Synthesis, characterization, electrochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes

Accepted Manuscript Synthesis, characterization, electerochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes Farsheed Shahbazi-Raz, Vahid Amani, Ehsan Bahojb Noruzi, Nasser Safari, Roman Boča, Ján Titiš, Behrouz Notash PII: DOI: Reference:

S0020-1693(15)00328-X http://dx.doi.org/10.1016/j.ica.2015.07.003 ICA 16596

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Inorganica Chimica Acta

Received Date: Revised Date: Accepted Date:

12 May 2015 6 July 2015 8 July 2015

Please cite this article as: F. Shahbazi-Raz, V. Amani, E.B. Noruzi, N. Safari, R. Boča, J. Titiš, B. Notash, Synthesis, characterization, electerochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes, Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.07.003

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Synthesis, characterization, electerochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes 3

Farsheed Shahbazi-Raz a, Vahid Amania, Ehsan Bahojb Noruzi a, Nasser Safaria,*, Roman Bočab,

4

Ján Titišb, Behrouz Notasha

5

a

Department of Chemistry, Shahid Beheshti University, P.O. Box 1983963113, G. C., Evin,

6 7

Tehran, Iran. b

Department of Chemistry, FPV, University of SS Cyril and Methodius, Trnava, Slovakia

8

9

Abstract

10

The complexes cis-[Fe(5,5'-dmbipy)2Cl2]X (X is Cl‾ in 1 and ClO4‾ in 2 and 5,5'-dmbipy is

11

5,5'-dimethyl-2,2'-bipyridine) were synthesized as precursors of new diiron complexes. The

12

diiron complex [Fe(5,5'-dmbipy)(NCS)2(μ-OCH3)]2 (3) was obtained from the reaction of KSCN

13

with 1 and 2. Complex 3 was obtained from the addition of KSCN to FeCl2.4H2O and then 5,5'-

14

dmbipy. A new binuclear iron(III) complex [Fe(4bt)(NCS)2(μ-OCH3)]2 (4) (4bt is 4,4'-bithiazole)

15

has also been synthesized from the reaction of [Fe(4bt)3](NO3)2 with KSCN in a mixture of

16

methanol/acetonitrile solvent. All complexes were characterized by elemental analysis, IR, UV-

17

Vis, and 1HNMR spectroscopy and their structures were studied by single-crystal X-ray

18

crystallography. The 1HNMR and magnetic investigation show that both paramagnetic centers in

19

3 and 4 complexes are coupled by an antiferromagnetic interaction. The electrochemical

20

behavior of complex 3 show FeII/FeIII and FeIII/FeIV redox couples, in which FeIII/FeIV show

21

quasi-reversible redox behavior in relatively low potential.

22

1

23

Keywords: Iron(III); 5,5'-Dimethyl-2,2'-bipyridine; 4,4'-Bithiazole; FeIII/FeIV redox couple;

24

Crystal structure; Dinuclear iron protein; Thermal analyses; Magnetism

25 26

* Author to whom correspondence should be addressed. e-mail: [email protected]

27 28

1. Introduction

29

Nonheme diiron complexes have received vast interest in the last decades, owing to the

30

diiron core found in the active sites of a number of proteins such as; ribonucleotide reductase

31

proteins, hydroxylase, methane monoxygenase, ruberythrin, ferritin ferroxidase and hemerythrin

32

[1-12]. Iron coordination and structure, especially iron-iron distances (3-3.5 Å), and bridging

33

ligands were found to be important factors for the function of the aforementioned protein which

34

range from O2 activation, electron transfer to oxygen carrier and iron storage [13-15]. Nitrogen

35

donor ligands such as histidines were found to be terminal ligands. Magnetic studies on the

36

proteins and related models show that when O2- is bridging the ligand, strong antiferromagnetic

37

coupling has occurred by super exchange mechanism with coupling constant in the range of -100

38

to -70 cm-1. For hydroxy bridging (OH-) ligand in diiron moiety a weaker antiferromagnetic

39

coupling constant has been reported in the range of -30 to -5 cm−1 [16-20]. However, alkoxide

40

bridged diiron centers as another class of bridging diiron core, not found in natural enzymes so

41

far, where studied in the model compounds and controversial J coupling from very weak J ≪−1

42

cm−1 to medium J = −30 cm−1 was reported [21-23].

43

The electrochemical studies for the biomimetic diiron model complexes would be valuable in

44

understanding the redox properties of the protein active sites in electron transfer, O2 activation

45

and O2 transfer proteins. One electron transfer pathway for 2FeII/FeII, FeIII and FeII,FeIII/2FeIII

2

46

redox coupling has been previously studied [24-31]. However, FeIII/FeIV couples were rare for

47

dinuclear nonheme iron model complexes, although it is an important possibility in the enzymes

48

[32]. Among the large number of mononuclear iron centers studied, an FeIII/FeIV couple was

49

observed in the [FeIV(O)(N4Py)]2+ family [33-36], in which the reversible FeIII/FeIV couple was

50

reported at low oxidation potential in protic solvent, although some precaution in the

51

interpretation of the FeIV oxidation state in the aforementioned complex was advised [31]. To

52

observe the reversible redox behavior in diiron core centers some criteria should be preserved

53

such as i, the terminal ligands should not be too sterically hindered to stabilize a dinuclear

54

complex instead of a mononuclear complex [37], ii, the complex scaffold should not be resistant

55

against metal oxidation state changes [38], and iii, the coordinated ligands should not be active in

56

the broad potential range.

57

Hetero ligand iron (III) complexes have recently been reported by our group [39-44]. In this

58

article, two new hetero ligand complexes; cis-[Fe(5,5'-dmbipy)2Cl2]X (X is Cl‾ in 1 and ClO4‾ in

59

2) were synthesized as precursors of new diiron complexes. The complex [Fe(5,5'-

60

dmbipy)(NCS)2(µ-OCH3)]2 (3) and [Fe(4bt)(NCS)2(µ-OCH3)]2 (4) have terminal nitrogenous

61

ligands and two methoxy bridged ironIII cores. All complexes were characterized by elemental

62

analysis, IR, UV-Vis, and 1H NMR spectroscopy and their structures were studied by single-

63

crystal X-ray crystallography. Magnetometric study on 4 indicates a medium size

64

antiferromagnetic coupling between iron centers with J = -34.2 cm-1. Magnetic coupling

65

accompanied with an Fe-Fe distance of 3.141 in 3 mimic that of the oxidized active site of

66

proteins such as SMMOHox (3.10 Å) which has a bridged carboxylate. Electrochemical

67

investigation of 3 shows semi-reversible FeIII/FeIV redox couple in methanol. FeIII/FeIV quasi-

68

reversible redox couple has been rarely observed for diiron centers [32].

69

3

70

2. Results and discussion

71

2.1.

