Magnetic relaxation in two chain-like Zn2Dy2 Schiff base coordination polymers bridged by tetraoxolene and its one-electron reduced radical

Abstract

In the process of solvothermal synthesis of one-dimensional (1D) Zn–Dy Schiff base coordination polymers, 25% of tetraoxolene anions (X₂tetraox²⁻) underwent a one-electron reduction in situ reaction to form X₂tetraox³˙⁻ radical anions, which was confirmed by using the ν_CO vibration Raman spectra. Both the X₂tetraox²⁻ anion and the X₂tetraox³˙⁻ radical anion act as bridging ligands to connect two Zn–Dy Schiff base structural units, [DyZn(L_Schiff)(NO₃)(MeOH)]²⁺ (H₂L_Schiff = N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane) and [DyZn(L_Schiff)(MeOH)₂]³⁺, and finally assemble into two ionic zigzag chain-like coordination polymers, [Dy₂Zn₂(L_Schiff)₂(X₂tetraox²⁻)_1.5(X₂tetraox³˙⁻)_0.5(NO₃)(MeOH)₃](ClO₄)_0.5·2MeOH [1: X = Cl and 2: X = Br]. The two 1D Zn–Dy heterometallic coordination polymers exhibit the properties of single-molecule magnets (SMMs) and exhibit two-step magnetic relaxation behaviors under a dc field of 1500 Oe. Their effective energy barriers are adjusted by halogenated groups on the bridging ligands X₂tetraox²⁻ and X₂tetraox³˙⁻.