Download Ch 22 Transition complexes

Chem 2
Chapter 22: The Transition elements and coordination compounds.
General Properties:
 The transition metals show great similarities within a given period and a group. Their
Chemistry does not change as number of valence electron change.
 They are metals good conductors of heat and electricity: Ex: Ag.
 More than one oxidation state.
 Complex ions: Species where transition metal ion is surrounded by a certain number of
ligands.
 Ligand: Molecules or ions that behave as Lewis bases.
 Paramagnetic-unpaired electrons.
Electronic Configurations:
 Cr:
 Cu:
 Mo3+
 Ag+
The energy of 3d orbitals in transition metal ions is less than 4s orbitals.
Atomic and Physical Properties of Transition Elements:
1. Atomic size decreases from left to right across the period , but then remain fairly constant.
2. Transition elements exhibit a small change in electronegativity. The values are intermediate.
3. First Ionization energies increase little.
4. Lanthanide contraction- 4f orbitals are filled, increases overall charge on nucleus and not the
size.
5. Nuclear charge increases down a group.
6. Heavier transition metals exhibit more covalent character.
7. First I.E increases down a transitional group.
8. Densities increase as atomic mass increases.
Chemical Properties:
1. They have multiple oxidation states.
2. +2 oxi state is most common as ns2 electrons are readily lost.
3. Ionic bonding occurs in lower O.S and covalent in higher O.S.
4. Electrons in a partially filled d sublevels can absorb visible wavelengths and hence their
compounds are colored.
5. They are paramagnetic (unpaired d electrons)
6. IE1 increases down a group.
Coordination compounds:
 They contain atleast one Complex ion , bonded to ligands and associated with other
counter ions.
 Coordination compound: Complex transitional metal ion attached to ligands.
 Two types of valance: 1. secondary Valence- Ability of metal ion to bind to a Lewis
base(ligands)-Coordination number.
2. Primary valence-Ability of metal ion to form ionic bonds with oppositely charged
ions.-Oxidation state.
 Complex ions: Species where transition metal ion is surrounded by a certain number of
ligands.
 Ligand: Molecules or ions that behave as Lewis bases.
1
1. The coordination number:
 Varies from 2-8.
 6 ligands-octahedral arrangement.
 4-Tetrahedral/Square planar.
 2- Linear.
 Most common coord. Number is 6.
2. Ligands:
 Neutral molecule or ion having a lone pair of electron that can be used to form a bond to
metal ion.
 Metal (Lewis acid-e pair acceptor) _______ Ligand ( Lewis base- e pair donor)
 Monodentate/ Unidentate ligand- Ligand forms 1 bond.CN-, H2O, NH3.
 Chelating ligands/ Chelates: Ligands have more than one atom with a lone pair of
electrons that can be used to bond a metal ion.
 Bidentate ligand- can form 2 bonds.Ex: ethylenediamine(en), oxalate
 Polydentate ligands- can form more than 2 bonds.Ex: EDTA- 6 bonds.
Nomenclature:
1. Name cation before anion.
2. In naming a complex ion, name ligands before the metal ion.
3. In naming ligands, add o to the root name of anion(chloro), Use the full name for a
neutral ligand .
4. Exceptions to # 3: aqua, ammine, methylamine, carbonyl, nitrosyl.
5. Use prefix mono, di, tri, tetra , penta and hexa for simple ligands.
6. Use prefix bis,tris,tetrakis for complicated ligands that alreadt have bi,tri.
7. Oxidation state for metal in Roman numerals in ()
8. When more than one type of ligand are present name alphabetically.
9. If complex ion has negative charge add the suffix -ate to the name of the metal.(Latin
name)
Iron
copper
lead
silver
gold
tin.
Isomerism:
 Same formula but different properties.
1. Structural isomerism: Isomers contain same atoms but different bonds.
A. Coordination isomerism: Composition of complex ion varies.
B. Linkage isomerism: Point of attachment of atleast one of the ligands differs.
2. Stereoisomers: All bonds are same but different spatial arrangements.
A. Geometrical isomerism –cis-trans-Atoms or group of atoms can assume different
positions around a rigid ring or bond.
B. Optical Isomerism: Have opposite effects on plane polarized light.
 Chiral: Objects that have nonsuperimposable mirror images.
 Enantiomers: Isomers that are nonsuperimposable mirror images of
each other.
The Crystal Field Model:
 It focuses on the energies of d orbitals.
 Metal –ligand bond is ionic.
2

Ligands are negative point charges.