Synthesis of 1-4

72

Complex 1 was obtained from the reaction of 1 equivalent of FeCl3.6H2O with 2 equivalents

73

of 5,5'-dmbipy in CH3OH at 40-45 °C during 30 min of reaction time and after one week the

74

solution was left aside at room temperature. Complex 2 was also obtained by the same method in

75

the presence of 4 equivalents of NaClO4 (yields 82.2% and 72% respectively). Complex 3 was

76

synthesized by two methods: in method I, 2 equivalents of KSCN were reacted with 1 equivalent

77

of [Fe(5,5'-dmbipy)2Cl2]X (X is Cl‾ in 1 and ClO4‾ in 2) in CH3OH at 40-45 °C for 30 min. In

78

method II, a mixture of 1 equivalent of FeCl2.4H2O and 2 equivalents of KSCN salts were

79

reacted with 1 equivalent of 5,5'-dmbipy in CH3 OH/CH3CN. At the end of the reaction, only

80

dimer complex 3 was obtained and no mononuclear ferric complex was observed. Oxidation of

81

Fe(II) to Fe(III) also occurred in the presence of air and MeO‾ anions were co-formed from the

82

solvent [21]. The complexes of 1 and 2 equivocally act as precursors for the synthesis of 3 dimer

83

in the presence of KSCN and in methanol medium. Complex 3 was also prepared directly by the

84

stoichiometric addition of chelating 5,5'-dmbipy ligand and KSCN to the iron(II) chloride in

85

methanol with 78% yield. However, direct reaction of FeCl2.4H2O with KSCN and 4,4'-

86

bithiazole in CH3OH/CH3CN resulted in [Fe(4bt)2(NCS)2] monomer which was synthesized by a

87

procedure which we have previously described [45] and no dimer complex 4 was isolated.

88

Therefore, the binuclear complex 4 was prepared by treating 1 equivalent of [Fe(4bt)3](NO3)2

89

complex with 2 equivalents of KSCN salt in CH3OH/CH3CN (1:1) in high yield (84%). The

90

synthetic routes of these complexes have been shown in scheme 1.

4

91

Scheme 1 The preparation method of 1-4. 93

2.2.

92

Spectroscopic characterization of 1-4

94

IR spectroscopy is a powerful technique for the identification of iron bipyridine and bithiazole

95

complexes, since a wealth of information is presented in the literature [46-49]. IR absorption of

96

the free ligands and complexes 1-4 are presented in Table 1. The strong C≡N (NCS-) stretching

97

mode for complex 3 was observed at 2033 cm-1, but in complex 4, two strong bands were

98

observed at 2019 and 2057 cm-1 assigned to the mentioned fragment [50-63], where this

5

99

character clearly distinguishes compound 4 from 3. Due to the difference between the two NCS-

100

ligands in complex 4, as we discussed in the x-ray structure section, two strong (NCS-) bands at

101

complex 4 instead of one strong band at complex 3 were observed.

102

In addition, a new signal at 1087 cm-1 in the IR spectra of 2 compared to 1 is assigned to ν(Cl-

103

O). The ν(C-O) from bridge methoxy groups is seen at 1033 cm-1 in 3 and 1021 cm-1 in 4 [54-

104

56]. The Fe-N(N-N) stretching vibrations for complexes 1-4 are seen at 267, 257, 258, 260 cm-1

105

and the Fe-N(NCS-) stretching vibrations for complexes 3 and 4 are seen at 303 and 300 cm-1,

106

respectively [51,57]. These bands confirm that the iron centers in 1-4 are high spin, since low

107

spin iron(III) complexes show 50-70 cm-1 higher FeIII-N frequencies [53]. The new signal at 489

108

cm-1 for 3 and 480 cm-1 for 4 and the lack of these signals in 1 and 2 leads to their assignment to

109

ν(Fe-O) from methoxy bridges [58-60].

110

The UV-Vis spectra of 1 and 2 have no spin allowed signals for d-d transitions, but a charge

111

transfer band (LMCT) is seen in the 360-376 nm region, in accordance with the high spin

112

character of the iron (III) center. The visible absorption of compound 3 and 4 illustrate two

113

bands, centered at 477 and 511 nm for 3 and one band centered at 417 nm for 4, which can be

114

assigned to LMCT [61], between the positively charged metal ion and the negatively charged

115

isothiocyanate ligands. These high-spin Fe(III) dimers have no spin-allowed d–d transitions and

116

no expectation of MLCT.

117

NMR spectroscopy reveals that the structures of compound 1, 2, 3 and 4 are held in solution.

118

Trace A of Fig.1 show the paramagnetic 1H NMR spectrum of complex 1 in CDCl3. The proton

119

signals of bipyridine are observed in the 8 to 10 ppm region and for the –CH3 in 2.85 ppm. The

120

sharp signal for 1 at 7.5 ppm is related to solvent. The 1H NMR spectrum of complex 2 is almost

121

the same as complex 1 in CD3CN (Fig. S1a). Trace B of Fig.1 shows the 1H NMR spectrum of

122

dimer complex 3 in CDCl3. The 1H NMR spectrum of 3 exhibits one singlet for methyl groups of 6

123

bridge methoxy ligand at 2.41 (H1) ppm and one singlet for methyl groups of 5,5′-dmbipy ligand

124

at 1.34 (H2) ppm. Three aromatic hydrogens of 5,5'-dmbipy ligand from 3 exhibit two doublets

125

at 7.63 (H3) and 8.25 (H4) ppm and one signal at 8.50 (H5) ppm, with a relative ratio of 1:1:1.

126

The 1H NMR spectrum of 4 exhibits one singlet for methyl group of bridge methoxy ligand at

127

2.35 ppm (H1) and two singlet bands at 7.95 (H2) and 9.11 (H3) ppm for aromatic protons of

128

4,4'-bithiazole ligand (Fig. S1b). The diamagnetism of 3 and 4 is against the paramagnetic nature

129

of Fe(III) centers especially high spin ones and can be explained with antiferromagnetism

130

phenomenon, happening between two Fe(III) centers with a short distance of 3.141 and 3.125 Å

131

for 3 and 4 respectively (see structure description section). In 1H NMR the peak of hydrogen of

132

methoxy group coordinated to Fe(III) paramagnetic complexes is observed around 100 ppm [41].

133

But, when methoxy group coordinated to two Fe(III) paramagnetic centers in 3 and 4 dimer

134

complexes the peak of CH3 group is shown around 2-3 ppm that shows dimeric nature of 3 and 4

135

are saved in solution.

136

137

2.3.

Thermal studies of 1and 3

138

The thermal stability of 1 and 3 have been determined on single-crystalline samples between

139

30-760 °C in an air atmosphere with a heating rate of 10 °C min-1 by thermogravimetric (TG)

140

and differential thermal analyses (DTA) (Fig. 2a). For complex 1 (Fig. 2a), TGA shows that

141

chemical decomposition starts at about 180 °C and ends at 750 °C with a weight loss of 88.1%

142

corresponding to the removal of three chloride ions and two 5,5'-dmbipy molecules (calcd:

143

89.5%). The remaining weight of 14.5% corresponds to the 0.5Fe2O3 (calcd. 15.1%). The DTA

144

curve of 1 displays two distinct endothermic peaks at 226 and 311 °C and three distinct

145

exothermic peaks at 261, 403 and 543 °C. The TGA curve of 3 (Fig. 2b) shows a four step 7

146

thermal decomposition. The first step between 200 and 315 °C with a mass loss of 3.6%

147

corresponds to the loss of two methyl groups from two methoxy groups (calcd. 3.8%). In the last

148

three steps between 320 and 630 °C, four NCS¯ anions, two oxygen atoms and two 5,5'-dmbipy

149

molecules are lost and the framework decomposes (77.6%, calcd: 75.5%). The final residual

150

weight is 19.1% corresponding to Fe2O3 (calcd. 20.7%). The DTA curve of 3 displays four

151

distinct exothermic peaks at 181, 340, 385 and 509 °C. For these complexes, the Fe2O3 was

152

characterized by XRD spectrum.

