Download Transition Elements/Coordination Chemistry

Transition Metals and Coordination Compounds
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Transition Metals and Coordination:
Homework:
Read Chapter 24
Bonus Ch 24: 19, 23, 25, 43, 47, 51, 59
Check for the MasteringChemistry.com assignment and complete before due date
For Fun:
How are transition metal reactions similar to Reality TV?
Gemstones:
The colors of rubies and emeralds are both due to the presence of Cr3+ ions. The
difference lies in the crystal hosting the ion…
Transition Metals:
Many colorful compounds have transition metals.
Both ionic and [complex coordination] compounds can be formed
The properties of the transition metals are similar to each other and very different to
the properties of the main group metals
high mp, high densities, moderate to very hard, very good electrical conductors
Transition metals have electron configurations that fill the d orbitals last, yet when
losing electrons the valence s electrons are generally lost first. When the atom zinc
loses two electrons to become Zn+2 it is the 4s2 electrons that are lost…
Zn [Ar] 4s23d10
Zn+2 [Ar] 3d10
Similarities in properties come from similarities in valence electron configuration
Transition Metals and Coordination Compounds
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Electron Configurations:
The difference in energy between ns and (n-1)d orbitals is not very large. This
causes some transition metal atoms to have irregular electron configuration patterns
like those below…
Cr = [Ar]4s13d5
Cu = [Ar]4s13d10
Mo = [Kr]5s14d5
Ru = [Kr]5s14d7
Pd = [Kr]5s04d10
Ag = [Kr]5s14d10
Electron configurations are experimentally determined.
Ni, Tc+2, and W behave predictably…
Ni
Tc2+
W
Atomic size:
The atomic radii of all the transition metals are very similar, with a small increase
in size down a column and a dip in size in the middle.
Transition Metals and Coordination Compounds
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Ionization Energy:
The 1st IE of the transition metals slowly increases across a series.
Electronegativity:
The electronegativity of the transition metals slowly increases across a series,
except for last element in the series
Oxidation States:
Unlike main group metals, transition metals often exhibit multiple oxidation states
Highest oxidation state is the same as the group number for Groups 3B to 7B
Transition Metals and Coordination Compounds
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Complex Ions:
Complex ion formation is a type of Lewis acid–base reaction. A bond forms
when a pair of electrons is donated by one atom creating a coordinate covalent
bond
When a transition metal cation combines with multiple anions or neutral molecules
it makes a complex ion
The attached anions or neutral molecules are called ligands
The overall charge on the complex ion can be positive or negative, depending on
the numbers and types of ligands attached
Names of Common Metals in Complex Ions:
Name in Cationic Complex, follow
with Roman numeral ( -- )
chromium (-?-), Cr+?
Cobalt (-?-), Co+?
Copper (-?-), Cu+?
Gold (-?-), Au+?
Iron (-?-), Fe+?
Lead (-?-), Pb+?
Manganese (-?-), Mn+?
Molybdenum (-?-), Mo+?
Nickel (-?-), Ni+?
Platinum (-?-), Pt+?
Silver, Ag+
Tin (-?-), Sn+?
Zinc, Zn+2
Name in Anionic Complex, follow
with Roman numeral ( -- )
chromate(-?-)
cobaltate(-?-)
cuprate(-?-)
aurate(-?-)
ferrate(-?-)
plumbate(-?-)
manganate(-?-)
molybdate(-?-)
nickelate(-?-)
platinate(-?-)
argentate
stannate(-?-)
zincate
Examples:
COMPLEX CATIONS:
[Cr(NH3)6]+3
[Fe(CO)6]
+3
[Pt(H2O)4]+2
hexaamminechromium(III)
hexacarbonyliron(III)
tetraaquaplatinum(II)
COMPLEX ANIONS:
[Cr(CN)6]-3
hexacyanochromate(III)
[Fe(Br)6]-3
hexabromoferrate(III)
[Pt(OH)4]-2
tetrahydroxoplatinate(II)
Transition Metals and Coordination Compounds
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Ligands:
Ligands must have a pair of nonbonding electrons that can be shared to form the
coordinate covalent bond with the transition metal cation. Some ligands form more
than one coordinate covalent bond if they have lone pairs on different atoms that
are separated enough so that both can bond to the metal
A chelate is a complex ion containing a multidentate ligand and the ligand is
called the chelating agent
(from Greek word chela = claw):
Example ligands:
Monodentate: H2O or NH3 (one atom in ligand has nonbonding electrons)
Bidentate:
Polydentate:
Ethylenediamine (en)
Ethylenediaminetetraacetate (EDTA)
Names and Formulas of Common Ligands:
Ligand (anions)
Name in complex ion
-1
Bromide, Br
bromo
-1
Chloride, Cl
chloro
-1
Hydroxide, OH
hydroxo
-1
Cyanide, CN
cyano
-1
Cyanate, OCN
cyanato (O to metal)
isocyanato(N to metal)
-1
Nitrite, NO2
nitro (N attaches to metal),
nitrito(O attaches to metal)
-2
Oxalate, C2O4 (ox)
oxalato
Ethylenediaminetetraacetate ethylenediaminetetraaceto
(EDTA)-4
Ligand (neutral molecules) Name in complex ion
Water, H2O
aqua
Ammonia, NH3
ammine
Carbon monoxide, CO
carbonyl
Ethylenediamine (en)
ethylenediamine
Transition Metals and Coordination Compounds
Geometries in Complex Ions:
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Transition Metals and Coordination Compounds
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Coordination Compounds:
When a complex ion combines with counter-ions to make a neutral compound it is
called a coordination compound
The primary valence is the
oxidation number of the metal
Coordination number (also
called secondary valence) is the
number of bonds (not ligands) to
the metal. Coordination numbers
range from 2 to 12, with the most
common being 6 and 4
Example:
[Co(NH3)6]Cl3
Naming Coordination Compounds:
1.
