Dinuclear Compounds Research Articles

Homo and hetero-bridged dinuclear copper(II) complex: Synthesis, X-ray structure and catalytic N-arylation

Two new dinuclear Cu(II) Schiff base compounds were synthesized, structurally characterized and their catalytic efficacy in N-arylation reaction was studied. Reaction of CuCl2 with two different polydentate Schiff base ligands viz. H2L1 (H2L1 = 1-(N-ortho-hydroxyacetophenimine)-ethane-2-ol) and H2L2 (H2L2 = 2-methoxy-6-[(2-hydroxyethylimino)methyl]phenol) has afforded two new very different in structure complexes [Cu2(HL1)2(µ-Cl)2]·(H2O)3 (1) and [Cu2L2(HL2)(µ-Cl)Cl]2·(H2O) (2). Complexes 1 and 2 were characterized by single crystal X-ray diffraction, FT-IR, elemental analysis, UV/Vis spectroscopic and TG/DTA studies. Complex 1 featured a simple dichloro-bridged dinuclear moiety, whereas 2 a hetero-bridged (chloro and phenolic oxygen) dinuclear compound. Catalytic efficacy towards N-arylation reactions between aryl iodide with aryl amine catalyzed by complexes 1 and 2 under homogeneous condition had been studied. Both the catalysts exhibited excellent catalytic efficacy in DMSO medium.

Efficient transfer of dithiolene ligands from nickel to cyclopentadienyl ruthenium complexes

The reaction of [CpRu(PPh3)2Cl] with [Ni(S2C2Ph2)2] in refluxing toluene produces the purple salt [CpRu(S2C2Ph2)(PPh3)][Cl], containing a rare example of a cationic dithiolene complex, in excellent yield. Chemical or electrochemical reduction of [CpRu(S2C2Ph2)- (PPh3)][Cl] causes a colour change to blue and formation of the corresponding neutral species [CpRu(S2C2Ph2)(PPh3)]. In contrast the reaction of [CpRu(CO)2Cl] with [Ni(S2C2Ph2)2] under similar conditions was unsuccessful, but dithiolene transfer could be induced at room temperature by the use of Me3NO as a decarbonylating agent. In this case the neutral paramagnetic complex [CpRu(S2C2Ph2)(CO)] was formed, together with a crystallographically characterised dinuclear compound [Ru2(μ-S2C2Ph2)(μ-CO)(CO)Cp2]. The different outcomes of these reactions are related to the σ-donor and π-acceptor properties of the ligands.

Crystal structures and luminescence properties of lanthanide complexes with 4-bromobenzoate and nitrogen heterocyclic ligands

Five crystals of lanthanide complexes with 4-bromobenzoate (p-BrBA), 2,4,6-tri(2-pyridyl)-1,3,5-trianzine (TPTZ) and 1,10-phenanthroline (Phen) ligands were synthesized. The structures of the complexes [Sm2(TPTZ-TPTZ)(p-BrBA)4] (1), [Eu2(TPTZ)2(p-BrBA)6] (2), [Tb(TPTZ)(p-BrBA)3(H2O)] (3), [Tb2(Phen)2(p-BrBA)2Ac4] (4) and [Dy2(Phen)2(p-BrBA)6] (5) were determined by single-crystal X-ray diffraction. The crystals 1, 5 belong to monoclinic crystal system, and the other three crystals belong to triclinic crystal system. The dinuclear compound [Sm2(TPTZ-TPTZ)(p-BrBA)4] possesses a coupled [TPTZ-TPTZ]2- ligand that coordinates with two Sm3+ ions in both tridentate and bidentate coordination modes. To investigate the luminescence properties of the complexes, six complexes with similar composition in the powder form were also synthesized, whose formulas are [Eu(TPTZ)(p-BrBA)3(H2O)2], [Tb(TPTZ)(p-BrBA)3(H2O)], [Eu2(Phen)(p-BrBA)3Ac3], [Tb(Phen)(p-BrBA)3], [Sm(TPTZ)(p-BrBA)3(H2O)] and [Dy(Phen)(p-BrBA)3]. The luminescence intensity, luminescence lifetime and quantum efficiency of Eu and Tb complexes with Phen ligand are remarkably superior to the corresponding TPTZ complexes. This difference may mainly result from the stronger structural rigidity of the Phen ligand, which reduces the non-radiative transition of the complexes.

