Control of Tc and spin bistability in the spin-crossover system, [Fe(4-NH2trz)3](R-SO3)2

The spin transition behavior of iron(II) complexes [Fe(4-NH2trz)3](CmH2m+1SO3)2 · 2H2O (4-NH2trz=4-amino-1,2,4-triazole, m=1~9) was investigated by the magnetic measurement. The transition temperature Tc became higher with increasing the length of alkyl chain of counter-ion, m, and saturated at m=5. The even-odd effect was observed in the hysteresis width, that is, the hysteresis width was wider for even m, narrower for odd m.