Synthesis,characterization, and fluorescence properties of dinuclear cadmium(II) complexes

Four dinuclear cadmium(II) complexes, [Cd₂(L¹)(μ₂-Cl)Cl₂] (1), [Cd₂(L²)(μ₂-Cl)Cl₂] (2), [Cd₂(L³)(μ₂-Cl)Cl₂] (3), and [Cd₂(L⁴)₃ClO₄] (4), where HL¹ = 4-methyl-2,6-bis(1-(2-piperidinoethyl)iminomethyl)-phenol, HL² = 4-methyl-2,6-bis(1-(2-pyrrolidinoethyl)iminomethyl)-phenol, HL³ = 4-methyl-2,6-bis(1-(2-morpholinoethyl)iminomethyl)-phenol and HL⁴ = 4-methyl-2,6-bis(cyclohexylmethyl)iminomethyl)-phenol, were synthesized. They were characterized by elemental analysis, FT-IR, UV–Vis, fluorescence and electronspray ionization mass spectroscopy. Complexes 1 and 4 were also characterized by single crystal X-ray analysis. The cadmiums atoms in 1 are linked by μ₂-chloride in a distorted square pyramidal geometry, whereas cadmium atom in 4 is in a distorted octahedral environment. The complexes show emission bands around 500 nm with excitation at 395 nm.     

Synthesis of mononuclear and dinuclear ruthenium(II) tris(heteroleptic) complexes via photosubstitution in bis(carbonyl) precursors

A novel, and quite general, approach for the preparation of tris(heteroleptic) ruthenium(II) complexes is reported. Using this method, which is based on photosubstitution of carbonyl ligands in precursors such as [Ru(bpy)(CO)(2)Cl(2)] and [Ru(bpy)(Me(2)bpy)(CO)(2)](PF(6))(2), mononuclear and dinuclear Ru(II) tris(heteroleptic) polypyridyl complexes containing the bridging ligands 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) and 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (Hbpzt) have been prepared. The complexes obtained were purified by column chromatography and characterized by HPLC, mass spectrometry, 1H NMR, absorption and emission spectroscopy and by electrochemical methods. The X-ray structures of the compounds [Ru(bpy)(Me(2)bpy)(bpt)](PF(6))x0.5C(4)H(10)O [1x0.5C(4)H(10)O], [Ru(bpy)(Me(2)bpy)(bpzt)](PF(6))xH(2)O (2xH(2)O) and [Ru(bpy)(Me(2)bpy)(CH(3)CN)(2)](PF(6))(2)xC(4)H(10)O (6xC(4)H(10)O) are reported. The synthesis and characterisation of the dinuclear analogues of 1 and 2, [{Ru(bpy)(Me(2)bpy)}(2)bpt](PF(6))(3)x2H(2)O (3) and [{Ru(bpy)(Me(2)bpy)}(2)bpzt](PF(6))(3) (4), are also described.     

Synthesis and structural characterization of ruthenium complexes with 1-aryl-imidazole-2-thione

Treatment of [RuCl₂(PPh₃)₃] with 2 equiv. Himt^MPh (Himt^MPh?=?1-(4-methyl-phenyl)-imidazole-2-thione) in the presence of MeONa afforded cis-[Ru(κ ²-S,N-imt^MPh)₂(PPh₃)₂] (1), while interaction of [RuCl₂(PPh₃)₃] and 2 equiv. Himt^MPh in tetrahydrofuran (THF) without base gave [RuCl₂(κ ¹-S-Himt^MPh)₂(PPh₃)₂] (2). Treatment of [RuHCl(CO)(PPh₃)₃] with 1 equiv. Himt^MPh in THF gave [RuHCl(κ ¹-S-Himt^MPh)(CO)(PPh₃)₂] (3), whereas reaction of [RuHCl(CO)(PPh₃)₃] with 1 equiv. of the deprotonated [imt^MPh]^? or [imt^NPh]^? (imt^NPh?=?1-(4-nitro-phenyl)-2-mercaptoimidazolyl) gave [RuH(κ ²-S,N-imt^RPh)(CO)(PPh₃)₂] (R?=?M 4a, R?=?N 4b). The ruthenium hydride complexes 4a and 4b easily convert to their corresponding ruthenium chloride complexes [RuCl(κ ²-S,N-imt^MPh)(CO)(PPh₃)₂] (5a) and [RuCl(κ ²-S,N-imt^NPh)(CO)(PPh₃)₂] (5b), respectively, in refluxing CHCl₃ by chloride substitution of the RuH. Photolysis of 5a in CHCl₃ at room temperature afforded an oxidized product [RuCl₂(κ ²-S,N-imt^MPh)(PPh₃)₂] (6). Reaction of 6 with excess [imt^MPh]^? afforded 1. The molecular structures of 1·EtOH, 3·C₆H₁₄, 4b·0.25CH₃COCH₃, and 6·2CH₂Cl₂ have been determined by single-crystal X-ray crystallography.     

