Hydrothermal synthesis and characterization of three one-dimensional chain materials formed by reduced tetra-capped Keggin polyoxoanions and [M(en)2]2+ (M = Cu, Co and Ni) cations

Three compounds based on polyoxometalate building blocks, [Cu(en)2]{[Cu(en)2]2[MoVI5MoV3VIV8O40(PO4)]} · 4H2O (1), [Co(en)2]{[Co(en)2]2[HMoVI4MoV4VIV8O40(PO4)]} · 5H2O (2) and [Ni(en)2]{[Ni(en)2]2[MoVI5MoV3VIV8O40(VO4)]} · 2H2O (3) (en = ethylenediamine), have been synthesized and characterized by elemental analysis, IR, XPS, XRD, TGA and single-crystal X-ray diffraction analysis. The result of structure determination shows that isomorphic compounds 1, 2 and 3 feature a one-dimensional chain built from the reduced tetra-capped pseudo-Keggin polyoxoanion, which is further interconnected by [M(en)2]2+ (M = Cu, Co and Ni) groups via the terminal oxygen atoms of polyoxoanions. The crystal data for these compounds are the following: 1, monoclinic, space group C2/c, a = 26.702(3) Å, b = 13.4539(14) Å, c = 19.5987(19) Å, β = 108.650(2)°, V = 6671.0(12) Å3, Z = 4; 2, monoclinic, space group C2/c, a = 26.244(3) Å, b = 13.5070(17) Å, c = 19.581(3) Å, β = 106.881(2)°, V = 6641.8(15) Å3, Z = 4; 3, monoclinic, space group C2/c, a = 26.2789(15) Å, b = 13.5408(6) Å, c = 19.6312(9) Å, β = 106.2590(10)°, V = 6706.1(6) Å3, Z = 4. Variable-temperature magnetic susceptibility measurements of compounds 1 and 3 reveal the feature of antiferromagnetic exchange in these compounds.