Electronic effects on the interactions of complexes [Ru(phen)2(p-L)] (L=MOPIP, HPIP, and NPIP) with DNA

In order to explore the electronic effects of Ru(II) complexes binding to DNA, a series of Ru(II) complexes [Ru(phen)₂ (p-MOPIP)]²⁺ (1), [Ru(phen)₂ (p-HPIP)]²⁺ (2), and [Ru(phen)₂(p-NPIP)]²⁺ (3) were synthesized and characterized by elementary, ¹H NMR, and ES-MS analysis. The binding properties of these complexes to CT-DNA were investigated with spectroscopic methods and viscosity experiments. Furthermore, the computations for these complexes applying the density functional theory (DFT) method have also been performed. The results show that all of these complexes can well bind to DNA in intercalation mode and DNA-binding affinity of these complexes is greatly influenced by electronic effects of intercalating ligands. The intrinsic binding constants for 1, 2, and 3 are 0.20, 0.69, and 1.56 × 10⁵ M⁻¹, respectively. This order is in accordance with that of the electron-withdrawing ability of substituent [-OR < -OH < -NO₂]. Such a trend in electronic effects of Ru(II) complexes binding to DNA can be reasonably explained by the DFT calculations.     

Ruthenium(II/III) mediated transformation of 1,2-bis(2′-pyridylmethyleneimino)benzene (L) to 2-(2′-benzimidazolyl)pyridine (L′H) and its in situ formed complexes with Ru(II): X-ray structure of trans-[Ru(PPh3)2(L′H)2](ClO4)2

A series of ruthenium (II) complexes of formulae trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ (1), [Ru(bpy)(L′H)₂](ClO₄)₂ (2), [Ru(bpy)₂(L′H)](ClO₄)₂ (3), cis-[Ru(DMSO)₂(L′H)₂]Cl₂ (4), and [Ru(L′H)₃](PF₆)₂ (5) (where L′H = 2-(2′-benzimidazolyl)pyridine) have been synthesized by reaction of the appropriate ruthenium precursor with 1,2-bis(2′-pyridylmethyleneimino)benzene (L). The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. All the complexes were found to be diamagnetic and hence metal is in +2 oxidation state. The molecular structure of trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ has been determined by the single crystal X-ray diffraction studies. The molecular structure shows that Ru(II) is at the center of inversion of an octahedron with N₄P₂ coordination sphere. The ligand acts as a bidentate N,N′donor. The electronic spectra of the complexes display intense MLCT bands in the visible region.Cyclic voltammetric studies show quasi-reversible oxidative response at 0.99-1.32 V (vs Ag/AgCl reference electrode) due to Ru(III)/Ru(II) couple.     

Alteration of molecular conformations and spectral properties for nickel(II), zinc(II) and copper(II) complexes having 3,8-di(thiophen-2′,2′′-yl)-1,10-phenanthroline ligands

Four transition metal complexes of 3,8-di(thiophen-2′,2″-yl)-1,10-phenanthroline (dtphen), formulated as [Ni(dtphen)₂(H₂O)₂]·(ClO₄)₂ (1), [Zn(dtphen)₂(H₂O)]·(ClO₄)₂ (2) [Cu(dtphen)₂(H₂O)]·(ClO₄)₂ (3), [Cu(dtphen)(phen)₂]·(ClO₄)₂ (4) (phen = 1,10-phenanthroline) with different metal-to-ligand ratios, were synthesized and characterized herein. The X-ray single-crystal diffraction studies of 1-4 exhibit that different molecular configurations for the dtphen ligand can be observed where the side thiophene rings adopt the trans/trans, trans/cis, trans/disorder and cis/cis conformations relative to the central 1,10-phenanthroline unit in different compounds. Fluorescence emission spectra of 1-4 in methanol show that the fluorescence emission of 2 is much stronger than the other three metal complexes, which is mainly due to its full d¹⁰ electronic configuration of Zn(II) ion.     

