English

• [FeFe]-hydrogenases, which are found in natural bacteria, can efficiently catalyze the reduction of protons to evolve dihydrogen as a renewable and clean energy^[1]. The structural elucidation of the active site of [FeFe]-hydrogenases was established in 1998^[2] and 1999^[3], featuring a butterfly di-iron cluster coordinated by carbonyls, cyanides, a bridged three-atom dithiolate, along with a [Fe₄S₄]-bearing cysteine. Previous studies focused on the biomimics for the bridged three-atom dithiolate and a lot of SCH₂CH₂CH₂S or SCH₂N(R)CH₂S bearing complexes were prepared^[4-9]. Encouraged by the ligands found in the di-iron center of the active site of [FeFe]-hydrogenases, some ligands like cyanides^[10-11], phosphines^[12-13], N-heterocyclic carbenes (NHC)^[14-15] and thioethers^[16-17] have been introduced into the di-iron center. Moreover, the electrocatalytic dihydrogen production by some biomimics was also investigated^[18-20]. However, research on the SCH₂CH₂S bearing complexes is more limited and only a few examples of SCH₂CH₂S bearing complexes have been studied^[21-23].

  The five-membered heterocycle isoxazole derivatives have attracted great concerns as a result of their wide application in biological activities such as antifungal^[24], cytotoxic^[25], herbicidal^[26], insecticidal^[27], and anti-inflammatory^[28]. We have previously reported that 1, 2, 3-thiadiazole^[29] or pyrazole^[30] containing di-iron complexes displayed some antifungal activities. Inspired by these findings, we recently developed research on the linkage of an isoxazole moiety with the di-iron cluster. Consequently, we have successfully synthesized four derivatives by esterification or CO exchange. Herein, in this paper, we report the synthesis and structural characterization of four isoxazole- containing di-iron complexes, namely [Fe₂(CO)₅(L)(μ-SCH₂CHCH₂OOC(5-C₃HNOCH₃)S)], where L=P(4-C₆H₄CH₃)₃ (3), P(4-C₆H₄F)₃ (4), P(2-C₆H₄OCH₃)₃ (5), as the biomimics for the [FeFe]-hydrogenases active site. Moreover, the electrocatalytic properties and the antifungal activity of these complexes are also presented.

  1.   Experimental

  1.1   Materials and methods

  Tri(p-tolyl)phosphine, tris(4-fluorophenyl)phosphine, tris(2-methoxyphenyl)phosphine, 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)^[31] and 5-methylisoxazole-4-carboxylic acid^[32] were synthesized by the reported methods. FTIR spectra were measured on a Nicolet 6700 FT-IR spectrometer. NMR spectra were obtained by a Bruker Avance 500 MHz spectrometer. Elemental analyses were performed on an Elementar Vario EL cube analyzer.

  1.2   Synthesis of complex [Fe₂(CO)₆(μ-SCH₂CHCH₂OOC(5-C₃HNOCH₃)S)] (2)

  To a mixture of complex 1 (0.201 g, 0.5 mmol), DMAP (0.024 g, 0.2 mmol) and 5-methylisoxazole-4-carboxylic acid (0.076 g, 0.6 mmol) in CH₂Cl₂ (20 mL), DCC (0.124 g, 0.6 mmol) was added. The mixture was stirred overnight. The solvent was evaporated. The crude product was purified by thin layer chromatography (silica gel G) with a mixture of CH₂Cl₂/petroleum ether (2∶3, V/V) as the eluent to afford complex 2 (0.228 g, yield: 89%). IR (CH₂Cl₂, cm^-1): ν_C≡O 2 077 (s), 2 037 (vs), 2 004 (vs), 1 996 (vs); ν_C=O 1 730 (m). ¹H NMR (500 MHz, CDCl₃): δ 8.49 (s, 1H, CH=N), 4.21 (dd, J=9, 14.5 Hz, 1H, OCH₂), 4.12 (dd, J=9.5, 14.2 Hz, 1H, OCH₂), 3.03-2.96 (m, 1H, SCH), 2.73 (s, 3H, CH₃), 2.72 (dd, J=10, 16 Hz, 1H, SCH₂), 1.95 (dd, J=7, 16.5 Hz, 1H, SCH₂). Anal. Calcd. for C₁₄H₉Fe₂NO₉S₂(%): C, 32.90; H, 1.78; N, 2.74. Found(%): C, 33.39; H, 1.63; N, 2.81.

