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Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor
Accepted Manuscript Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor
Arnd Vogler PII: DOI: Reference:
S1387-7003(17)30001-1 doi: 10.1016/j.inoche.2017.03.035 INOCHE 6602
To appear in:
Inorganic Chemistry Communications
Received date: Revised date: Accepted date:
1 January 2017 24 March 2017 30 March 2017
Please cite this article as: Arnd Vogler , Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Inoche(2017), doi: 10.1016/j.inoche.2017.03.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor. Arnd Vogler, Institute of Inorganic Chemistry, University Regensburg, Germany
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Abstract
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In analogy to peroxide , disulfide is an oxidant as well as a reductant. Accordingly, as a ligand of a
SC
reducing metal center, low-energy MLCT transitions can occur, while with oxidizing metals lowenergy LMCT transitions should be observed. Such MLCT and LMCT excitations are expected to
MA
suitable examples to explore this behavior.
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induce redox reactions. The complexes [ CpFe(II)(CO)2]2μ-S2 (Cp = C5H5) and { [Fe(III)(CN)5]2μ-S2}6- are
Keywords: Iron complexes, Disulfide complexes, Photoredox reactions, MLCT , LMCT
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Peroxide is oxidizing as well as reducing . It follows that with peroxide as a ligand low-energy MLCT as
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well as LMCT transitions may be present provided that the metals are reducing and oxidizing, respectively [1]. In terms of molecular orbitals, peroxide has available occupied MOs at relatively
CE
high energies and empty MOs at rather low energies. Accordingly, peroxide can function as CT acceptor and CT donor. MLCT excitation may lead to an oxidation of the metal and reduction of the
AC
peroxide to water. In contrast, LMCT excitation can induce the reduction of the metal and oxidation of peroxide to oxygen.
A variety of disulfide-bridged binuclear complexes has been prepared and characterized [2]. It is expected that their electronic structure resembles that of analogous peroxide complexes since O22and S22- are also electronically rather similar. As reducing and oxidizing metal centers, iron(II) and iron(III) were selected owing to their biological relevance. In particular, the combination Fe(II)-disulfide is of considerable interest, since such a
ACCEPTED MANUSCRIPT 2 complex is closely related to pyrite, Fe(II)(S22-). The valence band of pyrite is mainly derived from occupied iron d-orbitals while the conduction band is composed of empty sulfur orbitals [3]. In a molecular picture, this description corresponds to an iron-based HOMO and a sulfur- based LUMO. It follows, that such a complex should be characterized by a low-energy Fe(II) to disulfide MLCT transition. In this context, it should be emphasized that pyrite has been considered to play an
PT
important role as a direct source of energy for early life on earth [4]. Moreover, light absorption by pyrite can be viewed as photoredox process which finds its counterpart in molecular systems as
RI
suggested in the present study. As suitable complexes we selected Cp(CO)2Fe(II)(μ-S22-)Fe(II)(CO)2Cp
SC
[5] with Cp = cyclopentadienyl and [(CN)5Fe(III)(μ-S22-)Fe(III)(CN)5]6- as targets.
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The compound [Cp(CO)2Fe]2(S2) was prepared according to a literature procedure [5]. The anion {[Fe(CN)5]2(S2)}6- was unknown. Solutions of this complex were obtained by mixing aqueous solutions
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of Na2 [Fe(CN)5(NH3)] [6] and (NH4)2S2. This mixture turned instantly dark purple, but started immediately to decompose. It was not possible to isolate a pure material. Irradiations were
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limited by using Schott cutoff filters.
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performed with a high-pressure mercury lamp Osram 100 W/2. Long-wavelength irradiation was
Solutions of { [Cp(CO)2Fe]2 (S2)} in acetonitrile are yellow and display absorptions at λmax = 371 nm
AC
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and an inflection near 500 nm.
Fig. 1 Fe2 S2
Fig. 1 Spectral changes upon irradiation of 3.4 x 10-4 M {[Cp(CO)2Fe2](S2)} in acetonitrile in a 1-cm cell with white light, irradiation time: 0 min (a), ½ min (b), 20 min (c).
ACCEPTED MANUSCRIPT 3 These solutions are light-sensitive [7]. Irradiation with white light ( or λirr > 300 nm) was accompanied by the loss of the starting complex as indicated by the disappearance of the 371 nm absorption (Fig. 1). The photolyzed solution did not contain colloidal sulfur [8,9]. At this stage the final spectrum reveals the presence of Cp4Fe4S4 [10,11]. This complex is light-sensitive itself. Again, white light or λirr > 300 nm is effective, but much less efficient. Much longer irradiation times are now required. The
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concomitant spectral changes (Fig. 2) are very close to those, which had been observed when Cp4Fe4S4 was photolyzed directly [7]. Moreover, elemental sulfur and Fe2+ ions accumulated during
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the photolysis as it has been observed before.