Experimental and DFT studies on the DNA-binding trend and spectral properties of complexes [Ru(bpy)2L] (L = dmdpq, dpq, and dcdpq)

The trend in DNA-binding affinities and the spectral properties of a series of Ru(II) polypyridyl complexes, [Ru(bpy)₂(dmdpq)]²⁺ (1), [Ru(bpy)₂(dpq)]²⁺ (2), [Ru(bpy)₂(cndpq)]²⁺ (3) (bpy = 2,2′-bipyridine; dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline; dmdpq = di-methyl-dpq; dcdpq = di-cyano-dpq), have been experimentally and theoretically investigated. The DNA-binding constants K_b of the complexes were determined systematically with spectrophotometric titration. The density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out for these complexes. The experimental results show that these complexes bind to DNA in intercalation mode, and the order of their intrinsic DNA-binding constants K_b is K_b(1) < K_b(2) ? K_b(3). The substituents on the intercalative ligands of the complexes play a very important role in the control of DNA-binding affinities of the complexes, in particular, the stronger electron-withdrawing substituent (-CN) on the intercalative ligand can greatly improve the DNA-binding property of the derivative complex. The trend in DNA-binding affinities as well as the spectral properties of metal-ligand charge-transition (¹MLCT) of this series of complexes can be reasonably explained by applying the DFT and TDDFT calculations and the frontier molecular orbital theory.     

Tuning of redox potential and visible absorption band of ruthenium(II) complexes of (benzimidazolyl) derivatives: Synthesis, characterization, spectroscopic and redox properties, X-ray structures and DFT calculations

Six ruthenium(II) complexes have been prepared using the tridentate ligands 2,6-bis(benzimidazolyl) pyridine and bis(2-benzimidazolyl methyl) amine and having 2,2′-bipyridine, 2,2′:6′,2″-terpyridine, PPh₃, MeCN and chloride as coligands. The crystal structures of three of the complexes trans-[Ru(bbpH₂)(PPh₃)₂(CH₃CN)](ClO₄)₂ · 2H₂O (2), [Ru(bbpH₂)(bpy)Cl]ClO₄ (3) and [Ru(bbpH₂)(terpy)](ClO₄)₂ (4) are also reported. The complexes show visible region absorption at 402-517 nm, indicating that it is possible to tune the visible region absorption by varying the ancillary ligand. Luminescence behavior of the complexes has been studied both at RT and at liquid nitrogen temperature (LNT). Luminescence of the complexes is found to be insensitive to the presence of dioxygen. Two of the complexes [Ru(bbpH₂)(bpy)Cl]ClO₄ (3) and [Ru(bbpH₂)(terpy)](ClO₄)₂ (4) show RT emission in the NIR region, having lifetime, quantum yield and radiative constant values suitable for their application as NIR emitter in the solid state devices. The DFT calculations on these two complexes indicate that the metal t_2g electrons are appreciably delocalized over the ligand backbone.     

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)] and [Ru(bpy)2(nitatp)]

Two new ruthenium complexes [Ru(bpy)₂(mitatp)](ClO₄)₂1 and [Ru(bpy)₂(nitatp)](ClO₄)₂2 (bpy = 2,2′-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (¹O₂) was proved to contribute to the DNA photocleavage process, the ¹O₂ quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Synthesis, crystal structure, cytotoxic activities and DNA-binding properties of new binuclear copper(II) complexes bridged by N,N′-bis(N-hydroxyethylaminoethyl)oxamide

Two new μ-oxamido-bridged binuclear copper(II) complexes with formulae of [Cu₂(heae)(pic)₂] (1) and [Cu₂(heae)(Me₂phen)₂](ClO₄)₂ · H₂O (2), where heae and pic stand for the anion of N,N′-bis(N-hydroxyethylaminoethyl)oxamide and 2,4,6-trinitrophenol, respectively, and Me₂phen represents 2,9-dimethyl-1,10-phenanthroline; have been synthesized and characterized by elemental analyses, molar conductivity measurements, IR and electronic spectra studies. The crystal structures of the two binuclear copper(II) complexes have been determined by X-ray single-crystal diffraction. In both the two binuclear complexes the central two copper(II) atoms are bridged by trans-heae. In complex 1 the coordination environment around each copper(II) atom can be described as a distorted octahedral geometry, while in complex 2 each copper(II) atom displays a square-pyramid stereochemistry. Hydrogen bonding and π-π stacking interactions link the binuclear copper(II) complex 1 or 2 into a 3D infinite network. The cytotoxicities of the two binuclear copper(II) complexes were tested by Sulforhodamine B (SRB) assays against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549. Both of the two binuclear copper(II) complexes exhibit potent cytotoxic effects against SMMC-7721 and A549 cell lines. The interactions of the two binuclear complexes with herring sperm DNA (HS-DNA) are investigated by using absorption and emission spectra and electrochemical techniques and viscometry. The results suggest that both the two binuclear copper(II) complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 1.73 × 10⁵ M⁻¹ (1) and 1.92 × 10⁶ M⁻¹ (2). The influence of structural variation of the terminal ligands in the binuclear complexes on DNA-binding properties is preliminarily discussed.     

