English

• Due to the serious environmental problems caused by the widespread utilization of fossil fuels in the past centuries, the development of new energy sources has become more and more important. Among these new energy sources, H₂ is considered the best candidate to replace fossil fuels in the future because of its sustainability^[1]. Although Pt-based catalysts have exhibited a good efficiency in producing H₂ under the photochemical conditions^[2], their scarcity and expense hinder their development. It is well-known that Fe is one of the most abundant metals on the earth; however, Fe-based catalysts displayed low efficiency in producing H₂ under the photochemical and electrochemical conditions^[3-6]. On the other hand, [FeFe]-H₂ases are a type of natural enzyme that can reversibly convert protons to H₂ in nature with a turnover frequency (TOF) of 6 000-9 000 s^-1[7-8]. The structure of the active site of [FeFe]-H₂ases was established by X-ray crystallography, showing that a di-iron core ligated by a bridged dithiolate, carbonyls, cyanides, and a cysteinyl ligand^[9-10]. The elucidation of the active site of [FeFe]-H₂ases has inspired chemists to design and synthesize a library of analogues as the biomimics for producing H₂^[11-16].

  Thiazole-containing heterocyclic compounds have attracted great concern due to their various biological activities. For example, sulfonamide-containing thiazole derivatives exhibited insecticidal activity against the cotton leafworm, Spodoptera littoralis^[17]. Thiazole-containing compounds exhibited antibacterial activity against Methicillin-Resistant Staphylococcus aureus^[18]. Thiazole carboxamides exhibited fungicidal activity as succinate dehydrogenase inhibitors^[19]. N-(5-(3, 5-Methoxyphenyl)-(thiazole-2-yl))phenoxyacetamide derivatives exhibited herbicidal activity^[20].

  In this study, we combined the [FeFe]-H₂ases active site with a thiazole moiety to design a new hybrid that will present potential application in electrochemical proton reduction as well as some biological activities. Herein, this contribution will describe the synthesis, structural characterization, X-ray crystal structures, electrocatalytic proton reduction, and fungicidal activity of three di-ion complexes with a thiazole moiety as the biomimics for the [FeFe]-H₂ases active site.

  1.   Experimental

  1.1   Materials and methods

  Tri(p-tolyl)phosphine (tp), tris(4-fluorophenyl)phosphine (fp), 4-methylthiazole-5-carboxylic acid, 4-dimethylaminopyridine (DMAP), N, N′-dicyclohexylcarbodiimide (DCC), and Me₃NO·2H₂O were available commercially and used as received. Complex [Fe₂(CO)₆(μ-SCH₂CH(CH₂OH)S)] (1) was synthesized by the literature procedure^[21]. IR spectra were measured on a Nicolet 6700 FT-IR spectrometer. NMR spectra were analyzed by a Bruker Avance 500 MHz spectrometer. Elemental analyses were conducted on an Elementar vario EL cube analyzer. X-ray photoelectron spectroscopy (XPS) analyses were performed by a Thermo Scientific K-Alpha. Cyclic voltammograms were tested using a CHI 660E Electrochemical workstation.

  1.2   Synthesis of complex [Fe₂(CO)₆(μ-tedt)]

  To a mixture of complex 1 (0.402 g, 1 mmol), DMAP (0.048 g, 0.4 mmol), and 4-methylthiazole-5-carboxylic acid (0.172 g, 1.2 mmol) in CH₂Cl₂ (30 mL), DCC (0.309 g, 1.5 mmol) was added. The solution was stirred overnight, and the volatiles were reduced on a rotary evaporator. Complex [Fe₂(CO)₆(μ-tedt)] (2) (tedt=SCH₂CH(CH₂OOC(5-C₃HNSCH₃))S) was obtained by TLC with CH₂Cl₂/petroleum ether (3∶1, V/V) as the eluent. Yield: 0.481 g (91%). IR (KBr disk, cm^-1): ν_C≡O 2 076 (vs), 2 038 (vs), 2 011 (sh), 1 991 (vs), 1 973 (sh); ν_C=O 1 716 (s). ¹H NMR (500 MHz, CDCl₃): δ 8.81 (s, 1H, CH=N), 4.23-4.13 (m, 2H, OCH₂), 3.04-2.99 (m, 1H, SCH), 2.79 (s, 3H, CH₃), 2.72 (dd, J=7.7, 13.2 Hz, 1H, SCH₂), 1.98 (dd, J=5.2, 13.2 Hz, 1H, SCH₂). Anal. Calcd. for C₁₄H₉Fe₂NO₈S₃(%): C, 31.90; H, 1.72; N, 2.66. Found(%): C, 31.90; H, 2.04; N, 2.61.

