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Bis-pyridazine tectons support the structure of metallosupramolecular cavitand Cu2L4(4+), which is capable of selective encapsulation of SiF6(2-) anions by a set of multiple host-guest interactions.

This study presents a large-scale synthesis of water-soluble sodium fluosilicate (Na(2)SiF(6)) nanowires, which serve as a versatile template for producing nanotubes.

Two novel compounds, (L(1)H)(2)[SiF(6)] x 2H(2)O (1) and (L(2)H)(2)[SiF(5)(H(2)O)](2) x 3H(2)O (2), resulting from the reactions of H(2)SiF(6) with 4'-aminobenzo-12-crown-4 (L(1)) and monoaza-12-crown-4 (L(2)), respectively, were studied by X-ray diffraction and characterised by IR and (19)F NMR spectroscopic methods. Both complexes have ionic structures due to the proton transfer from the fluorosilicic acid to the primary amine group in L(1) and secondary amine group incorporated into the macrocycle L(2). The structure of 1 is composed of [SiF(6)](2-) centrosymmetric anions, N-protonated cations (L(1)H)(+), and two water molecules, all components being bound in the layer through a system of NH[...]F, NH[...]O and OH[...]F hydrogen bonds. The [SiF(6)](2-) anions and water molecules are assembled into inorganic negatively-charged layers via OH[dot dot dot]F hydrogen bonds. The structure of 2 is a rare example of stabilisation of the complex anion [SiF(5)(H(2)O)](-), the labile product of hydrolytic transformations of the [SiF(6)](2-) anion in an aqueous solution. The components of 2, i.e., [SiF(5)(H(2)O)](-), (L(2)H)(+), and water molecules, are linked by a system of NH[...]F, NH[...]O, OH[...]F, OH[dot dot dot]O hydrogen bonds. In a way similar to 1, the [SiF(5)(H(2)O)](-) anions and water molecules in 2 are combined into an inorganic negatively-charged layer through OH[...]F and OH[...]O interactions.

A new method for the stepwise synthesis of propylamines containing fragments of N-methyl propylamine as found in diatom bioextracts is presented and their activity in silicic acid condensation is described.

A systematic model study on the role(s) of putrescine homologues on silicification is presented and it is proposed that electrostatic forces between additive and silicic acid, and the hydrophobic behaviour of the additives are both important in silicification.

The highly siliceous cell walls of diatoms are probably the most outstanding examples of nanostructured materials in nature. Previous in vitro experiments have shown that the biomolecules found in the cell walls of diatoms, namely polyamines and silaffins, are capable of catalysing the formation of silica nanospheres from silicic/oligosilicic acid solutions. In a previous publication, silica precipitation was found to be strictly correlated with a phosphate-induced microscopic phase separation of the polyamines. The present contribution further characterises the phase separation behaviour of polyamines in aqueous solutions. In particular, a pronounced pH-dependence of the average particle diameter is found. It is, furthermore, shown that the ability of phosphate ions to form polyamine aggregates in aqueous solutions cannot be a purely electrostatic effect. Instead, a defined hydrogen-bonded network stabilised by properly balanced electrostatic interactions should be considered. Finally, solid-state 31P NMR studies on phase-separated polyamines, synthetic silica precipitates, and diatom cell walls from the species Coscinodicus granii support the assumption of a phosphate-induced phase separation process taking place during cell wall formation.

Biological organisms are able to direct the formation of patterned and hierarchical biomineral structures. Extractable organic materials have been found entrapped in diatom, sponge and plant biosilica, some of which have been isolated by selective chemical dissolution methods and their composition and structure studied. Information gained from the bioextracts has inspired materials chemists to design biomimetic analogues and develop bioinspired synthetic schemes for silica formation. The results obtained from bioinspired silicification investigations are hypothesised to arise from specific modes of action of the organic additives, which are described in this review. Specifically, additives in bioinspired silicification act either as catalysts, aggregation promoting agents or structure-directing agents or more typically, exhibit a combination of these behaviours.

Polyamines mimicking substances which occur naturally in biosilicas have been synthesized and show an accelerating effect on silica condensation, which depends on the chemical nature, the architecture (linear or branched), and the degree of polymerization.