Phase transition in metal hexammine complexes. II. The EPR spectra of Ni(NO3)26NH3 and Ni++ doped Zn(NO3)26NH3 and Cd(NO3)26NH3

Abstract

The cooperative effect of the ammonias in X(N03)26NH3 (X = Ni,Zn.Cd) was investigated by EPR.In Ni(N0 3 h 6NH 3 • the line width of the single EPR absorption line undergoes a sudden broadening at T c = 243 K. This effect is probably a result of a cooperative freezing of the degrees of freedom of rotation of the ammonias. giving the appearance of a crystal field on the Ni + + ions. The crystal field does not split the single line. probably because strong exchange effects assemble the lines. The crystal field parameter D = 0.425 cm-1 was evaluated by applying the Anderson and Weiss theory for the exchange narrowing of the linewidth. Small quantities of the Ni + + ions in Zn and Cd salts do not exhibit strong exchange effects. So the single EPR absorption line above T c goes to a split line below T c' For Ni: Zn(N03)26NH3. T c = 231 K and D = 0.606 em-I. For Ni: Cd(N03)26NH3. T c = 198 K and D ~ 0.3 em-I. Hysteresis in T c was also observed for all salts.

Preparation, characterization and crystal structure of [Ni(bpy)3][Fe(CN)5(NO)]3H2O and one-dimensional cyano-bridged [Ni(en)2Fe(CN)5(NO)]H2O

“…Since Ni(ll) has an even number of electrons, Kramer's theorem does not apply [ 20]. Nevertheless, in some cases of Ni(II)-doped low symmetry diamagnetic lattices, two resonances are observable at X-band [20][21][22]. One corresponds to the AMsffi 5:2 transition, while the other results from either the Ms ffiO--* Ms= + 1 orMs= -1 ~0 transition (depending on the sign of the zero field splitting D).…”

“…One corresponds to the AMsffi 5:2 transition, while the other results from either the Ms ffiO--* Ms= + 1 orMs= -1 ~0 transition (depending on the sign of the zero field splitting D). In the present work, the spin-Hamiltonian parameters of I and 2 were determined from the experimental data and fitted to the equation [21,22] Zf = gtSHS + Ds 2…”

Ligand field design enables quantum manipulation of spins in Ni2+ complexes

“…In the orbitally non-degenerate case, this can be achieved via incorporation of strong eld ligands, as D is inversely proportional to the energetic separation of excited states from the ground state. 25 Previously, the only examples of commercial frequency [26][27][28][29][30][31][32][33] which are exceptionally host-and counterion-dependent, due to the weak eld monodentate ligands and the exible primary coordination sphere. As a result, for a nickel coordination complex with the same coordinating ligands, D can vary by an order of magnitude as a function of counterion.…”