Mononuclear Compounds Research Articles

Anticancer evaluation of ruthenium(III) complexes with N-donor ligands tethered to coumarin or uracil moieties

In this study, the synthesis and characterization of new paramagnetic ruthenium(III) complexes: cis-[RuCl2(urdpa)] (1) {Hurdpa = 6-((bis(pyridin-2-ylmethyl)amino)methyl)uracil} and fac-[RuCl3(chrdpa)] (2) {chrdpa = 4-((bis(pyridin-2-ylmethyl)amino)methyl)-7-methoxycoumarin} are reported. These metal complexes have been comprehensively characterized by an array of physicochemical techniques and the X-ray solid-state structures of 1 and Hurdpa have been attained. Electronic spectroscopy Calf-Thymus DNA titrations revealed that both 1 and 2 are groove binders while molecular docking calculations indicated that the ligands’ steric factors dictate the mode of interaction of these individual ruthenium(III) species. These mononuclear ruthenium compounds were screened against cervical and breast cancer cell lines and show activity in the high micromolar range.

Synthesis and comparative studies of photophysical and electrochemical properties of three different types of new heteroleptic 5-arylazo-8-hydroxyquinoline complexes of rhodium including trans → cis isomerism studies

Refluxing [Rh(2-phpy)2(Cl)]2 separately with the equivalent amount of 5-phenylazo-8-hydroxyquinoline (Hq1), 5-(4-fluorophenylazo)-8-hydroxyquinoline (Hq2) and 5-(4-nitrophenylazo)-8-hydroxyquinoline (Hq3) in toluene in aerobic condition afforded mononuclear orange coloured compounds having general formula [Rh(2-phpy)2(q)] in excellent yields. The complexes were substantiated by IR, 1H NMR, ESI-mass, EPR, UV–Vis and emission spectra, cyclic voltammetry, single-crystal X-ray structure determinations and density functional theory (DFT) calculations. Synthesis and comparison of their photophysical and electrochemical properties of a new branch of rhodium(III) complexes of 8-hydroxyarylazo analogues are presented which are never studied before. The ground and excited-state geometries, absorption, and emission properties of the complexes were examined by DFT and TDDFT methods. The excitations and emissions are investigated by the natural transition orbital (NTO) analysis. The emission occurred via 3MLCT or 3ILCT transition by theoretical analysis of triplet state DFT calculations. The cis-trans isomerism studies for the azo complexes have been done by experimental as well as theoretical analysis.

Sensitized Photochemical CO2 Reduction by Hetero-Pacman Compounds Linking a ReI Tricarbonyl with a Porphyrin Unit.

The hetero-Pacman architecture places two different metal coordination sites in close proximity, which can support efficient energy and/or electron transfer and allow for cooperative activation of small molecules. Here, the synthesis of dyads consisting of a porphyrin unit as photosensitizer and a rhenium unit as catalytically active site, which are held together by the rigid xanthene backbone, is presented. Mononuclear [(NN)Re(CO)3 (Cl)] complexes for CO2 reduction in which NN represents a bidentate diimine ligand (e.g., bipyridine or phenanthroline) lack light absorption in the visible region, resulting in poor photocatalysis upon illumination with visible light. To improve their visible-light absorption, we have focused on the incorporation of a strongly absorbing free base or zinc porphyrin unit. Resulting photocatalytic experiments showed a strong dependence of the catalytic performance on both the type of photosensitizer and the excitation wavelengths. Most notably, the intramolecular hetero-Pacman system containing a zinc porphyrin unit showed much better catalytic activity in the visible region (excitation wavelengths >450 nm) than the free base porphyrin version or the corresponding mononuclear rhenium compound or an intermolecular system comprised of a 1:1 mixture of the mononuclear analogues.

