Assembling Anderson-type polyoxometalates with manganese(ii) in the presence of pyridylacrylic acidligands: a 2D layer and two polymorphs

Abstract

By introducing the flexible ligands 3- or 4-pyridylacrylic acid into the Anderson-type polyoxometalate system, three new hybrid frameworks were obtained: [(3-Hpya)₂Na][(3-Hpya)₂Mn(H₂O)₂][CrMo₆H₆O₂₄]·4H₂O 1 (3-Hpya = 3-(3-pyridyl)acrylic acid), α-(4-Hpya)₂{[(4-Hpya)₂(H₂O)₃Mn]₂[(H₂O)₄Mn(CrMo₆H₆O₂₄)₂]}·12H₂O 2-α, β-(4-Hpya)₂[(4-Hpya)₂(H₂O)₄Mn][CrMo₆H₆O₂₄]{[(4-Hpya)(H₂O)₃Mn]₂(CrMo₆H₆O₂₄)}·12H₂O 2-β, (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-α and 2-β were obtained. Polymorphism in 2-α and 2-β arises from the different connectivity between polyoxoanions and manganese units. Compound 2-α 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-β 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.