Two dinuclear lanthanide complexes based on a salicylamide imine multidentate ligand: Synthesis, structure and NIR emission properties

Two dinuclear lanthanide complexes, [Er2(HL)2(NO3)4]·2CH3CN∙CH3OH (1) and [Yb2(HL)2(NO3)4]·3CH3CN∙CH3OH (2) based on a salicylamide imine multidentate ligand, H3L = 1-(2-hydroxy-benzamido)-2-(3-hydroxy-naphthaleneamino)-ethane, were prepared and well characterized by elemental analysis, IR spectra, thermogravimetric analysis as well as X-ray diffraction analysis. Single crystal X-ray diffraction shows that the two phenol oxygen atom bridged dinuclear compounds are isomorphous where two deprotoned HL2− ligands possess the same coordination mode with the naphtol and amide oxygen atom coordinating to one Er(III) ion and phenol oxygen atom from salicylamide bridging two Er(III) ions. Photophysical studies indicates that 1 and 2 exhibit near-infrared emissions characteristic of Er(III) and Yb(III) ions and these effective sensitizations are approved by DFT calculation. The results presented herein indicate that the deprotoned HL2− not only offers a good protection for Er(III) and Yb(III) ions but also exhibits a good antennae effect with respect to Er(III) and Yb(III) ions as a result of efficient ligand to metal energy transfer.

Modulating Magnetic Property of Phthalocyanine Supported MII-DyIII (M = Ni, Zn) Heterodinuclear Complexes.

Three heterometallic dinuclear compounds, [MIIDyIII(L)(Pc)(ROH)]·ROH (R = CH3, M = Ni (1), Zn (2); R = C2H5, M = Zn (3)), were stepwise synthesized based on phthalocyanine (H2Pc) and one tripodal Schiff-base ligand 1,1,1-tris[(salicylideneamino)methyl]ethane (H3L). All of them have been studied structurally and magnetically. The six-coordinate MII ion and the seven-coordinate DyIII ion are bridged by two phenolic oxygen atoms to form an MII-LnIII heterodinuclear unit. Magnetic measurements indicate that the ferromagnetic NiII-DyIII interaction is operative in compound 1 and all three compounds exhibit the field-induced slow relaxation of magnetizations. In particular, compounds 2 and 3 have the improved magnetic performance. Ab initio calculations indicate that the weak NiII-DyIII interaction decreases the energy barrier, while the replacement of the paramagnetic NiII ion by the diamagnetic ZnII in compound 2 and 3 not only controls the magnetic interaction but also alters the local magnetic axes of DyIII ions to optimize the magnetic relaxation behavior.

Structural characterization and emission properties of mixed-ligand transition metal coordination complexes with dicarboxylic acids and pyrazinecarboxamide

Five new transition metal coordination compounds based on pyrazinecarboxamide and dicarboxylic acids have been prepared, and their structures have been characterized by IR spectroscopy and single crystal X-ray diffraction. The crystalline solids include one dinuclear compound [Cu2(mal)2(pca)2(H2O)2]·H2O (1), three one-dimensional coordination polymers [M(mal)(pca)(H2O)]n M = Co(II), Zn(II) (2, 3), [Cu2(CH3COO)4(pca)]n (4) and one two-dimensional coordination polymer [Cd(bdc)(pca)(H2O)]n (5), where pca = pyrazinecarboxamide, H2mal = malonic acid and H2bdc = 1,4-benzenedicarboxylic acid. The pca coordinates to the metal centers as a neutral ligand in chelating (1, 2, 3), bidentate bridging (4) and monodentate modes (5), while the bidentate acetate, malonate and benzenedicarboxylato anionic ligands provide extensions of structures. The new compounds 1, 3 and 5 reveal violet and ultraviolet luminescence upon excitation with ultraviolet light.

A Luminescent Thermometer Exhibiting Slow Relaxation of the Magnetization: Toward Self-Monitored Building Blocks for Next-Generation Optomagnetic Devices.

