Structurally diverse zinc(II) complexes containing tripodal tetradentate phenoxido-amines with promising antiproliferative effects.

Structurally diverse zinc(II) complexes with tripodal tetradentate phenolic-amines of variable substituents in the phenol and amine moieties were synthesized and thoroughly characterized. The two dinuclear [Zn2(L1)2](ClO4)2·MeOH (1), [Zn2(L2)2](ClO4)2 (2), and four mononuclear [Zn(L3)(H2O)]·MeOH (3), [Zn(L4)] (4), [Zn(L5)] (5) and [Zn(L6)] (6) complexes revealed distorted octahedral, trigonal-bipyramidal or tetrahedral geometries. The free HL1 and H2L3-6 ligands, and complexes 1-6 were evaluated for in vitro cytotoxicity against human cancer cell lines (A2780, A2780R, PC-3 and 22Rv1) and normal healthy MRC-5 cells. Overall results revealed high-to-moderate cytotoxicity (with the best IC50 values for complex 6 ranging from 2.4 to 4.5 µM), which is however, significantly higher than that of the reference drug cisplatin. The moderately active complexes 1-4 showed considerable selectivity on A2780 cells (IC50 ≈ 16.3-19.5 µM) over MRC-5 ones (with IC50 >50 µM for 1, 2 and 4, and with IC50 >25 µM for 3). The complexes 1, 2, and 6 and the ligand H2L6 were chosen for subsequent deeper biological evaluations. Their time-resolved cellular uptake and other cellular effects in A2780 cells were studied, such as cell cycle profile, intracellular ROS production, induction of apoptosis and activation of caspases 3/7. Complexes 1 and 2 caused significant G0/G1 cell cycle arrest in A2780 cells and antioxidant effects at normal conditions. They showed only limited effects on cellular processes connected with cytotoxicity, i.e. induction of apoptosis, depletion of mitochondrial membrane potential, and autophagy. These findings can be at least partly attributed to the low ability of the complexes to enter the A2780 cells and the depression of metabolic activity of the target cancer cells.

Magnetostructural Properties of Some Doubly-Bridged Phenoxido Copper(II) Complexes.

Three new tripod tetradentate phenolate-amines (H2L1, H2L4 and H2L9), together with seven more already related published ligands, were synthesized, and characterized. With these ligands, two new dinuclear doubly-bridged-phenoxido copper(II) complexes (3, 4), and six more complexes (1, 2, 5-8), a new trinuclear complex (9) with an alternative doubly-bridged-phenoxido and -methoxido, as well as the 1D polymer (10) were synthesized, and their molecular structures were characterized by spectroscopic methods and X-ray single crystal crystallography. The Cu(II) centers in these complexes exhibit distorted square-pyramidal arrangement in 1-4, mixed square pyramidal and square planar in 5, 6, and 9, and distorted octahedral (5+1) arrangements in 7 and 8. The temperature dependence magnetic susceptibility study over the temperature range 2-300 K revealed moderate-relatively strong antiferromagnetic coupling (AF) (|J| = 289-145 cm-1) in complexes 1-6, weak-moderate AF (|J| = 59 cm-1) in the trinuclear complex 9, but weak AF interactions (|J| = 3.6 & 4.6 cm-1) were obtained in 7 and 8. No correlation was found between the exchange coupling J and the geometrical structural parameters of the four-membered Cu2O2 rings.

Dinuclear doubly bridged phenoxido copper(II) complexes as efficient anticancer agents.

Two cationic [Cu2(L1-2)2](ClO4)2 (1, 2), and four neutral doubly bridged-phenoxido-copper(II) complexes [Cu2(L3-4)2] (3, 4) and [Cu2(L5-6)2(H2O)]‧2H2O (5, 6) as well as 1D polymeric catena-[Cu(L7)] (7), where HL1-2 and H2L3-7 represent tripodal tetradentate pyridyl or aliphatic-amino groups based 2,4-disubstituted phenolates, were synthesized and thoroughly characterized by various spectroscopic methods and single crystal X-ray analysis. The molecular structures of the complexes exhibited diverse geometrical environments around the central Cu(II) atoms. The in vitro antiproliferative activity of the isolated complexes and selected parent free ligands were screened against some human cancer cell lines (A2780, A2780R, PC-3, 22Rv1, MCF-7). The most promising cytotoxicity against cancer cells were obtained for 1-6, while complex 6 was found as the best performing as compared to the reference drug cisplatin. The cytotoxicity study of complex 6 was therefore extended to wider variety of cancer cell lines (HOS, A549, PANC-1, CaCo2, HeLa) and results revealed its significant cytotoxicity on all investigated human cancer cells. The cell uptake study showed that cytotoxicity of 6 (3 µM concentration and 24 h of incubation) against A2780 cells was almost independent from the intracellular levels of copper. The effect of complexes 4, 6 and 7 on cell cycle of A2780 cells indicates that the mechanism of action in these complexes is not only different from that of cisplatin but also different among them. Complex 7 was able to induce apoptosis in A2780 cells, while complexes 4 and 6 did not and on the other hand, they showed considerable effect on autophagy induction and there are some clues that these complexes were able to induce cuproptosis in A2780 cells.

