Chem 1120 1st Edition Lecture 25 Outline of Last Lecture I Isomers cont mainly optical II d Orbital Energies a Crystal Field Theory b d Orbital Splitting Outline of Current Lecture I Crystal Field Splitting and Magnetism a Ligand Field Stabilization II Tetrahedral Square Planar and Octahedral Complexes III Complex Color and Spectroscopy Current Lecture These 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 paramagnetic 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 of unpaired electrons Since more unpaired electrons means a greater magnetic moment ligands have dramatic effects on magnetic properties of complex This effect can be used in reverse If one measures magnetic properties of an Fe complex 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 orbitals Thus Cr3 d3 Co3 d6 and Fe2 d6 are especially inert as octahedral complexes Complexes which undergo rapid ligand exchange are labile and those which 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 ligands Metal complex can absorb a particular wavelength of light energy leading to an electronic transition excitation of an electron from one orbital to another 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 Spectroscopy sample is irradiated by light of various wavelengths energies The 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 absorbed If yellow light is absorbed purple light the complementary color is seen If green light is seen red light was absorbed Ligands change energy gaps and therefore change color complexes with no d orbitals are colorless along with complexes that have 10 d orbitals
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