HETEROCYCLIC-SYSTEMS CONTAINING TIN(IV) .10. CONTROL OF 3-CENTER INTERACTIONS X...SN-HAL IN STANNOCANES BY HALIDE TYPE

The stannocanes Cl-2/Br-2/I-2-Sn(SCH2CH2)(2)X OL = NMe, O, S) have been synthesized from SnHal(4) and (HSCH2CH2)(2)X. Assigned vibrational (IR and Raman) and NMR data (C-13,and Sn-119) and, for X = O and S, crystal structure determinations are given. All nine compounds comprise molecules in which the tin atom approaches a trigonal-bipyramidal pentacoordination with 2xS and Hal(eq) as equatorial ligands and with X and Hal, as axial ligands. The latter two bonds are described by means of a three-center, four-electron interaction X Sn-Hal for which a qualitative MO description in terms of frontier orbitals is given. A ''path'' from a tetrahedron to a trigonal bipyramid is controlled by four electronic factors (donor strength of X, electronegativity of Hal(ax), lone pair interaction of Hal(ax), type of equatorial ligands) and one steric factor (geometrical flexibility of X). These influences are discussed with respect to the structural and spectroscopic data (Pauling-type bond orders BO(X Sn) and BO(Sn-Hal), geometrical goodness of the trigonal bipyramids, force constants f(Sn-Hal), and Sn-119-NMR chemical shifts) of the nine compounds and are compared with the data of five analogous series taken from the literature. Regarding the influence of Hal(ax), the factors ''electronegativity'' and ''lone pair interaction'' are counteractive and cancel each other, between bromine and iodine. The donor strength of X in the nine compounds decreases in the following orders: NMe > S greater than or equal to O in the solid state and NMe > O > S in solution.