1/13/2015 1 george mason university general chemistry 212 chapter 23 transition elements...
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1/13/2015 1
George Mason UniversityGeneral Chemistry 212
Chapter 23Transition Elements
AcknowledgementsCourse Text: Chemistry: the Molecular Nature of Matter and
Change, 7th edition, 2011, McGraw-Hill Martin S. Silberberg & Patricia Amateis
The Chemistry 211/212 General Chemistry courses taught at George Mason are intended for those students enrolled in a science /engineering oriented curricula, with particular emphasis on chemistry, biochemistry, and biology The material on these slides is taken primarily from the course text but the instructor has modified, condensed, or otherwise reorganized selected material.Additional material from other sources may also be included. Interpretation of course material to clarify concepts and solutions to problems is the sole responsibility of this instructor.
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Transition Elements Properties of the Transition Elements
The Inner Transition Elements
Highlights of Selected Transition Elements
Coordination Compounds
Theoretical Basis for the Bonding and Properties of Complexes
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Transition Elements Main-Group vs Transition Elements
Most important uses of Main-Group elements involve the compounds made up of these elements
Transition Elements are highly useful in their elemental or uncombined form
Main –Group Transition Elements
Main-group elements change from metal to non-metal across a period
All transition elements are metals
Most main-group ionic compounds are colorless and diamagnetic (non-magnetic)
Many transition metal compounds are highly colored and paramagnetic
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Transition Elements Properties of Transition Elements
Recall: The “A” (Main Group) elements make up the “s” and “p” blocks
Transition Elements make up the
● “d” block (B group)
● “f” block elements (Inner Transition Elements)
As ions, transition metals (elements) provide fascinating insights into chemical bonding and structure
Transition metals play an important role in living organisms
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Transition Elements
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Transition Elements Electron Configurations of the Transition Metals
In the Periodic Table, the Transition metals, designated “d-block (B-Group)” elements, are located in:
● 40 elements in 4 series within Periods 4 -7
● Lie between the last ns-block elements in group [2A(2)] (Ca – Ra) and the first np-block elements in group [(3A(13)] (Ga & element 113 (unnamed)
● Each series represents the filling of the 5 d orbitals
l = 2 [ml = -2 -1 0 +1 +2]
(5 orbitals per period x 2 electrons per orbital x 4 Periods
= 40 Elements
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Transition Elements Condensed d-block ground-state electron configuration:
[noble gas] ns2(n-1)dx, with n = 4 -7; x= 1-10
(several aufbau build-up exceptions)
Partial (valence shell) electron configuration
ns2(n-1)dx
Recall: Chromium (Cr) and Copper (Cu) are exceptions to the above aufbau configuration setup
Expected: Cr [Ar] 4s23d4 Cu [Ar] 4s23d9
Actual: Cr [Ar] 4s13d5 Cu [Ar] 4s13d10
Reasons: change in relative energies of 4s & 3d orbitals and the unusual stability of ½ filled and
filled sublevels (level 4 relative to level 3)
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Transition Elements
Note Aufbau build up exceptions for “Cr” & “Cu”
Orbital Occupancy of the Period 4 Transition Metals
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Transition Elements The “Inner Transition” elements
Lie between the 1st and 2nd members of the “d-block” elements in Periods 6 & 7 (n=6 & n=7)
Condensed f-block ground-state electron configuration (Periods 6 & 7):
[noble gas] ns2 (n-2)f14(n-1)dx, with n = 6 -7
The 28 “f” orbitals are filled as follows:
l = 3 [ml = -3 -2 -1 0 +1 +2 +3]
7 orbitals per period x 2 electrons per orbital x 2 periods
= 28 Elements
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Transition Elements Transition Metal Ions
Form through the loss of the “ns” electronsbefore the (n-1)d electrons
Ex. Ti2+ [Ar] 3d2 4s2 → [Ar] 3d2 + 2e- (not [Ar] 4s2)
(Ti2+ also called d2 ion)
Ions of different transition metals with the same electron configuration often have similar properties
Ex. Mn2+ and Fe3+ are both d5 ions
Mn2+ [Ar] 3d54s2 → [Ar] 3d5 + 2e-
Fe3+ [Ar] 3d64s2 → [Ar] 3d5 + 3e-
Both Ions have pale colors in aqueous solutions
Both form complex ions with similar magnetic properties
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Practice ProblemWrite condensed electron configurations for the following ions:
Zr V3+ Mo3+
Vanadium (V) – Period 4
Zirconium (Zr) & Molybdenum (Mo) – Period 5
General Configuration: ns2(n-1)dx
a. Zr is 2nd element in the 4d series: [Kr] 5s24d2 (d2 ion)
b. V is the 3rd element in the 3d series: [Ar] 4s23d3
“ns” electrons lost first
In forming V3+, 3 electrons lost – two 4s & one 3d
V3+ = [Ar] 4s23d3 → [Ar] 3d2 (d2 ion) + 3e-
c. Mo lies below Cr in Period 5, Group 6B(6): [kr] 5s1 4d5
Note: Same electron configuration exception as Cr
Mo3+ = [Kr] 5s1 4d5 → [Kr] 4d3 (d3 ion) + 3 e-
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Transition Elements Trends of Transition Elements Across a Period
Transition elements exhibit smaller, less regular changes in
● Size
● Electronegativity
● First Ionization Energy
than the Main Group Elements in the same group
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Transition Elements Atomic Size
● General overall decrease across a period for both Main group and Transition group elements
● As the “d” orbitals are filled across a period, the change in atomic size within the transition elements evens out because the “d” orbitals are less effective in shielding the outer electrons from the increased nuclear charge
Transition Metals Main groupMain group
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Transition Elements Electronegativity
● Electronegativity generally increases across period
● Change in electronegativity within a series (period) is relatively small in keeping with the relatively small change in size
● Small electronegativity change in Transition Elements is in contrast with the steeper increase between the Main Group elements across a period
● Magnitude of Electronegativity in Transition elements is similar to the larger main-group metals
Transition Metals
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Transition Elements Ionization Energy
● Ionization Energy of Period 4 Main-group elements rise steeply from left to right as the electrons become more difficult to remove from the poorly shielded increasing nuclear charge, i.e., no “d” electrons; thus, electrons held tighter to nucleus
