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Spin‐Crossover Behaviors Based on Intermolecular Interactions for Cobalt(II) Complexes with Long Alkyl Chains
Author(s) -
Komatsu Yasuka,
Kato Kazuya,
Yamamoto Yuuki,
Kamihata Hidenobu,
Lee Young Hoon,
Fuyuhiro Akira,
Kawata Satoshi,
Hayami Shinya
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201101040
Subject(s) - chemistry , crystallography , spin crossover , terpyridine , hydrogen bond , octahedron , cobalt , spin transition , intermolecular force , triclinic crystal system , molecule , magnetic susceptibility , alkyl , stereochemistry , spin states , crystal structure , inorganic chemistry , organic chemistry , metal
A new family of terpyridine (terpy)‐based spin‐crossover cobalt(II) complexes, [Co(HO–C n ‐terpy) 2 ](BF 4 ) 2 [ n = 6 ( 1 ), 8 ( 2 ), 10 ( 3 ), 12 ( 4 ), and 14 ( 5 )] that possesses a hydroxy‐appended long alkyl chain present on the terpyridine skeleton was synthesized and characterized by X‐ray structure analysis and temperature‐dependent magnetic susceptibility. In the solid state, the compounds 1·H 2 O , 4 , and 5·H 2 O were crystallized in the triclinic P $\bar {1}$ space groups, and their central cobalt(II) ion was coordinated by six nitrogen atoms from two terpyridine units to form a pseudo‐octahedral symmetry. In the case of 1·H 2 O , one of the terminal hydroxy substituents was involved in hydrogen bonding with a water molecule. For compound 4 , on the other hand, both of terminal hydroxy units form a short intermolecular contact with the BF 4 – anion. The temperature‐dependent magnetic behavior of 1 and 2 showed a gradual spin crossover, whereas 3 and 4 revealed an abrupt spin transition with a wide thermal hysteresis loop (Δ T = 21 K, T 1/2 ↑ = 316 K, and T 1/2 ↓ = 295 K for 3 ; Δ T = 40 K, T 1/2 ↑ = 348 K, and T 1/2 ↓ = 308 K for 4 ), and 5 exhibits “reverse spin transition” (Δ T = 17 K, T 1/2 ↑ = 214 K, and T 1/2 ↓ = 231 K). It has been suggested that compounds 3 and 4 form stronger intermolecular interactions through the fastener effect and hydrogen bonding than 1 and 2 . On the basis of a comparison of the resulting magnetic behaviors of the compounds that contain long alkyl chains with a hydroxy group at the end, it was found that the long alkyl chains with the terminal hydroxy group could induce stronger intermolecular interactions between molecules. However, there are many short contacts through the counteranions for 5·H 2 O , but thermal motion of the long alkyl chains can be expected. Compound 5 exhibits “reverse spin transition” induced by a structural phase transition.