SYNTHESIS AND STRUCTURES OF ALKALI(ALKOXY) ANTIMONATES AND BISMUTHATES

As(OtBu)(3) does not form adducts with alkali metal tert-butoxides MOt Bu (M = Li, Na, K, Rb and Cs), whereas the corresponding Sb(OtBu)(3) ( 2) and Bi(OtBu)(3) (3) react with MOtBu (M = K, Rb, Cs) to yield M(OtB u)(4)Sb (M = K (6), Rb (7), Cs (8)) and M(OtBu)(4)Bi (M = 9). respecti vely. X-ray structure determinations for 6 and 9 show them to be one-d imensional coordination polymers composed of E(OtBu)(4) (E = Sb, Bi) u nits linked through potassium atoms. These E(OtBu), units display a Ps i-trigonal-bipyramidal coordination around the metal atom (Sb-O = 1.97 1(2) and 2.181(2) Angstrom, Bi-O = 2.068(8) and 2.275(8) Angstrom). Bo th the structures exhibit a planar four-coordinate environment of oxyg en around the potassium atoms (K-O = 2.650(2)-2.967(2) Angstrom in 6, 2.53(1)-3.15(1) Angstrom in 9). Compound 2 reacts with two equivalents of KOtBu to afford K2Sb(OtBu)(5) dioxane (10), which contains Sb2K2O5 cage units and can be described as an O-5 trigonal bipyramid with met al atoms inserted in the equatorial edges. Each metal atom is tetracoo rdinated by oxygen atoms of the cage (Sb-O = 1.979(3)-2.144(3) Angstro m, K-O = 2.592(3)-2.775(2) Angstrom). The dioxane molecules increase t he coordination number at each potassium atom to five by Forming bridg es between the molecules through K-O bonds. Reaction of 2 and 3 with N aOtBu produce the cluster compounds Na4Sb2O(OtBu)(8) (4) and Na4Bi2O(O tBu)(8) (5) in high yields. K4Sb2O(OtBu)(8) (11) is obtained in almost quantitative yield by heating KSb(OtBu)(4) in benzene for 24 h. Compo unds 4, 5 and 11 crystallise in rhombohedral lattices; the crystal str ucture analyses show a superposition of molecules, with an isotropic o xygen-centred Mb octahedron. The formation of these oxo-tert-butoxides is accompanied by evolution of isobutene. Addition of four equivalent s of THF to 11 gives K4Sb2O(OtBu)(8) . 4 THF (12). X-ray diffraction s tudies reveal a cis arrangement of the Sb atoms in the central OSb2K4 unit. K4Sb2O2(OiPr)(12) (13) is obtained as the major product on heati ng KSb(OtBu)(4) and subsequent reaction with isopropyl alcohol. In the crystal structure, two oxygen-centred Sb2K2 tetrahedra (K-O 2.693(4) Angstrom, Sb-O = 1.982(5) Angstrom) linked through iPrO-K bonds (2.726 (7)-2.738(7) Angstrom) are observed. In the reactions of KSb(OtBu)(4) (6) with the metal halides CaCl2, TlCl and CuI, a halide ion is transf erred to potassium; this results in formation of potassium halide, the corresponding alkoxide and Sb(OtBu)(3).