● In the Transition metals, however, the first ionization energies increase relatively little because of the combined effects of less effective shielding by the inner “d” electrons and the increasing nuclear charge
Transition Metals
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Transition Elements Trends Within (down) a Group (relative to main-group
elements) Vertical trends differ from those of the Main Group
elements Atomic Size
● Increases, as expected, from Period 4 to 5 where electron repulsion dominates the increasing nuclear charge
● No increase from Period 5 to 6● The Lanthanide Contraction describes the atomic
radius trend that the Lanthanide series exhibit● The Lanthanide Contraction refers to the fact that
the 5s and 5p orbitals penetrate the 4f sub-shell so the 4f orbital is not shielded from the increasing nuclear change, which causes the atomic radius of the atom to decrease
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Transition Elements
n=5
ml = 0
l=0(5s)
-1 0 +1
l=1(5p)
-2 -1 0 +1 +2
l=2 (5d)
-3 -2 -1 0 +1 +2 +3
l=3 (5f)
ml =
0
l=0(1s)
n=1
n=4
ml = 0
l=0(4s)
-1 0 +1
l=1(4p)
-2 -1 0 +1 +2
l=2 (4d)
-3 -2 -1 0 +1 +2 +3
l=3 (4f)
n=3
0
l=0(3s)
l=2 (3d)
-2 -1 0 +1 +2
l=1(3p)
-1 0 +1
n=2
0
l=0(2s)
l=1(2p)
-1 0 +1
n=6,7
ml = 0
l=0(6s,7s)
-1 0 +1
l=1(6p,7p)
-2 -1 0 +1 +2
l=2 (6d)
-3 -2 -1 0 +1 +2 +3
l=3 (6f)
Note: n > 7 &
l > 3 Sublevels
not utilized for
any element in
the current Period Table
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Transition Elements
Order of Sublevel Orbital Filling
Inner Transition Metals
Transition MetalsMain Group Metals
Main Group Non-metals
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Transition Elements Trends Within a Group (relative to main-group elements)
Electronegativity (EN) – Relative ability of an atom in a covalent bond to attract shared electrons ● EN of Main-group elements decreases down group
greater size means less attraction by nucleus Greater Reactivity
● EN in Transition elements is opposite the trend in Main-group elements because of less effective shielding of “d” orbitals
● EN increases from period 4 to period 5 No change from period 5 to period 6, since the change in
volume is small and Zeff increases ( weak shielding from f orbital electrons)
Transition metals exhibit more covalent bonding and attract electrons more strongly than main-group metals
The EN values in the heavy metals exceed those of most metalloids, forming salt-like compounds, such as CsAu and the Au- ion
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Transition Elements Trends Within a Group (relative to Main-group
elements)
Ionization Energy – Energy required to remove an electron from a gaseous atom or ion
● Main-group elements increase in size down a group, decreasing the Zeff , making it relatively easier to remove the outer electrons
● The relatively small increase in the size of transition metals because of ineffective shielding from the increasing nuclear charge (Zeff) by “d” orbital electrons makes it more difficult to remove a valence electron, resulting in a general increase in the first ionization energy down a group
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Transition Elements Trends Within a Group (relative to Main-group elements)
Density● Atomic size (volume) is inversely related to density
(As size increases density decreases)● Transition element density across a period initially
increases, then levels off, finally dips at end of series● From Period 5 to Period 6 the density increases
dramatically because atomic volumes change little while nuclear mass increases significantly
● Period 6 series contains some of the densest elements known:
Tungsten, Rhenium, Osmium, Iridium, Platinum, Gold
(Density 20 times greater than water,
2 times more dense than lead)
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Transition Elements
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Trends are unlike those for the Main-group elements in several ways 2nd & 3rd members of a transition group are nearly same size Electronegativity increases down a transition group 1st ionization energies are highest at the bottom of transition group Densities increase down a transition group (mass increases faster
than density
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Transition Elements Chemical Properties of the Transition Elements
Atomic & physical properties of Transitions elements are similar to Main group elements
Chemical properties of transition elements are very different from main group elements
Oxidation States
● Main-group elements display one, or at most two, oxidation states
● The ns & (n-1)d electrons in transition elements are very close in energy
All or most can be used as valence electrons in bonding – Transition metals can have multiple oxidation states
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Transition Elements
Oxidation State (Number)Magnitude of charge an atom in a covalent compound would have if its shared electrons were held completely by the atom that attracts them more strongly
Oxidation StateManganese (Mn) dx Electronic
Configuration
0 d5 [Ar] 4s2 3d5
+1 d5 [Ar] 4s1 3d5
+2 d5 [Ar] 3d5
+3 d4 [Ar] 3d4
+4 d3 [Ar] 3d3
+5 d2 [Ar] 3d2
+6 d1 [Ar] 3d1
+7 d0 [Ar]
Note: All 3 d5
Ex. MnO4- ; O.N. Mn +7
Ex. MnO2 ; O.N. Mn +4
Oxidation States and d-orbital Occupancy of thePeriod 4 Transition Metals
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Transition Elements Metallic Behavior
Atomic size and oxidation state have a major effect on the nature of bonding in transition metal compounds
Transition elements in their lower oxidation states behave more like metals – Oxides more basic
Transition elements in their higher oxidation states exhibit more covalent bonding – Oxides more acidic
Ex. TiCl2 (Ti2+) is an ionic solid
TiCl4 (Ti4+) is a molecular liquid
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Transition Elements Metallic Behavior
In the higher oxidation states:● The atoms have fewer electrons● The nuclear charge pulls remaining electrons closer,
decreasing the volume and increasing the density● The charge density (ratio of the ion’s charge to its
volume) increases● The increase in charge density leads to more
polarization of the electron clouds in non-metals ● The bonding becomes more covalent● The stronger the covalent bond, the less metallic● The oxides, therefore, become less basic
Ex. TiO (Ti2+) is weakly basic in waterTiO2 (Ti4+) is amphoteric, reacting with
both acid and base
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Transition Elements Electronegativity, Oxidation State, Acidity/Basicity
Why does oxide acidity increase with oxidation state?
