Metallacoronates or One-Dimensional Polymers through Self-Assembly—Influence of Templates and Hydrogen Bonding on Product Formation
✍ Scribed by Rolf W. Saalfrank; Ingo Bernt; Frank Hampel
- Publisher
- John Wiley and Sons
- Year
- 2001
- Tongue
- English
- Weight
- 157 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0044-8249
No coin nor oath required. For personal study only.
✦ Synopsis
Dedicated to Professor Dieter Sellmann on the occasion of his 60th birthday
Design and synthesis of supramolecular inorganic structures with novel properties have provided exciting new possibilities. [1] We reported on the template-mediated selfassembly of six-and eight-membered iron coronates [Na & Fe 6 (L 1 ) 6 ] (1) and [Cs & Fe 8 (L 1 ) 8 ] (2). [2] They were prepared from triethanolamine (H 3 L 1 ), iron(iii) chloride, and sodium hydride or cesium carbonate, respectively (Scheme 1). A common feature of complexes 1 and 2 is that the ethanolato m 1 -O donors solely function as ligands for the coordinative saturation of the iron centers, whereas the ethanolato m 2 -O donors are structure-determining. Consequently, reaction of N-substituted diethanolamines 3 (H 2 L 2 ) toluene (1 mL). The clear solution was heated to 45 8C. After 0.5 h the mixture became cloudy and after 16 h a gel had formed. The product was stored at 45 8C for 30 days. During this ageing period no significant syneresis (contraction) was observed. The gel was dried at 150 8C/10 À2 Torr. Analogous reactions with a tenfold amount of starting materials were also successful.
In a similar experiment B-trichloroborazene (3.9 g) and bis(trimethylsilyl)carbodiimide (9.5 mL) were dissolved in dry THF (50 mL). After 2.5 h reflux the content of the flask suddenly solidified to form a monolithic colorless gel body. The gel was dried at 140 8C/10 À2 mbar/2.5 h and 190 8C/ 10 À2 mbar/0.5 h. Owing to the short ageing period this xerogel contained significant amounts of chlorine (4.75 mass%) and silicon (6.3 mass%).
In other variants B-trichlorborazene (0.5 ± 1.5 g) was dissolved in toluene (5 ± 10 mL) or an excess of bis(trimethylsilyl)carbodiimide and stored at 45 8C. The mixtures formed a gel after 1 ± 3 days depending on the concentration. After an ageing period of 2 ± 40 days the gels were dried at 150 8C/10 À2 Torr.
The xerogels were pyrolyzed in Quartz Schlenk tubes under argon at 400, 600, 800, 1000, and 1200 8C for 2 h using a heating rate of 100 8C h À1 . Further annealing at 1600 and 1800 8C in Ar and at 2000 8C in He was performed in a graphite furnace. Heating rates of 600 8C h À1 up to 1200 8C followed by 300 8C h À1 and holding times of 4 h were applied.
The yield of the xerogels, based on the amount of B-trichloroborazene and the idealized structure depicted in Scheme 1, was 110 ± 125 %, which is because of residual trimethylsilyl end groups. The yield of the B/C/N material obtained at 1200 8C was 58 ± 61 % based on the xerogel. Using this amorphous product as a reference the ceramic (boron carbide) yield at 2000 8C is 56%.
The xerogels and pyrolysis products were investigated using FT-IR (Perkin-Elmer FTIR 1750, KBr pellets), Raman (Bruker IFS 55), and 11 B NMR spectroscopy (Bruker MSL 400 spectrometer, external standard: (CH 3 CH 2 ) 2 O ´BF 3 , 128.28 MHz) as well as nitrogen absorption measurements (Quantachrome Autosorb-3B), elemental analysis (see Table 1), X-ray diffraction (STOE STADI-P-diffractometer, Cu Ka ), and TGA-MS (Netzsch STA 429 coupled with a mass spectrometer Balzers QMG 420).