Ionic luminescent cyclometalated Ir(III) complexes with polypyridine co-ligands

Two novel ligands containing a functionalized N ∧ N chelating moiety (pbpy-OBut and tpy-COOH, respectively) were treated with [Ir(ppy)₂(μ-Cl)]₂ (ppy = 2-(2-pyridyl)phenyl), leading to the cationic cyclometalated complexes [Ir(ppy)₂(pbpy-OBut)]⁺ (2) (pbpy-OBut = 4-{4′-(4-phenyloxy)-6′-phenyl-2,2′-bipyridyl}butene) and [Ir(ppy)₂(tpy-COOH)]⁺ (3) (tpy-COOH = 4′-(4-carboxyphenyl)-2,2′:6′,2″-terpyridine). Complexes 2 and 3 exhibit intense room temperature luminescence both in solution and as solid films. Assignment of the emissive behavior to a ³LLCT (ppy-to-N ∧ N) excited state is proposed.     

Phosphorescence bioimaging using cyclometalated Ir(III) complexes

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Application of silver N-heterocyclic carbene complexes in O-glycosidation reactions

We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag–NHC) complexes. A set of four Ag–NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag–NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methylimidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag complexes of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-di-isopropylphenyl)imidazolium chloride failed to facilitate the reaction. The structures of the promoters were established by X-ray crystallography and these complexes were employed in the glycosidation of different glycosyl bromide donors with biologically valuable acceptors, such as estrone, estradiol, and various flavones. The products were obtained in yields considered good to excellent, and all reactions were highly selective for the β isomer regardless of neighboring group effects.     

Stereoselective synthesis of cyclometalated iridium(III) complexes: Characterization and photophysical properties

The stereoselective synthesis of a highly luminescent neutral Ir(III) complex comprising two bidentate chiral, cyclometalating phenylpyridine derivatives, and one acetylacetonate as ligands is described. The final complex and some intermediates were characterized by X-ray structural analysis, NMR-, CD-, and CPL-spectroscopy.     

Ab initio and DFT conformational study on N-nitrosodiethylamine, (C2H5)2N-N=O

Ab initio (MP2) and DFT (B3LYP) calculations, using the cc-pVTZ and aug-cc-pVTZ basis sets, have been performed to characterize some stationary points on the ground state potential energy surface of the title molecules. Several properties as, for instance, relative energies, the barriers for NO rotation around the NN bond, NBO charges on O and amino N atoms, as well as the dipole moments, have been calculated and analyzed in the light of the structures found. Both computational levels here employed yield three minima, in which the C₂NNO frame is ‘planar’ or ‘quasi-planar’. Important correlations between NBO charges and geometric parameters, as well as between some structural features and dipole moments are also discussed. A total of 17 structures have been found for the (C₂H₅)₂N-N=O molecule. Two ranges of values have been obtained for the dipole moment, with the largest values occurring for the structures in which the nitrogen lone pair is parallel to the NO group π system. For instance, these two ranges are from ~4.1 to 4.5 D, and from ~1.6 to 2.1 D, at the MP2/cc-pVTZ level. These ranges are consistent with a larger and a smaller contribution of a dipolar resonance structure, respectively. As the method or basis set changes the values of the dipole moments change by at most ~0.23 D.     

EPR and H NMR spectroscopy and DFT study of pentaammineruthenium(III)phenylcyanamide complexes

