Palladium(II) complexes of the macrocycle 3,3,7,7,11,11,15,15-octamethyl-1,9-dithia-5,13-diazacyclohexadecane. Crystal structure analysis of 3,3,7,7,11,11,15,15-octamethyl-1,9-dithia-5,13-diazacyclohexadecanepalladium(II) bis(hexafluorophosphate)

Abstract

The preparation of 1 : 1 complexes, (1a) and (1b), of palladium(II) chloride with the macrocycle 3,3,7,7,11,11,15,15- octamethyl-1,9-dithia-5,13-diazacyclohexadecane (L) and with its 2,2,16,16-tetradeuterio (L′) analogue is reported. These behave as 1 : 1 electrolytes in acetonitrile. Proton n.m.r. spectra of solutions of the complexes in acetonitrile or chloroform are consistent with the presence of two major stereoisomers, the proportions of which depend on the amount of water present in the solution. It is suggested that both isomers have trigonal bipyramidal structures with the nitrogen atoms occupying axial positions and differ only in the stereochemistries at nitrogen. The spectral properties of (1a) in aqueous solution are very similar to those of the derived PdL(PF₆)₂(2) and are consistent with the presence of two isomeric square planar dications. In contrast, an X-ray structural investigation of crystalline (2) shows the presence of only one isomer. Crystals of (2) are Monoclinic, a= 9.529(2), b= 10.750(2), c= 14.996(3)Å, β= 93.28(2)°, Z= 2, space group P2₁/n. The structure was solved by Patterson and Fourier techniques and refined by full-matrix least-squares methods to R= 0.042 and R′= 0.050 for 2 017 reflections with I > 3σ(I). The Pd atom lies on an inversion centre and has distorted square-planar co-ordination with Pd–S 2.307(1), Pd–N 2.090(4)Å, S–Pd–N 95.6(1)° and the PdS₂N₂ moiety necessarily planar. Both six-membered chelate rings adopt chair conformations, one of them being severely flattened. The PF₆^– anions are linked to the cation via N–H ⋯ F hydrogen bonds (N ⋯ F 3.064 Å) and the orientation adopted leads to fluorine atoms lying above and below the co-ordination plane with Pd ⋯ F 3.259 Å.