科研之友
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摘要
By introducing the flexible ligands 3- or 4-pyridylacrylic acid into the Anderson-type polyoxometalate system, three new hybrid frameworks were obtained: [(3-Hpya)(2)Na][(3-Hpya)(2)Mn(H2O)(2)] [CrMo6H6O24]center dot 4H(2)O 1 (3-Hpya 3-(3-pyridyl)acrylic acid), alpha-(4-Hpya)(2){[(4-Hpya) (2)(H2O)(3)Mn](2)[(H2O)(4)Mn(CrMo6H6O24)(])}center dot 12H(2)O 2-alpha,beta-(4-Hpya)(2)[(4-Hpya)(2)(H2O)(4)Mn] [CrMo6H6O24]{[(4-Hpya)(H2O)(3)Mn](2)(CrMo6H6O24)}center dot 12H(2)O 2-beta, (4-Hpya = 3-(4-pyridyl)acrylic acid). All compounds have been characterized by elemental analysis, IR and UV-vis spectroscopy, TG analysis, and single crystal X-ray diffraction. Compound 1 is made up of [CrMo6H6O24](3-) polyoxoanions covalently linked by Mn-3-Hpya and Na-3-Hpya complexes to yield an unprecedented 2D network, which represents the first example of 2D hybrid assemblies based on Anderson-type polyoxometalates and manganese complexes, displaying the common 2D(4,4) topological net. When the 4-Hpya ligand was used, two polymorphic compounds 2-alpha and 2-beta were obtained. Polymorphism in 2-alpha and 2-beta arises from the different connectivity between polyoxoanions and manganese units. Compound 2-alpha is a bi-supporting structure composed of a dimeric cluster containing two Anderson polyoxoanions connected by a bridging manganese group, and two Mn-4-Hpya complexes. Compound 2-beta is built up of bi-supporting polyoxometalate clusters, isolated Anderson polyoxoanions and Mn-4-Hpya fragments to yield a 3D supramolecular channel framework. Magnetic susceptibility studies performed on 1 and 2 reveal weak antiferromagnetic coupling between the metal centers in each case.
