Magneto-structural correlation in dimeric copper(II) benzoates

Synthesis and Characterization of a New Cu(II) Paddle-Wheel-like Complex with 4-Vinylbenzoate as an Inorganic Node for Metal-Organic Framework Material Design

A new Cu(II) paddle-wheel-like complex with 4-vinylbenzoate was synthesized using acetonitrile as the solvent. The complex was characterized by X-ray crystal diffraction, FT-IR, diffuse reflectance spectroscopy, thermogravimetric, differential scanning calorimetric, magnetic susceptibility, and electronic paramagnetic resonance analyses. The X-ray crystal diffraction analysis indicated that each copper ion was bound at an equatorial position to four oxygen atoms from the carboxylate groups of the 4-vinylbenzoate ligand in a square-based pyramidal geometry. The distance between the copper ions was 2.640(9) Å. The acetonitrile molecules were coordinated at the axial position to the copper ions. Exposure of the Cu(II) complex to humid air promoted the gradual replacement of the coordinated acetonitrile by water molecules, but the complex structure integrity remained. The EPR spectra exhibited signals attributed to the presence of a mixture of the monomeric (S = ½) and dimeric (S = 1) copper species in a possible 3:1 ratio. The magnetic studies revealed a peak at 50-100 K, which could be associated with the oxygen absorption capacity of the Cu(II)-vba complex.

Copper(II) 2,2-Bis(Hydroxymethyl)Propionate Coordination Compounds with Hexamethylenetetramine: From Mononuclear Complex to One-Dimensional Coordination Polymer

Three new copper coordination compounds derived from 2,2-bis(hydroxymethyl)propionic acid (dmpa) and hexamethylenetetramine (hmta) were obtained and their crystal structures were determined. The stoichiometry of the reagents applied in the syntheses reflects the metal to ligand molar ratio in the formed solid products. Due to the multiple coordination modes of the used ligands, wide structural diversity was achieved among synthesized compounds, i.e., mononuclear [Cu(dmp)₂(hmta)₂(H₂O)] (1), dinuclear [Cu₂(dmp)₄(hmta)₂] (2), and 1D coordination polymer [Cu₂(dmp)₄(hmta)]_n (3). Their supramolecular structures are governed by O—H•••O and O—H•••N hydrogen bonds. The compounds were characterized in terms of absorption (UV-Vis and IR) and thermal properties. The relationships between structural features and properties were discussed in detail. Owing to discrepancies in the coordination mode of a dmp ligand, bidentate chelating in 1, and bidentate bridging in 2 and 3, there is a noticeable change in the position of the bands corresponding to the stretching vibrations of the carboxylate group in the IR spectra. The differences in the structures of the compounds are also reflected in the nature and position of the UV-Vis absorption maxima, which are located at lower wavelengths for 1.

Structural, Spectroscopic, Thermal, and Magnetic Properties of a New Dinuclear Copper Coordination Compound with Tiglic Acid

The first coordination compound of copper and tiglic acid named tetrakis(μ-tiglato)bis(tiglic acid)dicopper(II) was synthesized and crystallized from water solution. Its structure was determined and analyzed based on X-ray diffraction measurement. The paddle-wheel coordination system of the investigated compound was compared with other similar copper structures known in the literature. The Hirshfeld analysis was used for the detailed analysis of intermolecular interaction. The new compound was also characterized in terms of infrared absorption, thermal, and magnetic properties. The antiferromagnetic coupling of copper ions was found.

Ring opening polymerization of d,l-lactide and ε-caprolactone catalysed by (pyrazol-1-yl)copper(ii) carboxylate complexes

1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc)₂] and C₆H₅COOH, 4-OH-C₆H₄COOH, 2-Cl-C₆H₄COOH and (3,5-NO₂)₂-C₆H₃COOH to afford the copper complexes [Cu₂(C₆H₅COO)₄(L)₂] (1), [Cu₂(4-OH-C₆H₄COO)₄(L)₂] (2), [Cu₂(2-Cl-C₆H₄COO)₄(L)₂]_n (3) and [Cu{(3,5-NO₂)₂-C₆H₃COO}₂L]_n (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7H₂O, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one. Catalysis studies performed with these complexes (1–4) showed that they initiate ring opening polymerization (ROP) of ε-caprolactone (ε-CL) under solvent-free conditions and d,l-lactide in toluene at elevated temperatures. Polycaprolactone (PCL) and poly(d,l-lactide) (PLA) obtained from the polymerization reactions are of low molecular weights (858 for PCL and 602 Da for PLA for initiator 1) and polydispersity indices (typically 2.16 for PCL and 1.64 for PLA with 1 as the initiator). End group analysis of the polymers, determined by MALDI-ToF MS, indicates that the polymers have benzoate, hydroxyl, methoxy and cyclic end groups.

