Synthesis and characterization of new oligomeric and polymeric complexes based on the [Cu(bpca)] unit [Hbpca = bis(2-pyridylcarbonyl)amine]

Five novel bpca-based Cu(II) polynuclear coordination compounds [Hbpca = bis(2-pyridylcarbonyl)amine] were prepared using the [Cu(bpca)(H₂O)₂](NO₃)·2H₂O (1) building block and characterized by single crystal X-ray diffraction. We have also isolated and characterized two new crystal forms of the starting species, with lower water contents. Three of the new products are dinuclear complexes obtained by reacting 1 with different rigid or flexible spacer ligands: [Cu₂(bpca)₂(H₂O)₂(bipy)](NO₃)₂·6H₂O (2) (bipy = 4,4′-bipyridine) and [Cu₂(bpca)₂(H₂O)₂(bpete)](NO₃)₂·xH₂O (3) [bpete = (E)-1,2-di(pyridin-4-yl)ethane] are linear dumbbell-like species with Cu?Cu separations of 11.075 and 13.275 Å, respectively. The third dinuclear compound, [Cu₂(bpca)₂(H₂O)₂(bpx)](NO₃)₂·8H₂O (4) [bpx = 1,4-bis((1H-pyrazol-1-yl)methyl)benzene], with the flexible bpx ligand, assumes an unusual S-shaped conformation and shows a quite shorter Cu?Cu contact of 6.869 Å only. We have also obtained a chiral 1D neutral polymeric complex, [Cu₃(bpca)₂(bipy)₃(NO₃)₄]·6H₂O (5), that shows a central linear -Cu-bipy-Cu- chain, with all these Cu atoms connected to two lateral [Cu(bpca)(NO₃)₂]⁻ groups on two opposite sides by means of bipy spacers. An unprecedented type of Cu(II) neutral trinuclear complex, [Cu₃(bpca)₂(H₂O)₂(NO₃)₂] (6), was obtained which has a centrosymmetric structure with two external [Cu(bpca)(NO₃)₂]⁻ units chelating on a central copper atom via the two pairs of carbonyl groups of the bpca ligands. The central metal is octahedral with two axial water molecules, while the two lateral Cu atoms are in square pyramidal geometry; the Cu?Cu separation is 5.205 Å. The magnetic properties of 6 have been rationalized through a ferromagnetic coupling between the central metal ion and the peripheral ones which are coupled by a smaller antiferromagnetic interaction. DFT calculations have been also performed in order to give a better insight into magnetic interactions.     

[Benzilato(2−)-O,O]bis[1,3-diphenylpropane-1,3-dionato(1−)-O,O]silicon(IV): a neutral heteroleptic hexacoordinate silicon(IV) complex with an SiO6 skeleton

Reaction of tetramethoxysilane with 1,3-diphenylpropane-1,3-dione and benzilic acid (molar ratio 1:2:1) in tetrahydrofuran/n-pentane yielded the neutral heteroleptic hexacoordinate silicon(IV) complex [benzilato(2−)-O¹,O²]bis[1,3-diphenylpropane-1,3-dionato(1−)-O,O]silicon(IV) (5). Compound 5 was structurally characterized by single-crystal X-ray diffraction, solid-state VACP/MAS NMR spectroscopy (²⁹Si), and solution NMR spectroscopy (¹H, ¹³C, ²⁹Si). The chiral silicon(IV) complex, with its octahedral SiO₆ coordination polyhedron, is configurationally stable in solution on the NMR time scale (solvent: CDCl₃; maximum temperature studied: 58 °C).     

The synthesis and characterisation of phenolate complexes of Cu(II) and Ni(II) that are capable of supporting a phenoxyl radical ligand

