Synthesis and structural characterization of silver(I) complexes with moon-shaped benzo[1,2-b;4,3-b′]dithiophene phosphine derivative ligands

New silver complexes of general formula [Ag(O₃SCF₃)(PPh₂{bzt})_n] (n = 1–3, bzt = benzo[1,2-b;4,3-b′]dithiophene) have been synthesized and characterized. Spectroscopic studies shown neutral ligand fluxionallity, typical of silver(I) complexes. The solid state structure of the complexes was determined by X-ray crystallographic studies, showing a decrease in structure complexity with increasing number of neutral ligands in silver coordination sphere: [Ag(O₃SCF₃)(PPh₂{bzt})] is a dimer with two bridging triflate anions, further linked into polymeric bidimensional chains along bc plane, through Ag?Ph close contacts; Ag(O₃SCF₃)(PPh₂{bzt})₂] is also a dimmer with two bridging triflate anions, displaying an interesting packing feature, with zig-zag alignment of bzt groups along direction b; [Ag(O₃SCF₃)(PPh₂{bzt})₃] is a monomer.     

N-Functionalised heterocyclic dicarbene complexes of silver: Synthesis and structural studies

A range of new diimidazolium salts, held together by an alkyl unit and bearing alcohol pendant arms on their nitrogen, was synthesized. A short modular reaction pathway leads to the N-heterocyclic carbene (NHC) precursors, differing by the flexibility of the bridge, the steric bulk of substituents in α-position of the OH groups and the anions. Treatment of diimidazolium salts with Ag₂O yields Ag^I(carbene)₂ complexes. The related trimethylene-bridged bis-NHC silver complexes 6 and 7 were crystallised with di-tosylate and di-hexafluorophosphate anions, respectively. Their X-ray structures revealed dimeric species, involving two ligands with different arrangements around the Ag cations, leading to crossed and parallel conformations.     

Redox-active antifungal cobalt(II) and copper(II) complexes with sterically hindered o-aminophenol derivatives

Co(II) complexes with 4,6-di(tert-butyl)-2-aminophenol (HL^I) and 2-anilino-4,6-di(tert-butyl)phenol (HL^II) have been synthesized and characterized by means of physico-chemical methods. The compounds HL^I and HL^II coordinate in their singly deprotonated forms and behave as bidentate O,N-coordinated ligands; their low-spin Co(II) complexes are characterized by CoN₂O₂ coordination modes and square planar geometry. Both the free ligands and their Co(II) and Cu(II) complexes (we have produced and characterized the latter before) exhibit a pronounced antifungal activity against Aspergillus niger, Fusarium spp., Mucor spp., Penicillium lividum, Botrytis cinerea, Alternaria alternata, Sclerotinia sclerotiorum, Monilia spp., which in a number of cases is comparable with that of Nystatin and Terbinafine or even higher. The reducing properties of the ligands and their metal(II) complexes, as well as their antifungal activities, were found to decrease in the order: Cu(L^I)₂ > Cu(L^II)₂ ? Co(L^I)₂ > Co(L^II)₂ > HL^I > HL^II.     

Asymmetric hydrogenation of alkenes with planar chiral 2-phosphino-1-aminoferrocene-iridium(I) complexes

The first highly enantioenriched and enantiopure planar chiral 2-phosphino-1-aminoferrocene ligands and their Ir(COD)BAr_F complexes are reported. The ligands display bidentate coordination behavior towards iridium, as indicated by trends in ³¹P and ¹H NMR spectra of the phosphine moieties and the α to nitrogen substituents of the amines. All of the new complexes showed good reactivity as catalysts in promoting asymmetric hydrogenation of several prochiral alkenes, with enantioselectivities up to 92%. Iridium complexes of dimethylaminoferrocene derivatives containing P-Ar groups [PPh₂ and P(o-tol)₂] gave the highest levels of asymmetric induction.     

