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

Rigid Core Anthracene and Anthraquinone Linked Nitronyl and Iminoyl Nitroxide Biradicals

The first syntheses of bis­(nitronyl nitroxide) and bis­(iminoyl nitroxide) (diNN, diIN) biradicals linked through rigid acene core conjugating anthracene (A) and anthraquinone (AQ) units are reported. Computational modeling predicts weak intramolecular exchange in AQ-linked systems, but A-linked biradicals to have ground state multiplicities consistent with the Borden-Davidson disjointness model. Solution electron spin resonance spectra showed inter-radical exchange-coupled triplet states, except for 2,6-AQ biradicals showing isolated spin spectra. Crystallography of the A-linked biradicals shows a key role for inter-radical contacts for molecular packing. DiINs showed lower-dimensional dyad packing with disorder at the radical units: the conformationally more symmetrical diNNs gave staircase one-dimensional or brickwork two-dimensional lattices. Core anthracene unit stacking was only seen in two systems with bromine on the central anthracene ring: the (large) bromine occupies alternate side placement in dyad stacks for the diIN, chain stacks for the diNN. Magnetism of 2,7-A-linked systems showed predominant ferromagnetic intramolecular triplet-singlet splitting of 24–28 K for diNNs and 8 K for diINs, plus weak antiferromagnetic (AFM) interactions from intermolecular contacts. The 2,6-A-linked biradicals showed AFM exchange between spins. Both A and AQ cores offer possibilities for electronic material development, with a combination of multiple radical spins and π-electron-rich acene cores

A Single-Chain Magnet with a Very High Blocking Temperature and a Strong Coercive Field

Two isostructural 1D complexes, [M­(hfac)₂NaphNN]_<i>n</i> [M = Mn^II (<b>1</b>) or Co^II (<b>2</b>); NaphNN = 1-naphthyl nitronylnitroxide], were synthesized and exhibit very strong antiferromagnetic metal–radical exchange coupling. Compound <b>2</b> shows slow magnetic relaxation behavior with a high blocking temperature (<i>T</i>_B ≈ 13.2 K) and a very high coercive field of 49 kOe at 4.0 K

An Angular Bis-Oxamate Tecton for the Construction of Heterobimetallic Coordination Polymers

Two novel heterobimetallic three-dimensional coordination polymers, [Cu₂Na₄L₂(CH₃OH)_2.3(H₂O)_5.2]·1.7H₂O (<b>1</b>) and [CuNa₂L­(H₂O)_3.88]·H₂O (<b>2</b>), have been obtained by assembling a bis-oxamate copper­(II) complex with sodium ions (<i>L</i> = 4,4′-sulfonylbis­(phenylene)­bis­(oxamate). Both coordination frameworks are constructed by connecting {Cu₄L₄} crosslike anionic units by sodium ions forming polymers with different topologies. The magnetic susceptibility data shows weak antiferromagnetic interaction for both compounds

Synthesis, Crystal Structures, and EPR Studies of First Mn^IIILn^III Hetero-binuclear Complexes

A new family of binuclear complexes [Mn^III­Ln^III­(dpm)₄­(MeO)₂­(Me­OH)₂] is reported (where Ln = La^III (<b>1</b>), Pr^III (<b>2</b>), and Eu^III(<b>3</b>)). These compounds were obtained from a one-pot reaction between 2,2,6,6-tetra­meth­yl-3,5-hep­tano­dione (Hdpm), Mn^II, and the respective Ln^III salt in the presence of sodium methoxide. The derivative containing the diamagnetic ion La^III has been synthesized in order to characterize the local anisotropy of the Mn^III ion. High-field electron paramagnetic resonance (HFEPR) spectroscopy shows that the Mn^III ion, with an elongated octahedral geometry in all compounds, has a significant axial zero-field splitting and a small rhombic anisotropy. Additionally, the HFEPR measurements indicate that there is almost no exchange between the spin carriers in these compounds, all of which exhibit field-induced slow relaxation of the magnetization