Terpy Ligand Research Articles

Cytotoxic gold(iii) complexes incorporating a 2,2':6',2''-terpyridine ligand framework - the impact of the substituent in the 4'-position of a terpy ring.

Two gold(iii) complexes incorporating 2,2':6',2''-terpyridine derivatives have been synthesised and characterized, and the possibility of tuning the cytotoxic activity by structural modifications of a terpy ligand has been examined. Both complexes [AuCl(4'-R1-terpy)](PF6)2 (1) and [AuCl(4'-R2-terpy)](PF6)2 (2), where R1 is 2-pyridyl and R2 is 3-pyridyl, show good anti-proliferative activities against HCT116, which are higher in relation to those of the free ligands, [AuCl(terpy)](PF6)2 and standard anticancer drug cisplatin. The cytotoxic properties of the gold complexes were examined by MTS assay, cell cycle and apoptosis analysis, ROS measurements, determination of mitochondrial membrane potential and mass, and staining of phosphatidylserine with Annexin-V antibody FITC-conjugated together with PI.

A ruthenium polypyridyl complex with the antihypertensive drug valsartan: Synthesis, theoretical calculations and interaction studies with human serum albumin

Coordination of widely used antihypertensive drug valsartan (val) to [Ru(bpy)(terpy)]2+ moiety resulted in the new complex [Ru(val)(bpy)(terpy)]+ which was characterized by electronic and vibrational spectroscopy, nuclear magnetic resonance, mass spectrometry, and electrochemistry. As probed by NMR, coordination of valsartan to Ru(II) occurred by tetrazol ring which is consistent with other spectroscopic and electrochemical data. Altogether, our data suggests that valsartan did not degrade upon coordination. Electronic-structure calculations performed at BP86/def2-TZVPP level of theory showed that the drug adopts the anti-configuration in [Ru(val)(bpy)(terpy)]+ due to hydrogen bonding interactions with terpy ligand and a Ru–Ntetrazole bond length of 2.050Å. Fluorescence spectroscopy binding studies of valsartan complex with human serum albumin indicated spontaneous interaction with a significant contribution of static mechanism. The Stern–Volmer quenching constant Ksv, and corresponding thermodynamic parameters ΔH, ΔS and ΔG were calculated. These parameters suggest that albumin-complex interaction is mainly entropy-driven and hydrophobic interactions predominate.

Carbonyl‐Terpyridyl‐Manganese Complexes: Syntheses, Crystal Structures, and Photo‐Activated Carbon Monoxide Release Properties

AbstractA set of tricarbonylmanganese(I) complexes derived from three differently substituted terpyridyl (terpy) ligands has been synthesized and characterized by various spectroscopic methods and single‐crystal X‐ray diffraction. The corresponding MnI dicarbonyl complexes, which are among the few examples of such compounds as yet described, were also prepared. The crystal structure of the Mn dicarbonyl species with the stabilizing p‐tolyl‐terpyridyl ligand was successfully obtained. The photochemical properties of all the tricarbonyl complexes have been investigated by using UV/Vis, IR, and NMR spectroscopy as characterization techniques; this detailed study shows the ability of the tricarbonyl MnI complexes to release one molar equivalent of CO in a perfectly controlled manner, a property useful for potential CO‐releasing molecules (CO‐RMs). The decarbonylation reaction is irreversible, and notably differs from what we had previously observed for the corresponding bipyridyl analogues as far as the products and kinetics are concerned. The comparison of the rate of CO decoordination of the different complexes is discussed.

Contractile and extensible molecular figures-of-eight.