● Metal with a higher oxidation state is more positively charged
● Attraction of electrons is increased, i.e., electronegativity increases
Effective Electronegativity = Valence State Electronegativity
● EN Cr – 1.6 Al – 1.5 (basic oxide) Cr3+ – 1.7 Cr6+ – 2.3 P – 2.1 (acidic oxides)
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Transition Elements Metallic Behavior
Reduction Strength (Redox)● Standard Electrode Potential,
Eo , generally decreases across a period
● As the value of Eo becomes more negative, i.e., at the beginning of the series, the ability of the species to act as a reducing agent increases
Thus, Ti2+, Eo = -01.63V, is a stronger reducing agent than Ni2+, Eo = -0.25V
All species with a negative value of Eo can reduce H+
2H+(aq) + 2e- H2(g) Eo = 0.0V) Note: Cu2+ (Eo = +0.34 V) cannot reduce H+
The magnitude of the Eo values between two species, and the relative degree of surface oxidation, determines the level of reactivity of the oxidation/reduction reaction in water, steam, or acid solution
Standard Electrode PotentialsOf Period 4 M2+ Ions
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Transition Elements Color in Transition Elements
Most Main-Group Ionic Compounds are colorless
● Metal ions have a filled outer shell
● With only much higher energy orbitals available to receive an “excited” electron, the ion does not absorb visible light
The partially filled “d” orbitals of the transition metals can absorb visible wavelengths and move to slightly higher energy “d” levels
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Transition Elements Magnetism in Transition Elements
Magnetic properties are related to electron sublevel occupancy
A “Paramagnetic” substance has atoms or ions with “unpaired” electrons
A “Diamagnetic” substance has atoms or ions with only “paired” electrons
Most Main-Group metal ions are diamagnetic (filled outer shells)
Many Transition metal compounds are paramagnetic because of unpaired electron in the “d” subshells
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Transition Elements Chemical Behavior Within a Group
Main_Group
● The decrease in Ionization Energy (IE) going down a group results in “increased reactivity”
Transition metals
● Ionization Energy increases down group
●
● The Standard Electrode Potential (Eo) also increases (becomes more positive)
Chromium is stronger reducing agent
Some Properties of Group 6B(6) Elements
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Transition Elements The Inner Transition Elements
Lanthanides (Rare Earth Elements)
(Cerium (Ce); Z = 58 – Lutetium (Lu); Z = 71)
Silvery, high melting point (800 – 1600oC) metals
Small variations in chemical properties makes them difficult to separate
Occur naturally in the +3 oxidation state as M3+
ions of very similar radii
Most lanthanides have the ground-state electron configuration filling the “f” subshell level
[Xe] 6s2 4fx 5d0 x varies across series (Period)
Exceptions – Ce, Gd, Lu have single e- in 5d orbital
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Sample ProblemFinding the Number of Unpaired Electrons
The alloy SmCo5 forms a permanent magnet because both Samarium and Cobalt have unpaired electrons
How many unpaired electrons are in the Sm atom (Z=62)?
Ans:
Samarium is the eighth element after Xe (Noble Shell)
[Xe] 6s2 4f6
Two (2) electrons go in the 6s sublevel
In general, the 4f sublevel fills before the 5d sublevel (slide 17)
Recall previous slide - only Ce, Gd, Lu have 5d electrons
Remaining 6 electrons go into the 4f orbitals
6s 4f 5d 6pSix unpaired electrons
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Transition Elements The Actinides:
(Thorium (Th); Z=90 - Lawrencium; Z=103)
All Actinides are Radioactive (Alpha (4He2) Decay
Only Thorium & Uranium occur in nature
Share very similar chemical & physical properties
Silvery and chemically reactive
Principal oxidation state is +3, similar to lanthanides
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Transition Elements Highlights of Selected Transition Metals
Period 4 – Chromium & Manganese Chromium
● Silvery, shiny metal with many colorful compounds● Cr2O3 acts as protective coating on easily corroded
(oxidized) metals, such as iron “Stainless” steels contain as much as 18 % Cr,
making them highly resistant to corrosion● Electron Configuration ([Ar] 4s1 3d5) with 6 valence
electrons occurs in all possible positive oxidation states
● Important ions Cr2+, Cr3+, Cr6+
Non-metallic character and oxide acidity increase with metal oxidation state
Cr2+ potential reducing agent (Cr loses additional electrons)
Cr6+ potential oxidizing agent (Cr gains electrons)
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Transition Elements Highlights of Selected Transition Metals
Chromium Chromium (II) – Cr2+
CrO is basic and largely ionic Forms insoluble hydroxide in neutral or basic
solution Dissolves in acid to yield Cr2+ ion and water
CrO(s) + 2H+ → Cr2+ (aq) + H2O(l)● Chromium(III) – Cr3+
Cr2O3 is amphoteric, similar properties as Aluminum
Dissolves in acid to yield violet Cr3+ ionCr2O3(s) + 6H+(aq) → 2Cr3+(aq) + 3H2O(l)
Reacts with base to form the green Cr(OH)4- ionCr2O3(s) + 3H2O + OH- → 2Cr(OH)4
-(aq)
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Transition Elements Highlights of Selected Transition Metals
Chromium (con’t)
● Chromium (VI) - Cr6+ (Deep Red)
● CrO3 is covalent and acidic
