resumo
New electron-transfer salts, [M(Cp*)(2)] [Ni(edt)(2)], with M = Fe and Cr, were prepared and shown to be isostructural by Xray crystallographic studies. The molecular structure of [Ni(edt)(2)](-) is reported here for the first time. The solid-state structure consists of an array of parallel alternating donors, [Fe(Cp*)(2)](. c), and accepters, [Ni(edt)(2)](.-), ..DADADA.. stacks along [101]. At high temperatures (T > 50-100 K), the magnetic susceptibility obeys the Curie-Weiss expression, with the theta values of -5 and -6.7 K for the Ni and Cr compounds respectively, revealing dominant AFM interactions. At low temperatures metamagnetic behavior was observed in case of [Fe(Cp*)(2)][Ni(edt)(2)], with T-N = 4.2 K and H-C = 14 kG at 2 K, resulting from high magnetic anisotropy, due to the coexistence of strong FM DA intrachain interactions and strong AFM (DA and AA) interchain interactions. Single-crystal magnetization measurements with [Fe(Cp*)(2)][Ni(edt)(2)] showed that the transition from the AFM state to the FM high-field state was induced by the application of a magnetic field parallel to the stacking axis. In these compounds the AFM interchain (DA and AA) interactions play a dominant role, due to the large spin density on the periphery of the acceptor and the close AA and DA interchain contacts. Above 4.2 K the Fe-57 Mossbauer spectra of [Fe(Cp*)(2)] [Ni(edt)(2)] exhibit the classical low spin Fe-III ferrocenium singlet. Below this temperature a poorly resolved hyperfine pattern is observed (estimated hyperfine field ca. 350 kG at 3.5 K). The analysis of the spectra obtained in applied fields of 20 kG and 50 kG is consistent with a strongly anisotropic g tensor. A pronounced temperature dependence of the spectra in a field of 50 kG suggests the presence of spin-lattice relaxation effects.
palavras-chave
CHARGE-TRANSFER SALTS; FERROMAGNETIC BEHAVIOR; COMPLEXES; TETRACYANOETHYLENIDE
categoria
Chemistry
autores
da Gama, V; Belo, D; Rabaca, S; Santos, IC; Alves, H; Waerenborgh, JC; Duarte, MT; Henriques, RT
nossos autores
