C.J. Ballhausen

Identification of the structure of the 3T1g (I) ← 3A2g band in the Ni(H2O)6 ++ complex

A detailed study of the low temperature absorption spectra of some 16 molecular crystals containing Ni(H2O)6 ++ has allowed us to identify the electronic and vibrational origins of the ‘red’ absorption band. A complete band contour analysis has been performed, which makes possible a discussion of the crossing of the 1Γ3 and 3Γ3 levels.

Confirmation of the red band system in MnO4 - as 1T1 ← 1A1 from the effect of pressure on single crystal absorption spectra

The application of uniaxial pressure to single crystals of LiClO4 . 3H2O/LiMnO4. 3H2O and Ba(ClO4)2. 3H2O/Ba(MnO4)2. 3H2O has led to a large splitting of the zerophonon origin line at 13 772 cm-1 in the absorption spectrum of the lithium salt and a much smaller splitting of the 14 247 cm-1 line in the corresponding spectrum of the barium salt. Furthermore, a third line at ∼ 13 764 cm-1 appears in the spectrum of the lithium salt at high pressures. The polarization behaviour of the three lines from the lithium salt is exactly as would be expected for a forbidden electric-dipole 1 T 1 ← 1 A 1 transition in the parent tetrahedral point group.

Electronic spectra of mono-substituted chromates

The electronic spectra of monosubstituted chromate ion derivatives, CrO3X-, where X-=F-, Cl-, Br- and IO3 -, have been measured at liquid helium temperature, employing a variety of sample forms. The observed electronic transitions correlate simply and directly with those of CrO4 2-, the lowest-lying transitions being only very weakly perturbed. Of particular interest is that the lowest excited state 1 Ea retains the peculiarities of the 1 T 1 parent state of CrO4 2-. The sharp line spectrum observed in Cr2O7 2- between 18 000 and 19 000 cm-1 is identified as 1 Ea (1 T 1 in T d) ←1 A 1 in a single O3CrO= chromophore. It is suggested that the observed features of the low-lying absorption bands can be explained by assuming that two spin-triplet states [3 E, 3 A 2] are located a few hundred wave numbers above the sharp 0-0 line of 1 Ea ←1 A 1.

The role of internal ligand modes in promoting radiationless transitions in metal complexes

The effect of internal ligand modes on the radiationless relaxation in metal complexes is considered. The theoretical model of the process is formulated within the framework of a dynamic coupling mechanism. The non-radiative rate constant is given as a product of an electronic and a vibrational factor, and it is concluded that it is the electronic factor that is rate-determining.

An extended Wolfsberg-Helmholz calculation on CuF6 -4

A semi-empirical calculation of the orbital energy levels of CuF6 -4 has been performed using the Wolfsberg-Helmholz approximations as extended by Ballhausen and Gray. The calculated value of 10Dq is rather insensitive to the initial assumptions and is in good agreement with experiments. The location of the ‘non-bonding’ t 1u level is on the other hand found to be very dependent upon the atomic wavefunctions used.

The electronic structure of the nitridoosmate(VIII) ion, OsO3N-

The electronic spectrum of the nitridoosmate(VIII) ion, OsO3N-, has been measured at liquid helium temperatures for thin films of the n-tetrabutyl-ammonium salt and for oriented, doped LiClO4. 3H2O single crystals. Four structured band systems, all individually composed of superimposed A 1 ← A 1 and E←A 1 transitions, are observed at energies comparable to those of the two lowest 1 T 2←1 A 1 transitions of OsO4. Prominent vibronic structure assigned to ν(Os-N) is observed for all of the bands. The bands are assigned to transitions to completely spin-orbit mixed states. The highest filled orbitals of OsO3N- are oxygen-localized and π non-bonding. The nitrido ligand appears to ‘dominate’ the π-bonding in the ion.

Stark effect in KCrO3Cl

The Stark effect has been measured on four lines in the crystal spectrum of KCrO3Cl. The two lines found at 5476 A and 5379 A represent 0-0 transitions to a split 1 E(C 3n ) state. From the directions of the permanent dipoles in the two excited states it is concluded that both states are distorted relative to the ground-state geometry. No indication of a resonance interaction in the unit cell was found.

A MO calculation of the static Jahn-Teller effect in CuF6 -4

Using the LCAO-MO wavefunctions estimated by an extended Wolfsberg-Helmholz method, the first order static Jahn-Teller effect in CuF6 -4 has been calculated. The bond length difference between the long and the short bonds is found to be some 0·2 a, in reasonable agreement with experiment.

The intensity and rotatory strength of the spin-forbidden Co(III) absorption band

The scrambling due to the spin—orbit coupling of the lowest excited singlet states 1 T 1g and 1 T 2g with 3 T 1g of diamagnetic Co(III) complexes is considered. Using a molecular orbital approach, this mixing is shown to account for the observed intensity of the 1 A 1g →3 T 1g band. Specifically it is found that it is the heavy atoms in the molecule which determines the intensity of the transition. This qualitatively explains the increasing intensity of the spin-forbidden band in the series of complexes Co(NH3)6 +3, Co(NH3)5F+2, Co(NH3)5Cl+2, Co(NH3)5Br+2 and Co(NH3)5I+2. Furthermore, the rotatory strength of the spin-forbidden band in Co(en)3 +3 is shown to be about 1 per cent of the rotatory strength for the 1 A 1→1 T 1 band.

The 4 A 2→2 E transitions of 2[Cr(en)3Cl3]KCl. 6H2O in strong magnetic fields

The Zeeman effect of the R absorption lines for the pure compound 2[Cr(en)3Cl3]KCl.6H2O has been measured photographically, using a strong pulsed magnet with fields of up to 200 000 gauss at 77 K. The results indicate g ∥ (4 A 2) = 1·82 , g ⊥(4 A 2) = 1·90 with g ∥(Ē) = -1·82 and g ∥ (2Ā) = 1·82. The uncertainties are of the order of ± 0·05.