Remaining Coordination Sites Research Articles

A study on complexation of Zn(II) salts with 4-aryl-2-(pyridin-2-yl)quinolines: The influence of anions on the complex structures and their luminescent properties

A novel ligand, 6‑methoxy-4-(4-methoxyphenyl)-2-(pyridin-2-yl)quinoline (PQ) was synthesized and studied for its interaction with ZnX2.nH2O (X: Cl-, OAc-,NO3−) to form three complexes of the type [Zn(X2)(PQ)(H2O)n] (Zn1-Zn3) with high yields, ranging from 75 to 94 %. The structures of Zn1–Zn3 were fully characterized using ESI mass spectrometry, IR and 1H NMR spectroscopy, and single-crystal X-ray diffraction (for Zn1 and Zn3). Spectroscopic analyses revealed that Spectroscopic analyses revealed that the central atom Zn(II) in Zn1, Zn2, and Zn3 has the coordination numbers of 4, 5, and 6, respectively. In these complexes, Zn(II) coordinates with the PQ ligand through its two nitrogen atoms, while the remaining coordination sites are occupied by anions such as Cl-, OAc, NO3−, or by H₂O. The results also indicate that the optical properties of the Zn(II) complexes depend not only on the primary organic ligand QP but also on the secondary inorganic ligands. In THF, the complexes Zn1 and Zn3, which contain chlorido and nitrato ligands exhibit intense fluorescence blue emissions at 443 and 462 nm with quantum yields of 0.66 and 0.70, respectively. Although the complex Zn2 has the weakest emission in THF, it exhibited the strongest blue emission intensity in solid state. In addition, computational studies provided insights into the structural and electronic properties, showing a strong correlation with experimental data. The calculated absorption and emission spectra were promarily based on the transition between HOMO and LUMO (π-π*) with high oscillator strength.

2D paddle wheel lanthanide metal-organic framework: Synthesis, structure and exploration of catalytic N-arylation reaction

Novel lanthanide based two-dimensional metal–organic framework (MOF) compound [Dy(NDC)(NO3)(DMA)2]n (1) [H2NDC = 2,6-naphthalenedicarboxylic acid and DMA = N,N-dimethylacetamide] has been synthesized through solvothermal route and structurally characterized. Structural analysis reveals that compound is crystallized in the orthorhombic crystal system with space group Pbca. MOF features “paddle-wheel” (PW) core building units which are constructed via carboxylato oxygen coordinated to lanthanide atoms. Remaining coordination sites of the octa-coordinated metal center are occupied by oxygen atoms of DMA and NO3− ions. Paddle-wheel cores of 1 are interconnected to each other to give rise to layered network structure. The morphology of the MOFs as well as different types of weak interactions possessed by the framework have been assessed using Hirshfeld surface analysis and fingerprint plots have been drawn to understand various interactions. Notably, compound 1 can efficiently catalyze the N-arylation reaction heterogeneously.

Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic Ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal Ions PdII, PtII, and RhIII.

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L1-L3 towards Platinum Group metal ions PdII, PtII, and RhIII. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H2O or MeOH/H2O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and 1H- and 13C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L1)Cl]2[Pd2Cl6], [Pt(L1)Cl](BF4), [Rh(L1)Cl2](PF6), and [Rh(L3)Cl2](BF4)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the PdII/PtII, and RhIII complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L3 with PtCl2 in MeCN/H2O gave by serendipity the complex [Pt(L3)(μ-1,3-MeCONH)PtCl(MeCN)](BF4)2·H2O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d8-d8 PtII-PtII ground-state nature for this compound, rather than the alleged d9-d7 PtI-PtIII mixed-valence character reported for related dinuclear Pt-complexes.

