From paramagnetic to single-molecule magnet behaviour in heterobimetallic compounds containing the tetrakis(thiocyanato-κN)cobaltate(II) anion

Four heterobimetallic compounds of formula [Ni(Me6trans[14]dieneN4)][Co(NCS)4] (1 and 2), [Ni(Me6trans[14]dieneN4)]2[Co(NCS)4](ClO4)2 · H2O (3) and [Ni(Me6trans[14]dieneN4)]2[Co(NCS)4](PF6)2 (4) (Me6trans[14]dieneN4 = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) have been synthesized and structurally characterized. Their structures are made of square planar [Ni(Me6trans[14]dieneN4)]2+ cations and tetrahedral [Co(NCS)4]2- anions. The variable-temperature magnetic properties of 2-4 mainly obey to the zero-field splitting effects (D) of the 4A2 ground term of the pseudotetrahedral [Co(NCS)4]2- anionic complex (2D is the energy gap between the ±1/2> and ±3/2> levels of the spin quadruplet when E = 0), the square planar nickel(II) unit being diamagnetic. The analysis of their magnetic data through the spin Hamiltonian H = D[Sz2 - S(S+1)/3] + E(Sx2 - Sy2) + gHS led to the following best-fit parameters: g = 2.216(17), D = +3.74(12) cm-1 and E/D = 0.0137 (6) (2), g = 2.335(20), D = +11.6(4) cm-1 and E/D = 0.002(4) (3) and g = 2.298(15), D = +7.29(17) cm-1 and E/D = 0.068(3) (4). Q-band EPR spectra on powdered samples of 2-4 in the temperature range 4.0-20 K support the positive sign of D for them. With an applied dc field the ac susceptibility data for 3 and 4 below 4.5 K reveal a slow magnetic relaxation which is characteristic for Single-Ion Magnet behaviour (SIM).

from #MedicinebyAlexandrosSfakianakis via xlomafota13 on Inoreader http://ift.tt/2AFwc6w
via IFTTT