Synthesis, spectral characterization, solution equilibria, in vitro antibacterial and cytotoxic activities of Cu(II), Ni(II), Mn(II), Co(II) and Zn(II) complexes with Schiff base derived from 5-bromosalicylaldehyde and 2-aminomethylthiophene

Schiff base namely 2-aminomethylthiophenyl-4-bromosalicylaldehyde (ATS)(4-bromo-2-(thiophen-2-yl-imino)methylphenol) and its metal complexes have been synthesized and characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, ESR and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:2 [M:L] ratio of the formula [ML2], where M represents Ni(II), Zn(II) and Cu(II) ions, while L represents the deprotonated Schiff base. IR spectra show that ATS is coordinated to the metal ions in a bidentate manner through azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria. A cytotoxicity of the compounds against colon (HCT116) and larynx (HEP2) cancer cells have been studied. Protonation constants of (ATS) ligand and stability constants of its Cu2+, Co2+, Mn2+, Zn2+ and Ni2+ complexes were determined by potentiometric titration method in 50% (v/v) DMSO-water solution at ionic strength of 0.1 M NaNO3.     

Luminescent complexes of Re(I) and Ru(II) with appended macrocycle groups derived from 5,6-dihydroxyphenanthroline: cation and anion binding

A range of ligands in which a macrocyclic unit is fused to a 1,10-phenanthroline unit has been prepared starting from 5,6-dihydroxyphenanthroline. The ligands are L1 in which the pendant ligand is 18-crown-6; L2, in which the pendant ligand is benzo-24-crown-8; and L(3), in which the macrocycle contains two carboxamide units. Ligands L1 and L2 can bind Group 1 and 2 metal cations in their crown-ether cavities; L3 contains two H-bond (amide) donors and is suitable for anion-binding. Luminescent complexes of the form [Ru(bipy)2L]2+, [ReL(CO)3Cl] and [RuL(CN)4]2- were prepared and some were structurally characterised; their interactions with various guest species were investigated by luminescence and NMR spectroscopy. For complexes with the crown ethers (L1 and L2), binding of K+ was rather weak, but the electrostatic effect due to the charge on the host complex was clear with [RuL1(CN)4]2- binding K+ more strongly than [Ru(bipy)2L1]2+. Binding to the pendant crown ethers was much stronger with Ba2+, and both [ReL1(CO)3Cl] and [ReL2(CO)3Cl] showed substantial luminescence quenching in MeCN on addition of Ba2+ ions, with binding constants of 4.5 x 10(4) M(-1) for [ReL1(CO)3Cl]/Ba2+ and 1.3 x 10(5) M(-1) for [ReL2(CO)3Cl]/Ba2+. Complexes [Ru(bipy)2L3]2+ and [ReL3(CO)3Cl], due to their H-bond donor sites, showed binding of dihydrogenphosphate to the macrocycle. Whereas [ReL3(CO)3Cl] showed 1 : 1 binding with (H2PO4)- in dmso with a binding constant of 65 M(-1), [Ru(bipy)2L3]2+ showed 1 : 2 binding, with microscopic association constants of ca. 1 x 10(6) and 1.6 x 10(6) M(-1) in MeCN. The fact that K2 > K1 suggests a cooperative interaction whereby binding of the first anion makes binding of the second one easier to an extent which overcomes electrostatic effects, and a model for this is proposed which also accounts for the substantial increase in luminescence from [Ru(bipy)2L3]2+ (5-fold enhancement) when the second (H2PO4)- anion binds. Both [Ru(bipy)2L3]2+ and [ReL3(CO)3Cl] undergo complete luminescence quenching and a change in colour to near-black in the presence of (anhydrous) fluoride in MeCN, probably due to deprotonation of the carboxamide group. These changes are however irreversible on a long timescale and lead to slow decomposition.     

