| Sumario: | The reaction of Cr(CH) and 1,2,4,5-tetracyanopyrazine (TCNP) forms [Cr(CH)][TCNP], and TCNP is reduced and forms the eclipsed π[TCNP] dimer. Diamagnetic [TCNP] has an intradimer separation of 3.14(2) Å. The intradimer C⋯C and N⋯N separations are 3.29(2) and 3.42(2) Å, respectively, and increase with the distance from the center Of the molecule, due to nitriles bending away from the plane of themolecule by 5 ± 1°. [TCNP] is best described by an atoms-in-molecules analysis as having a 2e/8c C-C bond involving the four C atoms from each six-member ring. The results of B3LYP/6-31 +G(d)- computed interactions indicate that the [TCNP]⋯[TCNP] interactions in an isolated [TCNP] are repulsive by 58.9 kcal/rnol, and that the stability of [TCNP] primarily originates from [TCNP]⋯cation electrostatic interactions, whose sum (-209.8 kcal/mol) exceeds the sum of the repulsive [TCNP]⋯[TCNP] and cation⋯cation interactions (140.3 kcal/mol).
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