Comparative structural description of five arene ruthenium(II) complexes of N,N-bidentate Schiff base ligands to related complexes from literature

A series of new half-sandwich Ru(II) complex salts of the general formula [(η6-arene)RuX(L)]PF6 (where arene = p-cymene, X = Br and ligand L1 = N-tert-butyl-N-(pyridyl methylene) amine (complex 1), ligand L2 = N-isopropyl-2-pyridine carbaldimine (complex 2), ligand L3 = (2,5-dimethyl-phenyl)-pyridin-2-yl methylene amine (complex 3), ligand L4 = (3,5-dimethyl-phenyl)-pyridin-2-yl methylene (complex 4) and arene = C6H6, X = I, ligand L5 = (4-bromo-phenyl)-pyridin-2-yl methylene (complex 5) have been synthesized by reacting the ruthenium arene precursors [(η6-arene)Ru(μ-X)X]2 with N,N-bidentate ligands in a 1:2 ratio. Full characterization of the complexes was accomplished by physicochemical and spectroscopic methods and X-ray structures of all the complexes 1–5. The crystal structures reveal that the ruthenium centers in 1–5 are coordinated to the N,N-bidentate ligand in a bidentate manner, to the respective halide, and to the arene ring to give a pseudo-tetrahedral geometry around them. The whole arrangement is referred to as the three-legged piano stool, in which the N,N-bidentate ligand and the halide (Br or I) serve as the base occupying three coordination sites, while the arene ring serves as the apex of the stool and occupy the remaining coordination sites.

Tuning the catecholase activity of bis(pyrazolyl)methane-based copper(II) complexes by substitutions of the ligand core: unraveling a dual O2/H2O2 oxidation mechanism

Five new dinuclear copper(II) complexes based on dicompartmental ligands of the general formula R1R2R1-C6(OH)[C(O)-NH-CH2-CH(pz)2]2 (pz = pyrazolyl ring, R1 = R2 = H: HHH-Cu2; R1 = H, R2 = t-Bu: HButH-Cu2; R1 = Me, R2 = H: MeHMe-Cu2; R1 = Me, R2 = Br: MeBrMe-Cu2; R1 = Me, R2 = NO2: MeNO2Me-Cu2) were prepared and characterized in both solution and solid state. The phenoxide moiety acts as a bridge between two copper(II) centers; the remaining coordination sites of the metals are filled by the deprotonated N-amide atoms, the nitrogen atoms originating from the bis(pyrazolyl)methane groups and one exogenous hydroxide bridge. The catecholase-type activity of these dicopper complexes was studied in methanol, using a combination of aerobic and anaerobic methods. These investigations revealed that the substitution pattern of the central arene ring has an impact on the catalytic activity of our complexes, with the catalytic activity increasing in the following order: HHH-Cu2 <HButH-Cu2 <MeNO2Me-Cu2 <MeBrMe-Cu2 <MeHMe-Cu2. H2O2 was identified as the byproduct of O2 reduction. Its influence on the catalytic mechanism has been examined and found to have an impact on the catecholase-type reaction using these catalysts. Based on these findings, a dual mechanism for the catechol oxidation is proposed, where both molecular oxygen and the formed hydrogen peroxide act concurrently as oxidants.

Synthesis, Characterization and Thermal Studies of a Nanosized 1D l-Arginine/Copper(II) Coordination Polymer by Sonochemical Method: A New Precursor for Preparation of Copper(II) Oxide Nanoparticles

In the present work, 1D-copper(II) coordination polymer, {[Cu(μ-l-Arg)2(H2O)]SO4}n (1); (l-Arg: l-Arginine), was synthesized and identified by elemental analysis, FT-IR spectroscopy, molar conductivity, thermal gravimetric analysis (TGA), differential thermal analysis (DTA) and single-crystal X-ray diffraction. The compound 1 was also prepared by a sonochemical process in the form of nanoparticles. The particle size and morphology of the synthesized nanoparticles were investigated by powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FE-SEM). In the crystal structure of 1, the copper atoms are coordinated in a distorted octahedral geometry. In this geometry, the cis-equatorial plane (N2O2) is constructed by two NO-donor l-Arg ligands. The remaining coordination sites in the apical positions are occupied by an oxygen atom of the neighboring l-Arg and the oxygen atom of a water molecule. In 1, infinite one-dimensional (1D) networks are constructed through carboxylate bridges. Finally, CuO nanoparticles were produced by thermal decomposition of the sonochemically prepared nanoparticles of 1, and characterized by FT-IR, XRD, FE-SEM and EDS.

