Seven new dinuclear iron(II) complexes of the general formula [Fe-2(II)(PMKT)(2)] (BF4)(4)center dot solvent, where PMRT is a 4-substituted-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole, have been prepared in order to investigate the substituent effect on the spin crossover event. Variable temperature magnetic susceptibility and Fe-57 Mossbauer spectroscopy studies show that two of the complexes, [Fe-2(II)(PMPT)(2)](BF4)(4)center dot H2O (N-4 substituent is pyrrolyl) and [Fe-2(II)(PM(Ph)AT)(2)](BF4)(4) (N-4 is N,N-diphenylamine), are stabilized in the [HS-HS] state between 300 and 2 K with weak antiferromagnetic interactions between the iron(II) centers. Five of the complexes showed gradual half spin crossover, from [HS-HS] to [HS-LS], with the following, T-1/2 (K) values: 234 for [Fe-2(II)(PMibT)(2)](BF4)(4)center dot 3H(2)O (N-4 is isobutyl), 147 for [Fe-2(II)(PMBzT)(2)](BF4)(4) (N-4 is benzyl), 133 for [Fe-2(II)((PMPhT)-Ph-CF3)(2)](BF4)(4)center dot DMF center dot H2O (N-4 is 3,5-bis(trifluoromethyl)phenyl), 187 for [Fe-2(II)(PMPhT)(2)](BF4)(4) (N-4 is phenyl), and 224 for [Fe-2(II)(PMC16T)(2)](BF4)(4) (N-4 is hexadecyl). Structure, determinations carried out for three complexes, [Fe-2(II)(PMPT)2](BF4)(4)center dot 4DMF, [Fe-2(II)(PMBzT)(2)](BF4)(4)center dot CH3CN, and [Fe-2(II)(PM(Ph)AT)(2)](BF4)(4)center dot solvent, revealed that in all three complexes both iron(II) centers are stabilized in the high spin state at 90 K. A general and reliable 4-step route to PMRT ligands is also detailed.