Synthesis and characterization of the chromium(III) complexes of ethylene cross-bridged cyclam and cyclen ligands

Dichloro(4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane)chromium(III) chloride, Dichloro(4,10-dibenzyl-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane) chromium(III) chloride, and Dichloro(4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2] hexadecane)chromium)(III) chloride have been prepared by the reaction of anhydrous chromium(III) chloride with the appropriate cross-bridged tetraazamacrocycle. Aquation of these complexes proved difficult, but Chlorohydroxo(4,11-dimethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane)chromium)(III) chloride was synthesized directly from chromium(II) chloride complexation followed by exposure or the reaction to air in the presence of water. The four complexes were characterized by X-ray crystal structure determination. All contain the chromium(III) ion in a distorted octahedral geometry and the macrocycle in the cis-V configuration, as dictated by the ethylene cross-bridge. Further characterization of the hydroxo complex reveals a magnetic moment of μ_eff = 3.95 B.M. and electronic absorbtions in acetonitrile at λ_max = 583 nm (ε = 65.8 L/cm mol), 431 nm (ε = 34.8 L/cm mol) and 369 nm (ε = 17 L/cm mol).     

Cobalt(III) complexes of some aromatic thiohydrazides - Synthesis, characterization and structure

[Co(NH₃)₅Cl]Cl₂ forms neutral 1:3 complex by reaction with aromatic thiohydrazides, i.e. thiobenzhydrazide, o-hydroxythiobenzhydrazide, thiophen-2-thiohydrazide and furan-2-thiohydrazide. All these complexes are diamagnetic and have been characterized by elemental analysis and combination of spectroscopic methods. Cyclic voltammometry of the complexes shows irreversible metal centered and ligand centered electron transfer reactions. One complex, tris-o-hydroxythiobenzhydrazidocobalt(III), has been crystallized from DMSO solution to produce solvated crystals and its structure has been established by X-ray crystallography. Cobalt(III) ion is linked through three hydrazinic nitrogen and three sulfur atoms of three identical deprotonated ligand molecules in a distorted octahedral environment. Involvement of -OH group in intramolecular and intermolecular hydrogen bonding is crucial for crystal formation.     

Manganese(II) complexes with V-shaped sulfonyldibenzoate: The 3D structures with interpenetrated threefold or tetra-nuclear manganese(II) units

Five Mn^II-sdba coordination polymers with mono-, di-, tri-, tetra-nuclear cores based on the V-shaped 4,4′-dicarboxybiphenyl sulfone (H₂sdba) ligands: [Mn(sdba)(phen)₂(H₂O)]_n·3nH₂O (1), [Mn₂(sdba)₂(μ-H₂O)(py)₄]_n (2), [Mn₃(sdba)₂(Hsdba)₂(2,2′-bipy)₂]_n (3), [Mn₄(sdba)₄(4-mepy)₂(H₂O)₄]_n·2nH₂O (4) and [Mn₄(sdba)₄(bpp)₄(μ-H₂O)₂]_n·0.5nH₂O (5) (phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine, 4-mepy = 4-picoline, bpp = 1,3-bi(pyridine-4-yl)propane) were hydrothermally synthesized and structurally characterized. The M-O-C metal clusters in above complexes act as SBUs, and the V-shaped sdba ligands link the SBUs to generate the novel frameworks. In complexes 1 and 3 their 1D chains are linked into the 2D planes through various hydrogen bonding. Complex 2 displays the 3D structure with interpenetrated threefold, while complexes 4 and 5 both exhibit the 3D structures with the tetra-nuclear Mn₄ units. The magnetic susceptibility studies in the 2-300 K range for these complexes reveal the existence of anti-ferromagnetic exchange interactions between the Mn^II ions.     

