Ligand Charge Transfer Transitions Research Articles

The second coordination sphere of FIH controls hydroxylation.

The factor inhibiting HIF (FIH) is a proximate oxygen sensor for human cells, hydroxylating Asn(803) within the α-subunit of the hypoxia inducible factor (HIF). FIH is an α-ketoglutatrate (αKG)-dependent, non-heme Fe(II) dioxygenase, in which Fe(II) is coordinated by a (His(2)Asp) facial triad, αKG, and H(2)O. Hydrogen bonding among the facial triad, the HIF-Asn(803) side chain, and various second-sphere residues suggests a functional role for the second coordination sphere in tuning the chemistry of the Fe(II) center. Point mutants of FIH were prepared to test the functional role of the αKG-centered (Asn(205) and Asn(294)) or HIF-Asn(803)-centered (Arg(238) and Gln(239)) second-sphere residues. The second sphere was tested for local effects on priming Fe(II) to react with O(2), oxidative decarboxylation, and substrate positioning. Steady-sate kinetics were used to test for overall catalytic effects; autohydroxylation rates were used to test for priming and positioning, and electronic spectroscopy was used to assess the primary coordination sphere and the electrophilicity of αKG. Asn(205) → Ala and Asn(294) → Ala mutants exhibited diminished rates of steady-state turnover, while minimally affecting autohydroxylation, consistent with impaired oxidative decarboxylation. Blue-shifted metal to ligand charge transfer transitions for (Fe+αKG)FIH indicated that these point mutations destabilized the π* orbitals of αKG, further supporting a slowed rate of oxidative decarboxylation. The Arg(238) → Met mutant exhibited steady-state rates too low to measure and diminished product yields, suggesting impaired substrate positioning or priming; the Arg(238) → Met mutant was capable of O(2) activation for the autohydroxylation reaction. The Gln(239) → Asn mutant exhibited significantly slowed steady-state kinetics and diminished product yields, suggesting impaired substrate positioning or priming. As HIF binding to the Gln(239) → Asn mutant stimulated autohydroxylation, it is more likely that this point mutant simply mispositions the HIF-Asn(803) side chain. This work combines kinetics and spectroscopy to show that these second-sphere hydrogen bonds play roles in promoting oxidative decarboxylation, priming Fe(II) to bind O(2), and positioning HIF-Asn(803).

Theoretical Study of Iridium Complexes with Phenylpyridine Based Ligands and Phosphines

Recently, iridium complexes with phenylpyridine based ligands and phosphines, Ir(C(see text for symbol)N)2 (PPh3)(CN), [(C(see text for symbol)N) = dfppy, dfMeppy] are reported as blue phosphorescent OLED materials. These iridium complexes have novel blue color and emit light at 441 nm to 439 nm. However, these complexes have low external quantum efficiency because they exhibit less MLCT than iridium complexes with phenylpyridine, and some other ancillary ligands. To improve quantum efficiency of iridium complexes with phenylpyridine based ligands and phosphines, a time dependent density functional theory (TDDFT) study of these phosphors was performed. Using these results, this paper discusses how the ancillary ligand influences the emission peak, as well as the metal to ligand charge transfer (MLCT) transition efficiency.

Influence of Mixed Thiolate/Thioether versus Dithiolate Coordination on the Accessibility of the Uncommon +I and +III Oxidation States for the Nickel Ion: An Experimental and Computational Study

