Unique Use of Dibromo-L-Tyrosine Ligand in Building of Cu(II) Coordination Polymer-Experimental and Theoretical Investigations.

Although the crystals of coordination polymer {[CuCl(µ-O,O'-L-Br2Tyr)]}n (1) (L-Br2Tyr = 3,5-dibromo-L-tyrosine) were formed under basic conditions, crystallographic studies revealed that the OH group of the ligand remained protonated. Two adjacent [CuCl(L-Br2Tyr)] monomers, bridged by the carboxylate group of the ligand in the syn-anti bidentate bridging mode, are differently oriented to form a polymeric chain; this specific bridging was detected also by FT-IR and EPR spectroscopy. Each Cu(II) ion in polymeric compound 1 is coordinated in the xy plane by the amino nitrogen and carboxyl oxygen of the parent ligand and the oxygen of the carboxyl group from the symmetry related ligand of the adjacent [Cu(L-Br2Tyr)Cl] monomer, as well as an independent chlorine ion. In addition, the Cu(II) ion in the polymer chain participates in long-distance intermolecular contacts with the oxygen and bromine atoms of the ligands located in the adjacent chains; these intramolecular contacts were also supported by NCI and NBO quantum chemical calculations and Hirshfeld surface analysis. The resulting elongated octahedral geometry based on the [CuCl(L-Br2Tyr)] monomer has a lower than axial symmetry, which is also reflected in the symmetry of the calculated molecular EPR g tensor. Consequently, the components of the d-d band obtained by analysis of the NIR-VIS-UV spectrum were assigned to the corresponding electronic transitions.

Hybrid Cu-Containing Compounds Based on Lacunary Strandberg Anions: Synthesis under Mild Conditions, Crystal Structure, and Magnetic Properties.

A one-pot reaction of a copper source (metallic powder Cu0 or Cu2+ salts) and bpy (bpy = 2,2'-bipyridine) in the presence of (NH4)2HPO4 and (NH4)6Mo7O24·4H2O yields heterometallic hybrid compounds of the general type {[Cu(bpy)n(H2O)m]p[P2MoxOy]}. The structures exhibit a number of phosphomolybdate POMs including not only a common Strandberg anion [P2Mo5O23]6- but also its unprecedented bi- and trilacunary derivatives [P2Mo3O18]8- and [P2Mo2O15]8-. The structural determinants including the metal source (copper powder vs copper salts), counterion of the salts, and stoichiometry of the reagents were examined. An ex situ EPR study revealed the formation of different CuII complexes in the reaction mixture depending on the copper precursor. The obtained compounds have been found to possess selectivity toward the sorption of methylene blue in a mixture of organic dyes. DC magnetic measurements of 1-3 indicate rather strong antiferromagnetic metal-metal exchange interactions. Compound 1 exhibits field-induced slow magnetic relaxation in AC magnetic measurements, which is a rarely observed phenomenon among Cu(II) complexes.

Isothiocyanate l-argininato copper(II) complexes - Solution structure, DNA interaction, anticancer and antimicrobial activity.

l-argininato copper(II) complexes have been intensively investigated in a variety of diseases due to their therapeutic potential. Here we report the results of comprehensive structural studies (ESI-MS, NIR-VIS-UV, EPR) on the complexes arising in aqueous solutions of two ternary copper(II) complexes with molecular formulas from crystal structures, [Cu(l-Arg)2(NCS)](NCS)·H2O (1) and [Cu(l-Arg)(NCS)2] (2) (l-Arg = l-arginine). Reference systems, the ternary Cu(II)/l-Arg/NCS- as well as binary Cu(II)/NCS- and Cu(II)/l-Arg, were studied in parallel in aqueous solutions by pH-potentiometric titration, EPR and VIS spectroscopy to characterize stability, structures and speciation of the formed species over the broad pH range. Comparative analysis of the obtained results showed that at a pH close to 7.0 mononuclear [Cu(l-Arg)2(NCS)]+ is the only species in water solution of 1, while equilibrium between [Cu(l-Arg)(SCN)]+ and binary [Cu(l-Arg)2]2+ was detected in water solution of 2. According to DNA binding studies, the [Cu(l-Arg)2(NCS)]+, [Cu(l-Arg)(SCN)]+ and [Cu(l-Arg)2]2+ species could be considered as strong minor groove binding agents causing, in the presence of H2O2, the involvement of ROS in plasmid damage. The human carcinoma cells (A549 cell line) were generally significantly more sensitive to cytotoxic and antiproliferative effect of compounds 1 and 2 than human normal cells. The studied compounds shown antimicrobial activity against bacteria belonging to Enterobacteriaceae family.