Manganese(II) complexes of a set of 2-aminomethylpyridine-derived ligands bearing a methoxyalkyl arm: syntheses, structures and magnetism

Four new ligands, N-(2-methoxyethyl)-N-(pyridin-2-ylmethyl)amine (mepma), N-(3-methoxypropyl)-N,N-bis(pyridin-2-ylmethyl)amine (mpbpa), N-(2-methoxyethyl)-N,N-bis(pyridin-2-ylmethyl)amine (mebpa) and 2-{[(2-methoxyethyl)(pyridin-2-ylmethyl)amino]methyl} phenol (Hmepap), and four of their complexes with manganese(II) halides, [MnCl₂(mepma)₂] (1), [MnCl(μ-Cl)(mpbpa)]₂ (2), [MnBr₂(mebpa)] (3) and [MnBr₂(MeOH)(Hmepap)] (4) have been synthesized and characterized. Single-crystal Xray studies revealed that in all four complexes, the Mn(II) coordination spheres are distorted octahedral. In 1 and 2, the ether oxygen atom does not coordinate to the Mn(II) centre, but in 3 and 4 it does. The mononuclear molecules of 1 are linked by double hydrogen bonds to form linear chains. Temperature dependent magnetic susceptibility measurements revealed that the Mn(II) ions in 1 interact antiferromagnetically, with J=−1.06 cm⁻¹. Compound 2 crystallizes as a double chloride-bridged dimer in which there is a weak ferromagnetic interaction (J=0.55 cm⁻¹) between the Mn(II) pair. The solution EPR spectrum of 2 suggests that in methanol compound 2 decomposes to a great extent to mononuclear species. In compound 3, mebpa acts as a tetradentate ligand with all of its nitrogen and oxygen atoms coordinated to the Mn(II) ion. Unexpectedly, in complex 4, the phenolic oxygen of Hmepap remains protonated and does not coordinate to the metal ion. Instead the oxygen from a methanol molecule coordinates the manganese centre. Hydrogen bonds between one of the two bromide ions, and the methanol and phenol hydroxyl groups, respectively, connect the mononuclear molecules of 4 into chains. No magnetic interactions were observed between the Mn(II) ions in 3 or 4.     

Anions as stabilizing ligands for Ni(III)(cyclam) in aqueous solutions

Several new anions were shown to be good stabilizing ligands for , (L = 1,4,8,11-tetraazacyclotetradecane, cyclam) in aqueous solutions. , phosphonates, phosphates, including the biological relevant ATP were shown to have the highest binding constants to the tervalent nickel ion. The results suggest that the charge density of the anion at the binding site and the basicity of the anion are the main factors affecting the binding constant to the central Ni(III) cation.     

Synthesis and structural determination of new octaethylporphyrin iron(III) complexes containing cyanamide derivatives as axial ligand

The reactions of heme, [OEPFeCl] where OEP is the dianion of octaethylporphyrin, with phenylcyanamide (pcyd) ligands have been studied. Four new porphyrin complexes, [OEPFe(L)] (L = pcyd (2), 2-Clpcyd (3), 2-Mepcyd (4), 2,4-Me₂pcyd (5)), have been isolated and characterized by spectroscopic methods. ¹H NMR spectroscopy reveals that the species [OEPFe(L)] are paramagnetic and iron is five-coordinate. The structure of [OEPFe(pcyd)] (2) has been determined by X-ray diffraction analysis. The four Fe-N, bond distances have average values of 2.062 Å. The average displacement of the iron(III) atom from the mean porphinato core is 0.45 Å. Electrochemical of [OEPFe(L)] (L = pcyd (2), 2-Clpcyd (3), 2-Mepcyd (4), 2,4-Me₂pcyd (5)) have been studied by cyclic voltammetry.     

