Photo-induced spin-transition:: the role of the iron (II) environment distortion

The [FeLn(NCS)(2)] iron(II) spin-crossover complexes cover a wide range of magnetic behaviour. Owing to the large number of known structural and magnetic data, this series is perfectly adapted to the investigation of the structure - magnetic properties relationship. In this paper we propose a new structural parameter, denoted Theta, which is used to correlate the features of the spin-crossover phenomena with the distortion of the iron environment. In particular, this parameter has shed light on the role of such distortion on the limiting temperature of photo-inscription, known as T(LIESST). A strong dependence of T(LIESST) on Theta is clearly demonstrated. The stronger the distortion the higher the T( LIESST) value. This structure - property dependence represents, for instance, a powerful tool to estimate the highest potential T( LIESST) value for a series of complexes. This limit in the [FeLn(NCS)(2)] series is estimated to be around 120 K, which probably prevents their use in any industrial application.