Synergic effect of two metal centers in catalytic hydrolysis of methionine-containing peptides promoted by dinuclear palladium(II) hexaazacyclooctadecane complex

The species obtained by the reaction of [Pd2([18]aneN6)Cl2](ClO4)2(where [18]aneN6 is 1,4,7,10,13,16-hexaazacyclooctadecane) with AgBF4 have been determined by electrospray ionization mass spectrometry (ESI-MS) to be an equilibrium mixture of three major types of dinuclear Pd(II) complex cations, [Pd2(mu-O)([18]aneN6)]2+, [Pd2(mu-OH)([18]aneN6)]3+ and [Pd2(H2O)(OH)([18]aneN6)](3+), in aqueous solution. The hydroxo-group-bridged one, [Pd2(mu-OH)([18]aneN6)]3+, is a dominant species, whose crystal structure has been obtained. The crystal structure of [Pd2(mu-OH)([18]aneN6)](ClO4)3 shows that each Pd(II) ion in the dinuclear complex is tetra-coordinated by three nitrogen atoms and one hydroxo group bridge in a distorted square configuration. The two Pd(II) ions are 3.09 A apart from each other. The dinuclear Pd(II) complex cations [Pd2(mu-OH)([18]aneN6)]3+ and [Pd2(H2O)(OH)([18]aneN6)]3+ can efficiently catalyze hydrolysis of the amide bond involving the carbonyl group of methionine in methionine-containing peptides with turnover number of larger than 20. In these hydrolytic reactions, the two Pd(II) ions are synergic; one Pd(II) ion anchors to the side chain of methionine and the other one delivers hydroxo group or aqua ligand to carbonyl carbon of methionine, or acts as a Lewis acid to activate the carbonyl group of methionine, resulting in cleavage of Met-X bond. The binding constant of dinuclear Pd(II) complex cations with AcMet-Gly and AcMet were determined by 1H NMR titration to be 282 +/- 2 M(-1) and 366 +/- 4 M(-1), respectively. The relatively low binding constants enable the catalytic cycle and the possible catalytic mechanism is proposed. This is the first artificial mimic of metallopeptidases with two metal active centers.     

Mass spectrometry assisted assignments of binding and cleavage sites of copper(II) and platinum(II) complexes towards oxidized insulin B chain

Interaction of cis-[Pt(en)(H2O)2]2+ and [CuL(H2O)]2+, where L is 2-[bis(2-aminoethyl)amino]ethanol, with oxidized insulin B chain in molar ratio of 1 : 1, 1 : 2 and 1 : 3 at pH 2.5 and 40 degrees C has been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). The results show that the binding sites of the two complexes with oxidized insulin B chain are terminal NH2, imidazole groups of His5 and His10. The hydrolytic cleavage studies show that the [CuL(H2O)]2+, upon a pendant hydroxyl group of the ligand, selectively cleaves the peptide bonds at Gly8-Ser9, Asn3-Gln4 and Phe1-Val2, and the cis-[Pt(en)(H2O)2]2+ only cleaves the peptide bond at His10-Leu11. This is the first report of cis-[Pt(en)(H2O)2]2+-promoted cleavage of His-X peptide bond.     

A highly selective fluorescence chemosensor for Pb(II) in neutral buffer aqueous solution

A 3,4-dimethylthieno[2,3-b]thiophene-based fluorogenic probe bearing benzo[d]-thiazole-2-thio unit (sodium 3,4-bis ((benzo[d]thiazol-2-ylthio)methyl) thieno [2, 3-b]thio-phene-2, 5-dicarboxylate) was developed as a novel fluorescent chemosensor with high selectivity towards Pb(II) over other cations tested. The new probe exhibited good water solubility and only sensed Pb(II) among metal ions examined in neutral 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer solution. The selectivity and sensitivity of fluorogenic probe to Pb(II) were discussed on the basis of experimental results.     

Structural and magnetic properties of layered copper(II) coordination polymers intercalating s and f metal ions

The nanoporous coordination polymer [Cu(pyrimidin-2-olate-N1,N3)2]n (1C) of the sodalite zeotype sorbs a variety of metal nitrates [M(NO3)m, M = Na+, K+, Rb+, Tl+, Ca2+, Sr2+, Ba2+, Pb2+, La3+, Nd3+, Gd3+, Er3+] from H2O/MeOH solutions, with a concomitant structural change to a layered [Cu(pyrimidin-2-olate-N1,N3)2]n.[M(NO3)m]n/2 (MNO3@1L) coordination framework. Single-crystal X-ray diffraction analyses revealed that the layers are based on Cu4(pyrimidin-2-olate-N1,N3)4 square grids of copper(II) ions bridged by N1,N3 exobidentate ligands, displaying a structural motif of the metallacalix[4]arene type in pinched cone conformation. The interlayer space is occupied by the guest metal nitrates, each metal being coordinated by (at least) the four oxygen atoms of a metallacalix[4]arene. Magnetic measurements on the MNO3@1L series denoted a weak ferromagnetic ordering taking place below the Néel temperatures (typically close to 35 K), arising from spin-canting phenomena of the antiferromagnetically coupled copper centers. When M = Nd3+, Gd3+, or Er3+, additional magnetic ordering is observed at lower temperatures, which, on the basis of static and dynamic magnetic susceptibility measurements, can be attributed to copper- lanthanide interactions.     

