J. Appl. Cryst. (2007). 40, 1135-1145 [ doi:10.1107/S0021889807048571 ]
Abstract: Variable-temperature X-ray crystal structure determinations (80-330 K) on compounds {Fe[tren(6-Mepy)3]}(ClO4)2 (1-Fe) {tren(6-Mepy)3 is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} and {Zn[tren(6-Mepy)3]}(ClO4)2 (1-Zn) {tren(6-Mepy)3 is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} were carried out together with a detailed analysis of the unit-cell volume and parameters in the spin transition region for (1-Fe). Both compounds crystallize in the monoclinic system and retained the space group P21/c at all measured temperatures. The Fe and Zn atoms are surrounded by six N atoms belonging to imine groups and pyridine groups of the trifurcated ligand, adopting a pseudo-octahedral symmetry. The average Fe-N bond lengths of 2.013 (1) Å (80 K) and 2.216 (2) Å (330 K) are consistent with a low-spin (LS) and a high-spin (HS) state for the iron(II) ions. In contrast to (1-Fe), the structures of (1-Zn) at low and high temperatures are similar and repeat the structural features of the high-spin structure of (1-Fe). The volume of the unit cell increases on heating from 80 to 330 K for (1-Fe) and (1-Zn). On the other hand, while the a, b and c cell parameters increase for (1-Fe), they show less variation for (1-Zn). For (1-Fe), variation of the unit-cell volume with temperature recalculated per Fe atom shows a change ![[Delta]](/logos/entities/Delta_rmgif.gif)
V = 27.16 Å3 during the spin crossover process. Magnetic susceptibility and Mössbauer spectroscopy studies performed on (1-Fe) reveal an inversion temperature, T1/2 of 233 K, where the molar fractions of LS and HS sites are both equal to 0.5. The variation in metal-ligand bond lengths, the distortion parameters and the cell parameters are very close to the character of the magnetic curve and the curve of ![[gamma]](/logos/entities/gamma_rmgif.gif)
HS (the molar fraction of HS molecules) derived from the Mössbauer data; this result shows the correlation between structure and physical properties in (1-Fe).
Keywords: spin transition; bistability; variable-temperature X-ray; cooperative effects; phase transitions.
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