Two large rings, 66- (m-66) and 78-membered (m-78) rings, each one incorporating two pairs of transition-metal-complexing units, have been prepared. The coordinating fragments are alternating bi- and tridentate chelating groups, namely, 2,9-diphenyl-1,10-phenanthroline (dpp) and 2,2',2',6''-terpyridine (terpy) respectively. Both macrocycles form molecular figures-of-eight in the presence of Fe(II) , affording a classical bis-terpy complex as the central core. The larger m-78 ring can accommodate a four-coordinate Cu(I) center with the formation of a {Cu(dpp)2 }(+) central complex and a highly twisted figure-of-eight backbone, whereas m-66 is too small to coordinate Cu(I) . Macrocycle m-78 thus affords stable complexes with both Fe(II) and Cu(I) ; the ligand around the metal changes from (terpy)2 to (dpp)2 . This bimodal coordination situation allows for a large amplitude rearrangement of the organic backbone. When coordinated to preferentially octahedrally coordinated Fe(II) or Cu(II) , the height of the molecule along the coordinating axis of the tridentate terpy ligands is only about 11 Å, whereas the height of the molecule along the same vertical axis is several times as large for the tetrahedral Cu(I) complex. Chemically or electrochemically driven contraction and extension motions along a defined axis make this figure-of-eight particularly promising as a new class of molecular machine prototype for use as a constitutive element in muscle-like dynamic systems.

Crystal structure of μ-peroxido-κ(4) O (1),O (2):O (1'),O (2')-bis-[(nitrato-κO)(2,2':6',2''-terpyridine-κ(3) N,N',N'')dioxidouranium(VI)

In the title dimeric complex, [{UO2(NO3)(C15H11N3)}2O2], a peroxide ion bridges the two uran­yl(VI) [O=U=O]2+ ions. The O—O bond length of the peroxide is 1.485 (6) Å and the mid-point of this bond is located at the inversion centre of the dimer. The U atom exhibits a distorted hexa­gonal–bipyramidal coordination geometry with two uran­yl(VI) O atoms occupying the axial positions and one O atom of the monodentate nitrate ion, both O atoms of the peroxide ion and the three N atoms of the chelating tridentate 2,2′:6′,2′′-terpyridine (terpy) ligand in the equatorial positions. Two of the N atoms of the terpy ligand lie above and below the mean plane containing the equatorial ligand atoms and the U atom [deviations from the mean plane: maximum 0.500 (2), minimum −0.472 (2) and r.m.s. = 0.2910 Å]. The dihedral angle between the terpy ligand and the mean plane is 35.61 (7)°. The bond lengths around the U atom decrease in the order U—N > U—Onitrate > U—Operoxo > U=O. The dimeric complexes pack in a three-dimensional network held together by weak π–π inter­actions [centroid–centroid distance = 3.659 (3) Å] between pyridyl rings of the terpy ligands in neighbouring dimers, together with inter­molecular C—H⋯O and C—H⋯π inter­actions. Weak intra­molecular C—H⋯O inter­actions are also observed.

Cyanide‐Bridged Tetranuclear REIII2FeIII2 (RE = Y, Tb, Dy) Molecular Squares with 2, 2′:6′,2′′‐Terpyridine as a Capping Ligand

Abstract Self‐assembly reaction between hydrated rare‐earth (RE) nitrates RE(NO3)3·6H2O with K3Fe(CN)6 in H2O/DMF solution by employing the tridentate ligand 2, 2′:6′,2′′‐terpyridine (terpy) as a capping ligand has yielded three cyanide‐bridged compounds [RE(terpy)(DMF)(H2O)2][Fe(CN)6]·6H2O [RE = Y (1), Tb (2), Dy (3)]. FT‐IR spectra confirmed the presence of terpy ligands and cyanide groups in compounds 1–3. Single‐crystal X‐ray structural analysis indicated that these compounds are isomorphous and adopt neutral [RE2Fe2] molecular squares, which are further linked through hydrogen bonding interactions to generate a three‐dimensional supramolecular network. Magnetic susceptibility measurements revealed that significant single ion magnetic anisotropy dominates the properties of these compounds.