Investigation of vanadium(III) and vanadium(IV) compounds supported by the linear diaminebis(phenolate) ligands: correlation between structures and magnetic properties.

A family of oxidovanadium(iv) compounds containing linear diaminebis(phenolate (salans) L1-5 ligands (L1 = [MeNCH2CH2NMe(CH2-4-CMe2CH2CMe3-C6H3O)2]2-; L2 = [MeNCH2CH2NMe(CH2-4-CH3-C6H3O)2]2-; L3 = [MeNCH2CH2NMe(CH2-4-Cl-C6H3O)2]2-; L4 = {MeNCH2CH2NMe[CH2-4,6-(CH3)2-C6H2O]2}2-; and L5 = {MeNCH2CH2NMe[CH2-4,6-(Br)2-C6H2O]2}2-) and non-oxidovanadium(iii) with L2,4 and acac ligands has been prepared and characterized by chemical and physical techniques. Reactions of [VO(acac)2] with ligand precursors H2L2,4 in toluene or hexane afforded vanadium(iii) compounds [V(L-κ4ONNO)(acac)] (1, L2; 2, L4), while the use of acetonitrile or ethanol led to the formation of dimeric oxidovanadium(iv) [(VO)2(µ-L-κ4ONNO)2] (3, L1; 4, L2; 5, L3) and monomeric [VO(L-κ4ONNO)] (6, L4, 7, L5) compounds. As shown by X-ray crystallography, compounds 1 and 2 are monomeric, in which the chelating ligands afford octahedral cis-α geometry at the vanadium center. In the dimeric structures of 3-5, the six-coordinate vanadium centers are bridged via two oxygen atoms of the L1-3 ligands while the L4,5 ligands generate square pyramidal structures of the monomeric 6 and 7 compounds. HFEPR studies allowed the determination of the spin Hamiltonian parameters of the S = 1 spin state of the monomeric V(iii) and dimeric V(iv), and S = ½ in monomeric V(iv) compounds. Magnetic measurements of 3-5 indicated weak ferromagnetic metal-metal exchange interactions. A reaction course for the deoxygenation and reduction of vanadyl-salan compounds is proposed.

Dinuclear Copper(II) Complexes with Schiff Bases Derived from 2-Hydroxy-5-Methylisophthalaldehyde and Histamine or 2-(2-Aminoethyl)pyridine and Their Application as Magnetic and Fluorescent Materials in Thin Film Deposition.

Two Cu(II) complexes, 1 and 2, with tridentate Schiff bases derived from 2-hydroxy-5-methylisophthalaldehyde and histamine HL1 or 2-(2-aminoethyl)pyridine HL2, respectively, were obtained and characterized by X-ray crystallography, spectroscopic (UV-vis, fluorescence, IR, and EPR), magnetic, and thermal methods. Despite the fact that the chelate formed by the NNO ligand donors (C26-C25H2-C24H2-N23=C23H-C22-C19Ph(O1)-C2(Ph)-C3H=N3-C4H2-C5H2-C6 fragment) are identical, as well as the synthesis of Cu(II) complexes (Cu:L = 2:1 molar ratio) was performed in the same manner, the structures of the complexes differ significantly. The complex 1, {[Cu2(L1)Cl2]2[CuCl4]}·2MeCN·2H2O, consists of [Cu2(L1)Cl2]+ units in which Cu(II) ions are bridged by the HL1 ligand oxygen and each of these Cu(II) ions is connected with Cu(II) ions of the next dimeric unit via two bridging Cl- ions to form a chain structure. In the dinuclear [Cu2(L2)Cl3]0.5MeCN complex 2, each Cu(II) is asymmetrically bridged by the ligand oxygen and chloride anions, whereas the remaining chloride anions are apically bound to Cu(II) cations. In contrast to the complex 1, the square-pyramidal geometry of the both Cu(II) centers is strongly distorted. The magnetic study revealed that antiferromagnetic interactions in the complex 2 are much stronger than in the complex 1, which was corresponded with magneto-structural examination. Thin layers of the studied Cu(II) complexes were deposited on Si(111) by the spin coating method and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), and fluorescence spectroscopy. The Cu(II) complexes and their thin layers exhibited fluorescence between 489-509 nm and 460-464 nm for the compounds and the layers, respectively. Additionally, DFT calculations were performed to explain the structures and electronic spectral properties of the ligands.

