Irene Bräunlich, Samuel Lienemann, Christiane Mair, Paul Smith and Walter Caseri

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Tuning the spin-crossover temperature of polynuclear iron(II) triazole complexes in solution by water and preparation of thermochromic fibers

Eidgenössische Technische Hochschule (ETH) Zürich, Department of Materials,

Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland

1 General

Sodium 2-naphthalene sulfonate (Na(2ns)) was purchased from Alfa Aesar GmbH (Karlsruhe, Germany), L-ascorbic acid from Hänseler AG (Herisau, Switzerland), 1-hexadecylamine and 4- dodecylbenzene sulfonic acid (mixture of isomers) from Sigma-Aldrich (Buchs, Switzerland), iron(II) chloride tetrahydrate and iron(0) powder (grain size 150 µm) from Merck Chemicals (Darmstadt, Germany), 1-octadecylamine and N-formyl hydrazine from ABCR GmbH & Co. KG (Karlsruhe, Germany) and 1-tetradecylamine and triethyl orthoformate from Acros (Geel, Belgium).

Differential scanning calorimetry was performed with a DSC822 instrument (Mettler Toledo, Greifensee, Switzerland) at heating rates of 10 °C/min under nitrogen atmosphere.

1H-NMR spectra were measured on a Bruker Ultrashield 300 MHz Fourier-transform spectrometer. The multiplicities are indicated as follows: s (singlet), t (triplet), m (multiplet).

Elemental analyses were performed by the microanalytic laboratory of the Laboratory of Organic Chemistry (LOC), ETH Zurich. Water content determination of iron-triazole solutions in toluene was carried out by a combustion analysis in which the exhaust was analyzed by Karl-Fischer titration.

2 Synthesis of the triazole ligands and Fe2+-triazole complexes a)

O O R O MeOH R N H2N + NH2 + N N H O - EtOH H N - H2O b)

MeOH 3 C trz 0 2+ - n Fe + 2 DBSA Fe (d) + 2 DBS (d) [Fe(Cntrz)3](DBS)2 - H2 c)

Fig. SI-1 Reaction schemes of the synthesis of alkyl-substituted triazole ligands according to Bayer [1] (a), Fe2+-triazole complexes with the counter ion DBS– (b) and Fe2+-triazole complexes with the counter ion 2ns– (c).

Synthesis of 4-octadecyl-1,2,4-triazole (C18trz)

4-Octadecyl-1,2,4-triazole was synthesized following the Bayer synthesis route.22 Triethylorthoformate (44.5 mmol, 7.4 mL) was added to a solution of N-formylhydrazine (29.7 mmol, 1:783 g) in methanol (20 mL). After heating the mixture under reflux to 70 °C for 2.5 h, 1- octadecylamine (29.7 mmol, 8.000 g) was added. The reaction was continued at 70 °C for 17 h. Subsequently, the mixture was allowed to cool down to room temperature and the solvent was evaporated with a rotary evaporator (330 mbar, 40 °C). Finally, the product was recrystallized

3 twice from hot n-heptane (300 mL) and dried in vacuo (0.1mbar, 12 h). Yield: 7.578 g (0.024 mmol, 79%), white crystals. Melting temperature: 79 °C. Elemental analysis for C20H39N3 (molar mass: 321.55 g/mol, calculated values in brackets): C 74.67% (74.71%), H 11.93% (12.22%), N

1 13.00% (13.07%). H-NMR (CDCl3, 300 MHz): 0.87 (m, 3 H, CH3), 1.25 (m, 14 H, CH2), 1.80

-1 (m, 2 H, N-CH2-CH2), 4.00 (t, 2 H, J(H, H) 7.2, N-CH2), 8.14 (s, 2 H, N=CH-N). MIR (in cm ): 641 (m), 719 (m), 883 (m), 959 (w), 984 (w), 1053 (m), 1081 (m), 1192 (m), 1472 (m), 1536 (w), 2851 (m), 2916 (s), 2976 (w), 3100 (w).

