Switching nuclearity and Co(ii) content through stoichiometry adjustment: {Co^II₆Co^III₃} and {Co^IICo₄^III} mixed valent complexes and a study of their magnetic properties

Abstract

We are reporting two new mixed valent Co(ii)/Co(iii) polynuclear complexes, {Co(II)6Co(III)3} and {Co(II)Co(III)4}, bearing different amount of Co(ii) ions in their cores, through the employment of the multidentate triethanolamine (teaH3) ligand in different stoichiometric ratios. We present a complete picture of the magnetic behaviour of both complexes through a combined usage of the susceptibility, magnetization and X-band EPR data as well as broken-symmetry DFT calculations. Compound shows an atypical spin-only behaviour, probably due to the presence of four and five coordinated Co(ii) sites as well as highly distorted six coordinated Co(ii) ions, promoting a high degree of orbital contribution quenching. Through the usage of a simplified exchange coupling scheme and relying on DFT based magneto-structural correlation we have been able to explain the observed diamagnetic ground state. Concerning compound , DC magnetic data supported by X-band EPR measurements suggest the existence of anisotropy with a zero-field splitting parameter D, at least in the range of 2-10 cm(-1). In agreement with this description, a slow relaxation of magnetization is observed after applying a small external magnetic field, under AC measurements. Field and temperature dependence of the characteristic relaxation time establishes a thermal barrier for magnetization reversal of about 25 cm(-1), which is in good agreement with the energy splitting of the |±1/2〉 and |±3/2〉 doublets established from static magnetic measurements.

Conductive Self-Assembled Monolayers of Paramagnetic {CoIICo4III} and {Co4IICo2III} Coordination Clusters on Gold Surfaces

“…The fifth cobalt site, located at the center of the molecule, displays a highly distorted tetrahedral geometry and is assigned the formal oxidation state +II [ Σ bv (Co II ) = 1.72]. The mixed-valent {Co 5 } core is thus similar to that observed in the other known Co 5 complexes (Englert and Strähle, 1987; Ferguson et al, 2006; Funes et al, 2015; Li et al, 2017) and comprises two {Co2IIICo II } triangles that share a common Co II vertex, an ~90° angle between the triangle planes. The Co III coordination spheres are composed of one bza·SMe − , two N - n -bda 2− , and two azide ligands.…”

Synthesis, magnetism and spectral studies of six defective dicubane tetranuclear {M4O6} (M = NiII, CoII, ZnII) and three trinuclear CdII complexes with polydentate Schiff base ligands

“…40 K), thus the local spin of the Co II ion is close to 1/2, therefore the Co II systems should be described by an effective spin S T = 1/2 with large anisotropy in a low temperature range. [87][88][89][90] Fig. 8 Temperature dependence of the χ M and χ M T data for 4 in the 2-300 K range.…”

A dinuclear Co(iii)/Co(ii) complex based on the H2pmide ligand showing field-induced SMM behaviour

“…As observed in these Co pivalate systems, chelating ligands with N donor atoms strongly favour Co(II) to Co(III) air oxidation, frequently affording mixed-valence complexes. [37][38][39][40][41][42][43][44][45][46][47] The complex crystallizes in a P2 1 /n monoclinic cell with the entire molecule as the asymmetric unit and without any crystallization solvent molecule.…”