The syntheses, spectra and structures of five-coordinate cobalt(II) complexes of pyrazolyl-containing ligands

Cobalt(II) chloride complexes of 2,6-bis(1-(pyridin-2-yl)pyrazol-3-yl)pyr ( L-1) and 2,6-bis(pyrazol-3-yl)pyridine (L-2) have been prepared and charact erised by electronic spectroscopy and single-crystal X-ray diffractometry. The spectra are normal for five-coordinate cobalt(II) complexes. [Co(L-1)Cl -2] is triclinic, crystallising in space group P (1) over bar with a = 9.53 0(4), b = 10.642(6), c = 12.675(5) Angstrom, alpha = 65.97(4), beta = 70.34 (4), gamma = 67.65(4)degrees. The structure was refined by least-squares te chniques to convergence at R = 0.036 for 2342 observed reflections. In this complex the potentially quinquedentate Ligand functions as a tridentate li gand. [Co(L-2)Cl-2] is monoclinic, crystallising in space group C2/c with a = 10.255(4), b = 17.138(4), c = 7.988(3) Angstrom, beta = 104.62(2)degrees . The structure was refined by least-squares techniques to convergence at R = 0.026 for 999 observed reflections. The structure of this complex is ext remely similar to that of dichloro(2,2':6',2 "-terpyridine)cobalt(II), with the tridentate ligand spanning the two axial sites and one equatorial site of an approximate trigonal bipyramid with the chloro ligands bound in the equatorial plane. (C) 1999 Elsevier Science S.A. All rights reserved.