화학공학소재연구정보센터
Inorganic Chemistry, Vol.58, No.1, 165-179, 2019
Wide-Range UV-to-Visible Excitation of Near-Infrared Emission and Slow Magnetic Relaxation in Ln(III)(4,4 '-Azopyridine-1,1 '-dioxide)[Co-III(CN)(6)](3-) Layered Frameworks
Trivalent lanthanide ions combined with two molecular linkers, organic 4,4'-azopyridine-1,1'-dioxide (apdo), and inorganic hexacyanidocobaltate(III), gave a series of magnetoluminescent coordination polymers, [{Ln(III)(apdo)-(H2O)(4)}{Co-III(CN)(6)}]center dot 2H(2)O (Ln = Nd, 1; Tb, 2; Dy, 3; Er, 4; Tm, 5; Yb, 6). They are hybrid organic-inorganic layered frameworks composed of cyanido-bridged {Ln(2)(mu-NC)(4)Co-2} squares linked by Ln-apdo-Ln bridges into a coordination network of a mixed 4- and 8-metal ring topology. Lanthanide-(III) complexes, [Ln(III)(mu-apdo)(2)(H2O)(4)(mu-NC)(2)](+), of a distorted dodecahedral geometry are isolated by diamagnetic [Co-III(CN)(6)](3-) and apdo linkers. As a result, 1-6 reveal field-induced slow relaxation of magnetization, with typical temperature-dependent relaxation of a single-ion origin for Nd-III-containing 1, Dy-III-containing 3, and Yb-III-containing 6. The related alternate-current magnetic data were precisely analyzed, indicating the multiple magnetic relaxation pathways, including a direct process, strong quantum tunneling of magnetization, non-negligible Raman processes, and crucial two-phonon Orbach thermal relaxation. The thermal energy barriers of the Orbach process, Delta E/k(B), are 15.1(9) K with tau(0) = 9.8(9) x 10(-6) s at H-dc = 4500 Oe, 16.1(8) K with tau(0) = 9.0(9) x 10(-5) s at H-dc = 1500 Oe, and 17.3(6) K with tau(0) = 3.2(7) x 10(-6) s at H-dc = 700 Oe, for 1, 3, and 6, respectively, proving the single-molecule magnet (SMM) behavior. Because of the presence of [Co(CN)(6)](3-), 1-6 show strong UV absorption, while the chromophoric apdo leads to the strong absorption in the-visible range. As a result, the visible 4f/3d metal-centered emission is quenched, but the near-infrared luminescence from Nd-III and Yb-III is observed in 1 and 6, respectively. It is realized by Co-to-Ln metal-to-metal, and apdo-to-Ln ligand-to-metal energy transfers; thus, broad UV-to-visible excitation can be explored. Compounds 1-6 form a novel family of functional bimetallic assemblies, incorporating NIR-emissive SMMs as presented for NdCo (1) and YbCo (6) derivatives.