Two new “onium” fluorosilicates, the products of interaction of fluorosilicic acid with 12-membered macrocycles: structures and spectroscopic properties

Abstract

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.

The variations in hydrogen bonding in hexafluorosilicate salts of protonated methyl substituted pyridines and tetramethylethylenediamine

“…Such unperturbed octahedral geometry of the [SiF 6 ] 2À anion can also be found in some other complexes with [SiF 6 ] 2À anion, as observed previously [9,12,14].…”

“…The hydrogen bonds between ions are much stronger than between molecules and can play dominant roles in crystal structures [15]. This hydrogen-bonding network is prone to incorporate during the crystallization the water molecules which participate in hydrogen bonding [4,9,[12][13][14].…”

“…The electrostatic attractive forces between these cations and the anions [SiF 6 ] 2À facilitates the formation of extensive N-HÁ Á ÁF hydrogen-bond interactions [4][5][6][7][8][9][10][11][12][13][14]. The hydrogen bonds between ions are much stronger than between molecules and can play dominant roles in crystal structures [15].…”

“…Most of the known structures with [SiF 6 ] 2À exhibit extensive hydrogen-bonding networks that mainly incorporate all fluorine atoms of [SiF 6 ] 2À [4][5][6][7][8][9][10][11][12][13][14]23]. The nitrogen bases used in syntheses of 1, 2, and 4 are sterically demanding due to methyl groups on the basic nitrogen atom (4) or …”

Binding of fluoro-containing anions to hexaazamacrocyclic ligand: Competitive interactions of fluoride and tetrafluoroborate anions with hexaprotonated [18]aneN6

“…Having a long-standing interest to the fluoro-containing anions (SiF À 5 , [SiF 5 Á H 2 O] À , SiF 2À 6 , GeF 2À 6 , BF À 4 ) we have studied the ways of their binding by the macrocyclic molecules [7] and alongside with the others [8] have estimated the possibilities of O-, O,N-crown ethers and azamacrocycles to elicit either the neutral (BF 3 Á H 2 O, SiF 4 Á 2H 2 O, GeF 4 Á 2H 2 O) or the aforementioned charged species from aqueous solutions. Particularly for the N,O-containing crown ethers and azamacrocycles easily protonating in the reaction medium the interaction with the anionic species has been demonstrated [9][10][11].…”