Copper(II) binding of prion protein’s octarepeat model peptides

The complexes between copper(II) and the synthetic octapeptide fragments of the prion protein Ac-GWGQPHGG-NH₂ (1), Ac-PHGGGWGQ-NH₂ (3) and the cyclic analogue c-(GWGQPHGG) (2) have been comparatively investigated by circular dichroism (CD), absorption (UV-Vis), and electron paramagnetic resonance (EPR) spectroscopic methods.The results suggest a similar copper(II) coordination behaviour of the two linear peptides. In both cases two major complex species were spectroscopically detected. The first one, existing in the range of pH 7-9, showed spectroscopic parameters attributable to a 3N complex species, while the 4N complex was the main species at strongly alkaline pH values. Copper(II) binding appears to be confined within the aminoacid sequence HGG.Cyclisation of the main chain, as in the peptide 2, was found to have remarkable effects on the copper(II) complex speciation especially at pH 7-8 where the 3N species predominated in the linear counterparts. By contrast the spectroscopic data obtained at pH 11 provided evidence of the restoration of the same set of donor atoms as in the linear peptides.     

Copper(II) nitrato and chloro complexes with sterically hindered tridentate ligands: Influence of ligand framework and charge on their structure and physicochemical properties

Copper(II) coordination complexes of the neutral ligand, tris(3-tert-butyl-5-methyl-1-pyrazolyl)methane (L2′), i.e. the copper(II) nitrato complexes [Cu(L2′)(NO₃)][Cu(NO₃)₄]_1/2 (1) and [Cu(L2′)(NO₃)](ClO₄) (2) and the copper(II) chloro complex [Cu(L2′)(Cl)](ClO₄) (3), and its anionic borate analogue, hydrotris(3-tert-butyl-5-methyl-1-pyrazolyl)borate (L2⁻), i.e. the copper(II) nitrato complex [Cu(L2)(NO₃)] (4) and the copper(II) chloro complex [Cu(L2)(Cl)] (5), were synthesized in order to investigate the influence of ligand framework and charge on their structure and physicochemical properties. While X-ray crystallography did not show any definitive trends in terms of copper(II) atom geometry in four-coordinate copper(II) chloro complexes 3 and 5, different structural trends were observed in five-coordinate copper(II) nitrato complexes 1, 2, and 4. These complexes were also characterized by spectroscopic techniques, namely, UV-Vis, ESR, IR/far-IR, and X-ray absorption spectroscopy.     

Synthesis and characterization of monomer and dimer complexes of porphyrin iron(III) with bridging phenylcyanamide ligands

Several new mono and dinuclear complexes of [(P)Fe^III(L)], in which P is the dianion of tetraphenylporphyrin(TPP) and tetramesitylporphyrin(TMP) and L is the monoanion of 4-azo(phenylcyanamido)benzene (apc) (1) and (2) or dianion 1,4-di cyanamidobenzene (dicyd) (3), (4), (7), (8) and 4,4′-azo-diphenylcyanamide (adpc) (5), (6), (9), (10) have been prepared by the reaction of [(P)Fe^IIICl] with appropriate thallium salts of phenylcyanamide derivatives. Each of the complexes has been characterized by FT-IR, UV-Vis, ¹H NMR, MALDI-TOF and EPR spectroscopic data. In non-coordinating solvents (such as toluene or chloroform) these complexes exhibit ¹H NMR spectra that are characteristic of high-spin (S = 5/2) species. The cyanamide group (NCN) of the bridging ligand is coordinated to Fe(III) ions through the nitrile-nitrogen. The iron(III) phenylcyanamide complexes are not reactive toward dioxygen, they convert into [TPPFe^IIICl] when treated with HCl. EPR and NMR have shown that in dinuclear complexes weak magnetic interactions take place between two iron(III) paramagnetic centers.     

H2O2 reactivity of a dinuclear copper(II) complex incorporating a constrained binucleating polyaminopyridyl ligand and a phosphodiester coligand