Syntheses and Characterization of Cyanide‐Bridged Bimetallic Compounds Zn(terpy)(H2O)M(CN)4 (terpy = 2,2′:6′,2′′‐ter­pyridine; M = Ni, Pd, Pt) with Linear Chains

AbstractThe self‐assembly reaction of zinc ions with tetracyanometalates in the presence of the tridentate chelated ligand 2,2′:6′,2′′‐terpyridine (terpy) yielded three cyanide‐bridged bimetallic compounds of general formula Zn(terpy)(H2O)M(CN)4 [M = Ni (1), Pd (2), Pt (3)]. Compounds 1–3 were characterized by X‐ray diffraction (XRD), infrared spectroscopy (IR), and thermogravimetric (TG) analysis. Single‐crystal XRD analysis revealed that compounds 1–3 are isostructural and the structure consists of [Zn(terpy)(H2O)]2+ moieties and [M(CN)4]2– units linked alternatively to generate a one‐dimensional (1D) linear chain. The chains are further connected together through hydrogen bonding and π–π stacking interactions, forming a 3D supramolecular network. IR spectroscopic analysis indicated the presence of cyanide groups and terpy ligands in the structure. TG and powder XRD results showed that compounds 1–3 have higher thermal stabilities and exhibited irreversible for desorption/resorption of one coordinated water molecule.

Synthesis, structures, and photoluminescence properties of lanthanide dicyanoaurates containing dimeric aurophilic interactions

The synthesis of a series of lanthanide dicyanoaurates containing the ancillary ligand 2,2′:6′,2″-terpyridine (terpy) have been carried out by reaction of Ln3+ nitrate salts with terpy and potassium dicyanoaurate. The resultant compounds, [Ln(C15H11N3)(H2O)(NO3)2Au(CN)2] (Ln=Eu, Tb, Dy, Ho, Er, Yb), form an isostructural series as established by single-crystal X-ray diffraction studies. These studies reveal the existence of two important non-covalent interactions in these compounds. Dimeric aurophilic interactions and terpyridine π-stacking are both present with distances of ∼3.5Å for each. Photoluminescence measurements illustrate that the Eu3+ and Tb3+ compounds display enhanced Ln-based emission due to intramolecular energy transfer from the coordinated terpy ligands. Additionally, a [Au(CN)2−]2 dimeric excimer produces a broad, green emission band in this class of compounds, albeit reduced in intensity in several of the compounds where a reasonable energy match exists with Ln3+ excitation bands.

Influence of the Ligand Field on Slow Magnetization Relaxation versus Spin Crossover in Mononuclear Cobalt Complexes

The electronic and magnetic properties of the complexes [Co(terpy)Cl2 ] (1), [Co(terpy)(NCS)2 ] (2), and [Co(terpy)2 ](NCS)2 (3) were investigated. The coordination environment around Co(II) in 1 and 2 leads to a high-spin complex at low temperature and single-molecule magnet properties with multiple relaxation pathways. Changing the ligand field and geometry with an additional terpy ligand leads to spin-crossover behavior in 3 with a gradual transition from high spin to low spin.

First Homoleptic Complexes of the Tridentate Pyridine‐2,6‐ditetrazolate Ligand

AbstractThe synthesis and spectroscopic characterisation of a series of homoleptic complexes of the tridentate pyridine‐2,6‐di(5‐tetrazolate) ligand (pydtz2–) with CoII, NiII, CuII and ZnII are reported. Single‐crystal XRD data reveals the formation of octahedrally configured complexes [M(pydtz)2]2– for M = Zn or [M(Hpydtz)(pydtz)]– for M = Co or Ni, whereas for M = Cu a polymeric structure [Cu(pydtz)(EtOH)]n crystallised. In the latter, alternate short and long Cu···Cu distances were found. Magnetic measurements and electron paramagnetic resonance (EPR) spectroscopy reveal noncoupled S = 1/2 CuII ions for [Cu(pydtz)(EtOH)]n, S = 1/2 low‐spin configuration for the CoII complex and an S = 1 ground state for the NiII derivative. At T < 16 K the latter shows anomalies that resemble those of single‐ion molecular magnets. The ligand strength of pydtz2– is markedly higher than that of the bioisosteric pyridine‐2,6‐dicarboxylate (pydic2–) ligand and is very similar to that of the well‐established 2,2′:6′,2″‐terpyridine (terpy) ligand as revealed by the ligand field bands of the Co, Ni and Cu complexes and the magnetism of the Co and Ni derivatives. Solution electrochemical investigations suggest that essentially ligand‐centred reduction at rather negative potentials and metal‐centred oxidation processes occur.

