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

Abstract

The (13)C chemical-shift tensor principal values for TTF and pi-[TTF](2)(2+) (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 pi-[TTF](2)(2+) is abnormal due to its two C-C and four S-S ca. 3.4 A intradimer separations, which is less than the sum of the sulfur van der Waals radii, and has a singlet (1)A(1g) electronic ground state. This study of TTF and [TTF](2)(2+) 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](2)(2+). 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.

A Tetrathiafulvalene (TTF)‐Conjugated Microporous Polymer Network

“…After iodine treatment of TTFCMP, the NMR spectrum of the polymer shows significant changes in peak intensities, as especially the carbons which can be assigned to the TTF moieties alter their response in the magnetic field from ethylene to aromatic character as reported for molecular TTF iodide salts 59. The significant increase in the intensity of the broad peak at δ =131 ppm can be explained by this deshielding effect on TTF, which yields a shift to lower fields, that is, in the region of thiophene‐like aromatic carbons.…”

Solid‐State 13C NMR Evidence for Long Multicenter Intradimer Bonding in Zwitterion‐like Structures

“…Previous work has demonstrated that 13 Cchemical shift tensors in neutralT TF and TCNE dramatically differ from those in p-[TTF] 2 2 + and p-[TCNE] 2 2À dimers. [13,19] Comparisons of relevant tensors are given in Tables S1-S3 and includes previously measured tensors from TCNE and [TCNE] 2À ,s tructures that do not form homo-dimers, but which exhibits integer oxidation states. Because dimerizationa nd oxidation/reduction occur simultaneously,anindependentcomparison of the influence in oxidation state cannot be made.…”

“…The β‐ and δ‐[TTF⋅⋅⋅TCNE] phases were prepared as described elsewhere . Previously reported 13 C chemical shift tensor data from six compounds were utilized as benchmark data including; neutral TCNE, [TDAE] 2+ [TCNE] 2 2− [TDAE=(Me 2 N) 2 CC(NMe 2 ) 2 ], {[NEt 4 ] + } 2 [TCNE] 2 2− , [TDAE] 2+ [TCNE] 2− , neutral TTF and [TTF] 2 2+ . The 13 C shift tensors for the β and δ‐polymorphs of [TTF⋅⋅⋅TCNE] were measured with the FIREMAT experiment on a CMX‐400 Chemagnetics spectrometer operating at 100.61 ( 13 C) and 400.08 MHz ( 1 H).…”

“…More recent work has also demonstrated that NMR shifts can reliably predict crystal structures and provide estimates of uncertainties in individual atomic positions . To understand the nature and strength of the intra‐dimer bonding in β and δ‐[TTF⋅⋅⋅TCNE] the 13 C shift tensors, reported here for the first time, are compared to previously reported benchmark experimental data for TTF, [TTF] 2 2 + , TCNE, [TCNE] 2 2− , and [TCNE] 2− …”

“…[22][23][24][25][26][27] More recent work has also demonstrated that NMR shifts can reliably predict crystal structures [28][29][30][31] and provide estimates of uncertainties in individual atomicp ositions. [32,33] To understand the nature and strength of the intra-dimer bonding in b and d-[TTF···TCNE] the 13 Cs hift tensors, reported here for the first time, are compared to previously reported benchmark experimental data for TTF, [TTF] 2 2 + + , [19] TCNE, [TCNE] 2 2À ,and [TCNE] 2À . [13] Previously,atheoretical study has evaluated the validity of the proposedl ong multi-center bonds in the a, b and d phases of [TTF···TCNE].…”