“Switching on” the single-molecule magnet properties within a series of dinuclear cobalt(iii)–dysprosium(iii) 2-pyridyloximate complexes

Abstract

The use of 2-pyridinealdoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), phenyl 2-pyridyl ketone oxime (phpaoH) and pyridine-2-amidoxime (NHpaoH) for the synthesis of dinuclear Co/Dy complexes is described in the absence or presence of an external base. Complexes [CoDy(pao)(NO)] (1), [CoDy(mepao)(NO)] (2), [CoDy(phpao)(NO)] (3) and [CoDy(NHpao)(NO)]·3MeOH (4·3MeOH) have been isolated and their structures have been determined by single-crystal X-ray crystallography. The complexes crystallize in non-centrosymmetric (2, 3) or centrosymmetric (1, 4·3MeOH) trigonal space groups and form a family of triply-oximate bridged dinuclear Co(iii)-Dy(iii) complexes. The crystals of 1, 3 and 4·3MeOH contain mixtures of Δ and Λ enantiomers, whereas complex 2 is enantiomerically pure (Λ). A 3-fold crystallographic axis (C) passes through two metal ions in all complexes. The low-spin Co and Dy ions are bridged by three oximate groups belonging to the η:η:η:μ 2-pyridyloximate ligands. The Co centre is octahedrally coordinated by the six nitrogen atoms of the deprotonated organic ligands in a facial arrangement. The Dy centre is bound to an O set of donor atoms, its coordination sphere being completed by three bidentate chelating nitrato groups. The coordination polyhedron around Dy in 1 is best described as the Johnson tricapped trigonal prism, while the coordination geometries of the Dy centres in 2, 3 and 4·3MeOH are best described as consisting of spherical tricapped trigonal prismatic coordination polyhedra. The spectroscopic data of the complexes are also reported and discussed in the infra-red region in terms of the coordination modes of the ligands involved. The magnetic properties of these complexes were studied between 300 and 1.8 K revealing mainly the depopulation of the Dym sublevels of the ground H state. The intrinsic magnetic anisotropy of the Dy centers is clearly observed by the non-superimposed magnetization (M) versus H/T data, but single-molecule magnet (SMM) properties were detected only for the mepao-containing complex 2. The origin of these properties in 2 is critically discussed and supported by computational studies.

Diversity of Coordination Modes in a Flexible Ditopic Ligand Containing 2-Pyridyl, Carbonyl and Hydrazone Functionalities: Mononuclear and Dinuclear Cobalt(III) Complexes, and Tetranuclear Copper(II) and Nickel(II) Clusters

“…Due to the meridional character of each anionic ligand, two pairs of trans coordination sites are each occupied by donor atoms of the same L − group (O1/N1, O2/N5), whereas the third pair of coordination sites consists of nitrogen atoms (N2, N6) from different ligands. The Co-(O, N) bond lengths are in the range 1.855(2)-1.927(2) Å and agree very well with values observed for low-spin Co(III) ions in octahedral environments[35,39,40]. The two Co-N bond lengths for each ligand differ [1.927(2) vs. 1.855(2) Å, and 1.915(2) vs. 1.857(2) Å]; the shorter bond distance (stronger bond) pertains to the hydrazone nitrogen atoms (N2, N6), probably due to the presence of some negative charge on these atoms (because of delocalization).The mononuclear cations of 4 form chains parallel to the [111] crystallographic direction through π-π stacking interactions between centrosymmetrically-related N(1)-and N(1 )-containing rings [symmetry code: (') = −x, −y + 1, −z + 1; the distance between the planes is 3.62(1)Å] and between centrosymmetrically-related N(4)-and N(4 )-containing rings [symmetry code: (') = −x + 1, −y + 2, −z + 2; the distance between the planes is 3.36(1) Å] (Figure 6).…”

Molecular and Polymer Ln2M2 (Ln = Eu, Gd, Tb, Dy; M = Zn, Cd) Complexes with Pentafluorobenzoate Anions: The Role of Temperature and Stacking Effects in the Structure; Magnetic and Luminescent Properties

“…The latter is suggested by the τ 0 values and also by approximation of the τ(1/T) plot by the sum of the Raman and QTM relaxation mechanisms (τ −1 = C Raman T nRaman + B; for complexes II and VII) or Raman and direct relaxation mechanisms (τ −1 = C Raman T nRaman + A direct TH 4ndirect ; for complex IX) over the entire temperature range. The relaxation times characteristic of over-barrier magnetization reversal corresponding to the Orbach mechanism should be~10 −10 -10 −12 s [53]. The τ 0 parameters of complexes II, VII, IX differ significantly from the indicated values.…”

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)

“…Thus, we tried to explain the experimental data excluding the Orbach regime from the analysis of relaxation processes according to ref. [ 74 ].…”