THE CRYSTAL AND MOLECULAR-STRUCTURE OF TRIS(TRANS-DICHLORO(MU-(1,2-BIS(3,5-DIMETHYLPYRAZOL-1-YL)ETHANE-N,N'))PALLADIUM(II)) - A MOLECULAR TRICORN

The ligand 1,2-bis(3,5-dimethylpyrazol-1-yl)ethane has been synthesised by the direct reaction of 1,2-dibromoethane and 3,5-dimethylpyrazole. The complex of this ligand with palladium(II) chloride has been prepared and the structure of its toluene solvate has been determined by X-ray crystallography. The compound crystallises in the triclinic space group P (1) over bar, a=11.088(5), b=13.786(5), c=21.169(9) Angstrom, alpha=86.96(3), beta=81.02(3), gamma=73.32(3)degrees with Z=2. Final residuals after least-squares refinement: R=0.030, R(w)=0.039. The compound has a trimeric structure which may be described as a 'molecular tricorn': the ligand bridges adjacent palladium centres, giving rise to a 21-membered trimetallic macrocycle. The overall structure closely approximates D-3 symmetry with approximate two-fold axes passing through each palladium atom and the centre of the 1,2-ethanediyl moiety opposite. An interesting feature of the structure is the close approach of several hydrogen atoms from the 1,2-ethanediyl groups to each palladium centre; these interactions are thought to be close-packing rather than agostic bonds.