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.

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.

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.

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.

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%.

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.

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.

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.

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.

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.

Dinuclear metallacycles with single M-O(H)-M bridges [M = Fe(II), Co(II), Ni(II), Cu(II)]: effects of large bridging angles on structure and antiferromagnetic superexchange interactions.

The reactions of M(ClO4)2·xH2O and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) in the presence of triethylamine lead to the formation of monohydroxide-bridged, dinuclear metallacycles of the formula [M2(µ-OH)(µ-Lm)2](ClO4)3 (M = Fe(II), Co(II), Cu(II)) or [M2(µ-OH)(µ-Lm*)2](ClO4)3 (M = Co(II), Ni(II), Cu(II)). With the exception of the complexes where the ligand is Lm and the metal is copper(II), all of these complexes have distorted trigonal bipyramidal geometry around the metal centers and unusual linear (Lm*) or nearly linear (Lm) M-O-M angles. For the two solvates of [Cu2(µ-OH)(µ-Lm)2](ClO4)3, the Cu-O-Cu angles are significantly bent and the geometry about the metal is distorted square pyramidal. All of the copper(II) complexes have structural distortions expected for the pseudo-Jahn-Teller effect. The two cobalt(II) complexes show moderate antiferromagnetic coupling, -J = 48-56 cm(-1), whereas the copper(II) complexes show very strong antiferromagnetic coupling, -J = 555-808 cm(-1). The largest coupling is observed for [Cu2(µ-OH)(µ-Lm*)2](ClO4)3, the complex with a Cu-O-Cu angle of 180°, such that the exchange interaction is transmitted through the dz(2) and the oxygen s and px orbitals. The interaction decreases, but it is still significant, as the Cu-O-Cu angle decreases and the character of the metal orbital becomes increasingly d(x(2)-y(2)). These intermediate geometries and magnetic interactions lead to spin Hamiltonian parameters for the copper(II) complexes in the EPR spectra that have large E/D ratios and one g matrix component very close to 2. Density functional theory calculations were performed using the hybrid B3LYP functional in association with the TZVPP basis set, resulting in reasonable agreement with the experiments.

Hydroxide-bridged cubane complexes of nickel(II) and cadmium(II): magnetic, EPR, and unusual dynamic properties.

The reactions of M(ClO4)2·xH2O (M = Ni(II) or Cd(II)) and m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) in the presence of triethylamine lead to the formation of hydroxide-bridged cubane compounds of the formula [M4(µ3-OH)4(µ-Lm)2(solvent)4](ClO4)4, where solvent = dimethylformamide, water, acetone. In the solid state the metal centers are in an octahedral coordination environment, two sites are occupied by pyrazolyl nitrogens from Lm, three sites are occupied by bridging hydroxides, and one site contains a weakly coordinated solvent molecule. A series of multinuclear, two-dimensional and variable-temperature NMR experiments showed that the cadmium(II) compound in acetonitrile-d3 has C2 symmetry and undergoes an unusual dynamic process at higher temperatures (ΔGLm‡ = 15.8 ± 0.8 kcal/mol at 25 °C) that equilibrates the pyrazolyl rings, the hydroxide hydrogens, and cadmium(II) centers. The proposed mechanism for this process combines two motions in the semirigid Lm ligand termed the "Columbia Twist and Flip:" twisting of the pyrazolyl rings along the Cpz­Cmethine bond and 180° ring flip of the phenylene spacer along the CPh­Cmethine bond. This dynamic process was also followed using the spin saturation method, as was the exchange of the hydroxide hydrogens with the trace water present in acetonitrile-d3. The nickel(II) analogue, as shown by magnetic susceptibility and electron paramagnetic resonance measurements, has an S = 4 ground state, and the nickel(II) centers are ferromagnetically coupled with strongly nonaxial zero-field splitting parameters. Depending on the Ni­O­Ni angles two types of interactions are observed: J1 = 9.1 cm(­1) (97.9 to 99.5°) and J2 = 2.1 cm(­1) (from 100.3 to 101.5°). "Broken symmetry" density functional theory calculations performed on a model of the nickel(II) compound support these observations.

