Chapter 24 Transition Metals and Coordination Compounds 2007, Prentice Hall Chemistry: A Molecular Approach, 1 st Ed. Nivaldo Tro Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA

Tro, Chemistry: A Molecular Approach2 Gemstones the colors of rubies and emeralds are both due to the presence of Cr 3+ ions – the difference lies in the crystal hosting the ion Some Al 3+ ions in Al 2 O 3 are replaced by Cr 3+ Some Al 3+ ions in Be 3 Al 2 (SiO 3 ) 6 are replaced by Cr 3+

Tro, Chemistry: A Molecular Approach3 Properties and Electron Configuration of Transition Metals the properties of the transition metals are similar to each other and very different tot he properties of the main group metals high melting points, high densities, moderate to very hard, and very good electrical conductors in general, the transition metals have two valence electrons – we are filling the d orbitals in the shell below the valence Group 1B and some others have 1 valence electron due to “promotion” of an electron into the d sublevel to fill it form ions by losing the ns electrons first, then the (n – 1)d

Tro, Chemistry: A Molecular Approach4 Atomic Size the atomic radii of all the transition metals are very similar small increase in size down a column

Tro, Chemistry: A Molecular Approach5 Ionization Energy the first ionization energy of the transition metals slowly increases across a series third transition series slightly higher 1 st IE trend opposite to main group elements

Tro, Chemistry: A Molecular Approach6 Electronegativity the electronegativity of the transition metals slowly increases across a series except for last element in the series electronegativity slightly increases down the column trend opposite to main group elements

Tro, Chemistry: A Molecular Approach7 Oxidation States often exhibit multiple oxidation states vary by 1 highest oxidation state is group number for 3B to 7B

Tro, Chemistry: A Molecular Approach8 Coordination Compounds when a complex ion combines with counterions to make a neutral compound it is called a coordination compound the primary valence is the oxidation number of the metal the secondary valence is the number of ligands bonded to the metal coordination number coordination number range from 2 to 12, with the most common being 6 and 4 CoCl 3  6H 2 O = [Co(H 2 O) 6 ]Cl 3

Tro, Chemistry: A Molecular Approach9 Coordination Compound

Tro, Chemistry: A Molecular Approach10 Complex Ion Formation complex ion formation is a type of Lewis acid- base reaction a bond that forms when the pair of electrons is donated by one atom is called a coordinate covalent bond

Tro, Chemistry: A Molecular Approach11 Ligands with Extra Teeth some ligands can form more than one coordinate covalent bond with the metal atom lone pairs on different atoms that are separate enough so that both can reach the metal chelate is a complex ion containing a multidentate ligand ligand is called the chelating agent

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Tro, Chemistry: A Molecular Approach13 EDTA a Polydentate Ligand

Tro, Chemistry: A Molecular Approach14 Complex Ions with Polydentate Ligands

Tro, Chemistry: A Molecular Approach15 Geometries in Complex Ions

Tro, Chemistry: A Molecular Approach16 Naming Coordination Compounds 1) determine the name of the noncomplex ion 2) determine the ligand names and list them in alphabetical order 3) determine the name of the metal cation 4) name the complex ion by: 1)name each ligand alphabetically, adding a prefix in front of each ligand to indicate the number found in the complex ion 2)follow with the name of the metal cation 5) write the name of the cation followed by the name of the anion

Tro, Chemistry: A Molecular Approach17 Common Ligands

Tro, Chemistry: A Molecular Approach18 Common Metals found in Anionic Complex Ions

Tro, Chemistry: A Molecular Approach19 Isomers Structural isomers are molecules that have the same number and type of atoms, but they are attached in a different order Stereoisomers are molecules that have the same number and type of atoms, and that are attached in the same order, but the atoms or groups of atoms point in a different spatial direction

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Tro, Chemistry: A Molecular Approach21 Linkage Isomers

Tro, Chemistry: A Molecular Approach22 Geometric Isomers geometric isomers are stereoisomers that differ in the spatial orientation of ligands cis-trans isomerism in octahedral complexes MA 4 B 2 fac-mer isomerism in octahedral complexes MA 3 B 3 cis-trans isomerism in square-planar complexes MA 2 B 2

Tro, Chemistry: A Molecular Approach23 Ex – Draw the structures and label the type for all isomers of [Co(en) 2 Cl 2 ] + the ethylenediamine ligand (en = H 2 NCH 2 CH 2 NH 2 ) is bidentate each Cl ligand is monodentate octahedral MA 4 B 2