Reactivity of [Mo(CO)3(NCMe)3] towards pyrimidine-2-thiol (pymSH) and thiophenol (PhSH) in the presence of phosphine auxiliaries: Synthesis of mono- and dinuclear complexes bearing κ2 and µ,κ2-pymS coordination motifs

The reaction of [Mo(CO)3(NCMe)3] with added thiol in the presence of a phosphine auxiliary has been investigated. Treatment of [Mo(CO)3(NCMe)3] with pyrimidine-2-thiol (pymSH) and PPh3 at 60 °C in MeCN afforded the known mononuclear compounds cis-[Mo(CO)4(PPh3)2] (1) and [Mo(к2-pymS)4] (2), and the new binuclear compound [Mo2(CO)4(μ,к2-pymS)2(PPh3)2] (3), which possesses idealized C2 symmetry. A different product distribution was found when dppm was employed as the phosphine ligand. Of the five reaction products isolated, three consisted of mononuclear compounds, [Mo(CO)4(к2-dppm)] (4), [Mo(CO)3(κ2-dppm)(κ1-dppm)] (5) and [Mo(CO)(к2-pymS)2(к2-dppm)] (6), with the remaining two products corresponding to dinuclear compounds, [Mo2(CO)6(μ,к1-pymS)2(μ,к2-dppm)] (7) and [Mo2(CO)4(μ,к2-pymS)2(к2-dppm)] (8). Products 6–8 are new and have been fully characterized in solution by IR and NMR spectroscopy, and by X-ray crystallography in the case of 6 and 7. The reaction of [Mo(CO)3(NCMe)3] with PhSH and dppm at 60 °C in MeCN was also examined to assess the effect of thiol on the product distribution. The two principal products isolated were identified as the mononuclear compound [Mo(CO)2(κ1-PhS)2(κ2-dppm)] (9) and the dinuclear compound [Mo2(CO)6(μ,κ1-PhS)2(μ,κ2-dppm)] (10). The bonding in compounds 3, 6 and 7 was also examined by DFT, and highlights between the computational and experimental structures are discussed.

Hydrogen bonding and π-π interactions in the cocrystal salt [Fe(bpe)2(H2O)4](TCEP)2·2(bpe) [bpe is trans-1,2-bis(pyridin-4-yl)ethene and TCEP is 1,1,3,3-tetracyano-2-ethoxypropenide

The cocrystal salt tetraaquabis[trans-1,2-bis(pyridin-4-yl)ethene-κN]iron(II) bis(1,1,3,3-tetracyano-2-ethoxypropenide)-trans-1,2-bis(pyridin-4-yl)ethene (1/2), [Fe(C12H10N2)2(H2O)4](C9H5N4O)2·2C12H10N2, is a rare example of a mononuclear FeII compound with trans-1,2-bis(pyridin-4-yl)ethane (bpe) ligands. The complex cation resides on a crystallographically imposed inversion center and exhibits a tetragonally distorted octahedral coordination geometry. Both the symmetry-independent bpe ligand and the cocrystallized bpe molecule are essentially planar. The 1,1,3,3-tetracyano-2-ethoxypropenide counter-ion is nonplanar and the bond lengths are consistant with significant electron delocalization. The extended structure exhibits an extensive O-H...N hydrogen-bonding network with layers of complex cations joined by the cocrystallized bpe. Both the coordinated and the cocrystallized bpe are involved in π-π interactions. Hirshfeld and fingerprint plots reveal the important intermolecular interactions. Density functional theory was used to estimate the strengths of the hydrogen-bonding and π-π interactions, and suggest that the O-H...N hydrogen bonds enhance the strength of the π-interactions by increasing the polarization of the pyridine rings.

Coordination Compounds of Palladium(II) and 4‐Amino‐1,2,4‐triazole

Mononuclear coordination compounds of the type [Pd(NH2trz)4]2+ with the counterions chloride, nitrate, trifluoromethanesulfonate, and methanesulfonate were synthesized and their structures identified with single‐crystal X‐ray diffraction. In case of the synthesis with methanesulfonate as the counterion the dominant product was of the generic formula [Pd2(NH2trz)3](CH3SO3)4, and the complex [Pd(NH2trz)4](CH3SO3)2 only emerged as a byproduct. While the structure of the byproduct could be analyzed by single‐crystal X‐ray diffraction, suitable crystals of the main product [Pd2(NH2trz)3](CH3SO3)4 could not be obtained. However, stoichiometry implies a polynuclear nature with NH2trz present in the rare μ3‐η1:η1:η1 coordination type, i.e. with NH2trz molecules coordinating to three palladium atoms. Accordingly, identification of solids by single‐crystal analysis alone can be misleading in particular with NH2trz as a ligand due to its versatile coordination behavior. Finally, analysis by differential scanning calorimetry (DSC) revealed that the complexes were thermally stable (the onset of decomposition well above 100 °C), with [Pd2(NH2trz)3](CH3SO3)4 being the most stable compound (onset of decomposition at 204 °C).