Octahedral complexes:
 Dz2 and dx2-y2 orbitals have lobes that point directly at the ligands.
 Dxy, dyz,dxy point their lobes between charges.
 Electrons fill the d orbitals farthest from the ligands to minimize repulsion.
 Dxy, dyz,dxy ( t2g set) are at lower energy in octahedral complex first.
 Dz2 and dx2-y2 (eg set) is at higher energy.
 Splitting of 3d orbital energies explains color and magnetism.
 Strong field case- splitting produced by ligands is very large, electrons will pair in lower
t2g orbitals. Diamagnetic (all electrons are paired)
 Weak field case-splitting produced by ligands is small, electrons will occupy all 5 orbitals
before pairing occurs. Paramagnetic( unpaired electrons)
1) Fe (CN)63- has one unpaired electron . Does the CN- ligand produce a strong or weak
field?
Spectrochemical series:
CN- > NO2- > en> NH3> H2O> OH-> F-> Cl-> Br-> IStrong field
High spin
Low spin
weak field ligands
(large ∆)
(small ∆)
Magnitude of ∆ increases as charge on metal ion increases.
2) Predict the number of unpaired electrons in the complex ion [Cr(CN)6] 4 –
Color of octahedral compounds:
 Absorbed color is different than observed color.
 Transition metals absorb colors in the visible region.
 ∆E=hc/ , ∆E= energy spacing, =walength needed to move an electron from t2g to eg.
Color of solution changes as the ligand changes.
In tetrahedral complexes:
 None of the 3d orbitals point at the ligands.
 Tetrahedral splitting is 4/9 times that of octahedral.
 Dxy, dyz,dxy are closer to pint charges than Dz2 and dx2-y2.
 Weak field case always applies in tetrahedral complexes.
3) Give the crystal field diagram for tetrahedral complex ion CoCl 4 2-
Practice Problems;
1. What are the oxidation numbers of the central metal atom in the following coordination
compounds? K3[Fe(CN)6], [Cr(NH3)4Br2]Br, [Ni(H2O)6]Cl2, Na2[TaF7] are
3
[A] 3, 3, 3, 5 [B] -3, 1, 2, 5 [C] 3, 3, 2, 7 [D] -3, 3, 2, 5 [E] 3, 3, 2, 5
2. Which of the following is a d7 ion?
[A] Cu(II)
[B] Co(II) [C] Mn(II)[D] Mn(IV)[E] At least two of these (a-d) are d7 ions.
3. True or false: Transition metals show great similarities both within a given period and within
a given vertical group.
4. What is the sum of the geometric and optical isomers that the complex ion Co(en)2Cl2+
exhibits?
[A] 0 [B] 1 [C] 3 [D] 2 [E] 4
5. The ____ isomer of the complex Ni(en)2Cl2 exhibits optical isomers, but the _____ isomer
does not.
[A] trans, cis [B] cis, trans [C] Both isomers exhibit optical isomers.
[D] Neither isomers exhibit optical isomers.
6. Which of the transition metals is the best conductor of heat and electric current?
[A] titanium [B] silver [C] tungsten [D] gold [E] copper
7. A complex ion is a charged species consisting of a metal ion surrounded by
[A] hydrogen ions. [B] ligands. [C] ligands and counter ions.
[D] other transition metals. [E] none of these
8. What is the electron configuration of the Mn(II) ion?
[A] [Ar] 4s23d3 [B] [Ar] 3d5 [C] [Ar] 4s23d5 [D] [Ar] 4s13d5 [E] none of these
9. The complex ions of Zn2+ are all colorless. The most likely explanation for this is:
[A] Zn2+ is paramagnetic.
[B] Zn2+ is not a transition metal ion.
[C] Zn2+ exhibits –d orbital” splittings in its complexes such that they absorb all wavelengths in
the visible region.
[D] Since Zn2+ is a d10 ion, it does not absorb visible light even though the –d orbital” splittings
are correct for absorbing visible wavelengths.
[E] None of these are correct.
10. The expected electron configuration of Cu+ is [Ar]3s13d9. (T/F)
11. Because they have the same atoms, bonds, and formulas, geometric isomers have the same
color.
12. Calculate the total number of unpaired electrons in the following complex ions: Zn(OH2)62+,
Ni(CN)42- (square planar), Co(NH3)63+ (strong field).