The EPR and ¹H NMR spectroscopy of seven [Ru(NH₃)₅L]²⁺ complexes, where L = 3,5-dimethoxyphenylcyanamide (MeO₂pcyd), 3,4,5-trimethoxyphenylcyanamide (MeO₃pcyd), 4-nitrophenylcyanamide (NO₂pcyd), 2,3-dichlorophenylcyanamide (Cl₂pcyd), 2,4,6-trichlorophenylcyanamide (Cl₃pcyd), 2,3,5,6-tetrachlorophenylcyanamide (Cl₄pcyd) and pentachlorophenylcyanamide (Cl₅pcyd), was performed. EPR spectra of the complexes showed an axial signal with g_|| and g_⊥ at high and low field, respectively. The g_|| axis is suggested to lie along the Ru-cyanamide bond. Gas-phase DFT calculations of [Ru(NH₃)₅ phenylcyanamide]²⁺ showed spin density localized mostly on the phenylcyanamide ligand, in disagreement with EPR data. DFT/polarizable continuum model (PCM, water solvation) calculations shifted spin density towards ruthenium so that spin density was shared between ruthenium and phenylcyanamide ligand. Proton contact shifts were determined from NMR and EPR data and were used to estimate spin density distributions on phenyl ring carbons. The results showed that the DFT/PCM calculation overestimated spin density on phenyl ring carbons by approximately one order of magnitude. Donor-acceptor interactions between the solute and solvent that are not fully accounted for in the DFT/PCM method are suggested to stabilize the Ru(III) oxidation state.     

Ab initio and DFT study of the aromaticity of some Fulvalenes derived from Methylidenecyclopropabenzene

Methylidencyclopropabenzene (MCPB) 1 and Fulvalenes 2–4 are molecules of special interest due to the relation between structure and aromaticity. The aim of this work was to analyze this relation and to quantify the aromaticity in 1–4 using different methods. Magnetic properties are directly related with aromaticity; here we studied the magnetic susceptibility and the anisotropy of the magnetic susceptibility. Nucleus indepedent chemical shift (NICS) and the anisotropy of the induced current density (ACID) were also employed. Tools of very different nature, geometric indexes HOMA and Bird, were determinated too for 1–4. All of these measures were found to be in agreement. Figure Both spatial NICS and ACID plot allow to show the aromaticity/antiaromaticity of a ring     

Ab initio DFT study of structural and mechanical properties of methane and carbon dioxide hydrates

The structural and mechanical properties of methane and carbon dioxide hydrates were investigated using density functional theory simulations. Well-established equations of state of solids and exchange-correlation functionals were used for fitting the unit lattice total energy as a function of volume, and the full second-order elastic constants of these two gas hydrates were determined by energy–strain analyses. The polycrystalline elastic properties were also calculated from the unit lattice results. The final results for methane hydrate agree well with available experimental data and with other theoretical results. The two gas hydrates were found to be highly elastically isotropic, but they differed significantly in shear properties. The presented results for carbon dioxide hydrates are the first complete set reported so far. The results are a significant contribution to the ab initio material characterisation of gas hydrates required for ongoing fundamental studies and technological applications.     

Synthesis and structures of mono- and tetra-nuclear silver complexes of styrene-containing N-heterocyclic carbene

Two tetra-nuclear Ag(I) complexes with styrene-functionalized N-heterocyclic carbene [AgL₂]₂[Ag₂X₄] (L = 1-methyl-3-(4-vinylbenzyl)imidazol-2-ylidene, X = Cl, 2a; X = I, 2b) were prepared by the reactions between the corresponding imidazolium salts with Ag₂O. The reaction mixture was further treated with AgBF₄ to give a mononuclear ion-pair complex [AgL₂][BF₄] (3). The molecular structures of these new Ag(I) complexes have been determined by X-ray diffraction analyses. 2a and 2b consist of two [Ag(L)₂]⁺ fragments with the central [Ag₂X₄]²⁻ anion held together by the close Ag(I)-Ag(I) interactions. Complex 3 is a mononuclear ion-pair complex with a linear bi-coordinate Ag fragment.     

