Aqua Ligands Research Articles

Strong CO2 Chemisorption in a Metal-Organic Framework with Proximate Zn-OH Groups.

A novel Zn benzotriazolate metal-organic framework (MOF), [Zn9(OAc)6(bbtm)6] (1, bbtm2- = bis(benzotriazolyl)methanone, OAc- = acetate), has been synthesized and structurally characterized using micro-crystal electron diffraction. The framework contains 12-connected nonanuclear Zn clusters with Zn-OAc groups separated by short intercluster Zn···Zn distances of 6.06 Å. Postsynthetic OAc-/OH- ligand exchange followed by thermal activation generates 1a-OH, which adsorbs CO2 at very low pressures (1.37 mmol/g at 2.5 mbar) and requires an unusually high desorption temperature (>160 °C). Diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations have been used to interrogate the CO2 binding mechanism in 1a-OH. The formation of unsymmetric bridging carbonate ligands within the Zn···Zn pockets accompanied by strong hydrogen bonding of the carbonate with a neighboring zinc aqua ligand explains the remarkably strong CO2 affinity of 1a-OH.

Synthesis, Biophysical Interaction of DNA/BSA, Equilibrium and Stopped-Flow Kinetic Studies, and Biological Evaluation of bis(2-Picolyl)amine-Based Nickel(II) Complex.

Reaction of bis(2-picolyl)amine (BPA) with Ni(II) salt yielded [(BPA)NiCl2(H2O)] (NiBPA). The Ni(II) in NiBPA bound to a BPA ligand, two chloride, and one aqua ligands. Because most medications inhibit biological processes by binding to a specific protein, the stopped-flow technique was used to investigate DNA/protein binding in-vitro, and a mechanism was proposed. NiBPA binds to DNA/protein more strongly than BPA via a static quenching mechanism. Using the stopped-flow technique, a mechanism was proposed. BSA interacts with BPA via a fast reversible step followed by a slow irreversible step, whereas NiBPA interacts via two reversible steps. DNA, on the other hand, binds to BPA and NiBPA via the same mechanism through two reversible steps. Although BSA interacts with NiBPA much faster, NiBPA has a much higher affinity for DNA (2077 M) than BSA (30.3 M). Compared to NiBPA, BPA was found to form a more stable BSA complex. When BPA and NiBPA bind to DNA, the Ni(II) center was found to influence the rate but not the mechanism, whereas, for BSA, the Ni(II) center was found to change both the mechanism and the rate. Additionally, NiBPA exhibited significant cytotoxicity and antibacterial activity, which is consistent with the binding constants but not the kinetic stability. This shows that in our situation, biological activity is significantly more influenced by binding constants than by kinetic stability. Due to its selectivity and cytotoxic activity, complex NiBPA is anticipated to be used in medicine.

Multifunctional Luminescent Sensor Based on the Pb2+ Complex Containing a Tetrazolato Ligand.

A series of luminescent Pb2+ complexes, [Pb(L1)2]n (1), [Pb(L2)2]n (2), [Pb(L3)(NO3)(H2O)2]n (3), [Pb(L3)(Br)(H2O)]n (4), [Pb(L3)(Cl)(H2O)]n (5), and [Pb(L4)(H2O)2] (6) have been synthesized by treatment of polydentate tetrazolato ligands with various hydrated Pb2+ salts (HL1 = 2-(1H-tetrazol-5-yl)pyridine, HL2 = 3-(1H-tetrazol-5-yl)isoquinoline, HL3 = 6-(1H-tetrazol-5-yl)-2,2'-bipyridine, and H2L4 = 6,6'-bis(1H-tetrazol-5-yl)-2,2'-bipyridine). These complexes have been characterized by IR, TGA, and elemental analysis. Their crystal structures have been determined by X-ray crystallography, and the phase purity of bulk samples were further confirmed by PXRD. Their luminescence properties have been investigated in detail, and their emission origin may involve ligand-centered π-π* transition, metal-centered s-p transition and charge-transfer character. It is interesting to note that 5 exhibits obviously enhanced red-shifted emission, whose photoluminescence quantum yield (PLQY = 16.5%) is much higher than the other compounds (≤2%). Most importantly, the emission property of 5 was strongly affected by temperature. When the temperature rises from 295 to 493 K, the emission maximum gradually shifts to high energy due to the loss of the aqua ligand. In contrast, when the temperature is lowered from 295 to 13 K, two emission bands were observed. The low-energy emission band exhibits a slight blue shift, while a new high-energy emission band appears at around 520 nm, which is assigned to ligand-centered phosphorescence. After removal of the coordinated aqua ligand, the emission of 5-H2O is very sensitive to the vapors of volatile primary amines and acids, although they have different response mechanisms. This result indicates that 5-H2O may be a potential multifunctional sensor for temperature, volatile amines, and acids. To decipher the emission origin, DFT calculations have also been carried out based on the structure units of these compounds.

