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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI
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Rezumat: The series of sodium/potassium salts of the sandwich-type heteropolyanions [Mn+3(H2O)x(BiW9O33)2](183n) (Mn+ = (VO)II, x = 0 and Mn+ = CrIII, MnII, FeIII, CoII, NiII, CuII, x = 3) was investigated by X and W bands ESR spectroscopy. In the complex with vanadium(IV) the unpaired electrons are trapped on the parent ions (gII = 1.899, g = 1.974, AII = 184 G, A = 69 G) and the VIV ions are prevalently dipolar coupled. In the case of the other trinuclear clusters, the metallic coupling is based on the superexchange mechanism realized through the heteropolyoxometalate frame. The isotropic exchange constants were estimated for the CrIII (J = 4.116 cm1) and MnII (J = 2.074 cm1) clusters from the temperature dependance of the linewidths of the HF-EPR signals. The g tensor is isotropic for the complexes with CrIII, MnII and FeIII (g 2.0), axial for the CuII cluster (gII = 2.080, g = 2.237) and rhombic for the NiII complex (gx = 2.201, gy = 2.211, gz = 2.292). The zero field splitting tensor is rhombic for the clusters of MnII (D = 0.381 cm1, E = 0.054 cm1 for the spin state S = 7/2) and NiII (D = 1.66 cm1, E = 0.18 cm1 for the spin state S = 1). Two species with different degrees of the rhombical distortion have been identified in case of the FeIII (D1 = 1.5 cm1, E1 = 0.12 cm1 and D2 = 1.5 cm1, E2 = 0.5 cm1) and CoII (gx1 = 5.021, gy1 = 3.561, gz1 = 2.401 and gx2 = 5.776, gy2 = 3.813, gz2 = 2.850) samples. |
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