153

2.4.

Description of the molecular structure of 1-4

154

Table 2 shows the details of the data collection and refinement of the X-ray crystal structure

155

determination for 1-4. Selected bond lengths and bond angles are presented in Table 3. The

156

asymmetric unit of 1 contains one half-molecule. The structures of 1 and 2 consist of one

157

[Fe(5,5'-dmbipy)2Cl2]+ cation and one X anion (X is Cl¯ in 1 and ClO4¯ in 2), Figs.3a and 3b. In

158

the cation part of these complexes, the Fe(III) atom has a distorted octahedral geometry

159

coordination with four N atoms from two 5,5'-dimethyl-2,2'-bipyridine ligands and two terminal

160

Cl atoms. The Fe-Nave bond distances for complex 1 and 2 are 2.15 and 2.17 Å, respectively.

161

The crystal structures of complexes 3 and 4 are orthorhombic and monoclinic respectively. In

162

spite of monomer 1 and 2, complexes 3 and 4 are a dimer with formula [Fe(5,5′-

163

dmbipy)(NCS)2(µ-OCH3)]2 (depicted in Fig. 4a) and [Fe(4bt)(NCS)2(µ-OCH3)]2 (depicted in Fig.

164

4b) respectively, where asymmetry unit consists of half of the dimer molecule as an inversion

165

center in the middle of methoxy bridges resulting in the other half of the dimer. Each Fe center is

166

surrounded with two nitrogen atoms from two isothiocynato ligands (cis) and two oxygen atoms

167

from two methoxo bridging ligands and two nitrogen atoms from one bidentate 5,5′-dmbipy

168

ligand for 3 and 4bt ligand for 4. The Fe-N distances reveal some distinction in the range of 2.068

169

2.18 Å for 3 and 2.03-2.19 Å for 4. The Fe-Nave distances for NCS‾ ligands are slightly shorter

170

than Fe-Nave distances for chelating ligands. The metal ligand bond distances were used to obtain

171

the spin state of the metal center. The Fe-Nave bond distances in high spin iron(III) bipyridine and

172

bithiazole complexes are around 2.2 Å and in related low spin Fe(III) complexes, Fe-N distances

173

less than 2Å were reported [62-64]. Therefore, the Fe-N bond distances here show that the

174

present complexes are unambiguously high spin d5. The Fe-N stretching frequency in infrared

175

spectra at 267, 257, 258 and 260 cm-1 for 1-4 provide additional evidence for the high spin

176

character. The two Fe-O bond lengths, involving methoxy bridge ligands are almost equal; 1.96

177

and 2.02 Å for 3 1.96 and 2.00 Å for 4. The O-Fe-O and Fe-O-Fe angles are 75.69 and 104.31°

178

for 3 and 76.05 and 103.95° for 4 respectively (Table 3). The distances and angles in the

179

Fe2(OCH3)2 rhombic ring for 3 and 4 quite resemble those observed for several reported

180

complexes with a four-membered Fe2(OCH3)2 ring, where the whole molecule has Ci symmetry

181

and the Fe2(OCH3)2 rhombus has a point of symmetry. The mentioned O-Fe-O angles, imposed

182

by the four-membered ring, and the bite angles of 5,5'-dmbipy ligands 75.26° for 3 and 4bt

183

ligands 74.83° for 4 (for N1-Fe1-N2) are the largest deviations that can be considered as the

184

main factors to cause a severely distortion in the iron local coordination geometry with [FeN4O2]

185

octahedral moiety. In these structures, the two iron (Fe3+) atoms are connected by two methoxy

186

bridging ligands and the Fe…Fe distance is 3.141 Å for 3 and 3.125 Å for 4; the Fe…Fe

187

distances found in non-heme binuclear ferric protein are; Active RNR(3.40 Å ), sMMO (3.10 Å),

188

rubrerythrin (3.30 Å) and Oxy hemerythrin (3.27 Å). Therefore, the Fe…Fe distances found in 3

189

and 4 resembles to that of sMMO and are close to that found for Oxy hemrythrin. These

190

distances are in the range of similar structures [65-68] and consequently result in a strong

191

antiferromagnetic interaction between two Fe(III) centers (see later parts).

9

192

Bikas et al., have synthesized Fe2(OCH3)2 core with methoy bridged. Their Fe…Fe distances

193

of 3.1-3.2 Å, O-Fe-O angels of 74.5-75.5°, Fe-O-Fe angels of 104.5-105.5° and very small

194

antiferromagnetic coupling of J ≪−1 cm−1 are contrary to our results which show a relatively

195

strong antiferromagnetic coupling of J ≈−34 cm−1 [21].

196

The hydrogen bondings of 1-4 are listed in Table S1. The packing diagrams of 1 and 2 are

197

shown in Fig. S2 and 3 and 4 are shown in Fig. S3. The bond lengths are in agreement with the

198

high spin state of Fe(III) ions in complexes 3 and 4, where there is no considerable difference

199

between the bond distances in these complexes and those found in complexes 1 and 2 with a high

200

spin Fe(III) center [69]. The two N-C bond lengths in isothiocyanato groups are almost equal for

201

complexes 3 and 4. As it was discussed in the IR section, compound 3 shows one sharp and

202

strong signal for the NCS group, while compound 4 shows two signals for the NCS group. Two

203

Fe-N-C angles in 3 have 6° differences, but the same Fe-N-C angles for two NCS ligands in one

204

iron center in 4 differ by about 16°. Detailed investigation on the weak sulfur interaction in 3

205

shows that S1 and S2 correspond to two NCS on one iron and have similar S···π and S···H

206

interactions. However in compound 4, the weak sulfur interactions for two NCS are distinct and

207

S4 has one NCS···SCN interaction plus two S4···S1 and S4···S2 interaction with sulfur in the

208

bithiazole rings. On the other hand, S3 has only one sulfur-sulfur interaction with S4 from NCS,

209

see Table 4, Figs 5a and 5b. To our knowledge this is a unique and interesting spectroscopic

210

indication for the effect of weak interaction seen in crystal packing.

211

212

Magnetic studies

213

Complex 4 behaves magnetically as a typical binuclear unit coupled by a medium-sized

214

antiferromagnetic interaction (Fig 6a). The effective magnetic moment at the room temperature 10

215

is only µeff = 6.87µB while the high-temperature limit for two Fe(III) centers is

216

µ eff = g av 2 ⋅ (5 / 2) ⋅ (7 / 2) µ B = 8.37 µB when gav = 2 is assumed. On cooling, the magnetic

217

susceptibility passes through a maximum and then it should drop to zero. However, the low-

218

temperature data is overlapped by the signal of a paramagnetic impurity arising from the

219

mononuclear fragments of the binuclear units. The magnetization taken at low temperature

220

reflects only the paramagnetic impurity and it adopts small values.

