Crystal structure and magnetic behavior of the decamethylferrocenium and decamethylchromocenium salts of bis(ethylenedithiolato)nickel, [M(Cp*)(2)][Ni(edt)(2)] - Magnetic anisotropy and metamagnetic behavior of [Fe(Cp*)(2)[Ni(edt)(2)]

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 studie s. The molecular structure of [Ni(edt)(2)](-) is reported here for the firs t time. The solid-state structure consists of an array of parallel alternat ing donors, [Fe(Cp*)(2)](. c), and accepters, [Ni(edt)(2)](.-), ..DADADA.. stacks along [101]. At high temperatures (T > 50-100 K), the magnetic susce ptibility 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 in teractions. 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, resul ting 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)] sh owed 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 axi s. In these compounds the AFM interchain (DA and AA) interactions play a do minant 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 Mossbau er spectra of [Fe(Cp*)(2)] [Ni(edt)(2)] exhibit the classical low spin Fe-I II ferrocenium singlet. Below this temperature a poorly resolved hyperfine pattern is observed (estimated hyperfine field ca. 350 kG at 3.5 K). The an alysis of the spectra obtained in applied fields of 20 kG and 50 kG is cons istent with a strongly anisotropic g tensor. A pronounced temperature depen dence of the spectra in a field of 50 kG suggests the presence of spin-latt ice relaxation effects.