RESUMO
The solvothermal reaction of DyCl3·6H2O, Ni(NO3)2·6H2O, and H4abtc ligands (H4abtc = 3,3',5,5'-azobenzene-tetracarboxylic acid) in the mixed DMF/H2O solvents (DMF = N,N-dimethylformamide) produced a three-dimensional (3D) Ni(II)-Dy(III) heterometallic coordination polymer (HCP) formulated as {[NH2(CH3)2]2[NiDy2(HCOO)2(abtc)2]}n (1). In 1, Dy(III) and Ni(II) ions interconnect through carboxylic O donors of abtc(4-) ligands to generate a linear trimer "Hourglass"-type {NiDy2} cluster, and the adjacent trinuclear {NiDy2} units are bridged by HCOO(-) groups to give a 1D "ladder" chain, which is further bridged by abtc(4-) ligands to form a new topology and named as "zsw3". Alternating-current magnetic susceptibility results indicate that 1 exhibits frequency-dependent out-of-phase signals with two relaxation processes, which suggests that it shows single-molecule magnet (SMM) behavior and represents the first example by using an SMM cluster as the building block to create a 3D Ni-Ln HCP, to the best of our knowledge. The energy barriers for 1 under a 1000 Oe applied direct current magnetic field are estimated from Arrhenius plots to be 40 and 42 K at higher and lower frequencies, respectively. Additionally, the crystalline structure of 1 could be stable to at least 310 °C, supported by thermogravimetric analyses and in situ variable-temperature powder X-ray diffraction patterns.
RESUMO
Three lanthanide coordination polymers (Ln-CPs) formulated as [Ln(azdc)(HCOO)]n [Ln = Gd(III) (1), Tb(III) (2), Dy(III) (3); H2azdc = 4,4'-azobenzoic acid] have been successfully obtained by the solvothermal reaction of Ln(III) ions with H2azdc ligands in the mixed solvent N,N-dimethylformamide (DMF)/H2O. Compared with our previous work on Ln-CPs with H2azdc ligands, [Gd2(azdc)3(DMA)2]n·2nDMA (1'; DMA = dimethylacetamide), in which the DMA molecules coordinate to Gd(III) ions that are replaced by HCOO(-) groups in 1, resulting in the distinct structures and properties of the final products. Adjacent Ln(III) ions in 1-3 are connected by HCOO(-) groups through bridging and chelating modes to give 2D layers, which are further linked by azdc(2-) ligands to produce 3D frameworks. Magnetic results declare that antiferromagnetic couplings exist in 1, although two different magnetic interactions among adjacent Gd(III) ions derived from antiferromagnetic interactions of the smaller Gd-O-Gd angles (Gd···Gd distances) and weak ferromagnetic interactions of the larger Gd-O-Gd angles (Gd···Gd distances) coexist in 1. Furthermore, the magnetocaloric effect (MCE) value of 1 is 1.5 times as large as that of 1'. More importantly, 1 exhibits excellent stabilities toward air, thermal, solvent, and acid/alkaline conditions. The results manifest that the crystalline structure of 1 can be stable at at least 425 °C supported by the in situ variable-temperature powder X-ray diffraction patterns and thermogravimetric analyses, in air for at least 3 months, and in common solvents for more than 1 week, as well as in aqueous solutions ranging from pH = 2 to 12 for more than 1 week.
RESUMO
We systematically studied the solvothermal reactions of transition-metal ions and H4abtc ligand and successfully isolated five metal-organic frameworks with various characterized tools, which are formulated as {[Mn2(abtc)(DMA)2.75]·1.25(DMA)}n (1), {[NH2(CH3)2][Co3(COOH)2.5(abtc)(H2O)2]2·H2O}n (2), {[Zn3(abtc)1.5(DMF)3]·1.75(DMF)}n (3), {[Zn2(abtc)(H2O)0.75(DMA)0.5]·3(DMA)·(H2O)}n (4), and {[Cd2(abtc)(DMA)2]·2(DMA)}n (5), (H4abtc = 3,3',5,5'-azobenzenetetracarboxylic acid, DMF = N,N-dimethylformamide, and DMA = N,N-dimethylacetamide). 1-5 all consist of {Mn(CO2)4}-type clusters and H4abtc ligands; however, they exhibit four distinct architectures resulting from different coordinated modes of H4abtc ligand. A pair of Mn(2+)ions in 1 forms a {Mn2(CO2)4} cluster, which further results in the "PtS"-type three-dimensional (3D) framework. In 2, three independent Co(2+) ions are bridged by COOH(-) groups to afford a {Co3} core, and {Co3} cores are connected by abtc(2-) to generate a "ZSW1"-type topology. Two types of {Zn2(CO2)4} secondary building units in 3 linked by abtc(2-) give the 3D "NbO"-type cage. When DMF is replaced by DMA and CH3OH, the scarce "nou"-type topology of 4 is obtained. And 5 is isomorphous to 1. Photoluminescence properties of 1-5 were characterized. Magnetic measurements demonstrate that dominant antiferromagnetic interactions exist in 1 and 2. In addition, 3 exhibits significant adsorption capability of CO2 and highly selective sorption of CO2 over N2.
RESUMO
Seven lanthanide coordination polymers (CPs), [Ln2(azdc)3(DMA)2]n·2n(DMA) (Ln = Sm(III) for 1, Eu(III) for 2, Gd(III) for 3, Tb(III) for 4, Dy(III) for 5, Ho(III) for 6, Er(III) for 7; H2azdc = 4,4'-azobenzoic acid, DMA = N,N-dimethylacetamide), have been successfully prepared with high yields via solvothermal methods and further studied by elemental analyses (EA), powder X-ray diffraction (PXRD), UV-vis spectra, photoluminescent spectra, thermogravimetric analyses (TGA), variable-temperature in situ PXRD analyses, and single-crystal X-ray diffraction. CPs 1-7 all consist of unique 1D lanthanide-carboxylate building units [Ln2(CO2)6]n constructed from the adjacent Ln(III) cations and carboxyl groups of the H2azdc ligands, which can further generate 3D frameworks with "fsy"-type topological structures via the link of azdc(2-). Furthermore, variable-temperature magnetic susceptibility measurements of 1-7 have been investigated. The results indicate that unusual ferromagnetic coupling between adjacent Gd(III) cations exists in 3, which is rarely reported in the Gd(III) complexes only bridged by µ1,3-COO groups. Meanwhile, the magnetic study reveals that 3 displays cryogenic magnetic refrigeration property, whereas 5 shows magnetic dynamics at low temperature.