Exchange coupling in spins quartet of dimeric polyoxoanions [M 4(H 2O) 2(GeW 9O 34) 2] 12− (M=Mn 2+, Cu 2+)

Magnetization and magnetic susceptibility of dimeric polyoxoanions [M 4(H 2O) 2(GeW 9O 34) 2] 12− (M=Mn 2+, Cu 2+) were investigated using an isotropic exchange coupling model with two coupling constant ( J and J′) within the spin quartet formed by M 4O 16 (M=Mn 2+, Cu 2+). The exchange couplings were found to be antiferromagnetic for both samples with the values ( J/ k B=−0.91±0.04 K and J′/ k B=−1.18±0.02 K) and ( J/ k B=−13.5±0.5 K and J′/ k B=−66±4 K) for the samples containing Mn 2+ and Cu 2+, respectively. Furthermore, X- and Q-Band powder electron paramagnetic resonance (EPR) measurements on the sample containing Cu 2+ 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.