221

The magnetic data for 4 was fitted by using a spin Hamiltonian

222



Hˆ = − J  −2 ( S Fe1 ⋅ S Fe2 ) + µ B Bg Fe  −1 ( SˆFe1 z + SˆFe2 z )

223

224

(1)

The presence of a paramagnetic impurity is covered by the correction

χ c = χ mol (1 − xPI ) + 2 xPI χ PI

(2)

225

where the χPI term is given by the Curie-Weiss law and gPI = 2.0 has been assumed. The

226

optimization routine converged to the following set of magnetic parameters: J/hc = -34.2 cm-1, g

227

= 2.176, xPI = 0.018, ΘPI = -1.79 K [R(χ) = 0.025]. A rather high-negative exchange coupling

228

constant matches the high Fe-O-Fe angle 103.9° on the superexchange path [70]. The Weiss

229

constant could reflect some intermolecular interactions along with some zero-field splitting at the

230

Fe(III) centers.

231

Although the molecular structure of 3 is similar to 4, the magnetic data is very different (Fig.

232

6b). The room-temperature value of the effective magnetic moments is µeff = 4.77 µB; on cooling

233

it decreases in a linear manner until T = 10 K and then it decreases more rapidly to the value of

234

µeff = 3.12 µB at T = 1.9 K. The susceptibility plotted vs the inverse temperature nearly follows a

235

straight line. Interpretation of such a behavior is not straightforward. First, the crystal structure of

11

236

3 is dissimilar to 4 due to the different intermolecular contacts leading to an extensive two-

237

dimensional network, so it is not appropriate to apply the same spin Hamiltonian as for 4.

238

Second, the differences in electron spectra also indicate a different electronic situation.

239

Moreover, when 4A2 local electronic state is close to the ground 6A1 term, then spin admixed

240

states will occur owing to which the apparent g-factor is geff < 2.0 and the apparent temperature-

241

independent paramagnetism (χTIP) is very high. A tentative fit of magnetic data gave J/hc = -120

242

cm-1, geff = 1.91, χTIP = 27 × 10-9 m3 mol-1, xPI = 0.16, and ΘPI = -0.17 K [R(χ) = 0.042, R(M) =

243

0.063]. The magnetization taken at low temperature saturates only to Mmol/NA = 1.60 µB and it

244

reflects only the presence of a paramagnetic impurity.

245

The Fe(III) complex containing the (µ-OCH3)2 bridge possess a J values in the range of -13 to

246

-35 cm-1 (Table 5). Most complexes have Fe-O-Fe angle between 103 and 105°. The Fe-O-Fe

247

angles correlate with J value in these complexes as shown in Fig. 7 (see also [70] and [71]).

248

Complex 4 possesses the angle Fe-O-Fe = 103.9° and the strongest J value observed for related

249

complexes (-34.2 cm-1). Some data (according to [72], [73], and [21]) lie out of the range for

250

similar complexes and should be interpreted with caution. Measurement of magnetic moment

251

and J value in diiron centers anzymes is useful tool for characterization of the active site of the

252

enzymes. Since diiron center with methoxy bridged are not found so far, but it can be a

253

possibility, these J value obtained in this work may rich data of magnetism and coupling constant

254

for use in related iron protein centers.

255

256

2.5.

Cyclic voltammetry

257

The cyclic voltammetric of complex 3 was recorded in the potential range from -2 to 2 V.

258

Electrochemical properties for complex 3 and 5,5′-dmbipy ligand were investigated in CH3OH 12

259

containing 0.1M nBu4NClO4 as a supporting electrolyte. The cyclic voltammetric of 5,5′-dmbipy

260

in CH3OH shows two oxidation peaks at 0.613 and 1.534 V and two reduction peaks at -1.667

261

and 0.03 V which are irreversible. The cyclic voltammetric of complex 3 in CH3OH at 100 mV

262

scan rate is listed in Table 6. The cyclic voltammetric of complex 3 in CH3OH at different scan

263

rates is listed in Table S2 and are shown in Fig. S4. Cyclic voltammetry experiments for complex

264

3 reveal one two-electron and four one-electron quasi-irreversible oxidation events. The cyclic

265

voltammetric of complex 3 in the range -0.2 to 1.5 V are shown in Fig 8. Within this region,

266

measurements revealed one quasi-reversible redox process at Epc= -0.0284 V with an associated

267

oxidation peak at Epa= 0.1020 V corresponding to 2FeII/FeIIFeIII and one quasi-reversible redox

268

process at Epc= 0.4911 V with an associated oxidation peak at Epa= 0.6723 V corresponding to

269

FeIIFeIII/2FeIII. These peaks also compare favorably to the values reported for dinuclear FeIII

270

complexes presented as a structural and functional model for non-heme diiron proteins [24-31].

271

Other redox processes seen at Epc= 0.9615 V and Epc=1.1226 V correspond to 2FeIII/FeIIIFeIV and

272

FeIIIFeIV/2FeIV respectively with an associated oxidation peak at Epa= 0.8708 V corresponding to

273

2FeIV/2FeIII. The FeIII/FeIV couples are rare for dinuclear nonheme iron model complexes. The

274

FeIII/FeIV couples were observed

275

cyclam2iPrO)=(1,3-bis[1,4,8,11-tetraazacyclododecane]-2-hydroxypropane] [85], which were

276

irreversible (1.8 and 1.9 V) corresponding to 2FeIII/FeIIIFeIV and FeIIIFeIV/2FeIV, respectively.

277

Our quasi-reversible and low potential FeIII/FeIV redox processes (0.9615 and 1.1226 V) indicate

278

that the F(IV) centers generated are stable [26]. However, this interpretation for observing FeIV

279

in complex 3 are just based on our cyclic voltammetric observation and should be treated by

280

cautious and more experimental result is needed to make sure existence of FeIV centers.

for

[(cyclam2iPrO)Fe2(µ-CF3SO3)](CF3SO3)2] [where

281

The reversible FeIII/FeIV couples were reported at low oxidation potential for mono-nuclear

282

center [FeIV(O)(N4Py)]2+ family exclusively in protic solvent [32-36], although some precaution 13

283

to interpret FeIV oxidation state in the aforementioned complex was advised [31]. The semi-

284

reversible observation for FeIII/FeIV redox couple has been rarely observed for diiron centers, in

285

spite of possible existence in diiron non-heme enzymes [32]. In cyclic voltammetric of complex

286

3 we observe two one-electron semi-reversible of FeIII/FeIV redox couples that mention to two

287

iron centers. Therefore we can conclude that 3 is dimer in solution state as well. However, under

288

high concentration of supporting electrolyte tetrabutylammonium perchlorate exact nature of

289

complexes may differ from solid structures.

290 291 292

3. Experimental

293

3.1.

Materials and instruments

294

All chemicals were purchased from Merck and Aldrich. Infrared spectra (4000-250 cm-1) of

295

solid samples were taken as 1% dispersion in CsI pellets using a Shimadzu-470 spectrometer. 1H

296

NMR spectra were recorded on a Bruker AC-300 MHz spectrometer operating in the quarter

297

mode. The spectra were collected over a 50-kHz band width with 16K data points and a 5-µs 45º

298

pulse. For a typical spectrum, between 1000 and 5000 transients were accumulated with a 50-ms

299

delay time. The signal-to-noise ratio was improved by apodization of the free induction decay.