  1.3   Syntheses of complexes [Fe₂(CO)₅(tp)(μ-tedt)] and [Fe₂(CO)₅(fp)(μ-tedt)]

  A solution of Me₃NO·2H₂O (0.017 g, 0.15 mmol) in MeCN (3 mL) was added to a mixture of complex 2 (0.079 g, 0.15 mmol) and tp (0.046 g, 0.15 mmol) or fp (0.047 g, 0.15 mmol) in CH₂Cl₂ (5 mL). The mixture was stirred for 1 h, and the solvents were reduced on a rotary evaporator. Complexes [Fe₂(CO)₅(tp)(μ-tedt)] (3) and [Fe₂(CO)₅(fp)(μ-tedt)] (4) were obtained by TLC using CH₂Cl₂/petroleum ether (3∶1, V/V) as the eluent.

  Complex 3: red solid, yield 0.105 g (87%). IR (KBr disk, cm^-1): ν_C≡O 2 045 (vs), 1 979 (vs), 1 934 (s); ν_C=O 1 719 (m). ¹H NMR (500 MHz, CDCl₃): δ 8.82 (s, 1H, CH=N), 7.45 (t, J=9 Hz, 6H, PhH), 7.18 (d, J=7 Hz, 6H, PhH), 4.03-3.88 (m, 2H, OCH₂), 2.72 (s, 3H, CH₃), 2.35 (s, 9H, 3PhCH₃), 1.88-1.85 (m, 1H, SCH), 1.35-1.26 (m, 2H, SCH₂). ³¹P{¹H} NMR (200 MHz, CDCl₃, 85% H₃PO₄): δ 60.26 (s). Anal. Calcd. for C₃₄H₃₀Fe₂NO₇PS₃(%): C, 50.83; H, 3.76; N, 1.74. Found(%): C, 50.32; H, 3.86; N, 1.46.

  Complex 4: red solid, yield 0.112 g (92%). IR (KBr disk, cm^-1): ν_C≡O 2 045 (vs), 1 994 (vs), 1 975 (vs), 1 939 (s); ν_C=O 1 717 (m). ¹H NMR (500 MHz, CDCl₃): δ 8.86 (br, 1H, CH=N), 7.56-7.51 (m, 6H, PhH), 7.12 (t, J=8.2 Hz, 6H, PhH), 4.02-3.91 (m, 2H, OCH₂), 2.72 (s, 3H, CH₃), 1.87 (s, 1H, SCH), 1.42 (d, J=6 Hz, 2H, SCH₂). ³¹P{¹H} NMR (200 MHz, CDCl₃, 85% H₃PO₄): δ 61.16 (s). ¹⁹F {¹H} NMR (470 MHz, CDCl₃, CF₃COOH): δ -108.36 (s). Anal. Calcd. for C₃₁H₂₁F₃Fe₂NO₇PS₃(%): C, 45.67; H, 2.60; N, 1.72. Found(%): C, 45.03; H, 2.97; N, 1.51.

  1.4   X-ray crystallography

  A single crystal was mounted on a Bruker D8 QUEST diffractometer. Data were collected at 296 K by using a graphite-monochromatic with Mo Kα radiation (λ=0.071 073 nm) in the ω-φ scan mode. Using OLEX2, the structures were solved by direct methods using the SHELXS program and refined by full-matrix least-squares techniques SHELXL on F ². Hydrogen atoms were located using the geometric method. Non-hydrogen atoms were refined with anisotropic thermal parameters. Details of crystal data, data collections, and structure refinements are listed in Table 1.

