Isomerism and CH-pi-interaction for dinuclear antimony(V) complexes with phenyl-benzylphosphonato bridges

Phenyl benzylphosphonic acids react with antimony(V) chloride, water and al cohol to yield the binuclear antimony(V) complexes Cl3Sb(O)[O2PRR'](OR ")Sb Cl3 1 to 6 with R = C6H5CH2, O2NC6H4CH2, R' = C6H5O, O2NC6H4O, (CH3)(3)C6H2 O and OR " = OH or OCH3, resp.. For 2, 4 and 6 with OR" = OCH, in solution, two isomers can be detected by NMR spectroscopy which slowly exchange R " at 25 degrees C. Upon warming to 120 degrees C the conversion increases. Fo r the hydroxo compounds 1, 3 and 5 (OR" = OH) there is a rapid exchange of the OH protons at 25 degrees C which can be frozen only by cooling below -8 0 degrees C. The crystal and molecular structures of 2 and 4 were determine d.