Tro, Chemistry: A Molecular Approach24 Optical Isomers optical isomers are stereoisomers that are nonsuperimposable mirror images of each other [Co(en) 3 ] 3+

Tro, Chemistry: A Molecular Approach25 Ex 24.7 – Determine if the cis-trans isomers of [Co(en) 2 Cl 2 ] + are optically active draw the mirror image of the given isomer and check to see if they are superimposable trans isomer identical to its mirror image no optical isomerism cis isomer mirror image is nonsuperimposable optical isomers

Tro, Chemistry: A Molecular Approach26 Bonding in Coordination Compounds Valence Bond Theory bonding take place when the filled atomic orbital on the ligand overlaps an empty atomic orbital on the metal ion explain geometries well, but doesn’t explain color or magnetic properties

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Tro, Chemistry: A Molecular Approach28 Bonding in Coordination Compounds Crystal Field Theory bonds form due to the attraction of the electrons on the ligand for the charge on the metal cation electrons on the ligands repel electrons in the unhybridized d orbitals of the metal ion the result is the energies of orbitals the d sublevel are split the difference in energy depends the complex and kinds of ligands crystal field splitting energy strong field splitting and weak field splitting

Tro, Chemistry: A Molecular Approach29 Splitting of d Orbital Energies due to Ligands in a Octahedral Complex

Tro, Chemistry: A Molecular Approach30 Strong and Weak Field Splitting

Tro, Chemistry: A Molecular Approach31 Complex Ion Color the observed color is the complimentary color of the one that is absorbed

Tro, Chemistry: A Molecular Approach32 Complex Ion Color and Crystal Field Strength the colors of complex ions are due to electronic transitions between the split d sublevel orbitals the wavelength of maximum absorbance can be used to determine the size of the energy gap between the split d sublevel orbitals E photon = h = hc/ = 

Tro, Chemistry: A Molecular Approach33 Ligand and Crystal Field Strength the strength of the crystal field depends in large part on the ligands strong field ligands include: CN ─ > NO 2 ─ > en > NH 3 weak field ligands include H 2 O > OH ─ > F ─ > Cl ─ > Br ─ > I ─ crystal field strength increases as the charge on the metal cation increases

Tro, Chemistry: A Molecular Approach34 Magnetic Properties and Crystal Field Strength the electron configuration of the metal ion with split d orbitals depends on the strength of the crystal field the 4 th and 5 th electrons will go into the higher energy d x2-y2 and d z2 if the field is weak and the energy gap is small – leading to unpaired electrons and a paramagnetic complex the 4 th thru 6 th electrons will pair the electrons in the d xy, d yz and d xz if the field is strong and the energy gap is large – leading to paired electrons and a diamagnetic complex

Tro, Chemistry: A Molecular Approach35 Low Spin & High Spin Complexes paramagnetic high-spin complex diamagnetic low-spin complex only electron configurations d 4, d 5, d 6, or d 7 can have low or high spin

Tro, Chemistry: A Molecular Approach36 Tetrahedral Geometry and Crystal Field Splitting because the ligand approach interacts more strongly with the planar orbitals in the tetrahedral geometry, their energies are raised most high-spin complexes

Tro, Chemistry: A Molecular Approach37 Square Planar Geometry and Crystal Field Splitting d 8 metals the most complex splitting pattern most are low-spin complexes

Tro, Chemistry: A Molecular Approach38 Applications of Coordination Compounds extraction of metals from ores silver and gold as cyanide complexes nickel as Ni(CO) 4 (g) use of chelating agents in heavy metal poisoning EDTA for Pb poisoning chemical analysis qualitative analysis for metal ions  blue = CoSCN +  red = FeSCN 2+

Tro, Chemistry: A Molecular Approach39 Applications of Coordination Compounds commercial coloring agents prussian blue = mixture of hexacyanoFe(II) and Fe(III)  inks, blueprinting, cosmetics, paints biomolecules porphyrin ring cytochrome C hemoglobin chlorphyll chlorophyll

Tro, Chemistry: A Molecular Approach40 Applications of Coordination Compounds carbonic anhydrase catalyzes the reaction between water and CO 2 contains tetrahedrally complexed Zn 2+

Tro, Chemistry: A Molecular Approach41 Applications of Coordination Compounds Drugs and Therapeutic Agents cisplatin  anticancer drug