The development and integration of Single-Molecule Magnets (SMMs) into molecular electronic devices continue to be an exciting challenge. In such potential devices, heat generation due to the electric current is a critical issue that has to be considered upon device fabrication. To read out accurately the temperature at the submicrometer spatial range, new multifunctional SMMs need to be developed. Herein, we present the first self-calibrated molecular thermometer with SMM properties, which provides an elegant avenue to address these issues. The employment of 2,2′-bipyrimidine and 1,1,1-trifluoroacetylacetonate ligands results in a dinuclear compound, [Dy2(bpm)(tfaa)6], which exhibits slow relaxation of the magnetization along with remarkable photoluminescent properties. This combination allows the gaining of fundamental insight in the electronic properties of the compound and investigation of optomagnetic cross-effects (Zeeman effect). Importantly, spectral variations stemming from two distinct thermal-dependent mechanisms taking place at the molecular level are used to perform luminescence thermometry over the 5–398 K temperature range. Overall, these properties make the proposed system a unique molecular luminescent thermometer bearing SMM properties, which preserves its temperature self-monitoring capability even under applied magnetic fields.

Influence of Common Anions on the Coordination of Metal Cations in Polyalcohols

Polyalcohols (polyols), such as ethylene glycol, have mild reducing ability. They are used in the so‐called polyol process to produce metallic nanoparticles of various kinds. In these syntheses, the effective reduction potential of the polyol strongly depends on the presence of other anions. Those anions compete against the polyol molecules for the direct bonding to the metal cations. As an indicator for the coordination behavior of polyols, we crystallized and structurally characterized 19 new coordination compounds with Mn, Co, Ni, Cu, Zn, Cd, Pb, or Bi. 15 of these compounds comprise nitrate ions, the others acetate ions. Compared to the already known chloride and sulfate analogues, nitrate shows an intermediate coordination affinity towards the metal cations considered here. While no direct metal–nitrate coordination occurs with Co2+, Ni2+, and Zn2+, mixed nitrate–polyol coordination environments are found for Mn2+, Cu2+, Cd2+, and Bi3+. Because of its strong chelating property, the acetate ion always coordinates the metal cation, competing with the polyol. The first mononuclear and dinuclear metal acetate diol coordination compounds were obtained with Co2+ and Cu2+, respectively. The coordination affinity of nitrate and acetate ligands in solid metal polyol complexes fully corresponds with our recent observations of the anion‐dependent reduction behavior of copper(II) salts in polyols.

Crystal structures and magnetism of novel dinuclear dipicolinate compounds containing neocuproine

Two novel dinuclear dipicolinate compounds of the formulae [Ni2(neo)(H2O)2(μ-dipic)(dipic)]∙6H2O (1) and [Co2(neo)(H2O)2(μ-dipic)(dipic)]∙0.5neo∙3H2O (2), where neo means neocuproine (2,9-dimethyl-1,10-phenanthroline) and dipic is dipicolinate (pyridine-2,6-dicarboxylate) ligand, have been synthesized, characterized by IR and VIS spectroscopy as well as by single crystal X-ray diffraction analysis and magnetic measurements. The Ni(II) or Co(II) metal centres are connected together through one μ-bridging dipicolinate ligand, while the second dipicolinate is only terminal chelating. The neocuproine molecule is in both cases coordinated in a bidentate chelating manner and the coordination sphere around Ni(II) or Co(II) atom is completed by terminal aqua ligands. Magnetic study revealed antiferromagnetic exchange interaction between the Ni(II) or Co(II) metal centres.

