THE CRYSTAL AND MOLECULAR-STRUCTURE OF 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 synthesise d by the direct reaction of 1,2-dibromoethane and 3,5-dimethylpyrazole . The complex of this ligand with palladium(II) chloride has been prep ared 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 com pound has a trimeric structure which may be described as a 'molecular tricorn': the ligand bridges adjacent palladium centres, giving rise t o a 21-membered trimetallic macrocycle. The overall structure closely approximates D-3 symmetry with approximate two-fold axes passing throu gh each palladium atom and the centre of the 1,2-ethanediyl moiety opp osite. An interesting feature of the structure is the close approach o f several hydrogen atoms from the 1,2-ethanediyl groups to each pallad ium centre; these interactions are thought to be close-packing rather than agostic bonds.