Topic 7: Introduction to Transition Metal Complexes
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3 d-block elements that don’t always behave as transition metals and why
No partially filled d-subshell Sc: electron configuration is [Ar] 3d^1 4s^2. It exists as Sc^3+: electron configuration is [Ar] 3d^0 4s^0 so behaves as an f-block element Zn, electron configuration is [Ar] 3d^10 4s^2. It exists as Zn^2+: electron configuration is [Ar] 3d^10 4s^0 Au electron configuration is [Xe] 4f^14 5d^10 6s^1. It exists as Au^+: electron configuration is [Xe] 4f^14 5d^10 6s^0 (not a transition metal) and Au^3+: [Xe] 4f^14 5d^8 6s^0 (is a transition metal)
What makes a d-block element a tradition element?
Form stable ions with partially filled d-subshell
Which orbital is filled first, 3d or 4s in transition metals + what are the exceptions? Does this differ on transition complexes/compounds
4s as lower in energy here Cr: [Ar] 3d^5 4s^1 (prefers to have 1 electron in each d orbital than paired in 4s) and Cu: [Ar] 3d^10 4s^1 (prefers to pair all 3d electrons over 4s) Yes, 3d filled first as lower in energy here
Calculate d^n
number of outer s + d electrons (group number)
Requirement for colourless transition metal complexes in terms of d-electrons
Entirely empty or entirely full d-subshells
Source of colour in transition metal complexes
d-electrons (unpaired) moving between d-orbitals and absorbing energy (light in visible region of spectrum) Ligand –> metal / metal –> ligand charge transfer (movement of electrons)
diamagnetic compounds contain … and are … from a magnetic field
only paired electrons repelled
paramagnetic compounds contain … and are … from a magnetic field
unpaired electron(s) attracted
Do paramagnetic or diamagnetic effects dominate?
paramagnetic
u eff =
root (n (n + 2)) n= dumber of unpaired electrons in d-subshell
Sc to Mn have … oxidation states + … number of oxidation states
increasing increased
Fe to Zn have … oxidation states + … possible oxidation states
lower fewer
High oxidation state complexes are … agents
oxidising
Low oxidation state complexes are … agents
reducing
Why is it energetically favourable to form ions from transition elements when it requires energy to remove electrons?
Solvation energy or lattice energy is more negative than the ionisation energy is positive. Overall release of energy
Why can’t all ions achieve high oxidation states e.g. Fe^+7
Energetically unfavourable Solvation energy or lattice energy is less negative than the ionisation energy is positive
dative bond
ligand donates pair of electrons to the central atom/ion
Pauling’s electroneutrality principle
Change of an atom or ion can only be +/-1 |z|>/= 1 So any charges higher, are very attracted to that change forming a bond, charge is then spread to ligands e.g. A metal with 2+ charge and bonded to 6 water will spread charge to Os and each will have an average charge of 1/3+. They will on average donate 1/3 of electron to 2+metal centre. This will continue to Hs, each having 1/6+ while the central metals and O will have a charge of 0
Transition metal complexes can be …
acidic
Electronegativity of … is … The range of metals is … to …
1.7 50% covalent and 50% ionic character 1.4 2.0
In higher oxidation states of the metal, bonds become more … because …
covalent the ligands have to donate more electron density to the ligand to satisfy Pauling’s
What metal charge is the most acidic? What coordinates
3^+ hydroxides instead of water
Ligands can be … such as, … such as … and occasionally … such as … They all donate …
neutral NH3 CO H2O PR3 SR2 anionic CN^- Me^- NH2^- Cl- I- cationic NO^+ 2 electrons
cisplatin is
[Pt(NH3)2(Cl)2]