Enabling Aromatic Hydroxylation in a Cytochrome P450 Monooxygenase Enzyme through Protein Engineering.

The cytochrome P450 (CYP) family of heme monooxygenases catalyse the selective oxidation of C-H bonds under ambient conditions. The CYP199A4 enzyme from Rhodopseudomonas palustris catalyses aliphatic oxidation of 4-cyclohexylbenzoic acid but not the aromatic oxidation of 4-phenylbenzoic acid, due to the distinct mechanisms of aliphatic and aromatic oxidation. The aromatic substrates 4-benzyl-, 4-phenoxy- and 4-benzoyl-benzoic acid and methoxy-substituted phenylbenzoic acids were assessed to see if they could achieve an orientation more amenable to aromatic oxidation. CYP199A4 could catalyse the efficient benzylic oxidation of 4-benzylbenzoic acid. The methoxy-substituted phenylbenzoic acids were oxidatively demethylated with low activity. However, no aromatic oxidation was observed with any of these substrates. Crystal structures of CYP199A4 with 4-(3'-methoxyphenyl)benzoic acid demonstrated that the substrate binding mode was like that of 4-phenylbenzoic acid. 4-Phenoxy- and 4-benzoyl-benzoic acid bound with the ether or ketone oxygen atom hydrogen-bonded to the heme aqua ligand. We also investigated whether the substitution of phenylalanine residues in the active site could permit aromatic hydroxylation. Mutagenesis of the F298 residue to a valine did not significantly alter the substrate binding position or enable the aromatic oxidation of 4-phenylbenzoic acid; however the F182L mutant was able to catalyse 4-phenylbenzoic acid oxidation generating 2'-hydroxy-, 3'-hydroxy- and 4'-hydroxy metabolites in a 83 : 9 : 8 ratio, respectively. Molecular dynamics simulations, in which the distance and angle of attack were considered, demonstrated that in the F182L variant, in contrast to the wild-type enzyme, the phenyl ring of 4-phenylbenzoic acid attained a productive geometry for aromatic oxidation to occur.

Assembly of Sn(IV)-Porphyrin Cation Exhibiting Supramolecular Interactions of Anion···Anion and Anion···π Systems

Trans-diaqua[meso-tetrakis(4-pyridyl)porphyrinato]Sn(IV) dinitrate complexes were assembled in a two-dimensional manner via hydrogen bonding between aqua ligands and pyridyl substituents. Interestingly, this supramolecular assembly was accompanied by unconventional noncovalent interactions, such as anion···anion and anion···π interactions, which were confirmed by X-ray crystallographic analysis. Two nitrate anions close to 2.070 Å were constrained in a confined space surrounded by four hydrogen-bonded Sn(IV)-porphyrin cations. The nitrate anion was also 3.433 Å away from the adjacent pyrrole ring, and the dihedral angle between the two mean planes was estimated to be 7.39°. The preference of the anion···π interaction was related to the electron-deficient π-system owing to the high-valent Sn(IV) center and cationic nature of the porphyrin complex. These two unconventional noncovalent interactions played an important role in the formation of a one-dimensional array with pairs of Sn(IV)-porphyrin cation and nitrate anion.

Highly Active Visible Light-Promoted Ir/g-C3N4 Photocatalysts for the Water Oxidation Reaction Prepared from a Halogen-Free Iridium Precursor