  1.3   Synthesis of complexes 3-5

  To a mixture of complex 2 (0.053 g, 0.1 mmol) and the corresponding phosphine ligand (0.1 mmol) in CH₂Cl₂ (5 mL), Me₃NO·2H₂O (0.011 g, 0.1 mmol) in MeCN (5 mL) was slowly added. The mixture was stirred at room temperature for 1 h. The solvent was evaporated. The crude product was purified by thin layer chromatography (silica gel G) with a mixture of CH₂Cl₂/ petroleum ether (1∶1, V/V) as the eluent to afford complexes 3-5.

  Complex 3: 0.061 g, yield: 77%. IR (CH₂Cl₂, cm^-1): ν_C≡O 2 046 (vs), 1 987 (vs), 1 937 (m); ν_C=O 1 730 (m). ¹H NMR (500 MHz, CDCl₃): δ 8.41 (s, 1H, CH=N), 7.47-7.43 (m, 6H, PhH), 7.18 (d, J=7 Hz, 6H, PhH), 3.97-3.89 (m, 2H, OCH₂), 2.68 (s, 3H, CH₃), 2.36 (s, 9H, 3CH₃), 1.88-1.85 (m, 1H, SCH), 1.30 (s, 2H, SCH₂). ³¹P{¹H} NMR (200 MHz, CDCl₃, 85% H₃PO₄): δ 60.26 (s). Anal. Calcd. for C₃₄H₃₀Fe₂NO₈PS₂(%): C, 51.86; H, 3.84; N, 1.78. Found(%): C, 51.75; H, 3.83; N, 1.71.

  Complex 4: 0.053 g, yield: 66%. IR (CH₂Cl₂, cm^-1): ν_C≡O 2 050 (vs), 2 039 (m), 1 991 (vs), 1 942 (m); ν_C=O 1 732 (m). ¹H NMR (500 MHz, CDCl₃): δ 8.42 (s, 1H, CH=N), 7.54-7.52 (m, 6H, PhH), 7.14-7.10 (m, 6H, PhH), 3.99-3.89 (m, 2H, OCH₂), 2.68 (s, 3H, CH₃), 1.80 (s, 1H, SCH), 1.46-1.44 (m, 2H, SCH₂). ³¹P{¹H} NMR (200 MHz, CDCl₃, 85% H₃PO₄): δ 61.15 (s). Anal. Calcd. for C₃₁H₂₁F₃Fe₂NO₈PS₂(%): C, 46.58; H, 2.65; N, 1.75. Found(%): C, 46.85; H, 2.78; N, 1.79.

  Complex 5: 0.058 g, yield: 70%. IR (CH₂Cl₂, cm^-1): ν_C≡O 2 052 (vs), 1 996 (vs), 1 969 (sh), 1 950 (sh); ν_C=O 1 728 (m). ¹H NMR (500 MHz, CDCl₃): δ 8.39 (s, 1H, CH=N), 7.84 (s, 2H, PhH), 7.39 (s, 4H, PhH), 6.89-6.84 (m, 6H, PhH), 3.92-3.87 (m, 2H, OCH₂), 3.74 (s, 2H, SCH₂), 3.55 (s, 9H, 3OCH₃), 2.66 (s, 3H, CH₃), 1.21-1.20 (m, 1H, SCH). ³¹P{¹H} NMR (200 MHz, CDCl₃, 85% H₃PO₄): δ 49.29 (s). Anal. Calcd. for C₃₄H₃₀Fe₂NO₁₁PS₂(%): C, 48.88; H, 3.62; N, 1.68. Found(%): C, 49.29; H, 3.65; N, 1.65.

