New Insight into the Nature of Cu(TCNQ): Solution Routes to Two Distinct Polymorphs and Their Relationship to Crystalline Films That Display Bistable Switching Behavior
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- 作者：Robert A. Heintz ; Hanhua Zhao ; Xiang Ouyang ; Giulio Grandinetti ; Jerry Cowen ; and Kim R. Dunbar
- 刊名：Inorganic Chemistry
- 出版年：1999
- 出版时间：January 11, 1999
- 年：1999
- 卷：38
- 期：1
- 页码：144 - 156
- 全文大小：470K
- 年卷期：v.38,no.1(January 11, 1999)
- ISSN：1520-510X
文摘
Syntheses and characterization of two polymorphs of Cu(TCNQ) have been carried out and the results correlatedto films of the materials. Reactions of CuI with TCNQ or [Cu(CH3CN)4][BF4] with TCNQ- lead to blue-purpleneedles of Cu(TCNQ) phase I (1). A slurry of this kinetic product in CH3CN yields a second crystalline phase ofCu(TCNQ), phase II (2), which exhibits a platelet morphology. Powder X-ray diffraction and scanning electronmicroscopy data revealed that both phases are present in films of Cu(TCNQ) formed by oxidation of Cu foil byTCNQ in CH3CN. X-ray photoelectron spectra of the two phases are indistinguishable from each other and areindicative of the presence of Cu(I). Single-crystal X-ray studies were undertaken on very small crystals of thetwo samples, the results of which reveal that subtle geometrical changes for the nitrile arrangements around thefour-coordinate Cu(I) centers lead to major changes in the architectural framework of the polymers. Phase I wasindexed in the tetragonal crystal system, but due to disorder and twinning, the crystal diffracted to only ~40
in2
. The data were solved and refined in the monoclinic Pn space group. The polymeric motif consists of Cuatoms surrounded by four nitrile lone pairs of independent TCNQ- molecules arranged in a distorted tetrahedralgeometry. A quadruply twinned crystal of Cu(TCNQ) phase II was indexed in the monoclinic system and resolvedby 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 interpenetratinglattices present. In phase I the TCNQ- units are involved in close 
-stacking interactions at ~3.24 Å whereas inphase II the closest approach of the rings is ~6.8 Å. In qualitative agreement with these observations are themagnetic properties; 1 is essentially diamagnetic and 2 displays Curie-Weiss behavior down to very lowtemperatures. 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 eVwhereas 2 is a very poor semiconductor with 
(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.
in2. The data were solved and refined in the monoclinic Pn space group. The polymeric motif consists of Cuatoms surrounded by four nitrile lone pairs of independent TCNQ- molecules arranged in a distorted tetrahedralgeometry. A quadruply twinned crystal of Cu(TCNQ) phase II was indexed in the monoclinic system and resolvedby 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 interpenetratinglattices present. In phase I the TCNQ- units are involved in close -stacking interactions at ~3.24 Å whereas inphase II the closest approach of the rings is ~6.8 Å. In qualitative agreement with these observations are themagnetic properties; 1 is essentially diamagnetic and 2 displays Curie-Weiss behavior down to very lowtemperatures. 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 eVwhereas 2 is a very poor semiconductor with (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.