Sulfur-rich nickel metalloenzymes are capable of stabilizing Ni(I) and Ni(III) oxidation states in catalytically relevant species. In an effort to better understand the structural and electronic features that allow the stabilization of such species, we have investigated the electrochemical properties of two mononuclear N(2)S(2) Ni(II) complexes that differ in their sulfur environment. Complex 1 features aliphatic dithiolate coordination ([NiL], 1), and complex 2I is characterized by mixed thiolate/thioether coordination ([NiL(Me)]I, 2I). The latter results from the methylation of a single sulfur of 1. The X-ray structure of 2I reveals a distorted square planar geometry around the Ni(II) ion, similar to what was previously reported by us for 1. The electrochemical investigation of 1 and 2(+) shows that the addition of a methyl group shifts the potentials of both redox Ni(II)/Ni(I) and Ni(III)/Ni(II) redox couples by about 0.7 and 0.6 V to more positive values. Through bulk electrolyses, only the mononuclear dithiolate [Ni(I)L](-) (1(-)) and the mixed thiolate/thioether [Ni(III)L(Me)](2+) (2(2+)) complexes were generated, and their electronic properties were investigated by UV-vis and EPR spectroscopy. For 1(-) (Ni(I), d(9) configuration) the EPR data are consistent with a d(x(2))(-)(y(2)) based singly occupied molecular orbitals (SOMOs). However, DFT calculations suggest that there is also pronounced radical character. This is consistent with the small g-anisotropy observed in the EPR experiments. The spin population (Mulliken analysis) analysis of 1(-) reveals that the main contribution to the SOMO (64%) is due to the bipyridine unit. Time dependent density functional theory (TD-DFT) calculations attribute the most prominent features observed in the electronic absorption spectrum of 1(-) to metal to ligand charge transfer (MLCT) transitions. Concerning 2(2+), the EPR spectrum displays a rhombic signal with g(x) = 2.236, g(y) = 2.180, and g(z) = 2.039 in CH(3)CN. The g(iso) value is larger than 2.0, which is consistent with metal based oxidation. The unpaired electron (Ni(III), d(7) configuration) occupies a Ni-d(z(2)) based molecular orbital, consistent with DFT calculations. Nitrogen hyperfine structure is observed as a triplet in the g(z) component of the EPR spectrum with A(N) = 51 MHz. This result indicates the coordination of a CH(3)CN molecule in the axial position. DFT calculations confirm that the presence of a fifth ligand in the coordination sphere of the Ni ion is required for the metal-based oxidation process. Finally, we have shown that 1 exhibits catalytic reductive dehalogenation activity below potentials of -2.00 V versus Fc/Fc(+) in CH(2)Cl(2).

Synthesis, structure, UV–Vis–IR spectra, magnetism and theoretical studies on CuII[(2-aminomethyl)pyridine](thiocyanate)2 and comparisons with an analogous CuII complex

The ligand influenced formation of the title complexes has been discussed in the light of the structure, spectral (IR and UV–Vis), RT magnetic and theoretical studies (DFT and TDDFT). Complex 2 , for which only a structure has been reported previously, has been thoroughly studied and compared with complex 1 with respect to the structure and spectral properties. In the unit cell, the monomeric complex 1 assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu 2+ , while the octahedral complex 2 assembles into a 2-D layer in the unit cell through the H-bonding interactions between amino H and the anionic S and N3 atom. The TDDFT analysis of the absorption spectra indicate that absorption maxima are at a relatively high energy and are mainly assigned to π → π∗ transitions (in pyridine) with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d–d transition band. ► Synthesis and structural details of a new copper complex, CuII[(2-aminomethyl)pyridine](thiocyanate) has been presented. ► The UV–Vis and IR spectra along with the geometrical aspects have been analyzed in depth with the help of theoretical (DFT and TDDFT) calculations. ► In addition, to highlight the ligand influence on the complex formation, Cu[(2-aminomethyl)pyridine]2(SCN)2 was also synthesised, structural and spectral characteristics were fully analyzed and compared with the title complex. The title complex was synthesized under self-assembly conditions using Cu(acetate) 2 ·H 2 O, 2-amp (= 2-aminomethylpyridine) and KSCN, and was characterized by IR, elemental analysis and single crystal structural analysis, and its spectral and RT magnetic properties were investigated. The asymmetric unit consists of a square planar Cu(II) center, with two ligand N atoms and two anionic Ns forming the square plane. In the unit cell, the monomeric complex assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu 2+ . Further, the structure was satisfactorily modeled by calculations based on Density Functional Theory (DFT), and the UV–Vis and IR spectra are analyzed in depth with the help of Time Dependent DFT (TDDFT). The results indicate that the absorption maxima are at relatively high energy and are mainly assigned to π → π ∗ transitions (in pyridine), with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d–d transition band. Also, it has been found that when the ligand ratio is modified, the formation of Cu(2-amp) 2 (SCN) 2 takes place under the same self-assembly conditions, whose structure only has been recently reported. Structural, spectral and theoretical comparisons are presented for both complexes.