Synthesis and characterization of tetraphenylporphyrin manganese(III) complexes of phenylcyanamide ligands

Several complexes of TPPMn-L, where TPP is the dianion of tetraphenylporphyrin and L is monoanion of 4-methylphenylcyanamide (4-Mepcyd) (1), 2,4-dimethylphenylcyanamide (2,4-Me₂pcyd) (2), 3,5-dimethylphenylcyanamide (3,5-Me₂pcyd) (3), 4-methoxyphenylcyanamide (4-MeOpcyd) (4), phenylcyanamide (pcyd) (5), 2-chlorophenylcyanamide (2-Clpcyd) (6), 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd) (7), 2,6-dichlorophenylcyanamide (2,6-Cl₂pcyd) (8), 4-bromophenylcyanamide (4-Brpcyd) (9), and 2,3,4,5-tetrachlorophenylcyanamide (2,3,4,5-Cl₄pcyd) (10), have been prepared from the reaction of TPPMnCl and thallium salt of related phenylcyanamide. Each of the complexes has been characterized by IR, UV-Vis and ¹H NMR spectroscopies.4-Methylphenylcyanamidotetraphenylporphyrin manganese(III) crystallized with one molecule of solvent CHCl₃ in the triclinic crystal system and space group with the following unit cell parameters of: a = 11.596(6) Å; b = 11.768(9) Å; c = 17.81(2) Å; and α, β, γ are 88.91(9)°, 88.16(7)°, 67.90(5)°, respectively; V = 2251(3) Å³; Z = 2. A total of 4234 reflections with I > 2σ(I) were used to refine the structure to R = 0.0680 and R_w = 0.2297. The Mn(III) shows slightly distorted square pyramidal coordination with the 4-methylphenylcyanamide in the axial position, coordinated from nitrile nitrogen. The reduction of each of the TPPMn-L complexes was also examined in dichloromethane and spectroelectrochemical behavior of (1) was investigated and compared to TPPMnCl.     

Synthesis of cobalt(III) complexes with novel open chain oxime ligands and metal-ligand coordination in aqueous solution

Cobalt(III) complexes with new open chain oxime ligands: N,N′-bis(2-hydroxyiminopropionyl)-1,2-aminoethane (H₂pen) and N,N′-bis(2-hydroxyiminopropionyl)-1,3-diaminopropane (H₂pap) have been investigated. Single crystals of Co(papH₋₁)(Im₂)·CH₃OH (1) and Co(papH₋₁)(MEA)₂·1.5H₂O (2) (where Im = imidazole, MEA = monoethanolamine) suitable for X-ray crystallography were grown by slow evaporation of methanol/water solutions at room temperature. The molecular structures have been determined using single-crystal X-ray diffraction methods. The potentiometric and spectrophotometric results in aqueous solution reveal that both of the open chain ligands show a very high efficacy in the coordination of Co(II) ions. As it has been indicated, differences between the two oxime ligands in complexing ability may be attributed to the longer -CH₂- chain in H₂pap and by that a better fit of the relatively large Co(II) ion to the accessible binding site. One of the complex species confirmed under inert atmosphere, namely of type Co(LH₋₁)⁻ (where L = pap or pen), has been shown as the “active” form, capable of dioxygen uptake followed by irreversible oxidation to Co(III).     

High-spin Schiff-base dinuclear iron(III) complexes bridged by N-oxide ligands

Synthesis and structure of dinuclear complexes [{Fe^III(L⁵)}b{Fe^III(L⁵)}](BPh₄)₂, where L⁵ is a pentadentate Schiff-base ligand, b is a bidentate N-oxide bridging ligand based on bipyridine, is reported. Magnetic behavior is investigated in terms of the magnetic susceptibility, magnetization, and Mössbauer spectroscopy revealing that the complexes are high-spin over the whole temperature region.     

Secondary ligand-metal interactions in rhodium(III) and iridium(III) phosphoramidite complexes