Insights into the Spin Dynamics of Mononuclear Cerium(III) Single-Molecule Magnets.

Four novel CeIII mononuclear complexes of formulas [Ce(ntfa)3(MeOH)2] (1), [Ce(ntfa)3(5,5'-Me2bipy)] (2), [Ce(ntfa)3(terpy)] (3), and [Ce(ntfa)3(bipy)2] (4), where ntfa = 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionato, 5,5'-Me2bipy = 5,5'-dimethyl-2,2'-dipyridyl, terpy = 2,2':6',2″-terpyridine, and bipy = 2,2'-bipyridine, have been synthesized and structurally characterized with CeIII displaying coordination numbers of 8, 8, 9, and 10, respectively. Magnetic measurements indicate that all the complexes show a field-induced single-ion magnet behavior under a small applied dc field. The magnetic analysis shows the relevance of the different spin relaxation mechanisms in the magnetic relaxation of the CeIII compounds, with special emphasis on the local-mode process. Multiconfigurational calculations were also performed to get more information on the axiality of the compounds.

Magnetic and Luminescence Properties of 8-Coordinate Holmium(III) Complexes Containing 4,4,4-Trifluoro-1-Phenyl- and 1-(Naphthalen-2-yl)-1,3-Butanedionates.

A new series of mononuclear Ho3+ complexes derived from the ß-diketonate anions: 4,4,4-trifluoro-1-phenyl-1,3-butanedioneate (btfa-) and 4,4,4-trifuoro-1-(naphthalen-2-yl)-1,3-butanedionate (ntfa-) have been synthesized, [Ho(btfa)3(H2O)2] (1a), [Ho(ntfa)3(MeOH)2] (1b), (1), [Ho(btfa)3(phen)] (2), [Ho(btfa)3(bipy)] (3), [Ho(btfa)3(di-tbubipy)] (4), [Ho(ntfa)3(Me2bipy)] (5), and [Ho(ntfa)3(bipy)] (6), where phen is 1,10-phenantroline, bipy is 2,2'-bipyridyl, di-tbubipy is 4,4'-di-tert-butyl-2,2'-bipyridyl, and Me2bipy is 4,4'-dimethyl-2,2'-bipyridyl. These compounds have been characterized by elemental microanalysis and infrared spectroscopy as well as single-crystal X-ray difraction for 2-6. The central Ho3+ ions in these compounds display coordination number 8. The luminescence-emission properties of the pyridyl adducts 2-6 display a strong characteristic band in the visible region at 661 nm and a series of bands in the NIR region (excitation wavelengths (λex) of 367 nm for 2-4 and 380 nm for 5 and 6). The magnetic properties of the complexes revealed magnetically uncoupled Ho3+ compounds with no field-induced, single-molecule magnet (SMMs).

Identification of potent anticancer copper(ii) complexes containing tripodal bis[2-ethyl-di(3,5-dialkyl-1H-pyrazol-1-yl)]amine moiety.

