Exchange coupling in spins quartet of dimeric polyoxoanions [M4(H2O)2(GeW9O34)2]12− (M=Mn2+, Cu2+)

Magnetization and magnetic susceptibility of dimeric polyoxoanions [M4(H2O)2(GeW9O34)2]12− (M=Mn2+, Cu2+) were investigated using an isotropic exchange coupling model with two coupling constant (J and J′) within the spin quartet formed by M4O16 (M=Mn2+, Cu2+). The exchange couplings were found to be antiferromagnetic for both samples with the values (J/kB=−0.91±0.04 K and J′/kB=−1.18±0.02 K) and (J/kB=−13.5±0.5 K and J′/kB=−66±4 K) for the samples containing Mn2+ and Cu2+, respectively. Furthermore, X- and Q-Band powder electron paramagnetic resonance (EPR) measurements on the sample containing Cu2+ were investigated and the experimental spectra were simulated using a triplet spin state S=1 and I=3, and including a small axial distortion D term. This leads to spin-Hamiltonian parameters of: |D|=0.44±0.01 GHz, g||=2.415±0.005, g⊥=2.070±0.005, A||=(40±1) G.