Electronic Structure of Mononuclear Bis(1,2-diaryl-1,2-ethylenedithiolato)iron Complexes Containing a Fifth Cyanide or Phosphite Ligand:  A Combined Experimental and Computational Study

• Published in: Inorganic chemistry 2006-09, Vol.45 (19), p.7877-7890
• Main Authors: Patra, Apurba K, Bill, Eckhard, Bothe, Eberhard, Chlopek, Krzysztof, Neese, Frank, Weyhermüller, Thomas, Stobie, Keira, Ward, Michael D, McCleverty, Jon A, Wieghardt, Karl
• Format: Article
• Language: English
• Subjects: Computer Simulation; Crystallography, X-Ray; Cyanides - chemistry; Electrochemistry; Electrons; Ferrous Compounds - chemistry; Ions - chemistry; Ligands; Models, Molecular; Molecular Structure; Oxidation-Reduction; Phosphites - chemistry; Solutions; Spectrum Analysis; Temperature
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic061171t

A series of mononuclear square-based pyramidal complexes of iron containing two 1,2-diaryl-ethylene-1,2-dithiolate ligands in various oxidation levels has been synthesized. The reaction of the dinuclear species [FeIII 2(1L•)2(1L)2]0, where (1L)2- is the closed shell di-(4-tert-butylphenyl)-1,2-ethylenedithiolate dianion and (1L•)1- is its one-electron-oxidized π-radical monoanion, with [N(n-Bu)4]CN in toluene yields dark green crystals of mononuclear [N(n-Bu)4][FeII(1L•)2(CN)] (1). The oxidation of 1 with ferrocenium hexafluorophosphate yields blue [FeIII(1L•)2(CN)] (1 ox), and analogously, a reduction with [Cp2Co] yields [Cp2Co][N(n-Bu)4][FeII(1L•)(1L)(CN)] (1 red); oxidation of the neutral dimer with iodine gives [FeIII(1L•)2I] (2). The dimer reacts with the phosphite P(OCH3)3 to yield [FeII(1L•)2{P(OCH3)3}] (3), and [FeIII 2(3L•)2(3L)2] reacts with P(OC6H5)3 to give [FeII(3L•)2{P(OC6H5)3}] (4), where (3L)2- represents 1,2-diphenyl-1,2-ethylenedithiolate(2−). Both 3 and 4 were electrochemically one-electron oxidized to the monocations 3 ox and 4 ox and reduced to the monoanions 3 red and 4 red. The structures of 1 and 4 have been determined by X-ray crystallography. All compounds have been studied by magnetic susceptibility measurements, X-band EPR, UV−vis, IR, and Mössbauer spectroscopies. The following five-coordinate chromophores have been identified:  (a) [FeIII(L•)2X] n , X = CN-, I- (n = 0) (1 ox, 2); X = P(OR)3 (n = 1+) )3 ox, 4 ox) with S t = 1/2, S Fe = 3/2; (b) [FeII(L•)2X] n , X = CN-, (n = 1−) (1); X = P(OR)3 (n = 0) (3, 4) with S t = S Fe = 0; (c) [FeII(L•)(L)X] n ↔ [FeII(L)(L•)X] n , X = CN- (n = 2−) (1 red); X = P(OR)3 (n = 1−) (3 red, 4 red) with S t = 1/2, S Fe = 0 (or 1). Complex 1 ox displays spin crossover behavior:  S t = 1/2 ↔ S t = 3/2 with intrinsic spin-state change S Fe = 3/2 ↔ S Fe = 5/2. The electronic structures of 1 and 1 ox have been established by density functional theoretical calculations:  [FeII(1L•)2(CN)]1- (S Fe = 0, S t = 0) and [FeIII(1L•)2(CN)]0 (S Fe = 3/2, S t = 1/2).