The influence of metal centres on the exchange interaction in heterometallic complexes with oxalate-bridged cations

A homochiral tartrate-bridged dinuclear chromium(III) complex anion with a resonance-assisted hydrogen bond for proton conduction

The synthesis of a homochiral building block based on L-tartrate-chromium(III) complex anions is reported. The dinuclear complex anion, which contains two bridging L-tartrate ligands and one aromatic N-donor ligand coordinated to chromium(III) ions, exhibits a boat conformation in which intramolecular resonance-assisted hydrogen bonding is present. The sodium L-tartrate-chromium(III) compound with the formula Na[Cr2(bpy)2(L-tart)2H]·9H2O (1) crystallizes from a methanol-water solution as a high water content material in the monoclinic space group P2. The as-synthesized compound is only stable at high relative humidity and undergoes structural transformations during drying, which are accompanied by water loss. However, these transformations are reversible and upon wetting, the material returns to its high water content structure. Based on a combination of experimental techniques (PXRD, in situ ATR-FTIR and EPR spectroscopy), the structure of the complex anions appears to be insensitive to the humidity variable processes (wetting and drying). Due to the presence of several hydrogen acceptor and donor groups in the L-tartrate-chromium(III) complex anion, we investigated the proton transport properties of a sodium L-tartrate-chromium(III) compound by impedance spectroscopy under dry and wet conditions at different temperatures. Since the relative humidity affects the structural transformations in this system, it also has a large influence on the proton conductivity, which varies by up to four orders of magnitude depending on the degree of hydration. These results confirm that the proton conductivity can be tuned in flexible structures in which non-covalent interactions determine the crystal packing.

Oxalate-based [CuIICrIII] coordination compounds affected by the tridentate ligand, simple anion, and reactant ratio: structural and magnetic features

In addition to the influence of terpyridine, those of the simple ion and reactant ratio on the nature of the bridge and the overall structure of seven novel oxalate-based [CuIICrIII] compounds reflecting magnetic properties were investigated.

Magnetic and Electrical Behaviors of the Homo- and Heterometallic 1D and 3D Coordination Polymers Based on the Partial Decomposition of the [Cr(C2O4)3]3- Building Block

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C₂O₄)]·1.5H₂O}_n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu₃(bpy)₃(CH₃OH)(H₂O)(C₂O₄)₄][Cu(bpy)Cr(C₂O₄)₃]·CH₂Cl₂·CH₃OH·H₂O}_n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C₂O₄)]_n of 1, with intra-chain super-exchange interaction 𝐽 = (−3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C₂O₄)₃]_nⁿ⁻ (Cr2–Cu4) with alternating [Cr(C₂O₄)₃]³⁻ and [Cu(bpy)]²⁺ units mutually bridged through the oxalate group. Another chain (Cr1–Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H₂O)(µ-C₂O₄)Cu(bpy)(CH₃OH)]²⁺ (Cu1–Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1−Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1–Cu3 and Cr2–Cu4. A 3D polymer {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) comprising three different metal centers (Ca²⁺, Cr³⁺ and Cu²⁺) oxalate-bridged, contains Ca²⁺ atoms as nodes connected with four Cr³⁺ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (6⁶) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [Cu^IICr^III], whose mutual interaction could possibly originate through the spin polarization of Ca²⁺ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.

An Oxalate-Bridged Copper(II) Complex Combining Monodentate Benzoate, 2,2'-bipyridine and Aqua Ligands: Synthesis, Crystal Structure and Investigation of Magnetic Properties