Crystal structures and magnetic properties of nitroxide radical-coordinated copper(II) and cobalt(II) complexes

The crystal structures and magnetic properties of three coordination compounds constructed from various nitroxide radicals L and MII(hfac)2(H2O)2 building blocks (M = Cu or Co and hfac = hexafluoroacetylacetonato) are described. In [(1)Cu(hfac)2]n, 4, the radical ligand L is coordinated to the metal through the oxygen atom of the nitroxide group and oxygen atom of its hydroxyl group, leading to a one-dimensional chain system. In [(2)2Cu(hfac)2]n, 5, two hydroxyl oxygen atoms of the radical ligand are coordinated to the metal, and the CoII centers adopt distorted octahedral geometry to give a mononuclear compound. For [(L)Cu(hfac)2]n, 6, the oxygen atom of the nitroxide group and nitrogen atom of the amino group of L are coordinated to the metal, leading to a one-dimensional chain system. The magnetic susceptibility study of the copper coordination compound 4 revealed weak ferromagnetic interactions between the metal center and the organic radical. The cobalt coordination compounds 5 and 6 both show antiferromagnetic interactions.

New Manganese Complexes Showing Axially-Compressed Octahedral Geometry: Structure and Magnetic Properties

The straightforward combination of commercial picolinaldehyde and 2-aminopyridine led to the preparation of N,1-di(pyridin-2-yl)methanimine ligand HL1. Under aerobic conditions, HL1 self-assembles with manganese (Mn) ions to afford two high-spin mononuclear Mn(III) complexes of general formula [MnL22]+Cl (1) and [MnL22]+(NO3) (2). Their synthesis is mediated via (in situ) ligand transformation and oxidation of initial Mn(II) ions. Such unexpected reorganization contributes in the stabilization of the complexes. The mononuclear compounds 1 and 2 display unusual Jahn-Teller distortion along the z-axis, as evidenced by single-crystal X-ray diffraction and do exhibit an S = 2 ground spin state.

Synthesis and Characterization of New Sandwiched and multi Decker Palladium Organometallic Compounds of alkylated S-Indacene

A synthesis of mono nuclear bis indacene mono metal compound of type [L-M-L] where (L is 2,6-diethyl-4,8-dimethyl-1,5-dihydro-s-indacene, M=Pd. Pd-bis (ƞ5-2,6-diethyl-4,8-dimethyl-1,5-dihydro-s-indaceneide) [Pd (Ic'H)2], and the oligomeric form of this compound is successfully prepared. The prepared compound is of the type [L-M-L-M-L-M-L] where M= Pd and L =-2,6-diethyl-4,8-dimethyl-1,5-dihydro-s-indaceneide)}] [Ic'Pd(μ-Ic’) Pd (g-Ic’)Pdlc’] the reaction yields a almost quantitative yield. The synthesized compounds were characterized by NMR (1H and 13C), and elemental analysis. The spectroscopic data reveals the formation Multidecker compound. This oligomer is further subjected to catalytic property study

Discrete mononuclear and dinuclear compounds containing a MoO22+core and 4-aminobenzhydrazone ligands: synthesis, structure and organic-solvent-free epoxidation activity

New aroylhydrazone molybdenum(vi) complexes have been synthesized, characterized and used as (pre)catalysts for epoxidation of cyclooctene using aqueous TBHP as the oxidant.

Designing a mononuclear DyIII single-molecule magnet (SMM) by using a N,O,N,O-based multichelating Schiff base ligand and a β-diketonate ligand

Two mononuclear LnIII compounds, in which each LnIII is eight-coordinated, namely [Ln(L)(tmpd)] (Ln = Dy (1) or Er (2)), have been prepared using a multichelating Schiff base ligand (H2L) and a bidentate chelating β-diketonate ligand (tmpd).

Structural characterization and gas-phase studies of the [Ag10H8(L)6]2+ nanocluster dication.