Synthesis of 4-hexadecyl-1,2,4-triazole (C16trz)

4-Hexadecyl-1,2,4-triazole was prepared analogously to 4-octadecyl-1,2,4-triazole using 1- hexadecylamine instead of 1-octadecylamine. Yield: 63%, white crystals. Melting temperature:

74 °C. Elemental analysis for C18H35N3 (molar mass: 293.50 g/mol, calculated values in brackets):

1 C 73.62% (73.66%), H 11.87% (12.02%), N 14.19% (14.32%). H-NMR (CDCl3, 300 MHz):

0.88 (m, 3 H, CH3), 1.25 (m, 12 H, CH2), 1.81 (m, 2 H, N-CH2-CH2), 4.00 (t, 2 H, J(H, H) 7.2, N-

-1 CH2), 8.14 (s, 2 H, N=CH-N). MIR (in cm ): 641 (m), 719 (m), 883 (m), 959 (w), 984 (w), 1053 (m), 1081 (m), 1192 (m), 1472 (m), 1536 (w), 2851 (m), 2916 (s), 2976 (w), 3100 (w).

Synthesis of 4-tetradecyl-1,2,4-triazole (C14trz)

4-Tetradecyl-1,2,4-triazole was prepared analogously to 4-octadecyl-1,2,4-triazole using 1- tetradecylamine instead of 1-octadecylamine. Yield: 70%, white crystals. Melting temperature:

66 °C. Elemental analysis for C16H31N3 (molar mass: 265.44 g/mol, calculated values in brackets):

1 C 72.63% (72.40%), H 11.73% (11.77%), N 16.13% (15.83%). H-NMR (CDCl3, 300 MHz):

0.88 (m, 3 H, CH3), 1.25 (m, 10 H, CH2), 1.81 (m, 2 H, N-CH2-CH2), 4.00 (t, 2 H, J(H, H) 7.2, N-

-1 CH2), 8.14 (s, 2 H, N=CH-N). MIR (in cm ): 641 (m), 719 (m), 883 (m), 959 (w), 984 (w), 1053 (m), 1081 (m), 1192 (m), 1472 (m), 1536 (w), 2851 (m), 2916 (s), 2976 (w), 3100 (w).

Synthesis of hexaaquairon(II) 2-naphthalene sulfonate ([Fe(H2O)6](2ns)2)

This salt was synthesized as reported previously [2].

4 Synthesis of [Fe(C18trz)3](2ns)2

C18trz (1.04 mmol, 334 mg) was dissolved in methanol (15 mL) and added to a solution of

[Fe(H2O)6](2ns)2 (0.35 mmol, 200 mg) and ascorbic acid (0.07mmol, 12 mg) in methanol (10 mL). A white powder precipitated immediately upon mixing of the two solutions. After stirring the suspension for 1 h the product was filtered off (the powder turned slightly pink), washed with methanol (20 mL) and dried in vacuo (0.1mbar, 12 h). Yield: 406 mg (0.28 mmol, 82%), pale pink powder. Elemental analysis for C80H131N9O6S2Fe ∙ 3H2O (molar mass: 1489.00 g/mol, calculated values in brackets): C 64.53% (65.32%), H 9.27% (9.25%), N 8.47% (8.57%). MIR (in cm-1): 567 (m), 676 (s), 745 (w), 817 (w), 1032 (s), 1092 (s), 1190 (s), 1213 (s), 1467 (w), 1558 (w), 2853 (m), 2924 (m), 2976 (w), 3100 (w).

Synthesis of [Fe(C16trz)3](2ns)2

[Fe(C16trz)3](2ns)2 was synthesized analogously to [Fe(C18trz)3](2ns)2 using C16trz instead of

C18trz. Yield: 84%, pink powder. Elemental analysis for C74H119N9O6S2Fe ∙ 2H2O (molar mass: 1386.82 g/mol, calculated values in brackets): C 64.28% (64.10%), H 8.77% (8.94%), N 9.04% (9.09%). MIR (in cm-1): 567 (m), 676 (s), 745 (w), 817 (w), 1032 (s), 1092 (s), 1190 (s), 1213 (s), 1467 (w), 1558 (w), 2853 (m), 2924 (m), 2976 (w), 3100 (w).

Synthesis of [Fe(C14trz)3](2ns)2

[Fe(C14trz)3](2ns)2 was synthesized analogously to [Fe(C18trz)3](2ns)2 using C14trz instead of

C18trz. Yield: 73%, pink powder. Elemental analysis for C68H107N9O6S2Fe ∙ H2O (molar mass: 1284.64 g/mol, calculated values in brackets): C 63.34% (63.58%), H 8.38% (8.55%), N 9.64% (9.81%). MIR (in cm-1): 567 (m), 676 (s), 745 (w), 817 (w), 1032 (s), 1092 (s), 1190 (s), 1213 (s), 1467 (w), 1558 (w), 2853 (m), 2924 (m), 2976 (w), 3100 (w).

