Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Aromatic N-oxide bridged copper(II) coordination polymers: Synthesis, characterization and magnetic properties

The complexes [Cu₂(o-NO₂-C₆H₄COO)₄(PNO)₂] (1), [Cu₂(C₆H₅COO)₄(2,2′-BPNO)]_n (2), [Cu₂(C₆H₅COO)₄(4,4′-BPNO)]_n (3), [Cu(p-OH-C₆H₄COO)₂(4,4′-BPNO)₂·H₂O]_n (4), (where PNO = pyridine N-oxide, 2,2′-BPNO = 2,2′-bipyridyl-N,N′-dioxide, 4,4′-BPNO = 4,4′-bipyridyl-N,N′-dioxide) are prepared and characterized and their magnetic properties are studied as a function of temperature. Complex 1 is a discrete dinuclear complex while complexes 2-4 are polymeric of which 2 and 3 have paddle wheel repeating units. Magnetic susceptibility measurements from polycrystalline samples of 1-4 revealed strong antiferromagnetic interactions within the {Cu₂}⁴⁺ paddle wheel units and no discernible interactions between the units. The complex 5, [Cu(NicoNO)₂·2H₂O]_n·4nH₂O, in which the bridging ligand to the adjacent copper(II) ions is nicotinate N-oxide (NicoNO) the transmitted interaction is very weakly antiferromagnetic.     

Syntheses, crystal structure and theoretical investigation of novel heteroleptic complexes of nickel(II) with N-R-sulfonyldithiocarbimate and phosphine ligands

Five new complexes of general formula: [Ni(RSO₂NCS₂)(dppe)], where R = C₆H₅ (1), 4-ClC₆H₄ (2), 4-BrC₆H₄ (3), 4-IC₆H₄ (4) and dppe = 1,2-bis(diphenylphosphino)ethane and [Ni(4-IC₆H₄SO₂NCS₂)(PPh₃)₂] (5), where PPh₃ = triphenylphosphine, were obtained in crystalline form by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate K₂(RSO₂NCS₂) and dppe or PPh₃ with nickel(II) chloride in ethanol/water. The elemental analyses and the IR, ¹H NMR, ¹³C NMR and ³¹P NMR spectra are consistent with the formation of the square planar nickel(II) complexes with mixed ligands. All complexes were also characterized by X-ray diffraction techniques and present a distorted cis-NiS₂P₂ square-planar configuration around the Ni atom. Quantum chemical calculations reproduced the crystallographic structures and are in accord with the spectroscopic data. Rare C-H···Ni intramolecular short contact interactions were observed in the complexes 1-5.     

Syntheses, crystal structure, spectroscopic characterization and antifungal activity of new N-R-sulfonyldithiocarbimate metal complexes

Five new compounds with the general formula of (Bu₄N)₂[M(RSO₂NCS₂)₂], where Bu₄N = tetrabutylammonium cation, (M = Ni, R = 4-FC₆H₄) (1), (M = Zn, R = 4-FC₆H₄, 4-ClC₆H₄, 4-BrC₆H₄, 4-IC₆H₄), (2), (3), (4) and (5), respectively, were obtained by the reaction of the appropriate potassium N-R-sulfonyldithiocarbimate (RSO₂NCS₂K₂) with nickel(II) chloride hexahydrate or zinc(II) acetate dihydrate in metanol:water 1:1. The elemental analyses and the IR data are consistent with the formation of the expected bis(dithiocarbimato)metal(II) complexes. The ¹H and ¹³C NMR spectra showed the signals for the tetrabutylammonium cation and the dithiocarbimate moieties. The compounds 1, 2 and 5 were also characterized by X-ray diffraction techniques. The nickel(II) is coordinated by two N-4-fluorophenylsulphonyldithiocarbimato(2-) ligands forming a planar coordination. The zinc(II) exhibits distorted tetrahedral configuration in compounds 2 and 5 due to the chelation effect of two sulfur atoms of the N-R-sulfonyldithiocarbimate ligands. The antifungal activities of the compounds were tested in vitro against Colletotrichum gloeosporioides, an important fungus that causes the plant disease known as anthracnose in fruit trees. All the complexes were active.     

