Interactions of zinc(II) complexes with 5′-GMP and their cytotoxic activity

The mechanism of substitution from tetrahedral [ZnCl₂(en)] and square-pyramidal [ZnCl₂(terpy)] complexes (where en = 1,2-diaminoethane or ethylenediamine and terpy = 2,2′:6′,2′′-terpyridine) by guanosine-5′-monophosphate (5′-GMP) have been investigated by ¹H NMR spectroscopy. The substitution reaction of [ZnCl₂(terpy)] complex is faster than the reaction of [ZnCl₂(en)], which was finished after 48?h. Information about the structures of the final products in solution were obtained from the DFT calculations (B3LYP/6-31G(d)) and experimental ¹H NMR data acquired during the course of the reaction. The cytotoxic activity of zinc(II) complexes was tested on human breast cancer cell line MDA-MB-231, human colon cancer cell line HCT-116 and normal human lung fibroblast cell line MRC-5. Both complexes reduced cell viabilities, while [ZnCl₂(terpy)] was significantly cytotoxic on MDA-MB-231 after 72?h, and HCT-116 after 24?h without dose dependence. The differences in reactivity toward 5′-GMP and cytotoxic activity of Zn(II) complexes may be attributed to the very stable square-pyramidal geometry of [ZnCl₂(terpy)] in solution, while weak ligand effect of the en compared to the terpy affected slow interaction of tetrahedral [ZnCl₂(en)] complex with the target bio-molecule.     

Substitution behavior of square-planar and square-pyramidal Cu(II) complexes with bio-relevant nucleophiles

Substitution reactions of [CuCl₂(en)] and [CuCl₂(terpy)] complexes (where en = 1,2-diaminoethane and terpy = 2,2′:6′,2″-terpyridine) with bio-relevant nucleophiles such as inosine-5′-monophosphate (5′-IMP), guanosine-5′-monophosphate (5′-GMP), L-methionine (L-Met), glutathione (GSH) and DL-aspartic acid (DL-Asp) have been investigated at pH 7.4 in the presence of 0.010 M NaCl. Mechanism of substitution was probed via mole-ratio, kinetic, mass spectroscopic and EPR studies at pH 7.4. In the presence of an excess of chloride, the octahedral complex anion [CuCl₄(en)]^2? is formed rapidly while equilibrium reaction was observed for [CuCl₂(terpy)]. Different order of reactivity of bio-molecules toward Cu(II) complexes was observed. Mass spectrum of [CuCl₂(terpy)] in Hepes buffer has shown two new signals at m/z = 477.150 and m/z = 521.00, assigned to [CuCl(terpy)]⁺-Hepes fragments of coordinated Hepes buffer. These signals also appear in the mass spectra of ligand substitution reactions between [CuCl₂(terpy)] and bio-molecules in molar ratio 1:1 and 1:2. According to EPR data, L-Met forms the most stable complex with [CuCl₂(en)] among the ligands considered, while [CuCl₂(terpy)] complex did not show significant changes in its square-pyramidal geometry in the presence of the buffer or bio-ligands.     

Interactions of nitrogen-donor bio-molecules with dinuclear platinum(II) complexes

Substitution reactions of the dinuclear Pt(II) complexes, [{Pt(en)Cl}₂(μ-pz)]²⁺ (1), [{Pt(dach)Cl}₂(μ-pz)]²⁺ (2) and [{Pt(dach)Cl}₂(μ-4,4?-bipy)]²⁺ (3), and corresponding aqua analogs with selected biologically important ligands, viz. 1,2,4-triazole, L-histidine (L-His) and guanosine-5?-monophosphate (5?-GMP) were studied under pseudo-first-order conditions as a function of concentration and temperature using UV–vis spectrophotometry. The reactions of the chloride complexes were followed in aqueous 25 mmol L^?1 Hepes buffer in the presence of 40 mmol L^?1 NaCl at pH 7.2, whereas the reactions of the aqua complexes were studied at pH 2.5. Two consecutive reaction steps, which both depend on the nucleophile concentration, were observed in all cases. The second-order rate constants for both reaction steps indicate a decrease in the order 1 > 2 > 3 for all complexes. Also, the pK_a values of all three aqua complexes were determined. The order of the reactivity of the studied ligands is 1,2,4-triazole > L-His > 5?-GMP. ¹H NMR spectroscopy and HPLC were used to follow the substitution of chloride in the dichloride 1, 2, and 3 complexes by guanosine-5?-monophosphate (5?-GMP). This study shows that the inert and bridging ligands have an important influence on the reactivity of the studied complexes.     