A series of heteroleptic copper(ii) complexes of the composition [Cu(L1-5)Cl]X, where X = ClO4 and/or PF6 and [bis(2-ethyl-di(3,5-dimethyl-1H-pyrazol-1-yl))-(6-methyl-(2-pyridylmethyl))]amine (L1), [bis(2-ethyl-di(3,5-dimethyl-1H-pyrazol-1-yl))-(3,4-dimethoxy-(2-pyridylmethyl))]amine (L2), [bis(2-ethyl-di(3,5-dimethyl-1H-pyrazol-1-yl)-(2-quinolymethyl)]amine (L3), [bis(2-ethyl-di(3,5-dimethyl-1H-pyrazolyl)-(di(3,5-dimethyl-1H-pyrazol-1-yl-methyl))]amine (L4) and [bis(2-ethyl-di(3,5-dimethyl-1H-pyrazol-1-yl)-(5-methyl-3-phenyl-1H-pyrazol-1-yl-methyl)]amine (L5), were prepared and thoroughly characterized including single-crystal X-ray diffraction technique. The in vitro cytotoxicity of complexes against A2780, A2780R, HOS and MCF-7 human cancer cell lines was evaluated using the MTT test. The results revealed that complexes [Cu(L1)Cl]PF6 (1-PF6), [Cu(L2)Cl]ClO4 (2-ClO4) and [Cu(L3)Cl]PF6 (3-PF6) are the most effective, with IC50 values ranging from 1.4 to 6.3 µM, thus exceeding the cytotoxic potential of metallodrug cisplatin (IC50 values ranging from 29.9 to 82.0 µM). The complexes [Cu(L4)Cl]PF6 (4-PF6) and [Cu(L5)Cl]PF6 (5-PF6) showed only moderate cytotoxicity against A2780, with IC50 = 53.6 µM, and 33.8 µM, respectively. The cell cycle profile, time-resolved cellular uptake, interactions with small sulfur-containing biomolecules (cysteine and glutathione), intracellular ROS production, induction of apoptosis and activation of caspases 3/7 were also evaluated in the case of the selected complexes. It has been found that the best performing complexes 1 and 2 cause cell arrest in the G2/M phase and induce apoptosis via the increase in production of ROS, dominantly due to the overproduction of superoxide.

Slow magnetic relaxation in penta-coordinate cobalt(II) field-induced single-ion magnets (SIMs) with easy-axis magnetic anisotropy.

Two penta-coordinate complexes of the general formula [Co(Ln)(NCS)]ClO4, where L1 = {bis[(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]-[(3,4-dimethoxypyridin-2-yl)methyl]}amine and L2 = {bis[(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]-[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]}amine, have been synthesized and thoroughly characterized. Each of the cobalt(ii) atoms is penta-coordinated in the {CoN5} donor set with a distorted square-pyramidal geometry in [Co(L1)(NCS)]ClO4·MeOH (1), while the vicinity of the central atom can be described as a distorted trigonal-bipyramidal geometry in [Co(L2)(NCS)]ClO4 (2) as revealed using the SHAPE analysis. Differences in interatomic parameters among the cobalt(ii) and donor atoms in 1 and 2 have definite impact on the magnetic features of both compounds. The complexes show an easy-axis magnetic anisotropy (D = -38.5 cm-1 for 1 and D = -8.5 for 2), and both complexes reveal a large rhombicity with E/D = 0.21 for 1 and E/D = 0.29 for 2. The ZFS parameters (g, D and E) were also calculated using CASSCF/NEVPT2 methods and they are in good agreement with those determined from experimental data. A frequency dependent out-of-phase susceptibility has been observed in external magnetic field (Bdc = 0.1 T) revealing the following parameters of slow relaxation of magnetization for 1: energy of the spin reversal barrier, Ueff = 16.0 cm-1 (Ueff/kB = 23.0 K) and the relaxation time, τ0 = 1.28 × 10-6 s. In the case of complex 2, no maxima of frequency dependent out-of-phase susceptibility have been observed and thus, the value of Ueff = 17 cm-1 has been estimated using the expression Ueff = |D| × (S2 - 1/4). It has been demonstrated that the degree of substitution and the type of substituents on the pyridyl moieties of the tripodal ligands (L1 and L2) used in these penta-coordinate cobalt(ii) complexes have significant impact on structural and magnetic features.

Five-Coordinated Geometries from Molecular Structures to Solutions in Copper(II) Complexes Generated from Polydentate-N-Donor Ligands and Pseudohalides.

