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complex: used by chemists for compounds that consist of (several) other compounds that can exist separately
Coordination compounds (complex)
2
ligands
central atom
coordination sphere (inner)
acceptor
donor
Lewis base
Lewis acid
No. of donors exceeds the
value of oxidation number
usually (poly-nuclear) ions + counterions
Coordination compounds (complex)
3
Some of further basic concepts
Coordination number: number of donor atoms coordinated in the inner sphere
Ligands: monodentate – a single donor atom (H2O, CN-, F- … )
polydentate – their geometry enables to occupy (bi-, tri- ...) more than a single coordination position several donor atoms (chelate agents) (e.g. ethylendiamin H2N-CH2-CH2-NH2)
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chelate complexes
Ethylendiamin (en)
EDTA
bridging ligands
Ethylendiamintetraacetate(4-)
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Coordination compounds: bonds/structure
Alfred Werner, Swiss, 1866-1919, Nobel Prize 1913
Showed that transition metals create complexes with square, tertrahedral, octahedral structure
e.g. cis-[PtCl2(NH3)2] trans-[PtCl2(NH3)2] diammin-dichloridoplatinum(II) complex
geometrical isomers
cis-
trans-
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Typical space structures of complexes
Trigonálny dodekaéder Trojnásobne zastrešená
trigonálna prizma
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Geometrical isomerism for octahedral structures
cis- trans- mer- fac-
Info: Optical isomerism: mirror image – enatiomers
chirality, chiral molecules
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Valence bond theory with hybrid AO in most cases enables explanation of the structure
coord. No. form of coord. sphere examples 2 – SP linear [CuCl2]- [Ag(S2O3)2]3-
4 – SP3 [Co(NCS)4]2- [NiCl4]2- D3S tetrahedron [BF3(NH3)]
4 – DSP2 [Mn(H2O)4]2+ [PdCl4]2- SP2D square [Pd(NH3)4] 2+ Ni(CN)4]2-
6 – D2SP3 [Fe(H2O)6]2+ SP3D2 octahedron [Fe(CN)6]3- [FeF6]3- [PdCl6]2-
Coordination compounds: bonds/structure
paramagnetic [NiCl4]2- unpaired electrons
Ni(II) -[NiCl4]2–
Ni2+
sp3
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28Ni 3d 4s 4p
High-spin complex
diamagnetic [Ni(CN)4]2- paired electrons
Ni(II) -[Ni(CN)4]2–
Ni 3d 4s 4p
Ni2+
dsp2
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Ni2+ valence
Low-spin complex
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metal-ligand bond is weaker than „usual“ covalent b.
??????
Some complexes use inner „d“ orbitals others use outer „d“ orbitals
Transition metal complexes use to be intensively colored
MO theory
simplified approximations
Coordination compounds: bonds/structure
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Crystal field theory Central atom in electrostatic field
of (ionic) ligands (as point charges) (electrostatic theory of ligand field)
Splitting of „d“ levels: octahedral complex
d
Ene
rgy Δ
Ligand field
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Why the transition metal complexes are colored?
d-d transitions
eg
t2g
splitting of „d“ levels: tetrahedral complex
d
Ene
rgy Δ
t2
e
Ene
rgy
octahedral
complex is violet
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low and high-spin complexes [Fe(CN)6]3- [FeF6]3-
Fe3+
[Fe(CN)6]3-
5d Fe0
4s
Δ
[FeF6]3- E
nerg
y
Δ
t2g
eg
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Relative ligand field strengths
High-spin complexes Low-spin complexes
Spectrochemical series
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Oxidation-reduction (redox) reactions: change of oxidation state
-IV, -III ... 0, I, II ... VIII oxidation
reduction
x BAox1 + y DCox2 x EAox1+m + y FCox2-n
Reducing agent (electron donor)
oxidizing agent (electron acceptor)
electron balance: donated e– = accepted e –
x.m = y.n
Example:
partial redox equations
Br2 2Br + 10e– 0 V
Cl + 2e– Cl I -I
Br2 + HCl O + H2O HBr O3 + HCl 0 I V -I
Br2 2Br + 10e – 0 V
5 Cl + 10e – 5 Cl I -I
balancing
5 2 5
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Oxidation-reduction (redox) reactions: disproportionation reactions
(dismutation reactions)
Cl2 + H2O HCl O + HCl 0 I -I
x BAox1 + y CAox1 x EAox1+m + y FAox1-n
(x+y) Aox1 x Aox1+m + y Aox1-n
3KCl O3 + KCl O3 3KCl O4 + KCl V V -I VII
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Introduction to electrochemistry: electrode, electrode potential
metal/H2O metal ions
hydrated metal ions
+ + + + +
+ + + + + +
equilibrium: M(s) = Mz+ + z.e-
Vel Vr Vr -Vel
in the solution according to cM z+
E = E0 + ln cM z+ R.T
z.F
Nernst equation – electrode potential
Faraday const. = NA.e
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Galvanic cells
Half cell Half cell
Galvanic cell
Interrupted circuit EMV = E2-E1 electromotoric voltage
In a closed circuit: electronic flow, ion flow (electric current) electric
work
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Standard electrode potentials
absolute n/a
25°C E = E0 + log cM z+ 0.059
z
Standard electrode potential: cM = 1.00 mol L-1 z+
Reference electrode: H3O+/H2
Standard hydrogen electrode: E0 =0.0 V
1) platinized platinum electrode 2) H2 blow (1 atm)
3) Solution of an acid [H3O+] = 1 mol L-1 4) hydroseal for prevention of O2 intervention
5) junction to the second half cell
H3O+ + e– = ½ H2 + H2O
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Standard electrode potential: measurement
Standard electrode potentials
reducing ability Noble m
etals non-noble
Metals with lower E0
reduce the cations of metals with higher E0
cathode
-1.18 eV
-0.13 eV
Mn+Pb2+ Mn2++Pb
Oxidation/reduction (redox) potentials:
redox system + indifferent (Pt) electrode
Ox + z e– = Red
reducing ability
E = E0
+ log 0.059
z [Ox] [Red]
Nernst-Peters equation
Electrode
Example: H2O2 +2H++Sn2+ Sn4++2H2O
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Reverse process: Electrolysis
+
E0=1.36 V
Na+ (aq) + e- = Na(s) E0= –2.07 V
2H2O(l) + 2e- → H2(g) + 2OH-(aq) Cl2(g) + 2e- → 2Cl-(aq)
E0= -0.83 V
preferable process
in progress: 2Cl-(aq) → Cl2(g) + 2e-
E = -0.41 V [OH-]=10-7
1.7-2.2 V
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Electrolysis from molten salts:
Cathode: Na+ + e– → Na(l) E° = –2.71 v
Anode: Cl– → ½ Cl2(g) + e– E° = –1.36 v
together: Na+ + Cl– → Na(l) + ½ Cl2(g) E° = –4.1 v
Na
Al