Structures and Spectroscopic Properties of [Ru(iph)(L)<sub>2</sub>]<sup>2+</sup> (L=cpy, mpy, npy) Complexes Containing Tetradentate Ligands

采用密度泛函的B3LYP和UB3LYP方法分别优化了一系列[Ru（iph）（L）2]2＋（L=cpy（1）,mpy（2）,npy（3）;其中iph为2,9-双（1′-甲基-2′-咪唑）-1,10-邻二氮杂菲,cpy为4-氰基嘧啶,mpy为4-甲基嘧啶,npy为4-氮二甲基嘧啶）配合物的基态和激发态结构.利用含时密度泛函理论（TD-DFT）方法,结合极化连续介质（PCM）模型计算了它们在丙酮溶液中的吸收和发射光谱.研究结果表明：优化得到的几何结构参数和相应的实验值符合得非常好.1和2的最高占据分子轨道主要由金属的d轨道和iph配体的π轨道构成,但是3主要占据在npy配体上,而它们的最低空轨道主要由iph配体的π反键轨道占据.因此,1和2的最低能吸收和发射属于金属到配体（MLCT）和配体内部（ILCT）的电荷转移跃迁,而3属于两个配体之间的电荷转移（LLCT）跃迁.三个配合物的最低能吸收分别在509nm（1）,527nm（2）和563nm（3）,其磷光发射分别在683nm（1）,852nm（2）和757nm（3）.这显示出通过调节L配体的π电子给予能力可以改变最低能吸收和发射的跃迁性质和发光颜色.

Electronic Structures and Second-Order Nonlinear Optical Properties of a Series of Pt―Pt Bond-Containing Metal Complexes

The electronic structures and second-order nonlinear optical (NLO) properties of a series of Pt―Pt bond-containing metal complexes were calculated using density factional theory (DFT) combined with the finite field (FF) method. The results show that the replacement of a conjugated ligand does not substantially affect the Pt―Pt bond. Additionally, the strength of charge transfer (CT) from the ligand to the metal group increases as the length of the conjugated ligand becomes longer. The first-order hyperpolarizabilities of these metal complexes increase as the length of the conjugated ligand becomes longer but this is not sensitive to the change in charge of these metal complexes. Complex IId containing a relevant long π-conjugated ligand possesses the largest first-order hyperpolarizability according to our DFT-FF calculations. Time-dependent (TD)-DFT calculations show that the π→π* intraligand mixing metal to ligand charge transfer transitions directly contribute to the second-order NLO response of the Pt―Pt bond-containing metal complex IId.

Optical oxygen sensing materials based on a novel dirhenium(I) complex assembled in mesoporous silica

A new dirhenium(I) complex fac-[{Re(CO)3(4,7-dinonadecyl-1,10-phenanthro -line)}2 (4,4′-bipyridyl)] (trifluoromethanesulfonate)2 (denoted as D-Re(I) ) is assembled in MCM-41 and SBA-15 type mesoporous silica support. The emission peaks of D-Re(I) in D-Re(I)/MCM-41 and D-Re(I)/SBA-15 are observed at 522 and 517nm, respectively. Their long excited lifetimes, which are of the order of microseconds, indicate the presence of phosphorescence emission arising from the metal to ligand charge-transfer (MLCT) transition. The luminescence intensities of D-Re(I)/MCM-41 and D-Re(I)/SBA-15 decrease remarkably with increase in the oxygen concentration, meaning that they can be used as optical oxygen sensing materials based on luminescence quenching. The ratios I0/I100 of D-Re(I)/MCM-41 and D-Re(I)/SBA-15 are estimated to be 5.6 and 20.1, respectively. The obtained Stern–Volmer oxygen quenching plots of the mesoporous sensing materials could be fitted well to the two-site Demas model and Lehrer model.