A combination of the exceptional stability of fac-[Ir(H2O)3(NO2)3] together with thermolability of nitro and aqua ligands and high solubility in various solvents makes it promising as a brand-new chlorine-free precursor of iridium for the preparation of heterogeneous catalysts. In the current work, a new technique of fac-[Ir(H2O)3(NO2)3] preparation based on hydrothermal treatment of (NH4)3[Ir(NO2)6] was developed. For this purpose, the influence of reaction parameters such as the reaction time, temperature, and pH of the solution on the process of hexanitroiridate salt hydrolysis was investigated. The synthesized fac-[Ir(H2O)3(NO2)3] solution in this optimized way was used for the preparation of the series of Ir/g-C3N4 catalysts, which were evaluated in the water oxidation reaction with NaIO4 utilized as a sacrificial reagent. A 20-fold enhancement of the oxygen evolution reaction (OER) activity was found to take place under visible light (λ = 411 nm) illumination of the systems. The highest rate of the photoinduced OER per iridium center was achieved by the Ir0.005/g-C3N4 (air, 400°C) catalyst with an exceptional turnover frequency value of 967 min-1 approaching the activity of known homogeneous iridium OER catalysts. The leaching experiments have shown that aquated Ir species are generated in a solution after prolonged functioning of the catalysts. Despite this, in the closed system the photodriven OER activity persists at a steady-state level evidencing an equilibrium achieved between dissolved and anchored Ir species forming catalytic tandem with the g-C3N4.

Gd(III) metal-organic framework as an effective humidity sensor and its hydrogen adsorption properties

Metal-organic frameworks (MOFs) represent a class of nanoporous materials built up by metal ions and organic linkers with several interesting potential applications. The present study described the synthesis and characterization of Gd(III)-based MOF with the chemical composition [Gd(BTC)(H2O)]·DMF (BTC – trimesate, DMF = N,N′-dimethylformamide), known as MOF-76(Gd) for hydrogen adsorption/desorption capacity and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning and transmission electron microscopy. The crystal structure of MOF-76(Gd) consists of gadolinium (III) and benzene-1,3,5-tricarboxylate ions, one coordinated aqua ligand and one crystallization DMF molecule. The polymeric framework of MOF-76(Gd) contains 1D sinusoidally shaped channels with sizes of 6.7 × 6.7 Å propagating along c crystallographic axis. The thermogravimetric analysis, heating infrared spectroscopy and in-situ heating powder X-ray diffraction experiments of the prepared framework exhibited thermal stability up to 550 °C. Nitrogen adsorption/desorption measurement at −196 °C showed a BET surface area of 605 m2 g−1 and pore volume of 0.24 cm3 g−1. The maximal hydrogen storage capacity of MOF-76(Gd) was 1.66 wt % and 1.34 wt % −196 °C and −186 °C and pressure up to 1 bar, respectively. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Gd) is a suitable material for moisture sensing application with a fast response (11 s) and recovery time (2 s) in the relative humidity range of 11–98%.

Tetra-aqua-dodekakis-μ2-chlorido-di-iodido-octa-hedro-hexa-niobium(12 Nb-Nb) tetra-hydro-furan octa-solvate.

The title compound, [Nb6Cl12I2(H2O)4]·8THF (THF is tetra-hydro-furan, C4H8O), comprises an uncharged niobium cluster unit surrounded by THF solvent mol-ecules. The edges of the {Nb6} octa-hedron are μ 2-coordinated by twelve chlorido ligands. Four in-plane (equatorial plane) aqua ligands and two iodido ligands coordinating above and below the plane are bound at the corners of the {Nb6} atomic octa-hedron. O-H⋯O hydrogen bonds are formed between the aqua ligands and the THF solvent mol-ecules; one THF molecule is disordered over two positions with the major component having a site occupancy of 0.64 (2).

A highly stable terbium(III) metal-organic framework MOF-76(Tb) for hydrogen storage and humidity sensing.

The present study described the synthesis and characterization of MOF-76(Tb) for hydrogen storage and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning, and transmission electron microscopy. The crystal structure of MOF-76(Tb) consists of terbium(III) and benzene-1,3,5-tricarboxylate(-III) ions, one coordinated aqua ligand and one crystallization N,N´-dimethylformamide molecule. The polymeric framework of MOF-76(Tb) contains 1D sinusoidally shaped channels with sizes of 6.6 × 6.6 Å propagating along c crystallographic axis. The thermogravimetric analysis of the prepared material exhibited thermal stability up to 600 °C. At 77 K and pressure up to 20 bar; 0.6 wt.% hydrogen storage capacity for MOF-76(Tb) was observed. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Tb) is not a suitable material for moisture sensing applications.

