Σύνθεση δομικός χαρακτηρισμός φασματοσκοπικές και μαγνητικές μελέτες πολυπυρηνικών ομομεταλλικών 3 d και ετερομεταλλικών 3d-4f συμπλόκων

Abstract

Seeking to study the coordination chemistry of the ligand di-2, 6-(2-pyridylcarbonyl) pyridine (dpcp) with 3d transition metal ions, the tetranuclear complexes [Cu4(N3)2{pyCO(OMe)pyCO(OMe)py}2(MeOH)2](ClO4)∙2MeOH (1∙2MeOH) and [Co4(N3)2(NO3)2{pyCO(OMe)pyCO(OMe)py}2]∙0.5MeOH (2∙0.5MeOH), the hexanuclear complex [Ni6(CO3)(N3)6{pyCOpyC(O)(OMe)py}3(MeOH)2(H2O)][Ni6(CO3)(N3)6{pyCOpyC(O) (OMe)py}3(MeOH)3](ClO4)2 (3∙1.8MeOH) and the dinuclear complex [Fe2{pyCO(OMe)py(Η)CO(OMe)py}2(MeO)2](ClO4)2∙(4∙MeOH) were synthesized. In addition, in order to study the coordination chemistry of the same ligand with mixed 3d transition metal ions and 4f lanthanide ions, the heterometallic dinuclear complexes [ΜIILnIII{pyCOH(OEt)pyCOH(OEt)py}3] (ClO4)2∙EtOH (5-16∙EtOH) were synthesized, with ΜΙΙ = CuΙΙ, CoΙΙ, NiΙΙ, ZnΙΙ, MnΙΙ, FeΙΙ [LnΙΙΙ = GdΙΙΙ (5 - 10), TbΙΙΙ (11 – 16) respectively]. All complexes were structurally characterized and complexes 4, 10 and 16 were characterized by Mossbauer spectroscopy. Magnetic properties measurements of complexes 1-3, 5 and 10 indicated the existence of ferromagnetic interactions, while those of 4, 6, 7 and 9 indicated the existence of antiferromagnetic interactions. For the in depth study of the family of basic iron (III) carboxylates [Fe3O(O2CR)6(H2O)3]A, two series of complexes were prepared with R = Cl3C, CHBr2, CH2F, CH2Cl, C(OH)Ph2, H, Ph, Cl(CH2)3, Me, CHMe2, Et and Me3C. For the former series (17 - 28) the counteranion (A-) is ClO4- and for the latter (29 - 40) is NO3-. Attempts to prepare the respective trifluoroacetate (R = CF3) complexes were unsuccessful and the reaction system lead to the tetranuclear “butterfly” complex [Fe4O2(O2CCF3)8(H2O)6] (41), irrespective of whether perchlorates or nitrates were used as counteranions. Mossbauer studies revealed very similar isomer shifts for all complexes in the region of 0.51 – 0.54 mms-1, and variable quadrupole splittings, ranging from 0.36 to 0.76 mms-1. Mossbauer studies of the complexes were carried out in frozen MeCN solutions in order to assess their stability in solution and they proved to be stable in MeCN solutions, except complex 29 (R = Cl3C, Α = NO3-), which dissociated to a butterfly-type complex. The high-symmetry cluster [Fe3O(O2CPh)6(py)3](ClO4)∙py (42) has been structurally characterized and its Inelastic Incoherent Neutron Scattering studies have been reported. These studies suggested the existence of a magnetic Jahn-Teller effect at lower temperatures. Seeking to study if there is any correlation between magnetic and structural symmetry, we undertook variable-temperature crystallographic studies on ESRF BM01A beamline. With the results of these data we concluded that the symmetry of the crystal remained. Moreover, we have discovered that this complex exhibits magnetic relaxation phenomena under weak magnetic fields, observed by ac magnetic susceptometry.