Substituent effect of the coordinated pyridine in a series of pyrazolato bridged dinuclear diiron(II) complexes on the spin-crossover behavior

摘要

Two series of pyrazolato bridged dinuclear NCS and NCBH_3 diiron(II) complexes with various types of 3- or 4-substituted pyridines,[{Fe(NCS or NCBH_3)(X-py)}_2(mu-bpypz)_2],were prepared and their variable-temperature magnetic susceptibilities were measured.There were found linear correlations of the spin-crossover temperatures T_c not only between the NCS and NCBH_3 complexes with the corresponding substituted pyridines,but also between the T_c and the Hammett constants,supporting the electronic substituent effect of the coordinated pyridine rather than a steric effect.The ligand field and the interelectronic repulsion parameters together with the thermodynamic data and/or cooperativity factor were discussed in relation with their spin-crossover behavior.