A Crystalline Supramolecular Rotor Functioned by Dual Ultrasmall Polar Rotators†

Comprehensive SummaryAs an extended model of conventional molecular rotors, a conceived construction of novel crystalline molecular rotor that simultaneously contains two discrete polar rotators is presented here. The supramolecular self‐assembly of 18‐crown‐6 host and two rotator‐containing ion‐pair guests affords a three‐in‐one cocrystal, (2‐NH3‐iBuOH)(18‐crown‐6)[ZnBr3(H2O)], in which the hydroxyl group and aqua ligand both function as ultrasmall polar rotators. On the basis of the variable‐temperature single‐crystal X‐ray diffraction, variable‐temperature/frequency dielectric response, density functional theory calculations, and molecular dynamics simulations, it is found that such dual polar rotators experience a gradually enhanced rotation with increasing temperature, and more importantly, could be controlled by a reversible polar‐to‐polar structural phase transition, i.e., from a “single‐(polar rotator)” state at low‐temperature phase to a “mixed‐dual‐(polar rotator)” state in the vicinity of transition, and to an unusual “synchronized‐dual‐(polar rotator)” state at high‐temperature phase.

Mixed crystal of bis-(ammonium/oxonium) tetra-aqua-μ3-fluorido-dodeca-kis-(μ2-tri-fluoro-acetato)octa-hedro-hexa-ytterbiate(III) tetra-hydrate, [(NH4)1-x (H3O) x ]2[Yb6F8(O2CCF3)12(H2O)4]·4H2O (x = 1/4), containing a hexa-nuclear ytterbium(III) carboxyl-ate complex with face-capping fluoride ligands and comprising an unusual kind of substitutional disorder.

The reaction of ytterbium metal with ammonium tri-fluoro-acetate in liquid ammonia resulted in a green substance comprising a substantial amount of ytterbium(II) tri-fluoro-acetate that is a useful precursor for the oxidative synthesis of the new ytterbium(III) compound, [(NH4)1-x (H3O) x ]2[Yb6F8(O2CCF3)12(H2O)4]·4H2O (x = 1/4), in aqueous tri-fluoro-acetic acid. This mixed ammonium/oxonium crystalline solid is the first example of a substance containing an octa-hedro-hexa-nuclear ytterbium(III) complex with μ3-face-capping fluorido ligands. The main structural features of its [Yb6F8] core are non-bonding Yb⋯Yb distances and Yb-F bond lengths of 3.7576 (3)-3.9413 (5) and 2.2375 (17)-2.3509 (17) Å, respectively. Yb-O bond lengths involving the O atoms of O,O'-bridging carboxyl-ato ligands and vertex-substituting aqua ligands are in the ranges 2.23 (4)-2.329 (2) and 2.448 (2)-2.544 (3) Å, respectively. These bond lengths are in accordance with expectations, taking into account lanthanoid contraction. Inter-estingly, there is a significant ammonium versus oxonium ion site dependence, not only of the hydrate water mol-ecule positions within the solid's hydrogen-bonding framework, but also of the coordination sites of one carboxyl-ato and one aqua ligand in the hexa-nuclear complex.

Synthesis and crystal structure of di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II) bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato)(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II).

In the asymmetric unit of the title compound, trans-di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II) trans-bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato-κO)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II), [Zn(C10H24N4)(H2O)2][Zn(C13H9O5P)2(C10H24N4)], both Zn atoms lie on crystallographic inversion centres and the atoms of the macrocycle in the cation are disordered over two sets of sites. In both macrocyclic units, the metal ions possess a tetra-gonally elongated ZnN4O2 octa-hedral environment formed by the four secondary N atoms of the macrocyclic ligand in the equatorial plane and the two trans O atoms of the water mol-ecules or anions in the axial positions, with the macrocyclic ligands adopting the most energetically favourable trans-III conformation. The average Zn-N bond lengths in both macrocyclic units do not differ significantly [2.112 (12) Å for the anion and 2.101 (3) Å for the cation] and are shorter than the average axial Zn-O bond lengths [2.189 (4) Å for phospho-nate and 2.295 (4) Å for aqua ligands]. In the crystal, the complex cations and anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles, the O-H groups of coordinated water mol-ecules and the P-O-H groups of the acids as proton donors, and the O atoms of the phospho-nate and carboxyl-ate groups as acceptors, resulting in the formation of layers lying parallel to the (110) plane.

