Anion-solvent dependence of bistability in a family of meridional N-donor-ligand-containing lron(II) spin crossover complexes

作者：Leita Ben A; Neville Suzanne M; Halder Gregory J; Moubaraki Boujemaa; Kepert Cameron J; Letard Jean Francois; Murray Keith S^*

来源：Inorganic Chemistry, 2007, 46(21): 8784-8795.

DOI：10.1021/ic7010919

Five mononuclear spin crossover iron(II) bis-meridional ligand complexes of the general formula [Fe(L)(2)](X)(2).solvent, have been synthesized, where X = BF4- or ClO4-; L = 2-(1-pyridin-2-ylmethyl-1H-pyrazol-3-yl)-pyrazine (picpzpz) or 2-(3-(2-pyridyl)pyrazol-1-ylmethyl)pyridine) (picpypz); solvent = MeOH or EtOH. The magnetic and structural consequences of systematic variation of meridional ligand, solvent, and anion, including a desolvated species, have been investigated. The complex [Fe(picpzpz)(2)](BF4)(2)center dot MeOH, 1 center dot MeOH, displays several unique properties including a two-step spin transition with a gradual higher-temperature step (T-1(1/2) = 197 K) and an abrupt low-temperature step with hysteresis (T-2(1/2) = 91/98 K) and a metastable intermediate spin state below 70 K with quench-cooling. Removal of the solvent methanol results in the loss of the abrupt step and associated hysteresis (T-1/2 = 150 K). The complexes [Fe(picpzpz)(2)](BF4)(2)-EtOH (1 center dot EtOH), [Fe(picpzpz)(2)](ClO4)(2)center dot MeOH (2 center dot MeOH), [Fe(picpzpz)(2)](ClO4)(2)center dot EtOH (2 center dot EtOH), and [Fe(picpypz)(2)](BF4)(2)center dot MeOH (3 center dot MeOH) all show gradual one-step spin transitions with T-1/2 values in the range 210-250 K. Photomagnetic LIESST measurements on 1 center dot MeOH reveal a near-quantitative excitation of,high-spin sites and a unique two-step relaxation process related to the two-step thermal spin transition (T-1(LIESST) = 49 K and T-2(LIESST) = 70 K). The structural consequences of the unusual spin transition displayed by 1 center dot MeOH have been investigated by single-crystal X-ray diffraction structural analyses between 25 and 293 K. Detailed characterization of the unit cell parameter evolution vs temperature reflects both the gradual high-temperature step and abrupt low-temperature step, including the thermal hysteresis, observed magnetically.

• 出版日期2007-10-15