transition metals and coordination...
TRANSCRIPT
Transition Metals and Coordination
Chemistry
Transition Metals
Similarities within a given period
and within a given group.
Last electrons added are inner electrons (d’s, f’s).
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Ce
Th
Pr
Pa
Nd
U
Pm Sm
Pu
Eu
Am
Gd
Cm
Tb
Bk
Dy
Cf
Ho
Es
Er
Fm
Tm
Md
Yb
No
Lu
Lr
Sc
Y
La
Ac
Ti
Zr
Hf
Unq
V
Nb
Ta
Unp
Cr
Mo
W
Unh
Mn
Tc
Re
Uns
Fe
Ru
Os
Co
Rh
Ir
Ni
Pd
Pt
Cu
Ag
Au
Zn
Cd
Hg
Uno Une Uun Uuu
Np
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Sc
Y
La*
Ac†
Ti
Zr
Hf
Unq
V
Nb
Ta
Unp
Cr
Mo
W
Unh
Mn
Tc
Re
Fe
Ru
Os
Co
Rh
Ir
Ni
Pd
Pt
Cu
Ag
Au
Zn
Cd
Hg
Ce
Th
Pr
Pa
Nd
U
Pm
Np
Sm
Pu
Eu
Am
Gd
Cm
Tb
Bk
Dy
Cf
Ho
Es
Er
Fm
Tm
Md
Yb
No
Lu
Lr
d-block transition elements
*Lanthanides
†Actinides
f-block transition elemen ts
Uns Uno Une Uun Uuu
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0.2
Ato
mic
ra
dii
(nm
)
Atomic number
La
Hf
Ta
WRe Os
Ir Pt
Au
Zr
Y
NbMo
Tc Ru
Rh Pd
Ag
Sc
Ti
VCr
Mn Fe Co NiCu
1st series (3d)
2nd series (4d)
3rd series (5d)
0.1
0.15
Multiple Oxidation States
Metallic Behavior/Reducing Strength
Lower oxidation state = more metallic
Color and Magnetism
e- in partially filled d sublevel absorbs visible light
moves to slightly higher energy d orbital
Magnetic properties due to unpaired electrons
Electronegativity increases down column
Chromium Chemical properties reflect oxidation state
Valence-State Electronegativity
Electronegativity, EN:
electron “pulling power”
Valence-state EN:
metal in higher oxidation state
is more positive
has stronger pull on electrons
is more electronegative
“Effective EN”
Manganese
Silver
Weak Reducing Agent, H2Q
Mercury
Coordination Compound
Consist of a complex ion and necessary counter ions
[Co(NH3)5Cl]Cl2
Complex ion: [Co(NH3)5Cl]2+
Co3+ + 5 NH3 + Cl-
= 1(3+) + 5 (0) + 1(1-)
= 2+
Counter ions: 2 Cl-
Complex ion remains intact upon dissolution in water
[Co(NH3)6]Cl3 [Pt(NH3)4]Br2
Complex Ion
Species where transition metal ion is surrounded
by a certain number of ligands.
Transition metal ion: Lewis acid
Ligands: Lewis bases
Co(NH3)63+
Pt(NH3)3Br+
Ligands
Molecule or ion having a lone electron pair that
can be used to form a bond to a metal ion
(Lewis base).
coordinate covalent bond: metal-ligand bond
monodentate: one bond to metal ion
bidentate: two bond to metal ion
polydentate: more than two bonds to a metal
ion possible
Formulas of Coordination Compounds
1. Cation then anion
2. Total charges must balance to zero
3. Complex ion in brackets
K2[Co(NH3)2Cl4]
[Co(NH3)4Cl2]Cl
Names of Coordination Compounds
1. Cation then anion
2. Ligands
in alphabetical order before metal ion
neutral: molecule name*
anionic: -ide -o
prefix indicates number of each
3. Oxidation state of metal ion in () only if more
than one possible
4. If complex ion = anion, metal ending -ate
Examples
K2[Co(NH3)2Cl4]
potassium diamminetetrachlorocobaltate(II)
[Co(NH3)4Cl2]Cl
tetraamminedichlorocobalt(III) chloride
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Isomers
(same formula but different properties)
Stereoisomers
(same bonds, different
spatial arrangements)
Structural
isomers
(different bonds)
Optical
isomerism
Geometric
(cis-trans)
isomerism
Linkage
isomerism
Coordination
isomerism
Structural Isomerism 1
Coordination isomerism:
Composition of the complex ion varies.
[Cr(NH3)5SO4]Br
and [Cr(NH3)5Br]SO4
Structural Isomerism 2
Ligand isomerism:
Same complex ion structure but point of
attachment of at least one of the ligands differs.
[Co(NH3)4(NO2)Cl]Cl
and [Co(NH3)4(ONO)Cl]Cl
Linkage Isomers
[Co(NH3)5(NO2)]Cl2 Pentaamminenitrocobalt(III)
chloride
[Co(NH3)5(ONO)]Cl2 Pentaamminenitritocobalt(III)
chloride
Stereoisomerism 1
Geometric isomerism (cis-trans):
Atoms or groups arranged differently spatially
relative to metal ion
Pt(NH3)2Cl2
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H3N
Co
H3N
NH3
NH3
Cl
Cl
H3N
Co
H3N
NH3
Cl
Cl
NH3
Cl
Cl
Co
Cl
Cl
Co
(a) (b)
Stereoisomerism 2
Optical isomerism:
Have opposite effects on plane-polarized light
(no superimposable mirror images)
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Unpolarized
light
Polarizing
filter
Polarized
light
Tube
containing
sample
Rotated
polarized light
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Left handRight hand
Mirror image
of right hand
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N
N
N
N
N
NCo
N
N
N
N
N
NCo
Mirror image
of Isomer I
Isomer I Isomer II
N
N
N
N
N
NCo
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Cl
Cl
N
N
N
NCo
Cl
Cl
N
N
N
NCo
Cl
Cl
N
N
N
NCo
Cl
Cl
N
N
N
NCo
Cl
Cl
N
N
N
NCo
Isomer IIIsomer I
cistrans
Isomer II cannot be
superimposed exactly
on isomer I. They are
not identical structures.
The trans isomer and
its mirror image are
identical. They are not
isomers of each other.
Isomer II has the same
structure as the mirror
image of isomer I.(b)(a)
Crystal Field Theory
Focus: energies of the d orbitals
Assumptions
1. Ligands: negative point charges
2. Metal-ligand bonding: entirely ionic
strong-field (low-spin): large splitting of d orbitals
weak-field (high-spin): small splitting of d orbitals
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eg(dz2, dx2 – y2)
t2g(dxz, dyz, dxy)
Free metal ion
3d orbital
energies
E
= crystal field splitting
High spin Low spin
[V(H2O)6]2+ [V(H2O)6]
3+
[Cr(NH3)6]3+ [Cr(NH3)5Cl]2+s
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–
–
–
––
–– ––
–
dz2 dx2 – y2
dxy dyzdxz
(a) (b)
Tetrahedral Complexes
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E
Free metal ion Complex
dz2
dxy
dxz dyz
dx2 - y2
M z
(b)
Free metal ion Complex
dx2 - y2
dxy
dz2
dxz dyz
M
(a)
x
y
E
Square Planar & Linear Complexes
Approach along x-and y-axes Approach along z-axis
Hemoglobin & Oxyhemoglobin