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2^′-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄) · H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case.     

New ruthenium(II) thiolato complexes: Synthesis, reactivity, spectral, structural and DFT studies

Ruthenium complexes [Ru(mpy)₂(DMSO)₂] (1) and [Ru(mbtz)₂(DMSO)₂] (2) containing 2-mercaptopyridine (mpy) and 2-mercaptobenzothiazole (mbtz) have been synthesized. Reactivity of 1 have been examined with 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), EPh₃ (E = P, As) and 1,2-bis(diphenylphosphino)-methane (dppm). It reacted with bipy or phen in DMF to afford [Ru(mpy)₂(bipy)] (3) and [Ru(mpy)₂(phen)] (4) while, its reaction with EPh₃ or dppm in common organic solvents failed to afford products containing EPh₃ or dppm. Complexes under investigation have been characterized by elemental analyses, spectral, electrochemical studies and structures of 1-4 have been determined crystallographically. Density functional theory calculations have been performed on 1-4 and the model complex [Ru(mpy)(PMe₃)₂] (5) using exchange correlation functionals BP86. Optimized bond length and angles are in good agreement with the structural data. The Ru-N and Ru-S bond distances in [Ru(mpy)₂]-moiety of 1 are relatively shorter than 5, indicating higher stability of 1 in comparison to 5. The WBI values of Ru-N1, Ru-N2, Ru-S1 and Ru-S2 bonds indicate Ru-mpy bonding trend as 3 > 4 > 1 > 5. There is an overall charge flow in the direction L → [Ru(mpy)₂] (L = DMSO, bipy, phen and PMe₃). Due to greater ionic character and Pauli repulsive interactions for Ru-PMe₃ bond in comparison to Ru-DMSO, the DMSO ligands in 1 may not be substituted by phosphine ligands experimentally.     

Luminescent probes for indole-binding proteins derived from ruthenium(II) polypyridine complexes

We report here the synthesis, characterisation, electrochemical, photophysical and protein-binding properties of four luminescent ruthenium(II) polypyridine indole complexes [Ru(bpy)₂(L1)](PF₆)₂ (1), [Ru(bpy)₂(L2)](PF₆)₂ (2), [Ru(L1)₃](PF₆)₂ (1a), and [Ru(L2)₃](PF₆)₂ (2a) (bpy = 2,2′-bipyridine; L1 = 4-(N-(2-indol-3-ylethyl)amido)-4′-methyl-2,2′-bipyridine; L2 = 4-(N-(6-N-(2-indol-3-ylethyl)hexanamidyl)amido)-4′-methyl-2,2′-bipyridine). Their indole-free counterparts, [Ru(bpy)₂(L3)](PF₆)₂ (3) and [Ru(L3)₃](PF₆)₂ (3a) (L3 = 4-(N-(ethyl)amido)-4′-methyl-2,2′-bipyridine), have also been synthesised for comparison purposes. Cyclic voltammetric studies revealed ruthenium-based oxidation at ca. +1.3 V versus SCE and diimine-based reductions at ca. −1.20 to −2.28 V. The indole moieties of complexes 1, 2, 1a and 2a displayed an irreversible wave at ca. +1.1 V versus SCE. All the ruthenium(II) complexes exhibited intense and long-lived orange-red triplet metal-to-ligand charge-transfer ³MLCT (dπ(Ru) → π*(L1-L3)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. The binding of the indole-containing complexes to bovine serum album (BSA) has been studied by quenching experiments and emission titrations.     