A novel series of mononuclear five-coordinated pseudohalido-Cu(II) complexes displaying distorted square bipyramidal: [Cu(L1)(NCS)2] (1), [Cu(L2)(NCS)2] (2) and [Cu(L3)(NCS)]ClO4 (5) as well as distorted trigonal bipyramidal: [Cu(isp3tren)(N3)]ClO4 (3), [Cu(isp3tren)(dca)]ClO4 (4) and [Cu(tedmpza)(dca)]ClO4·0.67H2O (6) geometries had been synthesized and structurally characterized using X-ray single crystal crystallography, elemental microanalysis, IR and UV-vis spectroscopy, and molar conductivity measurements. Different N-donor amine skeletons including tridentate: L1 = [(2-pyridyl)-2-ethyl)-(3,4-dimethoxy)-2-methylpyridyl]methylamine and L2 = [(2-pyridyl)-2-ethyl)-(3,5-dimethyl-4-methoxy)-2-methyl-pyridyl]methylamine, and tetradentate: L3 = bis(2-ethyl-di(3,5-dimethyl-1H-pyrazol-1-yl)-[2-(3,4-dimethoxy-pyridylmethyl)]amine, tedmpza = tris[(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]amine and isp3tren = tris[(2-isopropylamino)ethyl)]amine ligands were employed. Molecular structural parameters such as nature of coligand, its chelate ring size and steric environment incorporated into its skeleton, which lead to adopting one of the two limiting geometries in these complexes and other reported compounds are analyzed and correlated to their assigned geometries in solutions. Similar analysis were extended to other five-coordinated halido-Cu(II) complexes.

Copper(II) complexes based on tripodal pyrazolyl amines: Synthesis, structure, magnetic properties and anticancer activity.

The Cu(II) complexes [Cu(bpdmpz)Cl]ClO4 (1), [Cu(bdmpzp)Cl]ClO4 (2-ClO4), [Cu(bdmpzp)Cl]PF6 (2-PF6) and [Cu(tdmpza)Cl]ClO4 (3), bpdmpzp=[bis[((2-pyridylmethyl)-di(3,5-dimethyl-1H-pyrazolyl)methyl)]amine, bdmpzp=[bis((di(3,5-dimethyl-1H-pyrazolyl)methyl)-(2-pyridylmethyl)]amine and tdmpza=tris[di(3,5-dimethyl-1H-pyrazolyl)-methyl)]amine were synthesized and characterized by elemental analysis, magnetic and conductivity measurements, electrospray-ionization mass spectrometry, infrared and electronic spectroscopy, and X-ray crystallography. The magnetic properties of the complexes, measured at variable temperature, revealed weak antiferromagnetic intermolecular interactions. The cytotoxicity of the complexes 1, 2-ClO4, 3, and 4 ([Cu(bedmpzp)Cl]PF6, where bedmpzp=[bis(3,5-dimethyl-1H-pyrazol-1-yl-1-ethyl)-(2-pyridylmethyl)]amine), was investigated against four human cancer cell lines: A2780 (ovarian), A2780R (cisplatin-resistant variant), HOS (aggressive bone tumors), CaCo2 (epithelial colorectal adenocarcinoma) and on healthy human hepatocytes. The complex 4 was the most cytotoxic one, with IC50=1.4µM (A2780), 8.3µM (A2780R), 4.7µM (HOS) and 10.8µM (CaCo2). The mass spectrometry-based interaction studies, involving selected sulfur-containing biomolecules and small model proteins, revealed pro-oxidant effects of complexes 1 and 4 and differences in stability of both complexes in the mixtures containing the model protein cytochrome c after 24h incubation, complex 1 formed 1:1 adduct, the formation of which was accompanied by the loss of one dimethylpyrazole pendant arm from the bpdmpz ligand, while the complex 4 composition remained intact and the complex formed both 1:1 and 1:2 adducts (cytochrome c vs. Cu(II)-complex).

Dinuclear metal(ii)-acetato complexes based on bicompartmental 4-chlorophenolate: syntheses, structures, magnetic properties, DNA interactions and phosphodiester hydrolysis.