1,2,4-Triazolyl-carboxylate-based MOFs incorporating triangular Cu(II)-hydroxo clusters: topological metamorphosis and magnetism.

Bifunctional 1,2,4-triazole-carboxylate ligands, an achiral 1,2,4-triazol-4-yl-acetic acid (trgly-H) and a chiral (d)-2-(1,2,4-triazol-4-yl)-propionic acid (d-trala-H), derived from the corresponding α-amino acid precursors revealed unique binding abilities in the construction of Cu(II)-coordination polymers composing discrete triangular [Cu3(µ3-OH)] clusters. A related series of MOFs, [Cu3(µ3-OH)(trgly)3(SO4)]·2H2O (1a), [Cu3(µ3-OH)(trgly)3(H2O)3]SO4·16H2O (1b), Cu3(µ3-OH)(d-trala)3(ClO4)0.5](ClO4)1.5·1.5H2O (2), was prepared, and their crystal structures were determined by means of X-ray diffraction. Being singly deprotonated, the organic ligands act as multidentate µ3- or µ4-donors using tr and -COO(-) moieties. The generated [Cu3(µ3-OH)(tr)3] cluster core is primarily supported by three [-N-N-] triazole heterocycles in a basal plane and tripodal-assisted µ3-anions (SO4(2-): 1a; ClO4(-): 2) capping the axial faces. The carboxylate groups join the units into either two-dimensional (2D) layer (1a, 2) or 3D zeolite-like networks (1b). Compound 1b represents the topology of α-Po (pcu: 4(12).6(3)) and crystallizes in the noncentrosymmetric space group I4̅3m, in which the six-connected [Cu3(µ3-OH)] clusters and trgly self-assemble in an open-channel cubic array possessing ∼56% solvent-accessible volume. Upon slight thermal treatment (∼60 °C), the structure irreversibly shrinks to the nonporous 2D motif 1a that belongs to a uninodal (3,6) network type. In structure 2 (space group R32), due to the [-N-N-] triazole and 1,3-bidentate carboxylate binding mode, each organic ligand bridges three metal clusters affording cross-linking of two adjacent layers with the same (3,6) topology. The resultant 3,9-c net is novel and can be categorized as two-nodal with point symbol {4(18).6(18)}{4(2).6}3. Spin frustration and antisymmetric exchange effects, resulting in abnormally low g values in the S = 1/2 states, were observed in the magnetic properties and the EPR spectra.

Dinuclear complexes containing linear M-F-M [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)] bridges: trends in structures, antiferromagnetic superexchange interactions, and spectroscopic properties.

The reaction of M(BF(4))(2)·xH(2)O, where M is Fe(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II), with the new ditopic ligand m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (L(m)*) leads to the formation of monofluoride-bridged dinuclear metallacycles of the formula [M(2)(µ-F)(µ-L(m)*)(2)](BF(4))(3). The analogous manganese(II) species, [Mn(2)(µ-F)(µ-L(m)*)(2)](ClO(4))(3), was isolated starting with Mn(ClO(4))(2)·6H(2)O using NaBF(4) as the source of the bridging fluoride. In all of these complexes, the geometry around the metal centers is trigonal bipyramidal, and the fluoride bridges are linear. The (1)H, (13)C, and (19)F NMR spectra of the zinc(II) and cadmium(II) compounds and the (113)Cd NMR of the cadmium(II) compound indicate that the metallacycles retain their structure in acetonitrile and acetone solution. The compounds with M = Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) are antiferromagnetically coupled, although the magnitude of the coupling increases dramatically with the metal as one moves to the right across the periodic table: Mn(II) (-6.7 cm(-1)) < Fe(II) (-16.3 cm(-1)) < Co(II) (-24.1 cm(-1)) < Ni(II) (-39.0 cm(-1)) ≪ Cu(II) (-322 cm(-1)). High-field EPR spectra of the copper(II) complexes were interpreted using the coupled-spin Hamiltonian with g(x) = 2.150, g(y) = 2.329, g(z) = 2.010, D = 0.173 cm(-1), and E = 0.089 cm(-1). Interpretation of the EPR spectra of the iron(II) and manganese(II) complexes required the spin Hamiltonian using the noncoupled spin operators of two metal ions. The values g(x) = 2.26, g(y) = 2.29, g(z) = 1.99, J = -16.0 cm(-1), D(1) = -9.89 cm(-1), and D(12) = -0.065 cm(-1) were obtained for the iron(II) complex and g(x) = g(y) = g(z) = 2.00, D(1) = -0.3254 cm(-1), E(1) = -0.0153, J = -6.7 cm(-1), and D(12) = 0.0302 cm(-1) were found for the manganese(II) complex. Density functional theory (DFT) calculations of the exchange integrals and the zero-field splitting on manganese(II) and iron(II) ions were performed using the hybrid B3LYP functional in association with the TZVPP basis set, resulting in reasonable agreement with experiment.

