CH-PI INTERACTION IN BINUCLEAR ANTIMONY(V ) COMPLEXES WITH BRIDGING PHOSPHONATO LIGANDS

The binuclear antimony(V) complexes Cl3Sb(O)[R-3((RO)-O-1)PO2](OR2)SbC l3 with R-t = R-2 = CH3 and R-3 = C6H5 (1), (C6H5)(2)CH (2) and (C6H5C )(3) (3) are prepared by reaction of the corresponding methoxophosphon ic acids with antimony(V) chloride, water and methanol. 2 and 3 crysta llize in the monoclinic space group P2(1)/c with a = 966.8, b = 1603.4 , c = 1794.8 pm, beta = 91.4 degrees, Z = 4 and with a = 988.0, b = 15 92.8, c = 1816.0 pm, beta = 91.7 degrees and 2 = 4 resp.. The molecule s of 1 to 3 are formed from two octahedra sharing one edge with antimo ny as central atoms. Oxygen atoms are links between the antimony atoms which are bridged by the bidentate phosphonato ligands. The molecules of 2 and 3 show a significant CH-pi interaction between the CH3 group R-2 and a phenyl ring of the bridging phosphonato groups in the solid state as well as in solution. In solution the phosphonato groups are inverted rapidly and the R-2 groups undergo a slow intermolecular exch ange. Two isomers can be detected by NMR spectroscopy.