The homologous series M(TCNQ)2 (M = Mn(II), Fe(II), Co(II), and Ni(II); TCNQ = 7,7,8,8-tetracyanoquinodimethane) prepared from reactions of [M(CH3CN)6][BF4]2 and [n-Bu4N][BF4] in CH3CN has been carefully analyzed from the perspective of synthetic issues and
physical characterization, including complete magnetic analyses by the tools of dc and ac
magnetometry. The preparative method was optimized to definitively establish the reproducibility of the chemistry as judged by infrared spectroscopy, thermal gravimetric analysis,
powder X-ray crystallography, and elemental analysis. Scanning electron microscopic (SEM)
and transmission electron microscopic (TEM) studies results are also in accord with the
conclusion that these materials are pure, isostructural phases. The dc magnetic measurements reveal a spontaneous magnetization for the four materials at low temperatures with
a weak field coercivity of 20, 750, 190, and 270 G at 2 K for Mn(TCNQ)2, Fe(TCNQ)2, Co(TCNQ)2, and Ni(TCNQ)2, respectively. At low temperatures, ac susceptibility measurements
confirm the presence of a magnetic phase at 44, 28, 7, and 24 K for Mn(TCNQ)2, Fe(TCNQ)2,
Co(TCNQ)2, and Ni(TCNQ)2, respectively, but do not support the description of this system
as a typical magnet. In the absence of the ac magnetic data, the behavior is indicative of
ferri- or ferromagnetic ordering (depending on the metal), but in fact a complete investigation
of their physical properties revealed their true nature to be a glassy magnet. The glassiness,
which is a high magnetic viscosity known to originate from randomness and frustration, is
revealed by a frequency dependence of the ac susceptibility data and is further supported
by a lack of a lambda peak in the heat capacity data. These results clearly demonstrate
that molecule-based materials with a presumed magnetic ordering may not always be
exhibiting truly cooperative behavior.