Cooperative spin transition in a lipid layer like system.

A novel iron(II) mononuclear spin transition complex [FeL(py)(2)] displays an abrupt spin transition around 225 K accompanied by a very wide thermal hysteresis loop (∼50 K) that spreads out over 100 K. Crystal structure analysis in both low-spin and high-spin states reveals a lipid layer-like arrangement of the complex molecules and provides insights into the spin switching mechanism.