Oxotris(oxalate)niobate(V): An oxalate delivery agent in the design of building blocks

<p>This work concerns the oxalate delivery process that occurs when using (NH₄)₃[NbO(C₂O₄)₃]·6H₂O as a suitable oxalate source in the synthesis of two compounds, [Cu(dmphen)(C₂O₄)(H₂O)] (<b>1</b>) and [{Cu(dmphen)(CH₃OH)}₂(μ-C₂O₄)](ClO₄)₂ (<b>2</b>) (dmphen = 2,9-dimethyl-1,10-phenanthroline). {[Fe{HB(pz)₃}(CN)₂(μ-CN)]₂[{Cu(dmphen)}₂(μ-C₂O₄)]}∙<i>x</i>CH₃OH (<b>3</b>) (2.0 ≤ <i>x</i> ≤ 2.4) was obtained by reacting <b>2</b> and PPh₄[Fe{HB(pz)₃}(CN)₃]∙H₂O [ = tetraphenylphosphonium and  = tris(pyrazolyl)borate]. Crystal structures of <b>1</b>–<b>3</b> have been determined by single-crystal X-ray diffraction experiments: <b>1</b> is a mononuclear trigonal bipyramidal copper(II) species, <b>2</b> is a centrosymmetric oxalato-bridged dicopper(II) complex, and <b>3</b> consists of centrosymmetric tetranuclear units with intramolecular iron–copper and copper–copper distances around 5.010(1) and 5.1833(9) Å, respectively. Variable-temperature magnetic measurements of <b>2</b> and <b>3</b> were carried out from 50 to 350 (<b>1</b>) and 1.9 to 300 K (<b>3</b>). A strong antiferromagnetic interaction between copper(II) ions occurs in <b>2</b> (<i>J</i> = −340 cm⁻¹, the spin Hamiltonian being defined as ). Analysis of the magnetic data of <b>3</b> shows magnetic interactions across the oxalate (<i>J</i>₁ = −341 cm⁻¹) and single cyanide (<i>J</i>₂ = +12.9 cm⁻¹) … (<i>J</i>₂ = +12.9 cm⁻¹) bridges . Simple symmetry considerations of the interacting magnetic orbitals in <b>2</b> and <b>3</b> provide a clear picture of the exchange pathways involved in these complexes.</p

Structural Invariance of a ZnII Coordination Polymer with 5-Aminoisophthalic Acid under Different Synthetic Conditions

<div><p>A same coordination polymer [Zn(aip)(DMSO)] (aip: 5-aminoisophthalate and DMSO: dimethylsulfoxide) was synthesized using the same reactants (ZnSO4, aip and H2O/DMSO) but in different conditions, in which the stoichiometry (1:1-4:1 metal:ligand ratio), temperature (70 and 100 °C) and synthetic method (liquid-liquid diffusion, solvothermal and conventional with stirring) varied. A liquid assisted mechanochemical approach using ZnO as ZnII source instead ZnSO4, but keeping DMSO as milling liquid, also resulted in the same compound. This new coordination polymer was investigated using single-crystal X-ray diffraction technique, revealing a two-dimensional honeycomb-type network formation. The crystal structure was compared with either similar or isostructural compounds reported in the literature. Our studies show that the synthetic method and other synthetic variables do not affect the formation of [Zn(aip)(DMSO)] coordination polymers and probe the high stability (thermodynamic and kinetic) and structural invariance of this structure.</p></div

Lawsone Dimerization in Cobalt(III) Complexes toward the Design of New Prototypes of Bioreductive Prodrugs

Dimerization of lawsone occurs upon reaction with Co­(BF₄)₂·6H₂O and <i>N</i>,<i>N</i>′-bis­(pyridin-2-ylmethyl)­ethylenediamine (py₂en) to produce the mononuclear complex [Co^III(bhnq)­(py₂en)]­BF₄·H₂O (<b>1</b>). This complex has been investigated as a prototype of a bioreductive prodrug, where the bhnq^2– ligand acts as a model for cytotoxic naphthoquinones. Cyclic voltammetry data in aqueous solution have shown a <i>quasi</i>-reversible Co^III/Co^II process at <i>E</i>_1/2 = −0.26 V vs Fc/Fc⁺. Reactivity studies revealed the dissociation of bhnq^2– from the complex upon reduction of <b>1</b> with ascorbic acid, and a dependence of the reaction rate on the oxygen concentration suggests the occurrence of redox cycling