Synthesis, nucleic acid binding and cytotoxicity of oligonuclear ruthenium complexes containing labile ligands

We report the synthesis, nucleic acid binding and cytotoxicity of the complexes [Ru(terpy)(Me₂bpy)Cl]⁺, [Ru(terpy)(phen)Cl]⁺ and dinuclear [{Ru(terpy)Cl}₂(??-bb_n)]²⁺ {where Me₂bpy = 4,4??-dimethyl-2,2??-bipyridine; phen = 1,10-phenanthroline; and bb_n = bis[4(4??-methyl-2,2??-bipyridyl)]-1,n-alkane, with n = 7, 10, 12, 14}. The complexes were isolated from the reaction of the [Ru(terpy)Cl₃] precursor with the respective bidentate and di-bidentate bridging ligands. The time-course UV?CVisible spectroscopy of the reaction of the mono- and dinuclear complexes with guanosine 5-monophosphate (GMP) showed the movement of the metal-to-ligand charge transfer (MLCT) band to lower wavelengths, accompanied by a hypochromism effect. The formation of the aqua complex and phosphate-bound intermediates in the reaction were detected by the time-course ¹H NMR and ³¹P NMR experiments, which also demonstrated that the complex bound to the N7 guanine was the major product. The UV?CVisible and ¹H NMR studies showed no evidence of the interaction of the complexes with both adenosine 5-monophosphate (AMP) and cytidine 5-monophosphate (CMP). Cytotoxicity studies of these complexes against a murine leukemia L1210 cell line revealed that the dinuclear [{Ru(terpy)Cl}₂(??-bb_n)]²⁺ complexes were significantly more cytotoxic than mononuclear [Ru(terpy)(Me₂bpy)Cl]⁺. The [{Ru(terpy)Cl}₂(??-bb₁₄)]²⁺ complex appeared to be the most active (IC₅₀ = 4.2 ??M).     

New Ni(II)Cu(II)Ni(II) trinuclear complexes with an 5=3/2 high-spin ground

Four new heterotrinuclear complexes have been synthesized and characterized, namely {[Ni(L)₂]₂[Cu(opba)]}(ClO₄)₂, where opba denotes o-phenylenebis(oxamato) and L stands for 1,10-phenanthroline(phen) (1), 5-nitro-l,10-phenanthroline(NO₂-phen) (2), 2,2′-bipyridyl(bpy) (S) and 4,4′-dimethyl-2,2′-bipyridyl(Me₂bpy) (4). The temperature dependence of the magnetic susceptibility of {[Ni(phen)₂]₂[Cu(opba)]}(ClO₄)₂3H₂O has been studied in the 4–300 K range, giving the exchange integral J—109 cm^?1. The HMT vs. T plot exhibits a minimum at about 100 K, characteristic of this kind of coupled polymetallic complex with an irregular spin-state structure.     

Crystal structure of K[PtCl3(caffeine)] and its interactions with important nitrogen-donor ligands

The crystal structure of K[PtCl₃(caffeine)] was determined. The coordination geometry around platinum is square-planar formed by N9 of the caffeine ligand and three Cl^? ions. The bond lengths and angles of K[PtCl₃(caffeine)] were compared with those reported for [PtCl₃(caffeine)]^? and K[PtCl₃(theobromine)]. At the level of the statistical significance of the data we have compared, no differences in the bond distances and angles for any of these compounds were noticed. Weak interactions between K⁺ and Cl^? are responsible for the formation of 1-D polymeric chains in the crystal structure of the complex. The interactions of K[PtCl₃(caffeine)] with inosine (Ino) and guanosine-5′-monophosphate (5′-GMP) were studied by ¹H NMR spectroscopy at 295 K in D₂O in a molar ratio of 1 : 1. The results indicate formation of the reaction product [PtCl₃(Nu)] (Nu=Ino or 5′-GMP) with the release of caffeine from the coordination sphere of the starting complex. The higher stability of the bond between the Pt(II) ion and Ino or 5′-GMP compared to the stability of the platinum–caffeine bond is confirmed by density functional theory calculations (B3LYP/LANL2DZp) using as models 9-methylhypoxanthine and 9-methylguanine.     