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Fig. 2 Fe2S2
Fig. 2 Spectral changes upon irradiation of 6 x 10-4 M {[CpFe(CO)2]2}(S2) in acetonitrile with white
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light in a 1-cm cell for 15 min at later stages of the photolysis, starting from spectrum a
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(corresponding to spectrum (c) of Fig. 1), indicating the final loss of Cp4Fe4S4 (spectrum c) The second target of this study, the complex [Fe2(CN)10(S2)]6- , was unknown. Evidence for its generation was obtained, but the complex anion could be characterized only to a very limited extent owing to its facile decomposition. A variety of binuclear disulfide-bridged complexes [2], such as [Ru2(NH3)10(S2)]4+ [12,13] , are known although this isoelectronic ruthenium(III) complex is also not very stable. Upon addition of an aqueous solution of (NH4)2S2 (obtained by mixing of (NH4)2S and an equivalent amount of elemental sulfur) to an aqueous solution of [Fe(CN)5NH3]3-, a dark purple solution is instantly generated showing an intense absorption at λmax = 575 nm (Fig. 3) which
ACCEPTED MANUSCRIPT 4 resembles that of [Ru2(NH3)10(S2)]4+ with λmax = 725 nm.
ν
Abs
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1.0
600 (nm)
Fig.3 Fe2S2
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400 λ
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0.5
irradiation time (
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Fig. 3 The disappearance of [Fe2(CN)10(S2)]6- upon irradiation with white light in a 1-cm cell, from the top to the bottom) : approximately 15 sec intervals.
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Unfortunately, [Fe2(CN)10(S2)]6- decomposes rapidly in the dark as indicated by the facile
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disappearance of the purple color which occurs within about 20 minutes. Nevertheless, a careful examination shows that the binuclear iron disulfide complex is also light sensitive. The photolysis is
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achieved by irradiation with white light or long-wavelength irradiation (Fig. 3). The light-sensitivity is difficult to confirm since it can be proven only at rather high light intensities in order to compete
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successfully with the thermal decomposition. As a photoproduct, [Fe(II)(CN)5OH]4- may be formed. The photolyzed solution exhibits a long-wavelength absorption at λmax = 390 nm (see Fig. 3), which is consistent with the presence of [Fe(II)(CN)5(OH)]4- [14]. The formation of an iron(II) cyano complex is confirmed by the addition of Fe3+ to the photolyzed solution. In this case prussian blue is formed. Iron(III) cyano complexes would not form Prussian blue under these conditions. In addition, elemental sulfur was obtained as a further photoproduct. Elemental sulfur was extracted from the photolyzed aqueous solution with cyclohexane. Its presence was confirmed by its absorption maximum at 270 nm [8].
ACCEPTED MANUSCRIPT 5 In analogy to peroxide, disulfide has available an empty σ* orbital at relatively low energies. In combination with a reducing metal, a low-energy MLCT transition should be accessible. Accordingly, the long-wavelength absorption of [Cp2Fe2(CO)4](μ-S2) in acetonitrile (Fig. 1) at λmax = 373 nm (ε = 7.6x102 M-1cm-1) is assigned to a Fe(II) to σ* S22- MLCT transition. MLCT excitation leads to a photolysis which is suggested to proceed according to eq. 1. 2 [Cp2Fe(II)2(CO)4(S22-)
Cp4Fe(III)4S4 + 8 CO
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(1)
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The final spectrum of the photolyzed solution (Fig. 1) resembles that of an authentic sample of
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Cp4Fe4S4 [7]. This complex undergoes a further photolysis which is accompanied by spectral changes (Fig. 2) which a very similar to those in Fig. 2 of ref. [7]. Moreover, other observations (accumulation
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secondary photolysis can be described by eq. 2.
