LONE-PAIR-INDUCED CHIRALITY IN POLYOXOTUNGSTATE STRUCTURES - TIN(II) DERIVATIVES OF A-TYPE XW(9)O(34)(N-) (X=P,SI), INTERACTION WITH AMINO-ACIDS

Tin(II) tungstophosphate and tungstosilicate derivatives [Sn-3(II)(alp ha-PW9O34)(2)](12-) (1), [Sn-3(II)(alpha-SiW9O34)(2)](14-) (2), and [S n-3(II)(beta-SiW9O34)(2)](14-) (3) have been prepared by reaction of t in(LI) sulfate with Na8H[A,beta-PW9O34]. 24H(2)O, Na-10[alpha-SiW9O34] . xH(2)O, and Na-10[beta-SiW9O34]. 26H(2)O, respectively. Oxidation of 1 with Br-2 yields [(Hosn(IV)OH)(3)(PW9O34)(2)](12-) (1'). The new he teropolyanions were characterized by elemental analysis, infrared spec troscopy, multinuclear NMR, and X-ray crystallography. Crystals of Cs1 1H[Sn-3(II)(PW9O34)(2)]. 14H(2)O (anion 1) are triclinic, space group <(P)over bar 1>, with lattice constants a = 12.904(3) Angstrom, b = 18 .059(3) Angstrom, c = 21.618(3) Angstrom, alpha = 111.68(2)degrees, be ta = 94.04(2)degrees, gamma = 101.41(1)degrees, V = 4531.5(14) Angstro m(3), Z = 2. Crystals of Cs12.5H1.5[Sn-3(II)(alpha-SiW9O34)(2)]. 24.5H (2)O (anion 2) are triclinic, space group <(P)over bar 1>, with lattic e constants a = 13.101(5) Angstrom, b = 18.140(7) Angstrom, c = 21.367 (8) Angstrom, alpha = 111.54(4)degrees, beta = 92.22(4)degrees, gamma = 102.98(2)degrees, V = 4561(3) Angstrom(3), Z = 2. Both 1 and 2 have structures in which three Sn-II cations are sandwiched between XW(9) u nits. In 1 the coordination of each Sn is trigonal bipyramidal with th e ''equatorial'' unshared electron pair directed toward the center of the anion. The inequality of the equatorial (2.11 Angstrom) and axial (2.33 Angstrom) Sn-O bond lengths results in one PW9 group being rotat ed by 7 degrees with respect to the other PW9. The overall anion symme try is D-3. Anion 2 has a more pronounced (10 degrees) rotation of the SiW9 groups, which results in ''tetrahedral'' Sn coordination, again with the unshared electron pairs directed internally (overall anion sy mmetry C-3). The greater rotation in the structure of 2 may be a conse quence of electrostatic repulsions between the more highly charged SiW 9O3410- anions. All three anions display one-line Sn-119-NMR and two-l ine W-183-NMR (intensity 1:2) spectra, although the lines are broad (6 0-100 Hz) for 2 and 3 suggesting a slow fluxional process, probably ra cemization via an internal twist. In contrast, the two W-NMR lines of 1 are narrow and the more intense line shows two-bond coupling to P (1 .7 Hz). This line is split into two by the addition of the chiral amin o acids lysine, isoleucine, and histidine, but is unaffected by achira l glycine. Crystals of a lysine complex have been isolated, but have i n all cases so far proved to be disordered.