Canted Ferromagnetism and Other Magnetic Phenomena in Square-Planar, Neutral Manganese(II) and Iron(II) Octaethyltetraazaporphyrins
详细信息 查看全文
- 作者：Scott P. Sellers ; Brenda J. Korte ; Jeffrey P. Fitzgerald ; William M. Reiff ; and Gordon T. Yee
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：May 20, 1998
- 年：1998
- 卷：120
- 期：19
- 页码：4662 - 4670
- 全文大小：283K
- 年卷期：v.120,no.19(May 20, 1998)
- ISSN：1520-5126
文摘
Iron(II) octaethyltetraazaporphyrin has been discovered toexist as two polymorphs at roomtemperature, 
- and 
-Fe(OETAP). This has beenestablished by X-ray powder diffraction and scanningelectronmicroscopy. Both ac and dc SQUID magnetometry show that the phase is a soft molecular ferromagnetwith TCurie = 2.8 K. The phasepossesses the same number of unpaired spins and a similar gvalue, but itdoes not order above ~1 K. Zero-field splitting is likelycompeting with ferromagnetic coupling in thiscompound. 57Fe Mössbauer spectroscopy hasbeen used to support the local structural similarity betweenthetwo phases and to study the ferromagnetic transition. Theisomorphous manganese analogue of -Fe(OETAP),-Mn(OETAP), expected to be a ferromagnet with a higherTCurie, exhibits many characteristicsofferromagnetism, notably hysteresis at 1.8 K withHcoer = 2.5 kG and Mrem= 4 kemu-G/mol. However, incontrast to ferromagnetic -Fe(OETAP), -Mn(OETAP) showsstrongly frequency-dependent ac susceptibilityin the range from 1 to 1000 Hz, indicating that it exists in aspin-glass-like state. This result underscores theneed for frequency-dependent ac magnetometry to fully characterizeferromagnetic molecular materials.
- and -Fe(OETAP). This has beenestablished by X-ray powder diffraction and scanningelectronmicroscopy. Both ac and dc SQUID magnetometry show that the phase is a soft molecular ferromagnetwith TCurie = 2.8 K. The phasepossesses the same number of unpaired spins and a similar gvalue, but itdoes not order above ~1 K. Zero-field splitting is likelycompeting with ferromagnetic coupling in thiscompound. 57Fe Mössbauer spectroscopy hasbeen used to support the local structural similarity betweenthetwo phases and to study the ferromagnetic transition. Theisomorphous manganese analogue of -Fe(OETAP),-Mn(OETAP), expected to be a ferromagnet with a higherTCurie, exhibits many characteristicsofferromagnetism, notably hysteresis at 1.8 K withHcoer = 2.5 kG and Mrem= 4 kemu-G/mol. However, incontrast to ferromagnetic -Fe(OETAP), -Mn(OETAP) showsstrongly frequency-dependent ac susceptibilityin the range from 1 to 1000 Hz, indicating that it exists in aspin-glass-like state. This result underscores theneed for frequency-dependent ac magnetometry to fully characterizeferromagnetic molecular materials.