Synthetic, structural and spectroscopic studies of complexes derived from the copper(II) perchlorate/succinamic acid/N,N′-donor tertiary reaction systems

The use of succinamic acid (H₂sucm) in Cu(ClO₄)₂·6H₂O/N,N′-donor [2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), 4,4′-bipyridine (4,4′-bpy)] reaction mixtures yielded compounds [Cu₂(Hsucm)₃(bpy)₂](ClO₄)·0.5MeOH (1·0.5MeOH), [Cu₂(Hsucm)(OH)(H₂O)(bpy)](ClO₄)₂ (2), [Cu₄(Hsucm)₅(dmbpy)₄]_n(ClO₄)_3n·nH₂O ·0.53nMeOH (3·nH₂O·0.53nMeOH), [Cu₂(Hsucm)₂(dmbpy)₂(H₂O)₂](ClO₄)₂·2H₂O (4·2H₂O), [Cu₂(Hsucm)₂(phen)₂(H₂O)₂](ClO₄)₂·1.8MeOH (5·1.8MeOH), [Cu₂(Hsucm)₂(phen)₂(MeOH)₂](ClO₄)₂·MeOH (6·MeOH) and [Cu(Hsucm)₂(H₂O)(4,4′-bpy)]_n (7). The succinamate(−1) ligand exists in five different coordination modes in the structures of 1-7, i.e. the common syn, syn μ₂-κO:κO′ in 1-6, the μ₂-κ²O in 1, the μ₂-κ²O:κO′ in 1, the μ₃-κ²O:κ²O′ in 3, and the monodentate κO in 7. The primary amide group of Hsucm⁻ remains uncoordinated and participates in intra- and intermolecular hydrogen bonding interactions leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm⁻ ligands. The thermal decomposition of representative complexes was monitored by TG/DTG and DTA measurements.     

Ruthenium(II) complexes containing asymmetric 2-(pyrazin-2-yl)naphthoimidazole: syntheses, characterization, DNA-binding and photocleavage studies

A novel asymmetric bidentate ligand, 2-(pyrazin-2-yl)naphthoimidazole (PZNI), and its Ru(II) complexes [Ru(bpy)₂(PZNI)]²⁺ (1) and [Ru(phen)₂(PZNI)]²⁺ (2) have been synthesized and characterized by elemental analysis, mass spectra, ¹H NMR, and electronic spectroscopy. The electrochemical behaviors of the novel complexes were studied by cyclic voltammetry. The DNA-binding properties of the complexes were investigated by spectroscopic methods and viscosity measurements. The experimental results indicate that the complexes 1 and 2 interact with calf thymus DNA by intercalative mode via the terminal naphthyl ring into the base pairs of DNA. The two Ru(II) complexes have also been found to promote the cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation.     

Design,synthesis, DNA-binding affinity,cytotoxicity, apoptosis,and cell cycle arrest of Ru(II) polypyridyl complexes

A novel polypyridyl ligand CNPFIP (CNPFIP = 2-(5(4-chloro-2-nitrophenyl)furan-2-yl)-1H-imidazo[4,5f][1,10]phenanthroline) and its mononuclear Ru(II) polypyridyl complexes of [Ru(phen)₂CNPFIP]²⁺(1) (phen = 1,10-phenanthroline), [Ru(bpy)₂CNPFIP]²⁺(2) (bpy = 2,2′-bipyridine), and [Ru(dmb)₂CNPFIP]²⁺(3) (dmb = 4,4′-dimethyl-2,2′-bipyridine) have been synthesized successfully and characterized thoroughly by elemental analysis, UV/Vis, IR, NMR, and ESI-MS. The interaction of the Ru(II) complexes with calf thymus DNA (CT-DNA) was investigated by absorption titration, fluorescence, viscosity measurements. The experimental results suggest that three complexes bind to CT-DNA through an intercalative mode and the DNA-binding affinity of complex 1 is greater than that of complexes 2 and 3. The photocleavage of plasmid pBR322 DNA by ruthenium complexes 1, 2, and 3 was investigated. We have also tested three complexes for their antimicrobial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria. The in vitro cytotoxicity of these complexes was evaluated by MTT assay, and complex 1 shows higher cytotoxicity than 2 and 3 on HeLa cells. The induced apoptosis and cell cycle arrest of HeLa cells were investigated by flow cytometry for 24 h. The molecular docking of ruthenium complexes 1, 2, and 3 with the active site pocket residues of human DNA TOP1 was performed using LibDock.     