  1.4   X-ray crystallography

  The single crystals with suitable sizes were 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 structure was solved by direct methods using the SHELXS program and refined by full-matrix least-squares techniques SHELXL on F². Hydrogen atoms were located using the geometric method. Non-hydrogen atoms were refined with anisotropic thermal parameters. Note that the largest difference peaks of complexes 2 (2 710 e·nm^-3) and 5 (2 520 e·nm^-3) are relatively high because the isoxazole ring is disordered without treatment. Details of crystal data, data collections, and structure refinements are summarized in Table 1.

  Table 1

  

  Table 1.  Crystal data and structure refinement details for complexes 2, 4, and 5

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  Parameter	2	4	5
  Empirical formula	C14H9Fe2NO9S2	C31H21F3Fe2NO8PS2	C34H30Fe2NO11PS2
  Formula weight	511.04	799.28	835.38
  Crystal system	Monoclinic	Triclinic	Triclinic
  Space group	C2/c	P1	P1
  a/nm	4.130 4(7)	0.910 52(15)	1.106 42(6)
  b/nm	0.689 77(11)	1.216 98(19)	1.164 50(6)
  c/nm	1.389 8(2)	1.655 0(3)	1.536 95(8)
  α/(°)		89.638(5)	88.749(2)
  β/(°)	105.432(5)	79.658(4)	71.403(2)
  γ/(°)		68.440(4)	77.696(2)
  V/nm3	3.816 8(10)	1.674 2(5)	1.831 46(17)
  Z	8	2	2
  Dc/(g·cm-3)	1.779	1.585	1.515
  μ /mm-1	1.786	1.106	1.009
  F(000)	2 048.0	808.0	856.0
  Crystal size/mm	0.16×0.12×0.10	0.26×0.22×0.16	0.22×0.18×0.12
  2θ range/(°)	5.878-50.07	4.256-50.22	4.656-50.29
  h, k, l ranges	-48 ≤ h ≤ 48, -8 ≤ k ≤ 8, -16 ≤ l ≤ 16	-10 ≤ h ≤ 10, -14 ≤ k ≤ 14, -19 ≤ l ≤ 19	-13 ≤ h ≤ 13, -13 ≤ k ≤ 13, -18 ≤ l ≤ 18
  Reflection collected	23 366	42 954	35 209
  Independent reflection	3 268 (Rint=0.062 1)	5 929 (Rint=0.032 1)	6 479 (Rint=0.047 8)
  Data, restraint, number of parameters	3 268, 18, 253	5 929, 53, 434	6 479, 62, 464
  Goodness of fit on F 2	1.142	1.037	1.034
  Final R indices [I > 2σ(I)]	0.171 9, 0.394 0	0.056 5, 0.149 0	0.076 1, 0.217 0
  Final R indices (all data)	0.180 8, 0.397 7	0.070 2, 0.157 9	0.109 2, 0.242 0
  Largest diff. peak and hole/(e·nm-3)	2 710, -3 763	920, -628	2 520, -826

  1.5   Electrochemical experiment

  Electrochemical properties were studied by cyclic voltammetry (CV) in MeCN solution. Electrochemical measurements were carried out under nitrogen using a CHI 620 Electrochemical workstation. As the electrolyte, ⁿBu₄NPF₆ was recrystallized several times from a CH₂Cl₂ solution by the addition of hexane. CV scans were obtained in a three-electrode cell with a glassy carbon electrode (3 mm diameter) as the working electrode, a platinum wire as the counter electrode, and a non-aqueous Ag/Ag⁺ electrode as the reference electrode. The potential scale was calibrated against the Fc/Fc⁺ couple and reported versus this reference system.

  2.   Results and discussion

  2.1   Synthesis and characterization of complex 2

  As shown in Scheme 1, the ester-product 2 can be made by the reaction of complex 1 with 5-methylisoxazole-4-carboxylic acid assisted by the reagents DCC and DMAP. Complex 2 was isolated as a red solid and structurally identified by elemental analysis and FTIR, ¹H NMR spectroscopies. Four bands ranging from 2 077 to 1 996 cm^-1 (Fig. 1) were found in the FTIR spectrum, which can be designated as the stretching mode of terminal carbonyls, close to the corresponding values of the hexacarbonyl di-iron analogues^{[4, 6, 29]}. The ¹H NMR spectrum exhibited two quartets at δ 4.21 and 4.12 for the OCH₂ group.