Synthesis and spectroscopic characterization of polynuclear silver(I) complex with 2,2'-biquinoline

Polynuclear silver(I) complex, [Ag(NO3-O)(2,2'-bq-N,N')]n, was synthesized by the reaction of equimolar amount of silver(I) nitrate and 2,2'-biquinoline (2,2'-bq) in ethanol at room temperature. The characterization of the complex was established on the basis of elemental microanalysis, IR, NMR (1H and 13C) and UV-Vis spectroscopic techniques. The results of spectroscopic analyses revealed that in [Ag(NO3-O)(2,2'-bq-N,N')]n complex, 2,2'-bq ligand behaves as a chelate, while the remaining coordination sites are occupied by the oxygen atoms of two nitrates.

Design and synthesis of novel ditopic ligands with a pyrazole ring in the central unit

Four novel ditopic ligands that have a pyrazole ring in their central unit and are useful for the generation of coordination polymers have been synthesized. Two of these ditopic ligands present two carboxylate functions as coordinating groups, while the other two are hybrid ligands having only one carboxylate function and either tetrazolate or imidazole as the remaining coordination site. The ligands have been obtained through a multi-step reaction sequence that begins with the Claisen condensation of either 4-acetylbenzonitrile or 4-(1H-imidazol-1-yl)acetophenone with diethyl oxalate and has the Knorr pyrazole ring closure as its key step. Subsequently, the tetrazolate in one of the ligands is constructed through a [3 + 2] cycloaddition of azide anion to the cyano group, while hydrolysis of the ester and the cyano substituents generates the carboxylate function(s). The structure of the intermediates and of the target ligands has been investigated by solution NMR, special attention being given to keto–enol and pyrazole tautomerism when present. The structure of two ligands and a key intermediate has also been established by single-crystal X-ray diffraction.

New polynuclear 1,5-naphthyridine-silver(I) complexes as potential antimicrobial agents: The key role of the nature of donor coordinated to the metal center

New polynuclear silver(I) complexes with 1,5-naphthyridine (1,5-naph), [Ag(NO3)(1,5-naph)]n (Ag1), [Ag(CF3COO)(1,5-naph)]n (Ag2) and [Ag(CF3SO3)(1,5-naph)]n (Ag3) were synthesized by the reaction of the corresponding silver(I) salt and 1,5-naph in ethanol at room temperature. These complexes were characterized by NMR, IR and UV–Vis spectroscopy, while their crystal structures were determined by single-crystal X-ray diffraction analysis. In all these complexes, 1,5-naph acts as a bridging ligand between two Ag(I) ions, while the remaining coordination sites are occupied by oxygen atom(s) of the corresponding anion. The antimicrobial efficiency of these silver(I) complexes was evaluated against the broad panel of Gram-positive and Gram-negative bacteria and fungi. The complexes showed good to moderate antibacterial activity with the minimal inhibitory concentration (MIC) values being in the range 2.5–100 μg/mL (6.5–333.3 μM), while their antifungal activity against the investigated Candida spp. was significantly higher (MIC = 0.78–6.25 μg/mL; 2.6–20.8 μM). Moreover, complexes Ag1 and Ag2 effectively inhibited C. albicans biofilms formation, while Ag1 was also shown to inhibit the formation of mixed C. albicans/Pseudomonas aeruginosa biofilms. Toxicological evaluations on zebrafish (Danio rerio) embryos revealed that all silver(I) complexes could be applied as antifungal agents, whereas Ag3 had the best therapeutic potential showing both the lowest MIC values against the tested Candida strains and the non-toxic in vivo response in the zebrafish embryos at these doses.