Synthesis, chemical and physical properties of lanthanide(III) (Nd, Gd, Tb) complexes derived from (E)-ethyl 4-(2-hydroxybenzylideneamino)benzoate

The 1:2 reaction between Ln(NO3)3·6H2O (1) (Ln = Nd (a), Gd (b) or Tb (c)) and ((E)-ethyl 4-((2-hydroxybenzylidene)amino)benzoate) (LN,OH) in ethanol has provided access to the complexes [LnIII(LNH,O)2(NO3)3(H2O)] (2a–c) in good yield. The isomorphous structures of 2a–c have been determined by single-crystal X-ray crystallography. The LnIII ions in 2a–c are coordinated by 9 oxygen atoms: two from the phenolate oxygen atoms of the Schiff bases, six from three chelating nitrato groups and one aqua ligand. The ligands LN,OH behave as monodentate phenolate O–donors, whereby an additional hydrogen atom is bonded to the imino nitrogen atom, resulting in a formally neutral ligand that adopts an exceptionally unusual coordination mode engaging in the zwitterionic form. The nine donor atoms that define the coordination polyhedra surrounding the LnIII ion are best described as capped square antiprisms. The crystal structures are based on a variety of intermolecular interactions. Hirshfeld surface analysis was used to assess the degree of interactions between the molecules. Susceptibility measurements on 2a–2c confirm the occurrence of the free ion ground 2S+1LJ state at room temperature. However, the magnetization measurements at 2 K revealed a lack of saturation at the highest applied field of 70,000 Oe for both 2a and 2c, indicating the presence of substantial magnetic anisotropy in these compounds. On the other hand, 2b exhibits perfect paramagnetic behavior with magnetic saturation at high fields, indicating the absence of significant magnetic anisotropy in this compound. Solid-state IR and UV/VIS data are discussed in terms of the structural features. Solid 2a–c emit in the visible region upon UV-Excitation with the emission exhibiting dopant characteristics.

Structural characterization of sodium and potassium 3-nitrohydrogenphthalate coordination polymers

Abstract The synthesis, crystal structures and properties of two alkali metal 3-nitrohydrogenphthalates obtained by a 1:2 reaction of M2CO3 (M = K or Na) with 3-nitrophthalic acid (LH2) are reported. In the anhydrous potassium coordination polymer [K(LH)] (LH = 2-carboxy-3-nitrobenzoate) 1, the K+ cation is bonded to nine oxygen atoms from six symmetry related (LH)– ligands resulting in a distorted {KO9} coordination polyhedron. Five of the six oxygen atoms including a nitro oxygen atom of the crystallographically unique 2-carboxy-3-nitrobenzoate are involved in metal binding. The μ6-bridging mode of (LH)– places the K+ cations into the layers of the two-dimensional (2D) coordination polymer. Each {KO9} polyhedron in 1 shares edges with two other polyhedra along the b and c axes. A low temperature structure redetermination of [Na(L#H)(H2O)3]·H2O (L#H = 2-carboxy-6-nitrobenzoate) 2 has revealed that the (L#H)− anion is bonded to the Na+ cation in a monodentate fashion via the carbonyl oxygen atom of the –COOH group and two of the three unique aqua ligands exhibit a bridging bidentate mode stabilizing a chain polymer. The structure of compound 2 thus consists of chains of edge-sharing {NaO6} octahedra. Thermal decomposition of 1 or 2 results in the formation of metal carbonate residues.

Crystal structure of novel [Ni(2aepy)(2ampy)Cl(H2O)]Cl·H2O complex comprising both 2-aminoethylpyridine (2aepy) and 2-aminomethylpyridine (2ampy) ligands within the coordination sphere and comparison of its thermal properties with analogous Ni(II) complexes with 2ampy and 2aepy ligands

Nickel(II) chloride in the presence of both 2ampy and 2aepy yielded a novel heteroleptic complex [Ni(2aepy)(2ampy)Cl(H2O)]Cl·H2O (1). Its ionic crystal structure is built up of complex cations [Ni(2aepy)(2ampy)Cl(H2O)]+, chloride anions and water solvate molecules. Within the complex cation both 2ampy and 2aepy are coordinated to the Ni(II) atom and its hexacoordination is completed by chlorido and aqua ligands. The supramolecular structure of 1 is built up of 2D hydrogen bonded system. Thermal properties of 1 and two additional analogous nickel(II) complexes, namely [Ni(2ampy)2(H2O)2]Cl2 (2), and [Ni(2aepy)2Cl(H2O)]Cl·H2O (3) were studied in air up to 800 °C. Analysis of the weight losses coupled with MS analyses of the evolved gases and with IR study of the solid intermediates have shown that the thermal decompositions of all complexes 1–3 start with dehydration and continues by decomposition of the aminoalkylpyridine ligands. Only in the case of 2 formation of dehydrated compound [Ni(2ampy)2Cl2] is indicated. The order of the thermal stabilities of the respective complexes is 3 > 2 > 1 according to the starting temperatures of dehydration.

