Solid-state vibrational spectroscopy: Part VI. An infrared and raman spectroscopic study of transition metal(II)4-methylpyridine complexes

Infrared (4000–200 cm^?1) and Raman (3500–300 cm^?1 ) spectra are reported for metal(II) halide and thiocyanate 4-methylpyridine complexes of the following stoichiometries: (MX₂(4-Mepy)₂) {M = Mn, Co, Cu or Zn, X = Cl or Br; M = Mn, Ni or Zn, X = NCS}; (MX₂(4-Mepy)₄) {M = Mn, Fe, Co or Ni, X = Cl or Br; M = Mn, Fe, Co, W or Cu, X = NCS}. For a given series of isomorphous complexes there is a correlation between the sum of the differences between the liquid and ligand values of the ν₁, ν₂, ν₃, ν₄, ν₅, ν₆, ν₇, ν₈, ν₉, ν₁₀, ν₁₂, ν₁₃ and ν₁₄ modes of 4-methylpyridine and the strength of the metal-nitrogen bond. Comparison of the shift values of pyridine and 4-methylpyridine complexes supports the suggestion that, unlike the situation in the pyridine complexes, back-donation from the metal to the ligand is unimportant in the 4-methylpyridine complexes.