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Answers to Coordination Study Guide for CHEM 102

Answers to Study Guide for CHEM 102 on Coordination Chemistry

  1. Define:

    1. ligand - an ion or molecule that coordinates to a metal atom or metal ion to form a complex.

    2. sigma-donor ligand - a ligand that acts as a Lewis base donating electrons from a lone pair to the metal center.

    3. pi-acceptor ligand - ligand that donates a pair of electrons from a lone pair to the metal center but also has the ability to accept electron density from the metal d orbitals into either d orbitals or pi-antibonding orbitals.

    4. chelating ligand - a ligand able to occupy two or more sites in the coordination sphere of a complex, usually donating two or more pairs of electrons to the metal center.

    5. monodentate - refers to a ligand that donates only one electron pair to a ligand, it is not a chelating ligand (agent)

    6. multidentate - refers to a ligand that donates more than one pair of electrons to a metal center, a chelating ligand (agent)

    7. bidentate - refers to a ligand that donates two pairs of electrons to a metal center, a chelating ligand (agent)

    8. coordination sphere isomerism - refers to structural isomerism of coordination complexes in which the lignds in the inner coordination sphere differ.

    9. linkage isomerism - refers to structural isomers of coordination compounds in which a ligand differs in its mode of attachment to a metal ion.

    10. structural isomerism - refers to compounds which have the same formula but having differing bonding arrangements of the atoms.

    11. stereosiomerism - refers to compounds having the same formula and bonding arrangement but differing in the spatial arrangements of the atoms (cis, trans, fac, mer, a, eq, and optical isomers)

    12. enantiomers - isomers which are non-superimposable mirror images of each other

    13. dextrorotary - describes and enantiomer which rotates plane polarized light to the right

    14. levorotary - describes an enantiomer which rotates plane polarized light to the left

    15. spectrochemical series - A series used in crystal field theory. A series going from low field ligands to high field ligands. Low field ligands result in high spin complexes while high field ligands result in low spin complexes. In general sigma -donor ligands are low field ligands while pi -acceptor ligands are high field ligands. An abbreviated spectrochemical series is given here:

      Cl- < F- < H2O < NH3 < en < NO2- (N-bonded) < CN-
    16. crystal field theory - - a theory that accounts for the colors and magnetic and the other properties of transition metal complexes in terms of the splitting of the energies of the metal ion d orbitals by the electrostatic interaction with the ligands.

  2. What is the oxidation state of the central atom in the compounds below?

    1. RhCl3. 3 H2O

      Rh3+, 18 electrons around Rh, name: triaquotrichlororhodium (III)

    2. Co2+, 19 electrons around Co, name: hexacyanocobaltate (II) ion

    3. Fe2+, 18 electrons around Fe, name: bromodicarbonylcyclopentaidenyliron (II)

    4. Fe3+, 17 electrons around Fe, name: fac-triamminetrithiocyanatoiron (III)

    5. Cr0, 18 electrons around Cr, name: benzenetricarbonylchromium (0)

  3. What type of isomerism is demonstrated by the pairs of compounds below?

    1. linkage isomerism, Fe3+ for both structures, 17 electrons around Fe for both structures, name: left: hexathiocyanatoferrate (III) ion, right: hexaisothiocyanatoferrate (III) ion

    2. coordination sphere isomerism, Co2+ for each structure , 19 electrons around Co for each structure, name: left: hexaaquocobalte (II) chloride, right: tetraaquodichlorocobalt (II) dihydrate

    3. optical isomerism, Ni2+ for each structure, 16 electrons around Ni for each structure, name: bromocarbonylchloro(triphenylphosphine)nickel (II), determination of R & S beyond scope of CHEM 102

    4. cis-trans isomerism, Pt2+ for both structures, 16 electrons around Pt for both structures, name: left: cis-diamminedichloroplatinum (II), right: trans-diamminedichloroplatinum (II)

    fac-mer isomerism, Fe3+ for both structures, 17 electrons around Fe in each structure, name: left: fac-triamminetribromoiron (III), right: mer-triamminetribromoiron (III)

  4. Name all the compounds on the study guide using IUPAC nomenclature rules.

    Compounds are named in each example.

  5. How many electrons are around the central metal atom for all the drawn structures on the study guide? (including those below)

    Compounds have electron counts indicated in each example.

    1. 8 electrons around Ti, Ti4+, name: tetrachlorotitanium (IV)

    2. 16 electrons around Ni, Ni2+, name: dichlorobis(triphenylphosphine)nickel (II)

    3. 18 electrons around Ti, Ti2+, name: dicarbonylbis(cyclopentadienyl)titanium (II)

    4. 18 electrons around Fe, Fe0, name: (eq)tricarbonyl(a)bis(triphenylphosphine)iron (0)