Variable-temperature X-ray crystal structure determinations of {Fe[tren(6-Mepy)(3)]}(ClO4)(2) and {Zn[tren(6-Mepy)(3)]}(ClO4)(2) compounds: correlation of the structural data with magnetic and Mossbauer spectroscopy data

摘要

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 P2(1)/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) angstrom ( 80 K) and 2.216 ( 2) angstrom ( 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 V=27.16 angstrom(3) during the spin crossover process. Magnetic susceptibility and Mossbauer spectroscopy studies performed on ( 1-Fe) reveal an inversion temperature, T-1/2 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(HS) ( the molar fraction of HS molecules) derived from the Mossbauer data; this result shows the correlation between structure and physical properties in ( 1-Fe).