A Novel Strategy to Tune Magnetic Properties of Nickel(II)-Schiff Base Coordination Bridged Polysilsesquioxane

Abstract

In this paper, liquid state solvent-free organosilica-based nickel-bithiazole complexes (PBSIBTHM-Ni2+, PBSIBTMeM-Ni2+) were synthesized through sol–gel processes respectively, and these two metal complexes and their precursors were characterized. The precursors with bithiazole were successfully prepared, their inorganic and organic parts were connected on molecular level. The DSC results indicated they would all exist in liquid phase at temperature ranging from 180 K to 280 K. The UV-VIS showed that a red shift of the main electronic transitions from 254 to 268 nm of PBSIBTHM to PBSIBTHM-Ni2+, Δν = 14 (from 249 to 266 nm of PBSIBTMeM to PBSIBTMeM-Ni2+, Δν = 17). This verified the formation of a more extensive π→π* conjugating system due to coordination interaction between Ni2+ and PBSIBTHM or PBSIBTMeM. The magnetic measurement results of PBSIBTHM-Ni2+ and PBSIBTMeM-Ni2+ reflected they both exhibited ferromagnetic properties at low temperature. For PBSIBTMeM-Ni2+, it had a transition temperature (Ttran) at 160 K, and became an anti-ferromagnet above Ttran. For PBSIBTHM-Ni2+, it had a very high Curie-Weiss temperature (Tc = 253 K). This strategy was expected to find potential application in fabricating the complexes with desired physicochemical properties.