The influence of organic bases and substituted groups on coordination structures affording two mononuclear Dy(iii) single-molecule magnets (SMMs) and a novel Dy(iii)–K(i) compound with unusually coordinated fluorine atoms

Abstract

Two mononuclear Dy(III) compounds and one heteronuclear Dy(III)–K(I) compound, [Dy(tmpd)₃(4,4′-dmpy)] (1), [KDy₂(tmpd)₈]·C₅H₆N (2) and [Dy(tmpd)₃(dppz)] (3) (4,4′-dmpy = 4,4′-dimethyl-2,2′-bipyridyl, tmpd = 4,4,4-trifluoro-1-(4-methylphenyl)butane-1,3-dione, and dppz = dipyrido[3,2-a:2′,3′-c]phenazine), were synthesized by changing the organic bases and auxiliary ligands. The coordination environments of compounds 1 and 3 are different DyN₂O₆ configurations resulting from steric effects of different auxiliary ligands, while 2 has KF₆O₆ and DyO₈ coordination environments because of the introduction of an organic base (CH₃OK). The Dy(III) ions in compounds 1 and 2 have a triangular dodecahedral (D_2d) configuration and square antiprismatic (D_4d) configuration, respectively. Compound 3 contains two crystallographically equivalent Dy(III) ions of which the eight-coordinated geometries uniformly behave as distorted square antiprismatic (D_4d) configurations. Compound 2 affords a novel Dy(III)–K(I) compound with unusually coordinated fluorine atoms of trifluoromethyl groups of β-diketone ligands. 2 is a centrosymmetric structure in which the central K(I) ion is located at the middle of two Dy(III) ions, resulting in an icosahedral (I_h) configuration. Magnetic investigations demonstrate that 1 and 3 display slow magnetic relaxation behaviors. The effective barriers are 94.91 K in 1 and 82.44 K in 3. The M versus H data exhibit weak butterfly-shaped hysteresis loops at 2 K for 1 and 3. The uniaxial magnetic anisotropies, magnetostructural correlations and relaxation mechanism were investigated both experimentally and theoretically. The experimental and theoretical studies indicate that compound 1 exhibits the best magnetic properties among compounds 1–3. The theoretical predictions of quantum tunneling of magnetization time and effective barriers are consistent with the corresponding experimental values. Our results indicate that the different organic bases and substituted groups of auxiliary ligands play an important role in synthetic processes, finally affording distinct structures and magnetic properties.