New Cu^II and Ni^II complexes of potentially tridentate N₂O Schiff base ligands 1 and 2 have been synthesised and characterised. [Cu(2)(OH₂)]⁺ possesses a square planar geometry in the solid state whereas [Ni(1)₂] possesses a distorted octahedral geometry in which the amine donors of 1 coordinate weakly to the Ni^II centre. EPR spectroscopy demonstrates that the N₂O₂ coordination sphere of [Cu(2)(OH₂)]⁺ is retained in CH₂Cl₂ solution. [Cu(2)(OH₂)]⁺ exhibits a reversible one electron oxidation at E_1/2 = 0.54 V versus [Fc]⁺/[Fc], the product of which has been characterised by UV-Vis absorption and EPR spectroscopies. The spectroscopic signature of the oxidised product is consistent with the formation of a stable phenoxyl radical ligand bound to a Cu^II centre. [Ni(1)₂] possesses a reversible metal-based oxidation process at E_1/2 = 0.03 V versus [Fc]⁺/[Fc] and a further oxidation, attributed to the generation of a phenoxyl radical centre, at  = 0.44 V versus [Fc]⁺/[Fc]. UV-Vis absorption and EPR spectroscopic studies indicate that the lower potential process is a formal Ni^III/II couple. In contrast, the pro-ligands 1H and 2H exhibit chemically irreversible oxidation processes at  = 0.42 and 0.40 V versus Fc⁺/Fc, respectively, and do not support the formation of stable phenoxyl radical species.     

Synthesis and characterization of ruthenium(II) complexes bearing the bis(2-pyridylmethyl)amine ligand

The reaction of [Ru(CO)₂Cl₂]_n with bis(2-pyridylmethyl)amine (bpma) in refluxing ethanol followed by anion exchange yields two products: cis,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1a, 71%) and trans,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1b, 29%). Reaction of 1a with AgBF₄ in acetone, followed by acetonitrile and then anion exchange gave cis,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2a). In the same way, 1b afforded trans,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2b). Reaction of depolymerized [Ru(CO)₂Cl₂]_n with bpma in ethanol at room temperature afforded cis,cis-[Ru(η²-bpma)(CO)₂Cl₂] (3). In refluxing ethanol, 3 was converted to cis,fac-[Ru(bpma)(CO)₂Cl]Cl (1a-Cl). Heating 3 in chlorobenzene afforded 1b-Cl, exclusively; heating 3 in ethylene glycol gave mainly 1a-Cl. Heating 1a-Cl in ethanol resulted in no isomerization, but heating in chlorobenzene gave a mixture of 3 and 1b-Cl. Anion exchange for PF₆ with 1a-Cl and 1b-Cl afforded 1a and 1b, respectively, whereas anion exchange for BPh₄ afforded 1a-BPh₄. Compounds 1a, 1b, 2a and 3 have been structurally characterized.     

A [4+2] mixed ligand approach to ruthenium DNA metallointercalators [Ru(tpa)(N–N)](PF6)2 using a tris(2-pyridylmethyl)amine (tpa) capping ligand

A series of five tris(2-pyridylmethyl)amine (tpa) ruthenium complexes [Ru(tpa)(N–N)](PF₆)₂ with N–N = bpy (2,2′-bipyridine), phen (1,10-phenanthroline), dpq (dipyrido[3,2-d:2′,3′-f]quinoxaline), dppz (dipyrido[3,2-a;2′,3′-c]phenazine), and dppn (4,5,9,16-tetraazadibenzo[a,c]naphthacene) was prepared and characterized by NMR, UV–Visible (UV/Vis), and fluorescence spectroscopy as well as cyclic voltammetry. Structures optimized with density functional theory methods (DFT, BP86, TZVP) without constraints show C₁ symmetry while in solution, the ¹H and ¹³C NMR spectra are in accordance with an average C_s symmetry. This is thought to be due to a low energy barrier for flipping of the equatorial pyridine ring from one side of the N–N plane to the other. The electronic structure of the compounds was studied with DFT and a change in the highest occupied molecular orbital (HOMO) character from Ru t_2g for the bpy, phen, and dpq to N–N ligand-based for the dppz and dppn complexes was found. TDDFT calculations showed dominant N–N-based intra-ligand charge transfer (ILCT) transitions in the latter two complexes mixed with metal-to-ligand charge transfer (MLCT) bands found for all five compounds. DNA binding of the complexes was studied with UV/Vis titrations, the fluorescent ethidium bromide displacement assay, and CD spectroscopy. The affinity increases with the aromatic surface area of of the bidentate N–N ligand in the order bpy  phen < dpq < dppz  dppn. Viscosity measurements support an intercalative binding mode for the latter three compounds, while the others did not show a pronounced effect of the hydrodynamic properties of calf thymus (CT) DNA.     

