Solid-State NMR Spectra and Long, Intra-Dimer Bonding in the π-[TTF]22+ (TTF = Tetrathiafulvalene) Dication

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• 作者：Merrill D. Halling ; Joshua D. Bell ; Ronald J. Pugmire ; David M. Grant ; Joel S. Miller
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：June 24, 2010
• 年：2010
• 卷：114
• 期：24
• 页码：6622-6629
• 全文大小：273K
• 年卷期：v.114,no.24(June 24, 2010)
• ISSN：1520-5215

文摘

The ¹³C chemical-shift tensor principal values for TTF and π-[TTF]₂²⁺ (TTF = tetrathiafulvalene) dimer dications have been measured in order to better understand the electronic structure and long intradimer bonding of these TTF-based dimer structures. The structure of π-[TTF]₂²⁺ is abnormal due to its two C−C and four S−S ca. 3.4 Å intradimer separations, which is less than the sum of the sulfur van der Waals radii, and has a singlet ¹A_1g electronic ground state. This study of TTF and [TTF]₂²⁺ was conducted to determine how the NMR chemical-shift tensor principal values change as a function of electronic structure. This study also establishes a better understanding of the interactions that lead to spin-pairing of the monomeric radical units. The density functional theory (DFT) calculated nuclear shielding tensors are correlated with the experimentally determined principal chemical-shift values. The embedded ion method (EIM) was used to investigate the electrostatic lattice potential in [TTF]₂²⁺. These theoretical methods provide information on the tensor magnitudes and orientations of their tensor principal values with respect to the molecular frame. The experimental chemical-shift principal values agree with the calculated quantum mechanical chemical-shielding principal values, within typical errors commonly seen for this class of molecular system. Relatively weak Wiberg bond orders between the two [TTF]⁺ components of the dimer dication correlate with the long bonds linking the two [TTF]⁺ monomers and substantiate the claim that there is weak multicenter bonding present.