Crystal structure of butyl and propylN-(3-chloropropyl)-(2S)-alaninate

Abstract

The molecular spin-crossover, SCO, phenomenon, involving thermo-, photo-and piezo-chromic properties of a class of transition-metal complexes (3d 4 -3d 7 ), is one of growing importance in the area of functional materials, especially for application as molecular switches and in the field of information storage. These complexes are known to display a molecular bistability of high-spin (HS) and low-spin (LS) electronic configurations, which are distinguished by different occupation of antibonding e g and bonding t 2g d orbitals of the central metal ion. The course to the design of materials with adequate properties for industrial applications goes through the control of the physical -especially magnetic, optical and structural -properties modifications induced by the spin crossover. In order to better understand the phase transition mechanism of very gradual complete thermal spin transition, we have collected a series of complete diffraction patterns by single crystal X-ray diffraction versus the temperature. Thanks to these investigations, we were able to follow not only the evolution of cell parameters but also every Fe-N 6 octahedron geometric parameters as a function of the temperature every 5K. The accurate monitoring of inter-atomic distances such as the Fe…N distances and angles have well pointed out the anisotropic behavior of these parameters during the transition. Moreover, this study has revealed the physical mechanism of the propagation of the spin crossover along the material during the transition. Surprisingly for a gradual spin crossover, this mechanism appears different in nature in the cooling and in the warming modes.