Ligand-metal charge transfer LMCT transitions

Platinum(IV) is an oxidant therefore, ligand-metal charge-transfer (LMCT) transitions are prominent in the electronic spectra of its complexes and play important roles in the photosubstitution chemistry. This is especially true for the hexahalo complexes, [PtXj]. The aqueous hexachloroplatinate(IV) ion, [PtCl ] , undergoes both photoaquation ... 

Ligand-to-metal charge transfer (LMCT) transitions between the bonding ligand-centred MOs and antibonding metal-centred MOs. Such transitions are found where a ligand is easily oxidised and the metal is easily reduced. 

Fig. 1. Schematic orbital energy diagram representing various types of electronic transitions in octahedral complexes. A line connects an atomic orbital to that molecular orbital in which it has the greatest participation. 1 metal centered (MC) transitions 2 ligand centered (LC) transitions 3a ligand-to-metal charge transfer (LMCT) transitions 3b metal-to-ligand charge transfer (MLCT) transitions...

Ligand to metal charge transfer (LMCT) transition An electronic transition in a metal complex that corresponds to excitation populating an electronic state in which considerable electron transfer from a ligand to a metal center has occurred. 

The electronic absorption spectrum of Ti(norbomyl)4 (10) is shown in Fig. 1. The intense band at 245 nm ( = 29,200 moP cm" in hexane) was assigned to a fully allowed ligand-to-metal charge-transfer (LMCT) transition (18). The weaker band at 367 nm (e = 253 mol cm in hexane) and shoulders at 312 and 412 nm were attributed to other spin or orbitally forbidden LMCT transitions. Near-UV irradiation of yellow hexane solu-... 

For Cu+ (d °) and open-shell metal ions, the absorption spectra in the visible spectral range are totally different, and weak bands (e of the order of 10 M cm ) are found up to 600-700 nm. Cu.5+ exhibits the expected wide MLCT absorption (see above), whereas the bands observed for Ni-+ (d ) and Co + (d ) are assigned to metal-centered (MC) or ligand-to-metal-charge-transfer (LMCT) transitions. Finally, the Pd + (d ) catenate has to be considered a special case since it is actually a... 

Substitution of the active site Zn(II) of LADH by Co(II), Ni(II), Cu(II), or Fe(II) introduces spectroscopic probes, which are sensitive to the coordination geometry, the electrostatic environment, and the protein conformation. UV-visible absorbance signatures consisting of d- d and ligand-to-metal charge transfer (LMCT) transitions have proven to be useful probes of the site environment (3, 24-26, 29, 34, 35). The Co(II) and Ni(II) derivatives exhibit catalytic parameters (i.e., hydride transfer rates, Km and lq values) that are similar to those of the native Zn(II)-enzyme (25). The Cu(II) and Fe(II) enzymes show reduced reactivities and catalytic parameters, which indicate these derivatives are of limited use as analogues of the native enzyme (24). 

Fig. 3(A) shows the UV-Vis spectra of 0.1SnO2-MSM samples before and after calcination synthesized with varied periods of HT in comparison to that of commercial SnOa. Two absorption bands with maximum intensities at 220 and 270 nm were observed for the commercial SnOa. The former was assigned to the ligand to metal charge transfer (LMCT) transition from O to Sn, which was at octahedral (Oh) site. The latter band was the electron transition from the valance to conduction bands (band gap ca. 3.76 eV for bulk SnOa) [1]. Only one broad band of very weak intensity was observed in the spectra of the O.lSnOa-MSM samples before calcination, while two bands at 215 and 253 nm were seen for the samples after calcination. The broad band at ca. 205 210 nm for the uncalcined samples was assigned to the LMCT band of 0 to tetrahedral (Td) Sn ions in the silica lattice [17]. When the HT period was prolonged to 24 h, a shoulder appeared ca. 250 nm. These results imply that the Sn02 nanoparticles were probably formed after the HT treatment for 24 h.

The metal-peptide stoichiometry of the dimeric Cd peptide was studied by UV-Vis spectroscopy (77) as an absorption band at 238 nm is observed upon addition of Cd(II) to the peptide which is assigned to the ligand-to-metal charge-transfer (LMCT) transition of the newly formed Cd-S bonds. A Job plot demonstrated that the complex consists of 2 peptides and 1 metal ion. These results were supported by spectrophotometric titrations analyzed according to the following equilibrium (1) to yield n = 2 and IQ = 0.65 0.08 pM. 

Ligand-to-metal charge-transfer (LMCT) transitions. 

---