Chem 1120 1st Edition Lecture 25Outline of Last Lecture I. Isomers cont. (mainly optical)II. d-Orbital Energiesa. Crystal Field Theoryb. d-Orbital SplittingOutline of Current Lecture I. Crystal Field Splitting and Magnetisma. Ligand Field StabilizationII. Tetrahedral, Square Planar, and Octahedral ComplexesIII. Complex Color and SpectroscopyCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.I. Number of unpaired electrons determines whether the complex is para-magnetic (unpaired electrons) or diamagnetic (all electrons paired)Ligand Effect on Splitting Energy: Since ligands affect whether a complex is high or low spin, ligands affect the number ofunpaired electronsSince more unpaired electrons means a greater magnetic moment, ligands have dra-matic effects on magnetic properties of complexThis effect can be used in reverse: If one measures magnetic properties of an Fe com-plex with unknown ligands, the results would allow qualitative predictions on the d-orbital energy splitting by the ligands (are they strong or weak field ligands)HIGH SPIN, LOW SPIN CONFIGURATIONS A. Ligand field stabilization: the energy gained by putting electrons in lower energy or-bitalsThus, Cr3+(d3), Co3+(d6), and Fe2+(d6) are especially inert as octahedral com-plexes; Complexes which undergo rapid ligand exchange are labile and thosewhich undergo slow ligand exchange are inert.II. d-orbitals in tetrahedral fields: 3 on the top, 2 on the bottom d-orbitals in square planar complexes: 2 on the bottom, 1 above, another above, and a third above (3 singles stacked on top of the double) III. Color of a complex depends on the metal AND the ligandsMetal complex can absorb a particular wavelength of light energy, leading to an “electronic transition” (excitation of an electron from one orbital to an-other)More simply put, if there is an electron transition (or if there are d-orbitals), then there will be color. Although if a metal has 10 d-orbitals (completely filled) then there is no color*If on a test you’re asked to calculate the energy gap between orbitals, use E=hc/λSpectroscopy: sample is irradiated by light of various wavelengths/energiesThe absorption of light by solutions of transition metal compounds results in color because of the remaining, unabsorbed (transmitted) light**If light of one color is observed, the color opposite of it on the color wheel will be the color of light that was absorbedIf yellow light is absorbed, purple light (the complementary color) is seenIf green light is seen, red light was ab-sorbedLigands change energy gaps, and therefore change color:*complexes with no d-orbitals are colorless, along with complexes that have 10
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