Synthesis, characterization and photophysics of alkyne bridged bimetallic rhenium(I) and ruthenium(II) complexes

Six new homobimetallic and heterobimetallic complexes of rhenium(I) and ruthenium(II) bridged by ethynylene spacer [(CO)₃(bpy)Re(BL)Re(bpy)(CO)₃]²⁺ [Cl(bpy)₂Ru(BL)Ru(bpy)₂Cl]²⁺ and [(CO)₃(bpy)Re(BL)Ru(bpy)₂Cl]²⁺ (bpy = 2,2′-bipyridine, BL = 1,2-bis(4-pyridyl)acetylene (bpa) and 1,4-bis(4-pyridyl)butadiyne (bpb) are synthesized and characterized. The electrochemical and photophysical properties of all the complexes show a weak interaction between two metal centers in heterobimetallic complexes. The excited state lifetime of the complexes is increased upon introduction of ethynylene spacer and the transient spectra show that this is due to delocalization of electron in the bridging ligand. Also, intramolecular energy transfer from *Re(I) to Ru(II) in Re–Ru heterobimetallic complexes occurs with a rate constant 4 × 10⁷ s⁻¹.     

Redox-switchable π-conjugated systems bearing terminal ruthenium(II) complexes

p-Phenylenediamine bearing terminal bipyridyl moieties was synthesized by palladium-catalyzed amination. The corresponding ruthenium(II) complex was formed and characterized, providing a redox-switchable photoinduced electron-transfer system.     

Synthesis and characterization of electrochemiluminescent ruthenium(II) complexes containing o-phenanthroline and various alpha-diimine ligands

A series of o-phenanthroline-substituted ruthenium(II) complexes containing 2,2′-dipyridyl, 2-(2-pyridyl)benzimidazole, 2-(2-pyridyl)-N-methylbenzimidazole, 4-carboxymethyl-4′-methyl-2,2′-dipyridyl, and/or 4,4′-dimethyl-2,2′-dipyridyl ligands were synthesized and examined as potent electrochemiluminescent (ECL) materials. The characteristics of these complexes, regarding their electrochemical redox potentials and relative ECL intensities for tripropylamine were studied. As found in a 2,2′-bipyridyl-substituted ruthenium(II) complexes, a good correlation between the observed ECL intensity and the donor ability of α-diimine ligands was observed, i.e., the ECL intensity of the Ru(II) complex decreased with an increase in the ligand donor ability. The ECL efficiency increased as the number of substitutions of o-phenanthroline (o-phen) to metal complexes increased.     

Synthesis, characterization and DNA-binding studies of ruthenium(II) mixed-ligand complexes containing dipyrido[1,2,5]oxadiazolo[3,4-b]quinoxaline

A novel ligand dipyrido[1,2,5]oxadiazolo[3,4-b]quinoxaline (dpoq) and its complexes [Ru(bpy)₂(dpoq)]²⁺ and [Ru(phen)₂(dpoq)]²⁺ (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline) have been synthesized and characterized by elemental analysis, electrospray mass spectra and ¹H NMR. The interaction of Ru(II) complexes with calf thymus DNA (CT-DNA) was investigated by absorption spectroscopy, fluorescence spectroscopy, thermal denaturation and viscosity measurements. Results suggest that two Ru(II) complexes bind to DNA via an intercalative mode.     