  Table 1

  

  Table 1.  Crystal data and structure refinement details for complexes 2-4

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  Parameter	2	3	4
  Empirical formula	C14H9Fe2NO8S3	C34H30Fe2NO7PS3	C31H21F3Fe2NO7PS3
  Formula weight	527.10	803.44	815.34
  Crystal system	Monoclinic	Monoclinic	Triclinic
  Space group	C2/c	P21/n	P1
  a / nm	2.372 58(11)	1.442 02(8)	0.911 30(7)
  b / nm	1.331 61(6)	1.692 20(9)	1.215 14(9)
  c / nm	1.722 52(14)	1.622 73(9)	1.659 15(12)
  α / (°)			87.886(2)
  β / (°)	131.968 0(10)	110.600(2)	79.748(2)
  γ / (°)			68.474(2)
  V / nm3	4.046 3(4)	3.706 6(4)	1.681 0(2)
  Z	8	4	2
  Dc / (g·cm-3)	1.731	1.440	1.611
  μ / mm-1	1.784	1.041	1.161
  F(000)	2 112.0	1 648.0	824.0
  Crystal size / mm	0.44×0.34×0.22	0.26×0.22×0.16	0.36×0.24×0.12
  2θ range / (°)	5.96-50.874	4.69-50.19	4.32-50.098
  h, k, l ranges	-28 ≤ h ≤ 27, -15 ≤ k ≤ 16, -20 ≤ l ≤ 20	-17 ≤ h ≤ 17, -20 ≤ k ≤ 20, -19 ≤ l ≤ 18	-10 ≤ h ≤ 10, -14 ≤ k ≤ 14, -19 ≤ l ≤ 19
  Reflection collected	40 530	80 995	41 544
  Observed reflection	3 196	4 517	4 311
  Independent reflection	3 721 (Rint=0.044 1)	6 581 (Rint=0.096 0)	5 939 (Rint=0.060 2)
  Data, number of restraints, number of parameters	3 721, 1, 254	6 581, 65, 436	5 939, 1, 416
  Goodness of fit on F 2	1.062	1.054	1.059
  Final R indexes [I>2σ(I)]	R1=0.029 2, wR2=0.070 0	R1=0.077 8, wR2=0.208 3	R1=0.070 1, wR2=0.182 7
  Final R indexes (all data)	R1=0.036 9, wR2=0.073 8	R1=0.117 7, wR2=0.233 1	R1=0.103 3, wR2=0.202 4
  Largest diff. peak and hole / (e·nm-3)	425, -460	1 159, -1 043	1 963, -754

  1.5   Fungicidal activity

  Complexes 2-4 were studied by in vitro fungicidal activity against ten fungi at a mass fraction of 0.005% using the mycelial growth rate method^[22]. In comparison with the blank assay, the inhibition rate (R) was calculated by the following equation: R=(d_CK-d_AI)/d_CK×100%, where d_CK is the average diameter of mycelia for the blank assay, and d_AI is the average diameter of mycelia when the complexes are added. Each experiment was repeated three times.

  2.   Results and discussion

  2.1   Synthesis and characterization

  Reaction of the hydroxy-containing starting material 1 with 4-methylthiazole-5-carboxylic acid in the presence of DCC and DMAP gave the ester product 2 in a good yield. Further treatment of complex 2 with tri(p-tolyl)phosphine or tris(4-fluorophenyl)phosphine and Me₃NO·2H₂O as the decarbonylating agent gave the corresponding derivatives 3 and 4 in good yields. The mechanism for the synthesis of the derivatives 3 and 4 involves the removal of one CO of complex 2 by the decarbonylating agent Me₃NO·2H₂O to generate an intermediate species [Fe₂(CO)₅(L)] (L=MeCN or Me₃N) and CO₂, followed by the coordination of the phosphine ligand to form the product. The structures of the newly prepared complexes were elucidated by various methods, including elemental analysis, NMR, and IR spectroscopy. In the IR spectrum of complex 2, five absorption bands ranging from 2 076 to 1 973 cm^-1 were found for the stretching vibrations of the terminal carbonyls C≡O, close to the hexacarbonyl di-iron analogues^[23-24]. In the IR spectra of complexes 3 and 4, three or four absorption bands ranging from 2 045 to 1 934 cm^-1 were found for the stretching vibrations of the terminal carbonyls C≡O, moving to lower frequencies with respect to those of complex 2 because the phosphine ligands tri(p-tolyl)phosphine and tris(4-fluorophenyl)phosphine are better electron donor than CO^[25]. The ³¹P NMR spectra of complexes 3 and 4 displayed a single resonance at ca. δ 61, which can be assigned to the coordinated phosphine ligands, in accord with phosphine-containing di-iron analogues^[26-28].