The synthesis, characterization, and application in asymmetric catalytic cyclopropanation of Rh(III) and Ir(III) complexes containing (S_a,R_C,R_C)-O,O′-[1,1′-binaphthyl-2,2′-diyl]-N,N′-bis[1-phenyl-ethyl]phosphoramidite (1) are reported. The X-ray structures of the half-sandwich complexes [MCl₂(C₅Me₅)(1,κP)] (M = Rh, 2a; M = Ir, 2b) show that the metal-phosphoramidite bond is significantly shorter in the Ir(III) analog. Chloride abstraction from 2a (with CF₃SO₃SiMe₃ or with CF₃SO₃Me) and from 2b (with AgSbF₆) gives the cationic species [MCl(C₅Me₅)(1,2-η-1,κP)]⁺ (M = Rh, 3a; M = Ir, 3b), which display a secondary interaction between the metal and a dangling phenethyl group (NCH(CH₃)Ph) of the phosphoramidite ligand, as indicated by NMR spectroscopic studies. Complexes 3a and 3b slowly decompose in solution. In the case of 3b, the binuclear species [Ir₂Cl₃(C₅Me₅)₂]⁺ is slowly formed, as indicated by an X-ray study. Preliminary catalytic tests showed that 3a cyclopropanates styrene with moderate yield (35%) and diastereoselectivity (70:30 trans:cis ratio) and with 32% ee (for the trans isomer).     

Manganese (III) phthalocyanine-substituted cytochrome c

Manganese phthalocyanine-substituted cytochrome c has been prepared by the reaction of Mn(III) tetrasulfonated phthalocyanine with apocytochrome c in acetate buffer, pH 5.8. Its structure and properties have been investigated by difference spectroscopy, circular dichroism (cd), electron paramagnetic resonance (epr), electrophoresis, molecular weight estimation, and potentiometric measurements. The epr and spectroscopic data show that the manganese phthalocyanine-substituted cytochrome c represents the low spin, six-coordinated. Mn(Ill) complex with the metal ion in the plane of the phthalocyanine ring. The sixth ligand, which is coordinated axially to the metal ion, is probably the methionine-80. Electrophoresis and molecular weight studies show this complex to be a monomer. As is shown by cd experiments, Mn(III)L-apocyt has a more ordered structure than that of apocytochrome c. Its conformation is, however, significantly altered compared to native cytochrome c. The manganese(III)-phthalocyanine complex is able to combine with cyanide. The cyanide derivative gives a stable reduced form upon dithionite reduction. If, however, Mn(IlI)Lapocyt is reduced with dithionite before addition of cyanide, it loses its ability to coordinate with cyanide. Nitric oxide reacts with the manganese(III) complex to form, in all probability, the nitrosyl derivative. The half-reduction potential of Mn(IlI)L-apocyt is about +400 mV, and the complex is reduced by cytochrome c. Spectroscopic data suggest that the mechanism of this process is complicated.     

Iron(III), chromium(III) and cobalt(II) complexes with squarate: Synthesis, crystal structure and magnetic properties

The preparation and variable temperature-magnetic investigation of three squarate-containing complexes of formula [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (1) [Cr₂(OH)₂(C₄O₄)₂(H₂O)₄]·2H₂O (2) and [Co(C₄O₄)(H₂O)₄]_n (3) [H₂C₄O₄ = 3.4-dihydroxycyclobutene-1,2-dione (squaric acid)] together with the crystal structures of 1 and 3 are reported. Complex 1 contains discrete centrosymmetric [Fe₂(OH)₂(C₄O₄)₂(H₂O)₄] diiron(II) units where the iron pairs are joined by a di-μ-hydroxo bridge and two squarate ligands acting as bridging groups through adjacent oxygen atoms. Two coordinated water molecules in cis position complete the octahedral environment at each iron atom in 1. The iron-iron distance with the dinuclear unit is 3.0722(6) Å and the angle at the hydroxo bridge is 99.99(7)°, values which compare well with the corresponding ones in the isostructural compound 2 (2.998 Å and 99.47°) whose structure was reported previously. The crystal structure of 3 contains neutral chains of squarato-O¹,O³-bridged cobalt(II) ions where four coordinated water molecules complete the six-coordination at each cobalt atom. The cobalt-cobalt separation across the squarate bridge is 8.0595(4) Å. A relatively important intramolecular antiferromagnetic coupling occurs in 1 whereas it is very weak in 2, the exchange pathway being the same [J = −14.4 (1) and −0.07 cm⁻¹ (2), the spin Hamiltonian being defined as ]. A weak intrachain antiferromagnetic interaction between the high-spin cobalt(II) ions occurs in 3 (J = −0.30 cm⁻¹). The magnitude and nature of these magnetic interactions are discussed in the light of their respective structures and they are compared with those reported for related systems.     