The reactions between silver salts and borohydrides produce a rich set of products that range from discrete mononuclear compounds through to silver nanoparticles and colloids. Previous studies using electrospray ionization mass spectrometry (ESI-MS) to track the cationic products in solutions containing sodium borohydride, silver(i) tetrafluoroborate and the bisphosphine ligands, L, bis(diphenylphosphino)methane (dppm) and bis(diphenylphosphino)amine (dppa) have identified the dications [Ag10H8(L)6]2+. Here we isolate and structurally characterize [Ag10H8(dppa)6](BF4)2, and [Ag10H8(dppa)6](NO3)2via X-ray crystallography. Both dications have nearly identical structural features consisting of a Ag10 scaffold with the atoms lying on vertices of a bicapped square antiprism. DFT calculations were carried out to suggest potential sites for the hydrides. Ion-mobility mass spectrometry experiments revealed that [Ag10H8(dppa)6]2+ and [Ag10H8(dppm)6]2+ have similar collision cross sections, while multistage mass spectrometry experiments were used to compare their unimolecular gas-phase chemistry. Although the same initial sequential ligand loss followed by cluster fission and H2 evolution is observed, the more acidic N-H of the dppa provides a more labile H for H2 loss and H/D scrambling processes as revealed by isotope labelled experiments.

Effects of the Exchange Coupling on Dynamic Properties in a Series of CoGdCo Complexes.

Reaction of 2-hydroxy3-methoxybenzaldehyde ( o-vanillin) with 1,1,1-tris(aminomethyl)ethane, Me-C(CH2NH2)3, or with N, N', N''-trimethylphosphorothioic trihydrazide, P(S)[NMe-NH2]3, yields two tripodal LH3 and L1H3 ligands which are able to give cationic heterotrinuclear [LCoGdCoL]+ or [L1CoGdCoL1]+ complexes. The CoII ions are coordinated to these deprotonated ligands in the inner N3O3 site, while the GdIII ion is linked to three deprotonated phenoxo oxygen atoms of two anionic [LCo]- or [L1Co]- units. Air oxidation of these trinuclear complexes does not yield complexes associating CoIII and GdIII ions. With the first ligand, the structurally characterized resulting complex is the neutral mononuclear LCoIII compound, while in the second case, oxidation of the CoII ions turned out to be impossible. The [L1CoLnCoL1]+ complexes behave as single-molecule magnets with effective energy barriers for the reversal of magnetization varying from Ueff = 51.3 K, τo = 2 × 10-6 s for the yttrium complex to Ueff = 29.5, 29.4, 27.4 K and τo = 1.3 × 10-7, 1.47 × 10-7, 1.50 × 10-7 s for the gadolinium ones, depending on the used counteranions. The energy decrease is compensated by the suppression of quantum tunneling of magnetization in absence of applied field, thanks to the introduction of a ferromagnetic Co-Gd interaction. Current work also shows that uncritical use of conventional spin Hamiltonians, based on quenched orbital momenta, can be misleading and that ab initio calculations are indispensable for establishing the picture of real magnetic interaction. Ab initio calculations show that the CoII sites in the investigated compounds possess large unquenched orbital moments due to the first-order spin-orbit coupling resulting in strongly axial magnetic anisotropy. Although the CoII ions are not axial enough for showing slow relaxation of magnetization by themselves, blocking barriers of exchange type are obtained thanks to the exchange interaction with GdIII ions.

Encapsulation of Organic Dyes within an Electron‐Deficient Redox Metal‐Organic Tetrahedron for Photocatalytic Proton Reduction

AbstractThe design of artificial systems that mimic highly evolved and finely tuned natural photosynthetic systems is a subject of intensive research. By incorporating electron‐deficient anthraquinone within the ligand backbone, a redox‐active Ni‐based tetrahedron was developed as a redox vehicle for the construction of an artificial photosynthesis system. The tetrahedron can encapsulate fluorescein within its cavity for light‐driven H2 evolution, with the turnover number reaching 1200 moles H2 per mole redox catalyst. This well‐designed supramolecular system displayed a significantly superior activities compared with the reference mononuclear compound or introducing an inactive inhibitor (ATP), which confirmed this enzymatic photocatalytic behaviour.