300

Elemental analysis was performed using a Heraeus CHN-O Rapid analyzer. Melting point was

301

obtained by a Kofler Heizbank Rechart type 7841 melting point apparatus UV-Vis spectra were

302

recorded on a Shimadzu 2100 spectrometer using a 1 cm path length cell in CH3CN and CH3OH

303

at room temperature. Thermal behavior was measured with an STA 503 Bähr apparatus. The

304

susceptibility taken at B = 0.1 T has been corrected for the underlying diamagnetism and

305

converted to the effective magnetic moment. The magnetization has been measured down to 14

306

temperatures: T = 2.0 and T = 4.6 K. Voltammetric experiments were performed using a

307

µAutolab Type III electrochemical system. A conventional three-electrode cell consisting of a

308

glassy carbon working electrode (GCE) (2.0 mm in diameter), a platinum wire counter electrode

309

and a saturated Ag/AgCl reference electrode was used for voltammetric experiments. All

310

potentials reported in non aqueous solutions were measured versus a saturated Ag/AgCl

311

reference electrode which was used in combination with a salt bridge filled with the particular

312

electrolyte solution used in the experiment. Before each experiment, the GCE was cleaned by

313

polishing with 0.05 µm alumina slurry on a polishing cloth and rinsed thoroughly with doubly

314

distilled water. After each polishing step to get reproducible current-potential curves, cyclic

315

voltammetric was performed at CH3OH containing 0.1 M Bu4NClO4.

316

3.2.

317

5,5'-Dimethyl-2,2'-bipyridine (0.20 g, 1.10 mmol) in methanol (10 mL) was added to a solution

318

of FeCl3.6H2O (0.15 g, 0.55 mmol) in methanol (5 mL) and the resulting red solution was stirred

319

at 40-45 °C for 30 min. The greenish red precipitated product was recrystallized from

320

CH3CN:CH3OH (4:1). After two weeks, red block crystals of 1 were isolated (yield 0.24g, 0.45

321

mmol, 82.0%, m.p. 185 °C). IR (CsI, cm-1): 3043w, 2923w, 1606m, 1576w, 1547m, 1505m,

322

1479m, 1389s, 1247s,1165s, 1049s, 1000w, 838s, 826s,731s, 692m, 654s, 538w, 485w, 418s,

323

376w, 290s, 267s. UV-Vis (CH3OH, nm) 376, 294 and 266. 1H NMR (CDCl3, ppm): 2.83 (S,

324

3H), 7.72 (S, 1H), 8.33 (S, 1H) and 8.67 (S, 1H). Anal. Calc. for 1: C, 54.32; H, 4.52; N, 10.55.

325

Found: C, 53.91; H, 4.49; N, 10.50.

326

3.3.

Synthesis of complex cis-[Fe(5,5'-dmbipy)2Cl2]Cl (1)

Synthesis of complex cis-[Fe(5,5'-dmbipy)2Cl2]ClO4 (2)

15

327

Sodium perchlorate (0.10 g, 0.80 mmol) was added to a solution of FeCl3.6H2O (0.05 g, 0.20

328

mmol) in methanol (5 mL) and the resulting solution was stirred at 40-45 °C for 5 min. 5,5'-

329

Dimethyl-2,2'-bipyridine (0.07 g, 0.40 mmol) in methanol (10 mL) was added to the previous

330

solution and the resulting one was stirred at 40-45 ◦C for 20 min. The red precipitated product

331

was recrystallized from CH3CN/CH3OH (4:1) after one week, orange block crystals of 2 were

332

isolated (0.08g, 0.13 mmol, 72.0%, m.p. 276 °C). IR (CsI, cm-1): 3043w, 2925w, 1606m, 1575m,

333

1502m, 1479s, 1386s, 1316s, 1287w, 1235s, 1163s, 1086s, 1046s, 991s, 840s, 813m, 728m,

334

691m, 655m, 622s , 537w, 497w, 420m, 375w, 329s, 257s. UV-Vis (CH3OH, nm) 362, 300 and

335

270. 1H NMR (CDCN3, ppm): 2.53 (S, 3H), 7.89 (S, 1H), 8.30 (S, 1H) and 8.64 (S, 1H). Anal.

336

Calc. for 2: C, 48.47; H, 4.04; N, 9.42. Found: C, 48.18; H, 4.00; N, 9.34.

337

3.4.

Synthesis of complex [Fe(5,5'-dmbipy)(NCS)2(µ-OCH3)]2 (3)

338

This complex was prepared by two methods. Method I: the KSCN salt (0.07 g, 0.80 mmol) in

339

warm CH3CN (10 mL) was added to the solution of cis-[Fe(5,5'-dmbipy)2Cl2]X (1) and (2) (0.40

340

mmol) in CH3OH (5 mL) and then was stirred at 40-45 ◦C for 30 min. After one week, deep red

341

plate crystals of 3 were isolated (yield 0.10 g, 0.13 mmol, 65% for 1 and 0.11 g, 0.14 mmol,

342

71% for 2; m.p. 235 °C) where uncolored crystals of dissolved KCl and KClO4 salts were also

343

performed in the reaction moieties. IR (CsI, cm-1): 3090m, 2924w, 2855w, 2033s, 1611w,

344

1570m, 1475s, 1382w, 1243w, 1033s, 831m, 729m, 659m, 489s, 303s, 258s. UV-Vis (CH3OH,

345

nm) 511, 477, 307 and 257. 1H NMR (CDCl3, ppm): 1.62 (S, 6H), 2.41 (S, 3H), 7.63 (d, 2H),

346

8.25 (d, 2H) and 8.50 (S, 2H). Anal. Calc. for 3: C, 46.51; H, 3.87; N, 14.46. Found: C, 46.09; H,

347

3.85; N, 14.39.

348

Method II: the KSCN salt (0.08 g, 0.80 mmol) in CH3OH (10 mL) was added to a solution of

349

FeCl2.4H2O (0.08 g, 0.40 mmol) in warm CH3OH (10 mL). After filtration of KCl salt, 5,5'-

16

350

dmbipy (0.15 g, 0.80 mmol) in CH3CN (40 mL) was added to the filtered solution without

351

stirring. After two days, deep red plate crystals of 3 were isolated (yield 0.12 g, 0.15 mmol,

352

78.1%).

353

3.5.

354

Complex [Fe(4bt)3](NO3)2 was synthesized by our method [86]. KSCN salt (0.06 g, 0.64 mmol)

355

in warm CH3CN (10 mL) was added to the solution of [Fe(4bt)3](NO3)2 (0.22 g, 0.23 mmol) in

356

CH3OH (5 mL) and was stirred for 10 min at room temperature. After one week, deep red

357

prismatic crystals of 4 were isolated (yield 0.10 g, 0.13 mmol, 84.2%, m.p. 230 °C), where

358

uncolored crystals of 4,4'-bithiazole ligand and dissolved KNO3 salt were also performed in the

359

reaction moiety. IR (CsI, cm-1): 3090m, 2917w, 2873w, 2816w, 2057vs, 2019vs, 1604w, 1515m,

360

1430s, 1389w, 1357w, 1317m, 1243w, 1198w, 1155m, 1057m, 1021s, 974s, 911m, 881m, 828s,

361

767m, 647w, 480s, 374s, 300s, 260s. UV-Vis (CH3OH, nm) 417, 316 and 239. 1H NMR (DMSO-

362

d6, ppm): 2.48 (S, 3H), 7.93 (S, 2H) and 9.24 (S, 1H). Anal. Calc. for 4: C, 29.11; H, 1.88; N,

363

15.08. Found: C, 28.90; H, 1.87; N, 14.98.

364

3.6.