A series of dinuclear metal(ii)-acetato complexes: [Ni2(µ-L(Cl)O)(µ2-OAc)2](PF6)·3H2O (1), [Ni2(µ-L(Cl)O)(µ2-OAc)2](ClO4)·CH3COCH3 (2), [Cu2(µ-L(Cl)O)(µ2-OAc)(ClO4)](ClO4) (3), [Cu2(µ-L(Cl)O)(OAc)2](PF6)·H2O (4), [Zn2(µ-L(Cl)O)(µ2-OAc)2](PF6) (5) and [Mn2(L(Cl)-O)(µ2-OAc)2](ClO4)·H2O (6), where L(Cl)O(-) = 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenolate, were synthesized. The complexes were structurally characterized by spectroscopic techniques and single crystal X-ray crystallography. Six-coordinate geometries with doubly bridged acetato ligands were found in Ni(ii), Zn(ii) and Mn(ii) complexes 1, 2, 5 and 6, whereas with Cu(ii) complexes a five-coordinate species was obtained with 4, and mixed five- and six-coordinate geometries with a doubly bridged dimetal core were observed in 3. The magnetic properties of complexes 1-4 and 6 were studied at variable temperatures and revealed weak to very weak antiferromagnetic interactions in 1, 2, 4 and 6 (J = -0.55 to -9.4 cm(-1)) and ferromagnetic coupling in 3 (J = 15.4 cm(-1)). These results are consistent with DFT calculations performed at the B3LYP/def2-TZVP(-f) level of theory. Under physiological conditions, the interaction of the dinculear complexes 1-5 with supercoiled plasmid ds-DNA did not show any pronounced nuclease activity, but Ni(ii) complexes 1 and 2 revealed a strong ability to unwind the supercoiled conformation of ds-DNA. The mechanistic studies performed on the interaction of the Ni(ii) complexes with DNA demonstrated the important impact of the nickel(ii) ion in the unwinding process. In combination with the DNA study, the phosphatase activity of complexes 1, 3, and 5 was examined by the phosphodiester hydrolysis of bis(2,4-dinitrophenol)phosphate (BDNPP) in the pH range of 5.5-10.5 at 25 °C. The Michaelis-Menten kinetics performed at pH 7 and 10.7 showed that catalytic efficiencies kcat/KM (kcat = catalytic rate constant, KM = substrate binding constant) decrease in the order: Ni(ii), 1 > Zn(ii), 5 > Cu(ii), 3. A similar trend was also observed with the turnover numbers at pH = 7. The results are discussed in relation to the coordination geometry and nature of the metal center as well as the steric environment imposed by the compartmental phenoxido ligand.

Different topologies in three manganese-µ-azido 1D compounds: magnetic behavior and DFT-quantum Monte Carlo calculations.

The syntheses and structural characterization of three new monodimensional azido-bridged manganese(ii) complexes with empirical formulae [Mn(N3)2(aminopyz)2]n (1), [Mn(N3)2(4-azpy)2]n (2) and [Mn(N3)2(4-Bzpy)2]n (3) (pyz = pyrazine (1,4-diazine)), 4-azpy = 4-azidopyridine and 4-Bzpy = 4-benzoylpyridine) are reported. 1 is a monodimensional compound with double EO azido bridges, 2 is an alternating monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EE and 3 is a monodimensional compound with double end-on and double end-to-end azido bridges in the sequence di-EO-di-EO-diEO-di-EO-di-EE. The magnetic properties of 1-3 are reported. Periodic DFT calculations were performed to estimate the J values and quantum Monte Carlo simulations were carried out using the calculated J values to check their accuracy in comparison with the experimental magnetic measurements. From this theoretical analysis, two appealing features of the di-EO Mn(ii) compounds can be extracted: first, the exchange coupling becomes more ferromagnetic when the Mn-N-Mn bridging angle becomes larger and the spin density of the bridging nitrogen atoms has an opposite sign to that of the Mn(II) centers.

Mechanistic implications in the phosphatase activity of Mannich-based dinuclear zinc complexes with theoretical modeling.

An "end-off" compartmental ligand has been synthesized by an abnormal Mannich reaction, namely, 2-[bis(2-methoxyethyl)aminomethyl]-4-isopropylphenol yielding three centrosymmetric binuclear µ-phenoxozinc(II) complexes having the molecular formula [Zn2(L)2X2] (Zn-1, Zn-2, and Zn-3), where X = Cl(-), Br (-), and I (-), respectively. X-ray crystallographic analysis shows that the ZnO3NX chromophores in each molecule form a slightly distorted trigonal-bipyramidal geometry (τ = 0.55-0.68) with an intermetallic distance of 3.068, 3.101, and 3.083 Å (1-3, respectively). The spectrophotometrical investigation on their phosphatase activity established that all three of them possess significant hydrolytic efficiency. Michaelis-Menten-derived kinetic parameters indicate that the competitiveness of the rate of P-O bond fission employing the phosphomonoester (4-nitrophenyl)phosphate in 97.5% N,N-dimethylformamide is 3 > 1 > 2 and the kcat value lies in the range 9.47-11.62 s(-1) at 298 K. Theoretical calculations involving three major active catalyst forms, such as the dimer-cis form (D-Cis), the dimer-trans form (D-Trans), and the monoform (M-1 and M-2), systematically interpret the reaction mechanism wherein the dimer-cis form with the binuclear-bridged hydroxide ion acting as the nucleophile and one water molecule playing a role in stabilizing the leaving group competes as the most favored pathway.