Targeting [AuCl2(CN)2]− units as halophilic building blocks in coordination polymers

Several new [AuCl2(CN)2]−-containing complexes were synthesized with a range of ancillary ligands and first row transition metals. Use of Cu(II) and 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (Me2phen) with [nBu4N][AuCl2(CN)2] yielded the ionic compounds [Cu(phen)2(OHMe)][AuCl2(CN)2]2 (1) and {Cu(Me2phen)2[AuCl2(CN)2]}[AuCl2(CN)2] (2). Use of 2,2′;6′,2″-terpyridine (terpy) and Cu(NO3)2·3H2O or Cu(ClO4)2·6H2O instead yielded Cu(terpy)[AuCl2(CN)2]2 (3) and Cu(terpy)(μ-ClO4)[AuCl2(CN)2] (4), respectively. Compound (3) is molecular, with a single terpy ligand and two pendant [AuCl2(CN)2]− units bound to a Cu(II) centre, whereas 4 is a linear 1-D coordination polymer consisting of Cu(II) centres bridged by ClO4- moieties. Using Cu(II) and pyrazine (pyz) generates a1-D coordination polymer, Cu(pyz)(NCMe)2[AuCl2(CN)2]2·2MeCN (5) with bridging pyz units and pendant [AuCl2(CN)2]− and NCMe moieties. Upon switching to 4,4′-bipyridine (bipy), the 3-D coordination polymer, {Cu(bipy)2[Au(CN)2]}[AuCl2(CN)2] (6) results, which is built up of sheets of Cu(II)/bipy units bridged by [Au(CN)2]−. Free [AuCl2(CN)2]− anions sit in the network cavities, held by a rare, unsupported AuI⋯AuIII interaction of 3.4530(10)Å. The inability of [AuCl2(CN)2]− to act as a bridging unit in any of these ancillary ligand-containing structures is consistent with the behaviour of [AuBr2(CN)2]− in previous studies and shows that [AuCl2(CN)2]− holds no advantages over [AuBr2(CN)2]− in coordination polymer formation. In the absence of ancillary ligands, molecular Mn(OH2)4[AuCl2(CN)2]2 (7) and the 1-D coordination polymer Co(OH2)4[AuCl2(CN)2]2·2H2O (8), the first coordination polymer with [AuCl2(CN)2]− as the primary bridging moiety, were also prepared and structurally characterized.

Two New Copper(II) Complexes Based on Biphenyl-2,2’,6,6’-Tetracarboxylic Acid and Terpyridine: Synthesis, Crystal Structures, and Thermal Properties

Two new transition metal-organic complexes [Cu(H2bta) (Terpy)] (1) and [Cu2(Hbta)(Terpy)2(H2O)2]·(NO3)·2H2O (2) with biphenyl-2,2′,6,6′-tetracarboxylic acid (H4bta) and terpyridine (Terpy) ligands were obtained with the same chemicals in different pH by hydrothermal method and characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Complex 1 has a 1-D neutral coordination chain, whereas complex 2 exhibits a discrete structure, which is further associated together through hydrogen bonds and π ··· π interactons to give a 3D supramolecular structure. Additionally, the thermal stabilities of the two complexes were also investigated by thermogravimetric analysis.

Bis(tridentate) Ruthenium–Terpyridine Complexes Featuring Microsecond Excited-State Lifetimes

A series of heteroleptic bis(tridentate) ruthenium(II) complexes, each bearing a substituted 2,2':6',2″-terpyridine (terpy) ligand, is characterized by room temperature microsecond excited-state lifetimes. This observation is a consequence of the strongly σ-donating and weakly π-accepting tridentate carbene ligand, 2',6'-bis(1-mesityl-3-methyl-1,2,3-triazol-4-yl-5-idene)pyridine (C^N^C), adjacent to the terpy maintaining a large separation between the ligand field and metal-to-ligand charge transfer (MLCT) states while also preserving a large (3)MLCT energy. The observed lifetimes are the highest documented lifetimes for unimolecular ruthenium(II) complexes and are four orders in magnitude higher than that associated with [Ru(terpy)(2)](2+).