Role of architecture of N-oxide surfactants in the design of nanoemulsions for Candida skin infection.

In this work we present comprehensive research on the formation, stability and structural properties of oil-in-water (o/w) nanoemulsions with the ability for topical administration, penetration of the skin and acting as antifungal agents against C. albicans. The studied nanoemulsions were composed of different ratios of double-head - single-tail surfactants {1-bis{[3-(N,N-dimethylamino)ethyl]amido}alkane-di-N-oxides (Cn-MEDA), N,N-bis[3,3'-(dimethyl-amino)propyl]alkyl-amide di-N-oxides (Cn(DAPANO)2} and single-head - single-tail surfactants {2-(alkanoylamino)-ethyldimethyl-amine-N-oxides (Cn-EDA), and 3-(alkanoylamino) propyldimethylamine-N-oxides, (Cn-PDA)} added to the oil {isooctane IO, isopropyl myristate IPM or glyceryl monocaprylate GM as (O)} and to the water phase (W). The phase behavior of the systems was examined by a titration method. Morphology of the resulting colloids was characterized by scanning and transmission electron microscopy, the particle size and size distributions determined by dynamic light scattering, and kinetic stability by multiple light scattering. While both surfactant types resulted in quite stable nanoemulsions, the systems formed using a single-headed one-tail surfactant were slightly more stable with GM or IPM. The microenvironmental properties of the nanoemulsions were studied by an electron paramagnetic resonance technique to distinguish the molecular dynamics of the different spin probes localized in the particular regions of the surfactant layers, depending on the surfactant structure and the system preparation. Skin permeation studies were performed to monitor transport through the skin, and changes in skin structure were followed using differential scanning calorimetry. Moreover, the activities of curcumin-loaded nanoemulsions stabilized by N-oxide surfactants against Candida albicans fungus were evaluated. To estimate in vitro efficacy, the suitability of an N-oxide nanoemulsion dressing against wound infection with biofilm C. albicans was assessed according to the Antibiofilm Dressing's Activity Measurement. We expect that the nanoemulsion formulations tested in this study will have potential for application as topical delivery systems for pharmaceutically active compounds in skin-related conditions.

Synthesis, structure and biological evaluation of ruthenium(III) complexes of triazolopyrimidines with anticancer properties.

Six novel ruthenium(III) complexes of general formula [RuCl3(L)3] (1,3,5) and [RuCl3(H2O)(L)2] (2,4,6), where L stands for three different triazolopyrimidine-derived ligands, are reported. The compounds have been structurally characterized (IR, EPR, SCXRD), and their magnetic moments have been determined. The single-crystal X-ray diffraction study revealed a slightly distorted octahedral geometry of the Ru(III) complexes with mer configuration in 1 and 5, and fac configuration in 3. In 2 and 4, three chloride ions are in mer configuration and the two triazolopyrimidines are oriented trans mutually with the water molecule playing the role of the sixth ligand. All complexes have been thoroughly screened for their in vitro cytotoxicity against human breast cancer cell line MCF-7, human cervical cancer cell line HeLa, and L929 murine fibroblast cells, uncovering among others that the most lipophilic complexes 5 and 6, containing the bulky ligand dptp (5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine), display high cytotoxic activity against MCF-7, and HeLa cells. Moreover, it was also revealed that during the interaction of the complexes 1-6 with the cancer MCF-7 cell line, reactive oxygen species are released intracellularly, which could indicate that they are involved in cell apoptosis. Furthermore, extensive studies have been carried out to reveal the mechanism by which complexes 1-6 interact with DNA, albumin, and apotransferrin. The biological studies were complemented by detailed kinetic studies of the hydrolysis of the complexes in the pH range 5-8, to determine the stability of the complexes in solution. Six novel ruthenium(III) complexes with triazolopyrimidine derivatives demonstrated the potential for use as anticancer agents by maintaining the toxic effect on MCF-7 and HeLa cells.