Synthesis,characterization and antimicrobial studies on cis-platinum(II) complexes of 5-nitrosouracil derivatives

Two complexes were obtained during the reactions of 6-amino-1-methyl-5-nitrosouracil (AMNU) and 6-methylamino-1-benzyl-5-nitrosouracil (MABNU) with cis-diaquadiamineplatinum(II) nitrate complex, cis-[Pt(NH₃)₂(H₂O)₂](NO₃)₂. The complexes were isolated in good yields as powdery precipitates. They were characterized through their elemental analysis, infrared, UV–vis, and ¹H NMR spectroscopies as well as thermal analyses. The obtained results indicated that, pyrimidine bases substitute easily aqua ligands and interact with Pt(II) ions as a monodentate ligand in the neutral and ionic form for the ligands AMNU and MABNU, respectively. The exocyclic oxygen atoms are the most probable binding site. Square planar structures, cis-form, were proposed in both cases. The free ligands, and their Pt(II) complexes were screened for their antimicrobial activities.     

3,3-Bis(3,5-dimethylpyrazol-1-yl)propionic acid: A tripodal N,N,O ligand for manganese and rhenium complexes - Syntheses and structures

The tripodal N,N,O ligands 3,3-bis(3,5-dimethylpyrazol-1-yl)propionic acid (Hbdmpzp) (1) and 3,3-bis(pyrazol-1-yl)propionic acid (Hbpzp) (2) form the “missing link” between the well-known bis(pyrazol-1-yl)acetic acids and related ligands with a longer “carboxylate arm”. To illustrate the reactivity of this ligand, manganese and rhenium complexes bearing the ligand bdmpzp are reported. The complexes are compared to related compounds bearing other tripod ligands such as bis(3,5-dimethylpyrazol-1-yl)acetate (bdmpza) and 3,3-bis(1-methylimidazol-2-yl)propionate (bmip). Spectroscopic and structural data are used as a basis for comparison, as well as DFT calculations. Both ligands 1 and 2 and the complexes fac-[Mn(bdmpzp)(CO)₃] (3) and fac-[Re(bdmpzp)(CO)₃] (4) were characterised by X-ray crystallography.     

Microwave assisted synthesis,characterization and biological evaluation of palladium and platinum complexes with azomethines

Reactions of 3-acetyl-2,5-dimethylthiophene with thiosemicarbazide and semicarbazide hydrochloride resulted in the formation of new heterocyclic ketimines, 3-acetyl-2,5-dimethylthiophene thiosemicarbazone (C₉H₁₃N₃OS₂ or L¹H) and 3-acetyl-2,5- dimethylthiophene semicarbazone (C₉H₁₃N₃OS or L²H), respectively. The Pd(II) and Pt(II) complexes have been synthesized by mixing metal salts in 1:2 molar ratios with these ligands by using microwave as well as conventional heating method for comparison purposes. The authenticity of these ligands and their complexes has been established on the basis of elemental analysis, melting point determinations, molecular weight determinations, IR, ¹H NMR and UV spectral studies. These studies showed that the ligands coordinate to the metal atom in a monobasic bidentate manner and square planar environment around the metal atoms has been proposed to the complexes. Both the ligands and their complexes have been screened for their antimicrobial activities. The antiamoebic activity of both the ligands and their palladium compounds against the protozoan parasite Entamoeba histolytica has been tested.     

ESCA OF TETRAAZA MACROCYCLIC COMPLEXES OF SILVER(II)

Abstract

ESCA results for four tetraaza macrocyclic ligands and their silver(II) complexes have been measured. The Ag 3d binding energies of these complexes fall in the narrow range of 374.3–375.3 eV (3d_3/2) and 368.2–375.3 eV (3d_3/2) and 368.2–369.3 eV (3d_5/2) which are in agreement with the E_b values published previously for silver(II) complexes containing nitrogen donor ligands. Ring substitution with methyl groups has no pronounced influence on the Ag 3d, binding energies while ring size variation does cause a small shift in the binding energies. Ring strain energy is invoked as the probable reason for the observed effect.     

