Search

A new family of [3 + 3] hexanuclear 3d–4f complexes [(μ3-CO3){CoIILnIIIL(μ3-OH)(OH2)}3]-(ClO4)·mC2H5OH·nH2O (1–5) [Ln = La (1), Gd (2), Tb (3), Dy (4), and Ho (5)] have been prepared in moderate to high yields (62–78%) following a self-assembly reaction between the ligand 6,6′,6′′-(nitrilotris(methylene))tris-(2-methoxy-4-methylphenol) (H3L), Co(OAc)2·4H2O and the lanthanide ion precursors in the mandatory presence of tetrabutylammonium hydroxide. During the reaction, atmospheric carbon dioxide is fixed in the product molecule as a bridging carbonato ligand which connects all the three lanthanide centers of this molecular assembly through a rare η2:η2:η2–μ3 mode of bridging as revealed from X-ray crystallography. The metal centers in all these compounds, except the GdIII analogue (2), are coupled in antiferromagnetic manner while the nature of coupling in the CoII3GdIII3 complex is ferromagnetic. DFT calculations revealed that this ferromagnetic interaction occurs most likely by the CoII–GdIII superexchange, mediated via the bridging oxygen atoms. Only the CoII–DyIII compound (4) displayed a slow relaxation of the magnetization at a very low temperature as established by AC susceptibility measurements. The data provides an estimation of the activation energy U/kB = 9.2 K and the relaxation time constant τ0 = 1.0 × 10−7 s. [ABSTRACT FROM AUTHOR]

A new family of pentanuclear 3d–4f heterometal complexes of general composition [LnIII2(MIIL)3(μ3-O)3H](ClO4)·xH2O (1–5) [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 (3–5) 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 4F3/2 → 4I11/2 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 2–5 and thereby lower the population of the triplet state. [ABSTRACT FROM AUTHOR]

A new family of [2 × 2] tetranuclear 3d—4f heterometallic complexes have been synthesized. These are [Zn2Dy2L2(μ3-OH)2(μ4-OH)(dbm)2(MeOH)2]-(NO3)·2H2O·MeOH (3), [Ni2Dy2L2(μ3-OH)2(μ4-OH)-(dbm)2(MeOH)2](NO3)·MeOH (4), [Ni2La2L2(μ3-OH)2-(μ4-OH)(dbm)2(MeOH)2](CIO4)·H2O·2MeOH (5), [Ni2Tb2L2(μ3-OH)2(μ4-OH)(dbm)2 (MeOH)2]-(NO3)·MeOH (6), and [Ni2Gd2L2(μ2-OH)2(μ4-OH)-(dbm)2(MeOH)2](NO3)·MeOH (7), [H2L = N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyi)ethylenediamine and Hdbm = dibenzoylmethane] obtained through a single-pot synthesis using [Zn(HL)(dbm)] (for 3)/[Ni(HL)(dbm)] -2CH3OH (for 4, 5, 6, and 7) as 3d-metal ion precursors. Single-crystal X-ray diffraction analysis and electrospray ionization (ESI) mass spectroscopy have been used to establish their identities. Compounds are isostructural, in which the metal ions are all connected together by a bridging hydroxido ligand in a rare /i4-mode. In complexes 3–7, the metal ions are antiferromagnetically coupled. Taking a cue from the results of 3 and 5, precise estimations have been made for the antiferromagnetic Ni···Ni (JNi = –50 cm–1), Ni···Gd (JNiGd = –4.65 cm-1), and Gd···Gd (JGd = –0.02 cm–1) exchange interactions in 7, involving the gadolinium(III) ions. The Zn2IIDy2IIIcompound 3 has shown the tail of an out-of-phase signal in alternating current (AC) susceptibility measurement, indicative of slow relaxation of magnetization. Interestingly, the Ni2IIDy2II compound 4 in which both the participating metal ions possess large single ion anisotropy, has foiled to show up any slow magnetic relaxation [ABSTRACT FROM AUTHOR]

Abstract: Using di-2-pyridyl ketonoxime (Hdpko) as an oxime-based ligand in combination with several polyhydric alcohols, viz. ethanediol (H2ed), propanediol (H2pd) and pentaerythritol (H4per), we have synthesized a series of trinuclear complexes involving a linear MnII–MnIV–MnII core, viz. [Mn3(dpko)4(ed)Cl2]·2CH3CN·H2O 1, [Mn3(dpko)4(pd)Cl2]·CH3CN·H2O·0.5H2pd 2 and [Mn3(dpko)4(H2per)Cl2]·4H2O 3, respectively. The trinuclear complexes contain mixed valent MnII–MnIV–MnII units in a linear topology in which MnII and MnIV spin carriers are ferromagnetically coupled. The temperature dependence of the magnetic susceptibility has been fitted with a liner spin trimer model based on the H =−2J{S Mn1·S Mn2 + S Mn1′·S Mn2} Heisenberg Hamiltonian with J/k B =+1.4(1)K for 1; +4.9(1)K for 2 and +3.7(1)K for 3, leading for the three complexes to an S T =13/2 ground state. [Copyright &y& Elsevier]

Heterobimetallic compounds [L+OVv= O→Fe(metsalophen)(H2O)] (1) and [L20Vv=0→Fe- (metsalophen)(H2O)]CH3CN (2). where H2L1 and H2L2 are tridentate dithiocarbazate-based Schiff base ligands, containing a discrete Vv--μ-O--FeIII angular core have been synthesized for the first time through a targeted synthesis route: confirmation in favor of such a heterobimetallic core structure has come from singlecrystal X-ray diffraction analysis and electrospray ionization mass spectrometry. [ABSTRACT FROM AUTHOR]

A new family of [3 + 3] hexanuclear 3d-4f complexes [(μ 3 -CO 3 ){Co II Ln III L(μ 3 -OH)(OH 2 )} 3 ]-(ClO 4 )·mC 2 H 5 OH·nH 2 O (1-5) [Ln = La (1), Gd (2), Tb (3), Dy (4), and Ho (5)] have been prepared in moderate to high yields (62-78%) following a self-assembly reaction between the ligand 6,6',6''-(nitrilotris(methylene))tris-(2-methoxy-4-methylphenol) (H 3 L), Co(OAc) 2 ·4H 2 O and the lanthanide ion precursors in the mandatory presence of tetrabutylammonium hydroxide. During the reaction, atmospheric carbon dioxide is fixed in the product molecule as a bridging carbonato ligand which connects all the three lanthanide centers of this molecular assembly through a rare η 2 :η 2 :η 2 -μ 3 mode of bridging as revealed from X-ray crystallography. The metal centers in all these compounds, except the Gd III analogue (2), are coupled in antiferromagnetic manner while the nature of coupling in the CoGd complex is ferromagnetic. DFT calculations revealed that this ferromagnetic interaction occurs most likely by the Co II -Gd III superexchange, mediated via the bridging oxygen atoms. Only the Co II -Dy III compound (4) displayed a slow relaxation of the magnetization at a very low temperature as established by AC susceptibility measurements. The data provides an estimation of the activation energy U/k B = 9.2 K and the relaxation time constant τ 0 = 1.0 × 10 -7 s.