transition metals

what is a transition element?

* those with partially filled d-orbital shells = d block elements
* all metals
* act as lewis acids = accept electrons

what is the aufbau principle?

* electrons are added to the lowest energy orbitals first

what is hund’s rule?

* electrons in degenerate orbitals have the same spins

what is pauli’s exclusion principle?

* electrons in the same orbital must have opposite spins

for single metal atoms, what electronic configuration is observed?

4s orbitals fill before the 3d

what is the oxidation state of a TM?

the charge on the metal

= wide range possible

early TM = high oxidation states

late TM = low oxidation states = 2+ common

what is a coordination complex?

ligands bonded to a central metal atom/ion by coordinate (from ligand) covalent bonds

ie. lone pair of electrons donated to TM by ligands

what is observed in TM’s forming coordination complexes?

= 4s electrons are removed first

how can the number of d electrons of a transition metal be determined?

d electrons = group no. - oxidation state

\

how can transition metals be used in redox reactions?

= act as a catalyst by changing its oxidation state

oxidative addition:

Pd(0) + R-X = R-Pd(2+)-X

metal is oxidised and added to complex

reductive elimination:

R-Pd(2+)-R’ = Pd(0) + R-R’

what is extractive metallurgy? what are two types?

= purification of metals from their ores

1- pyrometallurgy

2- hydrometallurgy

explain process of pyrometallurgy

= uses heat

* roasting to form metal oxides
* smelting to reduce metal oxides to liquid/gaseous metal (often carbon reductant)

\
* large energy costs
* pollution from gases

explain process of hydrometallurgy

= uses aqueous chem

* metal ions ‘leached’ into solutions by various substances
* purified by precipitation or selective extractive as coordination complexes

\
* less energy intensive
* reagents recyclable
* smaller scale plants allow more versatility
* process lower grade ores (less metal content)

what are ligands? (coordination complexes)

* lewis bases = donate electrons
* neutral or negatively charged

what terms can be used to describe ligands?

monodentate

= lone pair donated from one donor atom of ligand

multidentate (chelating)

= lone pairs donated from more than one atom of ligand

ie. bidentate

= two lone pairs donated from two atoms

\
= complexes formed from multidentate ligands more stable than those of monodentate ligands

= ‘chelate effect’

= mulitdentate ligands displace monodentate ones

what is the coordination number of a coordination complex?

the number of donor **atoms** bonded to a metal

≠ the number of bonds

= range from 2 to 6 for transition metals

explain the notation of coordination complexes

inside square brackets = ligands coordinated to metal

outside square brackets = counterions

how does the coordination number relate to the shape of the coordination complex?

CN 2 = linear

CN 3 = trigonal planar

CN 4 = tetrahedral (more common) OR square planar

CN 5 = trigonal bipyramidal OR square pyramidal

CN 6 = octahedral

how do you name coordination complexes?

\+VE COORDINATION COMPLEX

prefix - ligand - metal (oxidation state) counterion

= anionic ligands first then neutral ligands

= anionic ligands end in ‘-o’

\-VE COORDINATION COMPLEX

counterion prefix - ligand - metal-ate (oxidation state)

NEUTRAL COMPLEX

prefix - ligand - metal (oxidation state if applicable)

what are some nomenclature for ligands?

ammonia = ammine

water = aquo

carbon monoxide = carbonyl

what are some latin names for coordination complexes?

iron - ferrate

lead - plumbate

copper - cuprate

silver - argentate

gold - aurate

explain coordinative/ionisation isomerism (coordination complexes)

* differ by switching a ligand between being bonded to the metal to acting as a counterion


* also by switching central metals where counterion is also metal with ligands

explain linkage isomerism

* differ by which atom of the ligand bonds to metal

= ligands must have more than one potential donor atom (ambidentate)

what does ambidentate mean?

= ligands with more than one potential donor atom

explain stereoisomerism

* same molecular formula but different spatial arrangement

square planar = cis/trans

octahedral (4x monodate, 2x monodate) = cis/trans

octahedral (3x 2 ligands) = facial (3 ligands on x, y, x axes) / meridional (3 ligands on one plane)

octahedral (3x bidentate ligands) = chirality (mirror image = enantiomer)

octahedral (2x bidentate, 2x monodentate) = cis/trans & cis chirality

what are the five degenerate d orbitals of transition metals?

3 x between axes

* d(xy)
* d(yz)
* d(xz)

2 x along axes

* d(x^2-y^2)
* d(z^2)

how does interaction with ligands effect the d orbitals?

* increases their energies, are no longer degenerate
* orbitals between axes are lower in energy since there is less ligand interaction = t(2g)
* orbitals along axes are higher in energy since there is more ligand interaction = e(g)

what is ΔO?

= crystal field splitting parameter

= difference in energies between t(2g) and e(g) orbitals

what are the two possible configuration for d4 in an octahedral crystal field?

t(2g)3 e(g)1 = high spin configuration

electrons fill e(g) before pairing in t(2g)

t(2g)4 = low spin configuration

electrons pair in t(2g) before filling e(g)

how does ΔO effect configuration?

ΔO > ‘electron pairing energy’ = low-spin complex

ΔO < ‘electron pairing energy’ = high-spin complex

what does ΔO depend on?

= strength of ligand field ie ‘spectrochemical series’

= increases down a row !! (**high** AND low spin only possible for 3rd row TM)

what can be used to measure magnetism?

= magnetic moment µ

= gouy balance to determine high or low spin configuration

what is paramagnetic vs diamagentic?

paramagnetic = slightly attracted to field = complex has unpaired electrons = high spin

diamagnetic = slightly repelled by field = complex has no unpaired electrons = low spin

what is crystal field stabilisation energy? (CFSE)

measure of energy difference from degenerate orbitals for different d configurations

e(g) = +3/5 ΔO

t(2g) = -2/5 ΔO

ie t(2g)2e(g)0: CFSE = 2 x (-2/5ΔO) = -4/5ΔO

what wavelength does the energy gap between t(2g) and e(g) relate to?

500nm = blue green

* photons of this wavelength are absorbed and electrons are promoted from t(2g) to e(g)


* therefore, complex colour is the remaining part of spectrum ie red-purple

how can the energy gap be determined?

using UV spectroscopy to find which wavelengths are absorbed

= size of energy gap and hence position of t(2g) and e(g)