A Dy-based complex with the magnetic relaxation behavior regulated by enclosing one DyIII ion into a Calix[8]arene ligand

A new DyNa complex [DyIIINaI(CH3CO2)2(DMF)3(H6C8A)]·4DMF (1, DMF = N,N-dimethylformamide, H8C8A = p-tert-butylcalix[8]arene) was obtained and it was characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, PXRD and magnetic properties. In 1, one DyIII and one NaIII were linked by two O atoms from two CH3CO2− and the two metal ions were enclosed into a H8C8A. The remaining coordination sites of the DyIII and NaI ions were occupied by three O atoms from three DMF coordinated molecules. The DyIII ion in 1 adopts eight coordinate with a triangular dodecahedron. Magnetic property studies indicated complex 1 show slow magnetic relaxation behavior under 1000 Oe applied dc field. Additionally, the orientation of the anisotropy axis for the DyIII in 1 was estimated by Magellan program and the anisotropic axis is aligned along Dy1-O2 bond with an angle of 12.608°.

Crystal structure, shape analysis and bioactivity of new LiI, NaI and MgII complexes with 1,10-phenanthroline and 2-(3,4-dichlorophenyl)acetic acid.

Reactions of 1,10-phenanthroline (phen) and 2-(3,4-dichlorophenyl)acetic acid (dcaH) with Mn(CO3) (M = LiI, NaI and MgII; n = 1 and 2) in MeOH yield the mononuclear lithium complex aqua[2-(3,4-dichlorophenyl)acetato-κO](1,10-phenanthroline-κ2N,N')lithium(I), [Li(C8H5Cl2O2)(C12H8N2)(H2O)] or [Li(dca)(phen)(H2O)] (1), the dinuclear sodium complex di-μ-aqua-bis{[2-(3,4-dichlorophenyl)acetato-κO](1,10-phenanthroline-κ2N,N')sodium(I)}, [Na2(C8H5Cl2O2)2(C12H8N2)2(H2O)2] or [Na2(dca)2(phen)2(H2O)2] (2), and the one-dimensional chain magnesium complex catena-poly[[[diaqua(1,10-phenanthroline-κ2N,N')magnesium]-μ-2-(3,4-dichlorophenyl)acetato-κ2O:O'] 2-(3,4-dichlorophenyl)acetate monohydrate], {[Mg(C8H5Cl2O2)(C12H8N2)(H2O)2](C8H5Cl2O2)·H2O}n or {[Mg(dca)(phen)(H2O)2](dca)·H2O}n (3). In these complexes, phen binds via an N,N'-chelate pocket, while the deprotonated dca- ligands coordinate either in a monodentate (in 1 and 2) or bidentate (in 3) fashion. The remaining coordination sites around the metal ions are occupied by water molecules in all three complexes. Complex 1 crystallizes in the triclinic space group P-1 with one molecule in the asymmetric unit. The Li+ ion adopts a four-coordinated distorted seesaw geometry comprising an [N2O2] donor set. Complex 2 crystallizes in the triclinic space group P-1 with half a molecule in the asymmetric unit, in which the Na+ ion adopts a five-coordinated distorted spherical square-pyramidal geometry, with an [N2O3] donor set. Complex 3 crystallizes in the orthorhombic space group P212121, with one Mg2+ ion, one phen ligand, two dca- ligands and three water molecules in the asymmetric unit. Both dcaH ligands are deprotonated, however, one dca- anion is not coordinated, whereas the second dca- anion coordinates in a bidentate fashion bridging two Mg2+ ions, resulting in a one-dimensional chain structure for 3. The Mg2+ ion adopts a distorted octahedral geometry, with an [N2O4] donor set. Complexes 1-3 were evaluated against urease and α-glucosidase enzymes for their inhibition potential and were found to be inactive.

Synthesis and structural analysis of polynuclear silver(I) complexes with 4,7-phenanthroline

New polynuclear silver(I) complexes, [Ag(CF3SO3)(4,7-phen)(CH3CN)]n (1) and [Ag(PO2F2)(4,7-phen)]n (2), were synthesized by the reaction of 4,7-phenanthroline (4,7-phen) and the corresponding AgX salt (X = CF3SO3 - and PF6 -) in 1:2 mole ratio, respectively, in methanol/acetone (1:1 volume ratio) at room temperature. The characterization of the complexes was established on the basis of elemental microanalysis, IR and NMR (1H and 13C) spectroscopic techniques, while their crystal structures were determined by single-crystal X-ray diffraction analysis. The results of spectroscopic and crystallographic analyses revealed that in these complexes, 4,7-phen behaves as a bridging ligand between two metal ions, while the remaining coordination sites of the Ag(I) ions are occupied by the oxygen atom of CF3SO3 - and an acetonitrile nitrogen atom in 1 or by two oxygen atoms from two PO2F2 -, formed after hydrolysis of PF6 -, in 2. In the solid state, both complexes are coordination polymers in which the geometry around the Ag(I) ions is distorted tetrahedral.