A dinuclear copper(II) complex [Cu₂(PD)(DPP⁻)₂](ClO₄)₂ (1) incorporating a constrained binucleating hexadenate ligand, PD (1,3-bis{bis[(2-pyridyl)ethyl]amino}benzene), and coligand, DPP⁻ (diphenylphosphate) was synthesized and characterized, with a specific outlook towards evaluating spectroscopic and H₂O₂ reactivity relevant to the active-sites of noncoupled dinuclear copper enzymes, DβM and PHM. In solution, complex 1 exhibits a broad ¹H NMR in the range −25 to +60 ppm and has a solution magnetic moment (μ) of ∼2.0 B.M./Cu(II), typical of a noninteracting dicopper(II) center. The room temperature H₂O₂ reactivity of 1 monitored by UV-Vis spectroscopy reveals the formation of a copper(II)-dioxygen intermediate 1a, which in turn leading to a arene ligand hydroxylation (PD-O⁻) and thus provide a new doubly-bridged dicopper(II) complex, [Cu₂(PD-O⁻)(DPP⁻)](ClO₄)₂ (2). The dioxygen intermediate produces OPPh₃ on treatment with PPh₃ revealing it is an electrophilic hydroperoxide oxidant. Solution magnetic moment of 1.61 B.M./Cu(II) indicates the product complex 2 is a moderately interacting dicopper(II) center and its ¹H NMR spans between −20 and +180 ppm. A comparison of the optical absorption features of complex 1a with related dinuclear hydroperoxo-copper(II) complexes is discussed.     

Structural and spectroscopic comparison of five-coordinate cobalt(II) and nickel(II) thiolato complexes with the related four-coordinate complexes

Five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co and Ni) (L1 = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion and HSMeIm = 2-mercapto-1-methylimidazole), were synthesized. These complexes were compared with the corresponding Cu(II) and Zn(II) complexes with the same ligands and were also compared with the related four-coordinate complexes [L1M(SC₆F₅)] (HSC₆F₅ = pentafluorobenzenthiol). All the complexes were characterized by X-ray crystallography and UV-Vis absorption, IR, ¹H NMR, and other spectroscopic techniques. All five-coordinate thiolato complexes, [L1M(SMeIm)] (M = Co, Ni, and Cu), form a distorted square pyramidal structure with a high spin state, and only [L1Zn(SMeIm)] takes a four-coordinate structure with a distorted tetrahedral configuration. The N21-M-S bond angles of the obtained five-coordinate complexes were proportional to the corresponding d value, which comes from between the equatorial basal plane with N4S ligand donor sets and metal ion. These observations and M-S bond distances affect on UV-Vis and far-IR spectral behavior.     

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.     

Copper complexes with new oxaaza-pendant-armed macrocyclic ligands: X-ray crystal structure of a macrocyclic copper(II) complex

The synthesis of new oxaaza macrocyclic ligands (2-4) derived from O¹,O⁷-bis(2-formylphenyl)-1,4,7-trioxaheptane and functionalized tris(2-aminoethyl)amine are described. Mononuclear copper(II) complexes were isolated in the reaction of the corresponding macrocyclic ligand and copper(II) perchlorate. The structure of the [Cu(2)](ClO₄)₂ complex was determined by X-ray diffraction analysis. The copper(II) ion is five-coordinated by all N₅ donor atoms, efficiently encapsulated by the amine terminal pendant-arm, with a trigonal-bipyramidal geometry. The complexes are further characterized by UV-Vis, IR and EPR studies. The electronic reflectance spectra evidence that the coordination geometry for the Cu(II) complexes is trigonal-bipyramidal with the ligands 1 and 2 or distorted square-pyramidal with the ligands 3 and 4. The electronic spectra in MeCN solutions are different from those in the solid state, which suggest that some structural modification may occur in solution. The EPR spectrum of powder samples of the copper complex with 2 presents axial symmetry with hyperfine split at g_// with the copper nuclei (I = 3/2), which is characteristic of weakly exchange coupled extended systems. The EPR parameters (g_// = 2.230, A_// = 156 × 10⁻⁴ cm⁻¹ and g_⊥ = 2.085) indicate a d_x²-y² ground state. The EPR spectra of the complexes with ligands 3 and 4 show EPR spectra with a poorly resolved hyperfine structure at g_//. In contrast, the complex with ligand 2 shows no hyperfine split and a line shape which was simulated assuming rhombic g-tensor (g₁ = 2.030, g₂ = 2.115 and g₃ = 2.190).     

Spectroscopic and structural studies of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one and of an unusual T4(2)7(2)6(2)7(2) water tape stabilized by the copper(II) coordination polymer

The solid-state structures of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one (HL) and the copper(II) complex [Cu(L⁻)₂(OH₂)]·2H₂O (1) are established by X-ray crystallography and also by means of physicochemical and spectroscopic methods. The molecules of HL form a self-complementary head-to-tail hydrogen-bonded dimer through C-H?N and C-H?O contacts to give an infinite 1D chain. The copper(II) complex (1) is five-coordinate with distorted trigonal-bipyramidal (TBP) geometry of the N₄O donor atoms. The electronic and EPR data are in agreement with the X-ray structure of 1, showing that HL coordinates to copper(II) centre as a mono-anionic ligand through deprotonated pyridone N atom and the tertiary benzimidazole nitrogen atom to form a neutral complex in which the water molecule occupies the fifth position. The 1D water tape, T4(2)7(2)6(2)7(2) is anchored to the host through hydrogen bonds between coordinated water molecule [O(3w)] as acting double H-donor, pyridone carbonyl groups [O(2) and O(1)] as double H-acceptor and the lattice water molecules [O(4w) and O(5w)] as double H-donor and single H-acceptor).     