We report the synthesis, structure and complete characterization of four new pyrazolyl carboxylate-based copper(ii) complexes that catalyze the ring opening polymerization of ε-caprolactone under solvent-free conditions and of d,l-lactide in toluene.

Copper(II) Carboxylates with 2,3,4-Trimethoxybenzoate and 2,4,6-Trimethoxybenzoate: Dinuclear Cu(II) Cluster and µ-Aqua-Bridged Cu(II) Chain Molecule

Copper(II) complexes with 2,3,4-trimethoxybenzoic acid (H234-tmbz) and 2,4,6-trimethoxybenzoic acid (H246-tmbz), [Cu2(234-tmbz)4(H2O)2] (6) and [Cu(246-tmbz)2(µ-H2O)2(H2O)2]n (7), were synthesized and characterized by elemental analysis, infrared and UV-vis spectra and temperature dependence of magnetic susceptibilities (1.9–300 K). The X-ray crystal structures revealed that the former 6 is a dinuclear cluster having syn-syn-bridged Cu2(µ-234-tmbz)4 core with Cu···Cu separation of 2.6009(7) Å, while the latter 7 is a µ-aqua-bridged chain molecule consisting of Cu(246-tmb)2(µ-H2O)2(H2O)2 units with Cu···Cu separation of 4.1420(5) Å. Temperature dependence of magnetic susceptibilities showed that an antiferromagnetic interaction with 2J = −272 cm−1 for 6 and a weak antiferromagnetic interaction with J = −0.21 cm−1 for 7, between the two copper(II) ions. The adsorption isotherm of 6 showed Types I behavior having a 125.4 m2g−1 of specific surface area.

A theoretical insight into the formation of chalcogen bonding (ChB) interactions involving coordinated DMSO molecules as σ-hole donors and benzoate groups as σ-hole acceptors in a dinuclear copper(ii) complex

The formation of two chalcogen bonding (ChB) interactions involving coordinated DMSO molecules as σ-hole donors and the O atoms of carboxylate groups as acceptors in a dimeric copper(ii) complex has been described.

Studies on the hard confinement effect on the RAFT polymerization of a monomeric ionic liquid. Unexpected triggering of RAFT polymerization at 30 °C

For the first time, the RAFT polymerization of a monomeric ionic liquid under hard confinement was successfully carried out.

Polymerization of Monomeric Ionic Liquid Confined within Uniaxial Alumina Pores as a New Way of Obtaining Materials with Enhanced Conductivity

Broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC) have been employed to probe dynamics and charge transport of 1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide ([bvim][NTf₂]) confined in native uniaxial AAO pores as well as to study kinetics of radical polymerization of the examined compound as a function of the degree of confinement. Subsequently, the electronic conductivity of the produced polymers was investigated. As observed, polymerization carried out at T = 363 K proceeds faster under confinement with some saturation effect observed for the sample in pores of smaller diameter. Obtained results were discussed in the context of the very recent reports showing that the free volume of the confined material is higher with respect to the bulk one. It was also noted that conductivity of poly[bvim][NTf₂] is significantly higher with respect to the macromolecules obtained upon bulk polymerization. Moreover, charge transport of the confined macromolecules is even higher when compared to the bulk monomeric ionic liquid at some thermodynamic conditions. Additionally, the molecular weight, M_w, of the confined-synthesized polymers is significantly higher with respect to the bulk-synthesized material. Interestingly, both parameters, (i) the enhancement of σ_dc and (ii) the increase in M_w, can be tuned and controlled by the application of the appropriate confinement. Consequently, those results are quite promising in the context of development of the fabrication of polymerized ionic liquids (PILs) nanomaterials with unique properties and morphologies, which can be further easily applied in the field of nanotechnology.

