Three series of heterometallic NiII–LnIII Schiff base complexes: synthesis, crystal structures and magnetic characterization?

Dalton Transactions Pub Date: 2017-08-28 DOI: 10.1039/C7DT02351K

Abstract

Three series of NiII–LnIII complexes were synthesized with the general formulae [(μ3-CO3)2{Ni(HL)(CH3–CH2OH)Ln(CH3COO)}2]·2CH3CH2OH (1–6) (Ln = Tb (1), Dy (2), Ho (3), Er (4), Tm (5), Yb (6); H3L = N,N′-bis(3-methoxysalicylidene)-1,3-diamino-2-prop-anol), [Ni(HL)Ln(dbm)3]·CH3OH2·2CH2Cl2 (7–10) (Ln = Tb (7), Eu (8), Gd (9), Ho (10); Hdbm = 1,3-diphenyl-1,3-propanedione) and [Ni(HL)(H2O)(tfa)Ln(hfac)2] (11–15) (Ln = Tb (11), Dy (12), Eu (13), Gd (14), Ho (15); Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione, tfa? = trifluoroacetate) using compartmental Schiff base ligands in conjunction with auxiliary ligands. For the NiII2LnIII2 series, the tetranuclear structure could be considered as two NiII–LnIII dinuclear subunits bridged by two carbonates derived from atmospheric carbon dioxide. The LnIII ions of complexes 1–6 were octa-coordinated with distorted triangular dodecahedral geometry, while the LnIII ions of the dinuclear complexes 7–15 were nona-coordinated with distorted muffin geometry. The magnetic properties of the three series complexes were studied using dc and ac magnetic measurements. For the NiII–GdIII complexes, the dc magnetic susceptibility measurements suggested the existence of the anticipated ferromagnetic interaction between NiII and GdIII ions. The fitting of the χMT vs. T data processed by PHI software provided the parameters g = 2.08 (J = +0.87 cm?1) for 9 and g = 2.02 (J = +1.83 cm?1) for 14. The interaction exchange was magneto-structurally correlated to the Ni–O–Gd angle (α) and Ni(μ-O)Gd dihedral angle (β). With an applied dc field, complexes 1 (Tb), 2 (Dy), 7 (Tb) and 12 (Dy) exhibited single magnetic relaxation with SMM parameters of Ueff/k = 13.60 K, 11.52 K, 7.69 K and 5.14 K, respectively. Analysis of the Cole–Cole plots for complexes 2 and 7 suggested that a single relaxation process was mainly involved in the relaxation process, with α values in the range of 0.37–0.17 and 0.14–0.11, respectively.

Graphical abstract: Three series of heterometallic NiII–LnIII Schiff base complexes: synthesis, crystal structures and magnetic characterization
Recommended Literature