Magnetic and structural properties of dinuclear singly bridged-phenoxido metal(II) complexes.

The reaction of a methanolic solution containing the bi-compartmental phenolic ligand 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-chlorophenol (L(Cl)-OH) with MCl2·nH2O in the presence of NH4PF6 or NaClO4 afforded the dinuclear bridged-phenoxido dichlorido-metal(ii) complexes [Co2(µ-L(Cl)O)(H2O)2Cl2][Co2(µ-L(Cl)O)(MeOH)2Cl2](PF6)2 (), [Ni2(µ-L(Cl)O)(MeOH)2Cl2]PF6 (), [Ni2(µ-L(Cl)O)(MeOH)(H2O)Cl2]ClO4·1.25H2O (), [Cu2(µ-L(Cl)O)Cl2]PF6·1/2MeOH () and [Zn2(µ-L(Cl)O)Cl2]PF6·MeOH (). The complexes were characterized by elemental microanalyses, conductivity measurements, IR and UV-Vis spectroscopy, mass spectrometry and single crystal X-ray crystallography. Each M(ii) center within the dinuclear complex cations is octahedrally coordinated in complexes , and five-coordinated distorted square pyramidal in and . Magnetic susceptibility measurements at variable temperature of the complexes revealed weak to moderate antiferromagnetic coupling with |J| values = 8.38, 39.0, 30.2 and 0.79 cm(-1), respectively. The results of DFT calculations correlate well with the experimentally determined antiferromagnetic coupling and show that the magnetic exchange coupling occurs mainly through the phenoxido bridge M-O-M. Implications of geometry around the central metal ion, MM distance, M-O-M bond angle and overlapping of magnetic orbitals on the magnetic exchange coupling are discussed.

Efficient hydrolytic cleavage of plasmid DNA by chloro-cobalt(II) complexes based on sterically hindered pyridyl tripod tetraamine ligands: synthesis, crystal structure and DNA cleavage.

Four new cobalt(ii) complexes [Co(6-MeTPA)Cl]ClO4/PF6 (2/2a), [Co(6-Me2TPA)Cl]ClO4/PF6 (3/3a), [Co(BPQA)Cl]ClO4/PF6 (4/4a) and [Co(BQPA)Cl]ClO4/PF6 (5/5a) as well as [Co(TPA)Cl]ClO4 (1) where TPA = tris(2-pyridylmethyl)amine, 6-MeTPA = ((6-methyl-2-pyridyl)methyl)bis(2-pyridylmethyl)amine, 6-Me2TPA = bis(6-methyl-2-pyridyl)methyl)-(2-pyridylmethyl)amine, BPQA = bis(2-pyridylmethyl)-(2-quinolylmethyl)-amine and BQPA = bis(2-quinolylmethyl)-(2-pyridylmethyl)amine were synthesized and structurally characterized. Single crystal X-ray crystallography confirmed the distorted trigonal bipyramidal geometries of complexes 2a-5a. Spectrophotometric titrations and conductivity measurements of the complexes in the CH3CN-H2O mixture showed that the chloro complexes exist in equilibrium with the corresponding hydrolyzed aqua species, [Co(L)(H2O)](2+). The pKa values of the coordinated H2O in aqua complexes vary from 8.4 to 8.7 (37 °C). The interactions of the complexes (1-5) with DNA have been investigated at pH = 7.0 and 9.0 (10 mM Tris-HCl buffer) and 37 °C where very high catalytic cleavage was observed. Under pseudo Michaelis-Menten kinetic conditions, the catalytic rate constants, kcat, decrease in the order 4>2>5>1>3. At pH 7.0 (10 mM Tris-HCl buffer) and 37 °C, the kcat value for complex 4 (6.02 h(-1)), where [Co(BPQA)(H2O)](2+) is the major species, corresponds to 170 million rate enhancement over the non-catalyzed DNA. Electrophoretic experiments conducted in the presence and absence of radical scavengers (DMSO, KI, NaN3) ruled out the oxidative mechanistic pathway of the reaction and suggested that the hydrolytic mechanism is the preferred one. This finding was in agreement with the observed increase in the kcat values at pH 9.0 compared to the corresponding values at pH 7.0 as a result of the increased concentration of the reactive hydroxo species, [Co(L)(OH)](+). The reactivity of the synthesized complexes in catalyzing the DNA cleavage is discussed in relation to the steric effect imposed by the coordinated pyridyl ligand around the central cobalt(ii) center.