The kinetics and mechanism of the substitution reactions of the aquapentacyanoruthenate(II) ion with naphthalene‐substituted ligands in aqueous medium

AbstractThe kinetics and mechanism of substitution reaction of [Ru(CN)5H2O]3− anion with two naphthalene‐substituted ligands viz. Ln = nitroso‐R‐salt (NRS) and α‐nitroso‐β‐naphthol (αNβN) have been studied spectrophotometrically by monitoring an increase in absorbance at λmax = 525 nm corresponding to metal to ligand charge transfer (MLCT) transitions due to formation of substituted [Ru(CN)5L]n−3 as a function of pH, ionic strength, temperature, a wide range of ligands concentration, and [Ru(CN)5H2O3−] under pseudo‐first‐order conditions. The experimental observation suggests that [Ru(CN)5H2O]3− ion interacts with both ligands, which finally get converted into corresponding, [Ru(CN)5L]n−3 complexes as a final reaction product. The reaction is found to obey first‐order dependence each in [Ru(CN)5H2O3−] and [Ln]. The substituted products, viz. [Ru(CN)5L]n−3, in each case have strong MLCT transitions in visible region. The substitutional lability of [Ru(CN)5H2O]3− has been discussed in terms of electronic effect on the MOH2 bond interactions. The kinetic observation suggests that the complexation reaction of [Ru(CN)5H2O]3− with both the ligands, i.e., NRS and αNβN, follows an ion pair dissociative mechanism. The thermal activation parameters ΔH≠ and ΔS≠ have been calculated using Eyring's equation and provided in support for the proposed mechanistic scheme. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 21–30, 2011

Synthesis, structure, spectroscopic properties, and theoretical studies of alkaline earth metal complexes of 1,3-bis(carboxymethyl)benzimidazolium

Alkaline earth metal complexes of 1,3-bis(carboxymethyl)benzimidazolium (HL) including [Mg(L) 2(H 2O) 4]·2H 2O ( 1), [Ca(L) 2(H 2O) 4]·2H 2O ( 2) and [Ba(L) 2(H 2O) 2·2H 2O] n ( 3) have been synthesized by a hydrothermal procedure and characterized by X-ray crystallography, spectroscopy and thermoanalysis. The results of X-ray crystallography revealed that complexes 1 and 2 are neutral monomers, while complex 3 is a polymeric species, and the carboxymethyl moiety of the deprotonated ligand (L −) acts as a bridge between metal ions. The spectroscopic properties of the complexes were evaluated through density functional theory (DFT) and time-dependent density functional theory (TD DFT) calculations. The results revealed that the absorption peaks in UV–Vis spectra were derived from ligand to ligand charge-transfer transitions (LLCT) and/or (p, π) → ( σ ∗, π ∗) intraligand charge-transfer (ILCT). HL and HL-based complexes displayed similar emission peaks in the near-UV region due to ligand-based LLCT. The results of the Fukui index of the complexes supported LLCT and ILCT mechanisms. In addition, the calculated value of the luminescence oscillator strength displayed a linear relationship with the charge distribution, and the DFT chemical reactivity index, and correlation coefficients ( R 2) of 0.999 and 0.996 were obtained, respectively. Thus, the results revealed that the emission strength of the complex can be controlled by coordinating the ligand to different metal ions.