  2.2   X-ray crystallography

  The structures of three complexes were further identified by X-ray crystallography. The molecular structures, drawn as thermal ellipsoids at a 30% probability, are shown in Fig.1, and the selected bond parameters are listed in Table 2. Complexes 2 and 3 crystallize in monoclinic space groups C2/c and P2₁/n, respectively, whereas complex 4 crystallizes in triclinic space group P1. All the complexes consist of a di-iron core ligated by a bridged dithiolate, which is linked with a thiazole moiety through an ester group and six terminal carbonyls or five terminal carbonyls and a phosphine ligand. The occupation of the phosphine ligands in complexes 3 and 4 is apical to the distorted octahedral arrangement of the Fe2 atom, in agreement with the similar analogues^[29-30]. The Fe1—Fe2 bond distances of complexes 3 [0.250 48(13) nm] and 4 [0.250 65(12) nm] are slightly longer than that of complex 2 [0.250 17(5) nm], possibly due to the electronic effect of the phosphine ligand, but much shorter than those of diphosphine-chelated analogues^[31-32] as well as natural [FeFe]-H₂ases^[9-10]. It is noteworthy that the methyl carbon C12 attached to the thiazole ring in complex 3 is disordered over two sites, with an occupancy of 0.57(2).

  Figure 1

  

  Figure 1.  Molecular structures of complexes 2 (a), 3 (b), and 4 (c) as thermal ellipsoids at a 30% probability

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  Table 2

  

  Table 2.  Selected bond lengths (nm) and angles (°) for complexes 2-4

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  Bond	2	3	4
  Fe1—Fe2	0.250 17(5)	0.250 48(13)	0.250 65(12)
  Fe1—S1	0.223 69(7)	0.224 66(18)	0.224 87(18)
  Fe1—S2	0.224 74(7)	0.225 16(19)	0.225 41(19)
  Fe2—S1	0.224 24(7)	0.224 22(19)	0.224 82(18)
  Fe2—S2	0.223 81(7)	0.225 28(18)	0.225 43(19)
  Fe2—P1		0.224 90(18)	0.223 36(18)
  S1—Fe1—Fe2	56.153(19)	56.00(5)	56.12(5)
  S1—Fe1—S2	80.33(2)	79.57(7)	79.19(7)
  S2—Fe1—Fe2	55.925(18)	56.24(5)	56.23(5)
  S1—Fe2—Fe1	55.94(2)	56.17(5)	56.14(5)
  S2—Fe2—Fe1	56.277(19)	56.19(5)	56.22(5)
  S2—Fe2—S1	80.41(2)	79.64(7)	79.20(7)
  P1—Fe2—Fe1		154.03(6)	156.39(6)
  Fe1—S1—Fe2	67.90(2)	67.83(6)	67.75(5)
  Fe2—S2—Fe1	67.80(2)	67.57(6)	67.55(6)

  2.3   XPS analysis

  To check the oxidation states of iron and sulfur, complexes 2-4 were characterized by XPS analysis. As shown in Fig.2a, two peaks centered at 708.6 and 721.5 eV were observed for the 2p_1/2 and 2p_3/2 ionizations of the Fe⁺ ions in complex 2, respectively, similar to the previously-reported di-iron analogues^[33-35]. As shown in Fig.2b, two peaks centered at 162.8 and 164.5 eV were observed for the 2p ionizations of the thiolate and thiazole sulfur atoms in complex 2, respectively, because Dey et al. reported 161.9^[33] or 162.4 eV^[34] for the thiolate sulfur atoms of the di-iron analogues. It can also be seen from Fig.2c and 2e that two peaks centered at 708.1, 721.1 eV (for complex 3) and 708.2, 720.9 eV (for complex 4) were observed for the Fe⁺ ions in complexes 3 and 4. Similarly, as shown in Fig.2d and 2f, two peaks centered at 162.6, 164.2 eV (for complex 3) and 162.6, 164.1 eV (for complex 4) were observed for the thiolate and thiazole sulfur atoms in complexes 3 and 4. It is worth pointing out that the binding energies of complexes 3 and 4 shift to lower energies relative to complex 2, probably due to the effect of the phosphine ligand.