365

The X-ray diffraction measurements were made on a STOE IPDS-II diffractometer with

366

graphite-monochromated Mo Kα radiation. For cis-[Fe(5,5'-dmbipy)2Cl2]Cl (1) a red block

367

crystal with dimensions 0.15×0.11×0.10 mm, cis-[Fe(5,5'-dmbipy)2Cl2]ClO4 (2) an orange block

368

crystal with dimensions 0.45×0.20×0.20 mm, [Fe(5,5'-dmbipy)(NCS)2(µ-OCH3)]2 (3) a plate

369

crystal with dimensions 0.4×0.15×0.10 mm and [Fe(4bt)(NCS)2(µ-OCH3)]2 (4) a red prism

370

crystal with dimensions of 0.35 × 0.25 × 0.23 mm were mounted on a glass fiber and used for

371

data collection. Cell constants and an orientation matrix for data collection were obtained by

Synthesis of complex [Fe(4bt)(NCS)2(µ-OCH3)]2 (4)

Crystal structure determination and refinement

17

372

least-square refinement of the diffraction data from 3254 for 1, 6899 for 2, 4645 for 3 and 3791

373

for 4. Data were collected at a temperature of 298(2) K for 1 and 120(2) for 2, 3 and 4 to a

374

maximum 2θ value of 58.40° for 1, 58.30° for 2, 58.38° for 3 and 58.30° for 4 and in a series of

375

ω scans in 1° oscillations and integrated using the Stoe X-AREA [87] software package. The

376

numerical absorption coefficient, µ, for Mo Kα radiation is 0.981 mm-1 for 1, 0.935 mm-1 for 2,

377

1.126 mm-1 for 3 and 1.647 mm-1 for 4. A numerical absorption correction was applied using X-

378

RED [88] and X-SHAAPE [89] software packages. The data were corrected for Lorentz and

379

polarizing effects. The structures were solved by direct methods [90] and subsequent difference

380

Fourier maps and then refined on F2 by a full-matrix least-squares procedure using anisotropic

381

displacement parameters [89]. All of the hydrogen atoms were located in a difference Fourier

382

map and then converged with R factors and parameter errors significantly better than for all

383

attempts to model the solvent disorder. Atomic factors are from the International Tables for X-ay

384

Crystallography [91]. All refinements were performed using the X-STEP 32 crystallographic

385

software package [92].

386

4. Conclusions

387

Two new mononuclear iron(III) complexes as precursors of a new diiron complex and the two

388

diiron complexes with two methoxy bridged ironIII core have been synthesized and characterized.

389

IR absorption of complex 4 shows two strong (NCS-) bands instead of one strong band in

390

complex 3. IR spectroscopy data confirms differences in NCS- groups in the structure of new

391

diiron complexes. The differences in NCS- groups have arisen from differences in the packing

392

structure of diiron complexes, as we expected which have arisen from differences in bond

393

lengths of NCS- groups. The Fe…Fe distance is 3.141 Å for 3 and 3.125 Å for 4 were analogous

394

to those found in non-heme binuclear ferric proteins (3-3.5 Å). Complex 3 resembles the features

18

395

of the complex 4 in many structural characteristics but their magnetic behavior is different. The

396

effective magnetic moment at room temperature is only µ eff = 6.87 µ B with coupling constant of J

397

= −34.2 cm−1 for 4. This result shows a relatively strong antiferromagnetic coupling, as one can

398

expect from comparison with reported methoxy bridged diiron complexes. Because of the very

399

low solubility of 4 in CH3OH, the cyclic voltammetric of this complex was not investigated. The

400

[(5,5'-dmbipy)(NCS)2(µ-OCH3)]2 (3) complex exhibits one two-electron redox wave which is

401

assigned to the 2FeI/2FeII couple and two one-electron redox waves which are assigned to the

402

2FeII/FeII,FeIII and FeII,FeIII/2FeIII couples, respectively. Such couples have been previously

403

observed for diiron Fe2O2 core complexes. Also two one-electron semi-reversible of FeIII/FeIV

404

redox couples has also been observed. The FeIII/FeIV redox couple has been rarely observed for

405

diiron centers.

406

Acknowledgements

407

Grant Agencies (Slovakia: VEGA 1/0522/14, VEGA 1/0233/12, APVV-0014-11) and Shahid

408

Beheshti University are acknowledged for financial support.

409

Electronic Supplementary Information

410

CCDC-1031457-1031460 contains supplementary crystallographic data for this paper. These

411

data can be obtained free of charge from the Cambridge Crystallographic Data Centre via

412

www.ccdc.cam.ac.uk/data_request/cif.ore-mail: [email protected]. X-ray crystallographic

413

data in CIF format for 1-4.

414 415 416

19

417

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[84] S. Dutta, P. Biswas, S. K. Duttab, K. Nag, New J. Chem., 33 (2009) 847.

535

[85] L. A. Berben, J. C. Peters, Inorg. Chem., 47 (2008) 11669.

536

[86] V. Amani, A. Abedi, N. Safari, Monatsch. Chem., 143 (2012) 589.

537

[87] Stoe & Cie, X–AREA, vesion 1.30: Program for the acquisition and analysis of data, Stoe &

538 539 540 541 542 543 544

Cie GmbH, Darmatadt, Germany, 2005. [88] Stoe & Cie, X-RED, version 1.28b: Program for data reduction and absorption correction, Stoe & Cie GmbH, Darmatadt, Germany, 2005. [89] Stoe & Cie, X-SHAPE, version 2.05: Program for crystal optimization for numerical absorption correction, Stoe & Cie GmbH, Darmatadt, Germany, 2004. [90] G.M. Sheldrick, SHELX-97: Program for crystal structure solution and refinement, University of Gottingen, Gottingen, Germany, 1997.

545

[91] Stoe & Cie, X-STEP32, Version 1.07b: Crystallographic package International Tables For

546

X-ray Crystallography, Vol C, Kluwer Academic Publisher, Dordrecht, The Netherlands,

547

1995.

548 549

[92] Stoe & Cie, X-STEP32, Version 1.07b: Crystallographic Package, Stoe & Cie, GmbH, Darmstadt, Germany, 2000.

550 551 552

25

553

Table 1 Selected IR frequencies (cm-1) of 5,5'-dimbipy, 4bt, perchlorate, 1, 2, 3 and 4. Compounds

ν(C-H)

ν(C-O)

ν(C≡N)NCS

ν(Fe-Cl)

ν(Fe-O)

ν(Fe-N)NCS

ν(Fe-N)N-N

5,5'-Dimbipy

2917,3010

ν(C=C), (C=N) 1370,1465,1553,1591

-

533,648,733,794,826

-

-

-

-

-

-

4bt

3046,3127

1390,1436,1514

-

530, 642, 736, 8322

-

-

-

-

-

-

NaClO4

-

-

1088

-

-

-

-

-

-

-

Complex 1

2923,3043

1389,1479,1576,1606

-

538,654,731,826,838

-

-

290

-

-

267

Complex 2

2925,3043

1386,1479,1575,1606

1087

537,655,728,814,840

-

-

329

-

-

257

Complex 3

2929,3090

1382,1475,1570,1611

-

659,729,831

1033

2033

-

489

303

258

Complex 4

2917,3090

1430,1515,1604

-

647,767,831

1021

2019,2057

-

480

300

260

ν(Cl-O)

ν(ring deformation)