  Scheme 1

  

  Scheme 1.  Synthesis of complex 2

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  Figure 1

  

  Figure 1.  FTIR spectra of complexes 2-5

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  2.2   Synthesis and characterization of complexes 3-5

  As displayed in Scheme 2, the phosphine-bearing analogues 3-5 can be got from the CO-interchange of complex 2 with a phosphine ligand tri(p-tolyl)phosphine, tris(4-fluorophenyl)phosphine, or tris(2-methoxyphenyl)phosphine assisted by the reagent Me₃NO∙2H₂O. Complexes 3-5 were isolated as red solids and structurally identified by elemental analysis and FTIR, ¹H NMR, ³¹P{¹H} NMR spectroscopies. Three to four bands in the region of 2 052-1 937 cm^-1 (Fig. 1) were observed in the FTIR spectra of complexes 3-5, assigning to the stretching mode of terminal carbonyls C≡O, migrating to lower energies with respect to those of complex 2 because of the phosphine ligands having better donation than carbonyl^[33-35]. In the ¹H NMR spectra of complexes 3-5, a multiplet at approximately δ 3.90 was found for the OCH₂ group, shifting to the higher field with respect to complex 2 probably due to the shielding effect of the phosphine ligand. In the ³¹P{¹H} NMR spectra of complexes 3-5, the singlets at δ 49-61 were observed for the ligated phosphine ligand, very close to those of phosphine-containing di-iron analogues^[36-38].

  Scheme 2

  

  Scheme 2.  Synthesis of complexes 3-5

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  2.3   X-ray crystallography

  Single crystal X-ray diffraction analysis was applied to characterize the molecular structures of the new complexes. The molecular structures presented as thermal ellipsoids are depicted in Fig. 2 and Table 2 lists the selected bond lengths and angles. Complex 2 crystallizes in monoclinic space group C2/c with four molecules in the unit cell whilst complexes 4 and 5 crystallize in triclinic space group P1 with two molecules in the unit cell. Fig. 2 shows that all the complexes consist of a di-iron sub-cluster with a bridged SCH₂CHS bearing an isoxazole moiety, six terminal CO or five terminal CO, and a phosphine ligand. Notably, all the P-donor ligands in complexes 4 and 5 possess an apical position of the pseudo-octahedral coordination arrangement of the Fe atom, in accord with monosubstituted di-iron analogues^{[29-30, 39-40]}. The Fe1—Fe2 bond length of complex 2 (0.249 6(4) nm) is very similar to that of complex [Fe₂(CO)₆(μ-SCH₂CH(CH₂OO CCH₃)S)] (0.249 67(11) nm)^[41] as well as 1, 2, 3-thiadiazole-bearing analogue [Fe₂(CO)₆(μ-SCH₂CHCH₂OOC(4-C₂N₂SCH₃)S)] (0.249 2(3) nm)^[29] indicating that the effect of isoxazole is consistent with methyl or 1, 2, 3-thiadiazole. The Fe1—Fe2 bond lengths of complexes 4 (0.250 29(9) nm) and 5 (0.252 00(12) nm) are mildly longer than complex 2 due to the coordination of P-donor ligand. Moreover, the Fe1—Fe2 bond lengths of complexes 4 and 5 are shorter than those in natural [FeFe]-hydrogenases^[2-3] along with those of P-donor ligand chelated analogues^[33-34].

  Figure 2

  

  Figure 2.  Molecular structures of complexes 2 (a), 4 (b), and 5 (c) as thermal ellipsoids at a 30% probability level

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  Table 2

  

