Cristobalite is the only corner-sharing tetrahedral framework that can maintain perfectly regular SiO4 tetrahedra throughout the entire 180° range of Si–O–Si angles. It is, thus, the ideal system for a study of the energy dependence of the Si–O–Si angle in a crystalline framework. Using the VASP first principles density functional code, we have derived energy versus Si–O–Si angle curves for pure silica and versus Ge–O–Ge angles for pure germania models of cristobalite. In addition, the frameworks of quartz, tridymite, and the zeolites sodalite (SOD) and metavariscite (BCT) were studied. The range of angles with low energies is larger for silica, though the lowest-energy Ge–O–Ge angle is always lower than the corresponding lowest-energy Si–O–Si angle in the same framework type. We discuss which framework types are possible for pure-silica and pure-germania based on a rigid tetrahedron model.

We present a novel open-framework oxide material constructed from Ge(10)(O,OH)(28) (Ge(10)) oxide clusters prepared via a nonsurfactant route. The material shows two distinct pore windows of 9.43 and 4.65 A and a low framework density structure of 12.7 Ge atoms per 1000 A(3). The topological study leads to the recognition of a newly observed trinodal 6,7-heterocoordinated net related to the 7-coordinated swh net. The structure displays large rigid cylinders showing features indicating a growth mechanism by hard-sphere packing of the inorganic moiety similar to that observed in mesoporous materials.

Six new zirconogermanates have been prepared under hydrothermal conditions using amines as bases. There are four new structure types (ASU-n) with a common motif of ZrGe(5). ASU-23 is a layered structure: ZrGe(3)O(8)(OH)F.[C(10)H(26)N(4)].H(2)O, space group P2(1)/n, a = 6.7957(8) A, b = 12.700(1) A, c = 24.293(3) A, beta = 97.936(2) degrees, V = 2076.4(4) A(3). ASU-24 is a pillared layered structure: Zr(3)Ge(6)O(18)(OH(2),F)(4)F(2).[C(6)H(18)N(2)].[C(6)H(17)N(2)](2).2H(2)O, space group P2(1)/n, a = 7.4249(3) A, b = 25.198(1) A, c = 11.3483(5) A, beta = 90.995(1) degrees, V = 2122.9(2) A(3). This material has the lowest framework density (FD) of any oxide material that we are aware of (FD = 8.48 metal atoms/nm(3)). Two other materials form three-dimensional open-frameworks, ASU-25: ZrGe(3)O(9).[C(3)H(12)N(2)], space group P112(1)/a, a = 13.1994(4) A, b = 7.6828(2) A, c = 11.2373(3) A, gamma = 91.233(3) degrees, V = 1139.29(5) A(3). The other is ASU-26: ZrGe(3)O(9).[C(2)H(10)N(2)], space group Pn, a = 13.7611(3) A, b = 7.7294(2) A, c = 11.2331(3) A, beta = 104.793(1) degrees, V = 1155.21(4) A(3). ASU-25 is related to the mineral umbite K(2)ZrSi(3)O(9).H(2)O. The germanium equivalent has been prepared through the inorganic route: K(2)ZrGe(3)O(9).H(2)O, space group P2(1)2(1)2(1), a = 13.6432(6) A, b = 7.4256(3) A, c = 10.3973(4) A, V = 1053.33(8) A(3). The structural relationships between ASU-25 and its inorganic counterpart are described. The thermal decomposition of the germanium umbite generated the cyclic trigermanate K(2)ZrGe(3)O(9), analogue of the mineral wadeite, crystallizing in the orthorhombic system, a = 7.076 A, b = 12.123 A, c = 10.451 A, V = 904.5 A(3).

Key indicators: single-crystal X-ray study; T = 298 K; mean (C-C) = 0.012 Å; R factor = 0.071; wR factor = 0.147; data-to-parameter ratio = 7.2.Magnesium acetate crystallizes upon reaction with imidazole in dimethylformamide at elevated temperatures to form the title magnesium acetate imidazole cluster species,with two Mg atoms in octahedral coordination. The complex has crystallographic twofold rotation symmetry. Each Mg atom is coordinated by two imidazole ligands, two linking acetate bridging ligands, a terminal acetic acid ligand, and a bridging O atom lying on the symmetry axis. ] M r = 575.14 Orthorhombic, Aba2 a = 8.6927 (14) Å b = 19.106 (3) Å c = 16.834 (3) Å V = 2795.8 (8) Å 3 Z = 4 Mo K radiation = 0.15 mm À1 T = 298 (2) K 0.12 Â 0.10 Â 0.05 mm Data collection Bruker SMART APEX diffractometer Absorption correction: multi-scan (SADABS; Bruker, 2004) T min = 0.986, T max = 0.994 10414 measured reflections 1287 independent reflections 1034 reflections with I > 2(I) R int = 0.112