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.

One of the most rapidly expanding areas of coordination chemistry research is the design of magnetic materials based on molecular building blocks. [1] A perusal of the literature reveals that a successful design strategy for preparing molecular magnets is the coordination of organic radicals such as nitronyl nitroxides [2] and organocyanides such as TCNE À C (tetracyanoethylene) [3] and TCNQ À C (7,7,8,8-tetracyanoquinodimethane) [4] to paramagnetic transition metal ions. The presence of both metal spins (typically S > 1/2) and organic spin carriers (S = 1/2) leads to strong local super-

One of the most rapidly expanding areas of coordination chemistry research is the design of magnetic materials based on molecular building blocks.[1] A perusal of the literature reveals that a successful design strategy for preparing molecular magnets is the coordination of organic radicals such as nitronyl nitroxides [2] and organocyanides such as TCNE À C (tetracyanoethylene) [3] and TCNQ À C (7,7,8,8-tetracyanoquinodimethane) [4] to paramagnetic transition metal ions. The presence of both metal spins (typically S > 1/2) and organic spin carriers (S = 1/2) leads to strong local super-

The syntheses, spectroscopic properties, redox chemistry, and solid-state structures of products obtained from the reaction of Re 2 Cl 4 (dppm) 2 (dppm = bis(diphenylphosphino) methane) with the polycyano acceptors TCNQ (7,7,8,8tetracyanoquinodimethanido) and DM-DCNQI (2,5-dimethyl-N,NЈ-dicyanoquinonediimine) are described. The compounds [Re 2 Cl 4 (dppm) 2 ] 2 (µ-TCNQ), 1, and [Re 2 Cl 4 (dppm) 2 ] 2 (µ-DM-DCNQI), 2, have been prepared by reaction of two equivalents of Re 2 Cl 4 (dppm) 2 with TCNQ and DMDCNQI, respectively, in THF or CH 2 Cl 2 . A single-crystal X-ray crystallographic study of [Re 2 Cl 4 (dppm) 2 ] 2 (µ-TCNQ)ؒ10THF revealed the presence of a trans-µ 2 bidentate mode for the bridging TCNQ ligand that joins two Re 2 Cl 4 (dppm) 2 molecules through equatorial positions. In a similar fashion, the compound [Re 2 Cl 4 (dppm) 2 ] 2 (µ-DM-DCNQI)ؒ10THF consists of two Re 2 units coordinated to the two nitrile positions of the DM-DCNQI ligand. The electronic properties of both compounds are unusual in that they exhibit intense, broad absorptions that span the near-IR region and extend into the mid-IR. The electrochemistry of the compounds consists of numerous oxidation and reduction processes in the range of ϩ2.0 to Ϫ2.0 V as determined by cyclic voltammetry. Both 1 and 2 exhibit temperature independent paramagnetism (TIP) with large χ TIP values of 7.29 × 10 Ϫ3 and 6.23 × 10 Ϫ3 emu mol Ϫ1 , respectively.