Article

Synthesis, structure, and magnetism of heterobimetallic trinuclear complexes {[L2Co2Ln][X]} [Ln = Eu, X = Cl; Ln = Tb, Dy, Ho, X = NO3; LH3 = (S)P[N(Me)N=CH-C6H3-2-OH-3-OMe]3]: A 3d-4f family of single-molecule magnets.

Department of Chemistry, Indian Institute of Technology-Kanpur, Kanpur-208016, India.
Inorganic Chemistry (Impact Factor: 4.59). 02/2009; 48(3):1148-57. DOI: 10.1021/ic801905p
Source: PubMed

ABSTRACT Sequential reaction of LH3 (LH3 = (S)P[N(Me)N=CH-C6H3-2-OH-3-OMe]3) with Co(OAc)2 x 4 H2O followed by reaction with lanthanide salts afforded trinuclear heterobimetalllic compounds {[L2Co2Ln][X]} [Ln = Eu (1), X = Cl; Ln = Tb (2), Dy (3), Ho (4), X = NO3] in excellent yields. These compounds retain their integrity in solution as determined by electrospray ionization mass spectrometry studies. The molecular structures of 1-4 were confirmed by a single-crystal X-ray structural study and reveal that these are isostructural. In all of the compounds, the three metal ions are arranged in a perfectly linear manner and are held together by two trianionic ligands, L3-. The two terminal Co(II) ions contain a facial coordination environment (3N, 3O) comprising three imino nitrogen atoms and three phenolate oxygen atoms. The coordination geometry about the cobalt atom is severely distorted. An all-oxygen coordination environment (12O) is present around the central lanthanide ion, which is present in a distorted icosahedral geometry. The coordination sphere around the lanthanide ion is achieved by utilizing three phenolate oxygen atoms and three methoxy oxygen atoms of each ligand. In all of these trinuclear complexes (1-4), the Co-Ln distances are around 3.3 A, while the Co-Co distances range from 6.54 to 6.60 A. The screw-type coordination mode imposed by the ligand induces chirality in the molecular structure, although all of the complexes crystallize as racemates. Magnetic properties of 1-4 have been studied in detail using dc and ac susceptibility measurements. Dynamic measurements reveal that 2-4 display a single-molecule magnet behavior, while the Co2Eu (1) analogue does not show any out-of-phase ac susceptibility.

0 Bookmarks
 · 
34 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A family of dinuclear 3d-4f heterobimetallic complexes [LNi(H2O)(μ-OAc)Ln(NO3)2]·CH3CN; {Ln = Dy(III) (), Tb(III) (), Ho(III) (), Gd(III) (), Er(III) (), Y(III) ()} have been synthesized by utilizing a ferrocene-based, dual compartmental ligand H2L. are isostructural and crystallize in the triclinic (P1[combining macron]) space group. In these complexes Ni(II) is present in the inner coordination sphere of the dianionic [L](2-) ligand; Ln(III) is encapsulated in the outer coordination pocket. Ni(II) shows a 2N, 4O coordination environment in a distorted octahedral geometry, while the Ln(III) ion possesses a 9O coordination environment in a distorted tricapped trigonal prismatic geometry. ESI-MS studies suggest that the structural integrity of is retained in solution. Electrochemical studies reveal that these complexes show a reversible one-electron response typical of the ferrocene motif along with an irreversible one-electron oxidation involving the Ni(II)/Ni(III) couple. Magnetic studies revealed the presence of ferromagnetic exchange coupling between Ni(II) and Ln(III) centers as shown by the increase of χMT value upon cooling below 50 K for compounds , , and . Further, dynamic magnetic susceptibility measurements () confirm the absence of an out-of-phase (χ'') signal at zero dc fields. However, when these measurements were carried out at 1000 Oe dc field the χ'' signal was observed, although maxima could not be detected up to 2 K.
    Dalton Transactions 05/2014; · 3.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Schiff base ligand N1,N3-bis(3-methoxysalicylidene)diethylenetriamine (H2 valdien) and the co-ligand 6-chloro-2-hydroxypyridine (Hchp) were used to construct two 3d-4f heterometallic single-ion magnets [Co2 Dy(valdien)2 (OCH3 )2 (chp)2 ]⋅ClO4 ⋅5 H2 O (1) and [Co2 Tb(valdien)2 (OCH3 )2 (chp)2 ]⋅ClO4 ⋅2 H2 O⋅CH3 OH (2). The two trinuclear [Co(III) 2 Ln(III) ] complexes behave as a mononuclear Ln(III) magnetic system because of the presence of two diamagnetic cobalt(III) ions. Complex 1 has a molecular symmetry center, and it crystallizes in the C2/c space group, whereas complex 2 shows a lower molecular symmetry and crystallizes in the P21 /c space group. Magnetic investigations indicated that both complexes are field-induced single-ion magnets, and the Co(III) 2 -Dy(III) complex possesses a larger energy barrier [74.1(4.2) K] than the Co(III) 2 -Tb(III) complex [32.3(2.6) K].
    Chemistry - An Asian Journal 05/2014; · 4.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sequential reaction of a multisite LH4 ligand {2-[2-hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino]-2-methylpropane-1,3-diol} with appropriate lanthanide salts followed by the addition of Ni(NO3 )2 ⋅6 H2 O in a 4:1:2 stoichiometric ratio in the presence of triethylamine afforded four heterobimetallic trinuclear complexes [Ni2 Gd(LH3 )4 ]⋅3 NO3 ⋅3 MeOH⋅H2 O ⋅CH3 CN (1), [Ni2 Tb(LH3 )4 ]⋅3 NO3 ⋅3 MeOH⋅CH3 CN (2), [Ni2 Dy(LH3 )4 ] ⋅3 NO3 ⋅3 MeOH⋅H2 O⋅CH3 CN (3), and [Ni2 Ho(LH3 )4 ]⋅3 NO3 ⋅3 MeOH⋅H2 O ⋅CH3 CN (4). Complexes 1-4 possess linear trimetallic cores with a central lanthanide ion. Magnetic studies revealed a predominant ferromagnetic interaction between the Ni and Ln centers. Alternating current susceptibility measurements of complex 3 showed a small frequency dependence of the out-of-phase signal, χ''M , under zero direct current field, but without achieving a net maximum above 2 K. Magnetic studies on 1 revealed that it has a significant magnetocaloric effect.
    Chemistry - An Asian Journal 05/2014; · 4.57 Impact Factor