Determine the name of the counter ions
2.
Determine the ligand names and list them in alphabetical order
3.
Determine the name of the metal cation
4.
Name the complex ion:
a)
naming each ligand alphabetically, adding a prefix in front of each
ligand to indicate the number found in the complex ion...
prefixes: mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca,
dodeca (12)
b)
following with the name of the metal cation
5.
Write the name of the cation followed by the name of the anion
Name the coordination compound:
[Co(NH3)6]Cl3
3 counter ions Cl-1
name____________
NH3 is neutral
name____________
So the charge of cobalt must be +3
Co+3 (in a cationic complex)
name____________
Name the cation then the anion
Name of the coordination compound _________________________________
Transition Metals and Coordination Compounds
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Name [Cr(H2O)5Cl]Cl2
Name K3[Fe(CN)6]
Identify the cation and anion, and
the name of the simple ion
[Cr(H2O)5Cl]+2 is a
complex cation,
Cl-1 is chloride
K+1 is potassium,
[Fe(CN)6]-3 is a complex
ion
Give each ligand a name and list
them in alphabetical order
H2O is aqua
Cl-1 is chloro
CN-1 is cyano
Cr+3 is chromium(III)
complex ion is a cation
Fe+3 is ferrate(III)
complex ion is anionic
Name the complex ion by adding
prefixes to indicate the number of
each ligand followed by the name
of each ligand followed by the
name of the metal ion
[Cr(H2O)5Cl] +2 is
pentaquachlorochromium(III)
[Fe(CN)6]-3 is
hexacyanoferrate(III)
Name the compound by writing
the name of the cation before the
anion. The only space is between
ion names.
[Cr(H2O)5Cl]Cl2 is
pentaquachlorochromium(III) chloride
K3[Fe(CN)6] is potassium
hexacyanoferrate(III)
Follow the naming rules
Name the metal ion
Try naming:
Na2CuBr4 and [Co(NH3)2(CO)4](NO3)3
Transition Metals and Coordination Compounds
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Isomers:
Structural isomers are molecules that have the same number and type of atoms,
but they are attached in a different order
Coordination isomers: ligand and counter ions exchange places
Linkage isomers: ligands attached to the central cation through different
ends of the ligand structure
[Co(NH3)5NO2]+2, pentaamminonitrocobalt (III) and pentaamminonitritocobalt (III)
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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
Geometric isomers: different special arrangements
Two identical ligands: tetrahedral or octahedral complex;
cis- adjacent , trans-opposite
Three identical ligand: octahedral complex; fac-all three ligands
adjacent, mer- the three ligands form an arc around the center
Optical isomers: nonsuperimposable mirror images
[Co(en)2Cl2]+1
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Bonding in Complex ions:
Valence Bond theory: Bonding takes place when the filled atomic orbital on the
ligand overlaps an empty atomic orbital on the metal ion. Explains geometries
well, but doesn’t explain color or magnetic properties.
Crystal Field theory: Bonds form due to the attraction of the electrons on the
ligand for the charge on the metal cation.
