First iron and cobalt(ii) hexabromoclathrochelates: structural, magnetic, redox, and electrocatalytic behavior

Abstract

Template condensation of dibromoglyoxime with n-butylboronic acid on the corresponding metal ion as a matrix under vigorous reaction conditions afforded iron and cobalt(ii) hexabromoclathrochelates. The paramagnetic cobalt clathrochelate was found to be a low-spin complex at temperatures below 100 K, with a gradual increase in the effective magnetic moment at higher temperatures due to the temperature 1/2↔3/2 spin crossover and a gap caused by the structure phase transition. The multitemperature X-ray and DSC studies of this complex and its iron(ii)-containing analog also showed temperature structural transitions. The variation of an encapsulated metal ion's radius, electronic structure and spin state caused substantial differences in the geometry of its coordination polyhedron; these differences increase with the decrease in temperature due to Jahn-Teller distortion of the encapsulated cobalt(ii) ion with an electronic configuration d(7). As follows from CV and GC data, these cage iron and cobalt complexes undergo both oxidation and reduction quasireversibly, and showed an electrocatalytic activity for hydrogen production in different producing systems.

Spin Crossover in 3D Metal Centers Binding Halide-Containing Ligands: Magnetism, Structure and Computational Studies

“…Interestingly, there is some shrinkage of the bonds, but it is negligible compared to what is usually observed for octahedral species. This is clearly shown in the experimental values [161].…”

“…Interestingly, there is some shrinkage of the bonds, but it is negligible compared to what is usually observed for octahedral species. This is clearly shown in the experimental values [161]. The monomeric [Co II (BTP) 2 ] 2+ showed gradual spin-crossover properties between 1.8-370 K, with some dependence on the anion (BF 4 − , ClO 4 − , and NCS − ).…”

“…Ferromagnetic exchange interactions were determined with the -2J approach for the binuclear species, and values of J = +2.57 and +2.98 cm -1 were obtained for X = Cl and Br, respectively. Voloshin and co-workers dedicated much attention to cobalt(II) clathrochelates, many of them bearing halogens, such as Cl [160] (L56, L57, 58) or Br [161] (L56) at the diimine or F at the boron (L58). The chloride derivatives were studied earlier.…”

Ferrocene-Containing Sterically Hindered Phosphonium Salts

“…At second oxidation potentials, irreversible oxidation of anionic fragments is observed [ 26 ]. In the cathode region ( Table 3 ), an irreversible reduction of the phosphonium fragment is observed for all salts.…”

Solvent-Induced Encapsulation of Cobalt(II) Ion by a Boron-Capped tris-Pyrazoloximate

“…The best available synthetic strategy toward clathrochelates with 3d-metal ions in their paramagnetic high-spin state is either to introduce electron-withdrawing substituents (such as halogen, perfluoroalkyl, perfluoroaryl, etc.) into their ribbed chelate fragments − (Scheme a) or to use tripodal ligands − pseudo-cross-linked by hydrogen bonds with counterions or other H-bond acceptors (Scheme b). The latter allowed obtaining , cobalt­(II) pseudoclathrochelates (such as shown in Scheme ) with the largest axial anisotropy of magnetic susceptibility tensor among known cobalt­(II) complexes, which resulted from an unusual trigonal-prismatic (TP, the distortion angle φ = 0°) coordination geometry.…”