1
Q
discovery of Blomstrand
A
- used titration to obtain precipitate of silver chloride upon addition of Ag+
- found that not all the chloride ions will be be precipitated (i.e. equivalents of the chloride ions precipitated varies for different complexes) upon addition of Ag+
- proposed that there must be two different types of chloride groups. chloride ions that are attached to NH3 will dissociate, while those attached to metals will not
- proposed that these two compounds have 2 types of valences: primary valence/ionizable valence and secondary valence/non-ionizable valence
- his proposal was based on measured equivalents
- structures he proposed were incorrect (did not match with Werner’s conductivity measurements)
2
Q
discovery of Alfred Werner
A
- measured conductivity to determine the number of ions released
- molar electric conductivity of platinum (IV) complexes
- proposed a different interpretation than Blomstrand
- proposed that these complexes have an octahedral shape
- this proposal matched with the experimental data: precipitation of the correct amount of AgCl upon addition of Ag+, conductivity measurements, number of isomers (cis and trans of [CoCl2(NH3)4]Cl)
- realizing that the cis-isomer of the complex would be chiral, he was able to use its optical activity properly to show that these species were octahedral
- replaced NH3 with ethylenediamine
- won Nobel Prize for Chemistry
- created the first optically active complex that did not contain carbon
3
Q
primary valence
A
ionizable valence
4
Q
secondary valence
A
non-ionizable valence
5
Q
complex
A
a chemical entity consisting of a central metal atom or ion surrounded by a set of ligands
6
Q
ligand
A
an ion or a molecule that binds to a metal
7
Q
coordination complex
A
- a complex that does not contain metal-carbon bonds
- also known as Werner complex
8
Q
organometallic complex
A
a complex with metal-carbon bonds
9
Q
coordination sphere
A
set of ligands around the central atom/ion
10
Q
coordination number (CN)
A
number of atoms directly attached to the central atom/ion
11
Q
coordination geometry
A
arrangement in space of the atoms linked to the metal
12
Q
chelating ligand
A
ligand capable of making several bonds to one metal
13
Q
monodentate ligand
A
ligand has one attachment point
14
Q
bidentate ligand
A
ligand has two attachment points
15
Q
tridentate ligand
A
ligand has three attachment points
16
Q
multidentate ligand
A
ligand has more than one attachment point
17
Q
bonding between ligand and metal
A
- a ligand binds to the metal center using its lone pair
- if the ligand has more than one lone pair, it will make more than one coordination bond
- covalent bond
- metal acts as a Lewis acid, ligand acts as a Lewis base
18
Q
factors that strongly influence coordination numbers and geometries
A
1) size of a metal
- larger metal leads to higher coordination number possible
2) size of ligands
- larger ligands leads to smaller coordination number
3) electronic effects
- d-electron configuration of a metal
- the type of metal: early vs late, light vs. heavy
- the type of ligand
19
Q
CN = 2
A
- observed almost exclusively in d10 complexes
- common for Ag(1+), Au(1+), Hg(2+)
- less common for Cu(1+), Zn(2+), Cd(2+)
- linear geometry (D∞h)
20
Q
CN = 3
A
- very rare
- trigonal planar geometry (expected), usually for d10 metals or ligands with stringent steric demands
- trigonal pyramidal for d0 metals and ligands with stringent steric demands
- D3h
21
Q
CN = 4
A
- very common
- tetrahedral (very common)
- square planar for d8 metals Rh(1+), Ir(1+), Pd(2+), Pt(3+), Au(3+)
- exception: Cu(2+) is the only non-d8 metal (its d9) that adopts a square planar complex
- tetrahedral (Td), square planar (D4h)
22
Q
CN = 5
A
- common
- trigonal bipyramidal (D3h), square pyramidal (C4v)