Synthesis,characterization and catalytic studies of ruthenium(II) chalconate complexes

Stable ruthenium(II) carbonyl complexes of the type [RuCl(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃ or Py; L = 2′‐hydroxychalcones) were synthesized from the reaction of [RuHCl(CO)(EPh₃)₂(B)] (E = P or As; B = PPh₃, AsPh₃ or Py) with 2′‐hydroxychalcones in benzene under reflux. The new complexes were characterized by analytical and spectroscopic (IR, electronic ¹H, ³¹P and ¹³C NMR) data. They were assigned an octahedral structure. The complexes exhibited catalytic activity for the oxidation of primary and secondary alcohols into their corresponding aldehydes and ketones in the presence of N‐methylmorpholine‐N‐oxide (NMO) as co‐oxidant and were also found to be efficient transfer hydrogenation catalysts. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and structure of three dichromium hexacarbonyl complexes with (CPPh2)2, (CHPPh2)2, and carbazole bridges

Three dichromium hexacarbonyl complexes containing (CPPh₂)₂, (CHPPh₂)₂, and carbazole as a conjugated bridging ligand are synthesized and exhibit a variety of electronic interactions between the metal centers, which can be modified by altering either the conjugated bridging nature or the ligand bound to the metals to induce peculiar asymmetry.     

Aryl-diamide bridged binuclear ruthenium (II) tris(bipyridine) complexes: Synthesis, photophysical, electrochemical and electrochemiluminescence properties

Several new symmetrical aromatic hydrocarbon bridged bipyridine ligands and their binuclear Ru (II) complexes have been designed, synthesized and characterized on the basis of ¹H NMR, MS and HRMS. Their absorption and emission properties, electrochemical behaviors and electrochemical luminescence were investigated. All ruthenium complexes show characteristic MLCT absorption and similar redox potential. Among the three complexes reported, 4c has the best electrochemical luminescence property.     

Synthesis,DNA-binding,and photocleavage studies of ruthenium(II) complexes with an asymmetric ligand

An asymmetric ligand (pdpiq?=?2-(pyridine-2-yl)-6,7-diphenyl-1-H-imidazo[4,5-g]quinoxaline) and its ruthenium complexes with [Ru(L)₂pdpiq]²⁺ (L?=?bpy (2,2′-bipyridine) or phen (1,10-phenanthroline)) have been synthesized and characterized by elemental analysis, ES-MS, and ¹H NMR. The DNA-binding behaviors of these complexes were studied by spectroscopic methods and viscosity measurements. The results indicate that the complexes can intercalate into DNA base pairs. When irradiated at 365?nm, the two complexes promote the cleavage of plasmid pBR322DNA. The mechanism of DNA cleavage is an oxidative process by generating singlet oxygen.     

Oligothiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes: Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence

A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinylenes have been synthesized and characterized by ¹H NMR, ¹³C NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and π-π^∗ transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped. All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)²⁺₃. The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)²⁺₃, due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E_1/2 = 0.96 V vs. Ag/Ag⁺) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product on the electrode surface. All these ruthenium complexes exhibited different ECL property in CH₃CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the reported complexes do not exceed that of Ru(bpy)²⁺₃, where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT,bis-2,2′-bipyridyl-(4-methyl-4′-(2-thienylethenyl)-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru3T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}}-2,2′-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2′-bipyridyl-ruthenium-bis-[2-((E)-4′-methyl-2, 2′-bipyridinyl-4)-ethenyl]-thienyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2′-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4′-methyl-2,2′-bipyridinyl-4)-ethenyl]-thienyl}-ethenyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate).     

