Coordination Flashcards
Transition metal definition
An element with an unfilled d- or f-orbital in at least one common oxidation state
Definition of complex
Positively charged central ion (possibly neutral), an acceptor, surrounded in a symmetrical manner by a shell of ions or molecules call ligands
Ligands are held to metal via…
dative bonds
Monodentate ligand definition and examples
Has one donor atom
eg OH2, Cl-, CN-
Bidentate ligand definition and examples
Has two donor atoms
eg bipy, acac-, en, dppe
Tridentate ligand definition and examples
Has three donor atoms
eg dien, terpy
Tetradenate ligand definition and examples
Has four donor atoms
eg tren, trien
Hexandentate ligand deifnition and examples
Has six donor atoms
eg [EDTA]4-
What is chelation?
Formation of complexes by chelate ligands
Simultaneous bonding of multiple donor atoms by forming rings around the central atom
Definition and examples of ambidentate ligands
Can bond with different atoms depending on metal and conditions
eg SCN- (thiocyanate) and NCS- (isothiocyanate)
NO2- (nitro) and ONO- (nitrito)
Special case CN- in prussion blue:
links through Fe(II) - C - N - Fe(III)
Possible shapes of complexes of metals with coordination number 4
Tetrahedral, square planar
Possible shapes of complexes of metals with coordination number 6
Octahedral
Possible shapes of complexes of metals with coordination number 5
Trigonal bipyramid, square-based pyramid
Order to put things in when writing metal complex formula
In square brackets, [ ], cation then anion
Metal ion first
Anionic ligands next (alphabetical)
Neutral ligands (alphabetical)
Types of isomerism
Ligand Linkage Ionisation Hydrate Coordination Polymerisation Geometric Optical
What is ligand isomerism?
Confined to organic ligands
- isomers of the ligand e.g. ortho, para,meta
What is linkage isomerism?
For ambidentate ligands only
- bonding with different atoms to central ion
What is ionisation isomerism?
Possible in compounds with a complex ion and counter-ion (also a ligand)
eg [PtCl2(NH3)4]Br2 and [PtBr2(NH3)4]CL2
What is hydrate isomerism?
Possible with water in or out of coordination sphere
eg [Cr(OH2)6]Cl3 and [CrCl(OH2)5]Cl2·H2O and [CrCl2(OH2)4]Cl·2H2O
What is coordination isomerism?
What is polymerisation isomerism?
Multiply the molecular formula by 2, 3 etc If oxidation number is +2, up to 3x If +3, up to 5x If +4, up to 7x Only works if all ligands are on metal
What is geometric isomerism?
Ligands bonded in a different order to the central metal ion
eg cis and trans
What is optical isomerism?
non-superimposable mirror images
Describe stability of complexes for reaction
M-L + L* M-L* + L
If reaction goes to RHS, L* makes a more stable complex with M than L
What are hard acids?
Most metals in normal oxidation states H+ All electropositive metals Have small atomic radius High effective nuclear charge High charge-to-radius ratio High energy LUMO
What are soft acids?
Cu(I), Rh(I), Ag(I), Au(I)
Pd(II), Pt(II), Cd(II), Hg(III), Au(III)
Have lower charge-to-radius ratio
What are hard bases?
Have low energy HOMO
F-, OH-, NH3, OH2, N
NO3-, SO4(2-)
ox(2-), CO3(2-)
What are soft bases?
Br-, I-, S, P
H-, C2H4, CN-
Most stable complexes formed are…
A hard acid with a hard base
A soft acid with a soft base
Assumptions made in Crystal Field Theory
Central metal ion = point positive charge
Ligands regarded as dipoles or anions
Ligands = point negative charges
Ionic lattice built from point positive and negative charges
Ionic bonding = electrostatic forces
d^n configuration =
No of electrons for ‘framework’
= group no. - oxidation state
Rules for electron filling
Electrons prefer to occupy orbital of lowest energy
Hund’s rule - if there is more than one degenerate orbital, electrons first occupy separate orbitals with parallel spins
Pauli Exclusion Principle - no more than 2 electrons can occupy a single orbital. If 2 electrons occupy a single orbital the spins must be paired
Energy is required to pair 2 electrons in a single orbital, the energy penalty for pairing 2 electrons = pairing energy, P
What is Δo and what factors affect its size?
As charge on metal increases, Δo gets larger
Δo(1st row) >∆o(2nd row) > ∆o(3rd row)
Stronger field ligands –> larger ∆o
Strongest field ligands
CN-, CO, PR3, NO2-
Weakest field ligands
I-, Br-, SCN-, Cl-
Describe octahedral crystal field splitting energy, ∆o
The energy between the lower dxy, dyz, dxz and higher d(z^2), d(x^2-y^2)
When ligands bond to the metal ion, the orbitals have different energies
Name of ligand: OH2
Aqua
Name of ligand: N2
Dinitrogen
Name of ligand: O2
Dioxygen
Name of ligand: NH3
Ammine
Name of ligand: CO
Carbonyl
Name of ligand: NO
Nitrosyl
Name of ligand: Cl-
Chloro
Name of ligand: Br-
Bromo
Name of ligand: OH-
Hydroxo
Name of ligand: CN-
Cyano
Naming complexes: if ligand already has prefix but there are more than 1 of them e.g. (dioxygen)2 use…
bis, tris, etc
Order of ions when naming complexes
Cation, then anion
Ligands are listen alphabetically before the metal (excluding prefixes)
Include oxidation number of metal
For anionic complexes add ‘ate’ to name
Name of ligand: PPh3
Triphenylphosphine
When is an octahedral complex low spin and high spin?
∆o high –> low spin
∆o low –> high spin
First row of d-block
Proton numbers 21-30
groups 3 - 12
How to work out group from top element
If in d-block: +18 for second element, +32 for third
Rest of table: +8 for second element, +18 for third, +18 for fourth, +32 for fifth