Lawsone Dimerization in Cobalt(III) Complexes toward the Design of New Prototypes of Bioreductive Prodrugs

Dimerization of lawsone occurs upon reaction with Co­(BF₄)₂·6H₂O and <i>N</i>,<i>N</i>′-bis­(pyridin-2-ylmethyl)­ethylenediamine (py₂en) to produce the mononuclear complex [Co^III(bhnq)­(py₂en)]­BF₄·H₂O (<b>1</b>). This complex has been investigated as a prototype of a bioreductive prodrug, where the bhnq^2– ligand acts as a model for cytotoxic naphthoquinones. Cyclic voltammetry data in aqueous solution have shown a <i>quasi</i>-reversible Co^III/Co^II process at <i>E</i>_1/2 = −0.26 V vs Fc/Fc⁺. Reactivity studies revealed the dissociation of bhnq^2– from the complex upon reduction of <b>1</b> with ascorbic acid, and a dependence of the reaction rate on the oxygen concentration suggests the occurrence of redox cycling

Alkaline Ion-Modulated Solid-State Supramolecular Organization in Mixed Organic/Metallorganic Compounds Based on 1,1′-Ethylenebis(4-aminopyridinium) Cations and Bis(oxamate)cuprate(II) Anions

Three new coordination compounds of formula (edap)₂­[Cu­(opba)]₂­·4H₂O (<b>1</b>), (edap)­[{Na₂(H₂O)₄}­{Cu₂(opba)₂}]­·2H₂O (<b>2</b>), and (edap)­[{K₂(H₂O)₂}­{Cu₂(opba)₂}]­·3H₂O (<b>3</b>) (edap = 1,1′-ethylenebis­(4-aminopyridinium) and opba = 1,2-phenylenebis­(oxamate)) were synthesized through the metathesis reaction involving A₂[Cu­(opba)] (A = Li⁺, Na⁺, and K⁺) and (edap)­Cl₂·2H₂O. Crystal structures of <b>1</b>–<b>3</b> and edap­(IO₃)₂­·4H₂O compound were elucidated by single crystal X-ray diffraction. Compounds <b>1</b>–<b>3</b> are built up from dinuclear copper­(II) entities, {[Cu­(opba)]₂}^4– with an asymmetric bis­(monatomic oxygen) bridge resulting from the parallel “out-of-plane” disposition of the planar mononuclear [Cu­(opba)]^2–. They possess distinct supramolecular arrangements of varying dimensionality (<i>n</i>D with <i>n</i> = 0 (<b>1</b>), 1 (<b>2</b>), and 2 (<b>3</b>)) in the solid state depending on the nature of the coordinated alkaline ion present alongside edap²⁺ counterions. While the {[Cu­(opba)]₂}^4– building blocks are well-isolated in <b>1</b>, they form either double chains or corrugated layers due to the coordination of the Na⁺ or K⁺ ions in <b>2</b> and <b>3</b>, respectively. Magnetic properties of <b>1</b>–<b>3</b> show a very weak antiferromagnetic coupling between the Cu^II ions through a double monatomic (μ-O) bridge (−<i>J</i> = 1.63(9) (<b>1</b>), 2.29(2) (<b>2</b>), and 1.65(3) cm^–1 (<b>3</b>)), the Hamiltonian being defined as <i><b>H</b></i> = −(<i><b>S</b></i>_{<i><b>1</b></i>}·<i><b>S</b></i>_{<i><b>2</b></i>}) + <i>g βH</i>(<i><b>S</b></i>_{<i><b>1</b></i>} + <i><b>S</b></i>_{<i><b>2</b></i>})

