[Fe(tvp)2 (NCS)2 ] (1) (tvp=trans-(4,4'-vinylenedipyridine)) consists of two independent perpendicular stacks of mutually interpenetrated two-dimensional grids. This uncommon supramolecular conformation defines square-sectional nanochannels (diagonal≈2.2 nm) in which inclusion molecules are located. The guest-loaded framework 1@guest displays complete thermal spin-crossover (SCO) behavior with the characteristic temperature T1/2 dependent on the guest molecule, whereas the guest-free species 1 is paramagnetic whatever the temperature. For the benzene-guest derivatives, the characteristic SCO temperature T1/2 decreases as the Hammet σp parameter increases. In general, the 1@guest series shows large entropy variations associated with the SCO and conformational changes of the interpenetrated grids that leads to a crystallographic-phase transition when the guest is benzonitrile or acetonitrile/H2 O.

Four tetrameric nickel(II) pseudohalide complexes have been synthesized and structurally, spectroscopically, and magnetically characterized. Compounds 1-3 are isostructural and exhibit the general formula [Ni(2)(dpk·OH)(dpk·CH(3)O)(L)(H(2)O)](2)A(2)·2H(2)O, where dpk = di-2-pyridylketone; L = N(3)(-), and A = ClO(4)(-) for 1, L = NCO(-) and A = ClO(4)(-) for 2, and L = NCO(-) and A = NO(3)(-) for 3. The formula for 4 is [Ni(4)(dpk·OH)(3) (dpk·CH(3)O)(2)(NCO)](BF(4))(2)·3H(2)O. The ligands dpk·OH(-) and dpk·CH(3)O(-) result from solvolysis and ulterior deprotonation of dpk in water and methanol, respectively. The four tetramers exhibit a dicubane-like core with two missing vertexes where the Ni(II) ions are connected through end-on pseudohalide and oxo bridges. Magnetic measurements showed that compounds 1-4 are ferromagnetic. The values of the exchange constants were determined by means of a theoretical model based on three different types of coupling. Thus, the calculated J values (J(1) = J(2), J(3), and D) were 5.6, 11.8, and 5.6 cm(-1) for 1, 5.5, 12.0, and 5.6 cm(-1) for 2, 6.3, 4.9, and 6.2 cm(-1) for 3, and (J(1), J(2), J(3), and D) 6.9, 7.0, 15.2, and 4.8 cm(-1) for 4.

A mullite single crystal with composition AlSiO exhibiting sharp satellite reflections was investigated by means of X-ray diffraction. For the refinement of a superspace model in the superspace group Pbam(α0½)0ss different scale factors for main and satellite reflections were used in order to describe an ordered mullite structure embedded in a disordered polymorph. The ordered fraction of the mullite sample exhibits a completely ordered vacancy distribution and can be described as a block structure of vacancy blocks (VBs) that alternate with vacancy-free blocks (VFBs) along a and c. The incommensurate nature of mullite originates from a modulation of the block size, which depends on the composition. The displacive modulation is analyzed with respect to the vacancy distribution and a possible Al/Si ordering scheme is derived, although the measurement itself is not sensitive to the Al/Si distribution. An idealized, commensurate approximation for 2/1 mullite is also presented. Comparison of the ordered superspace model with different preceding models reconciles many key investigations of the last decades with partly contradicting conclusions, where mullite was usually treated as either ordered or disordered instead of considering simultaneously different states of order.

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Destinezite, ideally Fe23+(PO4)(SO4)(OH)·6(H2O), is found as nodular lumps in hematite-rich epiclastic sediments accumulated in small crater lakes on the slopes of El Laco volcano. These lumps are almost entirely dominated by fine-grained destinezite replacing earlier lipscombite, and associated with gray hematite. The crystal structure of destinezite has been re-examined to test for possible differences with respect to the earthy and poorly crystalline destinezite that forms by weathering in cave soils and mine waste dumps. The structural refinements confirm that the differences are minor. The El Laco destinezite was refined in space group P1 with a = 9.5828(2), b = 9.7440(3), c = 7.3302(3) Å, and α = 98.796(3)°, β = 107.985(3)°, γ = 63.898(2)°, V = 584.50(4) Å3, and Z = 1. We measured by calorimetry the enthalpy and derived the entropy and the Gibbs free energy of formation of destine-zite (–4051.7 ± 4.3, –1518.5 ± 20.0, and –3598.9 ± 7.1 kJ/mol, respectively). This has allowed us to estimate the equilibrium constant in the temperature range 0–300 °C (log K = –27.97 ± 1.1). We can predict that destinezite coexists with hematite over the range of conditions that typically encompass the steam-heated hydrothermal environments recognized at El Laco. The presence of destinezite along with hematite and the occurrence of alunite, jarosite, and variscite in the system provide evidence of intense hydrothermal alteration during the extrusion of Fe-rich melts at El Laco volcano. The mineral assemblage and the available geochemical data suggest that destinezite formed in hydrothermal conditions by “maturation” of an immiscible Fe–P-rich melt. An unknown Fe–P–O phase produced by this melt was first replaced by lipscombite and later, owing to intense sulfidation, by destinezite. This replacement took place in the vadose zone above the paleowater table by relatively cool (<150 °C) groundwaters acidified by oxidation of magmatic SO2 to aqueous sulfate in a steam-heated system. Our model precludes other modes of formation, such as devitrification of hypothetical Fe–P–S–O-rich melts ejected from the volcano and supergene crystallization.