● Dissolves in water to form Chromic Acid (H2CrO4)
CrO3(s) + H2O(l) → H2CrO4(aq)
H2CrO4 yields yellow Chromate ion (CrO42-) in base
H2CrO4(aq) + 2OH-(l) → CrO42-(aq) + 2H2O(l)
Chromate ion forms orange dichromate (Cr2O72-)
ion in acid
2CrO42-(aq) + 2H+(aq) ⇆ Cr2O7
2-(aq) H2O(l)
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Transition Elements Highlights of Selected Transition Metals
Manganese Hard and Shiny Like Vanadium & Chromium used to make steel alloys Chemistry of Manganese is similar to Chromium Metal reduces H+ from acids to form Mn2+ ionMn(s) + 2H+(aq) → Mn2+(aq) + H2(g) Eo = 1.18 V
Manganese can use all its valence electrons (several oxidation states) to form compounds
Mn2+ Mn4+ Mn7+ most important As oxidation state rises from +2 to +7, the valence
state electronegativity increases and the oxides of Mn change from basic to acidic
Mn(II)O (basic) Mn(III)2O3 (amphoteric)
Mn(IV)O2 (insoluble) Mn(VII)2O7 (acidic)
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Transition Elements All Manganese species with oxidation states greater
than +2 act as oxidizing agents (gaining the electrons lost by the atoms being oxidized)
Mn7+O4-(aq) + 4H+ + 3e- → Mn4+O2(s) + 2H2O(l) Eo =
1.68
Mn7+O4-(aq) + 2H2O + 3e- → Mn4+O2(s) + 4OH- Eo =
0.59
(Mn7+O4- is a much stronger oxidizing agent in acid
solution than in basic solution – note difference in Eo values)
Oxidation StateManganese (Mn) dx Electronic
Configuration
0 d5 [Ar] 4s2 3d5
+1 d5 [Ar] 4s1 3d5
+2 d5 [Ar] 3d5
+3 d4 [Ar] 3d4
+4 d3 [Ar] 3d3
+5 d2 [Ar] 3d2
+6 d1 [Ar] 3d1
+7 d0 [Ar]
4s 3d 4p
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Transition Elements Manganese
Unlike Cr2+ & Fe2+, the Mn2+ (3d5) ion resists oxidation in air
● Recall: half-filled (-1/2 spin electrons missing) & filled sublevels are more stable than partially filled sublevels
● Cr2+ is a d4 species and readily loses a 3d electron to form the d3 ion Cr3+, which is more stable
● Fe2+ is a d6 species and removing a 3d electron yields the stable, half-filled d5 configuration of Fe3+
● Removing an electron from Mn2+ disrupts the more stable d5 configuration
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Transition Elements & TheirCoordination Compounds
Coordination Compounds (Complexes) Most distinctive aspect of transition metal chemistry Complex – Substances that contain at least one
complex ion Complex ion – Species consisting of a “central metal
cation” (either a main-group or transition metal) that is bonded to molecules and/or anions called “Ligands”
The Complex ion is typically associated with other (counter) ions to maintain neutrality
A coordination compound behaves like an electrolyte in water● Complex ion and counter ion separate● Complex ion behaves like a polyatomic ion – the
ligands and central atom remain attached
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Transition Elements & TheirCoordination Compounds
Components of Coordination Compound When solid complex dissolves in water, the complex
ion and the counter ions separate, but ligands remain bound to central atom
CentralAtom
Ligands CounterIons
[Co(NH3)6]Cl3(s)
OctahedralGeometry
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Transition Elements & TheirCoordination Compounds
Complex ions A complex ion is described by the metal ion
and the number and types of ligands attached to it● The bonding between metal and ligand
generally involves formal donation of one or more of the ligand's electron pairs
● The metal-ligand bonding can range from covalent to more ionic
● Furthermore, the metal-ligand bond order can range from one to three (single, double, triple bonds)
● Ligands are viewed as Lewis Bases (donate electron pairs), although rare cases are known involving Lewis acidic ligands
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Transition Elements & TheirCoordination Compounds
Complex ionsThe complex ion structure is related to
three characteristics:● Coordination Numbers
The number of ligand atoms that are bonded directly to the central metal ion
Coordination number is specific for a given metal ion in a particular oxidation state and compound
Coordination number in [Co(NH3)6]3+ is 6
The most common coordination number in complex ions is 6, but 2 and 4 are common, with a few higher
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Transition Elements & TheirCoordination Compounds
Complex ions Geometry – Depends on Coordination No. & Nature of
Metal IonMetal ion CN Shape dx
Cu+ 2 Linear d10
Ag+ 2 Linear d10
Au+ 2 Linear d10
Ni2+ 4 Octahedral Sq Planar d8
Pd2+ 4 Octahedral Sq Planar d8
Pt2+ 4 Octahedral Sq Planar d8
Cu2+ 4 Octahedral Sq Planar d9
Cu3+ 4 Tetrahedral d8
Zn2+ 4 Tetrahedral d10
Cd2+ 4 Tetrahedral d10
Mn2+ 4 Tetrahedral d5
Ti3+ 6 Octahedral d1
V2+ 6 Octahedral d3
Cr3+ 6 Octahedral d3
Mn2+ 6 Octahedral d5
Fe3+ 6 Octahedral d5
Co3+ 6 Octahedral d6
Coordination Numbers and Shapes of Some Complex Ions
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Transition Elements & TheirCoordination Compounds
Complex Ions
Donor Atoms per Ligand
● The Ligands of complex ions are “molecules” or “anions” with one or more donor atoms that each donate a lone pair of electrons to the metal ion to form a covalent bond
● Atoms with lone pairs of electrons often come from Groups 5A, 6A, or 7A (main-group elements)
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Transition Elements & TheirCoordination Compounds
