摘要
Compared to the tetrahedral {Fe(NO) <sub>2</sub> } <sup>9</sup> dinitrosyliron complexes (DNICs) [(L) <sub>2</sub> Fe(NO) <sub>2</sub> ] <sup>-</sup> (L = SR, imidazolate) displaying EPR signal g = 2.03, the newly synthesized six-/five-coordinate {Fe(NO) <sub>2</sub> } <sup>9</sup> DNICs [(TPA)Fe(NO) <sub>2</sub> ][BF <sub>4</sub> ] (1-TPA) (TPA = 2-[CH <sub>2</sub> -C <sub>5</sub> H <sub>4</sub> N] <sub>3</sub> N), [( <sup>iPr</sup> PDI)Fe(NO) <sub>2</sub> ][BF <sub>4</sub> ] (2- <sup>iPr</sup> PDI) ( <sup>iPr</sup> PDI = 2,6-[2,6- <sup>i</sup> Pr <sub>2</sub> -C <sub>6</sub> H <sub>3</sub> N = CMe] <sub>2</sub> C <sub>5</sub> H <sub>3</sub> N) and [(PyImiS)Fe(NO) <sub>2</sub> ] (4-PyImiS) (PyImiS = 2-[2-(C <sub>5</sub> H <sub>4</sub> N)CMe = N]C <sub>6</sub> H <sub>4</sub> S) exhibit the distinct EPR signal g = 2.015-2.018. The Fe K-edge pre-edge energy (7113.4-7113.6 eV) derived from the 1s→3d transition in the octahedral and square-pyramidal environment of the Fe center, falling within the range of 7113.4-7113.8 eV for the tetrahedral {Fe(NO) <sub>2</sub> } <sup>9</sup> DNICs, implicates that the iron cores of DNICs 1-TPA, 2- <sup>iPr</sup> PDI and 4-PyImiS are tailored to minimize the electronic changes accompanying changes in coordination geometry. In contrast to the thermally stable 1-TPA, 2- <sup>iPr</sup> PDI and 4-PyImiS, the spontaneous transformation of the proposed thermally unstable five-coordinate {Fe(NO) <sub>2</sub> } <sup>9</sup> DNIC [(PyPepS-H)Fe(NO) <sub>2</sub> ] <sup>-</sup> (6-PyPepS) (PyPepS-H = [SC <sub>6</sub> H <sub>4</sub> -o-NC(O)(C <sub>5</sub> H <sub>4</sub> N)]) into the {Fe(NO)} <sup>7</sup> -{Fe(NO)} <sup>7</sup> [(μ-PyPepS-H)Fe(NO)] <sub>2</sub> (7) along with release of nitroxyl demonstrates that the distinct electron-donating ability of the coordinated ligands ([PyPepS-H] > [PyImiS] ∼ [TPA] > [ <sup>iPr</sup> PDI]) regulates the stability and geometric structure of {Fe(NO) <sub>2</sub> } <sup>9</sup> DNICs. This study also shows the aspect of how the geometric structure of {Fe(NO) <sub>2</sub> } <sup>9</sup> DNICs imposed by the electron-donating ability and conformation of the coordinated ligands (tridentate [ <sup>iPr</sup> PDI] vs tridentate [PyImiS] vs tetradentate [TPA] vs tridentate [PyPepS-H] vs bidentate [SC <sub>6</sub> H <sub>4</sub> -o-NC(O) Ph] <sup>2-</sup> ) regulates the Fe-NO bonding of {Fe(NO) <sub>2</sub> } <sup>9</sup> DNICs and presumably the release of nitroxyl from DNICs. © 2012 Elsevier Inc.