DNA Binding and Gel Electrophoresis Studies of a Copper (II) Complex Containing Mixed Aliphatic and Aromatic Dinitrogen Ligands

The interaction of a novel mixed ligand copper (II) complex, [Cu(N-N)(L)(EtOH)](NO(3))(2) . 2H(2)O, in which N-N indicates 2,9-dimethyl-1,10-phenanthroline and L indicates N,N-dimethyltrimethylenediamine with calf thymus DNA was investigated by absorption, circular dichroism, voltammetric, and viscosimetric techniques. The absorption spectra of the complex with calf thymus DNA showed a marked hypochromism in the pi --> pi* and metal to ligand charge transfer (MLCT) transitions, with no obvious red shift attributed to a partial intercalation. The intrinsic binding constant (K(b)) was determined as 2 x 10(5) M(-1). There was slight to appreciable changes in the relative viscosity of DNA, which is consistent with enhanced hydrophobic interaction of the methyl-substituted phen ring and partial intercalation mode of binding. Electrochemical studies showed a decrease in the peak current, which is ascribed to the strong binding between Cu (II) complex and DNA. The fluorescence spectral characteristics showed that the Cu (II) complex is able to displace the methylene blue bound to DNA, but not as complete as intercalative molecules. It is remarkable that this mixed ligand complex, in contrast to [Cu(2,9-dmp)(2)](+) (2,9-dmp = 2,9-dimethyl-1,10-phenanthroline), which fails to cleave DNA, has ability to cleave the supercoiled plasmid DNA.

Synthesis, characterization and antibacterial activity of Pd(II), Pt(II) and Ag(I) complexes of 4-ethyl and 4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazides

Pd(II), Pt(II) and Ag(I) ions were found to form stable complexes with 4-(p-tolyl)- or 4-ethyl-1-(pyridin-2-yl)thiosemicarbazides (Hp-TPTS or HEPTS). The complex structure was elucidated by analysis (elemental and thermal), spectroscopy (electronic, IR and 1H NMR spectra) and physical measurements (magnetic susceptibility and molar conductance). The ligands coordinate to the metal ions as monobasic bidentate through nitrogen and sulfur atoms. The electronic spectra of the Pt(II) complexes in DMF showed a metal to ligand charge transfer transition at 11,935–13,260 cm−1. The structural, electronic and vibrational features of HEPTS and Hp−TPTS were discussed on the basis of semi-empirical quantum mechanic calculations [ZINDO/S and semi-empirical parameterization (PM3)]. The simulated IR and electronic spectra are found reasonable in accordance with the experimental data. Finally, the antibacterial activities of the ligands and their complexes were investigated and some were found promising.

Synthesis, antineoplastic and cytotoxic activities of some mononuclear Ru(II) complexes

A series of mononuclear Ru(II) complexes of the type [Ru(S)2(K)]2+, where S = 1,10-phenanthroline/2,2′-bipyridine and K = 4-OH-btsz, 4-CH3-btsz, 3,4-di-OCH3-btsz, 4-OH-binh, 4-CH3-binh, 3,4-di-OCH3-binh, were prepared and characterized by elemental analysis, FTIR, 1H-NMR, and mass spectroscopy. The complexes displayed metal–ligand charge transfer (MLCT) transitions in the visible region. These ligands formed bidentate octahedral ruthenium complexes. The title complexes were evaluated for their in vivo anticancer activity against a transplantable murine tumor cell line, Ehrlisch’s ascites carcinoma (EAC), and in vitro cytotoxic activity against human cancer cell lines Molt 4/C8 and CEM and murine tumor cell line L1210. The ruthenium complexes showed promising biological activity especially in decreasing tumor volume and viable ascites cell counts. Treatment with these complexes prolonged the life span of mice bearing EAC tumors by 10–52%. In vitro evaluation of these ruthenium complexes revealed cytotoxic activity from 0.21 to 24 μM against Molt 4/C8, 0.16 to 19 μM aginst CEM, and 0.75 to 32 μM against L1210.