Iron and cobalt complexes with the ligand (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp) and derivatives

A series of iron(II)/(III) and cobalt(II)/(III) complexes with the tetradendate tripodal ligands (2-aminoethyl)bis(2-pyridylmethyl)amine (uns-penp), its methylated derivatives Me₂-uns-penp and Me₄-uns-penp as well as the amide ligand N-acetyl-N,N-bis[(2-pyridyl)methyl]ethylenediamine (acetyl-uns-penp) were synthesized and structurally characterized. They have been investigated in regard to their reactivity towards dioxygen and/or hydrogen peroxide. Complexes of this type seem to have a high potential to be useful in the activation of dioxygen for selective oxidation reactions of organic substrates.     

Synthesis and theoretical analysis of the structures and bonding in five new neutral square planar bis[2,4-di(aryl)-1,3,5-triazapentadienato]nickel(II) complexes

Solvothermal reactions in methanol of nickel acetate tetrahydrate, Ni(OAc)₂ · 4H₂O, with benzonitrile derivatives NC(C₆H₄)X, where X is one of the electron withdrawing substituents -CN, -NO₂, or -CF₃, located at the m- or p-positions relative to -CN, yield complexes of the general formula Ni{HNC(R)-NC(R)-NH}₂. More specifically, 3-nitrobenzonitrile, 4-nitrobenzonitrile, 1,3-dicyanobenzene, 1,4-dicyanobenzene, and ααα-trifluoro-p-toluonitrile are found to react with Ni(OAc)₂ · 4H₂O to yield Ni{HNC(R)-NC(R)-NH}₂, where R = 3-(NO₂)C₆H₄, 4-(NO₂)C₆H₄, 3-(CN)C₆H₄, 4-(CN)C₆H₄, or 4-(CF₃)C₆H₄, respectively. Analogous reactions of nitriles lacking electron withdrawing groups do not occur under similar conditions. Solid-state structures have been determined for the complexes with p-NO₂, p-CN, and p-CF₃ substituents on the phenyl rings. In addition, we describe density functional theory (DFT) and natural bonding orbital theory (NBO) studies on a simplified analog of these compounds, aimed at understanding their molecular bonding. It is shown that the new compounds for which solid-state structures have been determined are model examples of coordination compounds containing robust ω-bonds.     

Synthesis, characterization and crystal structures of Cu(II) and Pd(II) complexes of the pentadentate mixed donor macrocycle, [17]aneNO2S2

An aza-oxa-thia macrocycle, 5,14-dioxa-2,17-dithia[6](1,2)benzeno[6](2,6)pyridinophane, L1, the related smaller macrocycle 2,14-dithia-11-oxa-[3](1,2)benzeno[6](2,6)pyridinophane, L2, and the complexes with Pd(II) and Cu(II) of the macrocycle, L1, have been synthesized. The crystal structure of L2 and those of the two metal complexes have been determined. In the complexes, the metal ions adopt exclusively square planar geometry in which the pyridine nitrogen, two sulfurs and one chlorine atom are coordinated and there is no appreciable interaction with the oxygen donors. Thus, the `hard-soft acid-base' principle is illustrated by the behaviour of L1. The structures of both complexes are compared with the previously reported mixed aza-thia macrocycle, 2,5,14,17-tetrathia[6](1,2)benzeno[6](2,6)pyridinophane. The crystal structure of the smaller macrocycle, L2, is also discussed and due to the nature of its smaller cavity, attempts to make complexes with it have not been successful.     

Scandium and yttrium complexes of a heteroscorpionate [N,N,O]-donor-set ligand: Synthesis, characterization and catalytic activity in ethylene polymerization

New scandium and yttrium complexes ScL₂(bpzmp)(THF) {L = Cl (1); L = CH₂Si(CH₃)₃ (3)}, YL₂(bpzmp) {L = Cl (2); L = OTf (5)} and Y(CH₂SiMe₃)₂(bpzmp)(THF) (4) bearing the heteroscorpionate bpzmp ligand {bpzmp = (3,5-^tBu₂-2-phenoxo)bis(3,5-Me₂-pyrazol-1-yl)methane} have been synthesized and characterized by means of NMR and Mass spectroscopy. The tridentate monoanionic ligand resulted κ³-coordinated to the metal via the oxygen and both the sp² nitrogen atoms of the heterocycles, producing complexes in C_S symmetry.The behavior of 1-4 in ethylene polymerization was investigated after proper activation with different activating agents. Complex 4, in combination with the Brönsted or Lewis acids [PhNMe₂H][B(C₆F₅)₄] or [Ph₃C][B(C₆F₅)₄], produced linear high molecular weight polyethylene in good yield.     