Synthesis,characterization and antimicrobial studies of mixed ligand silver(I) complexes of thioureas and triphenylphosphine; crystal structure of {[Ag(PPh3)(thiourea)(NO3)]2·[Ag(PPh3)(thiourea)]2(NO3)2}

Mixed ligand silver(I) complexes of triphenylphosphine and thioureas (thiourea (Tu), N-methylthiourea (Metu), N,N′-dimethylthiourea (Dmtu) and N,N′-diethylthiourea (Detu)) with the general formulae, [(Ph₃P)₂Ag(thione)]NO₃ and [(Ph₃P)Ag(thione)₂]NO₃, have been prepared and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ³¹P) spectroscopic methods. The crystal structure of one of them has been determined by X-ray crystallography. The spectral data of the complexes are consistent with sulfur coordination of the thiones to silver(I). The single crystal X-ray structure of complex 1, {[Ag(PPh₃)(thiourea)(NO₃)]₂·[Ag(PPh₃)(thiourea)]₂(NO₃)₂}, shows that the complex consists of two independent centrosymmetric binuclear units, each having the silver atoms coordinated to one PPh₃ and two bridging thiourea molecules. In one of the independent units the silver atom is additionally bound to a nitrate ion, leading to a tetrahedral geometry, while in the other unit the silver atom adopts a trigonal planar environment. Antimicrobial activities of the complexes were evaluated by their minimum inhibitory concentration and the results showed that the complexes show a wide range of activity against two gram-negative bacteria (Escherichiacoli, Pseudomonasaeruginosa) and molds (Aspergillusniger, Penicilliumcitrinum), while the activities were poor against yeasts (Candidaalbicans, Saccharomycescerevisiae). However, the title complex did not show activity against any tested microorganism.     

Copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole and 2-ethylamino-1,3,4-thiadiazole

The following copper(I) and silver(I) complexes of 2-amino-1,3,4-thiadiazole (atz) and 2-ethylamino-1,3,4-thiadiazole (eatz) have been prepared and studied by conductometric, IR and Raman methods: CuXL(X = Cl, Br, I; L = atz, eatz), CuXL₃(X = ClO₄, NO₃; L = atz, eatz), AgClO₄·1.5atz·1/3 EtOH, AgNO₃·2.5atz, AgClO₄·3eatz, AgNO₃·eatz. The ligands are bonded through the amine nitrogen atoms with ν(MN) bands in the 520–410 cm^?1 region. The CuXL complexes have a trigonal (N, 2X_b) coordination with a probable weaker axial interaction. The CuXL₃ and AgCIO₄·3eatz complexes probably have a trigonal pyramidal (3N,O) coordination. In the atz complexes of silver perchlorate and nitrate some ligand molecules are bridging. The AgNO₃·2.5atz complex is likely to have a dimeric structure with tetrahedral coordination of the silver ion.     

Synthesis of New Thiourea-Metal Complexes with Promising Anticancer Properties

In this work, two thiourea ligands bearing a phosphine group in one arm and in the other a phenyl group (T2) or 3,5-di-CF₃ substituted phenyl ring (T1) have been prepared and their coordination to Au and Ag has been studied. A different behavior is observed for gold complexes, a linear geometry with coordination only to the phosphorus atom or an equilibrium between the linear and three-coordinated species is present, whereas for silver complexes the coordination of the ligand as P^S chelate is found. The thiourea ligands and their complexes were explored against different cancer cell lines (HeLa, A549, and Jurkat). The thiourea ligands do not exhibit relevant cytotoxicity in the tested cell lines and the coordination of a metal triggers excellent cytotoxic values in all cases. In general, data showed that gold complexes are more cytotoxic than the silver compounds with T1, in particular the complexes [AuT1(PPh₃)]OTf, the bis(thiourea) [Au(T1)₂]OTf and the gold-thiolate species [Au(SR)T1]. In contrast, with T2 better results are obtained with silver species [AgT1(PPh₃)]OTf and the [Ag(T1)₂]OTf. The role played by the ancillary ligand bound to the metal is important since it strongly affects the cytotoxic activity, being the bis(thiourea) complex the most active species. This study demonstrates that metal complexes derived from thiourea can be biologically active and these compounds are promising leads for further development as potential anticancer agents.     

