Spectroscopic investigation of the cobalt(II), nickel(II), copper(II) and zinc(II) tetrahalometallates of theN-ethylmorpholinum cation

Summary Tetrahalometallates of the type (Etmorphl1)21MX4 (M = Co¹¹, Ni¹¹ or Zn¹¹ and with X = Cl, Br or l; M = Cu^II with X = CI or Br) and mixed tetrahalocuprates, Etmorphll)₂[CUX_mY_4–m] (X = Cl; N' = 13r; m = 1,2,3) of theN-ethylmorpholinium cation were prepared and investigated by means of spectroscopic and magnetic measurements. While the cobalt(II), nickel(II) and zinc(II) complexes appear to be essentially, tetrahedral, the copper(II) complexes are discussed on the basis of a distorted ('flattened') tetrahedral symmetry. The electronic spectra of the complexes are assigned on this basis. The far i.r. spectra of the complexes show bands which are unambiguously assignable to the metal-halogen stretching modes. The effects of the counter cation on the geometry around the metal ion, compared with that of the morpholinium and piperidinium cations, are discussed in relation to the pK_a of the amine.