Synthesis, structures and magnetic refrigeration properties of four dinuclear gadolinium compounds

Four new Gd2 compounds, [Gd2(L1)2(acac)2(CH3O)2] (1), [Gd2(L1)2(beac)2(OH)2] (2), [Gd2(L2)2(C4H10O3)2(CH3OH)2] (3) and [Gd2(L3)2(acac)2(CH3O)2] (4), were synthesized by solvent evaporation methods and studied by structural analyses and magnetic analyses. Crystallographic studies reveal that these compounds are dinuclear compounds and each center Gd(III) ion is eight-coordinated. The magnetic studies reveal that 1–4 display cryogenic magnetic refrigeration properties with −ΔSMax values of 24.80 J kg−1 K−1 for 1 (T = 3.0 K and ΔH = 7.0 T), 25.45 J kg−1 K−1 for 2 (T = 2.0 K and ΔH = 7.0 T), 21.12 J kg−1 K−1 for 3 (T = 3.0 K and ΔH = 7.0 T), and 31.33 J kg−1 K−1 for 4 (T = 2.0 K and ΔH = 7.0 T).

Modulating dynamic magnetic behaviors of dysprosium(III) dinuclear compounds based on a Schiff base-like ligand by using two different β-diketone coligands

Two new Dy2 compounds, namely, [Dy2(acac)2(H2L)2(CH3O)2] (1) and [Dy2(beac)2(H2L)2(CH3O)2] (2) (Hacac = acetylacetone, Hbeac = 1-benzoylacetone, and H3L = 2-[(2-hydroxybenzhydrazide)methyl]-8-hydroxyquinoline), have been successfully synthesized, structurally and magnetically characterized. The single-crystal X-ray diffraction data show that both 1 and 2 are phenoxo-O-bridged dinuclear complexes with similar structures; each eight-coordinated center Dy(III) ion is connected by one bidentate β-diketone coligand, one CH3O− and two μ-O bridging Schiff base ligands. The magnetic investigation reveal that 1 and 2 exhibit different magnetic relaxation behaviors with the anisotropic barriers of 2.17 K (1) and 20.56 K (2). The different SMMs behaviors of 1 and 2 originate from the different coordination environments of the central Dy(III) ions with different β-diketone coligands.

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.

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.

Effect of the change of the ancillary carboxylate bridging ligand on the SMM and luminescence properties of a series of carboxylate-diphenoxido triply bridged dinuclear ZnLn and tetranuclear Zn2Ln2 complexes (Ln = Dy, Er).

Eleven new dinuclear and tetranuclear compounds of general formulae [Zn(μ-L)(μ-X)Ln(NO3)2]·nS, [Zn2Dy2(μ3-L')2(μ-sal)2(NO3)(CH3OH)](NO3)·5CH3OH and [Zn2Er2(μ3-L')2(μ-sal)2(CH3OH)2](NO3)2·4CH3OH (X = benzoate, anthracenate, diclofenac, salicylate, 2,6-dihydroxybenzoate; Ln = Dy, Er; S = water, acetonitrile, methanol) were prepared from the N,N'-dimethyl-N,N'-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine compartmental ligand (H2L). Complexes 1-6 and 9-11 consist of diphenoxido-carboxylate triply bridged compounds, which differ mainly in the carboxylate bridging ligand. It should be noted that the acidic character of the salicylic acid promotes, in the presence of methanol, the methoxylation of the H2L ligand thereby yielding a hemiacetal H3L', which is able to connect the Ln(iii) ions of two ZnLn dinuclear units forming the Zn2Ln2 tetranuclear complexes 7 and 8. All compounds display SMM behaviour in the presence of an external field with effective energy barriers (Ueff) as high as 61 K. Magneto-structural data for these complexes reveal that their SMM behaviour is not only significantly affected by the type of Ln(iii) ion but also by the carboxylate bridging ligand connecting the Zn(ii) and Ln(iii) ions. Photoluminescence properties have also been accomplished, showing that the ligands are able to sensitize lanthanide centred emissions in the visible and near-infrared regions with variable capacity. Moreover, the analysis of the luminescence decay curves reveals emission lifetimes in the range of few microsecond or hundreds of nanoseconds for Dy(iii)-based or Er(iii)-based luminophores, respectively.

Influence of geometric isomerism on the binding of platinum anticancer agents with phospholipids.