Hydroquinone-bridged dinuclear Cu(II) complexes and single-crystalline Cu(II) coordination polymers

Cationic dinuclear Cu(II) complexes 3 and 4 have been prepared using the novel hydroquinone-based imine chelators 2,5-((i)Pr(2)NCH(2)CH(2)N[double bond, length as m-dash]CH)(2)-1,4-(OH)(2)-C(6)H(2) (1) and 2,5-(pyCH(2)CH(2)N[double bond, length as m-dash]CH)(2)-1,4-(OH)(2)-C(6)H(2) (2), respectively (py = 2-pyridyl). X-Ray quality crystals of both complexes were grown from their DMF solutions. The sterically more encumbered compound crystallizes in the form of discrete dinuclear entities with Cu(II) centres in a distorted square-planar ligand environment (one coordination site is occupied by a DMF molecule). The pyridyl derivative 4 features dinuclear hydroquinone-bridged subunits similar to 3. However, the Cu(II) ions are now six-coordinate with two DMF molecules at an axial and an equatorial position of a Jahn-Teller-distorted octahedron. Moreover, the dinuclear subunits are no longer isolated but linked with each other via bridging hydroquinone oxygen atoms which occupy the second apical position of each octahedron. The structure suggests that the magnetic properties of the resulting coordination polymer of 4 could be described by a model valid for dimerized spin chains. As a result of this analysis the antiferromagnetic coupling constants J(1)/k(B) = 9.9 K (intradimer) and J(2)/k(B) = 0.9 K (interdimer) are obtained. Both in 3 and in 4, the hydroquinone --> semiquinone transition of the central bridging unit (E degrees ' = + 0.57 V, 3; E degrees ' = + 0.51 V, 4; DMF; vs. SCE) displays features of chemical reversibility. In the case of , reduction of Cu(II) centres requires a peak potential of E(p) = - 0.42 V.     

Speciation of cyclo(Pro-Gly)<Subscript>3</Subscript> and its divalent metal-ion complexes by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to study the binding of selected group II and divalent transition-metal ions by cyclo(Pro-Gly)3 (CPG3), a model ion carrier peptide. Metal salts (CatXn) were combined with the peptide (M) at a molar ratio of 1:10 M/Cat in aqueous solvents containing 50% vol/vol acetonitrile or methanol and 1 or 10 mM ammonium acetate (NH4Ac). Species detected include [M+H]+, [M+Cat-H]+, [M2+Cat]2+, [M+Cat+Ac]+, and [M+Cat+X]+. The relative stabilities of complexes formed with different cations (Mg2+, Ca2+, Sr2+, Mn2+, Co2+, Ni2+, Cu2+, and Zn2+) were determined from the abundance of 1:1 and 2:1 M/Cat species relative to that of the unbound peptide. The largest metal ions (Ca2+, Sr2+, and Mn2+) formed the most stable complexes. Reducing the buffer concentration increased the overall extent of metal binding. Results show that the binding specificity of CPG3 depends upon the size of the metal ion and its propensity for electrostatic interaction with oxygen atoms. Product ion tandem mass spectrometry of [M+H]+ and [M+Cu-H]+ confirmed the cyclic structure of the peptide, although the initial site(s) of metal attachment could not be determined.     

NaCu(II)4] cluster from alkali template assembly of two asymmetric end-on azido-bridged [Cu(II)2] units

The cluster [NaCu4L2(N3)2](ClO4) [1; H3L is 2-(2'-hydroxyphenyl)-1,3-bis[3'-aza-4'-(2'-hydroxyphenyl)prop-4'-en-1'-yl]-1,3-imidazolidine] has been synthesized and structurally characterized. Complex 1 is formed by the template assembly of two [Cu2L(N3)] neutral fragments through their weak oxophilic interactions with a central Na+ cation as observed in metallacrowns. The cluster exhibits a combination of ferro- and antiferromagnetic interactions. End-on N3- bridging of copper ions within the [Cu(II)2] units facilitates stabilization of S = 1 magnetic subunits that mutually cancel via antiferromagnetic coupling as mediated by the O...Na+...O bridges.     

