d-block elements
Period –> 4 to 7
Groups –> 3 to 12
GEC: ns¹⁻² (n−1)d¹⁻¹⁰
Period 4 (3d): Sc Ti V Cr Mn Fe Co Ni Cu Zn
Period 5 (4d): Pd Ag Cd
Period 6 (5d): Pt Au Hg
f-block elements
Group - 3
last e⁻ –> (n−2)f¹⁻¹⁴, n=6,7
La(57) 4f series: 57-71 (Lathanides)
Ac(89) 5f series: 90-103 (Actinides)
Transition elements
An element having incompletely filled d subshell either in ground state or on of its common excited state(+2 for d-block)
Features of transition elements
High MP, BP, strong metallic bond
Show variable oxidation states
Form colourful compounds
Form Complexes
Form alloys & interstital compounds
Acts as good catalyst
Strength of metallic bond
Reactivity ∝ number of valence e⁻ participating
(number of ns e⁻ + number of unpaired (n−1)d e⁻)
Reactivity ∝ 1 / size of kernel
Variable Oxidation State
due to participation of unpaired e of (n-1)d, transition elements can show variable oxidation states
3d [ ↑↓ ] [ ↑↓ ] [ ↑↓ ] [ ↑ ] [ ↑ ] 4s [ ↑↓ ]
┊ ┊ | +2 |
┊ | +3 |
| +4 |
- Sc doesnt show variable state
- Cu in the only element state shows +1 state in 3d
- In gaseous phase, Cu+ is more stable than Cu2+
d–d transitions
In a complex, ligands create a crystal field → d-orbitals split (e.g., octahedral: t₂g and e_g).
then an electron can jump:
t2g→eg
This is a d–d transition → gives color.
similarly for f-f transitions
Why d⁰ and d¹⁰ can still be colored
No d–d transition possible → should be colorless.
Charge Transfer Transitions
LMCT:- ligand to metal charge transfer(d⁰)
MLCT:- Metal to ligand charge transfer(d¹⁰)
Formation of complexes
Made up of metals(central atom) + ligands(surrounding)
Coordination Number:- number of coordinate bonds per metal(2,4,6(most common))
Dentacity:- number of bonds per ligand
types of ligands
On the basis of charge
a) Anionic ligands : Examples: Cl⁻, OH⁻
b) Cationic ligands : Example: NO⁺
c) Neutral ligands : Examples: NH₃, H₂O, CO
On the basis of dentacity
a) Monodentate : Examples: NH₃, Cl⁻
b) Bidentate : Example: en (ethylenediamine)
c) Polydentate : Example: EDTA⁴⁻
d) Ambidentate : Example: CN⁻ (C or N donor)
e) Flexidentate : Examples: SO₄²⁻, CO₃²⁻ (can act as mono- or bidentate)
Chelating Ligands
Chelating ligands are polydentate ligands that bind to a metal ion through two or more donor atoms and form one or more ring structures with the metal.
Generally more stable
Werner theory
Metals have two valencies:
- Primary valency
– Equals oxidation state
– Ionizable
– Satisfied by anions (outside bracket) - Secondary valency
– Equals coordination number
– Non-ionizable
– Satisfied by ligands (inside bracket)
Secondary valencies are directional → fixed geometry
– CN 6 → Octahedral
– CN 4 → Tetrahedral / Square planar
Limitation:
Does not explain bonding, color, or magnetism.
