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

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>})

Solvent effects on the dimensionality of oxamato-bridged manganese(II) compounds

<p>Two new oxamate-containing manganese(II) complexes, [{Mn(H₂edpba)(H₂O)₂}₂]_n (<b>1</b>) and [Mn(H₂edpba)(dmso)₂]∙dmso∙CH₃COCH₃∙H₂O (<b>2</b>) (H₄edpba = <i>N,N′</i>-ethylenediphenylenebis(oxamic acid) and dmso = dimethylsulfoxide), have been synthesized and the structures of <b>1</b> and <b>2</b> were characterized by single crystal X-ray diffraction. The structure of <b>1</b> consists of neutral honeycomb networks in which each manganese(II) is six-coordinate by one H₂edpba²⁻ ligand and two carboxylate–oxygens from two other H₂edpba²⁻ ligands building the equatorial plane. Each manganese is connected to its nearest neighbor through two carboxylate(monoprotonated oxamate) bridges in an <i>anti</i>-<i>syn</i> conformation. A dmso solution of single crystals of <b>1</b> was placed under acetone atmosphere affording <b>2</b>, whereas putting <b>2</b> in equimolar water:ethanol mixture results in <b>1</b>. The molecular structure of <b>2</b> is made up of mononuclear manganese(II) units which are interlinked by weak C–H⋯π and edge-to-face π-stacking interactions leading to supramolecular chains along the crystallographic <i>b</i> axis. Magnetic measurements reveal the occurrence of an antiferromagnetic coupling between two manganese(II) ions through <i>anti-syn</i> carboxylate bridges for <b>1</b> [<i>J</i> = −1.18 cm⁻¹, the Hamiltonian being defined as <b><i>H</i> </b>= −<i>J</i> <b><i>S</i></b>₁^.<b><i>S</i></b>₂] and very weak intrachain ferromagnetic interactions in <b>2</b> [<i>J</i> = + 0.046 cm⁻¹, <b><i>H</i></b> = −<i>J</i> ∑_i<b><i>S</i></b>_i^.<b><i>S</i></b>_i + 1].</p

Photoluminescent and Slow Magnetic Relaxation Studies on Lanthanide(III)-2,5-pyrazinedicarboxylate Frameworks

In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide­(III) organic frameworks of formula {[Ln₂(2,5-pzdc)₃(H₂O)₄]·6H₂O}_<i>n</i> [Ln = Ce (<b>1</b>), Pr (<b>2</b>), Nd (<b>3</b>), and Eu (<b>4</b>)] and {[Er₂(2,5-pzdc)₃(H₂O)₄]·5H₂O}_<i>n</i> (<b>5</b>). Single-crystal X-ray diffraction on <b>1</b>–<b>5</b> reveals that they crystallize in the triclinic system, <i>P</i>1̅ space group with the series <b>1</b>–<b>4</b> being isostructural. The crystal structure of the five compounds are 3D with the lanthanide­(III) ions linked through 2,5-pzdc^2– dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·6⁴8)­(4²6²8²)-<b>mog</b> network. The photophysical properties of the Nd­(III) (<b>3</b>) and Eu­(III) (<b>4</b>) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of <b>4</b> were very sensitive due to the luminescence quenching of the ⁵D₀ level by O–H oscillators of four water molecules in the first coordination sphere leading to a quantum efficiency of 11%. Variable-temperature magnetic susceptibility measurements for <b>1</b>–<b>5</b> reveal behaviors as expected for the ground terms of the magnetically isolated rare-earth ions [²F_5/2, ²H₄, ⁴I_9/2, ⁷F₀, and ⁴I_15/2 for Ce­(III), Pr­(III), Nd­(III), Eu­(III), and Er­(III), respectively] with <i>M</i>_<i>J</i> = 0 (<b>2</b> and <b>4</b>) and ±1/2 (<b>1</b>, <b>3</b>, and <b>5</b>). Q-band electron paramagnetic resonance measurements at low temperature corroborate these facts. Frequency-dependent alternating-current magnetic susceptibility signals under external direct-current fields in the range of 100–2500 G were observed for the Kramers ions of <b>1</b>, <b>3</b>, and <b>5</b>, indicating slow magnetic relaxation (single-ion magnet) behavior. In these compounds, τ^–1 decreases with decreasing temperature at any magnetic field, but no Arrhenius law can simulate such a dependence in all the temperature range. This dependence can be reproduced by the contributions of direct and Raman processes, the Raman exponent (<i>n</i>) reaching the expected value (<i>n</i> = 9) for a Kramers system