Closely-related ZnII2LnIII2 complexes (LnIII = Gd, Yb) with either magnetic refrigerant or luminescent single-molecule magnet properties

摘要: The reaction of the compartmental ligand N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L) with Zn(NO3)2·6H2O and subsequently Ln(NO3)3·5H2O (Ln(III) = Gd Yb) triethylamine in MeOH using a 1:1:1:1 molar ratio leads to formation tetranuclear complexes {(μ3-CO3)2[Zn(μ-L)Gd(NO3)]2}·4CH3OH (1) and{(μ3-CO3)2[Zn(μ-L)Yb(H2O)]2}(NO3)2·4CH3OH (2). When was performed absence triethylamine, dinuclear compound [Zn(μ-L)(μ-NO3)Yb(NO3)2] (3) is obtained. structures 1 2 consist two diphenoxo-bridged Zn(II)-Ln(III) units connected by carbonate bridging ligands. Within units, Zn(II) Ln(III) ions occupy N3O2 inner O4 outer sites ligand, respectively. remaining positions on are occupied oxygen atoms belonging groups, bidentate nitrate ion 1, coordinated water molecule 2, leading rather asymmetric GdO9 trigonal dodecahedron YbO8 coordination spheres, Complex 3 made acetate-diphenoxo triply bridged Zn(II)Yb(III) where Yb(III) exhibits YbO9 environment. Variable-temperature magnetization measurements heat capacity data demonstrate that has significant magneto-caloric effect, maximum value -ΔSm 18.5 J kg(-1) K(-1) at T 1.9 K B 7 T. Complexes show slow relaxation single-molecule magnet (SMM) behavior under an applied direct-current field 1000 Oe. fit high-temperature Arrhenius equation affords effective energy barrier for reversal 19.4(7) τo 3.1 × 10(-6) s 27.0(9) 8.8 10(-7) 3, However, full range temperature indicates process could take place through Raman-like than activated Orbach process. chromophoric L(2-) able act as "antenna" group, sensitizing near-infrared (NIR) Yb(III)-based luminescence intramolecular transfer excited states accepting ion. These several bands 945-1050 nm region, corresponding (2)F5/2→(2)F7/2 transitions arising from splitting both multiplets. observed lifetimes τobs 0.515 10 μs shorter lifetime due presence one center (and lesser extent noncoordinated molecules), facilitating vibrational quenching via O-H oscillators. Therefore, combining field-induced SMM NIR luminescence, can be considered dual magneto-luminescent materials.