Mercury(II) ion-selective electrodes based on p-tert-butyl calix[4]crowns with imine units.

A PVC membrane incorporating p-tert-butyl calix[4]crown with imine units as an ionophore was prepared and used in an ion-selective electrode for the determination of mercury(II) ions. An electrode based on this ionophore showed a good potentiometric response for mercury(II) ions over a wide concentration range of 5.0 x 10(-5) - 1.0 x 10(-1) M with a near-Nernstian slope of 27.3 mV per decade. The detection limit of the electrode was 2.24 x 10(-5) M and the electrode worked well in the pH range of 1.3 - 4.0. The electrode showed a short response time of less than 20 s. The electrode also showed better selectivity for mercury(II) ions over many of the alkali (Na+, -1.69; K+, -1.54), alkaline-earth (Ca2+, -3.30; Ba2+, -3.32), and heavy metal ions (Co2+, -3.67; Ni2+, -3.43; Pb2+, -3.31; Fe3+, -1.82). Ag+ ion was found to be the strongest interfering ion. Also, sharp end points were obtained when the sensor was used as an indicator electrode for the potentiometric titration of mercury(II) ions with iodide and dichromate ions.     

Spectrophotometric analysis of 5-coordinate cobalt(II) species for ligand substitution of hexakis(acetonitrile)cobalt(II) with bulky 1,1,3,3-tetramethylurea in noncoordinating nitromethane.

The ligand substitution reaction of [Co(an)6]2+ (an = acetonitrile) with 1,1,3,3-tetramethylurea (TMU) in the noncoordinating solvent, nitromethane, was spectrophotometrically investigated by titration. The observed spectral changes were analyzed using a model with the four steps of ligand substitution. The component complexes involved in the substitution were found to be 6-coordinate [Co(an)6]2+ and [Co(an)5(tmu)]2+, 5-coordinate [Co(an)3(tmu)2]2+ and [Co(an)2(tmu)3]2+, and 4-coordinate [Co(tmu)4]2+. The logarithmic values of the stepwise equilibrium constant are 2.17 +/- 0.26, 1.06 +/- 0.15, 1.19 +/- 0.06, and -0.4 +/- 0.4 at 25 degrees C. The decrease in the coordination number of the Co(II) ion from 6 to 5 during the formation of [Co(an)3(tmu)2]2+ and from 5 to 4 during the formation of [Co(tmu)4]2+ is ascribed to the steric repulsion between the coordinating bulky TMU molecules.     

Dinuclear ruthenium(II) complexes as potential probes for RNA bulge sites

1H NMR spectroscopy and molecular modelling have been used to investigate the binding of the DeltaDelta-and LambdaLambda-enantiomers of the dinuclear ruthenium(II) complex [[Ru(Me2bpy)2]2(mu-bpm)]4+ [Me2bpy = 4,4'-dimethyl-2,2'-bipyridine; bpm = 2,2'-bipyrimidine] to an RNA tridecanucleotide duplex containing a single-base bulge [r(CCGAGAAUUCCGG)2]], and the corresponding control dodecanucleotide [r(CCGGAAUUCCGG)2]. Both enantiomers bound the control RNA sequence weakly. From upfield shifts of the metal complex H3 and H3' protons throughout the titration of the control dodecanucleotide with DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+, a binding constant of 1 x 10(3) M(-1) was determined. In NOESY spectra of the control sequence with added DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+, NOEs were only observed to protons from the terminal base-pair residues. No significant changes in chemical shift were observed for either the metal complex or RNA protons upon addition of the LambdaLambda-enantiomer to the control dodecanucleotide. The DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+ complex bound the bulge-containing RNA with a significantly greater affinity (6 x 10(4) M(-1)) than the non-bulge control RNA duplex. Competition binding experiments indicated that the LambdaLambda-isomer bound the tridecanucleotide with similar affinity to the DeltaDelta-enantiomer. Addition of DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+ to the bulge-containing tridecanucleotide induced selective changes in chemical shift for the base H8 and sugar H1' resonances from the adenine bulge residue, and resonances from nucleotide residues adjacent to the bulge site. Intermolecular NOEs observed in NOESY spectra of the tridecanucleotide with added DeltaDelta-[[Ru(Me2bpy)2]2(mu-bpm)]4+ confirmed the selective binding of the ruthenium complex at the bulge site. Preliminary binding models, consistent with the NMR data, showed that the ruthenium complex could effectively associate in the RNA minor groove at the bulge site.     