Synthesis, characterization and antimicrobial studies of mixed ligand silver(I) complexes of triphenylphosphine and heterocyclic thiones: Crystal structure of bis[{(μ-diazinane-2-thione)(diazinane-2-thione)(triphenylphosphine)silver(I) nitrate}]

Mixed ligand silver(I) complexes of triphenylphosphine and heterocyclic thiones (imidazolidine-2-thione (Imt), diazinane-2-thione (Diaz) and 2-mercaptopyridine (Mpy)) having the general formulae [(Ph₃P)Ag(thione)₂]NO₃ and [(Ph₃P)₂Ag(thione)]NO₃ were prepared and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ³¹P) spectroscopic methods. The crystal structure of one of the complexes, [Ag(Ph₃P)(Diaz)₂]₂(NO₃)₂ (1) was determined by X-ray crystallography. The title complex (1) is dinuclear, having each silver atom coordinated to three thione sulfur atoms of Diaz and to one phosphorus atom of PPh₃ in a nearly tetrahedral environment, with an average P-Ag-S bond angle of 108.5°. The spectral data of the complexes are consistent with sulfur coordination of the thiones to silver(I). Antimicrobial activities of the complexes were evaluated by minimum inhibitory concentrations and the results showed that the complexes exhibit a wide range of activity against two gram-negative bacteria (E. coli, P. aeruginosa) and molds (A. niger, P. citrinum), while the activities were poor against yeasts (C. albicans, S. cerevisiae).     

Synthesis,characterization and bioactivity of mixed-ligand Cu(II) complexes containing Schiff bases derived from S-benzyldithiocarbazate and saccharinate ligand and the X-ray crystal structure of the copper-saccharinate complex containing S-benzyl-β-N-(acetylpyrid-2-yl)methylenedithiocarbazate

Mixed-ligand complexes of general formula, [Cu(NNS)(sac)] (NNS′ = S-benzyl-β-N-(2-acetylpyrid-2-yl)methylenedithiocarbazate, NNS″ = S-benzyl-β-N-(2-benzoylpyrid-2-yl)methylenedithiocarbazate and NNS? = S-benzyl-β-N-(6-methylpyrid-2-yl)methylenedithio-carbazate, sac = the saccharinate anion) have been synthesized by reacting [Cu(sac)₂(H₂O)₄] · 2H₂O with the appropriate ligands in ethanol and characterized by various physico-chemical techniques. Magnetic and spectral evidence indicate that the complexes are four-coordinate in which the Schiff bases coordinate as NNS ligands and the sac- anion coordinates as a unidentate N-donor ligand. An X-ray crystallographic structural analysis of [Cu(NNS′)(sac)] shows that the complex has a distorted square-planar geometry with the Schiff base coordinated to the copper (II) ion as a uninegatively charged tridentate chelating agent via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulphur atom while the fourth coordination position is occupied by the N-bonded saccharinate anion. The complexes have been evaluated for their biological activities against selected pathogens and cancer cell lines. They display weak activity against the pathogenic bacteria and fungi. The complexes were highly active against the leukemic cell line (HL-60) but only [Cu(NNS′)(sac)] was found to exhibit strong cytotoxicity against the ovarian cancer cell line (Caov-3). All complexes were inactive against the breast cancer cell line (MCF-7).     