3,3'-di(pyrazinamoyl)-2,2'-bipyridine: rational ligand design for the self-assembly of a 1-D coordination polymer

A new ligand, 3,3'-di(pyrazinamoyl)-2,2'-bipyridine, L3H2 has been prepared and is comprised of distinct binding domains capable of facilitating the formation of coordination polymers. Reaction of L3H2 with [Cu2(OAc)4(H2O)2] in the presence of Et3N·HCl affords the complex {[Cu6(L3)2(Cl)2(OAc)6]·2H2O·2MeOH}n (1) in which the [L3](2-) anion binds two unique copper ions in a bis-tridentate fashion via amide and pyridyl N atoms. This bimetallic unit is linked to an equivalent unit via a pair of 1,3-acetato and μ-chloro bridges to afford a tetrameric [Cu4(L3)2Cl2(OAc)2] core. Coordination of one of the pyrazole substituents from each ligand to a third copper centre of a rigid paddlewheel [Cu2(OAc)4] unit leads to a unique 1-D polymeric structure. Magnetic studies of 1 reveal that the magnetism can be described in terms of two sets of exchange interactions; strong antiferromagnetic interactions between the two copper centres within the "paddle-wheel" (J/k = -190 K) and a combination of weaker ferro- and antiferro-magnetic interactions within the tetrameric core (J'/k = -5.7 K and J''/k = +2.1 K).

The synthesis, spectroscopy and X-ray single crystal structure of catena-[(μ-anacardato)-copper(II)bipyridine][Cu2{(μ-O2CC6H3(o-OH)(o-C15H31)}4(NC5H5)2]

Hydrogenation of crude anacardic acid gave a transparent crystalline product on recrystallization. When reacted with copper nitrate in the presence of pyridine it produced green crystals of a pyridine adduct of a dimeric copper(II) anacardate with the copper acetate structure. The X-ray single crystal structures of both anacardic acid and the copper complex were determined. Magnetic studies have confirmed strong antiferromagnetic coupling between copper(II) centre in the dimer. The exchange coupling constant was determined to be J = -324 cm(-1). The EPR spectra of the polycrystalline product are consistent with spin S = 1. The zero-field splitting parameter and g tensor values are |D| = 0.36 cm(-1), g(||) = 2.36 and g(⊥) = 2.06.

Different interpenetrated coordination polymers based on flexible dicarboxylate ligands: topological diversity and magnetism

This work evidently indicates that the effect of the secondary ligands, molar ratios and geometric preferences of the metal centers are critical on the resulting entangled motifs.

Synthesis, characterization and X-ray structural studies of four copper (II) complexes containing dinuclear paddle wheel structures

Background

Various dinuclear copper (II) complexes with octahedral geometry have been reported. The majority of these complexes contain N containing aromatic rings as axial ligands. There are also a few cases where the solvent used in the reaction occupies the axial position of the dinuclear copper (II) complex. This may occur by planned synthesis or some times by serendipity. Here we report some four copper (II) complexes containing solvent and or N containing heterocyclic ring as the axial ligand.

Results

Four compounds, each containing dinuclear Copper (II) units (with the most robust, frequently occurring paddle wheel structures) were synthesized and characterised by single crystal X-ray diffraction and by IR spectroscopy. The compounds 1 & 2 have the general formula Cu₂(RCOO) ₄(L)₂ [(for (1) RCOO= 4-Chloro Benzoate, L= Isopropanol; for 2 RCOO= Benzoate, L= 2-Amino-4,6-dimethyl pyrimidine )] while 3 & 4 have the general formula, Cu₂(RCOO) ₄(S)₂ Cu₂(RCOO) ₄(L)₂ [RCOO=5-Chloro-thiophene-2-carboxylate L= 2-Amino-4,6-dimethyl pyrimidine, for 3 S= ethanol; for 4 S= methanol ]. A wide range of hydrogen bonds (of the O-H…O, N-H…O and N-H…N type) and π-π stacking interactions are present in the crystal structures.