Synthesis and characterization of bis[salicylideneaminato] palladium(II) complexes. Molecular structure of bis[N-(n-butyl)(3-benzyloxy)-2-salicylideneaminato]-palladium(II), pd(C18H20NO2)2]

Transition metal compounds having liquid crystalline properties can be interesting materials for practical applications. Attempting to correlate mesomorphic properties with molecular structure and crystal packing mode, we have investigated some complexes obtained from Schiff bases of long chain aliphatic amines and salicylaldehyde or 2,3-dihydroxybenzaldehyde derivatives. The X-ray structural analysis of bis[N-(n-butyl)(3-benzyloxy)-2-salicylideneaminato] palladium [II] is also reported.     

Constitutional isomers, stereoisomers and conformers of bis[di-tert-butyl(trimethylsilyl)cyclopentadienyl]disulfane

Reaction of tBu₂(Me₃Si)C₅H₂Li with S₂Cl₂ leads to [tBu₂(Me₃Si)C₅H₂]₂S₂. This compound exists as a pair of diastereomers (1,2) with sulfur in an allylic position of the cyclopentadiene system. Each diastereomer exists as a racemate of RS,SR and RR,SS enantiomers, respectively. 1 rapidly, 2 slowly convert below room temperature to a pair of diastereomers (3,4) with sulfur in vinylic position. Again, each diastereomer exists as a racemate of RS,SR and RR,SS enantiomers. 3 and 4 are the stable constitutional isomers at ambient temperatures and do not interconvert. The structures of 2, 3 and 4 have been determined by single crystal X-ray diffraction.     

Molecular structure, bioavailability and bioactivity of [Cu(o-phen)2(cnge)](NO3)2.2H2O and [Cu(o-phen)(cnge)(H2O)(NO3)2] complexes

Two Cu(II) complexes with cyanoguanidine (cnge) and o-phenanthroline, [Cu(o-phen)(2)(cnge)](NO(3))(2).2H(2)O (1) and [Cu(o-phen)(cnge)(H(2)O)(NO(3))(2)] (2), have been synthesized using different experimental techniques and characterized by elemental analyses, FTIR, diffuse and UV-vis spectra and EPR and magnetic moment measurements techniques. The crystal structures of both complexes were solved by X-ray diffraction methods. Complex (1) crystallizes in the monoclinic space group C2/c with a=12.621(5), b=31.968(3), c=15.39(1)A, beta=111.68(4) degrees, and Z=8 and complex (2) in the monoclinic space group P2(1)/n with a=10.245(1), b=13.923(2), c=12.391(2)A, beta=98.07(1) degrees, and Z=4. The environments of the copper(II) center are trigonal bipyramidal (TBP) for [Cu(o-phen)(2)(cnge)](2+) and an elongated octahedron for [Cu(o-phen)(cnge)(H(2)O)(NO(3))(2)]. Solution studies have been performed to determine the species distribution. The superoxide dismutase (SOD) activities of both complexes have also been tested in order to determine if these compounds mimic the enzymatic action of the enzyme SOD that protects cells against peroxide radicals.     

Synthesis, structure, solution chemistry and the electronic effect of para substituents on the vanadium center in a family of mixed-ligand [VO(ONO)(ON)] complexes

Four tridentate dibasic ONO donor hydrazone ligands derived from the condensation of benzoylhydrazine with either 2-hydroxyacetophenone or its para substituted derivatives (H₂L^1-4, general abbreviation H₂L) have been used as primary ligands and 8-hydroxyquinoline (Hhq, a bidentate monobasic ON donor species) has been used as auxiliary ligand. The reaction of [V^IVO(acac)₂] with H₂L in methanol followed by the addition of Hhq in equimolar ratio under aerobic condition afforded the mixed-ligand oxovanadium(V) complexes of the type [V^VO(L)(hq)] (1-4) in excellent yield. The X-ray structure of the compound [V^VO(L⁴)(hq)] (4) indicates that the H₂L⁴ ligand is bonded with vanadium meridionally in a tridentate dinegative fashion through its deprotonated phenolic-O, deprotonated enolic-O and imine-N atoms. The V-O bond length order is: oxo < phenolato < enolato. ¹H NMR spectra of 4 in CDCl₃ solution indicates that it’s solid-state structure is retained in solution. Complexes are diamagnetic and exhibit only ligand to metal charge transfer (LMCT) transition band near 530 nm in CH₂Cl₂ solution in addition to intra-ligand π → π^∗ transition band near 335 nm and they display quasi-reversible one electron reduction peak near − 0.10 V versus SCE in CH₂Cl₂ solution. λ_max (for LMCT transition) and the reduction peak potential values of the complexes are found to be linearly related with the Hammett (σ) constants of the substituents in the aryloxy ring of the hydrazone ligands. λ_max and values show large dependence dλ_max/dσ = 32.54 nm and V, respectively, on the Hammett constant.     

