Comparison of the Structure of Advanced Organic Electrode Materials, TAPT and "TAQ", by Multinuclear NMR and...

The chemical structure of two insoluble tricyclic organic molecules made from the same precursor through different reported synthesis routes and forming promising electrode materials is compared by advanced solid-state 13C, 15N, 13C{1H}, 15N{1H}, and 15N-15N nuclear magnetic resonance (NMR). One synthesis resulted in TAPT, tetraamino-phenazine-1,4,6,9-tetrone, while several prominent publications identified the product of the other procedure as TAQ, with fewer lithium binding sites due to hydrogen atoms bonded to two nitrogen atoms, which also make the central ring antiaromatic. Peak positions in the 13C and 15N NMR spectra of TAPT and two "TAQ" materials, including 15N6-"TAQ", are similar and agree with chemical-shift predictions for TAPT. Differences in line broadening arise from different concentrations of unpaired electrons, confirmed by pronounced differences in spin-lattice relaxation times. Slow 15N{1H} and long-range 13C{1H} dipolar dephasing proves that like TAPT, "TAQ" does not contain central N-H groups. The aromatic pyrazine ring in TAPT and "TAQ" is confirmed by the 309 ppm chemical shift of the nonprotonated nitrogen atom. Moderate splittings of the 15NH2 and 13C-NH2 NMR signals are shown to be due to symmetry-lowering differences in hydrogen bonding. Mass spectra of TAPT and "TAQ" exhibit matching peaks. Quantum-chemical analyses show that formation of TAQ with its antiaromatic central ring is not thermodynamically favorable and that it would spontaneously tautomerize into a reduced form of TAPT. In conclusion, both TAPT and "TAQ" are tetraamino-phenazine-1,4,6,9-tetrone, and published studies of the properties of "TAQ" are therefore duplicative.