An unexpected μ4-oxido-bridged tetranuclear Cu(II) inverse coordination complex of a heptadentate bis(pyrazolyl)methane-based ligand: Synthesis, structure, spectroscopic properties, and catecholase activity

A new tetranuclear copper(II) complex, {But-C6H2(O)[CH = N-CH2-CH(pz)2]2}2Cu4(μ4-O)(OAc)4 (L2Cu4(μ4-O)(OAc)4, pz = pyrazolyl ring) has been prepared from the condensation reaction of 4-tert-butyl-2,6-diformylphenol with two equivalents of bis(pyrazolyl)ethanamine moieties in the presence of two equivalents of copper(II) acetate. The complex has been characterized by X-ray diffraction studies in solid state, as well as by UV–Vis, IR, and ESI spectroscopies. The structure of this inverse coordination complex consists of a central oxygen ion surrounded by four copper(II) cations residing in the corners of a distorted tetrahedron; the remaining coordination sites of the Cu2+ ions are filled by imine donors and acetate counter-ions, leaving the bis(pyrazolyl)methane donor groups uncoordinated to the copper(II) centers. In contrast to the solid-state structure, this compound was found to be dinuclear in solution, LCu2(OAc)2(OH). The complex catalyzes the oxidation of 3,5-di-tert-butylcatechol (DTBC) and 4-tert-butylcatechol (TBC) to their corresponding quinones. The catalytic mechanism was investigated using DTBC as a substrate, and it was found that the oxidation reaction occurs via two different pathways, one involving molecular oxygen and the other hydrogen peroxide as oxidants.

Formations of unexpected chloro-bridged bis(macrocycle) dicopper(II) complexes via decomposition of dichloromethane as a source of chloro-ligands

Abstract The 20-membered N3O2-macrocycle L reacts with copper(II) salts (NO3, ClO4) in dichloromethane/methanol to yield unexpected isostructural chloro-bridged dinuclear bis(macrocycle) copper(II) complexes of type [LCuII-(μ-Cl)2-CuIIL]X2 (1: X = NO3, 2: X = ClO4). Each complex contains two five-coordinate copper(II) ions which are bridged by two chloro-ligands, (μ-Cl)2, and the remaining coordination sites are completed by three nitrogens from the macrocycle. Notably, the chloro-bridging ligands are derived from the partial decomposition of the dichloromethane solvent molecules. Analogous reaction employing copper(I) chloride also afforded a similar dimer complex, [LCuII-(μ-Cl)2-CuIIL]Cl2 (3), suggesting such type of the chloro-bridged dicopper(II) complexes are thermodynamically stable under the reaction conditions employed in this work. Considering the τ values (0.45–0.52) for the five-coordinated copper(II) centers, complexes 1–3 present an intermediate geometry between square planar and trigonal bipyramidal arrangements.

Synthesis, structures and magnetic properties of three copper(II) complexes of 2-(1H-pyrazol-3-yl) pyridine

Three Cu(II) complexes: [Cu2(μ-L)2(HCOO)2(H2O)2] (1), [Cu2(μ-L)2(NO3)2] (2), and [Cu4(μ-L)6(CH3COO)2]·2H2O (3) constructed from 2-(1H-pyrazol-3-yl) pyridine (HL) were synthesized and structurally characterized by X-ray single-crystal diffraction. The X-ray analyses revealed that all three complexes feature a di-ligand-bridged Cu2 unit, which is nearly planar. Each deprotonated ligand chelates one copper atom by means of N,N(pyridine-pyrazole) pocket and simultaneously bridges the other one by the N,N(pyrazole) groups. The remaining coordination sites of the Cu(II) centers are either occupied by different anionic coligands to balance the charge, or bridged by another L to develop a tetranuclear structure. Magnetic investigations reveal that the distortion of the Cu(II) coordination geometry (as described by the τ values) and the coplanarity of the Cu–(N=N)2–Cu unit have cooperative effects on the antiferromagnetic strength of these systems.

