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A Variety of Spin‐Crossover Behaviors Depending on the Counter Anion: Two‐Dimensional Complexes Constructed by NH⋅⋅⋅Cl − Hydrogen Bonds, [Fe II H 3 L Me ]Cl⋅X (X = PF 6 − , AsF 6 − , SbF 6 − , CF 3 SO 3 − ; H 3 L Me = Tris[2‐{[(2‐methylimidazol‐4‐yl)methylidene]amino}ethyl]amine)
Author(s) -
Yamada Masahiro,
Hagiwara Hiroaki,
Torigoe Haruna,
Matsumoto Naohide,
Kojima Masaaki,
Dahan Françoise,
Tuchagues JeanPierre,
Re Nazzareno,
Iijima Seiichiro
Publication year - 2006
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500972
Subject(s) - crystallography , chemistry , monoclinic crystal system , hydrogen bond , imidazole , ion , bond length , crystal structure , spin crossover , stereochemistry , molecule , organic chemistry
A family of spin‐crossover (SC) complexes, [Fe II H 3 L Me ]Cl⋅X (X − = PF 6 − , AsF 6 − , SbF 6 − , CF 3 SO 3 − ), 1 – 4 , has been synthesized, in which H 3 L Me denotes the hexadentate N 6 tripod‐like ligand tris[2‐{[(2‐methylimidazol‐4‐yl)methylidene]amino}ethyl]amine, containing three imidazole groups, with a view to establishing the effect of the counter anion on the SC behavior. These complexes have been found to crystallize in the same monoclinic crystal system with similar cell dimensions. The general crystal structure consists of a two‐dimensional (2D) extended network constructed by NH⋅⋅⋅Cl − hydrogen bonds between Cl − and the imidazole NH groups of three neighboring [Fe II H 3 L Me ] 2+ ions, while the anion X exists as an isolated counter anion and occupies the space between the 2D sheets. Magnetic susceptibilities and Mössbauer spectra have revealed a variety of SC behaviors depending on the counter anion, including a one‐step HS ⇄ (HS + LS)/2 ( 1 , X = PF 6 − ), a two‐step HS ⇄ (HS + LS)/2 ⇄ LS with a slow thermal relaxation ( 2 , X = AsF 6 − ), a gradual one‐step HS ⇄ LS ( 3 , X = SbF 6 − ), and a steep one‐step HS ⇄ LS with hysteresis ( 4 , X = CF 3 SO 3 − ). The complexes assume the space group P 2 1 / n in the HS state, P 2 1 in the HS + LS state, and P 2 1 / n in the LS state. The FeN bond lengths and the N‐Fe‐N bond angles are indicative of the HS, HS + LS, and LS states. The molecular volumes, V , of the counter anions have been evaluated by quantum‐chemical calculations as follows: 53.4 Å 3 (BF 4 − ), 54.4 Å 3 (ClO 4 − ), 73.0 Å 3 (PF 6 − ), 78.5 Å 3 (AsF 6 − ), 88.7 Å 3 (SbF 6 − ), and 86.9 Å 3 (CF 3 SO 3 − ). The size and shape of the counter anion affects the flexible 2D network structure constructed by the hydrogen bonds, leading to modifications of the SC behavior. These estimated relative sizes of the counter anions correlate well with the observed SC behaviors.