Solid-State NMR of 1-Propyltetrazole Complexes of Iron(II) and Zinc(II). 1.1H Spin–Lattice Relaxation Time

✍ Scribed by Mónika Bokor; Tamás Marek; Kálmán Tompa

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 188 KB
• Volume: 122
• Category: Article
• ISSN: 1064-1858
• DOI: 10.1006/jmra.1996.0191

✦ Synopsis

Proton spin-lattice relaxation times were measured between 2.2 symmetry (Fig. 1) and the monodentate 1-propyltetrazole K and room temperature in [Zn(ptz) 6 ](BF 4 ) 2 (ptz Å 1-n-propylligands coordinate via their N(4) atoms. The two molecular 1H-tetrazole) and in the spin-crossover complex [Fe(ptz) 6 ](BF 4 ) 2 . structures are isomorphous. The [Zn(ptz) 6 ](BF 4 ) 2 crystals Three different types of intramolecular motion of the propyl group are rhombohedral (R3 V , Z Å 3) in the entire temperature are suggested in [Zn(ptz) 6 ](BF 4 ) 2 , namely tunneling and classical range studied while [Fe(ptz) 6 ](BF 4 ) 2 shows a crystallorotation of methyl groups and rotation of methylene groups. Corregraphic structural phase transition at Ç135 K (8, 9), simultalation times and activation energies are calculated for tunneling neously with the thermally induced low-spin (LS) to highrotation of the CH 3 group and for the classical (hindered) rotations spin (HS) transition. In the LS state the crystal structure is of -CH 3 and -CH 2 -CH 3 as reorientations over a three-well asymtriclinic (P1 V ) and above the spin crossover [at about 130 K, metrical potential. In [Fe(ptz) 6 ](BF 4 ) 2 the mechanism for the paramagnetic relaxation is found to be of the rapid-diffusion type with hysteresis; (1-9)] it is R3 V like the zinc complex; i.e., according to the theory of Lowe and Tse, and the intramolecular the crystal structures of the zinc and the HS iron complex motions are suggested to be the same as for the zinc complex. are the same. The relation of the phase transition to the spin