Lanthanide complexes sharp lines caused by screening

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Lanthanide complexes – sharp lines caused by “screening” of the f electrons by other orbitals One advantage of this is the use of holmium oxide filters (sharp lines) for wavelength calibration of UV spectrometers. See Shriver et al. Inorganic Chemistry, 2 nd Ed. Ch. 14
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Benzenoid aromatics From Crewes, Rodriguez, Jaspars, Organic Structure Analysis UV of Benzene in heptane Group K band ( ) B band ( ) R band Alkyl 208(7800) 260(220) -- -OH 211(6200) 270(1450) -O - 236(9400) 287(2600) -OCH 3 217(6400) 269(1500) NH 2 230(8600) 280(1400) -F 204(6200) 254(900) -Cl 210(7500) 257(170) -Br 210(7500) 257(170) -I 207(7000) 258/285(610/180 ) -NH 3 + 203(7500) 254(160) -C=CH 2 248(15000) 282(740) -C CH 248(17000) 278(6500 -C 6 H 6 250(14000) -C(=O)H 242(14000) 280(1400) 328(55) -C(=O)R 238(13000) 276(800) 320(40) -CO 2 H 226(9800) 272(850) -CO 2 - 224(8700) 268(800) -C N 224(13000) 271(1000) -NO 2 252(10000) 280(1000) 330(140)
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Substituent effects don’t really add up Can’t tell any thing about substitution geometry Exception to this is when adjacent substituents can interact, e.g hydrogen bonding. E.g the secondary benzene band at 254 shifts to 303 in salicylic acid In p-hydroxybenzoic acid, it is at the phenol or benzoic acid frequency
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Heterocycles Nitrogen heterocycles are pretty similar to the benzenoid anaologs that are isoelectronic. Can study protonation, complex formation (charge transfer bands)
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Quantitative analysis Great for non- aqueous titrations Example here gives detn of endpoint for bromcresol green Binding studies Form I to form II Isosbestic points Single clear point, can exclude intermediate state, exclude light scattering and Beer’s law applies Binding of a lanthanide complex to an oligonucleotide
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More Complex Electronic Processes Fluorescence: absorption of radiation to an excited state, followed by emission of radiation to a lower state of the same multiplicity Phosphorescence: absorption of radiation to an excited state, followed by emission of radiation to a lower state of different multiplicity Singlet state: spins are paired, no net angular momentum (and no net magnetic field) Triplet state: spins are unpaired, net angular momentum (and net magnetic field)
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