Syntheses and DNA-binding studies of two ruthenium(II) complexes containing one ancillary ligand of bpy or phen: [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)2

Two new ruthenium(II) complexes of [Ru(bpy)(pp[2,3]p)2](ClO4)2 and [Ru(phen)(pp[2,3]p)2](ClO4)(2) (bpy=2,2'-bipyridine, phen=1,10-phenanthroline, pp[2,3]p=pyrido[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline) have been synthesized and characterized by elemental analysis and 1H NMR spectra. The calf thymus DNA-binding properties of the two complexes were investigated by UV-visible and emission spectroscopy, competitive binding experiments with ethidium bromide and viscosity measurements. The results indicate that the two complexes intercalate between the base pairs of the DNA tightly with intrinsic DNA-binding constants of 3.08 x 10(6) and 6.53 x 10(6) M(-1) in buffered 50 mM NaCl, respectively, which are much larger than 6.9 x 10(5) M(-1) for [Ru(bpy)2(pp[2,3]p)](ClO4)2 containing two ancillary ligands of bpy.     

Water dimers connect [Cu(cda)(py)3] (cda = pyridine-4-hydroxy-2,6-dicarboxylate, py = pyridine) complex units to left- and right-handed helices that form a tubular coordination polymer through supramolecular bonding

The reaction between pyridine-4-hydroxy-2,6-dicarboxylic acid (cdaH₂) and Cu(NO₃)₂ · 3H₂O afford products that depend on the reaction conditions applied. In presence of excess of aqueous pyridine (1:2 v/v), equimolar amounts of the reactants form {[Cu(cda)(py)₃]₂ · 5H₂O}_n (1). In this complex, dimeric water clusters are H-bonded to carboxylate O atoms forming both left- and right-handed helices. These helices are further H-bonded to form a tubular coordination polymer. It crystallizes in the monoclinic space group P2₁/a with a = 14.235(5), b = 23.097(4), c = 15.542(6) Å, β = 114.392(5)°, V = 4654(2) Å³, Z = 4, R₁ = 0.0422, wR₂ = 0.0992, S = 0.899. When pyridine is used in place of aqueous pyridine, a new coordination polymer, {Cu(cda)(py)}_n(2) is formed that crystallizes in the monoclinic space group P2₁/c with a = 12.391(5), b = 12.770(5), c = 7.135(5) Å, β = 95.155(5)°, V = 1124(1) Å³, Z = 4, R₁ = 0.0415, wR₂ = 0.0882, S = 1.190. The structure of 2 consists of carboxylate-bridged [Cu(cda)(py)] units extending as a zigzag infinite chain where each metal ion shows square-pyramidal geometry. Variable temperature magnetic susceptibility measurements in the temperature range, 2-300 K for 2 is also reported.     

Mixed-ligand silver(I) complexes containing bis[2-(diphenylphosphino)phenyl]ether and pyridyl ligands

The reaction of [Ag₂(κ²-P,P′-DPEphos)₂(μ-OTf)₂] (1) (DPEphos = bis(2-(diphenylphosphino)phenyl]ether) with 1,10-phenanthroline (phen) and 4,4′-bipyridine in equimolar ratios afford, respectively, the mononuclear complex [Ag(κ²-P,P′-DPEphos)(phen)][OTf] (2) and the coordination polymer [Ag(κ²-P,P′-DPEphos)(μ-4,4′-bpy)]_n[OTf]_n (3). In complex 3, the silver atoms are bridged by 4,4′-bipyridine units to form a zigzag metallopolymer.     

