American Chemical Society
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Intrinsic Carrier Doping in Antiferromagnetically Interacted Supramolecular Copper Complexes with (Pyrazino)tetrathiafulvalene (Pyra-TTF) as the Ligand, [CuIICl2(pyra-TTF)] and (Pyra-TTF)2[CuI3Cl4(pyra-TTF)]

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posted on 2008-05-19, 00:00 authored by Shun Ichikawa, Shinya Kimura, Kazuyuki Takahashi, Hatsumi Mori, Gosuke Yoshida, Yuichi Manabe, Masaki Matsuda, Hiroyuki Tajima, Jun-ichi Yamaura
New supramolecular copper complexes with pyrazinotetrathiafulvalene (pyra-TTF) as the ligand, [CuIICl2(pyra-TTF)] (1) and (pyra-TTF)2[CuI3Cl4(pyra-TTF)] (2), have been synthesized by the diffusion method. Complex 1 is a black block crystal with a three-dimensional (3-D) supramolecular network; the linear chain [−CuIICl2−(pyra-TTF)−]n extends along the b axis, where the coordinated pyra-TTF donors are stacked in a head-to-tail and ring-over-bond configuration to construct two-dimensional (2-D) sheets, and between the sheets, there are C···Cl or H···Cl contacts. Even though the electron spin resonance (ESR) measurement reveals the nearly CuII state, complex 1 is a semiconductor with σRT = 1.0 × 10−4 S cm−1 and Ea = 0.33 eV. The high-frequency conductivity measurement also confirmed the intrinsic slight carrier doping from CuII to the pyra-TTF donor. This slight doping enhances not only the real and imaginary dielectric constants but also the antiferromagnetic interaction between CuII spins following the 2-D Heisenberg model with 2J = −20 K. In contrast, complex 2 is a very thin black needle. This needle crystal has two crystallographically independent pyra-TTF molecules, which are coordinated and noncoordinated donors. The coordinated donors composed a supramolecular chain [CuI3Cl4(pyra-TTF)0]n, whereas the noncoordinated donors formed conducting α′′-type pyra-TTF+0.5 sheets. This complex is semiconducting with σRT = 0.1 S cm−1 and Ea = 0.15 eV. Both complexes 1 and 2 demonstrate that the pyra-TTF molecule works not only as an oxidized donor by CuII to construct conducting sheets but also as a ligand coordinated to a Cu cation to form supramolecuar chains.