Complex formation reactions of two sterically hindered platinum(II) complexes with some N-bonding ligands

The kinetics of the complex formation reactions of two [(TL ^tBu)PtCl]⁺ and [Pt(tpdm)Cl]⁺ complexes (TL ^tBu = 2,6-bis[(1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine and tpdm = terpyridinedimethane) with N-donor ligands, l-histidine (L-His), inosine (Ino), inosine-5′-monophosphate (5′-IMP) and guanosine-5′-monophosphate (5′-GMP), were studied. All reactions were studied under pseudo-first-order conditions as a function of nucleophile concentration and temperature in aqueous 0.1 M NaClO₄ solution in the presence of 10 mM NaCl using variable-temperature Uv–Vis spectrophotometry. The order of reactivity of the studied ligands is L-His > Ino > 5′-GMP > 5′-IMP. This order of reactivity is in relation to their electronic properties and structures. The mechanism of the substitution reactions is associative in nature as supported by the negative entropy of activation.     

Interactions of binuclear copper(II) complexes with S-substituted thiosalicylate derivatives with some relevant biomolecules

Abstract

Interactions of copper(II) complexes which contain S-alkyl derivatives of thiosalicylic acid (alkyl?=?methyl, ethyl, propyl and butyl; aryl?=?benzyl), marked as 1–5, with guanosine-5′-monophosphate (5′-GMP) and calf thymus DNA (CT-DNA) were studied. Kinetics of substitution reactions of 1–5 with 5′-GMP and CT-DNA were investigated under pseudo-first-order conditions at 310 K and pH = 7.2 in 25?mM Hepes buffer using stopped-flow method. All complexes have high affinity toward studied bio-molecules. Additionally, interactions with CT-DNA were followed by absorption spectroscopy and fluorescence quenching measurements. The results indicate that complexes bind to DNA exhibiting high binding constants (K_b = 10⁴ M^?1). During the examination of competitive reactions with ethidium bromide (EB), results showed that complexes can replace EB-bound DNA. In addition, a new crystal structure of the binuclear Cu(II) complex with S-substituted thiosalicylate derivative has been reported. In the present series of Cu(II) complexes the crystal structure is the first example of a complex comprising an S-aryl derivative of thiosalicylate ligand. Through comparative study of structural properties of six molecules from four crystal structures we examined the structural variations, potentially important for biological activity of these complexes.     

Stereospecific π–π stacking interactions between pseudo-enantiomeric sulfur-bridged dinuclear Co(III)–Pd(II) and Co(III)–Pt(II) complexes with optically active propanediamines

Assemblies between pseudo-enantiomers with different d⁸ metal centers, Δ-[M(bpy){Co(aet)₂(R-pn)}]³⁺ (M?=?Pd or Pt, bpy?=?2,2′-bipyridine, aet?=?2-aminoethanethiolate, pn?=?1,2-propanediamine), and Λ-[M′(bpy){Co(aet)₂(S-pn)}]³⁺ (M′ ≠ M, M′?=?Pd or Pt), have been examined from stereo- and spectrochemical aspects. A mixture of equimolar amounts of the optically active sulfur-bridged dinuclear complex, Δ-[M(bpy){Co(aet)₂(R-pn)}](NO₃)₃·7H₂O, and its pseudo-enantiomer, Λ-[M′(bpy){Co(aet)₂(S-pn)}](NO₃)₃·7H₂O, in H₂O crystallizes as [M(bpy){Co(aet)₂(R-pn)}][M′(bpy){Co(aet)₂(S-pn)}](NO₃)₆·4H₂O, in which two complex cations with imperfect enantiomorphisms form a 1?:?1 π–π stacked unit.     

Synthesis and Luminescent Properties of an Acetylide-Bridged Dinuclear Platinum（Ⅱ） Terpyridyl Complex

An acetylide-bridged dinuclear platinum(Ⅱ) terpyridyl complex, [Pt(4‘-p-tolyl-terpy)-≡-phenyl-≡-(4‘-p-tolylterpy)Pt](ClO4)2 (1), has been successfully synthesized and its photophysical properties are reported.     

Mixed-Ligand Complexes of 2-(Aminomethyl)benzimidazole Palladium(II) with Various Biologically Relevant Ligands

cis-Dichloro(2-(aminomethyl)benzimidazole)palladium(II), [Pd(AMBI)Cl₂], was synthesized and characterized. The stoichiometry and stability constants of the complexes formed between [Pd(AMBI)(H₂O)₂]²⁺ with various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA constitutents. The results show the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of the chelate ring size of the dicarboxylic acid complexes on their stability constants is examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. Structural effects of the peptide on the amide deprotonation are investigated. DNA pyrimidinic constituents such as uracil, uridine, thymidine and thymine form 1:1 and 1:2 complexes, whereas purinic constituents such as inosine 5′-monophosphate (5′-IMP) and guanosine 5′-monophosphate (5′-GMP) form only 1:1 complexes. The concentration distribution of the complexes in solution was evaluated. The effect of increasing chloride ion concentration on the formation constant of CBDCA with Pd(AMBI)²⁺ was reported.     