Nitric oxide reduction of copper(II) complex with tetradentate amine ligand followed by ligand transformation

Copper(II) complex 1 with a tetradentate ligand L [L = tris(2-aminoethyl)amine, tren] has been prepared as its perchlorate salt. Single crystal X-ray structure of 1 indicates its trigonal bipyramidal shape in the solid state. The complex, in dry and degassed acetonitrile solvent, was made to react with nitric oxide gas and the copper(II) center has been observed to reduce to Cu(I) with simultaneous nitrosation followed by diazotization at the terminal primary amine positions of the ligand to result into cyclization product, 1-(2-aminoethyl)piperzine, L′ along with tris(2-aminoethyl)ammonium perchlorate, L′′-perchlorate. However, when an acetonitrile:water (10:1, v/v) mixture has been used as the solvent, the reduction of Cu(II) to Cu(I) is observed and the ligand is found to be precipitated out only as L′′-perchlorate. The reduction of Cu(II) to Cu(I) has been studied by UV-visible, ¹H NMR and EPR spectroscopic techniques and by X-ray single crystal structure determination. Both the L′ and L′′-perchlorate have been isolated from the reaction mixture and characterized by using microanalytical studies, various spectroscopic techniques and X-ray single crystal structure determination.     

N-terminal fragment of the anti-angiogenic human endostatin binds copper(II) with very high affinity

A histidine-rich peptide HSHRDFQPVLHL-NH₂ (L), identical with the N-terminal fragment of the anti-angiogenic human endostatin has been synthesized. Endostatin is a recently identified broad spectrum angiogenesis inhibitor, which inhibits 65 different tumor types. The N-terminal 25-mer peptide fragment of human endostatin has the same antitumor effect as the entire protein. The zinc(II) binding is crucial for the antitumor effect in both cases. Our peptide may provide all critical interactions for zinc(II) binding present in the N-terminal 25-mer peptide fragment. In addition, the N-terminus of human endostatin has a supposedly high affinity binding site for copper(II), similar to human serum albumin. Since copper(II) is intimately involved in angiogenesis, this may have biological relevance.In order to determine the metal binding properties of the N-terminal fragment of endostatin, we performed equilibrium, UV-visible (UV-vis), CD, EPR and NMR studies on the zinc(II) and copper(II) complexes of L. In the presence of zinc(II) the formation of a stable {NH₂, 3N_im, COO⁻} coordinated complex was detected in the neutral pH-range. This coordination mode is probably identical to that present in the zinc(II) complex of the above mentioned N-terminal 25-mer peptide fragment of human endostatin. Moreover, L has extremely high copper(II) binding affinity, close to those of copper-containing metalloenzymes, and forms albumin-like {NH₂, N⁻, N⁻, N_im} coordinated copper(II) complex in the neutral pH-range, which may suggest that copper(II) binding is involved in the biological activity of endostatin.     

Synthesis, characterization, crystal structures and photophysical properties of copper(I) complexes containing 1,1′-bis(diphenylphosphino)ferrocene (B-dppf) in doubly-bridged mode

Five copper(I) complexes having general formula [Cu₂(μ-X)₂(κ²-P,P-B-dppf)₂] (X = Cl(1), Br(2), I(3), CN(4), and SCN(5)) were prepared starting with CuX and B-dppf in 1:1 molar ratio in DCM-MeOH (50:50 V/V) at room temperature. The complexes have been characterized by elemental analyses, IR, ¹H NMR, ³¹P NMR and electronic spectral studies. Molecular structures for 1, 2 and 4 were determined crystallographically. Complexes 1, 2 and 4 exist as centrosymmetric dimers in which the two copper atoms are bonded to two bridging B-dppf ligands and two bridging (pseudo-)halide groups in a μ-η¹ bonding mode to generate nearly planar Cu₂(μ-η¹-X)₂ framework. Both bridging B-dppf ligands are arranged in antiperiplanar staggered conformation in 1 and 2 (mean value 56.40-56.76°), and twisted from the eclipsed conformation (mean value 78.19°) in 4. The Φ angle value in 4 is relatively larger as compared to 1 and 2. This seems to indicate that the molecular core [Cu₂(μ-η¹-X)₂] in 4 is a sterically demanding system that forces the B-dppf ligand to adopt a relatively strained conformation in comparison to less strained system in 1 and 2. All the complexes exhibit moderately strong luminescence properties in the solution state at ambient temperature.     

