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Synthesis and Characterisation of a New Series of Bistable Iron(II) Spin‐Crossover 2D Metal–Organic Frameworks
Author(s) -
Martínez Víctor,
Gaspar Ana Belén,
Muñoz M. Carmen,
Bukin Gennadiy V.,
Levchenko Georgii,
Real José Antonio
Publication year - 2009
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.200901391
Subject(s) - spin crossover , crystallography , monoclinic crystal system , orthorhombic crystal system , chemistry , spin transition , octahedron , crystal structure , pyridine , stereochemistry , medicinal chemistry
Twelve coordination polymers with formula {Fe(3‐Xpy) 2 [M II (CN) 4 ]} (M II : Ni, Pd, Pt; X: F, Cl, Br, I; py: pyridine) have been synthesised, and their crystal structures have been determined by single‐crystal or powder X‐ray analysis. All of the fluoro and iodo compounds, as well as the chloro derivative in which M II is Pt, crystallise in the monoclinic C 2/ m space group, whereas the rest of the chloro and all of the bromo derivatives crystallise in the orthorhombic Pnc 2 space group. In all cases, the iron(II) atom resides in a pseudo‐octahedral [FeN 6 ] coordination core, with similar bond lengths and angles in the various derivatives. The major difference between the two kinds of structure arises from the stacking of consecutive two‐dimensional {Fe(3‐Xpy) 2 [M II (CN) 4 ]} ∞ layers, which allows different dispositions of the X atoms. The fluoro and chloro derivatives undergo cooperative spin crossover (SCO) with significant hysteretic behaviour, whereas the rest are paramagnetic. The thermal hysteresis, if X is F, shifts toward room temperature without changing the cooperativity as the pressure increases in the interval 10 5 Pa–0.5 GPa. At ambient pressure, the SCO phenomenon has been structurally characterised at different significant temperatures, and the corresponding thermodynamic parameters were obtained from DSC calorimetric measurements. Compound {Fe(3‐Clpy) 2 [Pd(CN) 4 ]} represents a new example of a “re‐entrant” two‐step spin transition by showing the Pnma space group in the intermediate phase (IP) and the Pnc 2 space group in the low‐spin (LS) and high‐spin (HS) phases.