Structural and magnetic characterization of a novel series of dinuclear Cu(II) complexes bridging by 2,5-pyrazine dicarboxylate

A new series of dinuclear 2,5-pyrazine dicarboxylato-bridged copper(II) complexes were synthesized and characterized by spectroscopic techniques. The complexes have the general structural formula [Cu₂(L)₂(μ-pyzdc)](ClO₄)₂·nH₂O where L = TPA, n = 2 (1); L = pmedien, n = 2 (2); L = aepn, n = 3 (3); L = dpt, n = 2 (4); L = Medpt, n = 0 (5); L = dien, n = 0 (6) and L = MeDPA, n = 2 (7) with TPA = tris(2-pyridylmethyl)amine, pmdien = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine, aepn = N-(2-aminoethyl)-1,3-diaminopropane, dpt = dipropylene-triamine, Medpt = 3,3′-diamino-N-methyldipropylamine, dien = diethylenetriamine, MeDPA = N,N-di(2-pyridylmethyl)methylamine. In these complexes, the bridging nature of the 2,5-pyrazine dicarboxylato ligand (pyzdc) was confirmed by single-crystal X-ray crystallography. The structure of the TPA complex 1 consists of μ-pyzdc bridging two Cu(II) centers in a bis(monodentate) bonding fashion through a single oxygen atom supplied by each carboxylate group of the bridged pyzdc in a distorted trigonal bipyramidal geometry achieved by the four nitrogen atoms from the TPA ligand. In the complexes 2-5 derived from tridentate amines, the bridged pyzdc acts as a bis(bidentate) ligand in a distorted square pyramidal geometry achieved by one nitrogen and one carboxylate-oxygen of pyzdc, and by the three N-atoms of the amine coligands. The intradimer Cu?Cu distances in the complexes 2-5 are in the range 6.97-7.45 ? and in it is 10.96 ? in 1. The corresponding intermolecular distances are even shorter (5.34-7.99 ?). The susceptibility measurements at variable temperatures over the 5-300 K range reveal weak antiferromagnetic coupling with J values ranging from −0.61 to −4.78 cm⁻¹.     

Spectral and structural studies of a new oxalato-bridged dinuclear copper(II) complex having two 3-(thiophen-2-yl)-1,10-phenanthroline ligands in a trans configuration

In this paper, spectral and structural characterizations of a new dinuclear copper(II) complex (1), formulated as [Cu₂(3-(thiophen-2-yl)-1,10-phenanthroline)₂(μ-oxalate)(DMF)₂](ClO₄)₂ (DMF = N,N′-dimethylformamide), have been described. Two five-coordinate copper(II) centers are bridged by a four-dentate oxalate dianion forming a planar molecular geometry with the Cu-Cu separation of 5.117(4) Å. The two ligands in 1 adopt a trans configuration to each other and two monodentate DMF molecules are positioned at each side of the molecular plane. In addition, typical π-π stacking interactions are found between adjacent phenanthroline and thiophene rings forming a layered packing structure. A compressed pyramidal configurational alteration is observed for each copper(II) center when the temperature is decreased from 291(2) to 100(2) K.     

Synthesis and characterisation of bis(2,2′-bipyridine)(4-carboxy-4′-(pyrid-2-ylmethylamido)-2,2′-bipyridine)ruthenium(II) di(hexafluorophosphate): Comparison of spectroelectrochemical properties with related complexes

