Discrete unusual mixed-bridged trinuclear CoIII2CoII and pentanuclear NiII coordination complexes supported by a phenolate-based ligand: theoretical and experimental magneto-structural study

We report a combined computational and experimental magnetostructural correlation in trinuclear mixed valence cobalt and pentanuclear nickel complexes.

Variation of the Chain Geometry in Isomeric 1D Co(NCS)2 Coordination Polymers and Their Influence on the Magnetic Properties

Two different isomers of [Co(NCS)₂(4-chloropyridine)₂]_n (3C and 3L) were synthesized from solution and by thermal decomposition of Co(NCS)₂(4-chloropyridine)₂(H₂O)₂ (2), which show a different metal coordination leading to corrugated chains in 3C and to linear chains in 3L. Solvent mediated conversion experiments prove that 3C is thermodynamically stable at room temperature where 3L is metastable. Magnetic measurements reveal that the magnetic exchange in 3L is comparable to that observed for previously reported related chain compounds, whereas in 3C with corrugated chains, the ferromagnetic interaction within the chains is strongly suppressed. The magnetic ordering takes place at 2.85 and 0.89 K, for 3L and 3C, respectively, based on specific heat measurements. For 3L the field dependence of magnetic relaxations in antiferromagnetically ordered ferromagnetic chains is presented. In addition, 3L is investigated by FD-FT THz-EPR spectroscopy, revealing a ground to first excited state energy gap of 14.0 cm^-1. Broken-symmetry DFT calculations for 3C and 3L indicate a ferromagnetic intrachain interaction. Ab initio CASSCF/CASPT2/RASSI-SO computational studies reveal significantly different single-ion anisotropies for the crystallographically independent cobalt(II) centers in 3C and 3L. Together with the geometry of the chains this explains the magnetic properties of 3C and 3L. The ab initio results also explain the weaker exchange interaction in 3C and 3L as compared to previously reported [Co(NCS)₂(L)₂]_n compounds with linear chains.

Methylene spacer regulated variation in conformation of tetradentate N2O2 donor Schiff bases trapped in manganese(iii) complexes

The paper attempts to explain the distortion from planarity of tetradentate Schiff bases in octahedral manganese(iii) complexes.

Diversified magnetic behaviors of new nickel(ii) and copper(ii) azido coordination polymers templated by diethyl or triethyl amines

The reactions of Ni^II or Cu^II ions with N₃⁻ anions in the presence of templated diethyl or triethyl amines afford three new azido-bridged coordination polymers, which exhibit metamagnetism, spin glass and canted ferromagnetism, respectively.

Influence of metal coordination and co-ligands on the magnetic properties of 1D Co(NCS)2 coordination polymers

Two 1D Co(NCS)₂ coordination polymers were synthesized and their magnetic properties were investigated by susceptibility and specific heat measurements as well as DFT and ab initio calculations.

Slow magnetic relaxation in a dimeric Mn2Ca2 complex enabled by the large Mn(iii) rhombicity

A large single-ion transverse anisotropy at Mn(iii) sites induces slow magnetic relaxation at zero magnetic field of the ferromagnetic Mn dimers in a singular Mn₂Ca₂ complex.

Dimerization, redox properties and antioxidant activity of two manganese(III) complexes of difluoro- and dichloro-substituted Schiff-base ligands

Two mononuclear Mn^III complexes [Mn(3,5-F₂salpn)(H₂O)₂][B(C₆H₅)₄]·2H₂O (1·2H₂O) and [Mn(3,5-Cl₂salpn)(OAc)(H₂O)]·H₂O (2·H₂O), where H₂salpn=1,3-bis(salicylidenamino)propane, have been prepared and characterized. The crystal structure of 1·H₂O shows that this complex forms μ-aqua dimers with a short Mn⋯Mn distance of 4.93Å. Under anaerobic conditions, the two complexes are stable in solution and possess trans-diaxial symmetry with the tetradentate Schiff base ligand symmetrically arranged in the equatorial plane. When left in air, these complexes slowly dimerize to yield high-valent [Mn^IV₂(3,5-X₂-salpn)₂(μ-O)₂] in which each X₂-salpn ligand wraps the two Mn ions. This process is favored in basic medium where the deprotonation of the bound water molecule is concomitant with air oxidation. The two complexes catalyze the dismutation of superoxide (superoxide dismutase (SOD) activity) and peroxide (catalase (CAT) activity) in basic medium. The phenyl-ring substituents play an important role on the CAT reaction but have little effect on SOD activity. Kinetics and spectroscopic results indicate that 1 and 2 catalyze H₂O₂ disproportionation through a cycle involving Mn^III₂ and Mn^IV₂ dimers, unlike related complexes with a more rigid and smaller chelate ring, which employ Mn^III/Mn^VO monomers.

Solvent dependent reactivities of di-, tetra- and hexanuclear manganese complexes: syntheses, structures and magnetic properties

An unusual solvent effect on the synthesis of five manganese complexes [Mn2(L1)2(Py)4](), [Mn2(L1)2(DMSO)4](), [Mn4(L2)4(OH)4](), [Mn4(L3)2(DMSO)7(H2O)](), and [Mn6O2(L4)4(OAc)2(OMe)2(DMSO)4]·MeOH] (), (H3L1 = 5-(2-oxyphenyl)-pyrazole-3-carboxylic acid; H2L2 = 5-(2-oxyphenyl)-pyrazole-3-carboxylic acid amide; H4L3 = di-[5-(2-oxyphenyl)-pyrazole]-3-hydroxamic ether; and H2L4 = 5-(2-oxyphenyl)-pyrazole-3-carboxylic acid methyl ester) has been reported. Five complexes have been characterized by X-ray single crystal diffraction, IR, element analysis, thermogravimetric analysis and UV-vis spectra. The analysis reveals that complexes and are isostructural with a bimetallic six-membered ring and L1 from the decomposition of the original H4ppha (H4ppha = 5-(2-hydroxyphenyl)-pyrazole-3-hydroxamic acid) ligand. Complexes and are two tetranuclear clusters, and possesses an aza12-metallacrown-4 core with L2 from the amide functionalization of the decomposition L1; while represents a novel linear [Mn4N8O2] core with L3 from the condensation of L1 and H4ppha. Complex is the first Mn6 cluster linked by two stacked, off-set 8-azametallacrown-3 subunits with [M-N-N-M-N-N-M-O] connectivity, and L4 derived from the esterification of L1. The magnetic behaviour of complexes show the dominant antiferromagnetic interactions between metal centers, whereas complex further reveals the coexistence of antiferromagnetic and ferromagnetic interactions, and slow magnetic relaxation at T < 6 K with S = 4 ground state, as well as field induced magnetization saturation.

pH-controlled polymorphism in a layered dysprosium phosphonate and its impact on the magnetization relaxation

This communication reports two polymorphic dysprosium compounds that exhibit slow relaxation of magnetization with significantly different energy barriers.