A mixed-spin spin-crossover thiozolylimine [Fe L ] tetrahedral cage is reported. The self-assembly of a mixed-spin [Fe L ] tetrahedral cage is reported. The cage undergoes temperature induced spin-crossover with a 29 K hystereisis. Variable temperature X-ray photoelectron spectroscopy (VT-XPS), combined with SQUID data, allowed differentiation between the surface and bulk magnetic properties.