Tuning Photoluminescent Properties of Silver(I)-Based Coordination Networks through their Supramolecular Interactions

Eight novel luminescent silver­(I)-based coordination networks have been self-assembled from two flexible dicyanomethylene ligands bearing diethylene (<b>L1</b>) and triethylene glycol (<b>L2</b>) spacers and silver salts (AgClO₄ or AgBF₄) in dichloromethane/toluene or dichloromethane/benzene solvents. Single-crystal X-ray diffraction reveals a variety of geometries around the silver­(I) ion, resulting in mono-, bi-, and tetranuclear networks with rare topologies. The coordination networks show two-dimensional architectures through coordination of the cyano and glycolic groups to the silver­(I) ions. The three-dimensional supramolecular arrangement is formed through weak π···π and Ag···π interactions as well as hydrogen bonds between water molecules and ClO₄^– and BF₄^– counterions. The silver­(I)-based coordination networks display green to yellow emissions in the solid state, with quantum yields (Φ_em) varying from 1.1 to 8.5%. The emission properties are attributed to intraligand charge transfer and metal-perturbed intraligand transitions. Supramolecular interactions, such as Ag···π and π···π interactions, play an important role in the photophysical properties of these compounds

Influence of Synthetic Methods in the Structure and Dimensionality of Coordination Polymers

Eight different coordination polymers (CPs) of Co²⁺ and Zn²⁺ ions with rigid polycarboxylate ligands (fumaric acid (<i>fum</i>) and 2,5-dihydroxyterephalic acid (<i>dhbdc</i>)) have been synthesized using the same solvents, stoichiometry, and counterion but two different synthetic methods: liquid–liquid diffusion method–method A and pH control method–method B. The synthesis using method A resulted in four novel CPs: <i>trans</i>-Co­(dmso)₂­(H₂O)₂­(fum)]_<i>n</i> (<b>1</b>), [<i>trans</i>-Zn­(dmso)₂­(H₂O)₂­(fum)]_<i>n</i> (<b>2</b>), <i>trans</i>-Co­(dmso)₂­(H₂O)₂­(dhbdc)]_<i>n</i> (<b>3</b>), and [<i>trans</i>-Zn­(dmso)₂­(H₂O)₂­(dhbdc)]_<i>n</i> (<b>4</b>). Synthesis using method B resulted in one new ([Zn­(fum)­(OH)₂] (<b>6</b>)) and three previously described CPs ([Co₃(H₂O)₄­(OH)₂­(fum)₂]­·2H₂O (<b>5</b>), [Co₂(dobdc)] (<b>7</b>), and [Zn₂(dobdc)] (<b>8</b>), where <i>dobdc</i> = 2,5-dioxyterephtalic acid). The new CPs (<b>1</b>–<b>4</b>) were also structurally investigated by single-crystal X-ray diffraction techniques, which showed that all of them form one-dimensional (1D) CPs with linear chain structure: it was evidenced that (<b>1</b>) and (<b>3</b>) are isomorphus crystals of (<b>2</b>) and (<b>4</b>), respectively. The crystal structures of <b>1</b>–<b>4</b> were compared with similar 1D, two- and three-dimensional (2D and 3D) CPs reported in the literature. Intra- and interchain H-bond networks and coordination (<i>fum</i>, <i>dhbdc</i>, DMSO, water) as well as linkage (<i>fum</i> and <i>dhbdc</i>) isomerism guide the chain configuration (linear or zigzag). It was also demonstrated that the new series of 1D CPs synthesized here (<b>1</b>–<b>4</b>) can work as precursors for CP with higher dimensionality. Our studies showed that the synthetic method plays a crucial role in the crystal growth of coordination polymers

Crystal Engineering Applied to Modulate the Structure and Magnetic Properties of Oxamate Complexes Containing the [Cu(bpca)]⁺ Cation

