Two tetra-Cd^II-substituted vanadogermanate frameworks

Two new tetra-Cd^II-substituted vanadogermanate frameworks {(CdX)₄Ge₈V^IV₁₀O₄₆(H ₂O)[V^III(H₂O)₂]₄(GeO ₂)₄}·8H₂O (X = ethylenediamine (en, 1) and 1,2-diaminopropane (dap, 2)) were hydrothermally prepared and characterized by IR spectra, elemental analysis, powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and X-ray single-crystal diffraction. Both are isomorphic, and their 3-D frameworks are made up of tetra-Cd ^II-substituted {(CdX)₄Ge₈V^IV ₁₀O₄₆(H₂O)}^12- fundamental building units interconnected through planar tetra-V^III [V^III ₄O₂(H₂O)₈]^8- clusters and tetrahedral GeO₄ bridges. In the unique {(CdX)₄Ge ₈V^IV₁₀O₄₆(H₂O)} ^12- cage, four [Ge₂O₇] dimers and four CdO ₄N₂ trigonal prisms are alternately concatenated by μ₃-O bridges to create a round {Ge₈Cd₄O ₂₈(X)₄}^16- fragment, five VO₅ groups are linked by sharing edges to generate a pentanuclear [V₅O ₁₇] subunit, and then the {Ge₈Cd₄O ₂₈(X)₄}^16- fragment is sandwiched by two V ₅O₁₇ subunits via sharing O-atoms producing a D _4h-symmetric {(CdX)₄Ge₈V^IV ₁₀O₄₆(H₂O)}^12- cage with a free water molecule located at the center. As we know, both display unprecedented 3-D organic-inorganic hybrid frameworks built up from the largest number of transition-metal-substituted vanadogermanate {(CdX)₄Ge ₈V^IV₁₀O₄₆}^12- cluster shells linked by both GeO₄ tetrahedra and rare [V^III ₄O₂(H₂O)₈]^8- clusters. Magnetic measurements reveal the antiferromagnetic couplings within the magnetic vanadium centers.