The Fe[BF4](2) complex of the Schiff base podand tris [4-(thiazol-4-yl)-3-aza-3-butenyl] amine exhibits gradual thermal spin-crossover with T-1/2 approximate to 208 K in the solid state.. A weak discontinuity in the magnetic susceptibility curve at 190 K is associated with a reentrant symmetry-breaking transition involving a trebling of the unit cell volume (from P2(1)/c, Z = 4, to P2(1), Z = 12). The intermediate phase contains six independent cations in puckered layers of low-spin, and high-spin or mixed-spin, molecules with an overall 30% high-spin population at 175 K.