Effects of Metal Doping on the Spin-Crossover Propertiesof an Iron(II) Complex with Extended -ConjugatedSchiff-Base Ligand Having an N_4O_2Donor Set

摘要

The spin-crossover (SCO) complex [Fe(qnal)2]CH_2Cl_2(1), (Hqnal: N-(8-quinolyl)-2-hydroxy- 1 -naphthaldimine)with an N_4O_2donor set, has been synthesized and characterized. Investigation of magnetic properties shows that thecomplex exhibits an abrupt and complete spin transition with a 5 K wide thermal hysteresis loop. The X-ray diffractionanalysis of complex 1 reveals that the molecules are connected into a quasi one-dimensional chain through extended π-πinteractions between aromatic rings of ligands. The effects of metal doping on SCO properties have been investigated inthe mixed-metal system [Fe_(1-x)M_x(qnal)_2]CH_2Cl_2(M = zinc(II) and nickel(II)). The results reveal that metal dopingincreases the gradual character of spin transition, and no marked differences found between zinc and nickel doping, whichsuggest the dominant effect of the doping-degree (concentration) rather than metal species on cooperativity. However, themetal doping shows different effects on critical temperature (T_(1/2)),where a more pronounced descending ofT_(1/2)isobserved in response to increased Zn-doping than in Ni-doping, indicating the noticeable consequence of internal pressuredue to the different radii of doping metal ions.