A combined experimental and theoretical investigation on the role of halide ligands on the catecholase-like activity of mononuclear nickel(II) complexes with a phenol-based tridentate ligand.

Three new mononuclear nickel(II) complexes, namely, [NiL(1)(H2O)3]I2·H2O (1), [NiL(1)(H2O)3]Br2·H2O (2), and [NiL(1)(H2O)3]Cl2·2H2O (3) [HL(1) = 2-[(2-piperazin-1-ylethylimino)methyl]phenol], have been synthesized and structurally characterized. Structural characterization reveals that they possess similar structure: [NiL(1)(H2O)3](2+) complex cations, two halide counteranions, and lattice water molecules. One of the nitrogen atoms of the piperazine moiety is protonated to provide electrical neutrality to the system, a consequence observed in earlier studies (Inorg. Chem. 2010, 49, 3121; Polyhedron 2013, 52, 669). Catecholase-like activity has been investigated in methanol by a UV-vis spectrophotometric study using 3,5-di-tert-butylcatechol (3,5-DTBC) as the model substrate. Complexes 1 and 2 are highly active, but surprisingly 3 is totally inactive. The coordination chemistries of 1 and 2 remain unchanged in solution, whereas 3 behaves as a 1:1 electrolyte, as is evident from the conductivity study. Because of coordination of the chloride ligand to the metal in solution, it is proposed that 3,5-DTBC is not able to effectively approach an electrically neutral metal, and consequently complex 3 in solution does not show catecholase-like activity. Density functional theory (DFT) calculations corroborate well with the experimental observations and thus, in turn, support the proposed hypothesis of inactivity of 3. The cyclic voltametric study as well as DFT calculations suggests the possibility of a ligand-centered reduction at -1.1 V vs Ag/AgCl electrode. An electron paramagnetic resonance (EPR) experiment unambiguously hints at the generation of a radical from EPR-inactive 1 and 2 in the presence of 3,5-DTBC. Generation of H2O2 during catalysis has also been confirmed. DFT calculations support the ligand-centered radical generation, and thus a radical mechanism has been proposed for the catecholase-like activity exhibited by 1 and 2. Upon heating, 2 and 3 lose water molecules in two steps (first lattice waters, followed by coordinating water molecules), whereas 3 loses four water molecules in a single step, as revealed from thermogravimetric analysis. The totally dehydrated species are red, in all cases having square-planar geometry, and have amorphous nature, as is evident from a variable-temperature powder X-ray diffraction study.

Metal ions directing the geometry and nuclearity of azido-metal(II) complexes derived from bis(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)amine.

The reaction of a methanolic solution containing M(ClO(4))(2)·nH(2)O (M = Cu, Ni, Zn or Cd) or CoCl(2)·6H(2)O with bis(2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl)amine (bedmpza) in the presence of NaN(3) afforded the complexes [Cu(bedmpza)(µ(1,1)-N(3))](2)(ClO(4))(2) (1), [Ni(bedmpza)(N(3))(µ(1,1)-N(3))](2)·1.5H(2)O (2), [Co(bedmpza)(N(3))(2)] (3), [Zn(bedmpza)(N(3))]ClO(4) (4) and [Cd(bedmpza)(N(3))(µ(1,1)-N(3))](2)·1.5H(2)O (5). The five complexes were characterized by spectroscopic techniques and their molecular structures were determined by single crystal X-ray crystallography. The two mononuclear complexes 3 and 4 display distorted TBP and tetrahedral geometry, respectively with the azide ions acting as monodentate ligands. Doubly bridged end-on-azido dinuclear complexes were obtained in the remaining compounds. Compounds 2 and 5 are isomorphic with distorted octahedral geometry, whereas distorted square pyramidal geometry was determined in the Cu(II) complex 1. The magnetic properties for complexes 1 and 2 were investigated by measuring the magnetic susceptibilities at variable temperatures (300-2 K). The Ni(II) complex exhibits moderate ferromagnetic coupling, whereas [Cu(bedmpza)(µ(1,1)-N(3))](2)(ClO(4))(2) (1) which contains two crystallographic independent dinuclear subunits in the unit cell, with different Cu-N(N3)-Cu bond angles, reveals different signs in the magnetic coupling. The complex represents the first example in the literature that has simultaneously two moieties with ferro- (J = 15.4 cm(-1)) and antiferromagnetic (J = -18.9 cm(-1)) interactions.

