We focused on valence tautomeric complexes, 35),36) and found that several Co compounds show photo-induced magnetization effects because of the long-lived LMCT. 37),38) Figure 9 shows the magnetic properties of a switchable complex, [[Co.sup.III-LS](3,5-DBSQ)(3,5-DBCat)(tmeda)] (3,5-DBSQ = 3,5-di-tertbutyl-1,2-semiquinonate; 3,5-DBCat = 3,5-di-tertbutyl-1,2-catecholate; tmeda = N,N,N',N'-tetramethylethylenediamine).
When the LMCT band around the visible region was irradiated at 5 K, charge transfer from (dhbq)sup.3]- to Com was induced.
This coincides with the shift of (LMCT
) UV-vis band towards higher wavelengths for these three samples (Fig.
Analysis of the electronic structures and orbital components of the complexes indicates that these absorption bands mainly originate from the d(Ru)[pi] + p(QN and Cl ligands) [right arrow] (d(Ru) + [p.sup.*] (NO and QN ligands)) charge transfer processes, which were labeled as MLCT and LMCT
processes (L stands for NO, Cl, and QN ligands).
Two bands on the visible region at 383 and 445 nm may belong to S-Ni and O-Ni LMCT transitions [18, 19].
The main changes were in the visible region with a blue shift of LMCT band at 379 nm, respecting those of 1 (383 nm).
Co(II) gives absorption bands also at different wavelengths: due to the [S.sup.-] [right arrow] Co(II) ligand-to-metal charge transfer (LMCT
), an intense absorption band in the near UV, between 316 and 340 nm, can be observed.
And the peaks observed near 420 nm may be assigned as LMCT
due to the presence of ferrichexacyanate which is assumed by comparison with the solution spectrum of the complex.
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The high energy bands for this complex are observed at 263 and 346-371 nm, assignable to [pi] [right arrow] [[pi].sup.*] and [pi] [right arrow] [[pi].sup.*] LMCT
Similarly, the electronic spectra of Ni(II) complex exhibited absorption band at 22132 [cm.sup.-1] and assigned to be LMCT band and the d-d band suppressed by LMCT band.
Compound [pi] [right arrow] n [right arrow] LMCT [[pi].sup.*] [[pi].sup.*] ([cm.sup.-1]) ([cm.sup.-1]) L 36764 29239 L-Cu 35971 29069 22026 L-Co 36231 29068 -- L-Ni 36496 29069 22132 Compound d-d band Assignment Suggested structure L L-Cu 12345 [sup.2][B.sub.1g] Distorted [right arrow] octahedral [sup.2][B.sub.2g], Eg L-Co 16339,14836 [sup.4][T.sub.1g] Octahedral (F) [right arrow] [sup.4][T.sub.1g] (P) L-Ni -- [sup.3][A.sub.2g] Octahedral [right arrow] [sup.3][T.sub.1g] (F) Compound [[mu].sub.eff] (B.M) L L-Cu 4.52 L-Co 4.13 L-Ni 3.91 TABLE 4: Electrochemical parameters for Cu(II), Co(II), and Ni(II) complexes.