New members of a class of dinitrosyliron complexes (DNICs): the characteristic EPR signal of the six-coordinate and five-coordinate {Fe(NO)2}9 DNICs.
Compared to the tetrahedral {Fe(NO)(2)}(9) dinitrosyliron complexes (DNICs) [(L)(2)Fe(NO)(2)](-) (L=SR, imidazolate) displaying EPR signal g=2.03, the newly synthesized six-/five-coordinate {Fe(NO)(2)}(9) DNICs [(TPA)Fe(NO)(2)][BF(4)] (1-TPA) (TPA=2-[CH(2)-C(5)H(4)N](3)N), [((iPr)PDI)Fe(NO)(2)][BF(4)] (2-(iPr)PDI) ((iPr)PDI=2,6-[2,6-(i)Pr(2)-C(6)H(3)N=CMe](2)C(5)H(3)N) and [(PyImiS)Fe(NO)(2)] (4-PyImiS) (PyImiS=2-[2-(C(5)H(4)N)CMe=N]C(6)H(4)S) exhibit the distinct EPR signal g=2.015-2.018. The Fe K-edge pre-edge energy (7113.4-7113.6eV) derived from the 1s→3d transition in the octahedral and square-pyramidal environment of the Fe center, falling within the range of 7113.4-7113.8eV for the tetrahedral {Fe(NO)(2)}(9) DNICs, implicates that the iron cores of DNICs 1-TPA, 2-(iPr)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-(iPr)PDI and 4-PyImiS, the spontaneous transformation of the proposed thermally unstable five-coordinate {Fe(NO)(2)}(9) DNIC [(PyPepS-H)Fe(NO)(2)](-) (6-PyPepS) (PyPepS-H=[SC(6)H(4)-o-NC(O)(C(5)H(4)N)]) into the {Fe(NO)}(7)-{Fe(NO)}(7) [(μ-PyPepS-H)Fe(NO)](2) (7) along with release of nitroxyl demonstrates that the distinct electron-donating ability of the coordinated ligands ([PyPepS-H]>[PyImiS]~[TPA]>[(iPr)PDI]) regulates the stability and geometric structure of {Fe(NO)(2)}(9) DNICs. This study also shows the aspect of how the geometric structure of {Fe(NO)(2)}(9) DNICs imposed by the electron-donating ability and conformation of the coordinated ligands (tridentate [(iPr)PDI] vs tridentate [PyImiS] vs tetradentate [TPA] vs tridentate [PyPepS-H] vs bidentate [SC(6)H(4)-o-NC(O)Ph](2-)) regulates the Fe-NO bonding of {Fe(NO)(2)}(9) DNICs and presumably the release of nitroxyl from DNICs.
Department of Chemistry and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan.
Wei-Chih
WC
Shih
Tsai-Te
TT
Lu
Li-Bo
LB
Yang
Fu-Te
FT
Tsai
Ming-Hsi
MH
Chiang
Jyh-Fu
JF
Lee
Yun-Wei
YW
Chiang
Wen-Feng
WF
Liaw
D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000494:pharmacology; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008968:Molecular Conformation; D009569:Nitric Oxide / Q000737:chemistry*; D009589:Nitrogen Oxides / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics
D056831:Coordination Complexes; D008024:Ligands; D009589:Nitrogen Oxides; D009569:Nitric Oxide; C073661:dinitrosyl iron complex; D007501:Iron; C039900:nitroxyl