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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

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posted on 2006-09-18, 00:00 authored by Apurba K. Patra, Eckhard Bill, Eberhard Bothe, Krzysztof Chlopek, Frank Neese, Thomas Weyhermüller, Keira Stobie, Michael D. Ward, Jon A. McCleverty, Karl Wieghardt
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 [FeIII2(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)] (1ox), and analogously, a reduction with [Cp2Co] yields [Cp2Co][N(n-Bu)4][FeII(1L)(1L)(CN)] (1red); 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 [FeIII2(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 3ox and 4ox and reduced to the monoanions 3red and 4red. 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) (1ox, 2); X = P(OR)3 (n = 1+) )3ox, 4ox) with St = 1/2, SFe = 3/2; (b) [FeII(L)2X]n, X = CN-, (n = 1−) (1); X = P(OR)3 (n = 0) (3, 4) with St = SFe = 0; (c) [FeII(L)(L)X]n ↔ [FeII(L)(L)X]n, X = CN- (n = 2−) (1red); X = P(OR)3 (n = 1−) (3red, 4red) with St = 1/2, SFe = 0 (or 1). Complex 1ox displays spin crossover behavior:  St = 1/2St = 3/2 with intrinsic spin-state change SFe = 3/2SFe = 5/2. The electronic structures of 1 and 1ox have been established by density functional theoretical calculations:  [FeII(1L)2(CN)]1- (SFe = 0, St = 0) and [FeIII(1L)2(CN)]0 (SFe = 3/2, St = 1/2).