Structures and fragmentations of cobalt(II)-cysteine complexes in the gas phase

The electronebulization of a cobalt(II)/cysteine(Cys) mixture in water/methanol (50/50) produced mainly cobalt-cationized species. Three main groups of the Co-cationized species can be distinguished in the ESI-MS spectrum: (1) the cobalt complexes including the cysteine amino acid only (they can be singly charged, for example, [Co(Cys)n- H]+ with n = 1-3 or doubly charged such as [Co + (Cys)2]2+); (2) the cobalt complexes with methanol: [Co(CH3OH)n- H]+ with n = 1-3, [Co(CH3OH)4]2+; and (3) the complexes with the two different types of ligands: [Co(Cys)(CH3OH) - H]+. Only the singly charged complexes were observed. Collision-induced dissociation (CID) products of the [Co(Cys)2]2+, [Co(Cys)2 - H]+ and [Co(Cys) - H]+ complexes were studied as a function of the collision energy, and mechanisms for the dissociation reactions are proposed. These were supported by the results of deuterium labelling experiments and by density functional theory calculations. Since [Co(Cys) - H]+ was one of the main product ions obtained upon the CID of [Co(Cys)2]2+ and of [Co(Cys)2 - H]+ under low-energy conditions, the fragmentation pathways of [Co(Cys) - H]+ and the resulting product ion structures were studied in detail. The resulting product ion structures confirmed the high affinity of cobalt(II) for the sulfur atom of cysteine.     

Synthesis and multitopic complex formation of a photochromic bis(crown ether) based on benzobis(thiazole)

2,7-Bis[2-(6,7,9,10,12,13,15,16-octahydro-5,8,11,14,17-pentaoxabenzocyclopentadecen-2-yl)vinyl]-benzo[1,2-d;3,4-d']bisthiazole, 2, with crown ether styryl moieties substituted on a heterocyclic core, was synthesized and its complex forming ability with several metal cations was evaluated in acetonitrile by absorption and fluorescence spectroscopy. The results are compared to those for the analogous ligand possessing a single crown ether styryl moiety. Selective binding of the metal cation at the heterocyclic core of both ligands was observed only for Hg2+. Alkali and alkaline earth cations bind selectively at the crown ether moieties. Stability constants and pure spectra of defined stoichiometry were determined with the use of HYPERQUAD, a least-squares fitting program, and the results were validated in one case by subjecting the titration spectral matrix to singular value decomposition with self-modeling (SVD-SM). The multitopic ligand 2 forms relatively strong 2:2 stoichiometric complexes with K+, among the alkali metal cations, and Ba2+, among the alkaline earth metal cations, and is a promising selective optical sensor for these ions.     

A copper(II) ion-selective on-off-type fluoroionophore based on zinc porphyrin-dipyridylamino

A new copper(II) fluorescent sensor 5,10,15,20-tetra((p-N,N-bis(2-pyridyl)amino)phenyl)porphyrin zinc (1) has been designed and synthesized by the Ullmann-type condensation of bromoporphyrin zinc with 2,2'-dipyridylamine (dpa) under copper powder as a catalyst as well as with K2CO3 as the base in a DMF solution. It consists of two separately functional moieties: the zinc porphyrin performs as a fluorophore, and the dpa-linked-to-zinc porphyrin acts as a selected binding site for metal ions. It displays a high selectivity and antidisturbance for the Cu2+ ion among the metal ions examined (Na+, Mg2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+, and Fe3+) and exhibits fluorescence quenching upon the binding of the Cu2+ ion with an "on-off"-type fluoroionophoric switching property. The detection limit is found to be 3.3 x 10(-7) M (3s blank) for Cu2+ ion in methanol solution, and its fluorescence can be revived by the addition of EDTA disodium solution. The design strategy and remarkable photophysical properties of sensor 1 help to extend the development of fluorescent sensors for metal ions.     