Coordination compounds of Cd(II) with several bidentate-NN′ and tridentate-NN′N nitrogen donor ligands. Cd NMR studies of monomeric compounds containing nitrogen donor atoms

Reaction of CdCl₂ with N-alkylaminopyrazole ligands 1-[(2-ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[(2-(tert-butylamino)ethyl)]-3,5-dimethylpyrazole (deat), bis-[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae), and bis-[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) in absolute ethanol yields [CdCl₂(NN′)] (NN′ = deae (1), deat (2)), [CdCl₂(bdmae)] (3), and [CdCl(ddae)]₂[CdCl₄] (4). The Cd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR, ¹H, ¹³C{¹H} and ¹¹³Cd NMR spectroscopies, and X-ray diffraction methods. ¹H and ¹¹³Cd NMR experiments at variable temperature for 3 and 4 show that dynamic processes are taking place in solution. We report the measurements of ¹¹³Cd NMR chemical shift data for complexes 1-4 in solution. X-ray crystal structures for complexes 2 and 3 have been determined. The Cd(II) is coordinated to the deat ligand, in 2, by one nitrogen atom of the pyrazolyl group and one nitrogen atom of the amine. It finishes a tetrahedral geometry with two chlorine atoms. The bdmae ligand is linked to Cd(II), in 3, by two nitrogens atoms of the pyrazolyl groups and one amine nitrogen, along with two chlorine atoms, in a distorted trigonal bipyramidal geometry.     

Structural comparison of alkylated derivatives of (bmmp-dmed)Ni and (bmmp-dmed)Zn

The sulfur-alkylation of the nickel (1) and zinc (2) complexes of the dithiolate N₂S₂ ligand N,N′-bis-2-methyl-mercaptopropyl-N,N′-dimethylethylenediamine, H₂(bmmp-dmed), have been investigated. Reactions with iodomethane yield [(Me-bmmp-dmed)Ni]PF₆ (3), [(Me₂-bmmp-dmed)NiI₂] (4), and [(Me₂-bmmp-dmed)ZnI]₂[ZnI₄] (5). Addition of iodoacetamide yields [(AA₂-bmmp-dmed)Ni]I₂ (6) and [(AA₂-bmmp-dmed)Zn]I₂ (7). Each of the metal-thioether products (3-7) have been characterized spectroscopically and by X-ray crystallography. Structural data is compared with that of the previously reported thiolato precursors 1 and 2. Sulfur-alkylation of 1 results in small relative changes in the nickel-sulfur bond distance, whereas for 2, the zinc-sulfur bond distance increases significantly, but is not cleaved. The difference between nickel and zinc is attributed to the release of a π*-bonding interaction between the metal and sulfur upon alkylation that compensates for the decreased σ-donor ability of the thioether in the case of nickel, but not for zinc.     

Mono- and dinuclear (o-thioetherphenolato)-copper(II) complexes. Structural models for galactose oxidase

Three new o-thioetherphenol ligands have been synthesized: 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)ethane (H₂bse), 1,2-bis(3,5-di-tert-butyl-2-hydroxyphenylsulfanyl)benzene (H₂bsb), and 4,6-di-tert-butyl-2-phenylsulfanylphenol (Hpsp). Their complexes with copper(II) were prepared and investigated by UV-Vis-, EPR-spectroscopy; their electro- and magnetochemistry have also been studied: [Cu^II(psp)₂] (1), [Cu^II₂(bse)₂] (2), [Cu^II₂(bsb)₂] (3), [Cu^II(bsb)(py)₂] (4). The crystal structures of the ligands H₂bse, H₂bsb, Hpsp and of the complexes 1, 2, 3, 4 have been determined by X-ray crystallography.     