Copper(II) carboxylate dimers prepared from ligands designed to form a robust π···π stacking synthon: supramolecular structures and molecular properties.

The reactions of bifunctional carboxylate ligands (1,8-naphthalimido)propanoate, (L(C2)(-)), (1,8-naphthalimido)ethanoate, (L(C1)(-)), and (1,8-naphthalimido)benzoate, (L(C4)(-)) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) in methanol or ethanol at room temperature lead to the formation of novel dimeric [Cu(2)(L(C2))(4)(MeOH)(2)] (1), [Cu(2)(L(C1))(4)(MeOH)(2)]·2(CH(2)Cl(2)) (2), [Cu(2)(L(C4))(4)(EtOH)(2)]·2(CH(2)Cl(2)) (3) complexes. When the reaction of L(C1)(-) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) was carried out at -20 °C in the presence of pyridine, [Cu(2)(L(C1))(4)(py)(4)]·2(CH(2)Cl(2)) (4) was produced. At the core of complexes 1-3 lies the square Cu(2)(O(2)CR)(4) "paddlewheel" secondary building unit, where the two copper centers have a nearly square pyramidal geometry with methanol or ethanol occupying the axial coordination sites. Complex 4 contains a different type of dimeric core generated by two κ(1)-bridging carboxylate ligands. Additionally, two terminal carboxylates and four trans situated pyridine molecules complete the coordination environment of the five-coordinate copper(II) centers. In all four compounds, robust π···π stacking interactions of the naphthalimide rings organize the dimeric units into two-dimensional sheets. These two-dimensional networks are organized into a three-dimensional architecture by two different noncovalent interactions: strong π···π stacking of the naphthalimide rings (also the pyridine rings for 4) in 1, 3, and 4, and intermolecular hydrogen bonding of the coordinated methanol or ethanol molecules in 1-3. Magnetic measurements show that the copper ions in the paddlewheel complexes 1-3 are strongly antiferromagnetically coupled with -J values ranging from 255 to 325 cm(-1), whereas the copper ions in 4 are only weakly antiferromagnetically coupled. Typical values of the zero-field splitting parameter D were found from EPR studies of 1-3and the related known complexes [Cu(2)(L(C2))(4)(py)(2)]·2(CH(2)Cl(2))·(CH(3)OH), [Cu(2)(L(C3))(4)(py)(2)]·2(CH(2)Cl(2)) and [Cu(2)(L(C3))(4)(bipy)]·(CH(3)OH)(2)·(CH(2)Cl(2))(3.37) (L(C3)(-) = (1,8-naphthalimido)butanoate)), while its abnormal magnitude in [Cu(2)(L(C2))(4)(bipy)] was qualitatively rationalized by structural analysis and DFT calculations.

Halide and hydroxide linearly bridged bimetallic copper(II) complexes: trends in strong antiferromagnetic superexchange interactions.

