Phase relation and molecular motions of mixed-ligand complex [Zn(hfac)2(tmen)] as studied by calorimetry and 1H NMR measurement
✍ Scribed by T.M Yoshida; K Wada; M Oguni; T Chiba; Y Fukuda
- Book ID
- 104152114
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 184 KB
- Volume
- 60
- Category
- Article
- ISSN
- 0022-3697
No coin nor oath required. For personal study only.
✦ Synopsis
Heat capacities of a molecular mixed-ligand complex [Zn(hfac) 2 (tmen)] were measured in the temperature range between 13 and 383 K with an adiabatic calorimeter and the proton magnetic spin-lattice relaxation times (T 1 , T 1r and T 1D ) were measured in the range between 130 and 330 K, where hfac and tmen denote hexafluoroacetylacetonato and N,N,N H ,N H -tetramethylethylenediamine, respectively. The orientationally disordered crystalline phase, designated as phase I, was found to appear only in the supercooled meta-stable state: The temperature, enthalpy and entropy of the fusion were T fus 370 ^1 K, D fus H 2:2 ^0:1 kJ mol Ϫ1 and D fus S 5:8 ^0:3 J K Ϫ1 mol Ϫ1 , respectively. The small entropy was discussed in relation to the low globularity in the shape of the complex molecule. High-and low-temperature stable crystalline phases (II and III) were found: The temperature, enthalpy and entropy of the fusion from the phase II were T fus 375 ^1 K, D fus H 24:32 ^0:02 kJ mol Ϫ1 and D fus S 65:4 ^0:1 J K Ϫ1 mol Ϫ1 , respectively. The temperature, enthalpy and entropy of the III-to-II phase transition were T trs 293:8 ^0:1 K, D trs H 4:115 ^0:005 kJ mol Ϫ1 and D trs S 14:02 ^0:02 J K Ϫ1 mol Ϫ1 , respectively. Glass transitions were found at T g 114 ^1 K in phase III and at T g 116 ^1 K in the supercooled metastable phase II, respectively, and interpreted as attributed to the freezing-in of the rearrangement motion between d and l conformations of tmen. The energy difference between the two conformations was less than 0.25 kJ mol Ϫ1 , and the activation energy for the conformational change was D1 a 33 ^1 kJ mol Ϫ1 . The activation energy for the C 3 reorientation of methyl groups within the ligand tmen was D1 a 14 ^1 kJ mol Ϫ1 .