Cu(I) and Cu(II) helical complexes formed with oligobipyridine ligand

A new asymmetric oligobipyridine ligand, 1- (5’-methyl-2, 2’-bipyridin-5-y1)-2- (6’-methyl-2, 2’-bipyridin-6-yl)ethane (L), in which the bipyridine units are bridged by CH₂CH₂ at 5,6’-position has been synthesized. The ligand L reacts with Cu(I) and Cu(I1) ions giving double-stranded helical complexes [Cu ₂ ¹ L₂](C10₄)₂.Et₂0 (1) and [Cu ₂ ^II L₂,(OH)(H₂0) ] [ClO₄]₃(2), respectively. Complexes 1 and 2 were characterized by X-ray diffraction analyses, ES-MS, ESR and cyclic voltammetry, etc. Differing from the oligobipyridine ligands bridged by CH₂CH₂ at 6,6’-or 5,5’-position, the ligand L not only forms a double-stranded helicate with Cu(1) ion, but also gives a double-stranded helicate with Cu(I1) ion. The results show that the linkage mode of the spacer group to the bipyridine units exerts a great impact on the formation of helix. Project supported by the National Natural Science Foundation of China (Grant NO. 29601003).     

Photexcitation of aqueous ruthenium(II)-tris-(2,2'-bipyridine) with high-intensity femtosecond laser pulses

We report a femtosecond pump-probe study on the photochemistry of concentrated aqueous solutions of [RuII(bpy)3]2+, as a function of pump power (up to 2 TW/cm2) at 400 nm excitation. The transient absorption spectra in the 345-660 nm range up to 1 ns time delay enable the observation of the following photoproducts: the triplet 3MLCT (metal-to-ligand-charge-transfer) excited state, the reduced form [RuII(bpy)3]+, the oxidized species [RuIII(bpy)3]3+, and the solvated electron e(aq). The 3MLCT state is formed within the excitation pulse and undergoes vibrational relaxation in 3-5 ps, as evidenced by the shift of the ligand-centered (LC) absorption band below 400 nm. Even at the highest pump powers, the majority of e(aq) originates from multiphoton ionization of [RuII(bpy)3]2+ and not from the solvent, generating [RuIII(bpy)3]3+ as a byproduct. At 10 ps time delay, the total concentration of the three product species is balanced by the depleted concentration of [RuII(bpy)3]2+, even at the highest fluences used, indicating that no further reaction products significantly contribute to the overall photochemistry. On the 100 ps time scale, most probably diffusion-controlled reduction of ground-state [RuII(bpy)3]2+ by solvated electrons occurs, next to recombination between e(aq) and [RuIII(bpy)3]3+.     

Water exchange on seven-coordinate Mn(II) complexes with macrocyclic pentadentate ligands: insight in the mechanism of Mn(II) SOD mimetics

Seven-coordinate manganese(II) complexes [Mn(L)(H2O)2]2+, where L represents an equatorial pentadentate macrocyclic ligand with five nitrogen donor atoms, were studied with regard to their acid-base properties, water-exchange rate constants, and corresponding activation parameters (DeltaH, DeltaS, and DeltaV). Three of the studied complexes without imine bonds in the macrocyclic ligand are proven superoxide dismutase (SOD) mimetics. Their water-exchange parameters were compared with those of the imino groups containing complex [Mn(L1)(Cl)2] (dichloro-2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]-octadeca-1(18),2,12,14,16-pentaenemanganese(II)), which does not show SOD activity. In addition the X-ray crystal structure of a new complex, dichloro-2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]pyridine-manganese(II) [Mn(L2)(Cl)2], which is the acyclic analog of [Mn(L1)(Cl)2], is reported. Stability constants of the complexes and the pKa values of the ligands were measured by potentiometric titration. The titrations of [Mn(L1)(H2O)2]2+ and [Mn(L2)(H2O)2]2+ led to complicated species distribution curves because of their ligands containing imine bonds. Water exchange was measured by temperature- and pressure-dependent 17O NMR techniques. In addition to the measurements on [Mn(EDTA)(H2O)]2- and its derivatives, this is the only study of water exchange on seven-coordinate manganese complexes. The water exchange rate constants vary between 1.6 x 107 s-1 and 5.8 x 107 s-1 at 25 degrees C and are mainly controlled by the pi-acceptor abilities of the ligands. The exchange rate constant of the diaqua-1,4,7,10,13-pentaazacyclopentadecanemanganese(II) [Mn([15]aneN5)(H2O)2]2+ complex seems to be even higher but could not be exactly determined. On the basis of the obtained activation parameters, the exchange mechanism of the studied seven-coordinate manganese(II) complexes follows a dissociative pathway (Id mechanism). DFT calculations (UB3LYP/LANL2DZp) were performed to obtain the energy required for the dissociation of the coordinated water molecule, that is, the energy difference between the starting seven-coordinate complex and a six-coordinate intermediate. The results have been discussed in terms of the catalytic mechanism of the proven SOD mimetics.     