Complex Ions
Ligands are classified in terms of the number of donor atoms (teeth) that each uses to bond to the central metal ion
● Monodentate Ligands use a “single” donor atom
● Bidentate Ligands have two donor atoms
● Polydentate Ligands have more than two donor atoms
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Transition Elements & TheirCoordination Compounds
The Ligands contains one or more Donor atoms that have electron pairs to donate to
the Central Atom
Donor Atom
Some Common Ligands in Coordination Compounds
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Transition Elements & TheirCoordination Compounds
Complex Ions Chelates (Greek “chela” – crab’s claw)
● Bidentate and Polydentate ligands give rise to “rings” in the complex ion
● Ex: Ethylene Diamine (abbreviated (en) in formulas)(:N – C – C – N:)
forms a 5-member ring, with the two electron donatingN atoms bonding to the metal atomSuch ligands seem to grab the metal ion like claws
Ethylenediaminetetraacetate (EDTA)
Used in treating heavy-metal poisoning, by acting as a scavenger of lead andother heavy-metal ions, removing them from blood and other body fluids
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination Compounds
Important rules for writing formulas of coordinate compounds
● The cation is written before the anion
● The charge of the cation(s) is balanced by the charge of the anions
● In the complex ion, neutral ligands are written before anionic ligands
● The entire ion is placed in brackets, i.e., [ ]
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination Compounds
Coordination Compound Formulas
● Example # 1
Two compound cations (K+) – Total Charge +2Ion Central Metal Cation (Co2+) – Total Charge +2Neutral Ligands (2 NH3) – Total Charge 0
Counter Ions (4 Cl-) – Total Charge -4Net Charge on Complex Ion – - 2
[Co(NH3)2Cl4]-2
-2+ 2+ -2 3 2 4K [Co (NH ) Cl ]
2 3 2 4K [Co(NH ) Cl ]
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination Compounds
Coordination Compound Formulas
● Example # 2 – Complex Ion and Counter Ion
[Co(NH3)4Cl2]Cl
Counter Ion (Cl-) (not part of complex ion) – Total charge -1
Complex Ion - Neutral Ligands (4 NH3) – Total Charge 0
Complex Ion - Anion Ligands (2 Cl-) – Total Charge -2
Complex Ion - [Co(NH3)4Cl2]+ – Total Charge +1
Complex Ion - Central Metal Atom (Co) – Total Charge +3
[Co3+(NH3)4Cl-2]+Cl-
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination Compounds Example #3 – Complex Cation and Complex Anion
[Co(NH3)5Br]2[Fe(CN)6] Complex Cation - [Co(NH3)5Br]2+
Complex Cation Central Atom (Co+3) – Total charge +3 Complex Cation Neutral Ligands (5 NH3) – Total
Charge 0
Complex Cation Anionic Ligand (Br-) – Total Charge -1 Complex Anion ([Fe(CN)6]4-) – Total Charge -4
Complex Anion Central Cation (Fe2+) – Total Charge +2
Complex Anion Ligand (6 CN-1) – Total Charge -6 [Co3+(NH3)5Br-]2 [Fe2+(CN-)6]
2 x (3 - 1) = 4 2 - 6 = -4
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination CompoundsNaming Coordination Compounds
● RulesThe Cation is named before the AnionWithin the Complex Ion, the Ligands are named, in
alphabetical order, before the metal ionNeutral Ligands generally have the molecule
name, with exceptions Ex NH3 (ammine), H2O (aqua), C=O (carbonyl)
Anionic Ligands drop the –ide and add –o after the root name Ex. Cl- becomes “chloro”
A numerical prefix indicates the number of ligands of a particular type Ex di (2), tri (3), tetra (4)
[Co(NH3)4Cl2]Cl
Tetra ammine di chloro cobalt(III)chloride
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination Compounds
Di Bis II
Tri Tris III
Tetra Tetrakis IV
Penta pentakis V
Hexa Hexakis VI
Septa Septakis VII
Names of Some Neutraland Anionic Ligands
Names of Some Metals Ionsin Complex Anions
Numerical Prefixes usedIn Complex Anions
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination CompoundsNaming Coordination Compounds
● RulesSome ligand names already contain a
numerical prefix
Ethylenediamine
In these cases the number of ligands is indicated by such terms as:
bis (2) tris(3) tetrakis(4)
A compound with two ethylene ligands would contain the following ligand name
bis(ethylenediamine)
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Transition Elements & TheirCoordination Compounds
Formulas and Names of Coordination Compounds Naming Coordination Compounds
● Rules The oxidation state of the central metal ion is
given by a Roman numeral (in parentheses) only if the metal ion can have more than one state, as in the compound
[Co(NH3)4Cl2]Cl [Co3+(NH3)4Cl-2]Cl-
Tetra ammine di chloro cobalt(III)chloride If the complex ion is an anion, drop the ending
of the Central metal name and add “–ate”K[Pt(NH3)Cl5] K+[Pt4+(NH3)Cl-5]
-
Potassium ammine penta chloro platinate(IV)
Na4[FeBr6] Na+4[Fe2+Br-
6]
Sodium hexa bromo ferrate(II)
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Practice ProblemWhat is the systematic name of Na3[AlF6]?
Ans: Complex ion – [AlF6]3-
Ligands 6 (hexa) F- ions (Fluoro)
Complex ion is an “anion” (net charge -3)
End of metal ion Aluminum must be changed to –ate
Complex ion name – hexafluoroaluminate
Aluminum has only the +3 oxidation state so Roman numerals are not required
Na3+ is the positive counter ion; it is separated from the complex anion by a space
Na3[AlF6] Sodium Hexfluoroaluminate
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Practice ProblemWhat is the systematic name of [Co(en)2Cl2]NO3?
