Mössbauer study of the influence of ligands and anions of the second coordination sphere in Fe(II) complexes with 1,2,4-triazole and 4-amino-1,2,4-triazole on the temperature of the 1A 1⇆5 T 2 spin transitions

For Fe(II) complexes with 1,2,4-triazole (Tr) and 4-amino-1,2,4-triazole (ATr) in low-spin phases, it has been revealed that the ligand and anion of the second coordination sphere affect the electronic state of the central atom and the symmetry of its local environment. For low-spin phases, a correlation between the Mössbauer spectrum parameters—the chemical shift and the bandwidth of the weakly resolved quadrupole doublet—and the spin transition temperature T_c has been established. The mechanism of the influence of complex composition on the spin transition temperature is accounted for by assuming that T_c is determined by the lattice energy of a complex compound.