How accurate is density functional theory in predicting spin density? An insight from the prediction of hyperfine coupling constants.

Electron paramagnetic resonance (EPR) spectroscopy has been proven to be an important technique for studying paramagnetic systems. Probably, the most accessible EPR parameter and the one that provides a significant amount of information about molecular structure and spin density is the hyperfine coupling constant (HFCC). Hence, accurate quantum-chemical modeling of HFCCs is frequently essential to the adequate interpretation of EPR spectra. It requires the precise spin density, which is the difference between the densities of α- and ß-electrons, and thus, its quality is expected to reflect the quality of the total electron density. The question of which approximate exchange-correlation density functional yields sufficiently accurate HFCCs, and thus, the spin density remains open. To assess the performance of well-established density functionals for calculating HFCCs, we used a series of 26 small paramagnetic species and compared the obtained results to the CCSD reference values. The performance of DFT was also tested on EPR-studied o-semiquinone radical interacting with water molecules and Mg2+ cation. The HFCCs were additionally calculated by the DLPNO-CCSD method, and this wave function-based technique was found superior to all functionals we tested. Although some functionals were found, on average, to be fairly efficient, we found that the most accurate functional is system-dependent, and therefore, the DLPNO-CCSD method should be preferred for theoretical investigations of the HFCCs and spin density.

A Cu/Zn heterometallic complex with solvent-binding cavity, catalytic activity for the oxidation of 1-phenylethanol and unusual magnetic properties.

Mononuclear and polymeric complexes of zinc(ii) and copper(ii) have been synthesized using two isomers of the hemi-salen ligand with a different mutual orientation of donor atoms. The heterometallic Cu/Zn metallocycle features a catalytic niche filled with the molecule of water and molecules of methanol. This unusual compound exhibits both pronounced catalytic activity in the reaction of oxidation of a secondary alcohol to ketone and field induced slow magnetic relaxation, which is a very rare phenomenon among Cu(ii) complexes.

X-ray structure and magnetic and fluorescence characteristics of new Cu(ii) complexes with Schiff bases derived from 2-(2-aminoethyl)pyridine and 2-hydroxy-1-naphthaldehyde; morphology and fluorescence of their thin films.

Cu(ii) complexes with tridentate Schiff bases derived from 2-(2-aminoethyl)pyridine and 2-hydroxy-1-naphthaldehyde and COO-, Cl- and NO3- as ligands were obtained and characterized by crystal and molecular, spectroscopic (UV-Vis, fluorescence, IR, and EPR), magnetic and thermal methods. The X-ray crystal structure analysis revealed a distorted square planar geometry for [Cu(ii)(PEMN)CH3COO]CHCl3, 1, and [Cu(ii)(PEMN)Cl], 2, and a distorted square-pyramidal geometry for [Cu(ii)(PEMN)NO3], 3, corresponding to the values of EPR g-matrix diagonal components. The copper(ii) complexes exhibited fluorescence in solution in the range of 370-410 nm. Thin layers of the studied copper(ii) complexes were deposited on Si(111) by a spin coating method and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM) and fluorescence spectroscopy. For copper(ii) layers (2/Si), the most intense fluorescence band from an intraligand and a d-d transition between 490 and 550 nm was observed.

Copper(II) Complexes with Bulky N-Substituted Diethanolamines: High-Field Electron Paramagnetic Resonance, Magnetic, and Catalytic Studies in Oxidative Cyclohexane Amidation.

