Bond length and bonded radii variations in sulfide molecules and crystals containing main group elements

Molecular orbital calculations on 18 hydrosulfide molecules containing selected main group X-cations yield minimum energy bond lengths, R_t(XS), that reproduce those observed in chemically similar sulfide crystals. A least-squares analysis shows that R_t(XS) can be estimated by the equation R = l.83(s/r)^-0.21, where s is the Pauling bond strength and r is the row number of the X-cation in the periodic table, with 98% of the variation of R_t(XS) being explained in terms of a linear dependence on R. In addition, R serves to rank observed XS bond lengths in sulfide crystals for main group X-cations for rows 1 through 5 of the periodic table to within 0.12Å on average, with R accounting for 96% of the variation in the observed bond lengths.

Bonded radii obtained from electron density maps calculated for the molecules show that the radii of both the X-cations and S atom increase with R_t(XS). A similar trend has been found to hold for the bonded radii and the R_t(XO) bond lengths calculated for hydroxyacid molecules (Finger and Gibbs 1985). The radius of S is smaller (1.16Å) when bonded to highly electronegative atoms like 4-coordinate As and larger (1.67Å) when bonded to a considerably less electronegative atoms like 4-coordinate Li but is smaller than Shannon's (1.70Å) crystal radius and Pauling's ionic crystal radius (1.84Å).