  Figure 2

  

  Figure 2.  XPS spectra of complexes 2-4: Fe2p (a) and S2p (b) for complex 2; Fe2p (c) and S2p (d) for complex 3; Fe2p (e) and S2p (f) for complex 4

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  2.4   Cyclic voltammetry

  To study the redox activity of these complexes, cyclic voltammetry (CV) was conducted in an acetonitrile solution with ⁿBu₄NPF₆ as the supporting electrolyte at a scan rate of 0.1 V·s^-1. As shown in Fig.3a, the CV curve of complex 2 only possessed one irreversible reduction event at E_pc=-1.64 V (vs Fc/Fc⁺). With reference to the previous study^[36], we can designate this event to be the one-electron process Fe^ⅠFe^Ⅰ+e→Fe^ⅠFe⁰, as the aforementioned XPS analysis has confirmed the oxidation state of Fe⁺ in the di-iron complexes. In contrast, as shown in Fig.3b, the CV curve of complex 3 possessed two irreversible reduction events at E_pc=-1.86 and -2.15 V together with one irreversible oxidation event at E_pa=0.46 V. The assignments of the second reduction event and oxidation event are one-electron processes Fe^IFe⁰+e→Fe⁰Fe⁰ and Fe^IFe^I-e→Fe^IFe^Ⅱ, respectively, according to the reference results^[36]. It is noteworthy that the first reduction event of complex 3 was moving negatively by 0.22 V as compared to complex 2, consistent with the fact that the phosphine ligand increases the electron density on the di-iron core. Analogous to complex 3, as shown in Fig.3c, the CV curve of complex 4 possessed two irreversible reduction events at E_pc=-1.80 and -2.07 V together with one irreversible oxidation event at E_pa=0.54 V. Notably, all potentials for complex 4 were moving cathodically relative to the corresponding potentials for complex 3 which is consistent with the fact that tri(p-tolyl)phosphine is a better electron donor than tris(4-fluorophenyl)phosphine bearing an electron-withdrawing group.

  Figure 3

  

  Figure 3.  CV curves of complexes 2 (a), 3 (b), and 4 (c) in 0.1 mol·L^{-1 n}Bu₄NPF₆/MeCN at a scan rate of 0.1 V·s^-1

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  2.5   Electrocatalysis

  Electrocatalytic proton reduction by di-iron analogues has been extensively studied^[37-39]; thus, in this work, we carried out the hydrogen evolution reaction by adding a proton source into the acetonitrile solution under the electrochemical conditions. Fig.4 shows the CV curves of three complexes upon addition of 2-10 mmol·L^-1 acetic acid. It can be seen from Fig.4a that upon addition of the acid, the height of the reduction event was slightly enhanced; however, a new reduction event at ca. -2.2 V appeared, and its current height increased remarkably with continuous addition of the acid. This catalytic potential moved positively by ca. 0.3 V with respect to the acid blank without the catalyst^[40]. Further, as shown in Fig.5, the current height increased linearly with the acid concentration. The above-mentioned observations imply that proton reduction catalyzed by complex 2 occurs in this system^[41-43]. Besides, another catalytic reduction event at ca. -2.5 V was also observed, and we propose that this peak corresponds to the direct reduction of the acid at the electrode. Likewise, as shown in Fig.4b and 4c, catalytic waves at ca. -2.3 V were observed for complexes 3 and 4 along with the corresponding linear relationship of current height against the acid concentration (Fig.5), revealing that both complexes can also catalyze the proton reduction to H₂ under the same conditions.