Reported herein is a detailed NMR and DFT study of the interaction of the 15N-labelled dinuclear platinum anticancer compound [{cis-PtCl(NH3)2}2{μ-H2N(CH2)6NH2}]2+ (15N-1, 1,1/c,c) with 1,2-dihexanoyl-sn-glycero-3-phosphate (DHPA), as a comparison with an earlier study of the interaction of the same water-soluble phospholipid fragment with the geometric trans isomer (1,1/t,t). The reaction of 15N-1 with the sodium salt of DHPA was studied at 298 K, pH ∼ 5.6, by [1H,15N] HSQC 2D NMR spectroscopy. The NMR data, supported by DFT models, provide evidence that the monofunctional DHPA adduct of 15N-1 exists in two conformational forms, with different orientation of the (CH2)6 linker; one has an interaction between the unbound {PtN3Cl} moiety and the coordinated DHPA molecule. Similarly, two bifunctional adduct conformers are identified, in which one has an interaction between the phosphate groups of the two bound DHPA molecules. When compared to the previously reported reactions of 1,1/t,t with DHPA, equilibrium conditions of the 1,1/c,c reaction are reached more slowly (120 h), similar to the reaction with phosphate. The rate constant for the first step of DHPA binding (kL) is slightly lower (1.6 fold) for the cis-compared to the trans-isomer, whereas the rate constant for the reverse reaction is 4-fold lower, resulting in a much greater proportion of DHPA bound species at equilibrium.

Chiral dinuclear Ln(iii) complexes derived from S- and R-2-(6-methoxy-2-naphthyl)propionate. Optical and magnetic properties.

The reaction of LnCl3·6H2O with (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid (S-HL), best known as naproxen, and 1,10-phenanthroline (phen) in EtOH allows the isolation of dinuclear chiral compounds S-1-4 of the formula [Ln2(S-L)6(phen)2]·3DMF·H2O [Ln(iii) = Eu (1), Gd (2), Tb (3) and Dy (4)]. The use of the R-enantiomeric species of the HL ligand led to complexes R-1-4 with the formula [Ln2(R-L)6(phen)2]·3DMF·H2O. Compounds R- andS-1, 3 and 4 show strong sensitized metal-centred luminescence in the visible region. Moreover, Dy(iii) complexes R- andS-4 display field-induced single-molecule magnet (SMM) behaviour. For chiral and emissive compounds circularly polarized luminescence (CPL) measurements have also been performed.

Luminescent properties of a 3,5-diphenylpyrazole bridged Pt(ii) dimer.

We report the synthesis, electrochemistry, photophysical properties and electroluminescence of a highly luminescent pyrazolate-bridged platinum(ii) complex. The complex has the general formula of [((N^C^N)Pt)2(μ-pz)][PF6] where N^C^N = 1,3-di(2-pyridyl)benzene and μ-pz = 3,5-diphenylpyrazolate. The X-ray structure shows that the bridging pyrazolate ligand causes a close Pt-Pt interaction of 3.05(7) Å. The emission profile of the complex was determined in solution, glassy 2-methyltetrahydrofurane at 77 K, and the solid state at both room temperature and 77 K. Each emission profile displayed a strong red metal-metal-to-ligand charge transfer while the solution and glassy 2-methyltetrahydrofurane emission profiles also displayed a ligand-centred transition. The absolute quantum yields of the complex in solution and the solid state at room temperate are 86% and 39%, respectively. Light-emitting electrochemical cells (LEECs) of [((N^C^N)Pt)2(μ-pz)][PF6] were fabricated which displayed appreciable electroluminescence, among the brightest and most efficient LEECs from dinuclear compounds to date.

Mechanochemical and slow-chemistry radical transformations: a case of diorganozinc compounds and TEMPO.

