Synthesis, Structure, Luminescent, and Magnetic Properties of Carbonato-Bridged Zn2IILn2II Complexes [(μ4-CO3)2{ZnIILnLnII(NO3)}2) (LnIII = GdIII, TbIII, DyIII; L1 = N,N'-Bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato, L2 = N,N'-Bis(3-ethoxy-2-oxybenzylidene)-1,3-propanediaminato)

Carbonato-bridged Zn(2)(II)Ln(2)(III) complexes [(mu(4)-CO3)(2){Zn(II)L(n)Ln(III)(NO3)}(2)]center dot solvent were synthesized through atmospheric CO2 fixation reaction of [(ZnLn)-L-II(H2O)(2)]center dot xH(2)O, Ln(III)(NO3)(3)center dot 6H(2)O, and triethylamine, where Ln(III) = Gd-III, Tb-III, Dy-III; L-1 = N,N'-bis(3-methorry-2-oxybenzylidene)-1,3-propanediaminato, L-2 = N,N'-bis(3-ethorry-2-oxybenzylidene)1,3-propanediaminato. Each Zn(2)(II)Ln(2)(III) structure possessing an inversion center can be described as two di-mu-phenoxo-bridged {Zn(II)L(n)Ln(III)(NO3)} binuclear units bridged by two carbonato CO32- ions. The Zn-II ion has square pyramidal coordination geometry with N2O2 donor atoms of L-n and one oxygen atom of a bridging carbonato ion at the axial site. Ln(III) ion is coordinated by nine oxygen atoms consisting of four from the deprotonated Schiff-base L-n, two from a chelating nitrate, and three from two carbonate groups. The temperature-dependent magnetic susceptibilities in the range 1.9-300 K, field-dependent magnetization from 0 to 5 T at 1.9 K, and alternating current magnetic susceptibilities under the direct current bias fields of 0 and 1000 Oe were measured. The magnetic properties of the Zn(2)(II)Ln(2)(III) complexes are analyzed on the basis of the dicarbonato-bridged binuclear structure, as the Zn-II ion with d(10) electronic configuration is diamagnetic. ZnGd1 (L-1) and ZnGd2 (L-2) show a ferromagnetic Gd-III-Gd-III interaction with J(Gd-Gd)Zn(2)(II)Ln(2)(III) = +0.042 and +0.028 cm(-1), respectively, on the basis of the Hamiltonian H = -2J(Gd-Gd)(S) over cap (Gd1).(S) over cap (Gd2). The magnetic data of the complexes (Ln(III) = D 11) were analyzed by a spin Hamiltonian including the crystal field effect on the Ln(III) ions and the Ln(III)-Ln(III) magnetic interaction. The Stark splitting of the ground state was so evaluated, and the energy pattern indicates a strong easy axis (Ising type) anisotropy. Luminescence spectra of (Zn2Tb2III)-Tb-II complexes were observed, while those of (Zn2Dy2III)-Dy-II were not detected. The fine structure assignable to the D-5(4) -> F-7(6) transition of ZnTb1 and ZnTb2 is in good accord with the energy pattern from the magnetic analysis. The Zn(2)(II)Ln(2)(III) complexes (Ln(III) = Tb-III, Dy-III) showed an out-of-phase signal with frequency-dependence in alternating current susceptibility, indicative of single molecule magnet. Under a dc bias field of 1000 Oe, the signals become significantly more intense and the energy barrier, Delta/k(B), for the magnetic relaxation was estimated from the Arrhenius plot to be 39(1) and 42(8) K for ZnTb1 and ZnTb2, and 52(2) and 67(2) K for ZnDyl and ZnDy2, respectively.