  Table 2.  Selected bond lengths (nm) and angles (°) for complexes 2, 4, and 5

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  Bond	2	4	5
  Fe1—Fe2	0.249 6(4)	0.250 29(9)	0.252 00(12)
  Fe1—S1	0.223 6(6)	0.225 03(13)	0.225 80(18)
  Fe1—S2	0.224 1(6)	0.224 77(14)	0.225 2(2)
  Fe2—S1	0.224 6(6)	0.224 96(13)	0.225 50(19)
  Fe2—S2	0.224 8(6)	0.224 46(14)	0.224 91(19)
  Fe2—P1		0.223 27(12)	0.227 42(17)
  S1—Fe1—Fe2	56.34(17)	56.19(3)	56.00(5)
  S1—Fe1—S2	80.8(2)	79.66(5)	79.95(7)
  S2—Fe1—Fe2	56.34(17)	56.08(4)	55.90(5)
  S1—Fe2—Fe1	55.97(17)	56.22(4)	56.11(5)
  S2—Fe2—Fe1	56.08(17)	56.20(4)	56.00(5)
  S2—Fe2—S1	80.4(2)	79.74(5)	80.07(7)
  P1—Fe2—Fe1		156.01(5)	154.73(6)
  Fe1—S1—Fe2	67.69(18)	67.59(4)	67.89(5)
  Fe2—S2—Fe1	67.58(17)	67.72(4)	68.10(6)

  2.4   Electrochemical property

  CV technique was applied to study the electrochemical and electrocatalytic properties of the new complexes. The CV curves of complexes 2-5 are overlapped in Fig. 3 and the corresponding CV data are demonstrated in Table 3. The CV curve of complex 2 only had an irreversible reduction wave at -1.67 V, assigning to the one-electron reduction of Fe^ⅠFe^Ⅰ to Fe⁰Fe^Ⅰ according to the reported work^[42], and the potential was analogous to complexes [Fe₂(CO)₆(μ-SCH₂CHCH₂OOC(4-C₂N₂SCH₃)S)] (-1.64 V)^[29] and [Fe₂(CO)₆(μ-SCH₂CHCH₂OOC(CF₃C₃N₂CH₃)S)] (-1.64 V)^[30] revealing that the electronic effect of isoxazole is close to 1, 2, 3-thiadiazole and pyrazole. Nevertheless, the CV curves of complexes 3-5 have an irreversible reduction wave at -1.87, -1.81, or -1.83 V together with an irreversible oxidation wave at 0.51, 0.60, or 0.58 V assigning to the one-electron oxidation of Fe^ⅠFe^Ⅰ to Fe^ⅡFe^Ⅰ[42]. The potentials for the reduction and oxidation of complexes 3-5 were comparable to other phosphine-bearing analogues^{[29, 30]}. It is noteworthy that the reduction potentials for complexes 3-5 moved cathodically by approximately 0.2 V with respect to that of complex 2, which is consistent with the fact that the phosphine ligand can increase the electron density on the Fe center.

  Figure 3

  

  Figure 3.  CV curves of complexes 2, 3, 4, and 5 in 0.1 mol•L^{-1 n}Bu₄NPF₆/MeCN at a scan rate of 0.1 V•s^-1

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  Table 3

  

  Table 3.  CV data for complexes 2-5

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  Complex	Ep, c/V	Ep, a/V	Overpotential/V
  2	-1.67		0.63
  3	-1.87	0.51	0.76
  4	-1.81	0.60	0.83
  5	-1.83	0.58	0.74

  Moreover, the electrocatalytic properties of these complexes have been studied by adding HOAc as a proton source into the MeCN solution, and the results are displayed in Fig.S1-S4 (Supporting information). It can be seen that upon an increment of HOAc concentration (2-10 mmol·L^-1), the current heights of the reduction waves for complexes 2-5 were slightly grown up. However, new waves at -2.14 V (2), -2.26 V (3), -2.38 V (4), and -2.32 V (5) emerged and the current heights were significantly grown up linearly (Fig. 4) with successive increment of HOAc concentration. The catalytic potentials moved positively with respect to blank (HOAc without the di-iron complex)^[43]. Further, the catalytic current heights for complexes 3 and 4 were higher than HOAc blank^[43]. These electrochemical observations indicate that proton reduction catalyzed by complexes 2-5 occurs^{[42, 44-46]}.

