Charge Transfer Spectra - Summary

Ligand to Metal (LMCT) or Metal to Ligand (MLCT)

Jorgensen first defined the LMCT in octahedral hexahalides.

He defined four possible sets of transitions from the s- and p-hexahalide levels to d(t2g) and d(eg). These species were all low -spin. He screamed "EUREKA" when he noticed that for d6 species and above, only the two higher energy sets of transitions were observed.

MLCT bands shift to the RED (lower energy) for given metal as the ligand is EASIER to reduce (and vice versa).

MLCT bands shift to the RED (lower energy) for given ligand as the metal is EASIER to oxidize (and vice versa).

LMCT bands shift to the RED (lower energy) for given metal as the ligand is EASIER to oxidize (and vice versa).

LMCT bands shift to the RED (lower energy) for given ligand as the metal is EASIER to reduce (and vice versa).

e.g. MLCT; hn M(II) -->L< M(III) --->L < M(IV) --> L etc.

e.g. LMCT I- --> M < Br- --> M < Cl- --> M < F- --> M

and Se2- --> M < S2- --> M < O2- --> M

For unsaturated ligands, e.g. bipyridine, expect to see M --> p*

Transitions shifting to the red as the organic fragment gets more delocalized.

See: A.B.P. Lever, Charge Transfer Spectra of Transition Metal Complexes. J. Chem. Ed., 51, 612-616 (1974).

And the first and second editions of Lever, "Inorganic Electronic Spectroscopy" (Elsevier 1968, 1984)