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of elemental sulfur and Fe2+ ions, see above) agree also with those of ref.[7]. It follows that this
2 Cp2Fe(II) + 2 Fe2+ + 2
Cp4Fe(III)4S4
S2- + ¼ S8
(2)
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This photoredox reaction is concluded to be initiated by sulfide to Fe(III) LMCT excitation. As discussed above, the identity of [(NC)5Fe(III)(μ-S22-)Fe(III)(CN)5]6- is not quite clear, but our observations and some other arguments support our assumption. So it is rather reasonable to
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attribute the 575 nm absorption (Fig. 3) to a S22- to Fe(III) LMCT transition in analogy to a related
AC
ruthenium complex [12,13]. The observations during the photolysis of the binuclear iron complex are consistent with eq. 3.
[Fe(III)2(CN)10(S22-)]6- + 2 OH-
2 [Fe(II)(CN)5OH]4-
+
½ S8
(3)
In this context, it is of interest that the energy difference of the LMCT absorptions of [Fe(III)2(CN)10(S2)]6- (λmax = 575 nm) and [Fe(III)(CN)5(SCN)]3- (λmax = 478 nm) [15] amounts to 3500 cm-1. This agrees roughly with the energy difference of Δ = 4700 cm-1 for the LMCT absorptions of the corresponding Co(III) complexes (λmax = 313 nm for [Co(III)2(CN)10(S2)]6- [16] and 265 nm for [Co(III)(CN)5(SCN)]3- [17] ).
ACCEPTED MANUSCRIPT 6 In conclusion, disulfide serves as CT donor as well as acceptor ligand in binuclear iron(III) and iron(II) complexes. This observation is not only interesting in its own right, but may be also of importance in the field of iron sulfur proteins [18-20]. [1] A.Vogler, H.Kunkely, Coord. Chem.Rev. 250 (2006) 1622-1626
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[2] A.Müller, W.Jaegermann, J.H.Enemark, Coord.Chem.Rev. 46 (1982) 245-280
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[3] V.Eyert, K.-H.Höck, S.Fiechter, H.Tributsch, Phys.Rev.B 57 (1998) 6350-6359
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[4] E.Drobner, H.Huber, G.Wächtershäuser, D.Rose, K.O.Stetter, Nature 346 (1990) 742-744 [5] M.A.El-Hinnawi, A.A.Aruffo, B.D.Santarsiero, D.R.McAlister, V.Schomaker, Inorg.Chem. 22 (1983)
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1585-1590
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[6] G.Brauer, Handbuch der Präparativen Anorganischen Chemie. Ferdinand Enke, Stuttgart, 1954, p.1364
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[7] A.Vogler, Inorg.Chem.Commun. 64 (2016) 5-6 [8] H.Kunkely, A.Vogler, Z.Naturforsch. 53b (1998) 224-226
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[9] A.Vogler, H.Kunkely, Inorg. Chem. 27 (1988) 504-507
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[10] R.A.Schunn, C.J.Fritchie, C.T.Prewitt, Inorg.Chem. 5 (1966) 900-905 [11] C.H.Wei, G.R.Wilkes, P.M.Treichel, L.F.Dahl, Inorg.Chem. 5 (1966) 900-905 [12] C.R.Brulet, S.S.Isied, H.Taube, J.Am.Chem.Soc. 95 (1973) 4758-4759 [13] D.P.Fairlie, W.A.Wickramasinghe, K.A.Byriel, H.Taube, Inorg.Chem. 36 (1997) 2242-2243 [14] A.Lodziska, R.Gogolin, Rocziki Chemii 47 (1973) 497 [15] D.F.Gutterman, H.B.Gray, Inorg.Chem. 11 (1972) 1727-1733 [16] H.Siebert, S.Thym, Z.anorg.allg.Chem. 399 (1973) 107-114
ACCEPTED MANUSCRIPT 7 [17] V.Miskowski, H.B.Gray, Inorg.Chem. 14 (1975) 401-405 [18] H.Beinert, R.H.Holm, E.Münck, Science 277 (1997) 653-659 [19] H.Beinert, J.Biol.Inorg.Chem. 5 (2000) 2-15
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[20] L.Noodleman, T.Lovell, T.Liu, F.Himo, R.A.Torres, Opin.Chem.Biol. 6 (2002) 259-273.
