyclic voltammetry and UV-vis spectroscopy. The electrochemical studies on complex (1) reveal that the Ru(III)/Ru(II) couples are sensitive to the isomer (trans/cis) formed. The cis-(1) was confirmed by X-ray structure and (31)P{(1)H} NMR. Transfer-hydrogenation reactions for reduction of trans-4-phenyl-3-butene-2-one were conducted using complexes trans/cis-(1) and trans-(2). The electronic spectra of cis/trans-(1) in dichloromethane were calculated with the use of time-dependent DFT methods.

Catena-bis(aqua(3-oxy-2-pyridono)copper(II))μ-pyrazine diperchlorate: a perchlorate-bridged magnetic ladder

Reaction of Cu(ClO4)2 · 6H2O with pyrazine (pz) and 2,3-dihydroxy pyridine in aqueous solution generates bis(aqua(3-oxy-2-pyridono)copper(II))μ-pyrazine diperchlorate. The compound crystallizes in the triclinic space group P 1. The aqua(3-oxy-2-pyridono)copper(II) units are bridged by pyrazine to form a dimer. These dimers are further bridged by perchlorate to form a structural ladder parallel to the b-axis. Hydrogen bonding interactions and π-stacking of the pyridone rings also provide structural stability to the lattice and provide potential magnetic superexchange pathways. Temperature-dependent magnetic susceptibility data reveal a maximum in χ near 6 K and exhibit a rapid drop in χ at lower temperatures, in agreement with a singlet ground state. The use of several models for fitting the magnetic data gave values of approximately −10 K for the dimer interaction and approximately +1.5 K for the interdimer interaction.

Three new seco-ursadiene triterpenoids from Salvia syriaca.

Three new seco-ursadiene triterpenoids 1–3 together with 11 known compounds were isolated from Salvia syriaca of Jordanian origin. The compounds were identified by using NMR spectroscopy including extensive 2D NMR experiments and mass spectrometry. The structure of compound 3 was confirmed by X-ray crystallography, and the information thus obtained was used to confirm the stereochemistry of compounds 1 and 2. This is the second report of 17,22-seco-17(28),12-ursadien-22-oic acids.

Characterization and biological activities of two copper(II) complexes with dipropylenetriamine and diamine as ligands

Two new mixed-ligand copper(II) complexes, [Cu(dipn)(NN)]Br2(1-2) [dipn=dipropylenetriamine, NN=ethylenediamine (en) (1) and propylenediamine (pn) (2)], have been synthesized. These complexes were characterized by spectroscopic and thermal techniques. Crystal structure for 2 shows a distorted trigonal-bipyramidal geometry around Cu(II) ion with one solvate water molecule. Antimicrobial and antiproliferative assays were conducted to evaluate the biological activities of these complexes. The complexes exhibit a promising antimicrobial effect against an array of microbes at 200μg/mL concentration. The antiproliferative assay shows a high potential of these complexes to target Human keratinocyte cell line with IC50 values of 155 and 152μM. The absorption spectrum of 2 in water was modeled by time-dependent density functional theory (TD-DFT).

New isomeric Cu(NO2-phen)2Br]Br complexes: Crystal structure, Hirschfeld surface, physicochemical, solvatochromism, thermal, computational and DNA-binding analysis

Water soluble mono-cationic copper(II) complex of the general formula [Cu(NO2-phen)2Br]Br, (NO2-phen=5-nitro-1.10-phenantholine) was prepared in good yield under ultrasonic irradiation. The desired complex was isolated as a bromide salt and identified by MS, EA, UV-Vis., TG/DTA, FT-IR and XRD. The single-crystal X-ray diffraction and Hirschfield analysis revealed a square pyramidal distorted geometry around the Cu(II) center. The geometry of the [Cu(NO2-phen)2Br]+ complex was fully optimized with ab-initio methods and (DFT/B3LYP) density functional theory, then structural parameters were compared to the XRD data. The solvatochromism of [Cu(NO2-phen)2Br]Br complex was investigated in several polar solvents. Absorption and viscosity titration studies concluded that the [Cu(NO2-phen)2Br]Br complex is a very good CT-DNA binder.

Selective phytotoxic activity of 2,3,11β,13-tetrahydroaromaticin and ilicic acid isolated from Inula graveolens

Inula graveolens is a poisonous annual plant of Mediterranean origin. The invasive nature of the plant suggests that it may possess phytotoxic activity. The aim of this study was to assess the ability of I. graveolens to inhibit the growth of different plants in Petri dish and to identify the main bioactive compounds. Bio-guided fractionation of the plant extracts led to the isolation of 2,3,11β,13-tetrahydroaromaticin (THA) and ilicic acid. Both compounds showed selective and significant phytotoxic activity at 25 ppm. Root length of barley, oat, millet, tuberous canary grass and lentils were significantly reduced by 25 ppm of THA, while the root of cauliflower, cress and radish were similarly reduced by ilicic acid at 25 ppm. The structure of each compound was elucidated by using NMR and HR-MS. X-ray crystallography of THA is reported for the first time to confirm the relative stereochemistry of the compound.