STERIC PROPERTIES OF SULFOXIDE LIGANDS - SYNTHESIS AND CRYSTAL-STRUCTURE OF MER-[RUCL3(PH(2)SO)(3)]

Solid and circular cone angles and ligand profiles have been calculated for some sulfoxides, showing that S-bonded ligands are markedly bulkier than O-bonded ligands. An application of the cone angles to complexes of Ru-II and Ru-III showed that the bonding mode of sulfoxides appears to be the result of a balance between electronic and steric effects. The complex mer-[RuCl3(dpso)(3)] (dpso=Ph(2)SO) has been synthesized and structurally characterized: triclinic, space group P ($) over bar 1, Z=2 with a=10.315(3), b=13.093(4), c=15.692(5) Angstrom, alpha=102.98(2), beta=106.79(1), gamma=102.17(2)degrees. Two of the three sulfoxides are O- and one is S-bonded. One dpso-O is trans to dpso-S, while the other is trans to Cl. The co-ordination bond distances are consistent with the trans-influence order O < Cl < S. Strain-energy and conformational-entropy terms of three isomers of mer-[RuCl3(dpso)(3)] have been evaluated through molecular mechanics calculations. The energy difference of 7.6 kcal mol(-1) between the characterized complex and the linkage isomer with two trans dpso-S ligands indicates that the isomer isolated is probably favoured thermodynamically and suggests that the interligand steric interactions play an important role in the isomer stability.