  Figure 4

  

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

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  To estimate the catalytic capabilities of these complexes, overpotential and turnover frequency (TOF) were calculated by the known method^[47]. As revealed in Table 3, the overpotential for complex 2 (0.63 V) was lower than other complexes reflecting that the phosphine coordination will increase the overpotential, in agreement with recently reported work^[48]. Also notable in Fig. 4, the gradients of the dependence of catalytic current on the HOAc concentration of complexes 3 and 4 were steeper than other complexes suggesting that complexes 3 and 4 are more sensitive to HOAc^[42]. As observed in Fig. 5, the TOF values of complexes 3-5 were higher than complex 2 indicative of the phosphine coordination will increase the catalytic capability possibly due to the more basicity on the di-iron core for easily binding protons. Further, the TOF of complex 4 was higher than those of complexes 3 and 5 revealing that the phosphine ligand with electron-withdrawing group is more favorable for H₂ production than the corresponding ligand with electron-donating group. According to the results described above, an EECC (E=electrochemical, C=chemical) mechanism can be speculated for the electrocatalysis of H₂ production catalyzed by the isoxazole-bearing di-iron analogues.

  Figure 5

  

  Figure 5.  Plots of TOF versus the HOAc concentration for complexes 2-5

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  2.5   Antifungal activity

  The antifungal activity against P. infestans (PI), G. zeae (GZ), P. oryae (PO), P. capsici (PC), C. fragariae (CF), B. cinerea (BC), R. solani (RS), F. oxysporum (FO), C. arachidicola (CA) and P. piricola (PP) was tested at a mass fraction of 0.005% by a reported method^[49] and Table 4 lists the results. It revealed that complex 2 displayed moderate (40%-70%) activity against BC and RS and weak (10%-40%) activity against PI, GZ, PO, CF, and PP. Complexes 3-5 displayed weak activity against PI, PO, PC, BC, RS, and PP.

  Table 4

  

  Table 4.  Antifungal activity of complexes 2-5 at a mass fraction of 0.005%

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  Complex	Activity/%
  	PI	GZ	PO	PC	CF	BC	RS	FO	CA	PP
  2	16.7	26.9	33.3	3.4	21.4	50.0	65.2	8.7	7.1	28.6
  3	33.3	7.7	22.2	13.8	7.1	26.9	30.4	17.4	14.3	21.4
  4	16.7	11.5	11.1	31.0	14.3	38.5	30.4	8.7	7.1	10.7
  5	25.0	23.1	11.1	10.3	7.1	34.6	15.2	8.7	7.1	28.6

  3.   Conclusions

  In summary, we have presented the synthesis and spectroscopy of four isoxazole-bearing di-iron complexes. The X-ray crystallographic studies have shown that they consist of a di-iron sub-cluster with a bridged SCH₂CHS containing an isoxazole moiety, six terminal CO or five terminal CO, and an apically-ligated P-donor ligand. CV studies have revealed that these complexes can electrocatalyze the reduction of protons to dihydrogen by adding an acetic acid as a proton source into the solution. The antifungal activity studies have displayed that some complexes show moderate or weak activity.

  
  Supporting information is available at http://www.wjhxxb.cn
  
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  Scheme 1  Synthesis of complex 2

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  Figure 1  FTIR spectra of complexes 2-5

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  Scheme 2  Synthesis of complexes 3-5

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  Figure 2  Molecular structures of complexes 2 (a), 4 (b), and 5 (c) as thermal ellipsoids at a 30% probability level

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  Figure 3  CV curves of complexes 2, 3, 4, and 5 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  Dependence of catalytic current on the HOAc concentration for complexes 2-5

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  Figure 5  Plots of TOF versus the HOAc concentration for complexes 2-5

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  Table 1.  Crystal data and structure refinement details for complexes 2, 4, and 5