Synthesis,characterization and antimicrobial activities of novel silver(I) complexes with coumarin substituted N-heterocyclic carbene ligands

Eight new coumarin substituted silver(I) N-heterocyclic carbene (NHC) complexes were synthesized by the interaction of the corresponding imidazolium or benzimidazolium chlorides and Ag₂O in dichloromethane at room temperature. Structures of these complexes were established on the basis of elemental analysis, ¹H NMR, ¹³C NMR, IR and mass spectroscopic techniques. The antimicrobial activities of carbene precursors and silver NHC complexes were tested against standard strains: Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungi Candida albicans and Candida tropicalis. Results showed that all the compounds inhibited the growth of the all bacteria and fungi strains and some complexes performed good activities against different microorganisms. Among all the compounds, the most lipophilic complex bis[1-(4-methylene-6,8-dimethyl-2H-chromen-2-one)-3-(naphthalene-2-ylmethyl)benzimidazol-2-ylidene]silver(I) dichloro argentate (5e) was found out as the most active one.     

Remarkable chiral and luminescent properties of novel Yb(III) and Eu(III) complexes containing BINAPO ligand

Lanthanide complexes are of great importance for their prospective applications in wide range of science and technology. Chiral lanthanide complexes can constitute stereo-discriminating probes in biological media, owing to the luminescent properties of the rare-earth ions. Sensitized emission with narrow bandwidth, having fast radiation rate and high emission quantum efficiency are the main perspective for synthesizing the complexes. Attention has been given on remarkable chirality with high dissymmetry factors (g = Δε_ext/ε_max) of the complexes. For this purpose, beta-diketonato ligands with chiral BINAPO (1,1′-binapthyl phosphine oxide) ligand were chosen to achieve the goal. The complexes [Ln(TFN)₃(S-BINAPO)](TFN = 4,4,4-trifluoro-1(2-napthyl)-1,3-butanedione), [Ln(HFT)₃(S-BINAPO)] (HFT = 4,4,5,5,6,6,6-heptafluoro-1-(2-thienyl)-1,3-hexanedione) and [Ln(HFA)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) (where Ln = Yb, Eu) were synthesized. The complex, [Eu(TFN)₃(S-BINAPO)] gives strong red emission at 615 nm with narrow emission band (<10 nm) when excited by 465 nm light with quantum efficiency 86%. The dissymmetry factors (g = Δε_ext/ε_max) corresponding to the ⁷F₁ → ⁵D₀ transition at 590 nm is 0.091 for [Eu(TFN)₃(S-BINAPO)] and for [Yb(hfa)₃(S-BINAPO)](hfa = hexafluoroacetylacetonate) corresponding to the ²F_7/2 → ²F_5/2 transitions is 0.12, are among the largest values for both Eu and Yb complexes to date, respectively. The Eu complexes, [Eu(HFT)₃(S-BINAPO)] and [Eu(TFN)₃(S-BINAPO)] are found to be spontaneously emissive, showing bright red emission, when placed in sunlight or even in the laboratory when light is switched on.     

Solution chemistry and cytotoxic properties of novel organogold(III) compounds

The solution behaviour of some novel organogold(III) compounds was investigated, and their cytotoxic properties evaluated against a few human tumour cell lines (A2780/S, A2780/R, MCF7, HT29 and A549). Specifically, the following compounds were considered: [Au(bipy(dmb)-H)(2,6-xylidine-H)][PF(6)] (AuXyl) and [Au(bipy(dmb)-H)(p-toluidine-H)][PF(6)] (AuTol) (in which bipy(dmb)=6-(1,1-dimethylbenzyl)-2,2'-bipyridine), [Au(py(dmb)-H)(AcO)(2)] (AuPyAcO) (in which py(dmb)=2-(1,1-dimethylbenzyl)-pyridine) and [Au(pz(Ph)-H)Cl(3)]K (AuPzCl) (in which pz(Ph)=1-phenylpyrazole). The solution chemistry of these compounds, under physiological-like conditions, was investigated through UV-vis absorption and (1)H NMR spectroscopies. Significant cytotoxic effects in vitro were observed in selected cases.     