The novel coordination compounds [Cu2(H tBuDea)2(OAc)2] (1) and [Cu2(H nBuDea)2Cl2]· nH2O (2) have been prepared through the reaction of the respective copper(II) salts with N- tert-butyldiethanolamine (H2 tBuDea, for 1) or N-butyldiethanolamine (H2 nBuDea, for 2) in methanol solution. Crystallographic analysis reveals that, in spite of the common binuclear {Cu2(µ-O)2} core, the supramolecular structures of the complexes are drastically different. In 1 binuclear molecules are linked together by H-bonds into 1D chains, while in 2 the neighboring pairs of binuclear molecules are H-bonded, forming tetranuclear aggregates. Variable-temperature (1.8-300 K) magnetic susceptibility measurements of 1 and 2 show a dominant antiferromagnetic behavior. Both complexes are also studied by HF-EPR spectroscopy. While the interaction between Cu(II) centers in 1 can be described by a single coupling constant J = 130.1(3) cm-1 (using H = JS1 S2), the crystallographically different {Cu2(µ-O)2} pairs in 2 are expected exchange from ferro- to antiferromagnetic behavior (with J ranging from -32 to 110 cm-1, according to DFT calculations). Complexes 1 and 2 act as catalysts in the amidation of cyclohexane with benzamide, employing tBuOO tBu as oxidant. The maximum achieved conversion of benzamide (20%, after 24 h reaction time) was observed in the 1/ tBuOO tBu system. In the cases of tBuOO(O)CPh or tBuOOH oxidants, no significant amidation product was observed, while for tBuOO(O)CPh, the oxidative dehydrogenation of cyclohexane occurred, giving cyclohexene, to afford the allylic ester (cyclohex-2-en-1-yl benzoate) as the main reaction product.

Can Carbamates Undergo Radical Oxidation in the Soil Environment? A Case Study on Carbaryl and Carbofuran.

Radical oxidation of carbamate insecticides, namely carbaryl and carbofuran, was investigated with spectroscopic (electron paramagnetic resonance [EPR] and UV-vis) and theoretical (density functional theory [DFT] and ab initio orbital-optimized spin-component scaled MP2 [OO-SCS-MP2]) methods. The two carbamates were subjected to reaction with •OH, persistent DPPH• and galvinoxyl radical, as well as indigenous radicals of humic acids. The influence of fulvic acids on carbamate oxidation was also tested. The results obtained with EPR and UV-vis spectroscopy indicate that carbamates can undergo direct reactions with various radical species, oxidizing themselves into radicals in the process. Hence, they are prone to participate in the prolongation step of the radical chain reactions occurring in the soil environment. Theoretical calculations revealed that from the thermodynamic point of view hydrogen atom transfer is the preferred mechanism in the reactions of the two carbamates with the radicals. The activity of carbofuran was determined experimentally (using pseudo-first-order kinetics) and theoretically to be noticeably higher in comparison with carbaryl and comparable with gallic acid. The findings of this study suggest that the radicals present in soil can play an important role in natural remediation mechanisms of carbamates.

Strategies for overcoming tropical disease by ruthenium complexes with purine analog: Application against Leishmania spp. and Trypanosoma cruzi.

Tropical diseases currently constitute a major health problem and thus a challenge in the field of drug discovery. The current treatments show serious disadvantages due to cost, toxicity, long therapy duration and resistance, and the use of metal complexes as chemotherapeutic agents against these ailments appears to be a very attractive alternative. Herein, we describe three newly synthesized ruthenium complexes with a bioactive molecule, the purine analogue 5,6,7-trimethyl-1,2,4-triazolo[1,5-a]pyrimidine (tmtp): cis,fac-[RuCl2(dmso)3(tmtp)] (1), mer-[RuCl3(dmso)(H2O)(tmtp)]·2H2O (2) and fac,cis-[RuCl3(H2O)(tmtp)2] (3). Their structures were characterized using X-ray and spectroscopic methods (IR, NMR or EPR). The stability of the synthesized complexes 1-3 in various buffered solutions (pH=3-7.4) was monitored using conventional and stopped-flow techniques. The in vitro antiproliferative activity of all ruthenium complexes against promastigote forms of Leishmania spp. (L. infantum, L. braziliensis, and L. donovani) and epimastigote forms of Trypanosoma cruzi was investigated. Notably, the results showed that the activity of 1 against L. brasiliensis was more than three-fold higher than that of glucantime, and 1 showed no appreciable toxicity towards J774.2 macrophages. Additionally, 2 displayed even 141-fold lower toxicity against host cells than glucantime, demonstrating significantly higher selectivity than the reference drug. Therefore, 1 and 2 appear to be excellent candidates for further development as potential drugs for the effective treatment of leishmaniasis and Chagas disease. All novel complexes were also shown to be potent inhibitors of Fe-SOD in the studied species, while their effects on human CuZn-SOD were very low.

