SYNTHESIS, CHARACTERIZATION AND CRYSTAL-STRUCTURE OF TRANS-[2,6-BIS(3-PHENYLPYRAZOL-1-YL-KAPPA-N2)PYRIDINE-KAPPA-N]CHLOROBIS(TRIMETHYLPHOSPHINE)RUTHENIUM(II) PERCHLORATE - EVIDENCE FOR MERIDIONAL STERIC CROWDING

The synthesis, characterization, and crystal structure of trans-[RuL(Cl)(PMe3)2]ClO4 [L = 2,6-bis(3-phenylpyrazol-1-yl)pyridine] are reported. The complex crystallizes in the non-centrosymmetric trigonal space group P3(1)21 (no. 152) with a = 14.158(2), c = 14.493(3) angstrom, and Z = 3. Both the Ru(II)-containing cation and the perchlorate anion (which is disordered) lie on a crystallographic two-fold axis. This represents the first structural characterization of a transition-metal complex which utilizes a member of the family of bis(pyrazolyl)pyridine ligands. In addition, the crystal structure yields evidence that the ligand L may be sterically more suitable for co-ordination to a ruthenium(II) centre than the analogous diphenyl-substituted terpyridine ligand, dpt (6,6"-diphenyl-2,2':6'2"-terpyridine). For both tridentate ligands, the donor nitrogen atoms take up three meridional sites and the phenyl substituents are directed toward the fourth equatorial co-ordination site; however, due to the large distance between the two phenyl arms of L (relative to the dpt), the former ligand can be utilized in synthesising the present ruthenium(II) complex whereas the analogous dpt complex cannot readily be prepared.