Spectroscopic and electron paramagnetic resonance behavior of trinuclear metallic clusters encapsulated in [M-3(n+)(H2O)(x)-(BiW9O33)(2)]((18-3n)-) heteropolyanion (Mn+ = (VO)(II), x=0 and Mn+ = Cr-III, Mn-II, Fe-III, Co-II, Ni-II, Cu-II, x=3)

摘要

A new series of sodium/potassium salts of sandwich-type [M(n+)3((HO)-O-2)(x)(BiW9O33)2]((18-3n)-) heteropolyanions (Mn+ = (VO)(II), x = 0 (1) and Mn+ = Cr-III (2), Mn-II (3), Fe-III (4), Co-II (5), Ni-II (6), Cu-II (7), x = 3) were synthesized and characterized by means of elemental analyses, thermogravimetry, FT-IR, UV-VIS, EPR and HF-EPR spectroscopy. FT-IR data are proof of the heteropolyanion frame formation and indicate the co-ordination of each transition metal at two corner-shared octahedra from the trivacant Keggin fragments. The low shift of the nu (asym)(Bi-O-a) band in the spectra of the Cu-II and Fe-III compounds relative to the ligand spectrum suggests a sterically-inert S-2 lone pair on each Bi-III ion. The charge transfer band p(pi)(O-t)-->d(pi*)(W) at 193.6 nm is not affected by the co-ordination of the metals, but the p(pi)(O-c,O-e)--> d(pi*)(W) band shifts towards higher energies for Cr-III and Fe-III complexes or lower energies for the other complexes. d-d transitions obtained in the VIS spectra of the complexes have been interpreted in terms of five-co-ordination of every transition metal and a distorted square-pyramidal local symmetry. EPR and HF-EPR data show the presence of small antiferromagnetic interactions in the spin frustrated trinuclear metallic clusters (J = -4.116 cm(-1) for the Cr-III complex, J = - 2.074 cm(-1) for the Mn-II complex). Two species with different degrees of rhombical distortion have been identified in the case of the Fe-III (D-1 = 1.5 cm(-1), E-1 = 0.12 cm(-1) and D-2 = 1.5 cm(-1), E-2 = 0.5 cm(-1)) and Co-II (g(x1) = 5.021, g(y1) = 3.561, g(z1) = 2.401 and g(x2) = 5.776, g(y2) = 3.813, g(z2) = 2.850) samples. [References: 63]