Synthesis and computational studies of Mg complexes supported by 2,2′:6,2′′-terpyridine ligands

The reactions of the substituted 2,2':6,2''-terpyridine ligands, 4'-mesityl-2,2':6',2''-terpyridine (mesitylterpy) (1a), 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine (tri-(t)Buterpy) (1b) and 4'-phenyl-2,2':6',2''-terpyridine (phenylterpy) (1c) with Grignard reagents were investigated. When half an equivalent of mesitylterpy or tri-(t)Buterpy were treated with MeMgBr in diethyl ether, the only products were (R-terpy)MgBr(2) (R = mesityl (5a), or tri-(t)Bu (5b)) and Me(2)Mg and a similar reaction was observed in THF. Compounds 5a and 5b were characterized by X-ray crystallography. Changing the Grignard reagent to PhMgBr also generated 5a and 5b along with Ph(2)Mg, while the reaction between MeMgCl or PhMgCl and 1a or 1b generated (R-terpy)MgCl(2) (R = mesityl (6a), or tri-(t)Bu (6b)) and either Me(2)Mg or Ph(2)Mg, respectively. The products from reactions between phenylterpy (1c) and Grignard reagents were highly insoluble and could not be fully characterized but appeared to be the same as those from reactions with 1a and 1b. In contrast to other studies using tridentate nitrogen ligands, which formed either mixed halide alkyl species or dihalide and bis(alkyl) species depending on whether the Grignard reagent was reacted with the ligand in diethyl ether or THF, the formation of mixed halide, alkyl complexes of the type (R-terpy)MgR'X (R' = Me or Ph; X = Cl or Br) or dialkyl species such as (R-terpy)MgR'(2) (R' = Me or Ph) was not observed here, regardless of the reaction conditions. DFT studies were performed to complement the experimental studies. The experimental results could not be accurately reproduced unless π-stacking effects associated with free terpyridine were included in the model. When these effects were included, the calculations were consistent with the experimental results which indicated that the formation of the terpy Mg dihalide species and R'(2)Mg (R' = Me or Ph) is thermodynamically preferred over the formation of mixed alkyl halide Mg species. This is proposed to be due to the increased steric bulk of the terpy ligand in the coordination plane, compared with other tridentate nitrogen donors.

Theoretical Studies on Structures and Spectroscopic Properties of Highly Efficient Phosphorescent [Ru(terpy)(phen)X]+ Complexes

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of three mixed-ligand Ru(II) complexes [Ru(terpy)(phen)X]+ (terpy=2,2′,6′,2″-terpyridine, phen=1,10-phenanthroline, and X=—C≡CH (1), X=Cl (2), X=CN (3)) were investigated theoretically using the density functional theory method. The ground and excited state geometries have been fully optimized at the B3LYP/LanL2DZ and UB3LYP/LanL2DZ levels, respectively. The absorption and emission spectra of the complexes in CH3CN solutions were calculated by time-dependent density functional theory with the PCM solvent model. The calculated bond lengths of Ru—C, Ru—N, and Ru—Cl in the ground state agree well with the corresponding experimental results. The highest occupied molecular orbital were dominantly localized on the Ru atom and monodentate X ligand for 1 and 2, Ru atom and terpy ligand for 3, while the lowest unoccupied molecular orbital were π* (terpy) type orbital. Therefore, the lowest-energy absorptions of 1 and 2 at 688 and 631 nm are attributed to a dyz (Ru)+π/p(X)→π* (terpy) transition with MLCT/XLCT (metal-to-ligand charge transfer/X ligand to terpy ligand charge transfer) character, whereas that of 3 at 529 nm is related to a dyz(Ru)+π(terpy)→π*(terpy) transition with MLCT and ILCT transition character. The calculated phosphorescence of three complexes at 1011 nm (1), 913 nm (2), and 838 nm (3) have similar transition properties to that of the lowest-lying absorption. It is shown that the lowest lying absorptions and emissions transition character of these Ru(II) complexes can be tuned by changing the electron-withdrawing ability of the monodentate ligand.