This work deals with the crystal engineering features of four related copper­(II)-based compounds with formulas {[{Cu­(bpca)}₂­(H₂ppba)]·1.33DMF­·0.66DMSO}_<i>n</i> (<b>2</b>), [{Cu­(bpca)­(H₂O)}₂­(H₂ppba)] (<b>3</b>), [{Cu­(bpca)}₂­(H₂ppba)]­·DMSO (<b>4</b>), and [{Cu­(bpca)}₂­(H₂ppba)]­·6H₂O (<b>5</b>) [H₄ppba = <i>N</i>,<i>N</i>′-1,4-phenylenebis­(oxamic acid) and Hbpca = bis­(2-pyridylcarbonyl)­amide] and how their distinct molecular and crystal structures translate into their different magnetic properties. <b>2</b> and <b>3</b> were obtained through the hydrolytic reaction of the double-stranded oxamato-based dipalladium­(II) paracyclophane precursor of formula [{K₄(H₂O)₂}­{Pd₂(ppba)₂}] (<b>1</b>) with the mononuclear copper­(II) complex [Cu­(bpca)­(H₂O)₂]⁺, either in a water–DMSO–DMF solvent mixture or in water, respectively. The straightforward reaction of the neutral H₄ppba molecule with [Cu­(bpca)­(H₂O)₂]⁺ in a water–DMSO mixture afforded compound <b>4</b>, whereas compound <b>5</b> resulted from the reaction between the copper­(II) complex and the K₂ppba salt in water. The [Pd₂(ppba)₂]^4– tetraanionic unit which is present in <b>1</b> has a [3,3] metallacyclophane-type motif connected by two N–Pd–N bonds. This entity acts as a ligand toward partially hydrated potassium­(I) cations through its outer oxamate oxygens leading to a neutral three-dimensional network. The structure of <b>2</b> consists of neutral chains made up of double oxo­(carboxylate-oxamate)-bridged di­[{bis­(2-pyridylcarbonyl)­amidate}­copper­(II)] units are which connected by the extended H₂ppba^2– ligand, each of its oxamate fragments adopting a bidentate/outer monodentate coordination mode. Compounds <b>2</b>–<b>5</b> are neutral and centrosymmetric dicopper­(II) complexes which have in common the presence of peripheral bpca ligands and H₂ppba^2– as a bridge with each of its monoprotonated oxamate groups exhibiting rare monodentate (<b>3</b>) and bis-bidentate (<b>4</b> and <b>5</b>) coordination modes. Compounds <b>2</b>, <b>4</b>, and <b>5</b> share the same basic [{Cu­(bpca)}₂­(H₂ppba)] unit, but besides the difference in the cocrystallization solvent molecules and synthetic strategies, they feature very different crystal structures. To better understand the role of palladium­(II) ions in the formation of <b>2</b> and <b>3</b>, some studies were carried out using different mixtures of solvents such as water, DMSO, and DMF which revealed a major importance of DMF in the formation of <b>2</b> and the dependence on the palladium­(II) ions in the formation of <b>3</b>. A reaction pathway leading to the formation of <b>2</b> and <b>3</b> is then proposed. The variable-temperature (2.0–300 K) magnetic susceptibility measurements of <b>2</b>, <b>4</b>, and <b>5</b> revealed the occurrence of weak ferro- [<i>J</i> = +0.70 cm^–1 (<b>2</b>)] and antiferromagnetic interactions [<i>J</i> = −0.90 (<b>4</b>) and −0.79 cm^–1 (<b>5</b>)], the spin Hamiltonian being defined as <b>H</b> = −<i>J</i><b>S</b>₁·<b>S</b>₂. The different nature and strength of the magnetic coupling along this unique series of compounds are discussed in the light of the structural data, and they are compared with those of related dicopper­(II) systems

[Ag(L)NO₃] Complexes with 2‑Benzoylpyridine-Derived Hydrazones: Cytotoxic Activity and Interaction with Biomolecules