Dual-site aqua mononuclear nickel(II) complexes of non-heme tetradentate ligands: Synthesis, characterization and reactivity

Mononuclear compounds [Ni(BQCNMe2)(H2O)2](ClO4)21 and [Ni(BQCNH2)(H2O)2](ClO4)22 of N,N′-dimethyl-N,N′-di(quinolin-8-yl)cyclohexane-1,2-diamine (BQCNMe2) and N,N′-di(quinolin-8-yl)cyclohexane-1,2-diamine (BQCNH2) were synthesised and characterized by elemental analysis, IR/UV-Vis spectroscopy, cyclic voltammetry (CV)/differential pulse voltammetry (DPV) and X-ray powder pattern. [Ni(BQCNMe2)(en)](ClO4)23 and [Ni(BQCNMe2)(phen)](ClO4)24 were prepared by reacting 1 with ethylenediamine (en) and 1,10-phenanthroline (phen) respectively while [Ni(BQCNH2)(en)](ClO4)25 and [Ni(BQCNH2)(phen)](ClO4)26 were obtained from the reaction of 2. Compounds [Ni(BQENMe2)(en)](ClO4)27 and [Ni(BQENH2)(en)](ClO4)2.CH3CN 8 (BQENMe2 is N,N′-dimethyl-N,N′-bis(8-quinolyl)ethane-1,2-diamine) and BQENH2 is N,N′-bis(8-quinolyl)ethane-1,2-diamine) were synthesised similarly. Compounds 6 and 8 were characterized by single crystal X-ray diffractometry and their structural features are presented. The reactivity of 2 with H2O2/base was investigated. A new peak at 570 nm in the UV-Vis spectrum corresponding to 2a was obtained which on addition of 2-phenylpropionaldehyde (2-PPA) decays giving pseudo-first order rate constant of 9.2 × 10−3 s−1 and acetophenone as a major product. The catalytic hydroxylation of cumene and ethylbenzene by 1 and 2 in the presence of meta-chloroperbenzoic acid (m-CPBA) was investigated.

Synthesis and characterization of a series of transition metal compounds of thioether and disulfide ligands

A series of mononuclear metal compounds [MII(L1SCH3)Cl2] (M = Co, Cu, Fe, Mn, L1SCH3 = 2-(methylthio)-N,N-bis(pyridin-2-ylmethyl)aminoethane) has been synthesized and characterized. The structures and spectroscopic properties of these compounds are compared to the related dinuclear compounds [MII2(L1SSL1)Cl4] (M = Co, Cu, Fe), which were obtained from the reactions of disulfide ligand L1SSL1 with the corresponding metal chloride salts (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide). The crystal structures show that the metal centers in the mononuclear compounds [CoII(L1SCH3)Cl2], [CuII(L1SCH3)Cl2] and [MnII(L1SCH3)Cl2] are in trigonal-bipyramidal geometries coordinated by three nitrogen donors of the tetradentate ligand and two chloride ions, with configurations similar to that of metal centers in [CoII2(L1SSL1)Cl4] and [CuII2(L1SSL1)Cl4]. In contrast, the iron(II) center in [FeII(L1SCH3)Cl2] is coordinated by three nitrogen donors and one sulfur atom of the tetradentate ligand and two chloride ions in an octahedral geometry, which is similar to the geometry of one of the Fe(II) centers in the dinuclear compound [FeII2(L1SSL1)Cl4], where two iron(II) centers are in different geometries. UV–vis spectra of the mononuclear compounds are comparable to those of the related dinuclear compounds.

Field‐induced Slow Magnetic Relaxation Behavior in a Mononuclear Dy(III) Complex based on 8‐Hydroxyquinoline Derivate Ligand

A mononuclear DyIII compound [Dy(quinbeyz)(NO3)2(DMF)] (1) based on 8‐hydroxyquinoline derivative ligand [quinbeyz = 8‐hydroxyquinoline‐2‐carboxyaldehyde‐(benzoyl)hydrazine] was synthesized and characterized by single‐crystal X‐ray diffraction analysis. The crystal structure showed that the DyIII ion of the compound is nine‐coordinate in a distorted capped square antiprism arrangement with pseudo‐C4v symmetry. Direct‐current (dc) magnetic susceptibilities revealed that compound 1 showed easy axial magnetic anisotropy. The crystal field parameters (CFPs) were obtained from fitting of the magnetic data, and the orientation of the magnetic easy axis of the central DyIII atom for compound 1 was calculated by the electrostatic model. It can be helpful further to understand the magnetic anisotropy of DyIII and the magneto‐structural relationship. Alternating current (ac) magnetic measurements demonstrated that compound 1 exhibited field‐induced slow magnetic relaxation behavior. These results demonstrated that an approach to achieve mononuclear lanthanide single‐molecule magnets (SMMs) with pseudo‐C4v symmetry could be effectively constructed by using 8‐hydroxyquinoline derivative ligand.