Crystal structure of a looped-chain CoII coordination polymer: catena-poly[[bis-(nitrato-κO)cobalt(II)]bis-[μ-bis-(pyridin-3-ylmeth-yl)sulfane-κ2N:N']

The asymmetric unit of the title compound, [Co(NO3)2(C12H12N2S)2] n , contains a bis-(pyridin-3-ylmeth-yl)sulfane (L) ligand, an NO3- anion and half a CoII cation, which lies on an inversion centre. The CoII cation is six-coordinated, being bound to four pyridine N atoms from four symmetry-related L ligands. The remaining coordination sites are occupied by two O atoms from two symmetry-related nitrate anions in a monodentate manner. Thus, the CoII centre adopts a distorted octa-hedral geometry. Two symmetry-related L ligands are connected by two symmetry-related CoII cations, forming a 20-membered cyclic dimer, in which the CoII atoms are separated by 10.2922 (7) Å. The cyclic dimers are connected to each other by sharing CoII atoms, giving rise to the formation of an infinite looped chain propagating along the [101] direction. Inter-molecular C-H⋯π (H⋯ring centroid = 2.89 Å) inter-actions between one pair of corresponding L ligands and C-H⋯O hydrogen bonds between the L ligands and the nitrate anions occur in the looped chain. In the crystal, adjacent looped chains are connected by inter-molecular π-π stacking inter-actions [centroid-to-centroid distance = 3.8859 (14) Å] and C-H⋯π hydrogen bonds (H⋯ring centroid = 2.65 Å), leading to the formation of layers parallel to (101). These layers are further connected through C-H⋯O hydrogen bonds between the layers, resulting in the formation of a three-dimensional supra-molecular architecture.

A four-coordinate cadmium(II) polymer for efficient adsorption of Congo red, kinetic, isotherm, fluorescence and antibacterial activity

A 3-D cadmium-based coordination polymer, [CdCl2L]n (1) (where L = 1,1-(1,6-hexanediyl)bis(1,3-dihydro-3-methyl-1H-imidazole-2-thione), was synthesized and structurally characterized. The capability of the polymer as an efficient sorbent for Congo red (CR) removal from aqueous solution has been evaluated. Compound 1 has a tetrahedral arrangement with a CdS2Cl2 core. L in 1 is bidentate to two neighboring CdII centers via the methimidazole sulfurs to create 1D chains propagating along the c-axis. The remaining coordination sites are occupied by two terminal chlorides. The chains are further stabilized by intermolecular C–H⋯Cl hydrogen bonds between the chlorides and hydrogens of the imidazole rings. Parallel chains stack in the 3-D structure. The CdII polymer sorbent was characterized by infrared spectroscopy, elemental analysis, UV–vis, solid fluorescence and X-ray single-crystal diffraction. Sorption kinetics were studied by three kinetic models, second order, Elovich and intraparticle diffusion. The results indicate that the mechanism of the sorption process followed Elovich kinetic model. Sorption equilibrium was also studied with Langmuir, Temkin, and Freundlich isotherm models. The sorption process followed the Temkin isotherm. MIC, MBC, and DNA cleavage activities of 1 were also studied. Furthermore, the UV–vis and solid state fluorescence spectra of 1 were measured.

Gallium Complexation, Stability, and Bioconjugation of 1,4,7-Triazacyclononane Derived Chelators with Azaheterocyclic Arms.