Crystal structure of di-μ-chlorido-bis-{chlorido-[(-)-5,6-pinenebi-pyridine]-cobalt(II)} aqua-dichlorido[(-)-5,6-pinenebi-pyridine]cobalt(II).

The crystal structure of [Co2Cl4(C17H18N2)2][CoCl2(C17H18N2)(H2O)] or [Co(L)Cl(μ-Cl)]2[Co(L)(Cl)2(OH2)], where L is the enanti-opure bidentate ligand (-)-5,6-pinenebi-pyridine (C17H18N2), has been determined. Crystals suitable for X-ray structure analysis were obtained by slow evaporation of an ethano-lic solution containing equimolar amounts of L and CoCl2·6H2O. The CoII cations all have a coordination number of five, and in each case the coordination polyhedron is a trigonal bipyramid. The Co-N bonds lengths range from 2.037 (7) to 2.195 (7) Å, and Co-Cl bonds lengths range from 2.284 (2) to 2.509 (2) Å. The asymmetric unit contains two discrete complexes, one dinuclear and the other mononuclear. Between the two mol-ecules, two types of inter-molecular inter-actions have been evidenced: π-π stackings involving the bi-pyridine units, and O-H⋯Cl hydrogen bonds between the hydrogen atoms of the aqua ligand coordinating to the mononuclear complex and the non-bridging chlorido ligand coordinating to the dinuclear mol-ecule. These inter-actions lead to a two-dimensional supra-molecular arrangement parallel to the ab plane.

Bimetallic Organoplatinum(II)‐Ag(I) Cluster Cations with Ag−Pt Interactions Unsupported by Conventional Bridging Ligands

AbstractThe organoplatinum complex of a primary amine and AgClO4 aggregate in methanol to oligonuclear mixed‐metal species. A perchlorate salt 3 with the empirical formula C96H146Ag7Cl13N12O62Pt6 could be isolated and structurally characterized with the help of X‐ray diffraction at the DESY synchrotron. The product contains both a penta‐ and a tetra‐nuclear complex cation in which Ag(I) and Pt(II) alternate, held together without any conventional bridge. The cationic species feature short Ag⋅⋅⋅Pt distances between 2.7 and 2.9 Å and contacts longer than 2.4 Å between Ag and C atoms in aromatic rings. In addition to the interactions with Ag(I) cations, Pt(II) is in a square‐planar arrangement, coordinated by a chelating and a terminal amine and an aqua ligand. The central Ag(I) in the pentanuclear cation is located on a twofold crystallographic axis and not involved in any obvious coordinative bond; it exclusively shows short contacts to the neighboring Pt(II) ions and the Pt‐bonded, formally anionic carbon atoms of the cyclometallated organic ligand. Powder diffraction shows that 3 melts and re‐solidifies without decomposition.

An investigation into the coordination chemistry of tripodal “click” triazole ligands with Mn, Ni, Co and Zn ions

The steric influences of the triazole side chains in two tripodal chelating ligands tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) and tris[(1-phenyl-1H-1,2,3-triazol-4-yl)methyl]amine (TPTA) are explored through structural studies of four new mononuclear d-block metal complexes. The manganese(II) complex [Mn(TPTA)2](ClO4)2·H2O 1 includes two TPTA ligands each coordinated in a tridentate fashion to give an unusual trigonal prismatic coordination geometry with two non-coordinated pendant triazole groups which engage in weak hydrogen bonding interactions. [Ni(TBTA)(OH2)Cl]Cl·3H2O·MeCN 2 contains an octahedral nickel(II) centre bound by a tetradentate TBTA ligand along with aqua and chloride ligands, where the significant degree of lattice solvation leads to an extensive hydrogen bonding network linking complexes through hexa-aqua water clusters. The mononuclear copper(II) complex [Cu(TPTA)Cl2]·MeCN 3 contains no classical hydrogen bond donors but instead intermolecular aggregation takes place through chelating CH···Cl hydrogen bonds involving the acidic triazole CH groups which leads to close association of adjacent complexes. The zinc complex [Zn(TPTA)Cl]2[ZnCl4]·MeOH 4, in which cationic [Zn(TPTA)Cl]+ species are accompanied by tetrachlorozincate anions, exhibits a tris-triazole chelating coordination geometry for the TPTA ligand and associates through tetrameric π···π stacking interactions despite the positive charge present on each species. Structural analysis of these complexes, supported by solution-state mass spectrometry, NMR spectroscopic and magnetic susceptibility measurements, where applicable, provides new insights into the breadth of coordination geometries and intermolecular packing modes available to this important class of chelating ligand.