Electrostatic repulsion between the cations of (1-methyl-1H-imidazole-κN3)(2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)platinum(II) perchlorate nitromethane monosolvate prevents Pt...Pt interactions

The reaction between [Pt(terpy)Cl]·2H2O (terpy = 2′,2′′:6′,2′′-terpyridine) and 1-methyl­imidazole (MIm) in the presence of two equivalents of AgClO4 in nitro­methane yields the title compound, [Pt(C15H11N3)(C4H6N2)](ClO4)2·CH3NO2. The dicationic complexes are arranged in a staggered configuration. The torsion angle subtended by the 1-methyl­imidazole ring relative to the terpyridine ring is 114.9 (5)°. Inter­molecular C—H⋯O inter­actions between the perchlorate anions and the H atoms of the terpy ligand are observed. Consideration of related phenyl­bipyridyl complexes of platinum(II), which are monocationic, leads to the conclusion that the electrostatic repulsion between the dicationic chelates prevents the formation of Pt⋯Pt inter­actions. These inter­actions are a common feature associated with the monocationic species.

Complexation of Metal Ions, Including Alkali-Earth and Lanthanide(III) Ions, in Aqueous Solution by the Ligand 2,2′,6′,2′′-Terpyridyl

Some metal-ion-complexing properties of the ligand 2,2',6',2''-terpyridyl (terpy) in aqueous solution are determined by following the π-π* transitions of 2 × 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH ∼5, in the presence of electrolytes such as NaClO(4) or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at the ionic strength (μ) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K(1) values were determined for terpy with alkali-earth metal ions Mg(II), Ca(II), Sr(II), and Ba(II) and Ln(III) (Ln = lanthanide) ions La(III), Gd(III), and Lu(III) by titration of 2 × 10(-5) M free terpy at pH >5.0 with solutions of the metal ion. Log K(1)(terpy) was determined for Zn(II), Cd(II), and Pb(II) by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad π-π* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the π-π* transitions and thus broaden them. It is shown that log K(1)(terpy) for a wide variety of metal ions correlates well with log K(1)(NH(3)) values for the metal ions. The latter include both experimental log K(1)(NH(3)) values and log K(1)(NH(3)) values predicted previously by density functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]·CH(3)CH(2)OH·H(2)O (1) is reported as follows: triclinic, P1, a = 8.644(3) Å, b = 9.840(3) Å, c = 20.162(6) Å, α = 97.355(5)°, β = 97.100(5)°, γ = 98.606(5)°, V = 1663.8(9) Å(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) Å, while the four peripheral Ni-N bonds average 2.107(10) Å. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed.

Photodamage of a Mn(III/IV)-oxo mixed-valence compound and photosystem II: Evidence that a high-valent manganese species is responsible for UV-induced photodamage of the oxygen-evolving complex in photosystem II

The Mn cluster in photosystem II (PS II) is believed to play an important role in the UV photoinhibition of green plants, but the mechanism is still not clear at a molecular level. In this work, the photochemical stability of [Mn III(O) 2Mn IV(H 2O) 2(Terpy) 2](NO 3) 3 (Terpy = 2,2′:6′,2″-terpyridine), designated as Mn-oxo mixed-valence dimer, a well characterized functional model of the oxygen-evolving complex in PS II, was examined in aqueous solution by exposing the complex to excess light irradiation at six different wavelengths in the range of 250 to 700 nm. The photodamage of the Mn-oxo mixed-valence dimer was confirmed by the decrease of its oxygen-evolution activity measured in the presence of the chemical oxidant oxone. Ultraviolet light irradiation induced a new absorption peak at around 400–440 nm of the Mn-oxo mixed-valence dimer. Visible light did not have the same effect on the Mn-oxo mixed-valence dimer. We speculate that the spectral change may be caused by conversion of the Mn(III)O 2Mn(IV) dimer into a new structure - Mn(IV)O 2Mn(IV). In the processes, the appearance of a 514 nm fluorescence peak was observed in the solution and may be linked to the hydration or protonation of Terpy ligand in the Mn-oxo dimer. In comparing the response of the PS II functional model compound and the PS II complex to excess light radiation, our results support the idea that UV photoinhibition is triggered at the Mn 4Ca center of the oxygen-evolution complex in PS II by forming a modified structure, possibly a Mn(IV) species, and that the reaction of Mn ions is likely the initial step.