Equilibrium and <Superscript>1</Superscript>H NMR Kinetic Study of the Reactions of Dichlorido [S-Methyl-L-Cysteine(N,S)]Platinum(II) Complex with Some Relevant Biomolecules

The formation equilibria of the [Pt(SMC)(H₂O)₂]⁺ complex with some biologically relevant ligands such as L-methionine (L-met) and glutathione (GSH) were studied. The stoichiometry and stability constants of the formed complexes are reported, and the concentration distribution of the various complex species has been evaluated as a function of pH. The reaction between [PtCl₂(SMC)] and guanosine-5′-monophosphate (5′-GMP) was studied by ¹H NMR spectroscopy. The NMR spectra indicated that first step is the hydrolysis of the [PtCl₂(SMC)] complex and second step is the substitution of an aqua ligand, either in the cis or trans position with guanosine-5′-monophosphate in molar ratio 1:1. The values of rate constant showed faster substitution of coordinated H₂O in the trans position to the S donor atom of S-methyl-L-cysteine, whereas the slower reaction was assigned to the displacement of the cis coordinated aqua molecule. This is due to the strong trans labilization effect of coordinated sulfur. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Cytotoxic properties of platinum(IV) and dinuclear platinum(II) complexes and their ligand substitution reactions with guanosine-5′-monophosphate

The substitution reaction of the Pt(IV) complex [PtCl₄(bipy)] with guanosine-5??-monophosphate (5??-GMP) was studied by UV?CVis spectrophotometry. This reaction was investigated under pseudo-first-order conditions at 37?°C in 25?mM Hepes buffer (pH?=?7.2) in the presence of 10?mM NaCl to prevent the hydrolysis of the complex. The substitution of chlorides in [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complex by 5??-GMP was followed by ¹H NMR spectroscopy under second-order conditions. Very similar values for the rate constants of both substitution steps were obtained. The Pt(IV) complexes, [PtCl₄(bipy)] and [PtCl₄(dach)], as well as dinuclaer Pt(II) [{trans-Pt(NH₃)₂Cl}₂(??-pyrazine)](ClO₄)₂ (Pt1), [{trans-Pt(NH₃)₂Cl}₂(??-4,4??-bipyridyl)](ClO₄)₂?·?DMF (Pt2) and [{trans-Pt(NH₃)₂Cl}₂(??-1,2-bis(4-pyridyl)ethane)](ClO₄)₂ (Pt3) complexes, displayed potent cytotoxic activity against human ovarium carcinoma cell line TOV21G and lower activity toward human colon carcinoma HCT116 cell line at the same concentrations. Our data indicate that these platinum complexes could be explored further, as potential therapeutic agents for ovarian cancer.     

Systematic tuning of the reactivity of [RuII(terpy)(N^N)Cl]Cl complexes

Abstract

The substitution behavior of the [Ru^II(terpy)(ampy)Cl]Cl (terpy = 2,2′:6′,2′′-terpyridine, ampy = 2-(aminomethyl)pyridine) complex in water with several bio-relevant ligands such as chloride, thiourea and N,N′-dimethylthiourea, was investigated and compared with the reactivity of the [Ru^II(terpy)(bipy)Cl]Cl and [Ru^II(terpy)(en)Cl]Cl (bipy =2,2′-bipyridine and en?=?ethylenediamine) complexes. Earlier results have shown that the reactivity and pK_a values of Ru(II) complexes can be tuned by a systematic variation of electronic effects provided by bidentate spectator chelates. The reactivity of both the chlorido and aqua derivatives of the studied Ru(II) complexes increases in the order [Ru^II(terpy)(bipy)X]^+/2+?<?[Ru^II(terpy)(ampy)X]^+/2+?<?[Ru^II(terpy)(en)X]^+/2+. This finding can be accounted for in terms of π back-bonding effects provided by the pyridine ligands. The activation parameters for all the studied reactions support an associative interchange substitution mechanism.     