Reversible photoswitching between nitrito-N and nitrito-O isomers in trans-[Ru(py)4(NO2)2

Nitro-nitrito photoisomerisation is investigated in solid samples and solutions of trans-[Ru(py)(4)(NO(2))(2)]. Using light of wavelength 325 nm 50% of the N-bound Ru-NO(2) ligands can be switched to the O-bound Ru-ONO configuration (nitrito-N to nitrito-O isomerisation) at temperatures below T = 250 K in solids. The population of the isomeric configurations is determined with infrared spectroscopy from the decrease of the area of the nu(NO) stretching and delta(NO) deformation modes. In a frozen methanol-ethanol solution nearly 100% can be converted to the nitrito-O configuration. Upon heating above T = 250 K the Ru-NO(2) configuration is restored. The nitrito-O Ru-ONO configuration can be partially transferred back to the nitrito-N configuration by irradiation with light in the spectral range 405-442 nm. Using absorption spectroscopy on a frozen methanol-ethanol solution, two new bands at 447 and 380 nm are observed in the nitrito-O configuration compared to one at 334 nm of the nitrito-N ground state configuration. The photoconversion is initiated by the metal-to ligand charge transfer transition Ru(d) -->pi*(NO(2),py) as shown by the calculated partial density of states using Density Functional Theory. The calculations yield also the structure of the nitrito-N and nitrito-O isomer as well as the corresponding vibrational densities. The experimental structure of the ground state is determined using powder diffraction.

Multifunctional DNA Interactions of Ru−Pt Mixed Metal Supramolecular Complexes with Substituted Terpyridine Ligands

The coupling of a light absorbing unit to a bioactive site allows for the development of supramolecules with multifunctional interactions with DNA. A series of mixed metal supramolecular complexes that couple a DNA-binding cis-Pt(II)Cl(2) center to a ruthenium chromophore via a polyazine bridging ligand have been prepared, and their DNA interactions have been studied, [(TL)RuCl(dpp)PtCl(2)](PF(6)) (TL = tpy (2,2':6',2''-terpyridine), MePhtpy (4'-(4-methylphenyl)-2,2':6',2''-terpyridine), or (t)Bu(3)tpy (4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine). This series provides for unique tridentate coordinated Ru(II) systems to photocleave DNA with preassociation with the DNA target via coordination of the Pt(II) center. Electronic absorption spectroscopy of the complexes displays intense ligand-based pi-->pi* transitions in the UV region and metal to ligand charge transfer (MLCT) transitions in the visible region. The Ru(dpi)-->dpp(pi*) MLCT transitions occur at 545 nm, red-shifted relative to the 520 nm maxima for the monometallic synthons, [(TL)RuCl(dpp)](PF(6)). The title RuPt complexes display reversible Ru(II/III) oxidative couples at 1.10, 1.10, and 1.01 V vs Ag/AgCl for TL = tpy, MePhtpy, and (t)Bu(3)tpy, respectively. The TL(0/-) reduction occurred at -1.43, -1.44, and -1.59 V vs Ag/AgCl for TL = tpy, MePhtpy, and (t)Bu(3)tpy, respectively. These complexes display a dpp(0/-) couple (-0.50 -0.55, and -0.59 V) significantly shifted to positive potential relative to their monometallic synthons (-1.15, -1.16, and -1.22 V), consistent with the bridging coordination of the dpp ligand. Coupling of (TL)Ru(II)Cl(BL) subunit to a cis-Pt(II)Cl(2) site provides for the application of photochemically inactive Ru(II)(tpy)-based chromophores in DNA photocleavage applications. The [(TL)RuCl(dpp)PtCl(2)](+) complexes display covalent binding to DNA and photocleavage upon irradiation with visible light modulated by TL identity. The redox, spectroscopic, DNA-binding, and photocleavage properties of a series of supramolecular complexes are presented.