Manganese(III) and rhenium(II) complexes with bulky 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinonato ligands via carbonyls of corresponding metals

Four-coordinate complex Mn^III(ISQ-Prⁱ)(AP-Prⁱ) (1), where ISQ-Prⁱ = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate anion-radical, AP-Prⁱ = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-amidophenolate dianion, has been prepared by the reaction of Mn₂(CO)₁₀ with free 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinone (IBQ-Prⁱ) in the molar ratio 1:4 in toluene. In contrast to manganese, rhenium carbonyl reacts with o-iminobenzoquinone to form complex Re^II(ISQ-Prⁱ)₂(CO)₂ (2) with the retention of two carbonyls in coordination sphere of rhenium. The complexes have been characterized by IR, UV-Vis, and EPR spectroscopies. Molecular structures of compounds 1 and 2 have been determined by single-crystal X-ray crystallography. Compound 1 is centro-symmetric square-planar molecule with delocalized mixed valent state of AP-Prⁱ and ISQ-Prⁱ ligands. EPR spectrum of 1 in solid at 300-77 K is typical for manganese complexes with S = 3/2 state. The effective magnetic moment of 1 is 1.96 μ_B at temperature 5 K as it was established by variable-temperature magnetic susceptibility measurements. Six-coordinate octahedral complex 2 possesses an S = 1/2 ground state, which is attained via strong intramolecular antiferromagnetic interaction between t_2g orbital unpaired electron of the low spin Re^II ion and the unpaired electron on π-orbital of the radical ligand.     

An unexpected influence of the nature of the amine on the crystal structure of some Co(III)-Bi(III) heterobimetallic complexes

Two novel cobalt(III)-bismuth(III) heterometallic compounds [Co(NxH)₂(An)₂]₂[Bi(EDTA)(H₂O)]₂ · 7H₂O (1) and [Co(NxH)₂(p-Tol)₂][Bi(EDTA)] · 4H₂O (2) [An-aniline, p-Tol-para-toluidine, NxH-1,2-cyclohexanedionedioximate-ion, EDTA-ethylenediaminetetraacetate-ion] have been synthesized and characterized by NMR, thermogravimetry and single X-ray crystallography. Substitution of the aniline by para-toluidine molecules leads to radical changes in the anionic sub-lattice: from monomeric form to polymeric one. The coordination number of bismuth is 7+1 in 1, and 8 in 2; Bi coordination polyhedron in 1 can be described as a two-capped trigonal prism, while in 2 as a dodecahedron. The Co atoms in 1 and 2 have an octahedral coordination. NMR spectroscopy in DMSO solution confirms the trans-configuration of the complex cations in 1 and 2 by observation of a broad singlet of two symmetric hydrogen bonds. The NCH₂CH₂N component of EDTA ligand is in the domain of the fast exchange and the signal from this group is a singlet, while four acetate methylene protons give rise to an AB quartet system. It was shown that thermolysis of 1 and 2 occurs in three successive stages, via the dehydration, pyrolysis of the ligands and, finally, the formation of a sillenite-type phase Bi_26−xCo_xO_40−δ and small quantities of Co₃O₄.     

Polymerization study of o-Si(OH)4 and complexation with Am(III), Eu(III) and Cm(III)

