(Tetrakis(2-pyridylmethyl)ethylenediamine)iron(II) Perchlorate. Phase Transition Study about the First Rapidly Interconverting Ferrous Spin-Crossover Complex

✍ Scribed by Xavier Solans; Lena Ruiz-Ramirez; Rafael Moreno-Esparza; Manuel Labrador; Albert Escuer

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 298 KB
• Volume: 109
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1994.1109

✦ Synopsis

A detailed variable-temperature magnetic, thermal and singlecrystal and powder diffractometry study has been made on ([\mathrm{Fe}() tpen ()]\left(\mathrm{ClO}{4}\right){2} \cdot \frac{1}{2} \mathrm{H}{2} \mathrm{O}). (tpen (=) tetrakis(2-pyridylmethyl)ethy. lenediamine.) Solid-state magnetic susceptibilities measurement shows that this complex is a continuous/complete type (\mathrm{Fe}^{\mathrm{ll}}) spincrossover system as defined by Gütlich, with an effective critical temperature, (T{\mathrm{c}}), where there are equal amounts of high- and lowspin complexes, equal to (365 \mathrm{~K}). The ({ }^{57} \mathrm{Fe}) Mössbauer spectrum measured by Hendrickson shows that the interconversion rate between high- and low-spin states is faster than the Mössbauer time scale. Single-crystal diffractometry shows that the ([\mathrm{Fe}() tpen ()]\left(\mathrm{ClO}{4}\right){2} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}) crystallizes in the monoclinic space group (C 2 / c), which at (293 \mathrm{~K}) has a unit cell of (a=40.775(8) \AA, b=) 9.467(2) (\AA, c=23.851(5) \AA), and (\beta=108.32(6)^{\circ}) with (Z=12), and at (182 \mathrm{~K}) has a unit cell of (a=\mathbf{4 0 . 4 3 0 ( 3 )} \AA, b=9.460(1) \AA), (c=23.834(2), \AA), and (\beta=108.59(2)^{\circ}) with (Z=12). The refinements were carried out with 3228 and (3639(2.5 \sigma)) observed reflections at 293 and (182 \mathrm{~K}), respectively, to give (R=0.058) ( (\mathrm{w} R=) (0.061)) and (R=0.032(w R=0.036)). At both temperatures there are two crystallographically different ([\mathrm{Fe}(\mathrm{tpen})]^{+2}) cations, showing an octahedral coordination strongly distorted to trigonal geometry by the steric constraints produced by the hexadentate ligand. This distortion is different in the two nonequivalent cations, which is due to different intermolecular interaction produced by the perchlorate anions. An analysis of the changes in the structure of the two cations as a function of temperature from our results and