Influence of Zero-Field Splitting and State Mixing on Ferromagnetic Exchange in the Integrated-Stack Charge-Transfer Salt [Cp2Fe]+[Co(HMPA-B)]-
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We have prepared and studied the charge-transfer salts [Cp*2M]+[Co(HMPA-B)]- (M = Fe (1), Co (3), Cp* = pentamethylcyclopentadienyl, HMPA-B = bis(2-hydroxy-2-methylpropanamido)benzene). X-ray crystallographic analysis (orthorhombic Pmmn, a = 10.780(2) Å, b= 16.211(4) Å, c = 9.350(1) Å, V = 1634(1) Å3, R = 0.034, Rw = 0.038) shows 1 to form integrated stacks where the S=½ [Cp*2Fe]+ cation alternates with the planar [Co(HMPA-B)]- anion. Susceptibility measurements on 3, which contains the diamagnetic [Cp*2Co]+ cation, show that the Co111 of the anion exhibits a zero-field-split (D = 45 cm−1) S = 1 electronic configuration. The situation in the two-spin crystal, 1, is the inverse of that seen in the bulk ferromagnet [Cp*2Mn]+[TCNQ]-, where the cation has S = 1 and the anion has S = ½, but susceptibility measurements show that 1 does not order magnetically. Analysis of the interplay between exchange and a zero-field splitting (ZFS) on the anion indicates that 1 displays a substantial ferromagnetic coupling between cation and anion (J ≈ −7 cm−1 where H= JS1·S2). However, this exchange is manifest as an increase in the apparent g-values of the cation that arises from quantum-mechanical state mixing in the presence of the large ZFS. © 1994, American Chemical Society. All rights reserved.
author list (cited authors)
Eichhorn, D. M., Telser, J., Stern, C. L., & Hoffman, B. M.