Syntheses and structures’ influence on the nonlinear optical properties of o-ferrocenylbenzoate compounds

Two complexes containing o-ferrocenylbenzoate [o-⁻OOCH₄C₆Fc, Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)] components: {[Pb(η²-o-OOCH₄C₆Fc)₂(phen)](NO₃)} (phen = phenanthroline) (1) and {[Zn(η²-o-OOCH₄C₆Fc)₂(bpe)](CH₃OH)}_n (bpe = 1,2-bis(4-pyridyl) ethene) (2) have been synthesized and structurally characterized by single crystal X-ray diffraction. 1 gives a discrete mononuclear framework, 2 features an infinite 1-D chain structure constructed by the bpe linking two adjacent zinc (II) ions. The third-order nonlinear optical (NLO) properties of complexes 1, 2 and the reactant o-NaOOCH₄C₆Fc were determined by Z-scan techniques in DMF solution. The results show that the structures of complexes have great impact on NLO properties. Complex 1 and o-NaOOCH₄C₆Fc display self-defocusing behaviors, while complex 2 exhibits strong self-focusing effect. The solution-state differential pulse voltammograms of complexes 1, 2 and o-NaOOCH₄C₆Fc were investigated as well. The results reveal that the half-wave potential of the ferrocenyl moieties is strongly influenced by the Pb(II) or Zn(II) ions in complexes 1 and 2.     

Different coordination modes of 5,5-diethylbarbiturate in the copper(II) complexes with some aliphatic amines: Synthesis, spectroscopic, thermal and structural studies

Three new copper(II) complexes of 5,5-diethlybarbiturate (barb), [Cu(barb)₂(dmen)]·0.5H₂O (dmen = N,N-dimethylethylenediamine) 1, [Cu(barb)₂(bapa)] (bapa = bis(3-aminopropyl)amine) 2, and [Cu(barb)(apen)](barb)·2H₂O (apen = N,N′-bis(3-aminopropyl)ethylenediamine) 3, have been synthesized and characterized by chemical, spectroscopic and thermal methods. Single crystal X-ray diffraction studies revealed that all complexes are mononuclear. The copper(II) ion exhibits a square-pyramidal coordination geometry in 1 and 3, but a trigonal-bipyramidal geometry in 2. The barb ligand shows different coordination modes. 1 presents the unequal coordination of the barb ligands: one is monodentate (N) and the other one is bidentate (N, O). In 2, both barb ligands are N-coordinated, whereas in 3, one barb ligand is N-coordinated, while the second barb ligand behaves as a counter-ion. The dmen, bapa and apen ligands act as bi-, tri- and tetradentate ligands, respectively. All complexes display a hydrogen-bonded network structure. The IR spectroscopic analysis shows that the ν(CO) stretching frequencies do not correlate predictably with the coordination mode of the barb ligand in 1. Thermal analysis data for 1-3 are in agreement with the crystal structures.     

Assembly of anion-controlled cadmium(II) coordination polymers based on flexible bis(imidazole) derivative

Four Cd(II) metal-organic complexes, namely, [Cd(Cl)₂(bbdmbm)] (1), [Cd(NO₃)(N₃)(bbdmbm)_1.5] (2), [Cd(BBA)₂(bbdmbm)(H₂O)] (3), [Cd(DNBA)₂(bbdmbm)] (4), (bbdmbm = 1,1-(1,4-butanediyl)bis(5,6-dimethylbenzimidazole), HBBA = 4-bromobenzoic acid, and HDNBA = 3,5-dinitrobenzoic acid) have been obtained from hydrothermal reactions of different Cd(II) salts with the mixed ligands of bbdmbm and five anions (Cl⁻, NO₃⁻, N₃⁻, BBA and DNBA). Single crystal X-ray diffraction analyses reveal that the four complexes exhibit different structures. Complex 1 possesses a one-dimensional (1D) helical chain, which is finally extended into a two-dimensional (2D) supramolecular structure through π-π stacking interactions. Complex 2 shows a 1D ladderlike chain bridged by bbdmbm ligands with two kinds of coordination conformations. Complex 3 is a 1D coordination polymer and is ultimately extended into a 2D supramolecular network through H-bonding interactions. Complex 4 displays a dinuclear cluster, which is finally packed into a three-dimensional (3D) supramolecular framework through three kinds of π-π stacking interactions. The Cd(II) exhibits four different coordination modes in complexes 1-4, respectively. The results indicate that the anion ligands with different steric hindrance and size play important roles in the coordination modes of Cd(II) and construction of the title complexes, leading to the structural diversity. In addition, the conformations of bbdmbm ligand also show some effect on the final structures. Fluorescence properties of complexes 1-4 are reported in this paper.     