Centrosymmetric Binuclear Boron Compounds Derived from Dithiooxamides: Synthesis, Characterization, and Their Photophysical Properties

In this paper, we report the synthesis and characterization of new boron compounds derived from dithiooxamides. The compounds were characterized by NMR (1H and 13C), UV-vis, fluorescence spectroscopy, and high resolution mass spectrometry. The crystal structure of the mononuclear boron compound was determined by single-crystal X-ray diffraction analysis. The photophysical properties of the boron compounds were investigated, and we found moderate fluorescence emission (compound 2 ΦF: 4.07% and compound 4 ΦF: 2.89%). We also observed that the mononuclear complex presented greater stability. Compound 4 showed interesting luminescent properties; in solid state, it exhibited an increase in fluorescence by mechanostimuli by changing to a bright red color, and also in solution, it showed a decrease in fluorescence intensity when oxygen and air were supplied to the solution.

Solvatomorphism-Induced 45 K Hysteresis Width in a Spin-Crossover Mononuclear Compound.

Spin-transition compounds are coordination complexes that can present two stable or metastable high-spin and low-spin states at a given temperature (thermal hysteresis). The width of the thermal hysteresis (difference between the maximum and minimum temperature between which the compound exhibits bi-stability) depends on the interactions between the coordination complexes within the compound, and which may be modulated by the absence or presence of solvent within the structure. The new compound [Fe(3-bpp)2 ][Au(CN)2 ]2 (1, 3-bpp=2,6-di-(1H-pyrazol-3-yl)pyridine) was synthesized and its properties were compared with those of the solvated compound [Fe(3-bpp)2 ][Au(CN)2 ]2 ⋅2 H2 O (1.H2 O) already described. 1 has a two-steps thermal hysteresis of 45 K, in contrast to the compound 1.H2 O which exhibits a gradual conversion without hysteresis. This hysteretic transition is accompanied by a reversible reconstructive structural transition and twinning. This stepped behaviour is also observed in the photomagnetic properties despite the low efficiency of photoswitching. Single-crystal photocrystallographic investigations confirm this low conversion, which we attributed to the high energy cost to form the high-spin structure, whose symmetry differs from that of the low-spin phase.

Efficient copper-based DNA cleavers from carboxylate benzimidazole ligands.

Four copper(II) coordination compounds from 2-benzimidazole propionic acid (Hbzpr) and 4-(benzimidazol-2-yl)-3-thiobutanoic acid (Hbztb) were synthesized and fully characterized by elemental analyses, electronic spectroscopy, FT-IR and mass spectrometry. The molecular structure for the four complexes was confirmed by single-crystal X-ray crystallography. The DNA-interacting properties of the two trinuclear and two mononuclear compounds were investigated using different spectroscopic techniques including absorption titration experiments, fluorescence spectroscopy and circular dichroism spectroscopy. Trinuclear [Cu3(bzpr)4(H2O)2](NO3)2·3H2O·CH3OH (2) and [Cu3(bzpr)4Cl2]·3H2O (3) bind to DNA through non-intercalative interactions, while for mononuclear [Cu(bzpr)2(H2O)]·2H2O (1) and [Cu(bztb)2]·2H2O (4), at minor concentrations in relation to the DNA, a groove binding interaction is favored, while at higher concentrations an intercalative mode is preferred. The nuclease properties of all complexes were studied by gel electrophoresis, which showed that they were able to cleave supercoiled plasmid DNA (form I) to the nicked form (form II). Compound 4 is even capable of generating linear form III (resulting from double-strand cleavage). The proposed mechanism of action involves an oxidative pathway (Fenton-type reaction), which produces harmful reactive species, like hydroxyl radicals.