The stability constants of Am⁺³, Cm³⁺ and Eu³⁺ with ortho silicate, were measured at pH 3.50 and in ionic strengths of 0.20-1.00 M (NaClO₄) by the solvent extraction method. The Am⁺³, Cm³⁺ and Eu³⁺ forms 1:1 complex with ortho silicate ion at pH 3.60 with the stability constant (log β₁) value of 8.02 ± 0.10, 7.78 ± 0.08 and 7.81 ± 0.11, respectively. The stability of these metal ions decrease with increased ionic strength from 0.20 to 1.00 M (NaClO₄) for silicic acid concentrations of 0.002-0.020 M. Increasing silicic acid concentration above 0.02 M increased the amount of M³⁺ extracted into the organic phase, contrary to the trend usually observed for increased ligand concentration in solvent extraction. This reversed trend is likely due to the extraction of cationic species of silicic acid by HDEHP. Aging time (60-300 min) had no effect on the stability constant of these metal ions for 0.002-0.020 M silicic acid at pH 3.50 and I = 0.20 M (NaClO₄).The fraction of polymeric silicic acid present in solutions of 0.20-4.50 M NaClO₄ solutions at pH 3.0-10.0, T = 0-60 °C and aging time = 5-300 min was measured for determination of the silicomolybdate reaction to ascertain the proper conditions to study metal-silicate complexation.     

Synthesis, characterization and cytotoxic activity of gallium(III) complexes anchored by tridentate pyrazole-based ligands

Reactions of GaCl₃ with pyrazole-containing ligands of the pyrazole-imine-phenol (HL¹-HL³) or pyrazole-amine-phenol (HL⁴-HL⁶) types led to the synthesis of well-defined [GaL₂]⁺ homoleptic complexes (1-6). Complexes 1-6 were characterized by elemental analysis, ESI-MS (electrospray ionization-mass spectrometry), IR and NMR spectroscopies, and in the case of Complex 1 also by X-ray diffraction analysis. In complexes 1-3, the pyrazole-imine-phenolate ligands act as monoanionic chelators that coordinate to the metal in a meridional fashion, while 4-6 contain monoanionic and facially coordinated pyrazole-amine-phenolate ligands. Complexes 1-3 have a greater stability in solution compared to 4-6, which have shown a more pronounced tendency to release the respective ancillary ligands. The cytotoxicity of 1-6 and of the respective ligands (HL¹-HL⁶) was evaluated against human prostate cancer cells PC-3 and human breast cancer cells MCF-7. The substituents of the phenolate rings strongly influenced the cytotoxicity of the compounds. Complexes 3 and 6 that contain chloride substituents at the phenolate rings have shown the highest cytotoxicity, including in the cisplatin-resistant PC-3 cell line. The cytotoxic profile of 3 and 6 is very similar to the one displayed by the respective anchor ligands, respectively HL¹ and HL⁶. The cytotoxic activity of 3 and 6 is slightly increased by the presence of transferrin, and both complexes provoke cell death mainly by induction of apoptotic pathways.     

Synthesis and characterization of tetraphenylporphyrin iron(III) complexes with substituted phenylcyanamide ligands

Several five coordinate complexes of [(TPP)Fe^III(L)] in which TPP is the dianion of tetraphenylporphyrin and L is the monoanion of phenylcyanamide (pcyd) (1), 2,5-dichlorophenylcyanamide (2,5-Cl₂pcyd) (2), 2,6-dichlorophenylcyanamide (2,6-Cl₂pcyd) (3), and 2,3,4,6-tetrachlorophenylcyanamide (2,3,4,6-Cl₄pcyd) (4) have been prepared by the reaction of [(TPP)Fe^IIICl] with appropriate thallium salt of phenylcyanamide. Each of the complexes has been characterized by IR, UV-Vis and ¹H NMR spectroscopic data. Dark red-brown needles of [(TPP)Fe^III(2,6-Cl₂pcyd)] (C₅₁H₃₁Cl₂FeN₆ · CHCl₃) crystallize in the triclinic system. The crystal structure of Fe(III) compound shows a slight distortion from square pyramidal coordination with the 2,6-dichlorophenylcyanamide anion in the axial position through nitrile nitrogen atom. Iron atom is 0.47(1) Å out of plane of the porphyrin toward phenylcyanamide ligand. In non-coordinating solvents, such as benzene or chloroform, these complexes exhibit ¹H NMR spectra that are characteristic of high-spin (S = 5/2) species. The X-ray crystal structure parameters are also consistent with high-spin iron(III) complexes. The iron(III) phenylcyanamide complexes are not reactive toward molecular oxygen; however, these complexes react with HCl and produce TPPFe^IIICl.     

