...
AL SULT BIN MALIK PRIVATE SCHOOL
DEPARTMENT OF SCIENCE
CHEMISTRY
SEMESTER 1
CHEMISTRY OF TRANSITION ELEMENTS
• Transition element: a d-block element that forms one or more stable ions with incomplete d
orbita Is
1.1 Electronic Configurations
Element
Sc, scandium
Electronic Config.
[Ar] 3d 1 4s2
, , .. ,
..
, .. .. ,
2
2
..
Oxidation States
'
+3
' .
Ti, titanium
V, vanadium
[Ar] 3d 4s
[Ar] 3d 3 4s2
Cr, chromium
Fe, iron
[Ar] 3d 5 4s1
[Ar] 3d 5 4s 2
[Ar] 3d 6 4s 2
Co, cobalt
[Ar] 3d 7 4s2
+3,+4
+2,+3,+4,+S
+3,+6
+2,+4,+6, +7
+2,+3
+2,+3
Ni, nickel
(Ar] 3d 8 4s 2
+2
Cu,coppe r
[Ar] 3d 10 4s 1
+1, +2
Zn, Zinc
[Ar] 3d 10 4s2
+2
Mn, manganese
• Scandium and Zinc are not transition metals because:
o Sc 3• has no e-s in the d -orbital
o Zn 2• contains a full d-orbital
• Chromium and copper have anomalous configurations (places 1 e in 4s)
o Cr: 4s electron demoted to half-fill 3d shell
0
Cu: 4s electron demoted to full -full 3d shell creating a more stable
configuration .
• When electron
dd d, fill
b
to, ,
• When I ctron r mov d, r mov .
r on, Lis b ror
3d
1.2 Variab,le O idatio11 Sta e
• Small energy diff r -nee betwe · n 4s and 3d so el c rans from both subshells can be
removed to form a variety of oxidation sta tes
1
1
• All transition metar exhibit two or more oxidatio,n states
• Most common o idation state +2 when 2e s from 4s lost
• Transition elements show h,ighest oxidation states whe,n they combine with O or F (most
electro-ve)
• When tra ,n sition elemen1ts form compounds with high oxidation states above +4, they
form large oxoanions and are covalent (aci'dic o,xides) e.g. CrO - or Mn,Q ·
1
• When transition1 elements in lowe,r oxidation stat,es they form io,nic compounds (basiCA
oxides)
1.3 Complexes
• Complex: is a,n .ion or molecule formed by a central m,etal atom/ ion surrounded by o,ne
or more ligands
• A complex consists of.:
o Central transition metal ion ,(+ve) that c.an accept e·s
a Ligand (-ve): a specie,s that c,ontains a lone pair of e~s that forms a dative bond to a
central metal atom/,ion
• Coordination no.: number of coordinate or dative bo,nds t ,o the central meta i atom/ion
• Different metal ions show different ,coordination number with same liga .nds
• Transition metals form complexes because
Ion are small rn size so they hav,e a strong electric field ,around them which attract e·-rich
0
ligands
They have empty 4s and 4p orbitals that are hybridised and can accept ,e·
0
4
1.4 Ligand~
• Monodentate ligands· forms o nl
pair of es)
.
Anions
Halide ions
F, c1·, Br·, r
Sulphide
52N02, .
Nitrite
Hydroxide
OH·
Cyanide
CN·
Thiocyanate
SCN·
.
y one coo rdin ate bon d wi th centra l meta l ion (donates one
Neutral Ligands
Water
H20
Ammonia
NH3
Carbonyl
co
• Bidentate ligands: forms 2 coordinate bonds with central metal ion (dona t es 2 pairs of e·s
per molecule)
H2 C
CH 2
\
I
H2 N
~
/
M
0
0
11
11
C
C
\
I
NH 2
0
~
/
M
0
H2N - CH2 - CH2 - NH2
·o - co - co - o·
Ethylene diamine (en)
(neutral)
Oxalate ion
(oxalate-)
• Polydentate ligands: forms 2 or more coordinate bonds with central metal ion
-•O OCCH2
.
)
-:ooccH2
/
-.
Ethylene Dia mine Tetra Acetic Acid (EDTA)
/
C H2COO.