[Co(NH₃)₆]Cl₃
* Primary valency = 3 (3 Cl⁻ outside, ionizable)
* Secondary valency = 6 (6 NH₃ inside, non-ionizable)
VBT for complexes
a. under the influence of ligand field central atom can use its participating electrons(including n-1 d) for hybridisation
b. type of hybridisation depends upon coordination number and nature of metal and ligands
CN = 6 → Octahedral
* d²sp³ (inner orbital, low spin)
* sp³d² (outer orbital, high spin)
CN = 4
* sp³ → Tetrahedral
* dsp² → Square planar
CN = 2
* sp → Linear
electronic configuration in complexes
1) write config 2
) if SFL, fill like paired, else fill single single e in orbitals
3) THen remaining orbitals hybridisation like d2sp3
4) lowspin and diamagnetic if no unpaired
5) inner orbital complex if like inner d is only used
field strength order
X donor < O donor < N donor < C donor
(x and o are WFL, N and C are SFL)
exceptions:
H₂O with Co³⁺ → acts as Strong Field Ligand (SFL)
NH₃ with Mn²⁺, Fe²⁺, Co²⁺ → acts as Weak Field Ligand (WFL)
Heavy metals (4d and 5d series) → generally behave as Strong Field
Ni⁴⁺ → behaves as Strong Field (low spin)
CFT
1) all interactions are assumed to be 100% ionic
2) There are two types of interactions:
a) primary: b/w M and L, responsible for complex formation
b) secondary: b/w e- of metal and ligands, responsible for
properties of complexes
3) Due to secondary interactions d-subshell looses degeneracy resulting in t2g and eg
CFSE
in OH eg is at higher energy, in TH t2g is at higher energy
the more -ve the CSFE the more stable the compound
magnitude of Delta depends on
a) strength of ligand field
b) charge on metal ion
c) heavier metal
d) OH>TH(stable)
Effective Atomic Number (EAN)
EAN = (Atomic number of metal − Oxidation state)
+ (Number of electrons donated by ligands)
EAN sidguick rule
If EAN equals nearest noble gas atomic number → complex is especially stable.
this rule mostly fails
Nomenclature in Complexes
1) Cationic part is named before anionic part
2) Ligands are first listed in alphabetical order, followed by central atom
3) Naming of ligands
a) if anionic replace e with o, ide with o
b) if neutral NH₃ → ammine
H₂O → aqua
CO → carbonyl
c) if cationic add ium as suffix
(4) Number of ligands (prefix)
2 → di
3 → tri
4 → tetra
5 → penta
6 → hexa
For polydentate ligands:
use bis-, tris-, tetrakis-
5) Naming the Metal
If complex is neutral or cation → metal name unchanged.
If complex is anion → metal name ends in “-ate”.
Examples:
Fe → ferrate (in anionic complex)
Cu → cuprate
Ag → argentate
Au → aurate
Isomerism in complexes
Ionisation isomerism – Different ions in solution.
Example: [Co(NH₃)₆]Cl₃
Hydrate (solvate) isomerism – H₂O inside or outside coordination sphere.
Example: [Cr(H₂O)₆]Cl₃ vs [Cr(H₂O)₅Cl]Cl₂·H₂O
Linkage isomerism – Ambidentate ligand binds through different atoms.
Example: NO₂⁻ → nitro / nitrito
Coordination isomerism – Ligands/metal exchanged between cationic & anionic complexes.
Example: [Co(NH₃)₆][Cr(CN)₆] ↔ [Cr(NH₃)₆][Co(CN)₆]
Flashcards pending from stereoisomerism
Oxoanions of Cr
CrO₄²⁻ : chromate — yellow (Cr⁶⁺)
Cr₂O₇²⁻ : dichromate — orange (Cr⁶⁺)
Cr₂O₄²⁻ : chromite — blackish brown (Cr³⁺)
CrO₄²⁻ ⇌ Cr₂O₇²⁻
Properties of K2Cr2O7
Acts as oxidising agent
I⁻ → I₂
Sn²⁺ → Sn⁴⁺
Fe²⁺ → Fe³⁺
C₂O₄²⁻ → CO₂
SO₃²⁻ → SO₄²⁻
4K₂Cr₂O₇ —Δ→ 4K₂CrO₄ + 2Cr₂O₃ + 3O₂
Oxoanions of KMnO4
MnO₄²⁻ : manganate — green
MnO₄⁻ : permanganate — purple
MnO₄²⁻ : stable only in highly alkaline medium
(disproportionates in neutral / acidic medium → MnO₄⁻ + MnO₂ (neutral / slightly acidic) / Mn²⁺ (acidic))
Properties of KMnO4
2KMnO₄ —Δ→ K₂MnO₄ + MnO₂ + O₂
