Ethylenediamine-metal complexes shifts

In these dinitrile complexes, p(CN) are shifted to higher frequencies upon coordination. As in the case of ethylenediamine complexes (Sec. III-2), infrared spectroscopy has been used to determine the conformation of the ligand in metal complexes. The Cu(I) complex, which is known to contain the gauche conformation, exhibits two CH2 rocking modes at 966 and 835 cm , whereas the Ag(l) complex, Ag(sn)2Bp4, shows a single CH2 rocking mode at 770 cm , which is characteristic of the trcns conformation. ... 

All of the major bands of ethylenediamine listed in Table 5.7 are shifted to lower-wavenumber values when the ligand is complexed with zinc. The shifts may be attributed to the weakening of the N-H bonds, resulting from the drainage of electrons from the nitrogen atom when the metal ion is coordinated. 

---