[A] 3 [B] 4 [C] 2 [D] 1 [E] 0
13. Specify the number of unpaired electrons.
a) 0 b) 1 c) 2 d) 4 e) 5
NiCl42- (tetrahedral)
4
14. The complex FeL62+, where L is a neutral ligand, is known to be diamagnetic. The number
of d electrons in this complex ion is:
[A] 8 [B] 4 [C] 7 [D] 6 [E] 5
15. Fluoride ion ranks low in the spectrochemical series and produces a weak crystal field in
complex ions. Based on this information, predict the number of unpaired electrons in CoF63-.
[A] 1 [B] 2 [C] 3 [D ] 0[E] 4
16. The complex ion Co(NH3)62+ (three unpaired electrons) is classified as:
[A] strong field [B] no way to tell [C] weak field
17. Which of the following statements is true about the octahedral complexes of Ni2+?
[A] Both strong- and weak-field complexes are paramagnetic.
[B] Both strong- and weak-field complexes are diamagnetic.
[C] The strong-field complex is diamagnetic and the weak-field complex is paramagnetic.
[D] The strong-field complex is paramagnetic and the weak-field complex is diamagnetic.
18. How many unpaired electrons are there in Ir(Br)64-? (Br- is a weak-field ligand.)
[A] 3 [B] 4 [C] 0 [D] 1 [E] 2
19. A metal ion in a high-spin octahedral complex has two more unpaired electrons than the same
ion does in a low-spin octahedral complex. The metal ion could be:
[A] V2+ [B] Cr3+ [C] Cu2+ [D] Co2+ [E] Mn2+
20. Which of the following is true in describing the crystal field model?
[A] The ligands are treated as negative point charges.
[B] The electrons are assumed to be localized.
[C] The metal ion and ligand interaction is treated as a Lewis acid–base interaction.
[D] The metal ion–ligand bonds are considered to be completely ionic.
[E] None of these are true.
21. Which of the following are structural isomers?
I. coordination isomers
II. linkage isomers
III. geometric isomers
IV. optical isomers
[A] I, II [ B] II, IV [C] I, III, IV [D] II, III [E] I, III
22. Which complex ion shape is not capable of showing cis–trans isomerism?
[A] tetrahedral [B] octahedral [C] square planar [D] none of these
23. Define stereoisomerism.
24. The color of a transition metal complex results from:
[A] bending vibrations. [B] transition of an electron between an s and a p orbital.
[C] transition of an electron between d orbitals. [D] nuclear magnetic resonance.
[E] stretching vibrations.
5
25.
Consider the pseudo-octahedral complex of Cr3+ shown, where A and B represent Lewis bases
and where A produces a stronger crystal field than B. Draw an appropriate crystal field diagram
for this complex (include the electrons).
26. How many unpaired electrons are found in each of the following complex ions?
[Co(NH3)4]2+
27. All tetrahedral complex ions are high spin.(T/F)
28. How many unpaired electrons are found in each of the following complex ions?
[Cr(CN)4]229. Copper(I) complexes would be expected to be colorless.(T/F)
30. Transition metals display great similarities
[A] within a given period. [B] within a given vertical group. [C] with the semimetals.
[D] all of these [E] a and b only
***********************************************************************
Complete the blank spaces for the names and the formulas.
Transition Metal Complexes – Nomenclature
[Cu(NH3)4]SO4
K2[CoC4]
Co(phen)2C2
[Co(en)2(H2O)C]C2
[Ni(H2O)6]SO4
[Cr(en)2(CN)2]Cl
K[Pt(NH3)C5]
sodium hexabromoferrate(II)
sodium hexafluoroaluminate
6
dichlorobis(ethylenediamine)cobalt(III) nitrate
tetraamminebromochloropatinum(IV) chloride
hexaamminecobalt(III) tetrachloroferrate(III)
sodium hexanitrocobaltate(III)
K3[Fe(CN)6]
[Co(NH3)5Br]Br2
[Cr(NH3)(en)Cl2]Cl
Ni(CO)4
K2[Ru(NH3)5H2O]
sodium aquapentacyanocobaltate(III)
dichlorobisethylenediaminechromium(III) nitrate
triamminetrichlorocobalt(III)
ammonium diaquadioxalatoferrate(II)
hexaamminecobalt(III) hexacyanoferrate(III)
K2[Co(NH3)2Cl4]
[Co(NH3)5Br]2 [Fe(CN)6]
Na3[Fe(CN)5CO]
[Fe(H2O)4OH] SO4
[Co(NH3)4(NO3Cl] SO4
dibromobisethylenediamineplatinum(IV) perchlorate
sodium bisthiosulfatoargentate(I)
7
8