Synthesis and characterization of new platinum(II) phosphinate complexes

The syntheses of platinum(II) complexes of bis(dimethylphosphinylmethylene)amine and bis(aminomethyl)phosphinic acid were investigated. In the case of bis(dimethyl-phosphinylmethylene)amine the reaction with K₂[PtCl₄] yields the potassium amino-trichloroplatinate K[PtCl₃L] (L?=?bis(dimethylphosphinylmethylene)amine), which was characterized by multinuclear (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) NMR spectroscopy in solution. Bis(aminomethyl)phosphinic acid reacts with K₂[PtCl₄] under strictly controlled pH conditions to give colorless crystals of the cisplatin analog K[PtCl₂L′] (L′?=?bis(aminomethyl)phosphinate). This complex was characterized by multinuclear NMR spectroscopy in solution as well as by single-crystal X-ray diffraction in the solid state. The bis(aminomethyl)phosphinate coordinates to platinum via both amino functions, thus acting as a chelating ligand.     

Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes

We report the synthesis of free 1,6,7,12-tetraazaperylene (tape). Tape was obtained from 1,1'-bis-2,7-naphthyridine by potassium promoted cyclization followed by oxidation with air. Mono- and dinuclear ruthenium(II) 1,6,7,12-tetraazaperylene complexes of the general formulas [Ru(L-L)(2)(tape)](PF(6))(2), [1](PF(6))(2)-[5](PF(6))(2), and [{Ru(L-L)(2)}(2)(μ-tape)](PF(6))(4), [6](PF(6))(4)-[10](PF(6))(4), with{L-L = phen, bpy, dmbpy (4,4'-dimethyl-2,2'-bipyridine), dtbbpy (4,4'-ditertbutyl-2,2'-bipyridine) and tmbpy (4,4'5,5'-tetramethyl-2,2'-bipyridine)}, respectively, were synthesized. The X-ray structures of tape·2CHCl(3) and the mononuclear complexes [Ru(bpy)(2)(tape)](PF(6))(2)·0.5CH(3)CN·0.5toluene, [Ru(dmbpy)(2)(tape)](PF(6))(2)·2toluene and [Ru(dtbbpy)(2)(tape)](PF(6))(2)·3acetone·0.5H(2)O were solved. The UV-vis absorption spectra and the electrochemical behavior of the ruthenium(ii) tape complexes were explored and compared with the data of the analogous dibenzoeilatin (dbneil), 2,2'-bipyrimidine (bpym) and tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazin (tpphz) species.     

Synthesis,characterization, and antimicrobial activities of a dinuclear copper(II) complex with bis(2-[(2-hydroxy-ethylimino)-methyl]-4,6-diiodo-phenol)

A dinuclear copper(II) complex with a newly synthesized tridentate Schiff-base ligand 2-[(2-hydroxy-ethylimino)-methyl]-4,6-diiodo-phenol (HL), of formula [Cu₂L₂Cl₂?·?C₄H₈O] (1), was prepared. Both the ligand and the complex were characterized by X-ray crystallography, confirming that the Schiff base is tridentate and its dinuclear copper(II) complex is five-coordinate from one nitrogen and two oxygens from L and two chlorides. The complex was assayed for antibacterial (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter cloacae) activities by the MTT method. Complex 1 exhibited better antimicrobial activity than the ligand.     

Synthesis and characterization of dinuclear ruthenium complexes covalently linked to Ru(II) tris-bipyridine: an approach to mimics of the donor side of photosystem II

To mimic the electron-donor side of photosystem II (PSII), three trinuclear ruthenium complexes (2, 2a, 2b) were synthesized. In these complexes, a mixed-valent dinuclear Ru2(II,III) moiety with one phenoxy and two acetato bridges is covalently linked to a Ru(II) tris-bipyridine photosensitizer. The properties and photoinduced electron/energy transfer of these complexes were studied. The results show that the Ru2(II,III) moieties in the complexes readily undergo reversible one-electron reduction and one-electron oxidation to give the Ru2(II,III) and Ru2(III,III) states, respectively. This could allow for photooxidation of the sensitizer part with an external acceptor and subsequent electron transfer from the dinuclear ruthenium moiety to regenerate the sensitizer. However, all trinuclear ruthenium complexes have a very short excited-state lifetime, in the range of a few nanoseconds to less than 100 ps. Studies by femtosecond time-resolved techniques suggest that a mixture of intramolecular energy and electron transfer between the dinuclear ruthenium moiety and the excited [Ru(bpy)3]2+ photosensitizer is responsible for the short lifetimes. This problem is overcome by anchoring the complexes with ester- or carboxyl-substituted bipyridine ligands (2a, 2b) to nanocrystalline TiO2, and the desired electron transfer from the excited state of the [Ru(bpy)3]2+ moiety to the conduction band of TiO2 followed by intramolecular electron transfer from the dinuclear Ru2(II,III) moiety to photogenerated Ru(III) was observed. The resulting long-lived Ru2(III,III) state decays on the millisecond timescale.     