New Blue Phosphorescent Iridium Complexes with Various Ancillary Ligands Based on Fluorinated 2-Phenyl-4-Methylpyridine

In this study, a series of new blue phosphorescent iridium(III) complexes with ligands of (CF3)2Meppy [(CF3)2Meppy = 2-(3′,5′-bis-trifluoromethylphenyl)-4-methylpyridine] were successfully synthesized and their photophysical properties were systematically investigated. To analyze color tuning effected by changing the ancillary ligands, we have measured UV-absorption and photoluminescence (PL) spectra and have theoretically calculated the iridium complexes with different ancillary ligands using computational methods. The maximum emission spectrum of Ir[(CF3)2Meppy]2(acac), Ir[(CF3)2Meppy]2(pic), Ir[(CF3)2Meppy]2(taz) and Ir[(CF3)2Meppy]2(N4) were 473.5, 472, 475 and 468 nm, respectively. However, the PL efficiency was not improved by changing the picolinate ligands with other ancillary ligands, such as triazolate or tetrazolate ions. We discuss how the ancillary ligand influences both the emission peak and the metal to ligand charge transfer (MLCT) transition efficiency.

Substituent effects on the light-induced C–C and C–Br bond activation in (bisphosphine)(η2-tolane)Pt0 complexes. A TD-DFT study

A theoretical study of the steric and electronic effects of different substituents on the electronic ground and excited states of (bisphosphine)(eta2-tolane)Pt0 complexes is presented. A natural-bond-order (NBO) analysis has been performed to describe the bonding nature of the "hapto-like" coordination of the Pt atom to the alkyne bond of the tolane group. The results show an important contribution of the pi-back donation in all complexes, amounting to half of the energy associated to the sigma-bonding interaction. A TD-DFT study of the absorption spectra helps rationalizing the photochemistry of the complexes. Metal-ligand charge transfer (MLCT) transitions from the Pt atom to the alkyne are assigned as the photochemical "active" states responsible for C-C bond cleavage. Electronic excitations to the sigma* orbital of the C-Br bond are involved in C-Br bond activation. It is shown that both steric and electronic effects play an important role in determining the presence of these electronic excitations.

Synthesis, photophysical and oxygen-sensing properties of a novel bluish-green emission Cu(I) complex

A novel copper(I) complex [Cu(POP)(PTZ)]BF 4 (POP = bis[2-(diphenyl-phosphino)phenyl]-ether, PTZ = 5-(2-pyridyl)tetrazole) has been synthesized and characterized by elemental analysis, 1H NMR and IR. Complex [Cu(POP)(PTZ)]BF 4 shows bright bluish-green emission centered at 495 nm in solid-state at room temperature, arising from metal to ligand charge-transfer (MLCT) transition. The photoluminescence quantum yield measured in air is 0.12. The excited state lifetime of [Cu(POP)(PTZ)]BF 4 is on the order of microsecond indicating the presence of phosphorescent emission. The emission intensity of [Cu(POP)(PTZ)]BF 4 appears to be highly sensitive to the O 2 concentration, meaning it possesses oxygen-sensing property. The sensing performances of [Cu(POP)(PTZ)]BF 4/MCM-41 composite materials are evaluated and the system with 20 mg/g loading level exhibits the best sensitivity ( I 0/ I 100 > 11), and the shortest response time ( t ↓ < 5 s), which is attractive because copper(I) complexes are nontoxic and can be prepared at a fraction of the cost of noble metal-based ones.

DNA interaction studies of tridentate bridged Ru(II)–Pt(II) mixed-metal supramolecules

Reported herein are studies of the concentration and temperature dependent interactions with DNA of the stereochemically defined mixed-metal supramolecular complexes, [(tpy)Ru(tppz)PtCl](PF(6))(3) and [ClPt(tppz)Ru(tppz)PtCl](PF(6))(4) (tpy=2,2':6',2''-terpyridine and tppz=2,3,5,6-tetrakis(2-pyridyl)pyrazine). These metal complexes couple a ruthenium based light absorber (LA) to the bioactive platinum sites (BAS) using a tridentate bridging ligand (BL). The complexes exhibit intense Ru-->tppz(pi*) metal to ligand charge transfer (MLCT) transitions in the visible region and adopt a square planar geometry around the Pt(II) center. The effect of incubating these metal complexes with DNA on the subsequent migration of DNA through an agarose gel was found to be more dramatic than that observed for the well known anticancer drug, cis-[Pt(NH(3))(2)Cl(2)] (cisplatin). This effect was enhanced with increased incubation temperature. Unwinding of supercoiled plasmid DNA was found to be more pronounced for the trimetallic complex, [ClPt(tppz)Ru(tppz)PtCl](PF(6))(4), than for the bimetallic complex, [(tpy)Ru(tppz)PtCl](PF(6))(3).