0
\\
NCH2CH2N:
""
CH2coo:-
o Forms 6 coordinate bonds
- 4 from oxygen
- 2 from nitrogen
0
•M
• Pl
0
Ii
11
f I tl
r II t
c
t I
If Ii r1d
lJ I
rn
u
•
I
Jll1
r I
I
r
I
k
lJ
n
II r1
d L , 11
tl
on
t1 I
m I
-
11
Ill
h rg on ligand
l I ions n
011
m t I ion
Diagram
Coordination No.
& Shape
H
H
H
.O
•
.o.
••
,
,
..,.a
/
6
Octahedral
••
H
/ O:
H
.
H
[Fe,(Hzi0 )6] 2
2-
Cl
••
4
Tetrahedra l
,, Co
C ~-- -
•
•c1
Cl••
[CoC'l4) 2-
2-
.c
---·- ·•
.,
c.. 4
s.qua re Planar
(most Ni and Pt)
Jl
'#
c·/_
•
- - -- - •(
H
2
Linear
H
I
LZ S tereoiso111e1·is111
Geometric isomerism (els-trans)
Cl .
NH3
·.. Pt .
Cl.........
H3N.
. Cl
·.. Pt ..
" ' N H3
Cl_....-
cis-platin
"NH3
trans-platin
• C!s~~latin is an anticancer drug that acts by binding to DNA in cancer cells, preventing cell
d1v1s1on
1.1 Common Complexes
Ligand
H20
NH3 (drops)
NH3(excess)
OH·
Cu(//)
[Cu(H20)6] 2+
1
1
I
Cu(H20)4(0H)2
[ Cu(N H3)4( H20 )2] 2+
Cu(H20)4(QH)2
Cl·
[CuCl4J 2•
Co(II)
[Co(H20)6] 2+
Co(H20)4(QH)2
[Co(NH3)6] 2+
Co(H20)4(QH)2
[CoCl4J 2·
Copper Chemistry
1.
Reaction with Hydroxide Ions (OH-ions from alkali eg.NaOH)
Cu (l120) 4 (OH) 2
+
)f
· Not ligand exchange; hydroxide ions remove hydrogen ions from water ligand, this is a deprotonation
reaction .
2.
Reaction with Ammonia Solution
Small amount of ammonia
11 (11 )) (lfl)
I)
· In it i II , r n1 , i
E
I 1n
t
b
1
II
[ 'u l\l IJ
t<I
m
· Only
3
r
I ,uII I ff t f1 I
X
u
on
bov .
I I
u H
.
n i r1
t d
t
I
If 1
)
']
~1
l1lu(
a l'igand
at r n1 I u le r plac d
f the
ction
ith hloride Ions (Cl-ions from HCI)
4 1-
+
I I
· 6 water morecures replaced by 4 chloride ions
ote:
A green so lution is observed, however, the colour of [CuCl1] 2blue
Cu (H20) 6] 2-
and the yellow
[CuCl4 ] 2-
is yellow, this is because, both the
are present in the equilibrium mixture.
Cobalt Chemistry
Reaction with Hydroxide Ions (OH-ions from alkali eg.NaOH)
1.
OH-
Co (H20) 4 (OH) 2
+
· Not ligand exchange; hydroxide ions remove hydrogen ions from water ligand, this is a deprotonation
reaction.
2.
Reaction with Ammonia Solution
Small amount of ammonia
2 H3
Co (l I20) 4 (OI I) 2
2[ H1
· Initially, ammonin act
s as a llase and hyrfrc> •
gen ions drro PIIIIPcl c>f f lh(• ""
«•• ,1 h() /(>
Xt1,1q11,1 l<lrl .. , .
Excess ommon,a
rco (JI O)
(c·o(Nlla),, 12
· Ammonia repla
ces water as a ligand th e com le .
Co (~l13) i
h1 h ,
P x ion formed oxidises in air to losr an electron and
•
u
w c 1s dark solution.
form a complex
3.
Reaction with Chloride Ions (Cl- ions from HCI)
[Co (fi20) 6 2
+
.......
+
611.d)
. 6 water molecules replaced by 4 chloride ions
l igand Exchange and Stability Constant
· Ligand exchange; a more powerful ligand will substitute a less powerful ligand from a cation of the
complex and this can produce a change in colour and shape
Strength of Different Ligands;
EDTA>S >CN >I >52032 >Br>NH3> CI >H20
Strongest
weakest
· Exchange of ligands can be explained in terms of completing equilibria of forward & backward
reaction
· Equilibrium position lies towards more stable complex
· Adding excess weak ligand can shift equilibrium
backward and form weaker complex