Understanding Coordination Chemistry: Structures, Isomers, and Naming

 
Chapter 9
Coordination
Chemistry I
 
Structures
and Isomers
 
2
 
Coordination compounds
 
Central metal, neutral or cation
Ligand:  neutral molecule or anion
Ions for charge balance (if necessary)
Coordination number = number of ligand attachments
                      (commonly 4, 6, 5)
Geometric and optical isomers possible
K
f
 values: usually very large, >10
10
 
Naming Coordination Compounds
 
Cation + anion
Ligands + metal in coordination compound
Charge indicated by Roman numerals in
parentheses
If complex ion carries a negative charge, add -ate
to the name of the metal
Ligands are named in alphabetical order
Prefixes indicate the number of ligands
 
Naming Ligands
 
Neutral - aqua, ammine, carbonyl
Anion - chloro, nitro, sulfato
Cations are not common
Chelating - multidentate
ethylenediamine
EDTA
acac
Prefix if ligand is “complex” (neutral or name
contains a prefix)
2 (bis), 3 (tris), 4 (tetrakis)
 
10
 
Li
2
[CoF
6
]
 
 
VCl
3
(NMe
3
)
2
 
 
(NH
4
)
3
[Fe(CN)
5
CO]
 
 
 
K
3
[Ni(CN)
5
]
 
 
[Ru(bpy)
3
]Cl
2
 
Some examples...
 
Pt(NH
3
)
4
2+
[Co(NH
3
)
4
(H
2
O)
2
]Cl
2
Ligands shown in Tables in Chapter 9
Bridging ligands - 
μ
Naming rules in Chapter 9
Exercises 9-1 and 9-2
 
Common Structures
 
CN 1, 2, 3 - follow VSEPR
Bulky ligands, filled d-orbitals
Ag(I), Cu(I), Au(I)
CN 4 - Tetrahedral or Square Planar
d
10
 - tetrahedral; d
8
 - square planar
CN 5 - trigonal bipyramid or square pyramid
Similar energy
CN 6 - octahedral + distorted octahedron
CN 7, 8, ...  more unusual, but known
 
Coordination Compound Isomers
 
Stereoisomers
geometric and optical isomers
Structural
hydrate, solvent, ionization, linkage isomers
 
Geometric Isomers
 
CN 4 and 6 most common
cis, trans
fac, mer
Isomer designations for compounds containing
chelating ligands can get complicated (see
textbook), we will not use
 
Geometric + Optical Isomers
 
Octahedral geometry (consider monodentate
ligands only):  trans-pair method
Mabcdef:  Identify all trans pairs, then identify
optically active isomers
(ab)(cd)(ef), (ab)(ce)(df), (ab)(cf)(de), ......
Try Ma
2
b
2
cd
Diastereomer + mirror image = pair of enantiomers
Bidentate ligands? Use capital letters or “manual”
method to identify geometric isomers
M(AA)(BB)c
2
How many isomers?  How many chiral isomers?
 
16
 
18
 
Structural
 isomers
 
What is inside the coordination sphere?
CrCl
3
.
6H
2
O has three hydrate isomers:  non,
mono, and di-hydrate
Coordination isomers differ in what is inside the
coordination sphere of each metal
[Pt(NH
3
)
4
][PtCl
4
] vs. [PtCl(NH
3
)
3
][Pt(NH
3
)Cl
3
]
Ionization isomers give different number of ions
in solution or different ions in solution
[Co(NH
3
)
4
(NO
2
)Cl]Cl
[Co(NH
3
)
4
Cl
2
]NO
2
 
20
 
Linkage
 
Atom bonding to metal changes
NO
2
-
M-NO
2
 - nitro
M-ONO - nitrito
Can be converted by gentle heating
SCN
-
 bonds through S or N
DMSO - S or O
 
22
 
23
 
Chapter 10: Bonding
 
24
 
25
 
Experimental Evidence: Magnetic
Susceptibility
 
26
 
Magnetic Susceptibility
 
g = constant
S = spin quantum number (multiplicity) = 2(total spin) + 1
L = sum of the highest possible m
l
 values following Hund’s rule
 
27
 
Magnetic Susceptibility
 
28
 
Do some examples:
 
Bonding:
Sigma interactions
 
Bonding:
Sigma interactions
 
31
 
Bonding:
Sigma interactions
 
High Spin/Low Spin States
 
High Spin/Low Spin States
 
35
 
Ligand Field Splitting Trends
Spectrochemical Series
CO,CN
-
 > phen,bpy > NO
2
-
 > en > NH
3
 > NCS
-
 > H
2
O > F
-
 > RCO
2
-
 > OH
-
 > Cl
-
 > Br
-
 > I
-
 
Strong field
Low spin
Large 
Δ
o
 
Weak field
High spin
Small 
Δ
o
 
Slow Reactions (inert)                          Intermediate                      Fast Reactions (Labile)
 
Magnitude of Angular Overlap Interactions:
Charge on Metal
 
Magnitude of Angular Overlap Interactions
 
Ligand Field Splitting Trends
Spectrochemical Series
CO,CN
-
 > phen,bpy > NO
2
-
 > en > NH
3
 > NCS
-
 > H
2
O > F
-
 > RCO
2
-
 > OH
-
 > Cl
-
 > Br
-
 > I
-
 
Strong field
Low spin
Large 
Δ
o
 
Weak field
High spin
Small 
Δ
o
 
Slow Reactions (inert)                          Intermediate                      Fast Reactions (Labile)
 
Jahn-Teller Effect
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Exploring coordination chemistry involves understanding structures, isomers, naming conventions, and common coordination numbers, all essential in studying coordination compounds. Coordination compounds consist of central metals, ligands, and charge balancing ions. Naming involves listing cations, ligands, and metals with Roman numerals for charge indication. Ligands are named alphabetically, with prefixes indicating the number of ligands. The coordination number determines geometric and optical isomers. Common structures range from CN 1 to CN 8, with examples of different coordination geometries for various metal ions.