  Figure 4

  

  Figure 4.  CV curves of complexes 2 (a), 3 (b), and 4 (c) with HOAc (0-10 mmol·L^-1) in 0.1 mol·L^{-1 n}Bu₄NPF₆/MeCN at a scan rate of 0.1 V·s^-1

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  Figure 5

  

  Figure 5.  Dependence of catalytic current on the HOAc concentration for complexes 2-4

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  To evaluate the catalytic efficiency of these complexes in the hydrogen evolution reaction, TOF was used as a parameter for comparison. TOF can be calculated by a reported method^[44] and the relationship of TOF with the acid concentration is displayed in Fig.6. From Fig.6, we can conclude that the catalytic efficiencies of complexes 3 and 4 were better than that of complex 2 which is reflecting that the enhancement of electron density on the di-iron core will increase the catalytic efficiency for H₂ production, probably due to the easily binding for proton. In addition, the catalytic efficiency of complex 4 was the best among these complexes with a TOF of 23.5 s^-1 at 10 mmol·L^-1 HOAc concentration.

  Figure 6

  

  Figure 6.  Plots of TOF vs the added HOAc concentration for complexes 2-4

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  2.6   Fungicidal activity

  According to the previously-reported method^[45], we tested the fungicidal activity of these thiazole-containing analogues at a mass fraction of 0.005% against B. cinerea (BC), C. arachidicola (CA), C. fragariae (CF), F. oxysporum (FO), G. zeae (GZ), P. capsici (PC), P. infestans (PI), P. oryae (PO), P. piricola (PP), and R. solani (RS), and the results are listed in Table 3. Unfortunately, these complexes displayed relatively poor fungicidal activity.

  Table 3

  

  Table 3.  Fungicidal activity of complexes 2-4 at a mass fraction of 0.005%

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  Complex	R / %
  	PI	GZ	PO	PC	CF	BC	RS	FO	CA	PP
  2	25.0	26.9	11.1	20.7	35.7	30.8	30.4	8.7	14.3	7.1
  3	16.7	3.8	6.7	10.3	21.4	26.9	21.7	8.7	14.3	10.7
  4	16.7	15.4	6.7	17.2	7.1	19.2	30.4	17.4	14.3	14.3

  3.   Conclusions

  In this contribution, we have synthesized and characterized three di-iron analogues containing a thiazole moiety as potential catalysts for H₂ production. The X-ray crystallographic studies have revealed that these complexes consist of a di-iron core ligated by a bridged dithiolate bearing a thiazole moiety and six terminal carbonyls or five terminal carbonyls and an apically-ligated phosphine ligand. XPS analysis has confirmed the oxidation state of Fe⁺ in the complexes as well as thiolate sulfur and thiazole sulfur. CV studies have shown that these complexes can catalyze the reduction of protons to H₂, and the complexes containing phosphine ligands exhibited better efficiencies than the parent complex.

  
  
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  Figure 1  Molecular structures of complexes 2 (a), 3 (b), and 4 (c) as thermal ellipsoids at a 30% probability

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  Figure 2  XPS spectra of complexes 2-4: Fe2p (a) and S2p (b) for complex 2; Fe2p (c) and S2p (d) for complex 3; Fe2p (e) and S2p (f) for complex 4

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  Figure 3  CV curves of complexes 2 (a), 3 (b), and 4 (c) in 0.1 mol·L^{-1 n}Bu₄NPF₆/MeCN at a scan rate of 0.1 V·s^-1

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  Figure 4  CV curves of complexes 2 (a), 3 (b), and 4 (c) with HOAc (0-10 mmol·L^-1) in 0.1 mol·L^{-1 n}Bu₄NPF₆/MeCN at a scan rate of 0.1 V·s^-1

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  Figure 5  Dependence of catalytic current on the HOAc concentration for complexes 2-4

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  Figure 6  Plots of TOF vs the added HOAc concentration for complexes 2-4

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  Table 1.  Crystal data and structure refinement details for complexes 2-4

