T. G. Dunne
Spectra of ~r(lll)Complexes
Reed College
Portland, Oregon 97202
A n inorganic chemistry experiment
crystal field theory (1, 2) predicts for transition metal octahedral complexes that the d orhitals are split in the manner shown in Figure 1. The original assumption of this theory that the d electrons have a coulombic interaction with the ligands considered as point charges is certainly not correct, and a prim+ calculations of the crystal field splitting parameter, 10 Dq, based on this model are generally in poor agreement with experimental values obtained from visible spectra (3). However, because of the octahedral symmetry it is true that the splitting of the d levels predicted by crystal field theory is qualitatively correct. That is, whatever the nature of the ligand-metal interaction, the d,,, d, and d,, orbitals will form a threefold equivalent set (t set) and the d&,. and d,. orbitals will form a twefold equivalent (e set) in the complex.' Thus, 10 Dq, the energy difference between these two sets, may be determined by experiment, even though its accurate theroretical calculation is diicult. It is found that spectroscopically measured values of 10 Dq fall in a sequence of increasing energy which is quite independent of the metal ion. That is, although the value of 10 Dq for a given ligand is different for each metal ion, the qualitative sequence of increas ing energy on ligand substitution is essentially the same and therefore independent of the metal ion. This sequence, the so-called spectrochemical series ( I , $ ) , runs as follows: I- < Br- < Cl- < F - < CxHaOH < &O < NHa < Ethylenedittmine