Electrons on ligands repel electrons in unhybridized d orbitals of metal ion
d orbitals are split
The difference in energy depends on complex formed and kinds of ligands
crystal field splitting energy
strong field splitting and weak field splitting
Octahedral Complex: Higher energy for positions with greater orbital overlap, ligands
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Size of the crystal field splitting energy, ,
Depends on the kinds of ligands and their relative positions on the complex ion, as
well as the kind of metal ion and its oxidation state
Large
Small
Strong field ligands
weak field ligands
-1
-1
-1
CN > NO2 > en > NH3
> H2O > OH > F-1 > Cl-1 > Br-1 > I-1
Depends on the type of cation; increases as charge on metal increases and increases
down a group
Co3+ > Cr3+ > Fe3+ > Fe2+ > Co2+ > Ni2+ > Mn2+
Color and Complex Ions:
Transition metal ions show many intense colors in host crystals or solution
The color of light absorbed by the complex ion is related to electronic energy
changes in the structure of the complex
the electron “leaping” from a lower energy state to a higher energy state
The observed color is complementary color of one that is absorbed
Red-Purple: is least absorbed in
[Ti(H2O)6]+3
so that is the color
seen in a solution of [Ti(H2O)6]+3
Green and yellow are
absorbed the strongest,
the complementary colors
are “seen”
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Colors of complex ions:
Due to electronic transitions between split
d sublevel orbitals. The wavelength of
maximum absorbance can be used to
determine the size of the energy gap
between split d sublevel orbitals
Ephoton = h = hc/ =
h = 6.6262 x 10-34 J·s
c = 3.00 x 108 m/s
Try this:
[Cr(Cl)6]-3 has a maximum absorption spectrum at 735 nm.
Calculate the crystal field spitting energy in J/photon and kJ/mol.
Magnetic Properties and Crystal Field Strength: Octahedral-6 attached
The electron configuration of the metal ion with split d orbitals depends on the
strength of the crystal field
Weak field:
4th and 5th electrons will go into the higher energy if the energy gap is small
unpaired electrons = paramagnetic complex
Strong field:
4th thru 6th electrons will pair the electrons in dxy, dyz, dxz if energy gap is large
paired electrons = diamagnetic complex
Try this: The complex ion [AlF6]-3 is paramagnetic. Is the F-1 ligand inducing a strong or
weak field?
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Tetrahedral - 4 attached (not on test)
Ligands repel more strongly with the dxy, dyz, dxz orbitals in the tetrahedral geometry
Reversing the order of energies compared to the octahedral geometry
Almost all tetrahedral complexes are high spin, d orbitals interact with only four
ligands, so is generally smaller.
Square Planar (not on test)
Occurs in d8 metals; Pt2+, Pd2+, Ir+, Au3+
The most complex splitting pattern
Almost all are low-spin complexes
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Applications:
Extraction of metals from ores; silver and gold as cyanide complexes
Use of chelating agents in heavy metal poisoning; EDTA for Pb poisoning
Chemical analysis; qualitative analysis for metal ions
blue = [CoSCN]+
red = [FeSCN]2+
Ni2+ and Pd2+ form insoluble colored precipitates with
dimethylglyoxime
Commercial coloring agents; Prussian blue = mix hexacyanoferrate(II) and (III)
Biomolecules
porphyrin ring
cytochrome C
hemoglobin
chlorophyll
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Transition Metal and Coordination Compounds Practice Problems:
1. For each of the complexes below, give the coordination number, oxidation state of the
metal and the formula for the phosphate salt (if the complex is a cation) or the
aluminum salt (if the complex is an anion), and name the compound.
a) [Mo(CN)2(en)2]+1
b) [Co(H2O)(OH)2Br]-1
c) [Ag(NH3)2]+1
d) [PtCl2(NO2)2]-2
2. Write out formulas, given the following names.
a) Pentaaquabromochromium(III) bromide
b) Sodium Hexacyanocobaltate(II)
c) Bis(ethylenediamine)dinitroiron(III) chloride
d) Tetraamminediiodoplatinum(IV) tetraiodoplatinate(II)
3. [PdCl4]-2 is found to be diamagnetic. Is this structure tetrahedral or square planar
according to crystal field theory? Draw the energy orbital diagram.
4. Draw two linkage isomers of [Mn(NH3)5(NO2)]+2
5. a) Three complex ions of cobalt (III) absorb light at wavelengths at 290 nm, 440 nm,
770 nm. Match each complex ion to the appropriate wavelength and predict the color
you would expect each solution to be. Refer to the color wheel for complements,
400nm to700nm is visible.
Choices: [Co(CN)6]-3, [CoF6]-3, [Co(NH3)6]-3
b) Solve for the crystal field splitting energy in kJ/mol for [Co(NH3)6]-3.
For Fun:
How are transition metal reactions similar to Reality TV?
When you mix two parties together you are not sure of the outcome. There are a
variety of possible reactions that the parties may undergo.