Novoa Juan J, Stephens Peter W, Weerasekare Mahika, Shum William W, Miller Joel S
Departament de Química Física and IQTCUB, Facultat de Química, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona, Spain.
J Am Chem Soc. 2009 Jul 1;131(25):9070-5. doi: 10.1021/ja902790q.
The reaction of Cr(C(6)H(6))(2) and 1,2,4,5-tetracyanopyrazine (TCNP) forms [Cr(C(6)H(6))(2)][TCNP], and TCNP is reduced and forms the eclipsed pi-TCNP(2-) dimer. Diamagnetic TCNP(2-) has an intradimer separation of 3.14(2) A. The intradimer C...C and N...N separations are 3.29(2) and 3.42(2) A, respectively, and increase with the distance from the center of the molecule, due to nitriles bending away from the plane of the molecule by 5 +/- 1 degrees. TCNP(2-) 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(2-) are repulsive by 58.9 kcal/mol, and that the stability of TCNP(2-) 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).
Cr(C₆H₆)₂与1,2,4,5-四氰基吡嗪（TCNP）反应生成[Cr(C₆H₆)₂][TCNP]，且TCNP被还原并形成重叠的π-[TCNP]₂²⁻二聚体。抗磁性的[TCNP]₂²⁻的二聚体内间距为3.14(2) Å。二聚体内C...C和N...N间距分别为3.29(2) Å和3.42(2) Å，并且由于腈基偏离分子平面5±1°，其间距随离分子中心的距离增加而增大。通过分子中的原子分析，[TCNP]₂²⁻最好被描述为具有一个涉及每个六元环中四个C原子的2e⁻/8c C-C键。B3LYP/6-31+G(d)计算的相互作用结果表明，孤立的[TCNP]₂²⁻中的[TCNP]⁻...[TCNP]⁻相互作用具有58.9 kcal/mol的排斥力，并且[TCNP]₂²⁻的稳定性主要源于[TCNP]⁻...阳离子(+)静电相互作用，其总和（-209.8 kcal/mol）超过排斥性的[TCNP]⁻...[TCNP]⁻和阳离子(+)...阳离子(+)相互作用的总和（140.3 kcal/mol）。