Ans: Listed alphabetically, there are two Cl- (dichloro) and two “en” [bis(ethylenediamine)] ligands
Note: Alphabetically refers to the root chemical names:
Chloro & Ethylenediamine
The “Complex ion” is a “Cation,” with a charge of +1
[Co3+(en)2Cl-2]+
The metal name in a complex ion is unchanged - Cobalt
Because Cobalt can have several oxidation states,its charge must be specified - Cobalt (III)
One Nitrate ion (NO-3) balances the +1 complex cation
Dichloro bis (ethylene diamine)cobalt(III) nitrate
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Practice ProblemWhat is the formula of:
Tetra ammine bromo chlroro platinum(IV) chloride
Ans: The central atom of the complex cation is written first
Platinate(IV) Pt4+
The ligands follow in alphabetical order of root chemical name
Tetraammine (NH3) Bromo (Br-) Chloro (Cl-)
Complex ion formula - [Pt(NH3)4BrCl]2+ [Pt4+(NH3)4Br-Cl-]2+
To balance the +2 charge of the complex cation,2 Cl- counter ions are required
[Pt(NH3)4BrCl]Cl2
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Practice ProblemWhat is the formula of
Hexa ammine cobalt(III) tetra chloro ferrate(III)
Ans: Compound consists of two complex ions
Complex Cation – Six hexammine (NH3) & cobalt(III) (Co3+)
Complex Cation – [Co(NH3)6]3+ [Co3+(NH3)6]3+
Complex Anion – tetrachloro - 4 Cl-
Complex Anion – ferrate(III) - Fe3+
Complex Anion – [FeCl-4]-
Complex cation – balanced by 3 complex anions
Coordinate Compound – [Co(NH3)6][FeCl4]-3
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Transition Elements & TheirCoordination Compounds
Isomerism in Coordination Compounds Isomers are compounds with the same chemical
formula but different properties Constitutional (Structural) Isomers
● Two compounds with the same formula, but with atoms connected differently Two Types
Coordination Isomers – Composition of the complex ion changes but not the compoundEx. Ligand and counter ion exchange positions
[Pt(NH3)4Cl2](NO2)2 [Pt(NH3)4(NO2)2]Cl2Ex. Two sets of ligands reversed
[Cr(NH3)6][Co(CN)6] [Co(NH3)6][Cr(CN)6]
(NH3 is ligand of Cr3+ in one compound and of Co3+ in the other)
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Transition Elements & TheirCoordination Compounds
Constitutional (Structural) Isomers Linkage Isomers
Composition of the complex ion remains the same, but the attachment of the ligand donor atom changes
Some ligands can bind to the metal ion through either of two donor atomsEx. pentaamminenitrocobalt(III) chloride
[Co(NH3)5(NO2]Cl2
pentaamminenitritocobalt(III) chloride[Co(NH3)5(ONO]Cl2
Ex. Cyanate ion can attach via lone pair of electrons on
the Oxygen atom (NCO:)or the Nitrogen atom (isocyanato (OCN:) Other examples of alternate electron
donor pairs for Linkage Isomers
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Transition Elements & TheirCoordination Compounds
Constitutional (Structural) Isomers Stereo Isomers
Compounds that have the same atomic connections but different spatial arrangements of the atoms
Geometric Isomers (cis-trans isomers [diastereomers])
Atoms or groups of atoms arranged differently in space relative to the “Central” metal
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Transition Elements & TheirCoordination Compounds
Constitutional (Structural) Isomers Stereo Isomers Optical Isomers (enantiomers)
Occur when a molecule and its mirror image can not be superimposed
Optical isomers have distinct physical properties like other types of isomers, with one exception – the direction in which they rotate the plane of polarized light
Optical isomerism in an octahedral complex ion
Rotating structure I in the cis compound gives structure III, which is not the same as structure II, its mirror image, Image I & Image III are optical isomers
Rotating structure I in the trans compound gives structure III,which is the same as structure II, its mirror image, The trans compound does not have any mirror images
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Practice ProblemDraw all stereo isomers for the following
[Pt(NH3)2Br2] Cr(en)3]3+ (en = H2NCH2CH2NH2)
Pt
NH3Br
H3N Br
Pt
H3N Br
H3N Brtrans
Pt(II) complex is Square Planar GeometryTwo different monodentate ligandsGeometric Isomers Each isomer is superimposable on the mirror image – no optical isomerism
Ethylenediamine is a bidentate ligand
The Cr3+ has a coordination number of 6 and an octahedral geometry, similar to Co3+
The three bidendate ions are identical
No geometric isomerism
This complex ion has a nonsuperimposable mirror image
Optical Isomerism does occur
cis
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Transition Elements & TheirCoordination Compounds
Theoretical Basis for the Bonding and Properties of Complexes
Questions
● How do Metal Ligand bonds form
● Why certain geometries are preferred
● Why are complexes often brightly colored
● Why are complexes often paramagnetic – attracted to a magnetic field as a result of their electron pairs being unpaired
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Transition Elements & TheirCoordination Compounds
Theoretical Basis for the Bonding and Properties of Complexes Application of Valence Bond Theory to Complex Ions
● In the formation of a complex ion, the filled ligand orbital overlaps the empty metal-ion orbital
● The Ligand (Lewis Base) donates the electron pair and the metal-ion (Lewis Acid) accepts it to form one of the covalent bonds of the complex ion (Lewis adduct)
● When one atom in a bond donates both electrons the bond is referred to as a ”coordinate covalent bond”
● The number and type of metal-ion hybrid orbitals occupied by ligand lone pairs determine the geometry of the complex ion
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Transition Elements & TheirCoordination Compounds
Application of Valence Bond Theory to Complex Ions Octahedral Complexes (six electron groups about central
atom)● Ex. Hexaamminechromium(III) ion [CrNH3)6]3+
● Six hybrid orbitals are needed to make the ion● The six lowest energy orbitals of the Cr3+ ion
Two 3d, one 4s, three 4p
mix and become six equivalent d2sp3 hybrid orbitals that point to the corners of an octahedron
The six d2sp3 hybrid orbitals are filled with the six electron pairs from the six NH3 ligands