Spectroscopic and electrochemical properties of heteroleptic cationic copper complexes bis-(diphenylphosphino)alkane-(2,2′-biquinoline)copper(I). Crystal structure of bis(diphenylphosphino)ethane-(2,2′-biquinoline)copper(I) perchlorate

A series of [Cu^(I)(2,2′-biquinoline)(L)](ClO₄) complexes (L = bis(diphenylphosphino)methane (bppm), 1,2-bis(diphenylphosphino)ethane (bppe), 1,4-bis(diphenylphosphino)butane (bppb)) have been synthesized and characterized by elemental analysis, conductivity, ESI-mass, NMR and UV-Vis spectroscopies, cyclic voltammetry, X-ray diffraction ([Cu^(I)(2,2′-biquinoline)(bppe)](ClO₄)) and DFT calculations. These compounds are monometallic species in a distorted tetrahedral arrangement, in contrast with related compounds found as dinuclear according to diffraction studies. The spectroscopic properties are not directly correlated with the length of alkyl chain bridge between the bis-diphenylphosphine groups. In this way, the chemical shift of some 2,2′-biquinoline protons and the metal to ligand charge transfer (Cu to 2,2′-biquinoline) follows the order [Cu(2,2′-biquinoline)(bppm)](ClO₄), [Cu(2,2′-biquinoline)(bppb)](ClO₄), [Cu(2,2′-biquinoline)(bppe)](ClO₄). The same dependence is followed by the potentials to Cu(II)/Cu(I) couple. These results are discussed in terms of inter-phosphorus alkane chain length and tetrahedral distortions on copper.     

Heterometallic complexes derived from ruthenocene-functionalized dipyrromethenes

A new ligand based on a ruthenocene moiety appended by a diyrromethene (Rc-dpm) was synthesized. Two copper complexes, Cu(Rc-dpm)₂ (3) and Cu(Rc-dpm)acac (4), and one cobalt complex, Co(Rc-dpm)₃, 5, were prepared from the ligand. These complexes were characterized by a combination of UV-Vis spectroscopy, elemental analysis, and X-ray crystallography. Copper(II) complex 3 was found to be coordinated by two dipyrromethene ligands in a distorted square planar environment around the copper while complex 4 had one dipyrromethene ligand and an acac coordinated in a nearly idealized square planar copper geometry. The cobalt(III) complex 5 has an octahedral geometry around the cobalt via the coordination of three dipyyromethene ligands.     

Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Anticancer and antifungal activity of copper(II) complexes of quinolin-2(1H)-one-derived Schiff bases

The condensation of substituted aromatic aldehydes with 7-amino-4-methyl-quinolin-2(1H)-one (1) has lead to the isolation of quinolin-2(1H)-one derived Schiff bases (2-14). The copper(II) complexes (2a-14a) of the ligands were also prepared, and together with their corresponding free ligands were fully characterised by elemental analyses, spectral methods (IR, ¹H and ¹³C NMR, AAS, UV-Vis), magnetic and conductance measurements. The bidentate ligands coordinated to the copper(II) ion through the deprotonated phenolic oxygen and the azomethine nitrogen of the ligands in almost all cases. X-ray crystal structures of two of the complexes, 5a and 8a, confirmed the bidentate coordination mode. All of the compounds were investigated for their antimicrobial activities against the fungus, Candida albicans, and against Gram-positive and Gram-negative bacteria. The compounds were found to have excellent anti-Candida activity but were inactive against Staphylococcus aureus and Escherichia coli. Selected compounds (2-8 and 2a-8a) were also screened for their in vitro anticancer potential using the human hepatic carcinoma cell line, Hep-G₂. Several derivatives were shown to be active comparable to that of cisplatin.     

Coordination driven self-assembly of metallamacrocycles using ambidentate linkers and self-selection of single linkage isomer

Nicotinate-N-oxide and isonicotinate-N-oxide have been employed to synthesize four heterometallic metallamacrocycles [(dppf)₂Pd₂(nicotinate-N-oxide)₂](OTf)₂ (1), [(dppf)₂Pt₂(nicotinate-N-oxide)₂](OTf)₂ (2), [(dppf)₂Pd₂(isonicotinate-N-oxide)₂](OTf)₂ (3) and [(dppf)₂Pt₂(isonicotinate-N-oxide)₂](OTf)₂ (4). The complexes represent the first examples of metallamacrocycles driven by solely Pd(II)/Pt(II)-O coordination using carboxylate-N-oxide donor. All the complexes 1-4 are characterized by IR, UV-Vis, multinuclear NMR spectroscopic and ESI-MS studies. The molecular structures of the complexes 1 and 3 are unambiguously determined by single crystal X-ray diffraction analysis. Despite the possibility of formation of several linkage isomers due to ambidentate nature of the donors, exclusive formation of [2 + 2] self-assembled single isomeric metallamacrocycle in each case is interesting observation.     

