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Spin Crossover in a Series of Iron(II) Complexes of 2-(2-Alkyl-2H-tetrazol-5-yl)-1,10-phenanthroline:  Effects of Alkyl Side Chain, Solvent, and Anion

2-(2H-Tetrazol-5-yl)-1,10-phenanthroline (HL0), its alkyl-substituted derivatives (L n , where n = 1−8, 10, 12, 14, and 16, denoting the carbon atom number of the alkyl chain) at the 2H position of the tetrazole ring, and their iron(II) complexes (a for [Fe(L0)2], n a for [Fe(L n )2](ClO4)2, and n b...

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Bibliographic Details
Published in:Inorganic chemistry 2007-04, Vol.46 (7), p.2541-2555
Main Authors: Zhang, Wen, Zhao, Fei, Liu, Tao, Yuan, Mei, Wang, Zhe-Ming, Gao, Song
Format: Article
Language:English
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Summary:2-(2H-Tetrazol-5-yl)-1,10-phenanthroline (HL0), its alkyl-substituted derivatives (L n , where n = 1−8, 10, 12, 14, and 16, denoting the carbon atom number of the alkyl chain) at the 2H position of the tetrazole ring, and their iron(II) complexes (a for [Fe(L0)2], n a for [Fe(L n )2](ClO4)2, and n b for [Fe(L n )2](BF4)2) were synthesized and characterized. The crystal structures of a, a·CH 3 OH, 1a·CH 3 OH, 1b·CH 3 OH·CH 3 CN, 2a·H 2 O, 2b·H 2 O, 4b·CH 3 OH, 5a·H 2 O, 5b·H 2 O, 6a, 6b, 7a, 7b, and 16a are described, along with thermal analyses. a undergoes an abrupt spin crossover (SCO) at 255 K with a hysteresis loop of 6 K. a·CH 3 OH, 2a·H 2 O, and 2b·H 2 O exhibit irreversible SCO behaviors due to the loss of solvent molecules upon heating. 3a, 3b, 4a, and 5a·H 2 O show simple spin transitions above 350 K. The desolvated samples of 4b·CH 3 OH and 5b·H 2 O undergo two-step spin transitions. 16a exhibits a two-step SCO behavior between 100 and 300 K, corresponding to sequential phase transitions from the low-spin (LS) phase to the intermediate phase and then to the high-spin phase, respectively, proved by crystal structure analysis and 57Fe Mössbauer spectroscopy. 1a·CH 3 OH, 10a, 10b, 12a, 12b, 14a, 14b, and 16b show gradual and incomplete SCO behaviors after cooling down from 400 K. 1b·CH 3 OH·CH 3 CN, 6a, 6b, 7a, 7b, 8a, and 8b remain in the LS state even at 400 K. This proves that the alkyl side chains, together with the solvent molecules and anions, play a crucial role in the complicated SCO behaviors in this system.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic062062h