Aggregation of [Cu(II)4] building blocks into [Cu(II)8] clusters or a [Cu(II)4]infinity chain through subtle chemical control

Coordination complexes of the ligand H3L [1,3-bis(3-oxo-3-phenylpropionyl)-2-hydroxy-5-methylbenzene] with Cu(II) are reported. Clusters showing various nuclearities or modes of supramolecular organization have been prepared by slightly changing the reaction conditions and have been crystallographically characterized. The reaction of H3L with one equivalent of Cu(OAc)2 in DMF yields the dinuclear complex [Cu2(HL)2(dmf)2] (1). Reaction in MeOH of H3L with an increased amount of metal, in the form of Cu(NO3)2, and excess strong base (nBu4NOH) affords the cluster [Cu8(L)2(OMe)8(NO3)2] (2). Complex 2 is a dimer of two linear [Cu4] arrays bridged by methoxide ligands, where the polynucleating ligand is fully deprotonated. The [Cu4]2 clusters are linked to each other by NO3- bridges to form one-dimensional coordination polymers. The link between [Cu8] units and their relative spatial positioning can be modified by changing the anion of the Cu(II) salt, as demonstrated by the synthesis of the cluster polymers [Cu8(L)2(OMe)8Cl2] (3) and [Cu8(L)(OMe)7.86Br2.14] (4), where only NO3- has been replaced by Cl- or Br-, respectively. Similarly, when ClO4- is used, compound [Cu8(L)2(OMe)8(ClO4)2(MeOH)4] (5) can be isolated. It contains independent [Cu8] units. A slight change in the stoichiometry of the reaction leading to 2 affords the related complex catena-[Cu4(L)(OMe)3(NO3)2(H2O)0.36] (6). This polymer contains essentially the same [Cu4] moiety as 2, albeit organized in a completely different arrangement. Each [Cu4] unit in 6 is linked by OMe- ligands to two such equivalent groups to form an infinite chain. Magnetic susceptibility measurements reveal weak antiferromagnetic exchange between Cu(II) centers in 1 (J = -0.73 cm(-1)) and strong antiferromagnetic coupling within [Cu4] chains in 2, 5, and 6 (most negative J values of -113.8 and -177.3 cm(-1) for 2 and 6, respectively).     

Syntheses and properties of emissive iridium(III) complexes with tridentate benzimidazole derivatives

A series of novel emissive Ir(III) complexes having the coordination environments of [Ir(N--N--N)2]3+, [Ir(N--N--N)(N--N)Cl]2+, and [Ir(N--N--N)(N--C--N)]2+ with 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine (L1, N--N--N), 1,3-bis(1-methyl-benzimidazol-2-yl)benzene (L2H, N--C--N), 4'-(4-methylphenyl)-2,2':6',2' '-terpyridine (ttpy, N--N--N), and 2,2'-bipyridine (bpy, N--N) have been synthesized and their photophysical and electrochemical properties studied. The Ir(III) complexes exhibited phosphorescent emissions in the 500-600 nm region, with lifetimes ranging from approximately 1-10 micros at 295 K. Analysis of the 0-0 energies and the redox potentials indicated that the lowest excited state of [Ir(L1)(L2)]2+ possessed the highest contribution of 3MLCT (MLCT = metal-to-ligand charge transfer) among the Ir(III) complexes, reflecting the sigma-donating ability of the tridentate ligand, ttpy < L1 < L2. The emission quantum yields (phi) of the Ir(III) complexes ranged from 0.037 to 0.19, and the highest phi value (0.19) was obtained for [Ir(L1)(bpy)Cl]2+. Radiative rate constants (k(r)) were 1.2 x 10(4) s(-1) for [Ir(ttpy)2]3+, 3.7 x 10(4) s(-1) for [Ir(L1)(bpy)Cl]2+, 3.8 x 10(4) s(-1) for [Ir(ttpy)(bpy)Cl]2+, 3.9 x 10(4) s(-1) for [Ir(L1)2]3+, and 6.6 x 10(4) s(-1) for [Ir(L1)(L2)]2+. The highest radiative rate for [Ir(L1)(L2)]2+ with the highest contribution of 3MLCT could be explained in terms of the singlet-triplet mixing induced by spin-orbit coupling of 5d electrons in the MLCT electronic configurations.