Dinuclear Metallacycles with Single M-X-M Bridges (X = Cl-, Br-; M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)): Strong Antiferromagnetic Superexchange Interactions.

A series of monochloride-bridged, dinuclear metallacycles of the general formula [M2(µ-Cl)(µ-L)2](ClO4)3 have been prepared using the third-generation, ditopic bis(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]benzene (Lm), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*), M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO4)2·6H2O, MCl2, and the ligand, Lm or Lm*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M2(µ-Cl)(µ-L)2](BF4)3, L = Lm, M = Cu(II), and L = Lm*, M = Co(II), Cu(II), were prepared from the reaction of [M2(µ-F)(µ-L)2](BF4)3 and (CH3)3SiCl. The bromide-bridged complex [Cu2(µ-Br)(µ-Lm*)2](ClO4)3 was prepared by the first method. Three acyclic complexes, [Co2(µ-Lm)µ-Cl4], [Co2(µ-Lm*)Cl4], and [Co2(µ-Lm*)Br4], were also prepared. The structures of all [M2(µ-X)(µ-L)2]3+ (X = Cl-, Br-) complexes have two ditopic bis(pyrazolyl)methane ligands bridging two metals in a metallacyclic arrangement. The fifth coordination site of the distorted trigonal bipyramidal metal centers is filled by a bridging halide ligand that has an unusual linear or nearly linear M-X-M angle. The NMR spectra of [Zn2(µ-Cl)(µ-Lm*)2](ClO4)3 and especially [Cd2(µ-Cl)(µ-Lm*)2](ClO4)3 demonstrate that the metallacycle structure is maintained in solution. Solid state magnetic susceptibility data for the copper(II) compounds show very strong antiferromagnetic exchange interactions, with -J values of 536 cm-1 for [Cu2(µ-Cl)(µ-Lm)2](ClO4)3·xCH3CN, 720 cm-1 for [Cu2(µ-Cl)(µ-Lm*)2](ClO4)3, and 945 cm-1 for [Cu2(µ-Br)(µ-Lm*)2](ClO4)3·2CH3CN. Smaller but still substantial antiferromagnetic interactions are observed with other first row transition metals, with -J values of 98 cm-1 for [Ni2(µ-Cl)(µ-Lm*)2](ClO4)3, 55 cm-1 for [Co2(µ-Cl)(µ-Lm*)2](ClO4)3, and 34 cm-1 for [Fe2(µ-Cl)(µ-Lm*)2](ClO4)3. EPR spectra of [Cu2(µ-Cl)(µ-Lm*)2](BF4)3 confirm the dz2 ground state of copper(II). In addition, the sign of the zero-field splitting parameter D was determined to be positive for [Cu2(µ-F)(µ-Lm*)2](BF4)3. Electronic spectra of the copper(II) complexes as well as Mössbauer spectra of the iron(II) complexes were also studied in relation with the EPR spectra and magnetic properties, respectively. Density functional theory calculations were performed using ORCA, and exchange integral values were obtained that parallel but are slightly higher than the experimental values by about 30%.

Oxidation of 1-Methyl-1-phenylhydrazine with Oxidovanadium(V)-Salan Complexes: Insight into the Pathway to the Formation of Hydrazine by Vanadium Nitrogenase.