Diversity of coordination architecture of silver(Ι) complexes with different 2-aminopyrimidyl derivatives: Effect of counter anions and ligands

Five new silver(Ι) complexes of the formula [Ag(L₁)(CF₃SO₃)(H₂O)]_n (1), [Ag₄(L₁)₄(CF₃CO₂)₄]_n (2), [Ag₂(L₁)₄(ClO₄)₂] (3), [Ag(L₂)(ClO₄)]_n (4), and [Ag(L₃)(ClO₄)]_n (5) have been synthesized by reactions of varied silver(Ι) salts with the corresponding 2-aminopyrimidyl ligands (namely, 2-amino-4,6-dimethylpyrimidine (L₁), 2-amino-4-methoxy-6-methylprimidine (L₂), and 2-amino-4,6-dimethoxyprimidine (L₃)). The influences of counter anions and ligands on the structure of the complexes are discussed. Two complexes, 1 with one-dimensional (1D) zigzag chain and 2 with 1D ladder network are obtained by using the same ligand L₁ but different silver(Ι) salts. On the other hand, using the same silver(Ι) perchlorate but different ligands under the same synthetic conditions, complexes 3–5 are isolated, respectively. In the case of 3, two metal atoms and four L₁ ligands form dimeric [Ag₂(L₁)₄] unit further connected by intermolecular hydrogen bonds and π–π interactions to form an infinite 2D layer structure. Complex 4 displays a two-dimensional (2D) grid network. Complex 5 has a 1D zigzag chain but different from that of 1. An extended 3D framework arises from N–H···O intermolecular hydrogen bonds and Ag···O weak interaction. The results reveal that the nature of the counter anions and organic ligands all has great impact on the structure of the complexes. In addition, the hydrogen-bonding interactions and π–π stacking also play important roles in the formation of supramolecular architectures, for instance, to link low-dimensional entities to high-dimensional frameworks. The luminescence properties of the synthesized silver complexes were investigated in the solid state at room temperature.     

Ligational behavior of thiosemicarbazone,semicarbazone and thiocarbohydrazone ligands towards VO(IV), Ce(III), Th(IV) and UO2(VI) ions: Synthesis,structural characterization and biological studies

Mono- and binuclear VO(IV), Ce(III), Th(IV) and UO₂(VI) complexes of thiosemicarbazone, semicarbazone and thiocarbohydrazone ligands derived from 4,6-diacetylresorcinol were synthesized. The structures of these complexes were elucidated by elemental analyses, IR, UV–vis, ESR, ¹H NMR and mass spectra as well as conductivity and magnetic susceptibility measurements and thermal analyses. The thiosemicarbazone (H₄L¹) and the semicarbazone (H₄L²) ligands behave as dibasic pentadentate ligands in case of VO(IV) and UO₂(VI) complexes, tribasic pentadentate in case of Ce(III) complexes and monobasic pentadentate in case of Th(IV) complexes. However, the thiocarbohydrazone ligand (H₃L³) acts as a monobasic tridentate ligand in all complexes except the VO(IV) complex in which it acts as a dibasic tridentate ligand. The antibacterial and antifungal activities were also tested against Rhizobium bacteria and Fusarium-Oxysporium fungus. The metal complexes of H₄L¹ ligand showed a higher antibacterial effect than the free ligand while the other ligands (H₄L² and H₃L³) showed a higher effect than their metal complexes. The antifungal effect of all metal complexes is lower than the free ligands.     

Synthesis of rhodium N-heterocyclic carbene complexes and their catalytic activity in the hydrosilylation of alkenes in ionic liquid medium

Rhodium complexes bearing N-heterocyclic carbene (NHC) ligands were prepared from bis(η⁴-1,5-cyclooctadiene) dichlorodirhodium and 1-alkyl-3-methylimidazolium-2-carboxylate, and the catalytic properties of rhodium complexes prepared in the hydrosilylation of alkenes in ionic liquid media were investigated. It was found that both the catalytic activity and selectivity of the rhodium complexes bearing NHC ligands were influenced by the attached substituents of the imidazolium cation. Additionally, rhodium complexes bearing NHC ligands in ionic liquid BMimPF₆ could be reused without noticeable loss of catalytic activity and selectivity.     