Synthesis of [Fe(C18trz)3](DBS)2

5 4-Dodecylbenzene sulfonic acid (3.58 mmol, 1.169 g) was added to a mixture of Fe0 powder (grain size 150 µm; 1.79 mmol, 100 mg) and ascorbic acid (0.90 mmol, 158 mg) in methanol (25 mL). The mixture was stirred under reflux (70 °C) for 17 h. Thereafter, it was allowed to cool to room temperature, filtered and diluted with 50 mL of methanol. After addition of ascorbic acid (0.45 mmol, 98 mg) and a solution of 1-octadecylamine (5.37 mmol, 1.727 g) in methanol (40 mL) a white precipitate formed. The mixture was stirred for 40 min. The precipitate was filtered off (thereupon the powder turned pink) and dried in vacuo (0.1 mbar, 12 h). Yield: 2.692 g (1.62 mmol, 90%), pink soft substance. Elemental analysis for C96H175N9O6S2Fe ∙ 1.4 H2O (molar mass: 1696.69 g/mol, calculated values in brackets): C 67.60% (67.96%), H 10.62% (10.48%), N

-1 7.46% (7.43%), H2O 1.47% (1.49%). MIR (in cm ): 830 (w), 1010 (s), 1036 (s), 1127 (m), 1186 (s), 1216 (s), 1466 (w), 1557 (w), 2853 (m), 2924 (m), 2976 (w), 3100 (w).

[Fe(C16trz)3](DBS)2 was prepared analogously to [Fe(C18trz)3](DBS)2 using C16trz instead of

C18trz. Yield: 91%, pink soft substance. Elemental analysis for C90H163N9O6S2Fe ∙ 2 H2O (molar mass: 1623.34 g/mol, calculated values in brackets): C 66.66% (66.59%), H 10.11% (10.37%), N 7.89% (7.77%). MIR (in cm-1): 830 (w), 1010 (s), 1036 (s), 1127 (m), 1186 (s), 1216 (s), 1466 (w), 1557 (w), 2853 (m), 2924 (m), 2976 (w), 3100 (w).

[Fe(C14trz)3](DBS)2 was prepared analogously to [Fe(C18trz)3](DBS)2 using C14trz instead of

C18trz. Yield: 75%, pink soft substance. Elemental analysis for C84H151N9O6S2Fe ∙ 3 H2O (molar mass: 1557.20 g/mol, calculated values in brackets): C 64.64% (64.79%), H 9.77% (10.16%), N 8.04% (8.10%). MIR (in cm-1): 830 (w), 1010 (s), 1036 (s), 1127 (m), 1186 (s), 1216 (s), 1466 (w), 1557 (w), 2853 (m), 2924 (m), 2976 (w), 3100 (w).

6 Spin-Crossover temperatures of the solids measured by differential scanning calorimetry (DSC)

Table SI-1 Spin-crossover temperatures in °C during heating (↑) and cooling (↓) determined by DSC measurements at heating and cooling rates of 10 °C/min. The peaks detected for 2ns– complexes are very broad.

first heating subsequent heating / cooling [Fe(C18trz)3](DBS)2 60 ↑ 41, ↓ 33 [Fe(C16trz)3](DBS)2 60 ↑ 38, ↓ 28 [Fe(C14trz)3](DBS)2 61 ↑ 36, ↓ 27 [Fe(C18trz)3](2ns)2 62 ↑ ~15, ↓ ~12 [Fe(C16trz)3](2ns)2 65 ↑ ~20, ↓ ~15 [Fe(C14trz)3](2ns)2 no distinct peak, a reversible color change was observed at ~ 60 °C

References

1. Bayer HO, Cook RS, Von Meyer WC (1974) Fungicidal use of a 1,2,4-triazole nickel salt complex. US Patent 3,821,376, June 28, 1974.

2. Bräunlich I, Sánchez-Ferrer A, Bauer M, Schepper R, Knüsel P, Dshemuchadse J, Mezzenga R, Caseri W (2014) Polynuclear Iron(II)− Aminotriazole Spincrossover Complexes (Polymers) In Solution. Inorg Chem 53:3546