Thermal and light induced polymorphism in iron(II) spin crossover compounds

The spin crossover complexes (Fe[H2B(PZ)(2)](2)L) ([H2B(pz)(2)](-) = dihydrobis(pyrazolyl)borate, L = 2,2'-bipyridine (1), bipy and 1,10-phenanthroline, phen (2)) undergo both thermal and light induced spin crossover, but the structure of the low spin and light induced high spin states for 2 are different from that of the thermally induced high spin state and from those of 1.