Slow Magnetic Relaxation of [Et3NH]2Mn(CH3CN)4(H2O)2] [Mn10O4(biphen)4Br12] (biphen=2,2′-biphenoxide) at Very Low Temperature

✍ Scribed by A.L. Barra; Andrea Caneschi; Dante Gatteschi; David P. Goldberg; Roberta Sessolici

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 134 KB
• Volume: 145
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8185

✦ Synopsis

The high-5eld EPR spectra of a mixed valence cluster compound of formula [Et 3 NH] 2 [Mn(CH 3 CN) 4 (H 2 O) 2 ] [Mn 10 O 4 (biphen) 4 Br 12 ] con5rm that the high-spin ground state (S ‫؍‬ 12) of the cluster has a negative zero-5eld splitting, D ‫؊؍‬ 0.037(1) cm ؊1 . The reversal of the magnetization at low temperature should therefore overcome an energy barrier corresponding to "D"S 2 , which corresponds to ca. 7.7 K. Slow relaxation of the magnetization is detected below 1 K by ac magnetic susceptibility and the characteristic time follows approximately an Arrhenius law, where the height of the barrier is 7.0 K. The counterion, constituted by a manganese(II) complex, is easily oxidized, and aged samples seem to contain amorphous Mn 3 O 4 .