Δ O depends on both the metal and the ligand. Thus the energy difference between the t 2g and e g orbitals can range between the energy of a rather weak to a rather strong covalent bond. We will see that Δ O varies widely for transition metal complexes, from near-infrared to ultraviolet wavelengths. We would need an ultraviolet photon (E > 350 kJ/mol = 3.6 eV = 345 nm = 29,000cm -1) to break a C-C bond. If we compare this to the dissociation energy of a carbon-carbon single bond (350 kJ/mol), we see that the C-C bond has about twice the energy of a red photon. In other energy units, the same red photon has an energy of 2.0 eV (1 eV = 1240 nm) or 193 kJ/mol (1 eV = 96.5 kJ/mol). Energy gaps are often expressed by spectroscopists in terms of wavenumbers.įor example, a red photon has a wavelength of about 620 nm and a wavenumber of about 16,000 cm -1. \) is called the "wavenumber" and is the inverse of the wavelength, usually measured in cm -1.
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