Iron oligopyridine complexes as efficient catalysts for practical oxidation of arenes, alkanes, tertiary amines and N-acyl cyclic amines with Oxone

The iron complexes [Fe(qpy)](ClO4)2 (1) (qpy = 2, 2′ : 6′, 2′′ : 6′′, 2′′′ : 6′′′, 2′′′′-quinquepyridine), [Fe2(spy)2](ClO4)4 (2) (spy = 2, 2′ : 6′, 2′′ : 6′′, 2′′′ : 6′′′, 2′′′′: 6′′′′, 2′′′′′-sexipyridine), [Fe2(septipy)2](ClO4)4 (3) (septipy = 2, 2′ : 6′, 2′′ : 6′′, 2′′′ : 6′′′, 2′′′′ : 6′′′′, 2′′′′′ : 6′′′′′, 2′′′′′′-septipyridine) and SBA-15-supported iron terpyridine complex (4) are efficient catalysts for the practical oxidation of alkenes, arenes, alkanes, tertiary amines and N-acyl cyclic amines using Oxone as the oxidant. With 1, 2, 3 or 4 as the catalyst, a variety of electron-rich and electron-deficient alkenes were oxidized to the corresponding epoxides in high isolated yields (up to 99%). The reaction of arenes with Oxone afforded quinones in up to 91% isolated yields. Selective C–H bond oxidation of saturated alkanes to alcohols/ketones and demethylation of tertiary amines to secondary amines were achieved in good product yields. For the oxidation of N-acyl cyclic amines, the ring-opened products were obtained in up to 75% isolated yield with up to 96% substrate conversion. All of these iron complexes can efficiently catalyse the oxidative C–C bond cross-coupling reaction of tertiary amines with NaCN in up to 86% isolated yield using (tBuO)2 as the terminal oxidant. The oligopyridine ligands were oxidatively robust and could be re-used by the addition of iron(II) salt to generate the iron catalystsin situ. The active SBA-15-supported terpy ligand could be re-used for the oxidative catalysis for five consecutive runs without significant loss of catalytic activity.

Voltammetry and in situscanning tunnelling spectroscopy of osmium, iron, and ruthenium complexes of 2,2′:6′,2′′-terpyridine covalently linked to Au(111)-electrodes

We have studied self-assembled molecular monolayers (SAMs) of complexes between Os(II)/(III), Fe(II)/(III), and Ru(II)/(III) and a 2,2',6',2''-terpyridine (terpy) derivative linked to Au(111)-electrode surfaces via a 6-acetylthiohexyloxy substituent at the 4'-position of terpy. The complexes were prepared in situ by first linking the terpy ligand to the surface via the S-atom, followed by addition of suitable metal compounds. The metal-terpy SAMs were studied by cyclic voltammetry (CV), and in situ scanning tunnelling microscopy with full electrochemical potential control of substrate and tip (in situ STM). Sharp CV peaks were observed for the Os- and Fe complexes, with interfacial electrochemical electron transfer rate constants of 6-50 s(-1). Well-defined but significantly broader peaks (up to 300 mV) were observed for the Ru-complex. Addition of 2,2'-bipyridine (bipy) towards completion of the metal coordination spheres induced voltammetric sharpening. In situ STM images of single molecular scale strong structural features were observed for the osmium and iron complexes. As expected from the voltammetric patterns, the surface coverage was by far the highest for the Ru-complex which was therefore selected for scanning tunnelling spectroscopy. These correlations displayed a strong peak around the equilibrium potential with systematic shifts with increasing bias voltage, as expected for a sequential two-step in situ ET mechanism.