Abstract
Complexes [Fe~9~(X)~2~(O~2~CMe)~8~{(2‐py)~2~CO~2~}~4~] (X^−^=OH^−^ (1), N~3~^−^ (2), and NCO^−^ (3)) have been prepared by a route previously employed for the synthesis of analogous Co~9~ and Ni~9~ complexes, involving hydroxide substitution by pseudohalides (N~3~^−^, NCO^−^). As indicated by DC magnetic susceptibility measurements, this substitution induced higher ferromagnetic couplings in complexes 2 and 3, leading to higher ground spin states compared to that of 1. Variable‐field experiments have shown that the ground state is not well isolated from excited states, as a result of which it cannot be unambiguously determined. AC susceptometry has revealed out‐of‐phase signals, which suggests that these complexes exhibit a slow relaxation of magnetization that follows Arrhenius behavior, as observed in single‐molecule magnets, with energy barriers of 41 K for 2 (τ~0~=3.4×10^−12^ s) and 44 K for 3 (τ~0~=2.0×10^−11^ s). Slow magnetic relaxation has also been observed by zero‐field ^57^Fe Mössbauer spectroscopy. Characteristic integer‐spin electron paramagnetic resonance (EPR) signals have been observed at X‐band for 1, whereas 2 and 3 were found to be EPR‐silent at this frequency. ^1^H NMR spectrometry in CD~3~CN has shown that complexes 1–3 are stable in solution.