MULTINUCLEAR MAGNETIC-RESONANCE STUDY OF THE DILEADTRICHALCOGENIDE ANIONS PB(2)S(N)CH(3-N)(2-) (CH=SE OR TE), PB2SSETE2-, AND M(2)SE(3)(2-)(M=SN AND OR PB) AND THE CRYSTAL-STRUCTURES OF (2,2,2-CRYPT-K+)(2)SN2TE3(2-) AND (2,2,2-CRYPT-K+)(2)SN2SE3(2-)/

The new series of dileadtrichalcogenide anions Pb2SnSe3-n2- and Pb2SnT e3-n2- (n = 0-3) and Pb2SSeTe2- have been obtained by extraction of th e appropriate quaternary or quinternary alloys of the type KPb(x)S(y)C h(z) (Ch = Se, Te, or Se/Te) in ethylenediamine ten) and characterized in en solution by Se-77, Te-125, and Pb-207 NMR spectroscopy. The NMR findings indicate that the solution structures of the anions are base d on a trigonal bipyramid having axial lead atoms bonded to three chal cogen atoms in the equatorial plane. Direct and pairwise additivity tr ends among the Pb(2)S(n)Ch(3-n)(2-) (Ch = Se or Te) series show that ( 1)J((Pb-77Se)-Pb-207), delta(Pb-207), delta(Se-77), and delta(Te-125) decrease upon chalcogen atom substitution as follows: S --> Te > Se -- > Te >> S --> Se, The isostructural Sn2Se32- and SnPbSe32- anions have also been prepared in en by reaction of K2Se with SnSe and SnSe/PbSe mixtures, respectively, and represent the first examples of Sn(II) cha lcogenide anions. Both anions were characterized in en solution by Se- 77, Sn-117, Sn-119, and Pb-207 NMR spectroscopy. The two-bond Sn(II)-S n(II) and Sn(II)-Pb(II) coupling constants, (2)J(Sn-117-Sn-119) and (2 )J(Sn-119-Pb-207), have been observed for the first time and represent unusually large values [i.e., (2)J(Sn-119-Sn-117) = 1514 Hz and (2)J( Sn-119-Pb-207) = 1145 Hz]. After removal of the nuclear dependence to give reduced coupling constants, K-1(M-Ch), and after allowances for r elativistic effects, which are significant in the heavy-element spin-s pin couplings being considered, the magnitudes of the relativistically corrected reduced couplings, (K-1(M-Ch))(RC), of the tin, lead, and t in/lead trigonal bipyramidal cage anions are shown to be consistent wi th predominantly p-bonded cages. The syntheses and crystal structures are reported for two salts in which the Sn2Te32- and Sn2Se32- anions h ave been stabilized as a result of complexation of the potassium catio ns by ,21,24-hexaoxa-1,-10-diazabicyclo[8.8.8]hexacosane (2,2,2-crypt) . The crystal structure of (2,2,2-crypt-K+)(2)Sn2Te32- was determined at -100 and 24 degrees C; it crystallizes in the trigonal system P (3) over bar c1, with two molecules in a unit cell of dimensions a = 11.7 03(4) [11.817(9)] Angstrom and c = 21.945(6) [22.01(2)] Angstrom at -1 00 degrees C [24 degrees C] with R = 0.0628 [0.102] for 757 [305] obse rved (I > 2[2]sigma(I)) reflections. The compound (2,2,2-crypt-K+)(2)S n2Se32- crystallizes in the monoclinic system, space group P2(1)/n, wi th four molecules in a unit cell of dimensions a = 10.342(3) Angstrom, b = 46.976(6) Angstrom, c = 11.402(4) Angstrom, and beta = 90.15(3)de grees at 24 degrees C with R = 0.089 for 3016 observed (I > 2 sigma(I) ) reflections. In addition to 2,2,2-crypt-K+ cations, the compounds co ntain the trigonal-bipyramidal homopolyatomic anions Sn2Te32- and Sn2S e32- having approximate D-3h point symmetry. In Sn2Te32-, the Sn-Te di stances are 2.887(4) [2.887(8)] Angstrom with Sn-Te-Sn angles of 68.7( 1) [69.4(3)]degrees and Te-Sn-Te angles of 90.9(1) [90.8(2)]degrees an d an axial Sn...Sn distance of 3.270(6) [3.287(17)] Angstrom. In Sn2Se 32-, the Sn-Se distances are 2.637(3)-2.677(3) Angstrom with Sn-Se-Sn angles of 70.9(1)-71.1(1)degrees and Se-Sn-Se angles of 87.9(1)-92.1(1 )degrees and an axial Sn...Sn distance of 3.090(3) Angstrom. In both s tructures, the distance between the two axial tin atoms is substantial ly less than the accepted van der Waals contact.