Enhanced DNA photocleavage properties of Ru(II) terpyridine complexes upon incorporation of methylphenyl substituted terpyridine and/or the polyazine bridging ligand dpp (2,3-bis(2-pyridyl)pyrazine)

The heteroleptic complexes, [(MePhtpy)RuCl(dpp)](PF 6) and [(tpy)RuCl(dpp)](PF 6), have been synthesized, characterized, and investigated with respect to their photophysical, redox, and DNA photocleavage properties (where MePhtpy = 4′-(4-methylphenyl)-2,2′:6′,2′′-terpyridine and dpp = 2,3-bis(2-pyridyl)pyrazine, tpy = 2,2′:6′,2′′-terpyridine). The X-ray crystal structure confirms the identity of the new [(MePhtpy)RuCl(dpp)](PF 6) complex. These heteroleptic complexes were found to photocleave DNA in the presence of oxygen, unlike the previously studied complex, [Ru(tpy) 2](PF 6) 2. The photophysical, redox, and DNA photocleavage properties of the heteroleptic complexes were compared with those of the homoleptic complexes, [Ru(MePhtpy) 2](PF 6) 2 and [Ru(tpy) 2](PF 6) 2. The heteroleptic complexes showed intense metal to ligand charge transfer (MLCT) transition at lower energy ([(MePhtpy)RuCl(dpp)](PF 6), 522 nm; [(tpy)RuCl(dpp)](PF 6), 516 nm) and longer excited state lifetimes as compared to the homoleptic complexes. The [Ru(MePhtpy) 2] 2+ complex was found to photocleave DNA in contrast to [Ru(tpy) 2] 2+. The introduction of a methylphenyl group on the tepyridine ligand not only enhances the 3MLCT excited state lifetime but also increases the lipophilicity and thereby the DNA binding ability of the molecule. An increase in lipophilicity upon addition of a methylphenyl group on the 2,2′:6′,2′′-terpyridine ligand was confirmed by determination of the partition coefficient ([(MePhtpy)RuCl(dpp)](PF 6), log P = +1.16; [(tpy)RuCl(dpp)](PF 6), log P = −1.27). The heteroleptic complexes photocleave DNA more efficiently than the homoleptic complexes, with the greatest activity being observed for the newly prepared [(MePhtpy)RuCl(dpp)](PF 6) complex.

Synthesis and cytotoxicity of dinuclear complexes containing ruthenium(ii) bipyridyl units linked by a bis(pyridylimine) ligand

Enantiopure dinuclear ruthenium polypyridyl complexes of the form [Ru(2)(LL)(4)L(1)](PF(6))(4) (LL = 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen); L(1)= C(25)H(20)N(4) a bis(pyridylimine) ligand containing a diphenylmethane spacer) have been synthesized using the chiral building blocks cis-[Ru(bpy)(2)(py)(2)](2+) and cis-[Ru(phen)(2)(py)(2)](2+). These dinuclear ruthenium complexes have been characterised using NMR, mass spectrometry, UV-visible absorbance, circular dichroism and linear dichroism. The compounds exhibit good photo and thermal stability. The extinction coefficient for the bpy complex at 478 nm is epsilon(478) = 15,700 mol(-1) cm(-1) dm(3) and for the phen complex is epsilon(478) = 24,900 mol(-1) cm(-1) dm(3). Both complexes have their longest wavelength (metal to ligand charge transfer) transition predominantly x/y (short axis)-polarised while the transitions at shorter wavelength are a mixture of x/y and z-polarisations, similar to both the copper helicate and iron triple helicate studied previously. Cytotoxicity studies reveal that the compounds are dramatically less active against cancer cell lines than the recently reported supramolecular cylinders prepared from the same bis(pyridylimine) ligand.