In vitro antimicrobial studies of new benzimidazolium salts and silver N-heterocyclic carbene complexes

A series of new benzimidazolium salts (1a–g) were synthesized from the reaction of 1-(4-vinylbenzyl)benzimidazole with various alkyl halides. These salts were used to synthesize silver N-heterocyclic carbene (Ag-NHC) complexes (2a–f). The thirteen compounds were characterized by FT-IR, NMR (¹H and ¹³C) spectroscopic methods and an elemental analysis technique. These selected candidates were tested for their in vitro antimicrobial activities. Antibacterial and antifungal results indicated that the new salts, and particularly their silver complexes, were found to be strongly effective against seven Gram (?) bacterial strains, three Gram (+) bacterial strains and one yeast (Candida albicans).     

Bioorganometallics: First examples of cyclometalated iridium(III) complexes containing di- and tripeptide ester ligands

The synthesis of bis-cyclometalated [Ir(ptpy)₂(gly-gly-OEt)] (2, ptpy = 2-(p-tolyl)pyridinato; gly-gly-OEt = glycylglycine ethyl ester) and [Ir(ptpy)₂(gly-gly-gly-OEt)] (3, gly-gly-gly-OEt = glycylglycylglycine ethyl ester) from the reaction of [{Ir(μ-Cl)(ptpy)₂}₂] (1) with the corresponding peptide ester hydrochlorides in the presence of NaOMe is described. The molecular structure of 2 was confirmed by a single-crystal X-ray diffraction study. The compound crystallized from dichloromethane/iso-hexane in the space group P2₁/a. In the crystal packing the molecules of 2 exhibit N–H?O hydrogen bonds to the neighbor molecules to form dimeric units. The absorption and emission spectra of 2 and 3 were recorded and exhibit these compounds as strong green-emitting complexes.     

Ab initio and density functional theory (DFT) studies on triflic acid with water and protonated water clusters

The structure, stability and infrared spectral signatures of triflic acid (TA) with water clusters (W_n) and protonated water clusters (TAH⁺W_n, n?=?1???6) were computed using DFT and MP2 methods. Our calculations show that a minimum of three water molecules are necessary to stabilize the dissociated zwitterionic form of TA. It can be seen from the results that there is no significant movement of protons in smaller (n?=?1 and 2) and linear (n?=?1 – 6) types of water clusters. Further, the geometries of TAW_n clusters first form a neutral pair (NP) to contact ion pair (CIP), then form a solvent separated ion pair (SSIP) in a water hexamer. These findings reveal that proton transfer may take place through NP to CIP and then CIP to SSIP. The calculated binding energies (BEs) of ion pair clusters is always higher than that of NP clusters (i.e., more stable than the NP). Existing excess proton linear chain clusters transfer a proton to adjacent water molecules via a Grotthuss mechanism, whereas the same isomers in the branched motifs do not conduct protons. Examination of geometrical parameters and infrared frequencies reveals hydronium ion (H₃O⁺ also called Eigen cation) formation in both TAW_n and protonated TAW_n clusters. The stability of Eigen water clusters is three times higher than that of other non-Eigen water clusters. Our study shows clearly that formation of ion pairs in TAW_n and TAH⁺W_n clusters greatly favors proton transfer to neighboring water molecules and also enhances the stability of these complexes.     

Synthesis and antimicrobial studies of silver N-heterocyclic carbene complexes bearing a methyl benzoate substituent

Due to the properties of silver as an antimicrobial, our research group has synthesized many different silver carbene complexes. Two new silver N-heterocyclic carbene complexes derived from 4,5-dichloroimidazole and theobromine bearing methyl benzoate substituents were synthesized by in situ carbene formation using silver acetate as the base in the reaction. The new compounds were fully characterized by several methods including NMR spectroscopy and X-ray crystallography. Preliminary antimicrobial efficacy studies against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli were conducted. The results of this study demonstrated antimicrobial efficacy of the two complexes comparable to silver nitrate, showing their potential for use in the treatment of bacterial infections.     

