Stabilization of silicon tetrafluoride by crown ether complexation. Crystal and molecular structure of the host:guest complex 1:1:2 between trans-tetrafluoro-bis(aqua) silicon, 18-crown-6 and water

The product of the interaction of silicon tetrafluoride with a solution of 18-crown-6 in hexane has been obtained. The composition and structure of the compound [(trans-SiF 4 .2H 2 O).18C6.2H 2 O] (complex I) have been determined by X-ray methods. The compound (I) is monoclinic, space group P2 1 /a, a = 15.484(5), b = 9.651(3), c = 7.795(2) Å, γ = 121.45(3)°, Z = 2 for the composition C 12 H 32 F 4 O 10 Si. In the crystal of (I) the polymer-like structure is realized where water and [trans-SiF 4 .2H 2 O] moieties are connected with the host and between each other by the system of O-H ... O hydrogen bonds. O(H) ... O distances are in the limits 2.60(1)-2.91(1) Å. It was proved that in the process of crown ether complexation the hydratation of SiF 4 occurred with the formation of a trans-octahedral [SiF 4 .2H 2 O] moiety, Si-F and Si-O distances are equal to 1.658(7) and 1.853(9) Å, respectively. Between the individual chains there are only van der Waals interactions.