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

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

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

Vladimir-Prelog-Weg 5, 8093 Zürich, Switzerland

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 fromAcros (Geel, Belgium).

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

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

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

Synthesis of the triazole ligands and Fe2+-triazole complexes

a)

b)

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 underreflux to 70 °C for 2.5 h, 1-octadecylamine (29.7 mmol, 8.000 g) was added. Thereaction was continued at 70 °C for 17 h. Subsequently, the mixture was allowedto cool down to room temperature and the solvent was evaporated with a rotaryevaporator (330mbar, 40 °C). Finally, the product was recrystallized twice from hotn-heptane (300 mL) and dried in vacuo(0.1mbar, 12 h).Yield: 7.578 g (0.024mmol, 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 13.00% (13.07%). 1H-NMR (CDCl3,300 MHz): 0.87 (m, 3 H, CH3), 1.25 (m, 14 H, CH2), 1.80 (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-1): 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 using1-hexadecylamine instead of 1-octadecylamine.Yield: 63%, white crystals. Melting temperature: 74 °C. Elemental analysisfor C18H35N3(molar mass: 293.50 g/mol, calculated values in brackets): C 73.62%(73.66%), H 11.87% (12.02%), N 14.19% (14.32%). 1H-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-CH2), 8.14 (s, 2 H, N=CH-N). MIR (in cm-1): 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 using1-tetradecylamine instead of 1-octadecylamine.Yield: 70%, white crystals. Melting temperature: 66 °C. Elemental analysisfor C16H31N3(molar mass: 265.44 g/mol, calculated values in brackets): C 72.63%(72.40%), H 11.73% (11.77%), N 16.13% (15.83%). 1H-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-CH2), 8.14 (s, 2 H, N=CH-N). MIR (in cm-1): 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].

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

C18trz (1.04 mmol,334 mg) was dissolved in methanol (15 mL) and added to a solutionof [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 thetwo solutions. After stirring the suspension for 1 h the product was filtered off (thepowder 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 forC80H131N9O6S2Fe ∙3H2O (molar mass: 1489.00g/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)2was synthesized analogously to [Fe(C18trz)3](2ns)2using C16trzinstead of C18trz.Yield: 84%, pink powder. Elemental analysis for C74H119N9O6S2Fe ∙2H2O (molarmass: 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)2was synthesized analogously to [Fe(C18trz)3](2ns)2using C14trzinstead of C18trz. Yield: 73%, pink powder. Elemental analysis for C68H107N9O6S2Fe ∙H2O (molarmass: 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

4-Dodecylbenzene sulfonic acid (3.58 mmol,1.169 g) was added to a mixture ofFe0powder (grain size 150 µm; 1.79mmol,100 mg) and ascorbic acid (0.90 mmol,158 mg) in methanol (25 mL). The mixture was stirred under reflux (70 °C) for17 h. Thereafter, it was allowed to cool to room temperature, filtered and dilutedwith 50mL of methanol. After addition of ascorbic acid (0.45mmol,98 mg) anda solution of 1-octadecylamine (5.37 mmol,1.727 g) in methanol (40 mL) a whiteprecipitate formed. The mixture was stirred for 40 min. The precipitate was filtered off (thereupon the powder turned pink) and dried in vacuo (0.1mbar, 12 h).Yield: 2.692 g (1.62 mmol, 90%), pink soft substance. Elemental analysis forC96H175N9O6S2Fe ∙1.4H2O (molar mass: 1696.69 g/mol, calculated values in brackets):C 67.60% (67.96%), H 10.62% (10.48%), N 7.46% (7.43%), H2O 1.47% (1.49%).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).

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

[Fe(C16trz)3](DBS)2was prepared analogously to [Fe(C18trz)3](DBS)2using C16trz instead of C18trz.Yield: 91%, pink soft substance. Elemental analysis for C90H163N9O6S2Fe ∙2H2O(molar mass: 1623.34 g/mol, calculated values in brackets): C 66.66% (66.59%), H10.11% (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).

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

[Fe(C14trz)3](DBS)2was prepared analogously to [Fe(C18trz)3](DBS)2using C14trzinstead of C18trz.Yield: 75%, pink soft substance. Elemental analysis for C84H151N9O6S2Fe ∙3 H2O(molar mass: 1557.20g/mol, calculated values in brackets):C 64.64% (64.79%), H9.77% (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).

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

Table SI-1Spin-crossover temperatures in °C during heating (↑) and cooling (↓) determinedby DSC measurements at heating and cooling rates of 10 °C/min. The peaks detected for2ns–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-triazolenickel 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 Chem53:3546

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