From the green chemistry perspective, molecular solid-state transformations conducted under mild conditions are of great interest and desirability. However, research in this area lacked popularity in the previous century, and thus progressed slowly. In particular, the application of radical reactions in solid-state chemistry has been hampered by several long-standing challenges that are intrinsically associated with the apparent unpredictable nature of radical chemistry. We present a comparative study of model mechanochemical, slow-chemistry and solution radical reactions between TEMPO and homoleptic organozinc compounds (i.e., di-tert-butylzinc and diphenylzinc). In the case of the tBu2Zn/TEMPO reaction system only a dimeric diamagnetic complex [tBuZn(μ-TEMPO*)]2 is obtained in yields slightly varying with the method chosen. In contrast, when TEMPO is mixed with diphenylzinc in a 2 : 1 molar ratio a novel paramagnetic Lewis acid-base adduct [[Ph2Zn(η1-TEMPO)]·TEMPO] is isolated in high yields regardless of the applied methodology. This adduct is also formed in the slow-chemistry process when TEMPO is gently mixed with Ph2Zn in a 1 : 1 molar ratio and left for two weeks at ambient temperature. Within the next week the reaction mixture gives in high yield a diamagnetic dinuclear compound [PhZn(μ-TEMPO*)][PhZn(μ2-η1:η1-TEMPO*)] and biphenyl. The analogous reaction conducted in toluene results in a much lower conversion rate. The reported results open up a new horizon in molecular solid-state radical transformations.

Electron/energy transfer studies on hybrid materials based on dinuclear coordination compounds of twisted perylene diimide

To understand the influence of transition metal ion coordination on the properties and performance of the triads, the symmetric bridging ligand, 1,10-phenanthroline-perylene diimide-1,10-phenanthroline, 1,10-Phen-PDI-1,10-Phen (1) comprising four electron-donating 4-methoxyphenoxy bulky groups at bay-positions and its corresponding square-planar coordination compounds with dichloroplatinum(II), [{PtCl2}2-1] (2) and palladium(II) [{PdCl2}2-1] (3) were prepared in order to tune the photochemical and optical properties of these hybrid materials. These triads show strong electronic absorption bands attributed to the PDI and M(II)(1,10-Phen)Cl2 moieties in DMSO. UV–vis absorption spectra of the compounds were calculated using Time-Dependent Density Functional Theory (TDDFT) for the ground state optimized structures in DCM. Current results indicate that 2 has the lowest HOMO-LUMO gap (2.29 eV in DCM) among the investigated molecules. The energy and charge transfer processes with tailoring molecular structures are one of the important strategies for the design of future functional triads based on donor and acceptor moieties for hybrids optoelectronic devices. Thus, we studied linear absorption, fluorescence, and ultrafast transient absorption spectra measurements for the triads in DCM to investigate the impact of different functionalization strategies on the optical characteristics, photo-stability, and photo-induced charge-transfer (CT) processes. The observed ultrafast intramolecular charge transfer from donor units to acceptor part of 1–3 is related to fluorescence quenching and faster singlet state decay on transient absorption measurements. The intramolecular charge transfer mechanism was also compared with the unsymmetrical counterparts that were investigated previously. Symmetrical compounds exhibit faster charge transfer in comparison with the unsymmetrical compounds.

Activation by Oxidation: Ferrocene-Functionalized Ru(II)-Arene Complexes with Anticancer, Antibacterial, and Antioxidant Properties.

Organometallic Ru(II)-cymene complexes linked to ferrocene (Fc) via nitrogen heterocycles have been synthesized and studied as cytotoxic agents. These compounds are analogues of Ru(II)-arene piano-stool anticancer complexes such as RAPTA-C. The Ru center was coordinated by pyridine, imidazole, and piperidine with 0-, 1-, or 2-carbon bridges to Fc to give six bimetallic, dinuclear compounds, and the properties of these complexes were compared with their non-Fc-functionalized parent compounds. Crystal structures for five of the compounds, their Ru-cymene parent compounds, and an unusual trinuclear compound were determined. Cyclic voltammetry was used to determine the formal MIII/II potentials of each metal center of the Ru-cymene-Fc complexes, with distinct one-electron waves observed in each case. The Fc-functionalized complexes were found to exhibit good cytotoxicity against HT29 human colon adenocarcinoma cells, whereas the parent compounds were inactive. Similarly, antibacterial activity from the Ru-cymene-Fc compounds was observed against Bacillus subtilis, but not from the unfunctionalized complexes. In both cases, the IC50 values correlated quantitatively with the Fc+/0 reduction potentials. This is consistent with more facile oxidation to give ferrocenium, and subsequent generation of toxic reactive oxygen species, leading to greater cytotoxicity. The antioxidant properties of the complexes were quantified by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. EC50 values indicate that linking of the Ru and Fc centers promotes antioxidant activity.