Two Tetra-Cd^II-Substituted Vanadogermanate Frameworks

Abstract

Two new tetra-Cd^II-substituted vanadogermanate frameworks {(CdX)₄Ge₈­V^IV₁₀O₄₆(H₂O)­[V^III(H₂O)₂]₄­(GeO₂)₄}·8H₂O (X = ethylene­diamine (en, <b>1</b>) and 1,2-diamino­propane (dap, <b>2</b>)) 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^IV₁₀O₄₆­(H₂O)}^12– fundamental building units interconnected through planar tetra-V^III [V^III₄O₂(H₂O)₈]^8– clusters and tetrahedral GeO₄ bridges. In the unique {(CdX)₄Ge₈­V^IV₁₀O₄₆­(H₂O)}^12– cage, four [Ge₂O₇] dimers and four CdO₄N₂ trigonal prisms are alternately concatenated by μ₃-O bridges to create a round {Ge₈Cd₄O₂₈(X)₄}^16– fragment, five VO₅ groups are linked by sharing edges to generate a pentanuclear [V₅O₁₇] subunit, and then the {Ge₈Cd₄O₂₈(X)₄}^16– fragment is sandwiched by two V₅O₁₇ subunits <i>via</i> sharing O-atoms producing a <i>D</i>_4<i>h</i>-symmetric {(CdX)₄Ge₈­V^IV₁₀O₄₆­(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)₄Ge₈V^IV₁₀O₄₆}^12– cluster shells linked by both GeO₄ tetrahedra and rare [V^III₄O₂(H₂O)₈]^8– clusters. Magnetic measurements reveal the antiferromagnetic couplings within the magnetic vanadium centers