Note the lowest 6 energy levels for Cr3+ involve both n=3 & n=4 sublevelsThe 3d orbitals are of lower energy than the 4s and 4p orbitalsThe hybrid designation, d2sp3, follows this orderIf all the orbitals had the same “n” value, the order would have been sp3d2
ParamagneticUnpaired e-
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Transition Elements & TheirCoordination Compounds
Application of Valence Bond Theory to Complex Ions Square Planar Complexes (four electron groups about
central atom)● Metal ions with a d8 configuration usually form square
planar complexes● In the [Ni(CN)4]2- ion, the model proposes
one 3d, one 4s, two 4p for Ni2+
to from four dsp2 hybrid orbitals pointing the corners of a square accepting one electron pair from each of the four CN- orbitals
Note the filling of the first 4 unhybridized 3d orbitals after one 3d, one 4s and two 4p orbitals combine to form the four dsp2 hybrid orbitals
ParamagneticUnpaired e-
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Transition Elements & TheirCoordination Compounds
Application of Valence Bond Theory to Complex Ions Tetrahedral Complexes (four electron groups about central
atom)● Metal ions that have a filled d sublevel, such as Zn+2
[Ar] 3d10
often form Tetrahedral complexes● In the [Zn(OH)4]2- ion, the model proposes the lowest
available Zn2+ orbitals
one 4s, three 4p
mix to become four sp3 hybrid orbitals that point to the corners of a tetrahedron, occupied by four lone pairs, one from each of the four OH- ligands
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory
Valence Bond Theory pictures and rationalizes bonding and shape of molecules
VB theory gives little insight into the colors of coordination compounds and can be ambiguous with regard to magnetic properites
Crystal Field Theory explains color and magnetism
● Highlights the “effects” on the d-orbital energies of the metal ion as the ligands approach
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory
What is Color?
● White light is electromagnetic radiation consisting of “all” wavelengths () in the “visible” range
● Objects appear “colored” in white light because they absorb certain wavelengths and reflect or transmit others
● Opaque objects reflect light
● Clear objects transmit light
● If the object absorbs all visible wavelengths, it appears “black”
● If the object reflects all visible wavelengths, it appears “white”
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory What is Color?
● Each color has a “complimentary” color● An object has a particular color for two
reasons It reflects (or transmits) light of that color
or It absorbs light of the “complimentary”
color
Ex. If an object absorbs only red (compliment of green), it is interpreted as “green”
Colors with approximate wavelength ranges
Complimentary colors, such as red and green,lie opposite each other
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory
● In CF Theory, the properties of complexes result from the splitting of d-orbital energies
● Split d-orbital energies arise from “electrostatic” interactions between the positively charged metal ion cation and the negative charge of the ligands
● The negative charge of the ligand is either partial as in a polar neutral ligand like NH3, or full, as in an anionic ligand like Cl-
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory The ligands approach the metal ion along the mutually
perpendicular x, y, and z axes (octahedral orientation), minimizing the overall energy of the system
B & C Lobes of the dx2-y2 and dz2 orbitals lie directly in line with the approaching ligands and have stronger repulsions
D, E, F lobes of the dxy, dxz, and dyz orbitals lie “between” the approaching ligands, so the repulsion are weaker
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory An energy diagram of the orbitals shows all five d orbitals are
higher in energy in the forming complex than in the free metal ion, because of the repulsions from the approaching ligands
Crystal Field Splitting Energy - The d orbital energies are“split” with the two dx2-y2 and dz2 orbitals (eg orbital set) higher in energy than the dxy, dxz, and dyz orbitals (t2g orbital set)
Strong-field ligands, such as CN- lead to larger splitting energy Weak-field ligands such as H2O lead to smaller splitting energy
Crystal Field Splitting Energy
Forming Complex
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory
Explaining the Colors of Transition Metals
● Diversity in colors is determined by the energy difference () between the t2g and eg orbital sets in complex ions
● When the ions absorbs light in the visible range, electrons move from the lower energy t2g level to the higher eg level, i.e., they are “excited” and jump to a higher energy level
E electron = Ephoton = hv = hc/
● The substance has a “color” because only certain wavelengths of the incoming white light are absorbed
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Example – Consider the [Ti(H2O)6]3+ ion – Purple in
aqueous solution Hydrated Ti3+ is a d1 ion, with the d electron in one of the
three lower energy t2g orbitals
The energy difference (A) between the t2g and eg orbitals corresponds to the energy of photons spanning the green and yellow range
These colors are absorbed and the electron jumps to one of the eg orbitals
Red, blue, and violet light are transmitted as purple
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory
For a given “ligand”, the color depends on the oxidation state of the metal ion – the number of “d” orbital electrons available
A solution of [V(H2O)6]2+ ion is violet
A solution of [V(H2O)6]3+ ion is yellow
For a given “metal”, the color depends on the ligand
[Cr(NH3)6]3+ (yellow-orange)
[Cr(NH3)5]2+ (Purple)
Even a single ligand is enough to change the color
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Spectrochemical Series
● The Spectrochemical Series is a ranking of ligands with regard to their ability to split d-orbital energies
● For a given ligand, the color depends on the oxidation state of the metal ion
● For a given metal ion, the color depends on the ligand● As the crystal field strength of the ligand increases, the
splitting energy () increases (shorter wavelengths of light must be absorbed to excite the electrons