Solution and solid state study of copper(II) ternary complexes containing amino acids of interest for brain biochemistry - 1: Aspartic or glutamic acids with methionine or cysteine

Four new ternary complexes of Cu(II) containing aspartic or glutamic acids and methionine or cysteine as ligands were studied both in solution and in solid state. The solution study was performed using potentiometry, UV-Vis spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and electrochemistry. The stability constants of the ternary complexes were determined by potentiometry. The order of the values for the stability constants was CuGluMet (complex 4) < CuAspMet (complex 2) < CuGluCys (complex 3) < CuAspCys (complex 1), with complex 1 ≈ complex 3 ? complex 2 ≈ complex 4. This behavior was confirmed by the electronic spectra, EPR parameters and cyclic voltammetry. The compounds were synthesized in the solid state and characterized by thermogravimetry as well as vibrational and EPR spectroscopy. The results found in solid state are in agreement with the data found in solution studies where methionine, aspartic and glutamic acids coordinate to the copper(II) ion using the nitrogen atom of the amino group and one oxygen atom of the carboxylate group and cysteine coordinates through the nitrogen and sulfur atoms. The EPR data suggest that the complexes are square planar and that the complexes with cysteine as one of the ligands have some distortion.     

Synthesis and characterization of copper(II) complexes of 4-alkyl/aryl-1,2-naphthoquinones thiosemicarbazones derivatives as potent DNA cleaving agents

Copper (II) complexes of some alkyl/aryl-1,2 naphthoquinones thiosemicarbazone have been prepared and characterized. The crystal structure determined for one of the free ligands viz. 4-Pyrrolidine-1-yl-[1, 2] naphthaquinone thiosemicarbazone (5) indicates it to crystallize in the “E’ conformation which is supported by the NMR data. The ligands and copper complexes were evaluated for their DNA cleaving activities in case of circular double stranded plasmid DNA pBR322 under aerobic conditions. Amongst the ligands, compound 8 shows almost quantitative conversion to the linearized DNA in presence of H₂O₂ oxidant. All copper conjugates show more pronounced interaction with DNA while compounds 3 and 7 are able to yield linearized DNA in presence of the oxidant.     

Synthesis and characterization of [H2NC(S)NP(S)(OiPr)2] complexes of Co(II), Ni(II), Zn(II) and Cd(II)

Reaction of the potassium salt of the N-thiophosphorylthiourea H₂NC(S)NHP(S)(OiPr)₂ (HL) with Co(II), Ni(II), Zn(II) and Cd(II) cations in aqueous EtOH leads to the chelate complexes [ML₂] all showing a 1,5-S,S′-coordination formed by the CS and PS sulfur atoms of two deprotonated ligands L⁻. The structures of the resulting compounds were studied by IR, UV-Vis, ¹H, ³¹P{¹H} NMR spectroscopy and microanalysis. The metal center is found in a tetrahedral environment in [CoL₂], [ZnL₂] and [CdL₂]. According to NMR and UV-Vis spectroscopy the metal cation of [NiL₂] exhibits square planar coordination geometry in CH₂Cl₂, CHCl₃ and C₆H₆, while tetrahedral geometry is observed in acetone, DMSO and DMF. Regardless of the solvent used for the crystallization of [NiL₂], the molecular structure in the solid is always square planar as was confirmed by XRD of single crystals and magnetic measurements of the polycrystalline material. The magnetic and photoluminescent properties of all complexes are also reported.     

Ditopic bis(oxazolines): Synthesis and structural studies of zinc(II), copper(II) and nickel(II) complexes

The synthesis, crystal structures, magnetic and spectroscopic properties of zinc(II), nickel(II) and copper(II) dinuclear complexes 2-4 of a novel dinucleating polyoxazoline ligand 1 are reported. X-ray analysis revealed that the three complexes are centrosymmetric dinuclear species with an overall S shape, the bisoxazoline moieties pointing toward the aromatic core of the molecule. Magnetic susceptibility measurements suggest that there is a very weak exchange interaction between the copper or nickel ions in complexes 3 and 4.