We have recently introduced a 1,4,7-triazacyclononane (TACN) based chelating system with additional five-membered azaheterocyclic substituents for complexation of radioactive Cu2+ ions. In this work, we investigated the complexation properties of these novel chelators with Ga3+. In labeling experiments, we could show that the penta- and hexadentate imidazole derivatives NODIA-Me 4 and NOTI-Me 1 can be labeled with 68Ga in specific activities up to ∼30 MBq nmol-1, while the corresponding thiazole derivative NOTThia 2 did not label satisfactorily under identical conditions. NMR studies on the Ga complexes of 1 and the model compound NODIA-Me-NH-Me 5 revealed formation of rigid 1:1 chelates with a slow macrocyclic interconversion and inert Ga-N bonds to the methylimidazole residues on the NMR time scale. The TACN-derived bifunctional chelator NODIA-Me was furthermore conjugated to a prostate-specific membrane antigen (PSMA) targeting moiety to give the corresponding bioconjugate NODIA-Me-PSMA 7. Serum stability and ligand challenge experiments of 68Ga-7 confirmed formation of a stable complex for up to 4 h. The remaining coordination site of five-coordinate Ga complexes was found to be occupied by monodentate ligands including hydroxide and chloride anions depending on the conditions. According to density functional theory calculations, coordination of monodentate ligands as well as of the amide group for the bioconjugated ligand are energetically plausible. Finally, the labeled bioconjugate 68Ga-7 exhibited rapid renal clearance in biodistribution studies performed by small animal PET imaging with no indication of transchelation/demetalation in vivo. Altogether, our results provide strong evidence for a stable Ga complexation of our novel TACN-based chelators bearing imidazole arms. Despite the formation of two complexes incorporating different monodentate ligands in vitro, the imidazole type ligands show promise as chelating agents for the future development of gallium based radiopharmaceuticals.

Synthesis, crystal structures and antimicrobial activity of azido and isocyanato Zn(II) complexes with the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent

Two Zn(II) complexes with the condensation product of 2-quinolinecarboxaldehyde and trimethylammonium acetohydrazide chloride (Girard’s T reagent) (HLCl) and monodentate pseudohalides (azide and cyanate) have been synthesized and characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. In both complexes, the coordination surroundings of the Zn(II) ions consist of a deprotonated hydrazone ligand coordinated through an NNO set of donor atoms and two monodentate pseudohalides (N3– or NCO–) at the remaining coordination sites. The Zn(II) complexes showed low to moderate activity against laboratory control strains of pathogenic bacteria and fungi.

Calixsmaragdyrin: A Versatile Ligand for Coordination Complexes.

The Ru(II) and BF2 complexes of calixsmaragdyrin were prepared under simple reaction conditions and characterized by HR-MS, 1D and 2D NMR spectroscopy, optical spectroscopy, and electrochemistry, and the structure of the Ru(II) complex of calixsmaragdyrin was elucidated by X-ray crystallography. The crystal structure of the Ru(II) complex revealed that the Ru(II) ion is hexacoordinate with the three pyrrole nitrogen ligands from the tripyrrin unit of the calixsmaragdyrin macrocycle, and the remaining coordination sites of Ru(II) ion were occupied by two carbonyl groups and one hydroxyl (-OH) group. The calixsmaragdyrin macrocycle in the Ru(II) complex was distorted with a dome-like structure. In the BF2 complex of calixsmaragdyrin, the BF2 unit was bound to two pyrrolic nitrogens of the dipyrrin moiety of calixsmaragdyrin as deduced by detailed 1- and 2-dimensional NMR spectroscopy studies. The Ru(II) complex displayed a strong Soret-like absorption band at 449 nm with the absence of Q-bands, whereas the BF2 complex showed a Soret-like band at 475 nm with two well-defined Q-bands at 787 and 883 nm, respectively. Quantum mechanical DFT calculations yielded relaxed equilibrium structures that were similar to the X-ray crystal structures, and the related charge density distributions indicated that the d orbital of the Ru(II) ion was contributing to the HOMO and LUMO states. In addition, TD-DFT calculations successfully reproduced the large bathochromic shifts, oscillator strengths, and electronic transitions that were observed in the experimental absorption spectra of all three complexes. Both the Ru(II) and the BF2 complexes of calixsmaragdyrin were stable under redox conditions.