Synthesis and antitumor activity of new silver(I)-N-heterocyclic carbene complexes

Abstract

In this study, two novel benzimidazole-based N-heterocyclic carbene ligands (1a-b) and their silver(I) complexes (2a-b) were synthesized. All new compounds were characterized by FT-IR, LC-MS, ¹H NMR, and ¹³C NMR spectroscopies. The in vitro antitumor activities of NHC ligands (1a-b) and their silver(I) complexes (2a-b) against DU-145 human prostate cancer cells, MDA-MB-231 and MCF-7 human breast cancer cells and L-929 (normal cells adipose from mouse) were also determined using MTT analysis for 24?h, 48?h, and 72?h. The results showed that while NHC ligands did not have in vitro antitumor activity on MCF-7, MDA-MB-231 and DU-145 cells, Ag(I)-NHC complexes have in vitro antitumor activities. The in vitro antitumor activity of 2a was found to be lower than that of 2b. Ag(I)-NHC complexes were observed to have higher IC₅₀ values for non-cancerous cell lines than cancer cells.     

Dimeric and polymeric silver(I) saccharinato complexes of two bis(pyridine) ligands: Synthesis,structural, spectroscopic,fluorescent and thermal properties

The reaction of silver(I) with 1,2-bis[1-(pyridin-2-yl)ethylidene]hydrazine (bpeh) and N,N-bis(pyridin-2-ylmethyl)amine (bpma) in the presence of Na(sac) (sac = saccharinate) yielded [Ag₂(sac)₂(bpeh)] (1) and [Ag(sac)(bpma)]_n (2) with conformational chirality. Both complexes have been characterized by elemental analysis, IR, thermal analysis and X-ray single crystal diffraction. Complex 1 displays a binuclear composition, in which each silver(I) ion is bound to one monodentate sac ligand and one of the bidentate pyridylimino groups of the bpeh ligand in a distorted trigonal coordination geometry. Complex 2 is a one-dimensional helical polymer, in which silver(I) centers are bridged by tridentate bpma ligands, and each silver(I) ion is coordinated in a distorted tetrahedral geometry by one monodentate sac ligand, a bidentate pyridylamine group of one bpma ligand, and a py group of another bpma ligand. Weak intermolecular C–H?O hydrogen bonds and C–H?π interactions lead to assembly of 1 and 2 into three-dimensional supramolecular frameworks. Spectral and thermal analysis data for 1 and 2 are in agreement with the crystal structures. In addition, both complexes in the solid state display intraligand π–π∗ fluorescence.     

An iodide/anion exchange route to benzimidazolylidene silver complexes from benzimidazolium iodide: Crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate

Syntheses of N,N′-dibutylbenzimidazolylidene silver complexes having chloride, nitrate or cyanide as an anion part through an iodide/anion exchange from N,N′-dibutylbenzimidazolium iodide are described, representing a practical route to benzimidazolylidene silver complexes from readily accessible benzimidazolium iodide. The crystal structures of N,N′-dibutylbenzimidazolylidene silver chloride, bromide, cyanide and nitrate have been determined, showing a close ligand-unsupported Ag-Ag interaction in [(NHC)₂]Ag⁺[AgX₂]⁻ and a “T” shape geometry about the silver(I) cation in complexes of chloride, bromide and cyanide, but a nearly linear shape in the bis(N,N′-dibutylbenzimidazolylidene) silver complex [ with non-coordinating nitrate anion.     

N-(Pyridin-2-yl)picolinamide tetranickel clusters: Synthesis,structure and ethylene oligomerization

A series of N-(pyridin-2-yl)picolinamide derivatives was synthesized and characterized. Tetranickel complexes were obtained by stoichiometric reaction of NiBr₂ and corresponding ligands, and characterized by elemental and spectroscopic analysis. Moreover, the coordination pattern of complex 3a was confirmed by single-crystal X-ray diffraction. In the structure, two ligands linked two nickel atoms to form a unit, and two units were bridged via μ₃-OMe and μ₂-Br to form a tetranickel cluster. These Ni(II) complexes were investigated in ethylene oligomerization and found to exhibit remarkable catalytic activities upon activation with MAO. Reaction conditions as well as ligand environment significantly affected the catalytic performance of the nickel complexes; the highest activity could be achieved to be 2.7 × 10⁶ g mol⁻¹ Ni h⁻¹.