Novel 2-aminopyridine liganded Pd(II) N-heterocyclic carbene complexes: Synthesis,characterization, crystal structure and bioactivity properties

In this work, the synthesis, crystal structure, characterization, and enzyme inhibition effects of the novel a series of 2-aminopyridine liganded Pd(II) N-heterocyclic carbene (NHC) complexes were examined. These complexes of the Pd-based were synthesized from PEPPSI complexes and 2-aminopyridine. The novel complexes were characterized by using ¹³C NMR, ¹H NMR, elemental analysis, and FTIR spectroscopy techniques. Also, crystal structures of the two compounds were recorded by using single-crystal X-ray diffraction assay. Also, these complexes were tested toward some metabolic enzymes like α-glycosidase, aldose reductase, butyrylcholinesterase, acetylcholinesterase enzymes, and carbonic anhydrase I, and II isoforms. The novel 2-aminopyridine liganded (NHC)PdI₂(2-aminopyridine) complexes (1a-i) showed Ki values of in range of 5.78 ± 0.33–22.51 ± 8.59 nM against hCA I, 13.77 ± 2.21–30.81 ± 4.87 nM against hCA II, 0.44 ± 0.08–1.87 ± 0.11 nM against AChE and 3.25 ± 0.34–12.89 ± 4.77 nM against BChE. Additionally, we studied the inhibition effect of these derivatives on aldose reductase and α-glycosidase enzymes. For these compounds, compound 1d showed maximum inhibition effect against AR with a Ki value of 360.37 ± 55.82 nM. Finally, all compounds were tested for the inhibition of α-glycosidase enzyme, which recorded efficient inhibition profiles with Ki values in the range of 4.44 ± 0.65–12.67 ± 2.50 nM against α-glycosidase.     

Ab initio self-consistent field study of deoxyguanosine

The rotational energy of deoxyguanosine around the C₁–N₉ bond is calculated using the Hartree-Fock method with an STO-3G basis set.     

Benzimidazolium-based novel silver N-heterocyclic carbene complexes: synthesis,characterisation and in vitro antimicrobial activity

This study reports the synthesis, characterisation and antimicrobial activity of five novel silver N-heterocyclic carbene (Ag–NHC) complexes obtained by N-propylphthalimide and N-methyldioxane substituted benzimidazolium salts with silver oxide. The reactions were performed at room temperature for 24?h in the absence of light. The obtained complexes were identified and characterised by ¹H and ¹³C NMR, FT-IR and elemental analysis techniques. The minimum inhibitory concentration (MIC) of the complexes was determined for E. coli, P. aeruginosa, E. faecalis, S. aureus, C. tropicalis and C. albicans in vitro through agar and broth dilution. The results indicated that these complexes exhibit antimicrobial activity. In particular, complex 3 presented the significant broad spectrum antimicrobial activity.     

DFT/TDDFT computational study of the structural,electronic and optical properties of rhodium (III) and iridium (III) complexes based on tris-picolinate bidentate ligands

The electronic structures and spectroscopic properties of two complexes [M(pic)₃] (M = Ir, Rh) containing picolinate as bidentate ligands have been calculated by means density functional theory (DFT) and time-dependent DFT/TD-DFT using three hybrid functionals B3LYP, PBE0 and mPW1PW91. The PBE0 and mPW1PW91 functionals, which have the same HF exchange fraction (25%), give similar results and do not differ drastically from B3LYP results. Calculated geometric parameters of the complexes are in good agreement with the available experimental data. The UV absorptions observed in acetonitrile were assigned on the basis of singlet state transitions. The most intense band observed in the UV-C region corresponds to ligand-to-ligand charge transfer states (LLCT) in both complexes. The theoretical spectrum of the rhodium complex is characterized by a large degree of mixing between metal-to-ligand-charge-transfer (MLCT), LLCT and metal centered (MC) states in the UV-A region. The presence of low-lying excited states with MC character affects the absorption spectrum under spin-orbit coupling (SOC) effects and play important roles in the photochemical properties.

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Graphical abstract Frontier molecular orbital diagram of mer-M(pic)₃ (M=Ir, Rh).