Syntheses and characterization of two polymorphs of Cu(TCNQ) have been carried out and the results correlated to films of the materials. Reactions of CuI with TCNQ or [Cu(CH3CN)4][BF4] with TCNQ- lead to blue-purple needles of Cu(TCNQ) phase I (1). A slurry of this kinetic product in CH3CN yields a second crystalline phase of Cu(TCNQ), phase II (2), which exhibits a platelet morphology. Powder X-ray diffraction and scanning electron microscopy data revealed that both phases are present in films of Cu(TCNQ) formed by oxidation of Cu foil by TCNQ in CH3CN. X-ray photoelectron spectra of the two phases are indistinguishable from each other and are indicative of the presence of Cu(I). Single-crystal X-ray studies were undertaken on very small crystals of the two samples, the results of which reveal that subtle geometrical changes for the nitrile arrangements around the four-coordinate Cu(I) centers lead to major changes in the architectural framework of the polymers. Phase I was indexed in the tetragonal crystal system, but due to disorder and twinning, the crystal diffracted to only ∼40° in 2θ. The data were solved and refined in the monoclinic Pn space group. The polymeric motif consists of Cu atoms surrounded by four nitrile lone pairs of independent TCNQ- molecules arranged in a distorted tetrahedral geometry. A quadruply twinned crystal of Cu(TCNQ) phase II was indexed in the monoclinic system and resolved by deconvolution methods. The Cu(I) ions in phase II occupy the tetrahedral positions of a Cooperite structure (PtS), and the TCNQ- radicals occupy the square planar sites. In both phases there are two interpenetrating lattices present. In phase I the TCNQ- units are involved in close π-stacking interactions at ∼3.24 Å whereas in phase II the closest approach of the rings is ∼6.8 Å. In qualitative agreement with these observations are the magnetic properties; 1 is essentially diamagnetic and 2 displays Curie−Weiss behavior down to very low temperatures. The charge-transport properties of the samples revealed that, while they are both semiconductors, 1 is a good semiconductor with a room-temperature conductivity of 0.25 S cm-1 and a band gap of 0.137 eV whereas 2 is a very poor semiconductor with σ(rt) = 1.3 × 10-5 S cm-1 and a band gap of 0.332 eV. Cu(TCNQ) film devices have been found to switch between two states that exhibit very similar conducting properties.

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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.

Reactions of [M(MeCN) n ][BF 4 ] 2 salts with Bu 4 N(TCNQ) in MeOH yield M(TCNQ) 2 (MeOH) x (M ) Mn, 1; Fe, 2; Co, 3; Ni, 4, x ) 2-4), and reactions of MnCl 2 , FeSO 4 ‚7H 2 O, CoSO 4 ‚7H 2 O and NiCl 2 ‚6H 2 O in H 2 O produce M(TCNQ) 2 (H 2 O) 2 (M ) Mn, 5; Fe, 6; Co, 7; Ni, 8). Infrared spectroscopy, powder X-ray diffraction and thermogravimetric analyses of 1-8 indicate that the products prepared in the same solvent constitute isostructural families of compounds.[Mn(TCNQ-TCNQ)(MeOH) 4 ] ∞ (9) crystallizes in the triclinic space group P1 h, a ) 7.2966( 8Compound 9 contains TCNQligands that have undergone an unusual σ-dimerization to [TCNQ-TCNQ] 2that acts as a tetradentate ligand to Mn(II) ions to give a 2-D staircase polymeric motif. The layers are connected by hydrogenbonds between axially coordinated MeOH from adjacent layers and MeOH located between the layers. Compound 10 exhibits a zigzag polymeric motif with equatorially bound TCNQderived ligands of two types; the edges of the layers consist of cis-µ-TCNQmolecules involved in π-stacking with TCNQunits from another layer and σ-[TCNQ-TCNQ] 2acting as a tetradentate bridging ligand. Axial MeOH ligands are hydrogen-bonded to dangling nitrile groups of cis-µ-TCNQligands in the next layer. Mn(TCNQ) 2 (H 2 O) 2 (11) crystallizes in the monoclinic space group I2/a, a ) 12.5843(7) Å, b ) 13.7147(7) Å, c ) 13.3525(70 Å, β ) 92.887(1)°, V ) 2301.58 Å 3 , Z ) 4. This material adopts a double-layer motif consisting of Mn(II) ions bonded to syn-µ 2 -TCNQequatorial ligands and axial H 2 O molecules. Compounds 1-11 exhibit Curie-Weiss behavior with weak antiferromagnetic coupling being observed at low temperatures. The Zn(II) analogue of 10, [Zn(TCNQ)(TCNQ-TCNQ) 0.5 (MeOH) 2 ] ∞ (12) was also prepared: space group C2/c, a ) 14.2252(1) Å, b ) 27.3290(4) Å, c ) 13.1177(2) Å, β ) 90.074(1)°, V ) 5099.64(11) Å 3 , Z ) 8. Powder X-ray diffraction was used to probe structures 1-11, and it was found that 9 converts to a new phase with heating or exposure to X-rays that is related to disruption of the σ-dimer (TCNQ-TCNQ) 2ligands and loss of MeOH. The new phase, whose powder pattern is identical with that of a phase prepared from MeCN, exhibits ferromagnetic behavior.