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First Dicyanamide‐Bridged Spin‐Crossover Coordination Polymer: Synthesis, Structural, Magnetic, and Spectroscopic Studies
Author(s) -
Genre Caroline,
Jeanneau Erwann,
Bousseksou Azzedine,
Luneau Dominique,
Borshch Serguei A.,
Matouzenko Galina S.
Publication year - 2008
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.200700998
Subject(s) - dicyanamide , spin crossover , crystallography , chemistry , triclinic crystal system , stacking , ligand (biochemistry) , molecule , spin transition , crystal structure , spin states , perchlorate , coordination complex , stereochemistry , metal , inorganic chemistry , ion , organic chemistry , biochemistry , ionic liquid , receptor , catalysis
We report here on the synthesis and characterisation of a first iron(II) spin‐crossover coordination polymer with the dca spacer ligand, having the formula [Fe(aqin) 2 (dca)]ClO 4 ⋅MeOH (aqin=8‐aminoquinoline, dca=dicyanamide), which displays a two‐step complete spin transition. Variable‐temperature magnetic susceptibility measurements and Mössbauer spectroscopy have revealed that the two relatively gradual steps are centred at 215 and 186 K and are separated by an inflection point at about 201 K, at which 50 % of the complex molecules undergo a spin transition. The two steps are related to the existence of two crystallographically inequivalent metal sites, as confirmed by the structural and Mössbauer studies. The crystal structure was resolved at 293 K (HS form) and 130 K (LS form). Both spin‐state structures belong to the triclinic P $\bar 1$ space group ( Z =2). The complex assumes a linear chain structure, in which the active iron(II) sites are linked to each other by anionic dicyanamide ligands acting as chemical bridges. The Fe–Fe distances through the dca ligand are 8.119(1) and 7.835(1) Å in the high‐spin and low‐spin structures, respectively. The polymeric chains extend along a (1, 0, −1) axis and are packed in sheets, between which the perchlorate anions and methanol molecules are inserted. The complex molecules are linked together by π‐stacking interactions and H‐bonding between the H‐donor aqin ligands and the perchlorate ions. These structural features provide a basis for cooperative interactions in the crystal lattice. Analysis of the two‐step spin‐crossover character in this compound suggests that covalent interactions through the spacer ligand do not provide the main mechanism of cooperativity.