Synthesis,characterization and biological application of cyclometalated heteroleptic platinum(II) complexes

A series of square planar cyclometalated heteroleptic platinum(II) complexes of the type [(C^N)Pt(O^O)] [where, O^O is a β‐diketonato ligand of acetylacetone (acac), C^N = cyclometalating 7‐(4‐fluorophenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L¹), 7‐(4‐chlorophenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L²), 7‐(4‐bromophenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L³), 7‐(4‐methoxyphenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L⁴), 5‐phenyl‐7‐(p‐tolyl)pyrazolo[1,5‐a]pyrimidine (L⁵)] have been design, synthesized and characterized. All compounds have been screened for biological studies like in vitro antibacterial, in vitro cytotoxicity, cellular level cytotoxicity, absorption titration, viscosity measurements, fluorescence quenching analysis, molecular docking and DNA nuclease. The intrinsic binding constants (K_b) of compounds with HS‐DNA has been obtained in range of 2.892–0.242 × 10⁵ M^?1. All the compounds bound with HS DNA by partial intercalative mode of binding. MIC study has been carried out against Gram^(+ve) and Gram^(?ve) bacterial species. In vitro cytotoxicity against brine shrimp lethality bioassay has been also carried out. The LC₅₀ values of the ligands and complexes have been found in range of 56.49–120.22 μg/mL and 6.71–11.96 μg/mL, respectively.     

Synthesis and characterization of tris(heteroleptic) Ru(II) complexes bearing styryl subunits

We have developed and optimized a well-controlled and refined methodology for the synthesis of substituted π-conjugated 4,4'-styryl-2,2'-bipyridine ligands and also adapted the tris(heteroleptic) synthetic approach developed by Mann and co-workers to produce two new representative Ru(II)-based complexes bearing the metal oxide surface-anchoring precursor 4,4'-bis[E-(p-methylcarboxy-styryl)]-2,2'-bipyridine. The two targeted Ru(II) complexes, (4,4'-dimethyl-2,2'-bipyridine)(4,4'-di-tert-butyl-2,2'-bipyridine)(4,4'-bis[E-(p-methylcarboxy-styryl)]-2,2'-bipyridine) ruthenium(II) hexafluorophosphate, [Ru(dmbpy)(dtbbpy)(p-COOMe-styryl-bpy)](PF(6))(2) (1) and (4,4'-dimethyl-2,2'-bipyridine)(4,4'-dinonyl-2,2'-bipyridine)(4,4'-bis[E-(p-methylcarboxy-styryl)]-2,2'-bipyridine) ruthenium(II) hexafluorophosphate, [Ru(dmbpy)(dnbpy)(p-COOMe-styryl-bpy)](PF(6))(2) (2) were obtained as analytically pure compounds in high overall yields (>50% after 5 steps) and were isolated without significant purification effort. In these tris(heteroleptic) molecules, NMR-based structural characterization became nontrivial as the coordinated ligand sets each sense profoundly distinct magnetic environments greatly complicating traditional 1D spectra. However, rational two-dimensional approaches based on both homo- and heteronuclear couplings were readily applied to these structures producing quite definitive analytical characterization and the associated methodology is described in detail. Preliminary photoluminescence and photochemical characterization of 1 and 2 strongly suggests that both molecules are energetically and kinetically suitable to serve as sensitizers in energy-relevant applications.