  Parameter	2	3	4
  Empirical formula	C14H9Fe2NO8S3	C34H30Fe2NO7PS3	C31H21F3Fe2NO7PS3
  Formula weight	527.10	803.44	815.34
  Crystal system	Monoclinic	Monoclinic	Triclinic
  Space group	C2/c	P21/n	P1
  a / nm	2.372 58(11)	1.442 02(8)	0.911 30(7)
  b / nm	1.331 61(6)	1.692 20(9)	1.215 14(9)
  c / nm	1.722 52(14)	1.622 73(9)	1.659 15(12)
  α / (°)			87.886(2)
  β / (°)	131.968 0(10)	110.600(2)	79.748(2)
  γ / (°)			68.474(2)
  V / nm3	4.046 3(4)	3.706 6(4)	1.681 0(2)
  Z	8	4	2
  Dc / (g·cm-3)	1.731	1.440	1.611
  μ / mm-1	1.784	1.041	1.161
  F(000)	2 112.0	1 648.0	824.0
  Crystal size / mm	0.44×0.34×0.22	0.26×0.22×0.16	0.36×0.24×0.12
  2θ range / (°)	5.96-50.874	4.69-50.19	4.32-50.098
  h, k, l ranges	-28 ≤ h ≤ 27, -15 ≤ k ≤ 16, -20 ≤ l ≤ 20	-17 ≤ h ≤ 17, -20 ≤ k ≤ 20, -19 ≤ l ≤ 18	-10 ≤ h ≤ 10, -14 ≤ k ≤ 14, -19 ≤ l ≤ 19
  Reflection collected	40 530	80 995	41 544
  Observed reflection	3 196	4 517	4 311
  Independent reflection	3 721 (Rint=0.044 1)	6 581 (Rint=0.096 0)	5 939 (Rint=0.060 2)
  Data, number of restraints, number of parameters	3 721, 1, 254	6 581, 65, 436	5 939, 1, 416
  Goodness of fit on F 2	1.062	1.054	1.059
  Final R indexes [I>2σ(I)]	R1=0.029 2, wR2=0.070 0	R1=0.077 8, wR2=0.208 3	R1=0.070 1, wR2=0.182 7
  Final R indexes (all data)	R1=0.036 9, wR2=0.073 8	R1=0.117 7, wR2=0.233 1	R1=0.103 3, wR2=0.202 4
  Largest diff. peak and hole / (e·nm-3)	425, -460	1 159, -1 043	1 963, -754

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  Table 2.  Selected bond lengths (nm) and angles (°) for complexes 2-4

  Bond	2	3	4
  Fe1—Fe2	0.250 17(5)	0.250 48(13)	0.250 65(12)
  Fe1—S1	0.223 69(7)	0.224 66(18)	0.224 87(18)
  Fe1—S2	0.224 74(7)	0.225 16(19)	0.225 41(19)
  Fe2—S1	0.224 24(7)	0.224 22(19)	0.224 82(18)
  Fe2—S2	0.223 81(7)	0.225 28(18)	0.225 43(19)
  Fe2—P1		0.224 90(18)	0.223 36(18)
  S1—Fe1—Fe2	56.153(19)	56.00(5)	56.12(5)
  S1—Fe1—S2	80.33(2)	79.57(7)	79.19(7)
  S2—Fe1—Fe2	55.925(18)	56.24(5)	56.23(5)
  S1—Fe2—Fe1	55.94(2)	56.17(5)	56.14(5)
  S2—Fe2—Fe1	56.277(19)	56.19(5)	56.22(5)
  S2—Fe2—S1	80.41(2)	79.64(7)	79.20(7)
  P1—Fe2—Fe1		154.03(6)	156.39(6)
  Fe1—S1—Fe2	67.90(2)	67.83(6)	67.75(5)
  Fe2—S2—Fe1	67.80(2)	67.57(6)	67.55(6)

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  Table 3.  Fungicidal activity of complexes 2-4 at a mass fraction of 0.005%

  Complex	R / %
  	PI	GZ	PO	PC	CF	BC	RS	FO	CA	PP
  2	25.0	26.9	11.1	20.7	35.7	30.8	30.4	8.7	14.3	7.1
  3	16.7	3.8	6.7	10.3	21.4	26.9	21.7	8.7	14.3	10.7
  4	16.7	15.4	6.7	17.2	7.1	19.2	30.4	17.4	14.3	14.3

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