Molecular and electronic structure of square-planar gold complexes containing two 1,2-di(4-tert-butylphenyl)ethylene-1,2-dithiolato ligands: [Au(2L)2]1+/0/1-/2-. A combined experimental and computational study

Swarnalatha Kokatam, Kallol Ray, Joseph Pap, Eckhard Bill, William E. Geiger, Robert J. LeSuer, Philip H. Rieger, Thomas Weyhermüller, Frank Neese, Karl Wieghardt

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Abstract

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.

Original languageEnglish
Pages (from-to)1100-1111
Number of pages12
JournalInorganic Chemistry
Volume46
Issue number4
DOIs
Publication statusPublished - Feb 19 2007

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ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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