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

Selective Wrapping of Few-Walled Carbon Nanotubes by a Serpent-Like Heterobimetallic Coordination Polymer

In this work, selective interactions between the constituents of the composite CNT@MnCu (<b>2</b>) prepared using carbon nonotubes (CNTs) (<b>1</b>) and the heterobimetallic chain [MnCu­(opba)]_<i>n</i> (MnCu), opba = <i>o</i>-phenylenebis­(oxamate), were studied mainly by resonance Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM). An apparent interaction between CNTs and MnCu complex with the wrapping of the former by the heterobimetallic complex was observed in the microscopy images. The resonance Raman data suggest that the interations between MnCu complex and the CNTs are selective, occurring mainly with metallic CNTs independently of the diameter and excitation energy. However, for semiconducting CNTs, these interactions solely occur with tubes having diameters higher than ca. 1.47 nm

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

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

Dicopper(II) Metallacyclophanes with <i>N,N</i>′‑2,6-Pyridinebis(oxamate): Solution Study, Synthesis, Crystal Structures, and Magnetic Properties

The complexing ability of copper­(II) in solution by the ligand <i>N,N</i>′-2,6-pyridinebis­(oxamic acid) (H₄mpyba, H₄L) was determined through potentiometric and UV–vis spectroscopy at 25 °C and 0.15 M NaCl. The logarithms of the equilibrium constants for its copper­(II) complexes according to the eqs 2H₂L + 2Cu ⇆ [Cu₂(H₂L)₂], 2H₂L + 2Cu ⇆ [Cu₂(H₂L) (HL)] + H, 2H₂L + 2Cu ⇆ [Cu₂(HL)₂] + 2H, 2H₂L + 2Cu ⇆ [Cu₂(HL)­(L)] + 3H, and 2H₂L + 2Cu ⇆ [Cu₂L₂] + 4H were 12.02(7), 8.04(5), 1.26(6), −7.51(6), and −16.36(6), respectively. The knowledge of the solution behavior has supported the synthesis of three new compounds bearing the common building block Cu₂L₂^4–. Their formulas are (Me₄N)₄[Cu₂(mpyba)₂(H₂O)₂]·H₂O (<b>1</b>), (Me₄N)₄[K₂Na₂Cu₄(mpyba)₄(H₂O)_6.8]·1.6H₂O (<b>2</b>), and [Na₆Cu₂(mpyba)₂Cl₂(H₂O)₈]·7H₂O (<b>3</b>) (Me₄N⁺ = tetramethylammonium cation). The [Cu₂(mpyba)₂(H₂O)₂]^4– tetraanionic unit, which is present in <b>1</b>, has a [3,3] metallacyclophane-type motif connected by two N–Cu–N bonds. In <b>2</b>, a heterotrimetallic decanuclear nanocage is formed through front-to-front assembly of two [Cu₂(mpyba)₂]^4– units, which also coordinate to potassium­(I) and sodium­(I) cations by means of carboxylate oxygens from oxamate. The structure of <b>3</b> consists of heterobimetallic layers of formula [Na₆Cu₂(mpyba)₂Cl₂(H₂O)₈] and crystallization water molecules, which are interlinked by hydrogen bonds leading to a supramolecular three-dimensional network. The investigation of the magnetic properties of <b>1</b>–<b>3</b> in the temperature range 1.9–300 K shows the occurrence of ferromagnetic interactions between the dicopper­(II) metallacyclophane unit [<i>J</i> = +6.85 (<b>1</b>), +7.40 (<b>2</b>), and +7.90 cm^–1 (<b>3</b>); <i><b>H</b></i> = −<i>J<b>S</b></i>_Cu1·<i><b>S</b></i>_Cu2, where <i>S</i>_Cu1 = <i>S</i>_Cu2 = 1/2]. Theoretical calculations on <b>1</b>–<b>3</b> were carried to substantiate the nature and magnitude of the involved magnetic interactions and to support the occurrence of a spin polarization mechanism accounting for them

Influence of Copper(II) and Nickel(II) Ions in the Topology of Systems Based on a Flexible Bis-Oxamate and Bipyridine Building Blocks

Single crystals of the mononuclear bis-oxamate nickel­(II) complex [Ni­(bipy)­(H₂edpba)]·dmso (<b>1</b>) are obtained by reacting [Ni­(bipy)­Cl₂]·H₂O and the flexible K₂(H₂edpba) ligand [bipy = 2,2′<b>-</b>bipyridine; H₄edpba = <i>N</i>,<i>N</i>′-2,2′-ethylenediphenylenebis­(oxamic acid)]. The reaction of <b>1</b> with copper­(II) ions resulted in two products in which the replacement of the nickel­(II) ion by copper­(II) took place: the chain compound [Cu­(bipy)­(H₂edpba)]_<i>n</i>·3<i>n</i>H₂O·<i>n</i>dmso [dmso = dimethyl sulfoxide] (<b>2</b>) and the analogous chain compound without dmso crystallization molecules [Cu­(bipy)­(H₂edpba)]_<i>n</i>·1.5<i>n</i>H₂O (<b>3a</b>) in its polycrystalline form. The reaction of [Cu­(bipy)­Cl₂] and K₂(H₂edpba) yielded single crystals of [Cu­(bipy)­(H₂edpba)]_<i>n</i>·1.5<i>n</i>H₂O (<b>3b</b>). The H₂edpba^2– ligand exhibits the <i>anti</i> conformation in <b>1</b>, <b>2</b>, and <b>3b</b>, but it adopts different coordination modes: terminal bis-bidentate (<b>1</b>) and bridging bis-bidentate (<b>2</b> and <b>3b</b>) through the two pairs of carbonyl-oxygen atoms of the two oxamate arms. Magnetic susceptibility measurements carried out on a polycrystalline sample of <b>3b</b> in the temperature range 1.9–295 K showed the occurrence of very weak intrachain antiferromagnetic interactions [<i>J</i> = −0.40 cm^–1, the Hamiltonian being defined as <i><b>H</b></i> = −<i>J</i> ∑_<i>i</i><i><b>S</b></i>_<i>i</i>·<i><b>S</b></i>_<i>i</i>+1], in agreement with the large values of the copper–copper separation [8.308(3) Å]

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

Palladium(II)–Copper(II) Assembling with Bis(2-pyridylcarbonyl)amidate and Bis(oxamate) Type Ligands

Five new complexes of formula K₄[Pd₂(mpba)₂] · 4H₂O (<b>1</b>), {[K₄(H₂O)­(dmso)]­[Pd₂(mpba)₂]} (<b>2</b>), {[Cu­(bpca)]₄[Pd₂(mpba)₂]} · 6H₂O (<b>3</b>), {[Cu­(bpca)]₂[Pd­(opba)]} · 1.75dmso · 0.25H₂O (<b>4</b>), {[Cu­(bpca)]₂[Pd­(opba)]}_<i>n</i> · <i>n</i>dmso (<b>5</b>) [H₄mpba =1,3-phenylenebis­(oxamic acid), H₄opba = 1,2-phenylenebis­(oxamic acid), Hbpca = bis­(2-pyridylcarbonyl)­amide, and dmso = dimethyl sulfoxide] have been prepared and investigated by infrared spectroscopy, thermal analysis, single crystal X-ray diffraction, and magnetic susceptibility techniques. The structure of <b>2</b> consists of a [Pd₂(mpba)₂]^4– anionic entity in which the palladium­(II) cations are coordinated by two mpba ligands resulting in a dipalladium­(II) unit that acts as a ligand toward potassium­(I) cations leading to a neutral three-dimensional network. Compound <b>3</b> is a neutral hexanuclear complex where the dinuclear [Pd₂(mpba)₂]^4– unit adopts a tetrakis­(bidentate) coordination mode toward four [Cu­(bpca)]⁺ end-cap entities. This compound can be viewed as a “dimer of trimers” in which two Cu^II–Pd^II–Cu^II trinuclear units are connected by two mpba ligands. Compounds <b>4</b> and <b>5</b> have in common the presence of a [Pd­(opba)]^2– unit, which acts as a bis­(bidentate) ligand toward two [Cu­(bpca)]⁺ entities to afford neutral heterotrinuclear Cu^II–Pd^II–Cu^II motifs that are interlinked through weak double (<b>4</b>) and single (<b>5</b>) out-of-plane copper­(II) to carbonyl­(bpca)-oxygen atoms leading to uniform linear (<b>4</b>) and zigzag (<b>5</b>) chains of heterobimetallic trinuclear units. The investigation of the magnetic properties of <b>3</b>–<b>5</b> in the 1.9–300 K temperature range reveals the presence of very weak antiferromagnetic interactions between the copper­(II) ions. The nature and magnitude of these magnetic interactions are discussed in terms of orbital symmetry considerations