A series of oxidovanadium(V) complexes [VO(L-κ4O,N,N,O)(OR)] (1a, R = Et, L = L1; 1b, R = Me, L = L1; 2, R = Me, L = L2; 3, R = Me, L = L3) were synthesized by the σ-bond metathesis reaction between [VO(OR)3] and the linear diaminebis(phenol) derivatives H2L (salans) containing different para-substituents on the phenoxo group [CMe3CH2CMe2, L1; Me, L2; Cl, L3]. As shown by X-ray crystallography complexes 1a, 1b, and 2 exhibit cis-α geometry, do have a stereogenic vanadium center, and exist as a racemic mixture of the Δ cis-α and Λ cis-α enantiomers. In solution, as demonstrated by 1H and 51V NMR investigations, the structures of complexes 1-3 are consistent with their solid state. The reactions of 1b, 2, and 3 with NH2NMePh in n-hexane afforded the oxidovanadium(IV) [VO(L-κ4O,N,N,O)] (4, L1; 5, L2; 6, L3) and 1,4-dimethyl-1,4-diphenyl-2-tetrazene (Me2Ph2N4) (7) as the main products together with a small amount of hydrazido(2-) vanadium(V) [V(L3-κ4O,N,N,O)(NNMePh)(OMe)] (8). Proposed reaction course for the oxidation of NH2NMePh by 1b-3 is discussed. Compounds 4-8 were characterized by chemical and physical techniques including the X-ray crystallography for 4, 7, and 8. The solid-state (powder) electron paramagnetic resonance spectra and magnetic features strongly indicate that complexes 4-6 are formed as a mixture of a mononuclear (S = 1/2) and a dinuclear (S = 1) species.

Metal-Metal Interactions in Trinuclear Copper(II) Complexes [Cu3(RCOO)4(H2TEA)2] and Binuclear [Cu2(RCOO)2(H2TEA)2]. Syntheses and Combined Structural, Magnetic, High-Field Electron Paramagnetic Resonance, and Theoretical Studies.

The trinuclear [Cu3(RCOO)4(H2TEA)2] copper(II) complexes, where RCOO(-) = 2-furoate (1), 2-methoxybenzoate (2), and 3-methoxybenzoate (3, 4), as well as dimeric species [Cu2(H2TEA)2(RCOO)2]·2H2O, have been prepared by adding triethanolamine (H3TEA) at ambient conditions to hydrated Cu(RCOO)2 salts. The newly synthesized complexes have been characterized by elemental analyses, spectroscopic techniques (IR and UV-visible), magnetic susceptibility, single crystal X-ray structure determination and theoretical calculations, using a Difference Dedicated Configuration Interaction approach for the evaluation of magnetic coupling constants. In 1 and 2, the central copper atom lies on an inversion center, while in the polymorphs 3 and 4, the three metal centers are crystallographically independent. The zero-field splitting parameters of the trimeric compounds, D and E, were derived from high-field, high-frequency electron paramagnetic resonance spectra at temperatures ranging from 3 to 290 K and were used for the interpretation of the magnetic data. It was found that the dominant interaction between the terminal and central Cu sites J12 is ferromagnetic in nature in all complexes, even though differences have been found between the symmetrical or quasi-symmetrical complexes 1-3 and non-symmetrical complex 4, while the interaction between the terminal centers, J23, is negligible.

Zinc(II) and copper(II) complexes with hydroxypyrone iron chelators.

High stability of the complexes formed at physiological pH is one of the basic requisites that a good iron chelator must possess. At the same time the chelating agent must be selective toward iron, i.e., the stability of iron complexes must be significantly higher than that of the complexes formed with essential metal ions, in order that these last ones do not perturb iron chelation. In the frame of our research on iron chelators we have designed and synthesized a series of tetradentate derivatives of kojic acid, and examined their binding properties toward Fe(3+) and Al(3+). In this paper, for a characterization of the behavior of the proposed iron chelating agents in biological fluids, their complex formation equilibria with copper(II) and zinc(II) ions have been fully characterized together with a speciation study, showing the degree at which the iron chelators interfere with the homeostatic equilibria of these two essential metal ions.

Toward an Understanding of the Ambiguous Electron Paramagnetic Resonance Spectra of the Iminoxy Radical from o-Fluorobenzaldehyde Oxime: Density Functional Theory and ab Initio Studies.