Sterically-controlled nuclearity in new copper(II) complexes with di-compartmental ligands: Formation of antiferromagnetically coupled angular trimer and mononuclear inclusion complex

Two new copper(II) complexes, [Cu₃(L¹)₂(H₂O)₂](ClO₄)₂ (1) and [CuL²⊂ (H₂O)] (2) have been derived from two di-compartmental Schiff base ligands H₂L¹ and H₂L², respectively. Depending on slight modification of the substituent group of the potentially N₂O₄ donor ligands, tri- and mononuclear structures are obtained, which have been confirmed by single-crystal X-ray diffraction studies. Both complexes have been characterized by elemental analysis, IR, UV-vis and EPR spectroscopy. Complex 1 consists of an angular trinuclear array of copper ions, while complex 2 consists of a mononuclear copper center. Variable temperature magnetic susceptibility measurements have been performed to investigate the magnetic behaviour of complex 1 and the result indicates a strong antiferromagnetic exchange interaction (J = −120.1(2) cm⁻¹) between the adjacent copper(II) centers through two double μ₂-phenoxo bridges. Complex 2 is a mononuclear inclusion compound encapsulating one water molecule in the vacant external compartment of the ligand through hydrogen-bonding interactions.     

Preparation and characterization of two supramolecular complexes with 5-amino-2,4,6-triiodoisophthalic acid under N-donor auxiliary ligand intervention

Assemblies of 5-amino-2,4,6-triiodoisophthalic acid (H₂ATIBDC) with Cd(II) and Zn(II) in the presence of N-donor auxiliary ligand, 1,4-bis(1,2,4-triazol-1-yl)butane (btb), at ambient conditions yield two new supramolecular complexes, [Cd(ATIBDC)(btb)(H₂O)₂]·3H₂O (1), and [Zn(ATIBDC)(btb)]·2H₂O (2). Generally, these two complexes display 1D ATIBDC²⁻-bridged coordination arrays. Distinct extended 3D network architectures are further constructed with the help of weak secondary interactions especially aromatic stacking, halogen bonding, and hydrogen bonding as supramolecular driving forces. It is worthy to mention that halogen bonds (C-I?π and C-I?N/O) play important roles in the supramolecular assembly. The pentameric cluster (H₂O)₅ in 1 assembles into highly ordered helical infinite chains. Complex 2 exhibits the fascinating single-walled tube-like chain structure. It loses crystallinity rapidly in the air and leads to the formation of [Zn(ATIBDC)(btb)]·H₂O (2A). Thermal stabilities and solid state fluorescent properties of complexes 1 and 2A have been studied.     

Synthesis, crystal structure, spectral and magnetic studies and catecholase activity of copper(II) complexes with di- and tri-podal ligands

Five complexes of copper(II) acetate with Schiff base ligands based on salicylaldehyde and N,N-dimethylamino)ethyl/propyl amine and their reduced products, have been synthesized and characterized by various spectroscopic methods. The solid state structures of 1, 2 and 3 have been determined using single crystal X-ray diffraction method. The structures of the other two compounds have been proposed on the basis of spectroscopic and physical methods. The compounds 1, 3 and 4 are dinuclear complexes of the tridentate ligands, where the two Cu(II) centers have square pyramidal geometry with bridging acetate or phenoxo groups. Each arm of the tripodand ligand forms a mononuclear, magnetically dilute complex 5 having five coordinated Cu(II) ions. Complex 2 is mononuclear with a square pyramidal stereochemistry. The catalytic performance of the oxidation of 3,5-di-tert-butylcatechol to quinone was studied using UV-Vis absorption spectral methods. Complex 4 exhibits the highest activity with a turnover number of 41 h⁻¹ while other showed lower rates of oxidation. A kinetic treatment on the basis of Michaelis-Menten model was applied. Ease of removal of the exogenous acetate ligands and easy access to the Cu(II) ions have been seen to affect the activity in the complexes. At the same time presence of two endogenous phenoxo bridges in the dinuclear complexes reduces the activity.     