Characterising lone-pair activity of lead(II) by 207Pb solid-state NMR spectroscopy: coordination polymers of [N(CN)2]- and [Au(CN)2]- with terpyridine ancillary ligands

A series of lead(II) coordination polymers containing [N(CN)₂]^? (DCA) or [Au(CN)₂]^? bridging ligands and substituted terpyridine (terpy) ancillary ligands ([Pb(DCA)₂] ( 1 ), [Pb(terpy)(DCA)₂] ( 2 ), [Pb(terpy){Au(CN)₂}₂] ( 3 ), [Pb(4′‐chloro‐terpy){Au(CN)₂}₂] ( 4 ) and [Pb(4′‐bromo‐terpy)(μ‐OH₂)_0.5{Au(CN)₂}₂] ( 5 )) was spectroscopically examined by solid‐state ²⁰⁷Pb MAS NMR spectroscopy in order to characterise the structural and electronic changes associated with lead(II) lone‐pair activity. Two new compounds, 2 and [Pb(4′‐hydroxy‐terpy){Au(CN)₂}₂] ( 6 ), were prepared and structurally characterised. The series displays contrasting coordination environments, bridging ligands with differing basicities and structural and electronic effects that occur with various substitutions on the terpyridine ligand (for the [Au(CN)₂]^? polymers). ²⁰⁷Pb NMR spectra show an increase in both isotropic chemical shift and span (Ω) with increasing ligand basicity (from δ_iso=?3090 ppm and Ω=389 ppm for 1 (the least basic) to δ_iso=?1553 ppm and Ω=2238 ppm for 3 (the most basic)). The trends observed in ²⁰⁷Pb NMR data correlate with the coordination sphere anisotropy through comparison and quantification of the Pb? N bond lengths about the lead centre. Density functional theory calculations confirm that the more basic ligands result in greater p‐orbital character and show a strong correlation to the ²⁰⁷Pb NMR chemical shift parameters. Preliminary trends suggest that ²⁰⁷Pb NMR chemical shift anisotropy relates to the measured birefringence, given the established correlations with structure and lone‐pair activity.     

A novel one-dimensional copper(II) imino nitroxide polymer

A copper(II) complex [Cu(im2-py)(4,4′-bipy)(NO₃)](NO₃)·1.5H₂O (im2-py?=?2-(2′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl; 4,4′-bipy?=?4,4′-bipyridyl) has been synthesized by reaction of Cu(NO₃)·3H₂O with im2py and 4,4-bipyridyl in methanol solution. Its crystal structure has been determined by X-ray diffraction. The structure shows that each copper ion is coordinated by a bidentate imino nitroxide radical, two 4,4′-bipyridyl ligands and a nitrate group to form a distorted square pyramidal environment. The crystal structure consists of chains of copper ions linked by 4,4′-bipyridyl.     

Kinetics and mechanism of the substitution reactions of some monofunctional Pd(II) complexes with different nitrogen-donor heterocycles

Substitution reactions of five monofunctional Pd(II) complexes, [Pd(terpy)Cl]⁺ (terpy = 2,2′;6′,2″-terpyridine), [Pd(bpma)Cl]⁺ (bpma = bis(2-pyridylmethyl)amine), [Pd(dien)Cl]⁺ (dien = diethylenetriamine or 1,5-diamino-3-azapentane), [Pd(Me₄dien)Cl]⁺ (Me₄dien = 1,1,7,7-tetramethyldiethylenetriamine), and [Pd(Et₄dien)Cl]⁺ (Et₄dien = 1,1,7,7-tetraethyldiethylenetriamine), with unsaturated N-heterocycles such as 3-amino-4-iodo-pyrazole (pzI), 5-amino-4-bromo-3-methyl-pyrazole (pzBr), 1,2,4-triazole, pyrazole, pyrazine, and imidazole were investigated in aqueous 0.10 M NaClO₄ in the presence of 10 mM NaCl using variable-temperature stopped-flow spectrophotometry. The second-order rate constants k₂ indicate that the reactivity of the Pd(II) complexes decrease in the order [Pd(terpy)Cl]⁺ > [Pd(bpma)Cl]⁺ > [Pd(dien)Cl]⁺ > [Pd(Me₄dien)Cl]⁺ > [Pd(Et₄dien)Cl]⁺. The most reactive nucleophile of the heterocycles is pyrazine, while the slowest reactivity is with pyrazole. Activation parameters were determined for all reactions and negative entropies of activation, ΔS^≠, supporting an associative mode of substitution. The reactions between [Pd(bpma)Cl]⁺ and 1,2,4-triazole, pzI, and pzBr were also investigated by ¹H NMR to define the manner of coordination. These results could be useful for better explanation of structure-reactivity relationships of Pd(II) complexes as well as for the prediction of potential targets of Pd(II) complexes toward common N-heterocycles, constituents of biomolecules and different N-bonding pharmaceutical agents.     

