title: 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.
abstract: From the reaction of in situ generated 1,2-di(4-tert-butylphenyl)ethylene-1,2-dithiol, 2LH2, and Na[AuCl4].2H2O 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 pi 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 CH2Cl2, 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 pi 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 [AuIII(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 pi 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.
authors.affiliation: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.
authors.forename: Swarnalatha
authors.initials: S
authors.lastname: Kokatam
authors.forename: Kallol
authors.initials: K
authors.lastname: Ray
authors.forename: Joseph
authors.initials: J
authors.lastname: Pap
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: William E
authors.initials: WE
authors.lastname: Geiger
authors.forename: Robert J
authors.initials: RJ
authors.lastname: LeSuer
authors.forename: Philip H
authors.initials: PH
authors.lastname: Rieger
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermüller
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Karl
authors.initials: K
authors.lastname: Wieghardt
mesh_terms: D000465:Algorithms; D003460:Crystallization; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004583:Electrons; D005030:Ethylenes / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry; D013055:Spectrophotometry, Infrared; D014050:Toluene / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D005030:Ethylenes; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; D014050:Toluene; D006046:Gold; C036216:ethylene; C006862:butylphen; C004848:dithiol