Use of 6-methylpyridine-2-carbaldehydeoxime in nickel(II) carboxylate chemistry: synthetic, structural and magnetic properties of penta and hexanuclear complexes.

The use of 6-methylpyridine-2-carbaldehydeoxime ligand (6-mepaoH), in nickel(II) chemistry has been investigated and three new clusters isolated in mild conditions. Depending on the nature of the metal starting salts and the reaction conditions, the Ni(II)/6-mepaoH system has provided access to the complexes [Ni(6)(O(2)CPh)(6)(6-mepao)(6)] (1), [Ni(6)(O(2)CMe)(6)(6-mepao)(6)] (2) and [Ni(5)(3-Cl-BzO)(4)(6-mepao)(4)(6-mepaoH)(2)(N(3))(2)] (3), where 3-Cl-BzO(-) is the 3-chlorobenzoate anion. Compounds 1 and 2 are two new members of the [Ni(6)(O(2)C-R)(oximato)(6)] family of hexanuclear complexes whereas 3 exhibits an unusual irregular bowtie topology including end-on azido bridges. The structures of the three compounds have been determined by single-crystal X-ray crystallography. Variable-temperature dc magnetic susceptibility studies were carried out for 1-3. The data indicate antiferromagnetic exchange for complexes 1 and 2 and ferrimagnetic interaction for complex 3.

Bridging, terminal, free, anti and gauche BPA ligands in a 1D hybrid organic-inorganic Mn(II)-cyanate system.

A hybrid organic-inorganic chain compound of the family Mn(II)-bpa-(NCO) is presented. It contains, unusually, five different dispositions for the bpa [1,2-bis(4-pyridyl)ethane] ligand. Water molecules and free bpa ligands occupy the voids of the structure. The compound shows significant antiferromagnetic-type interactions as a consequence of different exchange pathways.

Assembly of [Mn(II)2Mn(III)2] S = 9 clusters via azido bridges: a new single-chain magnet.

In the present work, we report a new manganese single-chain magnet built from tetranuclear Mn(II)(2)Mn(III)(2) mixed-valence units linked by end-on azido and oximato bridges. All of the intra- and intercluster interactions involve end-on azido bridges, resulting in one ferromagnetic chain of ferromagnetic clusters with local ground state S = 9.

Trinuclear, tetranuclear, and polymeric Cu(II) complexes from the first use of 2-pyridylcyanoxime in transition metal chemistry: synthetic, structural, and magnetic studies.

The first use of 2-pyridylcyanoxime, (py)C(CN)NOH, in transition metal chemistry is described. Depending on the nature of the metal starting material and the reaction conditions employed, the Cu(II)/(py)C(CN)NOH system has provided access to complexes [Cu(3)O{(py)C(CN)NO}(3)(NO(3))(H(2)O)(2)(MeOH)] (1), [Cu(4)O{(py)C(CN)NO}(4)(O(2)CMe)(2)] (2), [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)](2n)·n[Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)] (3), and [Cu{(py)C(CN)NO}(2)](n) (4). The molecule of 1 consists of three Cu(II) atoms in a strictly equilateral arrangement bridged by a central µ(3)-oxide group. The molecule of 2 consists of a tetrahedron of Cu(II) atoms held together by a central µ(4)-oxide ion, four η(1):η(1):η(1):µ-(py)C(CN)NO(-) ligands and two η(1):η(1):µ-MeCO(2)(-) groups. The crystal structure of 3 consists of [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)](2n) double chains and discrete cluster [Cu(4)(OH)(2){(py)C(CN)NO}(2)(O(2)CPh)(4)] molecules. The crystal structure of 4 consists of neutral polymeric chains based on centrosymmetric mononuclear [Cu{(py)C(CN)NO}(2)] units. The Cu(II) atoms are doubly bridged by the oximate groups of two η(1):η(1):η(1):µ-(py)C(CN)NO(-) ligands. Variable-temperature, solid-state direct current (dc) magnetic susceptibility studies were carried out for 1-4. The data indicate very strong antiferromagnetic exchange interactions for 1-3. The obtained J values are discussed in depth on the basis of the structural parameters of the complexes, literature reports, and existing magnetostructural correlations.