- trigonal bipyramidal geometry is slightly more common than square pyramidal geometry, but the energy difference is very small
23
Q
CN = 6
A
- very common
- octahedral (very common) (Oh)
- trigonal prismatic (rare) (D3h): mostly found for d0 metals with certain ligands
- octahedral geometry is sometimes distorted towards square planar (stretched/squashed) or trigonal prismatic
- distortions can be explained by Jahn-Teller theorem
- distortions observed for d4 high-spin, d7 low-spin, and d9
24
Q
CN = 7
A
- relatively rare
- observed with very small ligands or with early 2nd or 3rd row TM
- more common for lanthanides and actinides
- capped-octahedral (C3v), capped trigonal-prismatic (C2v), pentagonal-bipyramidal (D5h)
25
CN = 9
- relatively rare
- for d0 TM, [TcH9]2- and [ReH9]2-
- more common for Sc, Y, f-elements
26
CN = 10-12
- complexes of f-elements
| - complexes containing [BH4]- or related ligands
27
CN = 8
square antiprismatic, dodecahedral
28
types of structural isomerism
ionization isomers, hydration isomers, coordination isomers, linkage isomers
29
types of stereoisomerism
diastereoisomers, enantiomers
30
ionization isomers
- these result from the interchange of an anionic ligand within the first coordination sphere with an anion outside the coordination sphere
- Ex: [Co(NH3)5Br][SO4] and [Co(NH3)5(SO4)]Br
- can be distinguished through chemical means, IR spectra, X-ray diffraction
31
hydration isomers
result from the interchange of H2O and another ligand in the coordination sphere
32
coordination isomers
- result from the interchange of ligands between the two metal centres
- possible only for salts in which both cation and anion are complex ions
33
linkage isomers
- arise when one or more of the ligands can coordinate to the metal ion in more than one way
- these ligands are ambidentate
34
enantiomers
- optical isomers
| - two molecular species which are non-superposable mirror images of each other
35
diastereoisomers
- two molecular species which are not mirror images of each other
- mer- and fac-isomers for octahedral complexes
36
fac-isomers
ligands of same type occupy the same face
37
mer-isomers
ligands of same type do not occupy the same face
38
Kf
- formation constant of a complex
- expresses the coordinating strength of a ligand relative to the strength of the solvent molecules (usually water)
- [products]/[reactants]
39
Kd
[reactants]/[products]
40
stepwise constant
- Kfn = [MLn]/[M][L]^n for M+nL ≤≥ MLn
| - typically lie in the order Kn > Kn+1
41
overall formation constant
ßn = [MLn]/[M][L]^n = Kf1*Kf2*Kfn for M+nL ≤≥ MLn
42
chelate effect
- refers to the greater stability of a complex containing a coordinated polydentate ligand compared with a complex containing an equivalent number of analogous monodentate ligands
- mainly an entropic effect (i.e. reason why chelate effect is associated with greater stability is because of the increase in entropy that it provides)
43
macrocycle effect
- refers to the greater stability of a complex containing a macrocyclic ligand compared with a complex containing a comparable acyclic (open-chain) ligand
- mainly an entropic effect
44
Irving-Williams series
- relative stability of the M2+ complexes for the 3d metals
- Ba(2+) < Sr(2+) < Ca(2+) < Mg(2+) < Mn(2+) < Fe(2+) < Co(2+) < Ni(2+) < Cu(2+) > Zn(2+)
- order is insensitive to the choice of ligands
- correlates with ionic radius
45
carbonyl (mond) process for Ni purification
1) Ni is reacted with Syngas at 200˚C to remove oxygen, leaving impure Ni. Impurities include Fe and Co. NiO(s) + H2(g) --> Ni(s) + H2O(g)
2) the impure nickel is reacted with excess CO at 50-60˚C to form Ni(CO)4. Ni(s) + 4CO(g) --> Ni(CO)4(g)
3) the mixture of excess carbon monoxide and nickel carbonyl is heated to 220-250˚C. On heating, nickel tetracarbonyl decomposes to give nickel: Ni(CO)4(g) --> Ni(s) + 4CO(g)