Centrosymmetric [Cu(2)(µ-X)(µ-L(m)*)(2)](ClO(4))(3) (X = F(-), Cl(-), Br(-), OH(-), L(m)* = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene)], the first example of a series of bimetallic copper(II) complexes linked by a linearly bridging mononuclear anion, have been prepared and structurally characterized. Very strong antiferromagnetic exchange coupling between the copper(II) ions increases along the series F(-) < Cl(-) < OH(-) < Br(-), where -J = 340, 720, 808, and 945 cm(-1). DFT calculations explain this trend by an increase in the energy along this series of the antibonding antisymmetric combination of the p orbital of the bridging anion interacting with the copper(II) d(z(2)) orbital.

Heterometallic Co(III)4Fe(III)2 Schiff base complex: structure, electron paramagnetic resonance, and alkane oxidation catalytic activity.

The heterometallic complex [Co(4)Fe(2)OSae(8)]·4DMF·H(2)O (1) was synthesized by one-pot reaction of cobalt powder with iron chloride in a dimethylformamide solution of salicylidene-2-ethanolamine (H(2)Sae) and characterized by single crystal X-ray diffraction analysis, magnetic measurements, high frequency electron paramagnetic resonance (HF-EPR), and Mössbauer spectroscopies. The exchange coupling in the Fe(III)-Fe(III) pair is of antiferromagnetic behavior with J/hc = -190 cm(-1). The HF-EPR spectra reveal an unusual pattern with a hardly detectable triplet signal of the Fe(III) dimer. The magnitude of D (ca. 13.9 cm(-1)) was found to be much larger than in related dimers. The catalytic investigations disclosed an outstanding activity of 1 toward oxidation of cycloalkanes with hydrogen peroxide, under mild conditions. The most efficient system showed a turnover number (TON) of 3.57 × 10(3) with the concomitant overall yield of 26% for cyclohexane, and 2.28 × 10(3)/46%, respectively, for cyclooctane. A remarkable turnover frequency (TOF) of 1.12 × 10(4) h(-1) (the highest initial rate W(0) = 3.5 × 10(-4) M s(-1)) was achieved in oxidation of cyclohexane. Kinetic experiments and selectivity parameters led to the conclusion that hydroxyl radicals are active (attacking C-H bonds) species. Kinetic and electrospray ionization mass spectrometry (ESI-MS) data allowed us to assume that the trinuclear heterometallic particle [Co(2)Fe(Sae)(4)](+), originated from 1 in solution, could be responsible for efficient generation of hydroxyl radicals from hydrogen peroxide.

Heterometallic Cu/Co and Cu/Co/Zn complexes bearing rare asymmetric tetranuclear cores: synthesis, structures, and magnetic and catalytic properties toward the peroxidative oxidation of cycloalkanes.

The three novel heterometallic complexes [CuCo(III)Co(II)(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.55)(H(2)O)(0.45)](H(2)O)(0.45) (1), [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(CH(3)OH)(0.74)(H(2)O)(0.26)](H(2)O)(0.26) (2), and [CuCo(III)Zn(2)(MeDea)(3)Cl(3)(DMF)] (3) have been prepared using a one-pot reaction of copper powder with cobalt chloride (1) and zinc nitrate (2, 3) in a methanol (1, 2) or dimethylformamide (3) solution of N-methyldiethanolamine. A search of the Cambridge Structural Database shows that the tetranuclear asymmetric cores M(4)(µ(3)-X)(µ-X)(5) of 1-3 represent an extremely rare case of M(4)X(6) arrays. The magnetic investigations of 1 disclose antiferromagnetic coupling in a Co(II)-Cu(II)-Co(II) exchange fragment with J(Co-Cu)/hc = -4.76 cm(-1), J(Co-Co)/hc = -2.76 cm(-1), and D(Co)/hc = +34.3 cm(-1). Compounds 1-3 act as precursors for the mild peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone with overall yields up to 23%. The synthetic and structural features as well as the thermogravimetric behavior and electrospray ionization mass spectrometry data are discussed.

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.