ACCEPTED MANUSCRIPT
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Graphical abstract
ACCEPTED MANUSCRIPT 9
Highlights
• Disulfide (S
22 )
is a CT acceptor and a CT donor
S22- serves also as bridging ligand in binuclear Fe(II) and Fe(III) complexes
• These complexes are characterized by Fe(II) to S
22
MLCT and S22- to Fe(III) LMCT transitions
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•
Fe2S2
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SC
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• MLCT and LMCT excitation initiate photoredox reactions
Arnd Vogler PII: DOI: Reference:
S1387-7003(17)30001-1 doi: 10.1016/j.inoche.2017.03.035 INOCHE 6602
To appear in:
Inorganic Chemistry Communications
Received date: Revised date: Accepted date:
1 January 2017 24 March 2017 30 March 2017
Please cite this article as: Arnd Vogler , Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Inoche(2017), doi: 10.1016/j.inoche.2017.03.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
Photoredox reactions of binuclear iron(II) and (III) disulfide complexes. Disulfide as CT acceptor and donor. Arnd Vogler, Institute of Inorganic Chemistry, University Regensburg, Germany
PT
Abstract
RI
In analogy to peroxide , disulfide is an oxidant as well as a reductant. Accordingly, as a ligand of a
SC
reducing metal center, low-energy MLCT transitions can occur, while with oxidizing metals lowenergy LMCT transitions should be observed. Such MLCT and LMCT excitations are expected to
MA
suitable examples to explore this behavior.
NU
induce redox reactions. The complexes [ CpFe(II)(CO)2]2μ-S2 (Cp = C5H5) and { [Fe(III)(CN)5]2μ-S2}6- are
Keywords: Iron complexes, Disulfide complexes, Photoredox reactions, MLCT , LMCT
D
Peroxide is oxidizing as well as reducing . It follows that with peroxide as a ligand low-energy MLCT as
PT E
well as LMCT transitions may be present provided that the metals are reducing and oxidizing, respectively [1]. In terms of molecular orbitals, peroxide has available occupied MOs at relatively
CE
high energies and empty MOs at rather low energies. Accordingly, peroxide can function as CT acceptor and CT donor. MLCT excitation may lead to an oxidation of the metal and reduction of the
AC
peroxide to water. In contrast, LMCT excitation can induce the reduction of the metal and oxidation of peroxide to oxygen.
A variety of disulfide-bridged binuclear complexes has been prepared and characterized [2]. It is expected that their electronic structure resembles that of analogous peroxide complexes since O22and S22- are also electronically rather similar. As reducing and oxidizing metal centers, iron(II) and iron(III) were selected owing to their biological relevance. In particular, the combination Fe(II)-disulfide is of considerable interest, since such a
ACCEPTED MANUSCRIPT 2 complex is closely related to pyrite, Fe(II)(S22-). The valence band of pyrite is mainly derived from occupied iron d-orbitals while the conduction band is composed of empty sulfur orbitals [3]. In a molecular picture, this description corresponds to an iron-based HOMO and a sulfur- based LUMO. It follows, that such a complex should be characterized by a low-energy Fe(II) to disulfide MLCT transition. In this context, it should be emphasized that pyrite has been considered to play an
PT
important role as a direct source of energy for early life on earth [4]. Moreover, light absorption by pyrite can be viewed as photoredox process which finds its counterpart in molecular systems as
RI
suggested in the present study. As suitable complexes we selected Cp(CO)2Fe(II)(μ-S22-)Fe(II)(CO)2Cp
SC
[5] with Cp = cyclopentadienyl and [(CN)5Fe(III)(μ-S22-)Fe(III)(CN)5]6- as targets.
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The compound [Cp(CO)2Fe]2(S2) was prepared according to a literature procedure [5]. The anion {[Fe(CN)5]2(S2)}6- was unknown. Solutions of this complex were obtained by mixing aqueous solutions
MA
of Na2 [Fe(CN)5(NH3)] [6] and (NH4)2S2. This mixture turned instantly dark purple, but started immediately to decompose. It was not possible to isolate a pure material. Irradiations were
PT E
limited by using Schott cutoff filters.
D
performed with a high-pressure mercury lamp Osram 100 W/2. Long-wavelength irradiation was
Solutions of { [Cp(CO)2Fe]2 (S2)} in acetonitrile are yellow and display absorptions at λmax = 371 nm
AC
CE
and an inflection near 500 nm.
Fig. 1 Fe2 S2
Fig. 1 Spectral changes upon irradiation of 3.4 x 10-4 M {[Cp(CO)2Fe2](S2)} in acetonitrile in a 1-cm cell with white light, irradiation time: 0 min (a), ½ min (b), 20 min (c).
