Electronic Transition and Magnetic Coupling Regulation in Trimetallic Complexes Featuring a New Bridging Ligand Obtained by Oxidative Addition

Abstract

A series of trimetallic complexes [Fe III (μ-L)(py)] 2 M II (py) n (n = 2, M II = Mn II , 1; Fe II , 2; Co II , 3; Zn II , 4; n = 3, M II = Cd II , 5) with a new bridging ligand L 4− (deprotonated 1,2-N 1 ,N 2 -bis(2-mercaptoanil) oxalimidic acid) were synthesized and fully characterized by elemental analysis, single-crystal X-ray crystallography, IR, and Mossbauer spectra. Interestingly, the bridging ligand was obtained by oxidative addition of the (gma • ) 3− ligand from the mononuclear precursor Fe(gma)py (gma = glyoxalbis(2-mercaptoanil)). In the obtained complexes, the bridging ligand L 4− coordinates to the terminal Fe III ions (intermediate-spin with S Fe = 3/2) by the N, S atoms, and coordinate to the central metal M II ion by the four O atoms. The resonance structure of the bridging ligand can be described as the two 4π-electron delocalized systems connected by one single-bond (C 1 −C 2 ), which is different from the electronic structure of the precursor Fe(gma)py. Remarkably, the magnetic coupling interaction can be regulated through the central metal. The ferromagnetic coupling constant J gradually decreases as M II changes from Fe II to Co II and Mn II , while the paramagnetic behaviors are presented when M II = Zn II and Cd II , confirmed by the magnetic susceptibility measurements and further supported by using the PHI program. Furthermore, the bridging ligand to the terminal Fe III charge transfer (LMCT) transitions emerged in all complexes but the central Fe II to terminal Fe III charge transfer (MMCT) only presented in complex 2, strongly supported by the UV/vis−NIR electronic spectra and TDDFT calculations.