Atmospheric C02 fixation of [NiII(3-MeOsaItn)(H20)2]-2.5H20 [3-MeOsaltn = N,N'-bis(3-methoxy-2-oxybenzylidene)- 1,3-propanediaminato], LnIII (N03)3-6H20, and triethylamine occurred in methanol/ acetone, giving a first series of carbonato-bridged NiII2LnIII2 complexes [(μ4-C03)2{NiII(3-MeOsaltn)(MeOH)-LnIII(N03)}2] (lGd, 1Tb, and IDy). When the reaction was carried out in acetonitrile/water, it gave a second series of complexes [(μ4-C03)2{NiIII(3-MeOsaltn)(H20)-LnIII(N03)}2]-2CH3CN-2H20 (2Gd, 2Tb, and 2Dy). For both series, each NiII2LnIII2 structure can be described as two di-μ<-phenoxo-bridged NiIILnIII binuclear units bridged by tvvo carbonato C032- units to form a carbonato-bridged (μ4-C03)2{NiII2LnIII2} structure. The high-spin NiII ion has octahedral coordination geometry, and the LnIII ion is coordinated by 09 donor atoms from NiII(3-MeOsaltn), bidentate N03-, and one and two oxygen atoms of two C032- ions. The N03- ion for the first series roughly lie on Ln--O(methoxy) bonds and are tilted toward the outside, while for the second series, the two oxygen atoms roughly lie on one of the Ln--O(phenoxy) bonds due to the intramolecular hydrogen bond. The temperature-dependent magnetic susceptibilities indicated a ferromagnetic interaction between the NiII and LnIII ions (LnIII - GdIII, TbIII, DyIII) for all of the complexes, with a distinctly different magnetic behavior between the two series in the lowest-temperature region due to the LnIII--LnIII magnetic interaction and/or different magnetic anisotropics of the TbIII or DyIII ion. Alternating-current susceptibility measurements under the 0 and 1000 Oe direct-current (dc) bias fields showed no magnetic relaxation for the NiII2GdIII2 a complexes but exhibited an out-of-phase signal for NiII2TbIII2 and NiII2DyIII2 indicative of slow relaxation of magnetization. The energy barriers, Δ/kg for the spin flipping were estimated from the Arrhenius plot to be 12.2(7) and 6.1(3) Kfor 1Tb and 2Tb, respectively, and 18.1(6) and 14.5(4) K for IDy and 2Dy, respectively, under adcbias field of 1000 Oe. Compound IDy showed relatively slow relaxation of magnetization reorientation even at zero dc applied field with Δ/fcB = 6.6(4) K. [ABSTRACT FROM AUTHOR]