Systematic characterization on electronic structures and spectra for a series of complexes, M(IDB)Cl2 (M = Mn, Fe, Co, Ni, Cu and Zn): a theoretical study

Theoretical studies on the coordination stabilities, spectra and DNA-binding trend for the series of metal-varied complexes, M(IDB)Cl₂ (M = Mn, Fe, Co, Ni, Cu and Zn; IDB = N, N -bis(2-benzimidazolylmethyl) amine), have been carried out by using the DFT/B3LYP method and PCM model. The calculated coordination stabilities (S) for these complexes present a trend of S(Ni) > S(Co) > S(Fe) > S(Cu) > S(Zn) > S(Mn). It has been estimated from the molecular orbital energies of the complexes that the DNA-binding affinities (A) of the complexes are in the order of A(Zn) < A(Mn) < A(Fe) ≈ A(Co) < A(Ni) < A(Cu). The studied results indicate that the Cu, Ni and Co complexes with large coordination stabilities present the low virtual orbitals, consequently yielding to the favorable DNA-binding affinities. The spectral properties of excitation energies and oscillator strengths for M(IDB)Cl₂ in the ultraviolet region were calculated by TD-DFT/B3LYP method.     

Syntheses, structures and bioactivities of silver(I) complexes with dithioether ligands that contain a di- or triethylene glycol chain and different terminal groups

A series of flexible dithioethyl ligands that contain ethyleneoxy segments were designed and synthesized, including bis(2-(pyridin-2-ylthio)ethyl)ether (L¹), 1,2-bis(2-(pyridin-2-ylthio)ethoxy)ethane (L²), bis(2-(benzothiazol-2-ylthio)ethyl)ether (L³) and 1,2-bis(2-(benzothiazol-2-ylthio)ethoxy)ethane (L⁴). Reactions of these ligands with AgNO₃ led to the formation of four new supramolecular coordination complexes, [Ag₂L¹(NO₃)₂]₂ (1), [Ag₂L²(NO₃)₂] (2), [AgL³(NO₃)]_∞ (3) and [AgL⁴(NO₃)] (4) in which the length of the (CH₂CH₂O)_n spacers and the terminal groups of ligands cause subtle geometrical differences. Studies of the inhibitory effect to the growth of Phaeodactylum tricornutum show that all four complexes are active and the compound 4 has the highest inhibitory activity.     

Preparation,characterization and crystal structures of manganese(II), iron(III) and copper(II) complexes of the bis[di-1,1-(2-pyridyl)ethyl]amine (BDPEA) ligand; evaluation of their DNA cleavage activities

The synthesis of a new tetrapyridyl ligand, bis[di-1,1-(2-pyridyl)ethyl]amine (BDPEA), is described. Complexation of this ligand with manganese(II), iron(III) or copper(II) chlorides afforded mononuclear complexes: Mn(BDPEA)Cl2 (1) [Fe (BDPEA)Cl2]Cl (2) and [Cu(BDPEA)Cl]Cl (3). In all cases, BDPEA is coordinated to the metal center by three pyridine nitrogen atoms and the secondary amine. The geometrical environments around the metals in Mn(BDPEA)Cl2 and [Fe(BDPEA)Cl2]Cl are best described as distorted octahedrals and in [Cu (BDPEA)Cl]Cl as a slightly distorted square pyramid. The DNA cleavage activities of manganese(II), iron (III) or copper(II) complexes of both BDPEA and another tetrapyridyl ligand, bis[di(2-pyridyl) methyl]amine (BDPMA), in the presence of an oxidant (H2O2) or a reducing agent (ascorbate) with air, are reported. The iron(III) complexes exhibited significantly enhanced efficiencies, compared to copper(II) complexes. [Fe(BDPEA)Cl2]Cl is found to be the most active DNA cleaver, in agreement with a better stability of BDPEA in oxidizing conditions.     

Syntheses and structures of lanthanide complexes containing a bis(imidazolin-2-imino)pyridine pincer ligand

The Lewis acid-base reaction of 2,6-bis[1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine (TL^tBu) and LnCl₃ in THF leads to the corresponding neutral lanthanide complexes of type [(TL^tBu)LnCl₃], Ln = Y (1a), Er (1b), Lu (1c). The yttrium and lutetium complexes have been characterized by X-ray diffraction analysis. The solid state structures reveal that the bulky TL^tBu ligand causes steric crowding around the lanthanide atoms by coordinating to the metal center in a tridentate fashion. In addition, remote C-H?Ln interactions (H?Ln ca. 2.7 Å) involving one of the ^tBu methyl groups are observed in both cases. A DFT (density functional theory) calculation on 1a was able to reproduce this interaction, which was additionally characterized by means of an H?Y compliance constant and by employing the AIM (atoms in molecules) theory.