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Chem 3II3 > Part 2 - Coordination Complexes > Flashcards

Part 2 - Coordination Complexes Flashcards

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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)
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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
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3
Q

primary valence

A

ionizable valence

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4
Q

secondary valence

A

non-ionizable valence

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5
Q

complex

A

a chemical entity consisting of a central metal atom or ion surrounded by a set of ligands

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6
Q

ligand

A

an ion or a molecule that binds to a metal

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7
Q

coordination complex

A
  • a complex that does not contain metal-carbon bonds

- also known as Werner complex

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8
Q

organometallic complex

A

a complex with metal-carbon bonds

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9
Q

coordination sphere

A

set of ligands around the central atom/ion

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10
Q

coordination number (CN)

A

number of atoms directly attached to the central atom/ion

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11
Q

coordination geometry

A

arrangement in space of the atoms linked to the metal

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12
Q

chelating ligand

A

ligand capable of making several bonds to one metal

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13
Q

monodentate ligand

A

ligand has one attachment point

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14
Q

bidentate ligand

A

ligand has two attachment points

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15
Q

tridentate ligand

A

ligand has three attachment points

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16
Q

multidentate ligand

A

ligand has more than one attachment point

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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
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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

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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
Q

CN = 9

A
  • relatively rare
  • for d0 TM, [TcH9]2- and [ReH9]2-
  • more common for Sc, Y, f-elements
26
Q

CN = 10-12

A
  • complexes of f-elements

- complexes containing [BH4]- or related ligands

27
Q

CN = 8

A

square antiprismatic, dodecahedral

28
Q

types of structural isomerism

A

ionization isomers, hydration isomers, coordination isomers, linkage isomers

29
Q

types of stereoisomerism

A

diastereoisomers, enantiomers

30
Q

ionization isomers

A
  • 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
Q

hydration isomers

A

result from the interchange of H2O and another ligand in the coordination sphere

32
Q

coordination isomers

A
  • 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
Q

linkage isomers

A
  • arise when one or more of the ligands can coordinate to the metal ion in more than one way
  • these ligands are ambidentate
34
Q

enantiomers

A
  • optical isomers

- two molecular species which are non-superposable mirror images of each other

35
Q

diastereoisomers

A
  • two molecular species which are not mirror images of each other
  • mer- and fac-isomers for octahedral complexes
36
Q

fac-isomers

A

ligands of same type occupy the same face

37
Q

mer-isomers

A

ligands of same type do not occupy the same face

38
Q

Kf

A
  • 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
Q

Kd

A

[reactants]/[products]

40
Q

stepwise constant

A
  • Kfn = [MLn]/[M][L]^n for M+nL ≤≥ MLn

- typically lie in the order Kn > Kn+1

41
Q

overall formation constant

A

ßn = [MLn]/[M][L]^n = Kf1Kf2Kfn for M+nL ≤≥ MLn

42
Q

chelate effect

A
  • 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
Q

macrocycle effect

A
  • 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
Q

Irving-Williams series

A
  • 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
Q

carbonyl (mond) process for Ni purification

A

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)

Chem 3II3 (3 decks)

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