ACCEPTED MANUSCRIPT 3 These solutions are light-sensitive [7]. Irradiation with white light ( or λirr > 300 nm) was accompanied by the loss of the starting complex as indicated by the disappearance of the 371 nm absorption (Fig. 1). The photolyzed solution did not contain colloidal sulfur [8,9]. At this stage the final spectrum reveals the presence of Cp4Fe4S4 [10,11]. This complex is light-sensitive itself. Again, white light or λirr > 300 nm is effective, but much less efficient. Much longer irradiation times are now required. The
PT
concomitant spectral changes (Fig. 2) are very close to those, which had been observed when Cp4Fe4S4 was photolyzed directly [7]. Moreover, elemental sulfur and Fe2+ ions accumulated during
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SC
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the photolysis as it has been observed before.
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Fig. 2 Fe2S2
Fig. 2 Spectral changes upon irradiation of 6 x 10-4 M {[CpFe(CO)2]2}(S2) in acetonitrile with white
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light in a 1-cm cell for 15 min at later stages of the photolysis, starting from spectrum a
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(corresponding to spectrum (c) of Fig. 1), indicating the final loss of Cp4Fe4S4 (spectrum c) The second target of this study, the complex [Fe2(CN)10(S2)]6- , was unknown. Evidence for its generation was obtained, but the complex anion could be characterized only to a very limited extent owing to its facile decomposition. A variety of binuclear disulfide-bridged complexes [2], such as [Ru2(NH3)10(S2)]4+ [12,13] , are known although this isoelectronic ruthenium(III) complex is also not very stable. Upon addition of an aqueous solution of (NH4)2S2 (obtained by mixing of (NH4)2S and an equivalent amount of elemental sulfur) to an aqueous solution of [Fe(CN)5NH3]3-, a dark purple solution is instantly generated showing an intense absorption at λmax = 575 nm (Fig. 3) which
ACCEPTED MANUSCRIPT 4 resembles that of [Ru2(NH3)10(S2)]4+ with λmax = 725 nm.
ν
Abs
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1.0
600 (nm)
Fig.3 Fe2S2
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400 λ
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0.5
irradiation time (
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Fig. 3 The disappearance of [Fe2(CN)10(S2)]6- upon irradiation with white light in a 1-cm cell, from the top to the bottom) : approximately 15 sec intervals.
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Unfortunately, [Fe2(CN)10(S2)]6- decomposes rapidly in the dark as indicated by the facile
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disappearance of the purple color which occurs within about 20 minutes. Nevertheless, a careful examination shows that the binuclear iron disulfide complex is also light sensitive. The photolysis is
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achieved by irradiation with white light or long-wavelength irradiation (Fig. 3). The light-sensitivity is difficult to confirm since it can be proven only at rather high light intensities in order to compete
AC
successfully with the thermal decomposition. As a photoproduct, [Fe(II)(CN)5OH]4- may be formed. The photolyzed solution exhibits a long-wavelength absorption at λmax = 390 nm (see Fig. 3), which is consistent with the presence of [Fe(II)(CN)5(OH)]4- [14]. The formation of an iron(II) cyano complex is confirmed by the addition of Fe3+ to the photolyzed solution. In this case prussian blue is formed. Iron(III) cyano complexes would not form Prussian blue under these conditions. In addition, elemental sulfur was obtained as a further photoproduct. Elemental sulfur was extracted from the photolyzed aqueous solution with cyclohexane. Its presence was confirmed by its absorption maximum at 270 nm [8].
ACCEPTED MANUSCRIPT 5 In analogy to peroxide, disulfide has available an empty σ* orbital at relatively low energies. In combination with a reducing metal, a low-energy MLCT transition should be accessible. Accordingly, the long-wavelength absorption of [Cp2Fe2(CO)4](μ-S2) in acetonitrile (Fig. 1) at λmax = 373 nm (ε = 7.6x102 M-1cm-1) is assigned to a Fe(II) to σ* S22- MLCT transition. MLCT excitation leads to a photolysis which is suggested to proceed according to eq. 1. 2 [Cp2Fe(II)2(CO)4(S22-)
Cp4Fe(III)4S4 + 8 CO
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(1)
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The final spectrum of the photolyzed solution (Fig. 1) resembles that of an authentic sample of
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Cp4Fe4S4 [7]. This complex undergoes a further photolysis which is accompanied by spectral changes (Fig. 2) which a very similar to those in Fig. 2 of ref. [7]. Moreover, other observations (accumulation
MA
secondary photolysis can be described by eq. 2.
