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Pentanuclear 3d–4f Heterometal Complexes of MII3LnIII2 (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties

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posted on 2015-10-19, 00:00 authored by Manoranjan Maity, Mithun Chandra Majee, Sanchita Kundu, Swarna Kamal Samanta, E. Carolina Sañudo, Sanjib Ghosh, Muktimoy Chaudhury
A new family of pentanuclear 3d–4f heterometal complexes of general composition [LnIII2(MIIL)33-O)3H]­(ClO4xH2O (15) [Ln = Nd, M = Zn, 1; Nd, Ni, 2; Nd, Cu, 3; Gd, Cu, 4; Tb, Cu, 5] have been synthesized in moderate yields (50–60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., N,N-bis­(2-hydroxy-3-methoxy-5-methylbenzyl)-N,N-diethylethylenediamine (H2L). Single-crystal X-ray diffraction analyses have been used to characterize these complexes. The compounds are all isostructural, having a 3-fold axis of symmetry that passes through the 4f metal centers. The [MIIL] units in these complexes are acting as bis-bidentate metalloligands and, together with μ3-oxido bridging ligands, complete the slightly distorted monocapped square antiprismatic nine-coordination environment around the 4f metal centers. The cationic complexes also contain a H+ ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper­(II) complexes (35) show a changeover from antiferromagnetic in 3 to ferromagnetic 3d–4f interactions in 4 and 5. For the isotropic CuII–GdIII compound 4, the simulation of magnetic data provides very weak Cu–Gd (J1 = 0.57 cm–1) and Gd–Gd exchange constants (J2 = 0.14 cm–1). Compound 4 is the only member of this triad, showing a tail of an out-of-phase signal in the ac susceptibility measurement. A large-spin ground state (S = 17/2) and a negative value of D (−0.12 cm–1) result in a very small barrier (8 cm–1) for this compound. Among the three NdIII2MII3 (M = ZnII, NiII, and CuII) complexes, only the ZnII analogue (1) displays an NIR luminescence due to the 4F3/24I11/2 transition in NdIII when excited at 290 nm. The rest of the compounds do not show such NdIII/TbIII-based emission. The paramagnetic CuII and NiII ions quench the fluorescence in 25 and thereby lower the population of the triplet state.