The new complex, [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂ NHCO-bpy)](PF₆)₂ · 3H₂O (1), where 4-HCOO-4′-pyCH₂NHCO-bpy is 4-(carboxylic acid)-4′-pyrid-2-ylmethylamido-2,2′-bipyridine, has been synthesised from [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ (H₂dcbpy is 4,4′-(dicarboxylic acid)-2,2′-bipyridine) and characterised by elemental analysis and spectroscopic methods. An X-ray crystal structure determination of the trihydrate of the [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ precursor is reported, since it represented a different solvate to an existing structure. The structure shows a distorted octahedral arrangement of the ligands around the ruthenium(II) centre and is consistent with the carboxyl groups being protonated. A comparative study of the electrochemical and photophysical properties of [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂NHCO-bpy)]²⁺ (1), [Ru(bpy)₂(H₂dcbpy)]²⁺ (2), [Ru(bpy)₃]²⁺ (3), [Ru(bpy)₂Cl₂] (4) and [Ru(bpy)₂Cl₂]⁺ (5) was then undertaken to determine their variation upon changing the ligands occupying two of the six ruthenium(II) coordination sites. The ruthenium(II) complexes exhibit intense ligand centred (LC) transition bands in the UV region, and broad MLCT bands in the visible region. The ruthenium(III) complex, 5, displayed overlapping LC bands in the UV region and a LMCT band in the visible. 1, 2 and 3 were found, via cyclic voltammetry at a glassy carbon electrode, to exhibit very positive reversible formal potentials of 996, 992 and 893 mV (versus Fc/Fc⁺) respectively for the Ru(III)/Ru(II) half-cell reaction. As expected the reversible potential derived from oxidation of 4 (−77 mV (versus Fc/Fc⁺)) was in excellent agreement with that found via reduction of 5 (−84 mV (versus Fc/Fc⁺)). Spectroelectrochemical experiments in an optically transparent thin-layer electrochemical cell configuration allowed UV-Vis spectra of the Ru(III) redox state to be obtained for 1, 2, 3 and 4 and also confirmed that 5 was the product of oxidative bulk electrolysis of 4. These spectrochemical measurements also confirmed that the oxidation of all Ru(II) complexes and reduction of the corresponding Ru(III) complex are fully reversible in both the chemical and electrochemical senses.     

Dinuclear copper(I) complexes containing diimine and phosphine ligands: Synthesis, copper-copper separation and photophysical properties

Dinuclear copper(I) complexes with bridging bis(dicyclohexylphosphino)methane (dcpm) or bis(diphenylphosphino)methane (dppm) and 2,2′-bipyridine or 2-[N-(2-pyridyl)methyl]amino-5,7-dimethyl-1,8-naphthyridine (L), [Cu₂(bpy)₂(dppm)₂](BF₄)₂ (1), [Cu₂(bpy)₂(dcpm)](BF₄)₂ (2), [Cu₂(L)(dppm)](BF₄)₂ (3) and [Cu₂(L)(dcpm)](BF₄)₂ (4) were prepared, and their structures were determined by X-ray crystal analysis. Two-, three-, and four-coordinate copper(I) centers are found in these complexes. Compounds 3 and 4 show close Cu^I?Cu^I separations of 2.664(3) and 2.674(1) Å, respectively, whereas an intramolecular copper-copper distance of 3.038 Å is found in 2 having only dcpm as an additional bridge. Powdered samples of 1, 3, and 4 display intense and long-lived phosphorescence with λ_max at 533, 575, and 585 nm at room temperature, respectively. In the solid state, 2 exhibits only a weak emission at 555 nm. The time-resolved absorption and emission spectra of these complexes were investigated. The difference in the emission properties among complexes 1-4 suggests that both Cu^I?Cu^I distances and coordination environment of the copper(I) centers affect the excited-state properties.     

Different coordination modes of 5,5-diethylbarbiturate in the copper(II) complexes with some aliphatic amines: Synthesis, spectroscopic, thermal and structural studies

Three new copper(II) complexes of 5,5-diethlybarbiturate (barb), [Cu(barb)₂(dmen)]·0.5H₂O (dmen = N,N-dimethylethylenediamine) 1, [Cu(barb)₂(bapa)] (bapa = bis(3-aminopropyl)amine) 2, and [Cu(barb)(apen)](barb)·2H₂O (apen = N,N′-bis(3-aminopropyl)ethylenediamine) 3, have been synthesized and characterized by chemical, spectroscopic and thermal methods. Single crystal X-ray diffraction studies revealed that all complexes are mononuclear. The copper(II) ion exhibits a square-pyramidal coordination geometry in 1 and 3, but a trigonal-bipyramidal geometry in 2. The barb ligand shows different coordination modes. 1 presents the unequal coordination of the barb ligands: one is monodentate (N) and the other one is bidentate (N, O). In 2, both barb ligands are N-coordinated, whereas in 3, one barb ligand is N-coordinated, while the second barb ligand behaves as a counter-ion. The dmen, bapa and apen ligands act as bi-, tri- and tetradentate ligands, respectively. All complexes display a hydrogen-bonded network structure. The IR spectroscopic analysis shows that the ν(CO) stretching frequencies do not correlate predictably with the coordination mode of the barb ligand in 1. Thermal analysis data for 1-3 are in agreement with the crystal structures.