  Parameter	2	4	5
  Empirical formula	C14H9Fe2NO9S2	C31H21F3Fe2NO8PS2	C34H30Fe2NO11PS2
  Formula weight	511.04	799.28	835.38
  Crystal system	Monoclinic	Triclinic	Triclinic
  Space group	C2/c	P1	P1
  a/nm	4.130 4(7)	0.910 52(15)	1.106 42(6)
  b/nm	0.689 77(11)	1.216 98(19)	1.164 50(6)
  c/nm	1.389 8(2)	1.655 0(3)	1.536 95(8)
  α/(°)		89.638(5)	88.749(2)
  β/(°)	105.432(5)	79.658(4)	71.403(2)
  γ/(°)		68.440(4)	77.696(2)
  V/nm3	3.816 8(10)	1.674 2(5)	1.831 46(17)
  Z	8	2	2
  Dc/(g·cm-3)	1.779	1.585	1.515
  μ /mm-1	1.786	1.106	1.009
  F(000)	2 048.0	808.0	856.0
  Crystal size/mm	0.16×0.12×0.10	0.26×0.22×0.16	0.22×0.18×0.12
  2θ range/(°)	5.878-50.07	4.256-50.22	4.656-50.29
  h, k, l ranges	-48 ≤ h ≤ 48, -8 ≤ k ≤ 8, -16 ≤ l ≤ 16	-10 ≤ h ≤ 10, -14 ≤ k ≤ 14, -19 ≤ l ≤ 19	-13 ≤ h ≤ 13, -13 ≤ k ≤ 13, -18 ≤ l ≤ 18
  Reflection collected	23 366	42 954	35 209
  Independent reflection	3 268 (Rint=0.062 1)	5 929 (Rint=0.032 1)	6 479 (Rint=0.047 8)
  Data, restraint, number of parameters	3 268, 18, 253	5 929, 53, 434	6 479, 62, 464
  Goodness of fit on F 2	1.142	1.037	1.034
  Final R indices [I > 2σ(I)]	0.171 9, 0.394 0	0.056 5, 0.149 0	0.076 1, 0.217 0
  Final R indices (all data)	0.180 8, 0.397 7	0.070 2, 0.157 9	0.109 2, 0.242 0
  Largest diff. peak and hole/(e·nm-3)	2 710, -3 763	920, -628	2 520, -826

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  Table 2.  Selected bond lengths (nm) and angles (°) for complexes 2, 4, and 5

  Bond	2	4	5
  Fe1—Fe2	0.249 6(4)	0.250 29(9)	0.252 00(12)
  Fe1—S1	0.223 6(6)	0.225 03(13)	0.225 80(18)
  Fe1—S2	0.224 1(6)	0.224 77(14)	0.225 2(2)
  Fe2—S1	0.224 6(6)	0.224 96(13)	0.225 50(19)
  Fe2—S2	0.224 8(6)	0.224 46(14)	0.224 91(19)
  Fe2—P1		0.223 27(12)	0.227 42(17)
  S1—Fe1—Fe2	56.34(17)	56.19(3)	56.00(5)
  S1—Fe1—S2	80.8(2)	79.66(5)	79.95(7)
  S2—Fe1—Fe2	56.34(17)	56.08(4)	55.90(5)
  S1—Fe2—Fe1	55.97(17)	56.22(4)	56.11(5)
  S2—Fe2—Fe1	56.08(17)	56.20(4)	56.00(5)
  S2—Fe2—S1	80.4(2)	79.74(5)	80.07(7)
  P1—Fe2—Fe1		156.01(5)	154.73(6)
  Fe1—S1—Fe2	67.69(18)	67.59(4)	67.89(5)
  Fe2—S2—Fe1	67.58(17)	67.72(4)	68.10(6)

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  Table 3.  CV data for complexes 2-5

  Complex	Ep, c/V	Ep, a/V	Overpotential/V
  2	-1.67		0.63
  3	-1.87	0.51	0.76
  4	-1.81	0.60	0.83
  5	-1.83	0.58	0.74

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  Table 4.  Antifungal activity of complexes 2-5 at a mass fraction of 0.005%

  Complex	Activity/%
  	PI	GZ	PO	PC	CF	BC	RS	FO	CA	PP
  2	16.7	26.9	33.3	3.4	21.4	50.0	65.2	8.7	7.1	28.6
  3	33.3	7.7	22.2	13.8	7.1	26.9	30.4	17.4	14.3	21.4
  4	16.7	11.5	11.1	31.0	14.3	38.5	30.4	8.7	7.1	10.7
  5	25.0	23.1	11.1	10.3	7.1	34.6	15.2	8.7	7.1	28.6

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