Synthesis, characterizations and crystal structures of antimony(III) complexes with nitrogen-containing ligands

Six antimony adducts with N-donor neutral ligands (1,10-phenanthroline, 4,4′-bipyridine) have been obtained following the reaction of antimony halides with phenanthroline and 4,4′-bipyridine. By changing the solvent and stoichiometry, we obtained six different complexes, Sb(phen)Cl₃ (1), Sb(phen)Br₃ (2), Sb₂(phen)₄Br₈ (3) and Sb(bpy)Cl₃ (4), Sb(bpy)₂Cl₃ (5), Sb(bpyH · bpyH₂)Br₆ (6) (where phen = 1,10-phenanthroline, bpy = 4,4′-bipyridine). All the complexes have been characterized via elemental analysis, FT-IR and NMR (¹H, ¹³C) spectroscopy. The crystal structures of complexes 2, 3 and 6 have been determined by X-ray single crystal diffraction.The structural analysis show that the coordination sphere around antimony atom in complex 2 is a distorted square pyramid, coordinated by three bromine atoms and two nitrogen atoms from phen. In complex 3, the central antimony atom is six-coordinated through four bromine atoms and two nitrogen atoms forming a distorted octahedral geometry. Besides that, there are also uncoordinated 1,10-phenanthroline bonded by hydrogen bonds and π-π stacking interactions, which is rarely observed in previous reports. The crystal structure of complex 6 consists of bpyH · bpyH₂ trications and hexabromoantimonate trianions. The antimony atom in the anion has a distorted octahedral environment. Additionally, all complexes present a 3D framework built up by N-H?Br, C-H?Br and C-H?Cl weak hydrogen bonds interactions.     

Hydrogen bonding in diruthenium(II,III) tetraacetate complexes with biologically relevant axial ligands

Three diadduct complexes of the mixed-valent form of diruthenium tetraacetate, [Ru₂(μ-O₂CCH₃)₄L₂](PF₆), where L are the biologically relevant ligands imidazole, 1, 7-azaindole, 2, and caffeine, 3, were synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy and X-ray crystallography. In order to further elucidate the potential interactions of these dimers with DNA, the nature of the ligand coordination and the secondary inter- and intramolecular hydrogen-bonding interactions in all three complexes were assessed. Complex 1 · CH₂Cl₂ shows, exclusively, intermolecular interactions with the counterion whereas complexes 2 · ClCH₂CH₂Cl and 3 · OC(CH₃)₂ · H₂O, in addition to extensive intermolecular interactions, show intramolecular hydrogen bonding from the axial ligand to the bridging acetate oxygens, locking the ligand mean planes in place between the bridging acetate mean planes. In addition, all three complexes display π-π stacking of axial ligand rings on adjacent diadduct units.     

Versatile coordination behavior of N,N-di(alkyl/aryl)-N′-benzoylthiourea ligands: Synthesis, crystal structure and cytotoxicity of palladium(II) complexes

The synthesis and characterization of Pd(II) complexes with the general formula cis-[Pd(L-O,S)₂] (HL = N,N-diethyl-N′-benzoylthiourea, N,N-diisobutyl-N′-benzoylthiourea or N,N-dibenzyl-N′-benzoylthiourea) and trans-[PdCl₂(HL-S)₂] (HL = N,N-diphenyl-N′-benzoylthiourea, N,N-di-n-butyl-N′-benzoylthiourea or N,N-diisopropyl-N′-benzoylthiourea) are reported. These complexes were formed from the reaction between PdCl₂ and N,N-di(alky/aryl)-N′-benzoylthiourea in acetonitrile with the formulation dependent on the nature of HL. The new Pd(II) complexes have been characterized by analytical and spectral (FT-IR, UV-Vis, ¹H NMR and ¹³C NMR, Mass) techniques. The molecular structures of two of the complexes (1 and 5) have been conformed by X-ray crystallography. Complex 1 shows cytotoxicity against human breast cancer cells.