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  1. Chapter 9 Coordination Chemistry I Structures and Isomers

  2. 2

  3. Coordination compounds Central metal, neutral or cation Ligand: neutral molecule or anion Ions for charge balance (if necessary) Coordination number = number of ligand attachments (commonly 4, 6, 5) Geometric and optical isomers possible Kf values: usually very large, >1010

  4. Naming Coordination Compounds Cation + anion Ligands + metal in coordination compound Charge indicated by Roman numerals in parentheses If complex ion carries a negative charge, add -ate to the name of the metal Ligands are named in alphabetical order Prefixes indicate the number of ligands

  5. Naming Ligands Neutral - aqua, ammine, carbonyl Anion - chloro, nitro, sulfato Cations are not common Chelating - multidentate ethylenediamine EDTA acac Prefix if ligand is complex (neutral or name contains a prefix) 2 (bis), 3 (tris), 4 (tetrakis)

  6. Li2[CoF6] VCl3(NMe3)2 (NH4)3[Fe(CN)5CO] K3[Ni(CN)5] [Ru(bpy)3]Cl2 10

  7. Some examples... Pt(NH3)42+ [Co(NH3)4(H2O)2]Cl2 Ligands shown in Tables in Chapter 9 Bridging ligands - Naming rules in Chapter 9 Exercises 9-1 and 9-2

  8. Common Structures CN 1, 2, 3 - follow VSEPR Bulky ligands, filled d-orbitals Ag(I), Cu(I), Au(I) CN 4 - Tetrahedral or Square Planar d10 - tetrahedral; d8 - square planar CN 5 - trigonal bipyramid or square pyramid Similar energy CN 6 - octahedral + distorted octahedron CN 7, 8, ... more unusual, but known

  9. Coordination Compound Isomers Stereoisomers geometric and optical isomers Structural hydrate, solvent, ionization, linkage isomers

  10. Geometric Isomers CN 4 and 6 most common cis, trans fac, mer Isomer designations for compounds containing chelating ligands can get complicated (see textbook), we will not use

  11. Geometric + Optical Isomers Octahedral geometry (consider monodentate ligands only): trans-pair method Mabcdef: Identify all trans pairs, then identify optically active isomers (ab)(cd)(ef), (ab)(ce)(df), (ab)(cf)(de), ...... Try Ma2b2cd Diastereomer + mirror image = pair of enantiomers Bidentate ligands? Use capital letters or manual method to identify geometric isomers M(AA)(BB)c2 How many isomers? How many chiral isomers?

  12. 16

  13. 18

  14. Structural isomers What is inside the coordination sphere? CrCl3.6H2O has three hydrate isomers: non, mono, and di-hydrate Coordination isomers differ in what is inside the coordination sphere of each metal [Pt(NH3)4][PtCl4] vs. [PtCl(NH3)3][Pt(NH3)Cl3] Ionization isomers give different number of ions in solution or different ions in solution [Co(NH3)4(NO2)Cl]Cl [Co(NH3)4Cl2]NO2

  15. 20

  16. Linkage Atom bonding to metal changes NO2- M-NO2 - nitro M-ONO - nitrito Can be converted by gentle heating SCN- bonds through S or N DMSO - S or O

  17. 22

  18. Chapter 10: Bonding 23

  19. 24

  20. Experimental Evidence: Magnetic Susceptibility 25

  21. Magnetic Susceptibility g = constant S = spin quantum number (multiplicity) = 2(total spin) + 1 L = sum of the highest possible mlvalues following Hund s rule 26

  22. Magnetic Susceptibility 27

  23. Do some examples: 28

  24. Bonding: Sigma interactions

  25. Bonding: Sigma interactions

  26. 31

  27. Bonding: Sigma interactions

  28. High Spin/Low Spin States

  29. High Spin/Low Spin States

  30. 35

  31. Ligand Field Splitting Trends Spectrochemical Series CO,CN- > phen,bpy > NO2- > en > NH3 > NCS- > H2O > F- > RCO2- > OH- > Cl- > Br- > I- Strong field Low spin Large o Weak field High spin Small o Slow Reactions (inert) Intermediate Fast Reactions (Labile)

  32. Magnitude of Angular Overlap Interactions: Charge on Metal

  33. Magnitude of Angular Overlap Interactions

  34. Ligand Field Splitting Trends Spectrochemical Series CO,CN- > phen,bpy > NO2- > en > NH3 > NCS- > H2O > F- > RCO2- > OH- > Cl- > Br- > I- Strong field Low spin Large o Weak field High spin Small o Slow Reactions (inert) Intermediate Fast Reactions (Labile)

  35. Jahn-Teller Effect

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