From the reaction of in situ generated 1,2-di(4-tert-butylphenyl)ethylene- 1,2-dithiol, 2LH2, and Na[AuCl4]·H 2O in 1,4-dioxane, green brown crystals of diamagnetic [N(n-Bu) 4][AuIII(2L)2] (1) were obtained. As shown by cyclic voltammetry, 1 is a member of an electron-transfer series comprising the dianion [AuII(2L)2] 2-, the monoanion [AuIII(2L)2] -, the neutral species [AuIII(2L •)(2L)]0 ↔ [AuIII( 2L)(2L•)]0, and the monocation [AuIII(2L•)2]+. (2L•)1- represents the π radical anion (Srad = 1/2) of the one-electron oxidized closed-shell dianion ( 2L)2-. Oxidation of 1 in CH2Cl2 with ferrocenium hexafluorophosphate affords green, paramagnetic microcrystals of [AuIII(2L•)(2L)] ↔ [AuIII(2L)(2L•)] (2) (S = 1/2). Complexes 1 and 2 have been characterized by X-ray crystallography. Both species possess square-planar monoanions and neutral molecules, respectively. From the oxidation reaction of 1 or [N(n-Bu)4][AuIII( 3L)2] with 2-3 equiv of [NO]BF4 in CH 2Cl2, a green solution of [AuIII( 2L•)2]+ and green microcrystals of [AuIII(3L•)2]BF4 (3) were obtained, respectively; (3L)2- represents the dianion 1,2-di(4-diphenyl)ethylene-1,2-dithiolate, and (3L •)1- is its π radical monoanion. The electronic structures of this series of gold species have been elucidated by UV-vis, EPR spectroscopies, and DFT calculations. It is shown computationally by density functional theoretical (DFT) methods that the electronic structure of [Au III(1L•)2]+ is best described as a singlet diradical (St = 0); the ligand mixed valency in the neutral species 2 is of class (III) (delocalized); the monoanion in 1 contains a AuIII ion and two closed-shell dianionic ligands; and the corresponding dianions [Au(L)2]2- are best described as an intermediate AuII/AuIII species with a metal-ligand delocalized SOMO (25% Au 5d, 75% 3p of four S atoms). (1L) 2- is the dianion 1,2-di(phenyl)ethylene-1,2-dithiolate, and ( 1L•)1- is the π radical monoanion. The neutral species [PdII(2L•)2] (4) has also been synthesized and characterized by X-ray crystallography. Its electronic structure is the same as described for [AuIII( 1L•)2]+ (singlet diradical), whereas that of the monoanion [PdII(2L•) (2L)]- ↔ [Pd(2L)(2L •)]- corresponds to that of the neutral gold complex 2. Anodic oxidation of the analogous monoanion [AuIII(mnt) 2]-, where mnt = maleonitriledithiolate, gave the neutral complex [Au(mnt)(mnt•)] (E1/2 = 0.91 V vs Fc +/Fc). The optical and EPR spectroscopies of [Au(mnt)(mnt •)] were consistent with those observed for the corresponding di(tert-butylphenyl)-ethylenedithiolate complex 2.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry