Pyrazoles and imidazoles as ligands. Part IV. Ligand‐field spectra of tetragonal coordination compounds containing the ligand 3(5)‐methylpyrazole

Ligand‐field spectra of compounds with the formula M(anion)2(MPZ)4 in which MPZ is 3(5)‐methylpyrazole are discussed. The metal ions under investigation are Mn, Fe, Co, Ni and Cu(II), and the anions are NO3−, Cl−, Br−, I−, ClO4− and BF4−. The spectrochemical parameters Dqxy, B, Ds and Dt are calculated from the spectral data for a number of isomorphous compounds. The alterations of these parameters are discussed as a function of the metal ions and the anions. Compared with other tetragonal compounds the distortion from octahedral symmetry in the present compounds is quite large. The origin of this strong tetragonal distortion seems to be the hydrogen‐bond formation between the coordinated ligands and the coordinated anions, weakening the metal‐anion bond in the z‐direction. The tetragonal species M(anion)2(MPZ)4 also have been investigated in solutions of acetone, nitromethane and methylene chloride. For some compounds this tetragonal species also exists in solution, but for some other compounds ligand exchange and/or dissociation occurs, as concluded from spectral absorptions in combination with conductivity measurements.