transotion metals Flashcards
what are transition metals
elements with partially filled d or f subshells
what are the tzy orientations for d orbitals
dxy, dzx and dyz
most stable oxidation state of Ca
2+
most stable oxidation state of Sc
3+
most stable oxidation state of Ti
4+
most stable oxidation state of V
+4
most stable oxidation state of Cr
+3
most stable oxidation state of Mn
+2
most stable oxidation state of Fe
+3
most stable oxidation state of Co
+2
most stable oxidation state of Ni
+2
most stable oxidation state of Cu
+2
most stable oxidation state of Zn
+2
Applications of transition metals
Fe is alloyed for structural materials
Cu is an electrical conductor
MnO2, NI and Zn make batteries
magnets
Cu and Co make catalysts
and Fe, Co and Zn make pharmaceuticals
pigments
factors that determine coordination number
size of central atom
steric interactions between ligands
electronic interactions
What are the posibble isometric positions for a compund with a CN number of 6
3 for planar hexagonal
3 for trigonal pryamidal
2 for octohedral
What are the types of opticalisomeration called when there are 3 of the same group and 3 of another
mer - planar
fac - non planar
types of distortion in CN 6 complexes
tetragonal distortion - stretching non polar axis (up + down , left and right) 4 fold rotation symmetry
axis triagonal distortion - diagonal along 3 fold rotation
When are tetrahedral complexes favoured
CN of 4 central atom is small and the ligands are large (eg halogen)
What dictates hard or soft coordination centres
polorisability
charge density (charge to size density)
nature od the bonding (ionic vs more covalent)
differences between hard and soft centres
polarisabilty - hard very little effect
- soft highly polarisable
Nature of bonding- hard highly ionic
- partly covalent in soft
form there strongest bond with O (which is hard) are hard
form strongest bonds with S or P which are soft are soft
What assumptions does crystal field theory make
complexes are extreme hard interactions between central atom and negative ligands
bonding energy produced is through ionic interactions
the d orbitals interact with ligands to different extents making the orbital split into different groups based on energy
How does crystal field theory suggest that repultion is minimised in ligands
large repulson between ligand and d orbital so the ligands form between the the split energy groups in order to minimise interaction with electron cloud repulsion
how to calculate CFSE
low spin case the number of ligands x -0.4 + pairing energy P.
high spin case the first 3 ligands x -0.4 + the other number of ligands x +0.6
why does low spin d6 only have 2P
pairing 2 electrons is required even when in the high spin conformation this is present in further higher conformations too.
Whats the Jahn-Teller theorem
if electrons are unequally distributed among orbitals of the same energy then the complex distorts so the orbitals no longer have the same energy
Which are the complexes that have a large complex distortion as told by the Jahn-Teller
d4 high spin, d7 low spin, d9 high spin complexes
How does the Jahn-teller complex manifest in octohedral complexes
tetragonal elongation leads to less repulsion between apical ligands and occupied orbitals in the z direction
When does it become energetically favourable to form a square planar complex instead of an octohedral
when the energy difference in d exceeds the pairing energy
How to calculate the delta T value
the same as CFSE but without the pairing energy and the number of pairs swaps (2 sets on the lower energy half and 3 on the top) 0.6 is negative and for the bottom set 0.4 is positive and for the top set
how to calculate wave length
lamda = planck constant x speed of light / delta O
how is absorbance measured
A = molar absorption coefficient x cooncentration x path length
how the same metal core with the same oxidation state have different colour
the ligands binded
larger ligands = higher energy light absorbed so red
smaller ligands = lower energy light absorbed so blue
what is the spectrochemical field order
I- < Br- < S2- < SCN- (s) < Cl- < F- < OH- < CH3CO2-< H2O < SCN- (n) < pyridine < NH3 < en < bipyridine < NO2- <CN- < CO This end is strong field
Factors affecting how much the crystal field splits (colour stuff)
the nature of the ligands (spectrochemical series) , the coordination geometry and number of ligands,
the nature of the metal ion
when colour transitions occur whats causing them
oscillating electromagnetic fields
what is the probability of a transition dependent upon
a colour is allowed to transition to a more intense colour but not a lighter one
laporte selection rule in an allowed transition the quantumnumber must change by add or minus 1 so d->d transitions are forbidden
parity selection rule (symmetry selection rule) S and D orbitals have a centre of symmetry but p orbital does not
so D and S are gerade (g) whereas P which doesnt have a line of symmetry is ungerade (u) the d orbitals in a octohedral field t2g and eg as these are both gerade transitons between them are forbidden as well as u -> utransitions
spin selection rule: an electron can move from ground state to excited state to an empty orbital but not to form a pair
charge transfer transitions are allowed - electrons move temporarily from ligand orbitals to orbitals with metal character intense colour change
When does the magnetic field have influence on complexes
when there are unpaired electrons they will align with the magnetic field which is paramagnetism and the strength of this is dependent upon how many unpaired electrons there are
how do you calculate the magnetic moment
calculated using spin only equation
mu eff = root n(n+2) where n = the number of unpaired electrons
What is diamagnetism
its the effect of the magnetic field on paired electrons which does occur but is smaller
how to work out whether a complex was high spin or low spin from magnetism
calculate the magnetic moment
compare this to a literature know value and judge accordingly
what is ferromagnetism
an increased degree of magnetism where the spins spontaneously realign in the same direction below critical temperature (curie)
What are the different terms used to refer to the kinetics of a reaction and their thermodynamic basis?
thermodynamically unstable complexes that survive for long periods are called inert
complexes that form rapid equalibriums are called labile
how does a lower activation energy increase rate of reaction
stabilisation of the transitions state
destabilisation of the ground state
what are the major factors affecting rate
the oxidative state of the metal
the distribution of 3d electrons
What reflects the thermodynamic stability of a compound
equilibrium formation constant (Kf)or dissociation constant (Kd) for a reaction of a metal cation + a ligand
How to workout the overall formation constant
Bn is the easiest to find by finding the ln of all the constituent reaction constants in log form added together to find the lnBn which can then be undone using exponentials
Enthalpic effects on the stability of complexes
bond strength
effect of CFSE
steric repulsions between ligands
electrostatic repulsion between ligands
entropic effects on the stability of complexes
changes in solvation
number and size of chelate rings
what is the chelate effect
complexes with multidetate ligands are more stable then equivalent complexes with monodentate ligands
