Structural, magnetic and photomagnetic study of the [Fe(PM-NEA)2(NCS)2] spin crossover complex

摘要

The new spin-crossover compound [Fe(PM—NEA)2(NCS)2] with PM-NEA=N-(2-pyridylmethylene)-4-(naphthalene-1-ethynyl)aniline has been synthesized. The temperature dependence of χ_MT (χ_m = molar magnetic susceptibility and T = temperature) has revealed a very gradual complete spin conversion between LS (S = 0) and HS (S = 2) states with T_(1/2) of about 204 K. At 10 K the well-known LIESST (light-induced excited spin state trapping) effect has been observed within the SQUID cavity, by irradiating a powder sample with a Kr~+ laser coupled with an optical fibre. The HS → LS relaxation after LIESST has been analyzed with a stretched exponential behaviour. This is consistent with structural analysis, since the presence of naphthalene rings induces a less compact crystal packing than in already reported [Fe(PM—L)2(NCS)2] crystal structures. In particular, the intermolecular interaction network shows a noteworthy dissymmetry on each side of the complex. Furthermore, the structure—property relationship confirms the important role of the metal coordination sphere distortion on the T_(1/2) value.