Formation of coordination polymer and molecular complex of 4,4′-bipyridyl-N,N′-dioxide of manganese and zinc

A 1D-coordination polymer [{Mn₃(C₆H₅COO)₆(BPNO)₂(MeOH)₂}(MeOH)₂]_n (1) having benzoate as the anionic ligand and 4,4′-bipyridyl-N,N′-dioxide (BPNO) as bridging ligand is synthesized by reacting benzoic acid with manganese(II) acetate tetrahydrate followed by reaction with 4,4′-bipyridyl-N N′-dioxide. The bridging bidentate BPNO ligands in this coordination polymer along with the benzoate bridges hold the repeated units. The chain like structure in one dimension by benzoate bridges are connected to each other through the μ³-η²:η¹ bridges of BPNO ligands. This coordination polymer can be transformed to a molecular complex [Mn(H₂O)₆](C₆H₅COO)_2.4BPNO (2). In this complex the BPNO remains outside the coordination sphere but they are hydrogen bonded to water molecules to form self assembled structure. The reaction of 3,5-pyrazoledicarboxylic acid (L₁H2) and BPNO with manganese(II) acetate or zinc(II) acetate led to molecular complexes with composition [M₂(L₁)₂(H₂O)₆].BPNO·xH₂O {where M = Mn(II) (3), Zn(II)(4)}. These molecular complexes of BPNO are characterised by X-ray crystallography. The complexes 3-4 are binuclear carboxylate complexes having M₂O₂ core formed from carboxylate ligands with two metal ions.     

Synthesis of new palladium(II) compounds with several bidentate nitrogen-donor ligands: Structural analyses by H and C{H} NMR spectroscopy and crystal structures

The reaction of [PdCl₂(CH₃CN)₂] with N-alkylaminopyrazole (NN′) ligands, 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[2-(ⁱpropylamino)ethyl]-3,5-dimethylpyrazole (deai), and 1-[2-(^tbutylamino)ethyl]-3,5-dimethylpyrazole (deat), affords a series of square planar Pd(II) complexes [PdCl₂(NN′)] (NN′ = deae (1), deai (2) and deat (3)). The solid-state structures of complexes 1 and 3 were determined by single crystal X-ray diffraction studies. The NN′ ligands are coordinated through the N_pz and N_amine atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition. These palladium(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Cyanato bridged binuclear nickel(II) and copper(II) complexes with pyridylpyrazole ligand: Synthesis, structure and magnetic properties

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)]₂(PF₆)₂ (1) and copper(II) complex [Cu(L)(NCO)]₂(PF₆)₂ (2), where L is N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N₄-coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2. The variable temperature magnetic susceptibility data, measured from 2 to 300 K, show weak antiferromagnetic interaction with J value −6.2(1) cm⁻¹ for complex 1, whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1) cm⁻¹.     

Synthesis and transition metal complexes of 3,3-bis(1-vinylimidazol-2-yl)propionic acid, a new N,N,O ligand suitable for copolymerisation

