| Abstract
| - We report on the synthesis and characterization of a first iron(II) spin-crossovercoordination polymer of formula [Fe(pyim)2(bpy)](ClO4)2·2C2H5OH, where pyim = 2-(2-pyridyl)imidazole and bpy = 4,4‘-bipyridine, with zigzag chain structure. The chains arelinked by π stacking into a two-dimensional network. Variable-temperature magneticsusceptibility measurements have revealed the occurrence of the HS ↔ LS transition withouthysteresis. The spin conversion temperature T1/2 (temperature for which the HS fraction isequal to 0.5) is found equal to 205 K. The crystal structure was resolved at 293 K (high-spinform) and at 173 K (low-spin form). Both spin-state structures belong to the monoclinic spacegroup C2/c (Z = 4). The complex assumes one-dimensional zigzag chain structure, in whichthe iron(II) active sites are linked to each other by a chemical bridge as the rigid rodlike4,4‘-bipyridine molecule. The Fe−Fe separation via the bpy ligand equals 11.523(2) and11.201(2) Å in the high-spin and low-spin structures, respectively. The polymeric chainsextended along the c axis are stacked in the b direction forming two-dimensional sheets ofbound molecules. The sheets are linked together by several intermolecular H-bonds in thea direction. The ensemble of structural features of the complex, potentially leading to thecooperativity, provides a basis for strong interactions. However, they are not strong enoughin comparison with the HS−LS energy gap and result in a relatively gradual spin transitionof the complex. The structural features and magnetic properties of the complex have beendiscussed and compared with those for earlier reported iron(II) spin-crossover coordinationpolymers.
- The new compound [Fe(pyim)2(bpy)](ClO4)2·2C2H5OH, where pyim = 2-(2-pyridyl)imidazole and bpy = 4,4‘-bipyridine, has been synthesized and its structure, and magnetic properties have been investigated. This complex represents the first structurally characterized example of iron(II) spin-crossover coordination polymer with infinite zigzag chains linked by π stacking into two-dimensional network.
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