Iminoxy radicals (R1R2C═N­O•) possess an inherent ability to exist as E and Z isomers. Although isotropic hyperfine couplings for the species with R1 = H allow one to distinguish between E and Z, unequivocal assignment of the parameters observed in the EPR spectra of the radicals without the hydrogen atom at the azomethine carbon to the right isomer is not a simple task. The iminoxyl derived from o-fluoroacetophenone oxime (R1 = CH3 and R2 = o-FC6H5) appears to be a case in point. Moreover, for its two isomers the rotation of the o-FC6H5 group brings into existence the syn and anti conformers, depending on the mutual orientation of the F atom and C═N­O• group, making a description of hyperfine couplings to structure even more challenging. To accomplish this, a vast array of theoretical methods (DFT, OO-SCS-MP2, QCISD) was used to calculate the isotropic hyperfine couplings. The comparison between experimental and theoretical values revealed that the E isomer is the dominant radical form, for which a fast interconversion between anti and syn conformers is expected. In addition, the origin of the significant AF increase with solvent polarity was analyzed.

pH-dependent formation of Hg(II)-semiquinone complexes from natural phenols.

The ability of various natural phenols to form Hg(II)-semiquinone complexes was tested in the pH range of 2.8-12. EPR experiments performed at 9.6 and 34 GHz (the X- and Q-band, respectively) revealed that the complexes formed at low and high pH values exhibit a significant dissimilarity between their g-matrices (g-tensors), strongly suggesting that the complexes differ structurally. Our previous investigation on the low pH complex (Chemosphere 2015, 119, 479-484) had shown the Hg(II) ion to be tetracoordinated by two ligands, one of the ligands being monoprotonated with the unpaired electron mainly located on it. In order to reveal the molecular structure of the high pH form a DFT-based theoretical analysis was carried out in this work. For all the optimized model structures the g-matrices were computed and compared with their experimental counterparts. Good agreement was observed only if the geometry of the model Hg(II) complex was planar and the coordination sphere was composed of one fully deprotonated radical ligand and hydroxyl anions.

Syntheses, structural, magnetic, and electron paramagnetic resonance studies of monobridged cyanide and azide dinuclear copper(II) complexes: antiferromagnetic superexchange interactions.

The reactions of Cu(ClO4)2 with NaCN and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) yield [Cu2(µ-CN)(µ-Lm)2](ClO4)3 (1) and [Cu2(µ-CN)(µ-Lm*)2](ClO4)3 (3). In both, the cyanide ligand is linearly bridged (µ-1,2) leading to a separation of the two copper(II) ions of ca. 5 Å. The geometry around copper(II) in these complexes is distorted trigonal bipyramidal with the cyanide group in an equatorial position. The reaction of [Cu2(µ-F)(µ-Lm)2](ClO4)3 and (CH3)3SiN3 yields [Cu2(µ-N3)(µ-Lm)2](ClO4)3 (2), where the azide adopts end-on (µ-1,1) coordination with a Cu-N-Cu angle of 138.0° and a distorted square pyramidal geometry about the copper(II) ions. Similar chemistry in the more sterically hindered Lm* system yielded only the coordination polymer [Cu2(µ-Lm*)(µ-N3)2(N3)2]. Attempts to prepare a dinuclear complex with a bridging iodide yield the copper(I) complex [Cu5(µ-I4)(µ-Lm*)2]I3. The complexes 1 and 3 show strong antiferromagnetic coupling, -J = 135 and 161 cm(-1), respectively. Electron paramagnetic resonance (EPR) studies coupled with density functional theory (DFT) calculations show that the exchange interaction is transmitted through the dz(2) and the bridging ligand s and px orbitals. High field EPR studies confirmed the dz(2) ground state of the copper(II) ions. Single-crystal high-field EPR has been able to definitively show that the signs of D and E are positive. The zero-field splitting is dominated by the anisotropic exchange interactions. Complex 2 has -J = 223 cm(-1) and DFT calculations indicate a predominantly d(x(2)-y(2)) ground state.