A dinuclear copper(II) complex of formula [{Cu(bipy)(bzt)(OH₂)}₂(μ-ox)] (1) (where bipy = 2,2′-bipyridine, bzt = benzoate and ox = oxalate) was synthesised and characterised by diffractometric (powder and single-crystal XRD) and thermogravimetric (TG/DTG) analyses, spectroscopic techniques (IR, Raman, electron paramagnetic resonance spectroscopy (EPR) and electronic spectroscopy), magnetic measurements and density functional theory (DFT) calculations. The analysis of the crystal structure revealed that the oxalate ligand is in bis(bidentate) coordination mode between two copper(II) centres. The other four positions of the coordination environment of the copper(II) ion are occupied by one water molecule, a bidentate bipy and a monodentate bzt ligand. An inversion centre located on the ox ligand generates the other half of the dinuclear complex. Intermolecular hydrogen bonds and π-π interactions are responsible for the organisation of the molecules in the solid state. Molar magnetic susceptibility and field dependence magnetisation studies evidenced a weak intramolecular–ferromagnetic interaction (J = +2.9 cm⁻¹) between the metal ions. The sign and magnitude of the calculated J value by density functional theory (DFT) are in agreement with the experimental data.

Oxalato bridged coordination polymer of manganese(iii) involving unconventional O⋯π-hole(nitrile) and antiparallel nitrile⋯nitrile contacts: antiproliferative evaluation and theoretical studies

Unconventional O⋯π-hole(nitrile) and antiparallel nitrile⋯nitrile contacts have been theoretically investigated for a Mn(iii) coordination polymer considering cytotoxicity, apoptosis, ROS generation, molecular docking and pharmacophore features.

Ladder-like [CrCu] coordination polymers containing unique bridging modes of [Cr(C2O4)3]3- and Cr2O72

Three heterometallic one-dimensional (1D) coordination polymers {A[CrCu₂(bpy)₂(C₂O₄)₄]·H₂O}_n [A = K⁺ (1) and NH₄⁺ (2); bpy = 2,2'-bipyridine] and [(Cr₂O₇)Cu₂(C₂O₄)(phen)₂]_n (3; phen = 1,10-phenanthroline) with uncommon topology have been synthesized using a building block approach and characterized by single-crystal X-ray diffraction, IR and impedance spectroscopies, magnetization measurements, and DFT calculations. Due to the partial decomposition of the building block [Cr(C₂O₄)₃]^3-, all three compounds contain oxalate-bridged [Cu₂(L)₂(μ-C₂O₄)]²⁺ units [L = bpy (1 and 2) and phen (3)]. In compounds 1 and 2 these cations are mutually connected through oxalate groups from [Cr(C₂O₄)₃]^3-, thus forming ladder-like topologies. Unusually, three different bridging modes of the oxalate ligand are observed in these chains. In compound 3 copper(ii) ions from cationic units are bridged through the oxygen atoms of Cr₂O₇^2- anions in a novel ladder-like mode. Very strong antiferromagnetic coupling observed in all three compounds, determined from the magnetization measurements and confirmed by DFT calculations (J = -343, -371 and -340 cm^-1 for 1, 2 and 3, respectively), appears between two copper(ii) ions interacting through the oxalate bridge.

Dimensionality controlled by light exposure: 1D versus 3D oxalate-bridged [CuFe] coordination polymers based on an [Fe(C2O4)3]3− metallotecton

The studied heterometallic [CuFe] compounds, based on an [Fe(C₂O₄)₃]³⁻ building block and containing a 3D network or 1D ladder-like chains, were synthesized depending on whether the test tube with the same reaction layers was exposed to daylight or not.

Magneto-structural correlations in oxalate-bridged Sr(ii)Cr(iii) coordination polymers: structure, magnetization, X-band, and high-field ESR studies

Magneto-structural correlations in 1D oxalate-bridged Sr(ii)Cr(iii) coordination polymers with two crystallographically and magnetically non-equivalent Cr(iii) ions are studied by HF-ESR spectroscopy.

Coordination ability of amino acid hydrazide ligands and their influence on magnetic properties in copper(ii) coordination polymers

Copper(ii) coordination polymers constructed from newly synthesized amino acid hydrazides and 4,4′-bipyridine exhibit antiferromagnetic ordering mediated through hydrazide bridges.