Complexes [Ag­(H2BzPh)­NO₃] (<b>1</b>), [Ag­(H2Bz<i>p</i>CH₃Ph)­NO₃] (<b>2</b>), [Ag­(H2Bz<i>p</i>ClPh)­NO₃] (<b>3</b>), and [Ag­(H2Bz<i>p</i>NO₂Ph)­NO₃] (<b>4</b>) were synthesized with 2-benzoylpyridine benzoylhydrazone (H2BzPh) and its <i>para</i>-methyl-benzoylhydrazone (H2Bz<i>p</i>CH₃Ph), <i>para</i>-chloro-benzoylhydrazone (H2Bz<i>p</i>ClPh), and <i>para</i>-nitro-benzoylhydrazone (H2Bz<i>p</i>NO₂Ph) derivatives. Experimental data indicate that the nitrate ligand binds more strongly to the silver center through one of the oxygen atoms, whereas the second oxygen atom from nitrate and the hydrazone oxygen makes much weaker interactions with the metal. Dissociation of nitrate most probably occurs in solution and in biological media. Interestingly, theoretical calculations suggested that when dissociation of the nitrate takes place, all bond orders involving the metal and the atoms from the hydrazone ligand increase significantly, showing that the bonding of nitrate results in the weakening of all other interactions in the metal coordination sphere. Upon complexation of the hydrazones to silver­(I), cytotoxicity against B16F10 metastatic murine melanoma cells increased in all cases. Complexes (<b>1–3</b>) proved to be more cytotoxic than cisplatin. All compounds were more cytotoxic to B16F10 cells than to nontumorigenic murine Melan-A melanocyte cells. Interestingly, the selectivity index (SI = IC_{50 non‑malignant cells}/IC_{50 tumor cells}) of complex (<b>1</b>), SI = 23, was much higher than that of the parent hydrazone ligand, SI = 9.5. Studies on the interactions of complexes (<b>1–3</b>) with DNA suggested that although (<b>1–3</b>) interact with calf thymus DNA by an intercalative mode, direct covalent binding of silver­(I) to DNA probably does not occur. Complexes (<b>1–3</b>) interact in vitro with human serum albumin indicating that these compounds could be transported by albumin

A Two-Dimensional Oxamate- and Oxalate-Bridged Cu^IIMn^II Motif: Crystal Structure and Magnetic Properties of (Bu₄N)₂[Mn₂{Cu(opba)}₂ox]

A new compound of formula (Bu₄N)₂[Mn₂{Cu­(opba)}₂ox] (<b>1</b>) [Bu₄N⁺ = tetra-<i>n</i>-butylammonium cation, H₄opba = 1,2-phenylenebis­(oxamic acid), and H₂ox = oxalic acid] has been synthesized and magneto-structurally investigated. The reaction of manganese­(II) acetate, [Cu­(opba)]^2–, and ox^2– in dimethyl sulfoxide yielded single crystals of <b>1</b>. The structure of <b>1</b> consists of heterobimetallic oxamato-bridged Cu^IIMn^II chains which are connected through bis-bidentate oxalate coordinated to the manganese­(II) ions to afford anionic heterobimetallic layers of 6³-hcb net topology. The layers are interleaved by <i>n</i>-Bu₄N⁺ counterions. Each copper­(II) ion in <b>1</b> is four-coordinate in a square planar environment defined by two amidate-nitrogen and two carboxylate-oxygen atoms from the two oxamate groups of the obpa ligand. The manganese­(II) ion is six-coordinate in a somewhat distorted octahedral surrounding that is built by two oxalate-oxygen and four carbonyl-oxygen atoms from two [Cu­(opba)]^2– units. The magnetic properties of <b>1</b> in the temperature range 1.9–300 K correspond to those expected for the coexistence of intralayer antiferromagnetic interactions of the type copper­(II)–manganese­(II) across oxamato and manganese­(II)–manganese­(II) through oxalato bridges plus a weak spin canting in the very low temperature domain. Simulation of the magnetic data through quantum Monte Carlo methodology reveals the magnitude of the intralayer magnetic interactions [<i>J</i>_CuMn = −32.5(3) cm^–1, and <i>J</i>_MnMn = −2.7(3) cm^–1], their values being within the range of those previously observed in lower nuclearity systems