NU
of elemental sulfur and Fe2+ ions, see above) agree also with those of ref.[7]. It follows that this
2 Cp2Fe(II) + 2 Fe2+ + 2
Cp4Fe(III)4S4
S2- + ¼ S8
(2)
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D
This photoredox reaction is concluded to be initiated by sulfide to Fe(III) LMCT excitation. As discussed above, the identity of [(NC)5Fe(III)(μ-S22-)Fe(III)(CN)5]6- is not quite clear, but our observations and some other arguments support our assumption. So it is rather reasonable to
CE
attribute the 575 nm absorption (Fig. 3) to a S22- to Fe(III) LMCT transition in analogy to a related
AC
ruthenium complex [12,13]. The observations during the photolysis of the binuclear iron complex are consistent with eq. 3.
[Fe(III)2(CN)10(S22-)]6- + 2 OH-
2 [Fe(II)(CN)5OH]4-
+
½ S8
(3)
In this context, it is of interest that the energy difference of the LMCT absorptions of [Fe(III)2(CN)10(S2)]6- (λmax = 575 nm) and [Fe(III)(CN)5(SCN)]3- (λmax = 478 nm) [15] amounts to 3500 cm-1. This agrees roughly with the energy difference of Δ = 4700 cm-1 for the LMCT absorptions of the corresponding Co(III) complexes (λmax = 313 nm for [Co(III)2(CN)10(S2)]6- [16] and 265 nm for [Co(III)(CN)5(SCN)]3- [17] ).
ACCEPTED MANUSCRIPT 6 In conclusion, disulfide serves as CT donor as well as acceptor ligand in binuclear iron(III) and iron(II) complexes. This observation is not only interesting in its own right, but may be also of importance in the field of iron sulfur proteins [18-20]. [1] A.Vogler, H.Kunkely, Coord. Chem.Rev. 250 (2006) 1622-1626
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[2] A.Müller, W.Jaegermann, J.H.Enemark, Coord.Chem.Rev. 46 (1982) 245-280
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[3] V.Eyert, K.-H.Höck, S.Fiechter, H.Tributsch, Phys.Rev.B 57 (1998) 6350-6359
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[4] E.Drobner, H.Huber, G.Wächtershäuser, D.Rose, K.O.Stetter, Nature 346 (1990) 742-744 [5] M.A.El-Hinnawi, A.A.Aruffo, B.D.Santarsiero, D.R.McAlister, V.Schomaker, Inorg.Chem. 22 (1983)
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1585-1590
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[6] G.Brauer, Handbuch der Präparativen Anorganischen Chemie. Ferdinand Enke, Stuttgart, 1954, p.1364
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[7] A.Vogler, Inorg.Chem.Commun. 64 (2016) 5-6 [8] H.Kunkely, A.Vogler, Z.Naturforsch. 53b (1998) 224-226
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[9] A.Vogler, H.Kunkely, Inorg. Chem. 27 (1988) 504-507
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[10] R.A.Schunn, C.J.Fritchie, C.T.Prewitt, Inorg.Chem. 5 (1966) 900-905 [11] C.H.Wei, G.R.Wilkes, P.M.Treichel, L.F.Dahl, Inorg.Chem. 5 (1966) 900-905 [12] C.R.Brulet, S.S.Isied, H.Taube, J.Am.Chem.Soc. 95 (1973) 4758-4759 [13] D.P.Fairlie, W.A.Wickramasinghe, K.A.Byriel, H.Taube, Inorg.Chem. 36 (1997) 2242-2243 [14] A.Lodziska, R.Gogolin, Rocziki Chemii 47 (1973) 497 [15] D.F.Gutterman, H.B.Gray, Inorg.Chem. 11 (1972) 1727-1733 [16] H.Siebert, S.Thym, Z.anorg.allg.Chem. 399 (1973) 107-114
ACCEPTED MANUSCRIPT 7 [17] V.Miskowski, H.B.Gray, Inorg.Chem. 14 (1975) 401-405 [18] H.Beinert, R.H.Holm, E.Münck, Science 277 (1997) 653-659 [19] H.Beinert, J.Biol.Inorg.Chem. 5 (2000) 2-15
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[20] L.Noodleman, T.Lovell, T.Liu, F.Himo, R.A.Torres, Opin.Chem.Biol. 6 (2002) 259-273.
ACCEPTED MANUSCRIPT
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Graphical abstract
ACCEPTED MANUSCRIPT 9
Highlights
• Disulfide (S
22 )
is a CT acceptor and a CT donor
S22- serves also as bridging ligand in binuclear Fe(II) and Fe(III) complexes
• These complexes are characterized by Fe(II) to S
22
MLCT and S22- to Fe(III) LMCT transitions
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•
Fe2S2
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• MLCT and LMCT excitation initiate photoredox reactions