The new N,N,O heteroscorpionate ligand 3,3-bis(1-vinylimidazol-2-yl)propionic acid (Hbvip) (5) was synthesised in five steps starting from 1-vinylimidazole. This ligand is closely related to 3,3-bis(1-methylimidazol-2-yl)propionic acid (Hbmip), but contains two vinyl linker groups which can be used for radical-induced polymerisation reactions. The κ³-N,N,O coordination behaviour of 5 was proven by the synthesis of the tricarbonyl complexes [Re(bvip)(CO)₃] (6), [Mn(bvip)(CO)₃] (7) and [Cu(bvip)₂] (8). To obtain good yields of 6, it was synthesised in water instead of THF. The ligand as well as all three complexes were characterised by X-ray crystallography. Copolymerisation of 5 with pure methyl methacrylate (MMA) or a combination of MMA and ethylene glycol dimethacrylate (EGDMA) led to the solid phases P1 and P2. Polymer-bound rhenium and manganese tricarbonyl complexes could be obtained by the reaction of deprotonated P1 with [MBr(CO)₅] (M = Re, Mn) and also by copolymerisation of 6 and 7 with MMA. In both cases, the facial tripodal binding behaviour was evidenced by IR spectra of the polymers. Furthermore, the content of metal incorporated in the polymers was determined by elemental analysis, AAS or ICP-OES measurements. Reaction of the deprotonated solid phase P1 with copper(II) chloride led to a blue solid-phase (P1-Cu). The UV-Vis absorption maximum of P1-Cu is found at 615 nm, which is almost identical to that found for 8. Thereby, it seems likely that P1 is flexible enough to form bisligand complexes with copper(II). This means that the copper centres act as a kind of crosslinking agents. In contrast, the heterogeneous reaction of P2 with copper(II) chloride yielded a lime green solid phase (P2-Cu). The bathochromic shift of the absorption maximum by 102 nm suggests one-sided bound copper centres.     

Suzuki-Miyaura cross-coupling of aryl chlorides catalyzed by palladium precatalysts of N/O-functionalized pyrazolyl ligands

A series of palladium complexes, trans-[1-(R)-pz^3,5-Me₂]₂PdCl₂ {R = CH₂CONH(2,6-i-Pr₂-C₆H₃) (1b) and 2-(OH)-C₆H₁₀ (2b)}, supported over N/O-functionalized pyrazole derived ligands effectively catalyzed the more challenging Suzuki-Miyaura cross-coupling of a variety of activated aryl chlorides with phenyl boronic acid in air in a mixed-aqueous medium (DMF:H₂O, v/v = 9:1) in moderate to excellent yields. Besides the commonly encountered C_sp2-C_sp2 coupling, the 1b and 2b precatalysts also catalyzed the relatively difficult C_sp2-C_sp3 coupling of benzyl chloride with phenyl boronic acid. The 1b and 2b complexes were synthesized by the direct reaction of the respective N/O-functionalized pyrazolyl ligands, 1a and 2a, with (COD)PdCl₂ in 62-66% yields. The stability of the pyrazole-palladium interaction in the 1b and 2b complexes has been attributed to the deeply buried N_pyrazole-Pd interaction as evidenced from the density functional theory (DFT) studies.     

Iron(III) Schiff base complexes of arginine and lysine as netropsin mimics showing AT-selective DNA binding and photonuclease activity

Iron(III) complexes [Fe(L)₂]Cl (1-3), where L is monoanionic N-salicylidene-arginine (sal-argH for 1), hydroxynaphthylidene-arginine (nap-argH for 2) and N-salicylidene-lysine (sal-lysH for 3), were prepared and their DNA binding and photo-induced DNA cleavage activity studied. Complex 3 as its hexafluorophosphate salt [Fe(sal-lysH)₂](PF₆)·6H₂O (3a) was structurally characterized by single crystal X-ray crystallography. The crystals belonged to the triclinic space group P-1. The complex has two tridentate ligands in FeN₂O₄ coordination geometry with two pendant cationic amine moieties. Complexes 1 and 2 with two pendant cationic guanidinium moieties are the structural models for the antitumor antibiotics netropsin. The complexes are stable and soluble in water. They showed quasi-reversible Fe(III)/Fe(II) redox couple near 0.6 V in H₂O-0.1 M KCl. The high-spin 3d⁵-iron(III) complexes with μ_eff value of ∼5.9 μ_B displayed ligand-to-metal charge transfer electronic band near 500 nm in Tris-HCl buffer. The complexes show binding to Calf Thymus (CT) DNA. Complex 2 showed better binding propensity to the synthetic oligomer poly(dA)·poly(dT) than to CT-DNA or poly(dG)·poly(dC). All the complexes displayed chemical nuclease activity in the presence of 3-mercaptopropionic acid as a reducing agent and cleaved supercoiled pUC19 DNA to its nicked circular form. They exhibited photo-induced DNA cleavage activity in UV-A light and visible light via a mechanistic pathway that involves the formation of reactive hydroxyl radical species.