Complexation of alkali triflates by crown ethers:: Synthesis and crystal structure of [Na(12-crown-4)2][SO3CF3], [Na(15-crown-5)][SO3CF3], [Rb(18-crown-6)][SO3CF3], and [Cs(18-crown-6)][SO3CF3]

Complexes of trifluoromethanesulfonates (triflates) with alkali metals Na, Rb, Cs have been prepared in the presence of various macrocyclic polyether crowns [(12-crown-4), (15-crown-5) and (18-crown-6)]. Depending on the combination of alkali ion with crown, the complexes include separated ion pairs [Na(12-crown-4)(2)] [SO3CF3] (1) and contact ion pairs [Na(15-crown-5)] [SO3CF3] (2), [Rb(18-crown-6)] [SO3CF3] (3), and [Cs(18-crown-6)] [SO3CF3] (4). in which the triflate acts as a bidentate ligand. It is shown that the choice of crown ether is of paramount importance in determining the solid-state structural outcome. The complex resulting from the pairing of crown ether (1) develops, when the crown ether is too small in relation to the alkali ion radius. When the cavity size of the crown ether is matched with the alkali ion radius, simple monomeric structures are identified in 2, 3 and 4. The title compounds crystallize in the monoclinic crystal system: 1: space group P2/c with a = 9.942(3), b=11.014(2), c=10.801(3) angstrom, beta= 97.30(2)degrees, V = 1173.1(4) angstrom(3), Z=2, R1= 0.0812, wR2 = 0.1133: 2: space group P2(1)/m with a=7.949(2), b=12.063(3), c =9.094(2) angstrom, beta= 105.98(2)degrees, V = 838.3(4) angstrom(3), Z = 2, R1 = 0.0869, wR2 = 0.1035: 3: space group P2(1)/c with a = 12.847(5), b = 8.448(2), c = 22.272(6)A, P = 122.90(3)degrees, V = 2029.5(1) angstrom(3), Z = 4, R1 = 0.0684, wR2 = 0. 1044: 4: space group P2(1)/n with a = 12.871(3), b 8.359(1), c = 19.019(4) angstrom, beta = 92.61(2)degrees, V = 2044.2(6) angstrom(3), Z=4, R1 = 0.0621, wR2 = 0.0979.