PROTONATION CONSTANTS OF 2,6-BIS(2-PYRIDYL)PYRIDINE AND 2,4,6-TRIS(2-PYRIDYL)-1,3,5-TRIAZINE AND FORMATION CONSTANTS OF THEIR BINARY AND TERNARY IRON(II) COMPLEXES

Abstract

Equilibrium constants involving the ternary mixed ligand iron(II) complex [Fe(TPTZ)(terpy)]²⁺, determined spectrophotometrically at 23° and μ=0.5 M, are reported. Acidity constants of the protonated ligands and formation constants of the binary iron(II) complexes [Fe(TPTZ)₂]²⁺ and [Fe(terpy)₂]²⁺, measured as an adjunct to determining the ternary complex constants, are also reported. The results are of interest in elucidating mixed-ligand complexation effects as well as in confirming or correcting previously reported equilibrium constants of the binary complexes.     

Structurally characterized homotrinuclear Salamo‐type nickel(II) complexes: Synthesis,solvent effect and fluorescence properties

Four new solvent‐induced Ni(II) complexes with chemical formulae [{NiL(μ₂‐OAc)(MeOH)}₂Ni]·2MeOH ( 1 ), [{NiL(μ₂‐OAc)}₂(n‐PrOH)(H₂O)Ni]·n‐PrOH ( 2 ), [{NiL(μ₂‐OAc)(DMF)}₂Ni] ( 3 ) and [{NiL(μ₂‐OAc)(DMSO)}₂Ni]·2DMSO ( 4 ), (H₂L = 4‐Nitro‐4′‐chloro‐2,2′‐[(1,3‐propylene)dioxybis(nitrilomethylidyne)]diphenol) have been synthesized and characterized by elemental analyses, FT‐IR, UV–Vis spectra and X‐ray crystallography. X‐ray crystal structure determinations revealed that each of the Ni(II) complexes 1–4 consists of three Ni(II) atoms, two completely deprotonated (L)^2? units, two μ₂‐acetate ions and two coordinated solvent molecules (solvents are methanol, n‐propanol, water, N,N‐dimethylformamide and dimethyl sulphoxide, respectively). Although the four complexes 1–4 were synthesized in different solvents, it is worthwhile that the Ni(II) atoms in the four complexes 1–4 adopt hexa–coordinated with slightly distorted octahedral coordination geometries, and the ratios of the ligand H₂L to Ni(II) atoms are all 2: 3. The complexes 1–4 possess self‐assembled infinite 1D, 3D, 1D and 2D supramolecular structures via the intermolecular hydrogen bonds, respectively. In addition, fluorescence behaviors were investigated in the complexes 1–4 .     

Three trinuclear Ru(II) complexes containing 4,5-diazafluorene and 2,2′-bipyridine: synthesis,absorption spectrum,luminescence, and redox behavior

Three heterotopic ligands L¹, L², and L³ have been prepared by the reaction of 4,4′-bis(bromomethyl)-2,2′-bipyridine with 4,5-diazafluoren-9-oxime, 9-(2-hydroxy)phenylimino-4,5-diazafluorene, and 9-(4-hydroxy)phenylimino-4,5-diazafluorene, respectively, in DMF. The three ligands consist of two 4,5-diazafluorene units and one 2,2′-bipyridine unit. Ru(II) complexes [{Ru(bpy)₂}₃(μ₃-L^1?3)](PF₆)₆ (bpy = 2,2′-bipyridine) were prepared by refluxing Ru(bpy)₂Cl₂·2H₂O and the ligands in 2-methoxyethanol. The three Ru(II) complexes display metal-to-ligand charge-transfer absorption at 445–450 nm and one Ru(II)-centered oxidation at 1.32 V in CH₃CN solution at room temperature. Upon excitation into the metal-to-ligand charge-transfer band, the emission intensities of [{Ru(bpy)₂}₃(μ₃-L²)]⁶⁺ and [{Ru(bpy)₂}₃(μ₃-L³)]⁶⁺ are almost equal to that of [{Ru(bpy)₂}₃(μ₃-L¹)]⁶⁺ in CH₃CN solution at room temperature, but weaker than that of [{Ru(bpy)₂}₃(μ₃-L¹)]⁶⁺ in EtOH–MeOH (4?:?1, v/v) glassy matrix at 77 K.