Fig. 1. (a) (Top) A representation of the phonon interactions in the Raman process. (bottom) A representation of phonon interactions in the local modes process. (b) Molecular structures of 1, 2, and 3. Grey, blue, red, and orange represent carbon, nitrogen, oxygen and copper, respectively. Hydrogen atoms are omitted for clarity. 1 is best described as pseudo-tetrahedral, whereas 2 and 3 are square planar.