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Practice ProblemRank the following ions in terms of the relative value of and of the energy of visible light absorbed
[Ti(H2O)6]3+ Ti(NH3)6]3+ Ti(CN)6]3+
Ans:
Oxidation State of Ti is +3 in all formulas
From the spectrochemical series table, the ligand strength is in the order:
CN- > NH3 > H2O
Relative size of , thus, the energy of light absorbed is
Ti(CN)6]3+ > Ti(NH3)6]3+ > [Ti(H2O)6]3+
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Transition Elements & TheirCoordination Compounds
Explaining the Magnetic Properties of Transition Metal Complexes The splitting of energy levels influence magnetic
properties Affects the number of unpaired electrons in the
metal ion “d” orbitals According to Hund’s rules, electrons occupy orbitals one
at a time as long as orbitals of “equal energy” are available
When “all” lower energy orbitals are “half-filled (all +½ spin state)”, the next electron can● Enter a half-filled orbital and pair up (with a –½ spin
state electron) by overcoming a repulsive pairing energy (Epairing) or
● Enter an empty, higher energy orbital by overcoming the crystal field splitting energy ()
● The relative sizes of Epairing and () determine the occupancy of the d orbitals
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Explanation of Magnetic Properties
● The occupancy of “d” orbitals, in turn, determines the number of unpaired electrons, thus, the paramagnetic behavior of the ion
● Ex. Mn2+ ion ([Ar] 3d5) has 5 unpaired electrons in 3d orbitals of equal energy
● In an octahedral field of ligands, the orbital energies split
● The orbital occupancy is affected in two ways: Weak-Field ligands (low ) and High-Spin
complexes Strong-Field ligands (high ) and Low-Spin
complexes(from spectrochemical series)
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Explanation of Magnetic Properties
● Weak-Field ligands and High-Spin complexes● Ex. [Mn(H2O)6]2+ Mn2+ ([Ar] 3d5)
● A weak-field ligand, such as H2O, has a “small” crystal field splitting energy ()
● It takes less energy for “d” electrons to move tothe “eg” set (remaining unpaired) rather thanpairing up in the “t2g” set with its higherrepulsive pairing energy (Epairing)
● Thus, the number of unpaired electrons in aweak-field ligand complex is the same as inthe free ion
● Weak-Field Ligands create high-spin complexes,those with a maximum of unpaired electrons
● Generally Paramagnetic
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Explanation of Magnetic Properties
● Strong-Field Ligands and Low-Spin Complexes● Ex. [Mn(CN)6]4-
● Strong-Field Ligands, such CN-, cause large crystal field splitting of the d-orbital energies, i.e., higher ()
● () is larger than (Epairing)
● Thus, it takes less energy to pair up in the “t2g“ set than would be required to move up to the “eg” set
● The number of unpaired electrons in aStrong-Field Ligand complex is less thanin the free ion
● Strong-Field ligands create low-spin complexes,i.e., those with fewer unpaired electrons
● Generally Diamagnetic
Fewerunpaired electrons
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Explaining Magnetic Properties
● Orbital diagrams for the d1 through d9 ions in octahedral complexes show that both high-spin and low-spin options are possible only for:
d4 d5 d6 d7 ions● With three “lower” energy t2g orbitals available,
the d1, d2, d3 ions always form high-spin (unpaired) complexes because there is no need to pair up
● Similarly, d8 & d9 ions always form high-spin complexes because the 3 orbital t2g set is filled with 6 electrons (3 pairs)The two t2g orbitals must have either two d8 or one d9 unpaired electron
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory
Explaining Magnetic Properties
high spin: weak-field
ligand
low spin: strong-field
ligand
high spin: weak-field
ligand
low spin: strong-field
ligand
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Practice ProblemIron(II) forms an essential complex in hemoglobin
For each of the two octahedral complex ions
[Fe(H2O)6]2+ [Fe(CN)6]4-
Draw an orbital splitting diagram, predict the number of unpaired electrons, and identify the ion as low-spin or high spin
Ans:
Fe2+ has the [Ar] 3d6 configuration
H2O produces smaller crystal field splitting () than CN-
The [Fe(H2O)6]2+ has 4 unpaired electrons (high spin)
The [Fe(CN)6]4- has no unpaired electrons (low spin)
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory Four electron groups about the central atom
● Four ligands around a metal ion also cause d-orbital splitting, but the magnitude and pattern of the splitting depend on the whether the ligands are in a “tetrahedral” or “square planar” arrangement
● Tetrahedral – AX4 ● Octahedral – AX4E2 (2 ligands along “z” axis
removed)
Splitting of d-orbital energies by
a square planar field of ligands.
Splitting of d-orbital energies by a tetrahedral field of ligands
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory (Splitting) Tetrahedral Complexes
● Ligands approach corners of a tetrahedron● None of the five metal ion “d” orbitals is directly in
the path of the approaching ligands● Minimal repulsions arise if ligands approach the
dxy, dyz, and dyz orbitals closer than if they approach thedx2-y2 and dz2 orbitals (opposite of octahedral case)
● Thus, the dxy, dyz, and dyz orbitals experience more electron repulsion and become higher energy
● Splitting energy of d-orbital energies is “less” in a tetrahedral complex than in an octahedral complex
tetrahedral < octahedral
● Only high-spin tetrahedral complexes are known because the magnitude of () is small (weak)
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Transition Elements & TheirCoordination Compounds
Crystal Field Theory (Splitting) Square Planar Complexes
● Consider an Ocatahedral geometry with the two z axis ligands removed, no z-axis interactions take place
● Thus, the dz2, dxz an dyz orbital energies decrease● The two ‘d” orbitals in the xy plane (dxy, dx2-y2)
interact most strongly with the approaching ligands● The (dxy, dx2-y2) orbital has its lobes directly on the x,y
axis and thus has a higher energy than the dxy orbital
● Square Planar complexes are generally strong field – low spin and generally diamagnetic
● D8 metals ions such as [PdCl4]2- have 4 pairs of the electrons filling the lowest energy levels and are thus, “diamagentic”