Field-induced slow magnetic relaxation in a hydrogen-bonding linked Co(II) 1D supramolecular coordination polymer

Coordination polymers of a bis-isophthalate bridging ligand with single molecule magnet behaviour of the CoII analogue

A linear diamine-bisisophthalate bridging linker N,N'-bis(1,3-dicarboxyphenyl-5-methylene)-1,3-dimethylpropanediamine, designed to incorporate amine/ammonium functionalities in the core of the ligand, has been isolated as the pentahydrate of its dihydrochloride salt (H6L)Cl2·5H2O. Using this compound, four new coordination polymers have been formed, namely poly-[M(H2L)]·4.5H2O (1M, where M = Co, Zn, Cd) and poly-[Cd(H2L)(OH2)]·DMF·7H2O (2). Compounds 1M are isostructural 2D coordination polymers that contain 1D channels occupied by water molecules. In the case of 1Co these form a well ordered hydrogen-bonding network as determined by single crystal X-ray studies. Compound 2, synthesised under similar conditions, is a 1D coordination polymer in which the metal is partially solvated. DC and AC magnetic studies of 1Co, which posseses a mononuclear cobalt(ii) node, revealed single molecule magnet behaviour (SMM) with an effective barrier height Ueff of 37.7 K and τ0 = 1.02 × 10-9 s, among the highest reported for CoII coordination polymers.

Field-induced slow magnetic relaxation in pseudooctahedral cobalt(ii) complexes with positive axial and large rhombic anisotropy

The preparation, X-ray crystal structure, spectroscopic and variable-temperature dc and ac magnetic properties of two six-coordinate cobalt(ii) complexes of formula [Co(bim)₄(tcm)₂] (1) and [Co(bmim)₄(tcm)₂] (2) are reported.

The influence of pseudohalide ligands on the SIM behaviour of four-coordinate benzylimidazole-containing cobalt(ii) complexes

Three, mononuclear complexes of the formula [Co(bmim)2(SCN)2] (1), [Co(bmim)2(NCO)2] (2) and [Co(bmim)2(N3)2] (3) [bmim = 1-benzyl-2-methylimidazole] were prepared and structurally analyzed by single-crystal X-ray crystallography. The cobalt(ii) ions in 1-3 are tetrahedrally coordinated with two bmim molecules and two pseudohalide anions. The angular distortion parameter δ was calculated and the SHAPE program (based on the CShM concept) was used for 1-3 to estimate the angular distortion from an ideal tetrahedron. The molecules of 1-3 are effectively separated, and the values of the shortest distance of cobalt-cobalt are 8.442(6) and 6.774(8) Å for 1, 10.349(8) and 10.716(8) Å for 2 and 6.778(1) and 9.232(1) Å for 3. Direct current (dc) magnetic susceptibility measurements on the crushed crystals of 1-3 were carried out in the temperature range 1.9-295 K. The variable-temperature magnetic data of 1-3 mainly obey the zero-field splitting effect (D) of the 4A2 ground term of the tetrahedral cobalt(ii) complexes (2D being the energy gap between the |±1/2 and |±3/2 levels of the spin). The analysis of their magnetic data through the Hamiltonian H = D[S2z - S(S + 1)/3] + E(Sx2 - Sy2) + gβHS led to the following best-fit parameters: g = 2.29, D = -7.5 cm-1 and E/D = 0.106 (1), g = 2.28, D = + 6.3 cm-1 and E/D = 0.007 (2) and g = 2.36, D = + 6.7 cm-1 and E/D = 0.090 (3). The signs of D for 1-3 were confirmed by Q-band EPR spectra on powdered samples in the temperature range 4.0-20 K. Field-induced SIM behaviour was observed for 1-3 below 4.0 K, and the frequency-dependent maxima of χ''M were observed for 1 and only incipient signals of χ''M occurred for 2 and 3. The values of the exponential factor (τ0) and activation energy (Ea) for 1-3 which were obtained from the Arrhenius plot suggest a single relaxation process characteristic of an Orbach mechanism.

Slow Magnetic Relaxation in a Series of Mononuclear 8-Coordinate Fe(II) and Co(II) Complexes

A series of homoleptic mononuclear 8-coordinate Fe^II and Co^II compounds, [Fe^II(L²)₂](ClO₄)₂ (2), [Fe^II(L³)₂](ClO₄)₂ (3), [Fe^II(L⁴)₂](ClO₄)₂ (4), [Co^II(L¹)₂](ClO₄)₂ (5), [Co^II(L²)₂](ClO₄)₂ (6), [Co^II(L³)₂](ClO₄)₂ (7), and [Co^II(L⁴)₂](ClO₄)₂ (8) (L¹ and L² are 2,9-dialkylcarboxylate-1,10-phenanthroline ligands; L³ and L⁴ are 6,6'-dialkylcarboxylate-2,2'-bipyridine ligands), have been obtained, and their crystal structures have been determined by X-ray crystallography. The metal center in all of these compounds has an oversaturated coordination number of 8, which is completed by two neutral homoleptic tetradentate ligands and is unconventional in 3d-metal compounds. These compounds are further characterized by electronic spectroscopy, cyclic voltammetry (CV), and magnetic measurements. CV measurements of these complexes in MeCN solution exhibit rich redox properties. Magnetic measurements on these compounds demonstrate that the observed single-ion magnetic (SIM) behavior in the previously reported [Fe^II(L¹)₂](ClO₄)₂ (1) is not a contingent case, since all of the 8-coordinate compounds 2-8 exhibit interesting slow magnetic relaxation under applied direct current fields.

One-dimensional cobalt(ii) coordination polymer featuring single-ion-magnet-type field-induced slow magnetic relaxation

Single-ion-magnet-type field-induced double magnetic relaxation was observed in a one-dimensional cobalt(ii) coordination polymer which shows easy-axis anisotropy with D = −33.9 cm⁻¹ and an energy barrier of U_eff = 38.8 K.

A cyano-bridged coordination nanotube showing field-induced slow magnetic relaxation

Field-induced slow magnetic relaxation was observed in a cyano-bridged nanotube constructed from a pentagonal bipyramidal Co^II unit and a hexacyanocobaltate(iii) anion.

Probing the influence of molecular symmetry on the magnetic anisotropy of octahedral cobalt(ii) complexes

A series of field-induced cobalt(ii) SIMs exhibit varying axial zero-field splitting parameter D values from positive to negative with the increased distortion of the octahedral geometry.

Single-ion magnet behaviour in mononuclear and two-dimensional dicyanamide-containing cobalt(ii) complexes

The magneto-structural features of one mononuclear and two layered Co(ii) complexes being new examples of Single-Ion Magnets (SIMs) are reported.

Group 9 and 10 complexes with the bidentate di(1H-indazol-1-yl)methane and di(2H-indazol-2-yl)methane ligands: synthesis and structural characterization

Ni, Pd and Co bis(indazol-1-yl)methane complexes assemble into 3D-networks based on intermolecular electrostatic, H-bonds and aromatic interactions.