554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572

26

573

Table 2 Crystallographic and structure refinement data for 1-4. 1 2 C24H24Cl3FeN4 C24H24Cl3FeN4O4 530.67 594.67 298(2) 120(2) 0.71073 0.71073 Monoclinic Triclinic P2/n Pī 0.15×0.11×0.10 0.45×0.20×0.20 10.334(2) 8.7239(17) 8.9378(18) 11.038(2) 13.136(3) 15.493(3) 90.00 69.60(3) 98.11(3) 87.43(3) 90.00 67.82(3) 1201.1(4) 1288.4(6) 2 2 1.467 1.533 2.28 - 29.20 2.53-29.15 546 610 0.981 0.935 -14 ≤ h ≤14 -11 ≤ h ≤11 Index ranges -10 ≤ k ≤ 12 -15 ≤ k ≤ 14 -18 ≤ l ≤ 18 -21 ≤ l ≤ 21 Data collected 13922 14435 Unique data (Rint) 3254, (0.0740) 6899,(0.0432) Final R1, wR2a (Obs. data) 0.0581, 0.1132 0.0385,0.0846 Final R1, wR2a (All data) 0.0853, 0.1223 0.0556,0.0901 Goodness of fit on F2 (S) 1.121 1.019 Largest diff peak and hole /e.Å-3 0.440, -0.344 0.411,-0.482 a R1 = Σ||Fo|-|Fc||/Σ|Fo|, wR2 = [Σ(w(Fo5-Fc2)2)/Σw(Fo2)2]1/2.

Formula Formula weight Temperature /K Wavelength λ /Å Crystal system Space Group Crystal size /mm a /Å b /Å c /Å α /° β /° γ /° Volume/Å3 Z Density (calc.) /g cm-1 θ ranges for data collection F(000) Absorption coefficient /mm-1

574 575 576 577 578 579 580 581 582 583

27

3 C30H30Fe2N8O2S4 774.60 120(2) 0.71073 Orthorhombic Pbca 0.40×0.15×0.10 12.204(2) 16.034(3) 17.604(3) 90.00 90.00 90.00 3444.6(12) 4 1.494 2.31-29.19 1592 1.126 -16 ≤ h ≤14 -18 ≤ k ≤ 21 -24 ≤ l ≤ 20 15088 4645,(0.1229) 0.0869,0.1688 0.1650,0.1969 1.049 0.507,-0.868

4 C18H14Fe2N8O2S8 742.63 120(2) 0.71073 Monoclinic P21/n 0.35×0.25×0.23 11.1512(6) 9.5581(3) 13.6514(7) 90.00 103.04(4) 90.00 1417.49(11) 2 1.740 2.62 - 29.15 748 1.647 -15≤ h ≤ 14 -13≤ k ≤ 11 -18≤ l ≤ 18 9619 3791 (0.0349) 0.0329, 0.0722 0.0435, 0.0754 1.060 0.512, -0.390

584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606

Table 3 Selected bond distances (Å) and angles (°) for 1-4. Complex 1 2.169(3) N2-Fe1-Cl1a 96.56(7) 2.130(2) N1-Fe1-Cl1a 166.55(7) 2.2661(11) N2-Fe1-Cl1 92.50(7) 165.76(14) N1-Fe1-Cl1 90.58(7) 75.80(9) N1a-Fe1-Cl1 166.55(7) 93.09(9) Cl1-Fe1-Cl1a 100.92(6) 78.96(13) Complex 2 Fe1-N1 2.1394(19) N2-Fe1-N3 79.64(6) Fe1-N4 2.147(2) N1-Fe1-Cl1 94.94(5) Fe1-N2 2.1825(17) N4-Fe1-Cl1 93.09(5) Fe1-N3 2.1937(18) N2-Fe1-Cl1 164.30(5) Fe1-Cl1 2.2487(7) N3-Fe1-Cl1 88.40(5) Fe1-Cl2 2.2597(9) N1-Fe1-Cl2 96.11(5) N1-Fe1-N4 164.45(7) N4-Fe1-Cl2 95.00(6) N1-Fe1-N2 75.57(7) N2-Fe1-Cl2 93.09(5) N4-Fe1-N2 91.03(7) N3-Fe1-Cl2 167.38(4) N1-Fe1-N3 92.07(7) Cl1-Fe1-Cl2 100.42(3) N4-Fe1-N3 75.27(7) Complex 3 Fe1-O1 1.958(3) Fe1-O1-Fe1b 104.31(15) Fe1-N1 2.180(4) N1-Fe1-N2 75.26(17) Fe1-N2 2.168(4) N1-Fe1-N3 91.77(17) Fe1-N3 2.031(5) N1-Fe1-N4 95.34(19) Fe1-N4 2.058(7) O1b-Fe1-N1 164.65(15) Fe1-O1b 2.020(4) N2-Fe1-N3 165.74(18) Fe1…Fe1 3.141(1) N2-Fe1-N4 83.86(19) C13-N3 1.113(7) O1-Fe1-N2 95.63(16) C14-N4 1.034(8) N3-Fe1-N4 91.6(2) O1-Fe1-N1 91.84(15) O1b-Fe1-N3 98.29(16) O1-Fe1-N2 90.59(16) O1b-Fe1-N4 95.93(17) O1-Fe1-N3 95.82(18) C13-N3-Fe1 159.9(5) O1-Fe1-N4 169.50(17) C14-N4-Fe1 153.3(6) O1-Fe1-O1b 75.69(15) Complex 4 Fe1-O1 2.0039(15) Fe1-O1-Fe1c 103.95(6) Fe1-N1 2.1715(17) N1-Fe1-N2 74.83(6) Fe1-N2 2.1900(17) N1-Fe1-N3 87.96(7) Fe1-N3 2.0270(19) N1-Fe1-N4 95.32(7) Fe1-N4 1.9997(19) O1c-Fe1-N1 163.23(6) Fe1-O1c 1.9623(15) N2-Fe1-N3 162.50(7) Fe1…Fe1 3.1245(5) N2-Fe1-N4 85.76(7) C8-N3 1.174(3) O1c-Fe1-N2 93.16(6) C9-N4 1.167(3) N3-Fe1-N4 92.83(8) O1-Fe1-N1 92.00(6) O1c-Fe1-N3 104.33(7) O1-Fe1-N2 89.95(6) O1c-Fe1-N4 95.42(7) O1-Fe1-N3 93.87(7) C8-N3-Fe1 158.88(17) O1-Fe1-N4 170.24(7) C9-N4-Fe1 174.35(17) O1-Fe1-O1c 76.05(6) Symmetry codes: (a) 3/2-x,y,1/2-z; (b) –x,2-y,1-z; (c) 1-x,1-y,-z N1-Fe1 N2-Fe1 Cl1-Fe1 N2-Fe1-N2a N1-Fe1-N2 N1-Fe1-N2a N1-Fe1-N1a

607 608

28

609 610

Table 4 Selected bond distances S…S (Å) for complex 4. S1...S4a 3.469(8) S4…S2c 3.383(8) b S3...S4 3.499(8) Symmetry codes: (a)1/2-x,-1/2+y,1/2-z; (b) x,-1+y,z; (c) 1-x,2-y,-z

611 612 613 614 615

Table 5 Relative bond angles and bond lengths of reported bis methoxido-bridged iron(III) complexes. Fe-O-Fe

J/cm-1

Ref

3.125

103.95

-34.2

This work

L=(N-N-O)