Conclusions

All compounds contain the dinuclear units, in which two Cu (II) ions are bridged by four syn, syn-η¹:η¹:μ carboxylates, showing a paddle-wheel cage type with a distorted octahedral geometry. The compounds 1 &2 contain a single dimeric unit while 3 &4 contain two dimeric units. The structures 3 and 4 are very interesting co-crystals of two paddle wheel molecules. Also it is interesting to note that the compounds 3 &4 are isostructural with similar cell parameters. Both the compounds 3 &4 differ in the solvent molecule coordinated to copper in one of the dimeric units. In all the four compounds, each of the copper dimers has an inversion centre. Every copper has a distorted octahedral centre, formed by four oxygen atoms (from different carboxylate) in the equatorial sites. The two axial positions are occupied by copper and the corresponding ligand.

Thermal stability and electrochemical behaviour of Tetrakis-μ-benzoatodicopper(II)

Copper(II) benzoate (CuB) was synthesized and structurally characterized to have a binuclear, paddle-wheel structure. The complex was found to be thermally stable up to 230°C, and underwent four stages of decomposition, loss of CO2, C6H6, CH3CH2-OCH2CH3 and some aliphatic unsaturated organic materials. The DSC curve shows two endotherms at 80.0°C and 230.0°C respectively, indicating that the initial weight loss can be attributed to solvated molecules and the starting of the major decomposition process, (shown in the TG analysis). Cyclic voltammetry studies in a mixed-solvent system of methanol and ethanoic acid (20:1 v/v) show three cathodic peaks, at −0.13 V, −0.35 V and −0.74 V, representing a step-wise electron transfer process, and two overlapping anodic peaks at +0.31 V and +0.46 V. The high value of ΔE ranging from 400 mV to 1200 mV indicates that the redox process is accompanied by an extensive structural reorganization of the complex in the solution creating a different geometrical environment around the central copper ion.

Tetra-kis(μ(2)-2,2-dimethyl-propanoato-κO,O')bis-[(pyridine-κN)copper(II)]: a monoclinic polymorph

The structure of the dinuclear title complex, [Cu(2)(C(5)H(9)O(2))(4)(C(5)H(5)N)(2)], represents a monoclinic polymorph of the previously reported triclinic form [Blewett et al. (2006 ▶). Acta Cryst. E62, m420-m422]. Each carboxyl-ate group is bidentate bridging and the distorted octa-hedral geometry about each Cu(II) atom is completed by a pyridine N atom and the other Cu atom [Cu⋯Cu = 2.6139 (7) Å]. In the crystal, mol-ecules are connected into supra-molecular chains via π-π inter-actions formed by the pyridine rings [centroid-centroid distance = 3.552 (3) Å] and these are connected into a two-dimensional array in the ac plane by C-H⋯π contacts. One of the tert-butyl groups is disordered over two orientations in a 0.734 (6):0.266 (6) ratio.

Bond-valence approach to the copper-copper and copper-oxygen bonding in binuclear copper(II) complexes: Structure of tetrakis(2-fluoro-benzoato-O,O´)-bis(2-fluorobenzoate-O) dicopper(II)

The crystal and molecular structure of tetrakis(2-fluorobenzoato-O,O´)-bis(2-fluorobenzoate-O) dicopper(II) - C42H26Cu2F60O12 - has been determined at room temperature. The blue-green crystals are monoclinic, space group P21/n (No.14), with unit cell parameters a=10.633(3) Å, b= 12.528(3) Å, c=14.729(3) Å, β = 91.62(4)°, Z= 2, Dm= 1.62 and Dx= 1.64 g/cm3. The final R value for independent reflections is equal to 0.045. The structure consists of two centrosymmetric units [Cu2(2FbzO)4(2HFbzO)2] (abbreviation 2FbzO stands for 2-fluorobenzoate, abbr. 2HFbzO for 2-fluorobezoic acid). These units are mutually held by Van der Waals forces. Within the binuclear unit the Cu atom is pentacoordinated by four carboxylic O atoms in the basal plane of tetragonal pyramid (Cu–O bond lengths being 1.962(3) Å, 1.963(2) Å, 1.958(2) Å and 1.996(2) Å and one apical O atom from HFbzO molecule, with Cu-O bond length 2.193(2) Å. The apical Cu(II)–O bond length predicted by bond valence method is 2.16 Å. The Cu...Cu distance is 2.6086(8) Å and the displacement of Cu atom from the basal plane is 0.1905(6) Å. Nonbonding character of Cu(II)...Cu(II) contact in 16 binuclear carboxylic complexes is proved.