Novel heterometallic Zn(II)-L-Cu(II) complexes: studies of the nucleophilic substitution reactions, antimicrobial, redox and cytotoxic activity

New heterometallic complexes [{ZnCl(terpy)(μ-pyrazine)CuCl(terpy)}] (ClO4)2 (Zn-L1-Cu) and [{ZnCl(terpy)(μ-4,4′-bipyridyl)CuCl(terpy)}] (ClO4)2 (Zn-L2-Cu) (where terpy = 2,2′:6′,2′′-terpyridine, L1 = pyrazine, L2 = 4,4′-bipyridyl) were synthesized. The substitution reactions with biologically important nucleophiles were investigated at pH 7.4 by UV-Vis spectrophotometric method. The obtained results have shown different orders of reactivity of guanosine-5′-monophosphate (5′-GMP), inosine-5′-monophosphate (5′-IMP) and glutathione (GSH) toward heterometallic Zn(II)-L-Cu(II) complexes. Spectrophotometric titration of diaqua Zn-L-Cu complexes has shown that aqua ligands coordinated to both metal centers can exhibit different pK a values depending on the distance between them. Both synthesized complexes showed moderate antimicrobial activity against most of the tested bacterial and fungal strains. The cytotoxic activity of heteronuclear Zn-L1-Cu and Zn-L2-Cu complexes was determined on human colorectal cancer (HCT-116) and human healthy lung pleura (MRC-5) cell lines. Both complexes exerted significant cytotoxic effects, especially after 72 h (IC50 < 0.01 µM) and significantly reduced cell viability. Complexes induced a significant increase in reactive radical species which consequently induced cell death and thus lower IC50 values. As the response of the cells to an increased radical level induced by treatment, glutathione level also increased in a time and dose-dependent manner.

Zinc(II) and copper(II) complexes constructed from new bis(1H-1,2,3-triazole-4-carboxylate)-based ligands

Using triazolyl based ligands bearing carboxylate groups and cationic species [Cu(NN)(acac)(H2O)]+ and [Zn(NN)2(acac)]+ seven new coordination complexes have been synthesized: [Cu2(bipy)2(7a-2H)(H2O)2](7a-2H)⋅2H2O⋅4DMF 8, [Cu(phen)(7a-2H)]⋅7H2O 9, [Zn(bipy)(7a-2H)]⋅6H2O⋅DMF 10, [Zn(phen)(7a-2H)]⋅4H2O⋅2DMF 11, [Cu(phen)(7b-2H)(H2O)]⋅3H2O 12, [Zn(bipy)2(7b-2H)2(H2O)2]⋅4H2O 13 and [Zn(phen)(7b-2H)(H2O)2]⋅2H2O 14, 7a = 1,1′-(sulfonylbis(4,1-phenylene))bis(1H-1,2,3-triazole-4-carboxylic acid), 7b = 1,1′-(1,4-phenylene)bis(1H-1,2,3-triazole-4-carboxylic acid), bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline, acac− = acetylacetonate anion. Compound 8 is a dinuclear complex, where 7a-2H dianions function as bridging and uncoordinated ligand. Compounds 9-11 are 1-D coordination polymers with the angular spacer 7a-2H connecting the metal nodes in zig-zag chain motives. The mono- (12, 14) and dinuclear (13) units are generated by employing 7b as ligand. The supramolecular solid-state architecture is sustained by the presence of π-π stacking interactions (involving the pyridyl and phenyl group of the bis(1H-1,2,3-triazole-4-carboxylate) anions and co-ligand molecules) and hydrogen bonds (established between the aqua ligands, lattice water molecules and carboxylate groups).