3.1664

104.89

-0.08

21

[Fe2(OMe)2L4]

L=(O-O)

3.103

102.00

-15.4

72

Λ,Λ-

L=(N2O2)

3.195

106.54

-18.0

73

[Fe2(OMe)2L4]

L=(O-O)

3.087

103.70

-19.0

72

[Fe2L2(OMe)2L'4]·2MeOH

L=(N-N)

3.191

104.70

-26.8

74

3.153

104.50

-28.6

74

Complex

Denatet of

Fe…F

ligands

e

[Fe2(OMe)2L2(NCS)4]

L=(N-N)

[Fe2(OMe)2L2Cl2]

[Fe2(OMe)2L2]2.Et2O.H2O

L'= (O )monodentate ‫־‬

[Fe2L2(OMe)2L'4]·2MeOH

L=(N-N) L'= (O )monodentate ‫־‬

[Fe2(OMe)2L2Cl4]

L= (N-NH2)

3.180

104.44

-29.4

75

[Fe2(OMe)2L2(N3)4]

L=(N-NH)

3.137

104.08

-13.9

76

[Fe2(OMe)2L2(NCS)4]

L=(N-NH)

3.141

104.50

-19

76

[Fe2L2(OMe)2(CH3OH)2]

L=(O-Se-O)

3.188

106.11

-13.2

77

[Fe2(OMe)2L4]

L=(N-O)

3.085

102.73

-27.4

78

[Fe2(OMe)2L4]

L=(N-O)

3.090

103.50

-26

79

[Fe2(OMe)2L2Cl2]

L=(N-NH-N)

3.089

103.41

-27.05

80

[Fe2(OMe)2L2(NCS)2]

L=(N-N-O)

3.178

105.75

-29.45

81

[Fe2(OMe)2L2Cl2]

L=(O-N-NH)

3.25

104.35

-27.3

82

[Fe2L2(OMe)2]

L=(O4)

3.1345

104.20

-12.1

83

[Fe2L2(OMe)2]

L=(O4)

3.164

104.97

- 13.5

84

616 617

29

618

Table 6 Cyclic voltammetric data for complex 3 in CH3OH solution. Redox couple

Epc

Epa

E1/2

∆E

2FeII/FeIIFeIII II

III

Fe Fe /2Fe III

-0.0284

0.1020

0.0368

0.1304

III

0.4911

0.6723

0.5817

0.1812

IV

0.8708

0.9615

0.9162

0.0907

IV

0.8708

1.1226

0.9967

0.2518

III

2Fe /Fe Fe III

IV

Fe Fe /2Fe

619 620 621 622

(a)

623 624 625

(b)

30

626 627

Fig. 1 Paramagnetic 1H NMR of complexes (a) 1 and (b) 3 in CDCl3. * is unknown impurity.

628

629

31

630 631 632

Fig. 2 Thermal behavior of: (a) 1 and (b) 3.

633

32

634

(a)

635 636 637 638

(b)

639 640 641

Fig. 3 The molecular structure of (a) 1 with the atom-numbering scheme and 40% probability

642

displacement ellipsoids and (b) 2 with the atom-numbering scheme and 50% probability displacement

643

ellipsoids. Symmetry code for 1 is 3/2-x,y,1/2-z.

644

33

645

(a)

646 647

648 649 650 651 652

(b)

Fig. 4 Labeled diagram of (a) 3 and (b) Labeled diagram of 4. Thermal ellipsoids are at 50% probability level. Symmetry codes (a) for 3 is –x,2-y,1-z and (b) for 4 is 1-x,1-y,-z.

34

653

(a)

654 655

(b)

656

657 658

Fig. 5 Crystal packing diagrams for complex (a) 3 and (b) 4. Some S atom interactions are shown as blue

659

dash lines.

660

35

661

(a)

8

T = 2.0 K 0.1

2

T = 4.6 K

Mmol/(NAµB)

4

χmol/(10−6 m3 mol−1)

µeff./µB

6

0.5

0.0 0

50

100

150

200

0.0

0 0

50

100

150

200

250

0

300

1

2

3

4

5

6

7

B/T

T/K

662

(b) 2

8 χmol/(10−6 m3 mol−1)

6

10

T = 2.0 K

8 6 4 2

Mmol/(NAµB)

663

0.0

0.1

0.2

0.3

0.4

0.5

4

8

χmol/(10−6 m3 mol−1 )

µeff./µB

0

2

T = 4.6 K 1

6

4

2

0 0

50

0 0

50

100

150

200

250

300

0 0

1

2

3

4

5

6

7

B/T

T/K

664 665

Fig. 6 Magnetic functions for the complex (a) 4 and (b) 3. Left – temperature dependence of the effective

666

magnetic moment (inset – molar magnetic susceptibility); right – field dependence of the magnetization

667

per formula unit. Lines – fitted data.

668

36

20 0 -20

J/cm

-1

-40 -60 -80 -100 -120 -140 90

100

110

120

130

140

150

α(Fe-O-Fe) /o 669 670

Fig. 7 Correlation between Fe-O-Fe bond angles and J values. Empty circles – data collected by Gorun

671

and Lippard [71]; full points – data according to Table 5. Confidence and prediction intervals are shown

672

at the 95 % probability level. Correlation line: J[cm-1] = 388 – 3.92 α[deg]; r = –0.86.

673 674

37

675 676

Fig. 8 Cyclic voltammograms of complex 3 in CH3OH in the region of -0.2 to 1.5 V. 677

38

Graphical Abstract

Synthesis, characterization, electerochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes Farsheed Shahbazi-Raz, Vahid Amani, Ehsan Bahojb Noruzi, Nasser Safari, Roman Boča, Ján Titiš and Behrouz Notash

Synthesis, characterization, electerochemical and magnetic study of mixed ligand mono iron and O-methoxy bridged diiron complexes Farsheed Shahbazi-Raz, Vahid Amani, Ehsan Bahojb Noruzi, Nasser Safari, Roman Boča, Ján Titiš, Behrouz Notash

The complexes cis-[Fe(5,5'-dmbipy)2Cl2]Cl and cis-[Fe(5,5'-dmbipy)2Cl2]ClO4 (5,5'-dmbipy is 5,5'-dimethyl-2,2'-bipyridine) were synthesized as precursors of new diiron complexes. The diiron complex [Fe(5,5'-dmbipy)(NCS)2(μ-OCH3)]2 was obtained from the reaction of KSCN with cis-[Fe(5,5'-dmbipy)2Cl2]Cl and cis-[Fe(5,5'-dmbipy)2Cl2]ClO4. Complex [Fe(5,5'-dmbipy)(NCS)2(μ-OCH3)]2 was obtained from the addition of KSCN to FeCl2.4H2O and then 5,5'-dmbipy. A new binuclear iron(III) complex [Fe(4bt)(NCS)2(μ-OCH3)]2 (4bt is 4,4'-bithiazole) has also been synthesized from the reaction of [Fe(4bt)3](NO3)2 with KSCN in a mixture of methanol/acetonitrile solvent.

712

•

Two new mononuclear iron(III) complexes and two new methoxy bridge diiron(III) complexes were synthesized and fully characterized.

713 714

•

Structures of dimeric iron are preserved in solution.

715

•

Iron centers are diamagnetically coupled in dimmer complexes.

716

•

Evidence for FeIII/FeIV redox couples is presented by electrochemistry.

717

41