Two Tetra-CdII-Substituted Vanadogermanate Frameworks

Two new tetra-CdII-substituted vanadogermanate frameworks {(CdX)4Ge8­VIV10O46(H2O)­[VIII(H2O)2]4­(GeO2)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-CdII-substituted {(CdX)4Ge8­VIV10O46­(H2O)}12– fundamental building units interconnected through planar tetra-VIII [VIII4O2(H2O)8]8– clusters and tetrahedral GeO4 bridges. In the unique {(CdX)4Ge8­VIV10O46­(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 via sharing O-atoms producing a D4h-symmetric {(CdX)4Ge8­VIV10O46­(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)4Ge8VIV10O46}12– cluster shells linked by both GeO4 tetrahedra and rare [VIII4O2(H2O)8]8– clusters. Magnetic measurements reveal the antiferromagnetic couplings within the magnetic vanadium centers.