Abstract
Abstract A series of {Fe(NO)2}9 LMW-DNICs with the formula [(RS)2Fe(NO)2]- (R = 2-C7H4NS (1), o-NHCOCH3-C6H4 (2), C4H3S (3), o-NH2-C6H4 (4), C6H5 (5)) have been prepared and characterized by means of IR, UV-vis, EPR, cyclic voltammetry magnetic susceptibility and X-ray crystallography. The electron-donating ability of thiolate ligands exerts an influence on the redox potential E1/2: 1, -0.93 V; 2, -1.30 V; 3, -1.31 V; 5, -1.33 V. The corresponding stretching frequencies of the NO bands of complexes 1 – 5 decrease in the order: 1, 1716, 1766; 2, 1705, 1752; 3, 1698, 1743; 4, 1693, 1739; 5, 1693, 1737 cm-1, showing a correlation between the redox potential and the NO stretching frequency. The increased stability of complex 2 as compared with others may be ascribed to intramolecular [N-H····S] interactions in the solid state, even in solution. Kinetic study indicates that LMW-DNICs coordinated with stronger electron-donating thiolates are more stable toward NO release than those with weaker ones. At room temperature, complexes 2, 3 and 5 exhibit a well-resolved five-line EPR spectrum with signal at g = 2.038, 2.027, 2.028, and the hyperfine coupling constants of 2.27, 2.38 and 2.47 G, respectively, the characteristic g value of DNICs. Magnetism study implicates that the ground state electronic configuration of LMW-DNICs {Fe(NO)2}9 motif is best described as a resonance hybrid of {Fe-1(+NO)2}9 and {Fe+1(˙NO)2}9. From this perspective, the nature of thiolate ligands plays a crucial role in finely tuning stability of LMW-DNICs and ability of NO release.