Download Inorganic Chemistry Basics

Inorganic Chemistry Basics
Lewis acid = electron pair acceptor (e.g. H+, Al3+, BF3, CO2, SiF4)
Lewis base = electron pair donor (e.g. NH3, PF3, Hal-, HS-, H2O, OH-)
Lewis acids and bases form Lewis acid/base adducts (e.g. BF3←NH3)
All metal ions (Mn+) are Lewis acids
Ligands are Lewis bases
Pearson’s concept of hard and soft acids and bases (HSAB):
Hard: less easily polarizable (usually ions of high charge and/or small radius)
Soft: more easily polarizable (usually ions of low charge and/or large radius)
Hard acids prefer hard bases, soft acids prefer soft bases
i.e. more stable acid-base complexes are formed with hard/hard or
soft/soft combinations
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The HSAB concept is useful for predicting stability and
reactivity:
CuF + HI
s h
CuI + HF
hs
s s
h h
Periodic trends for acids (simplified):
Increasing
hardness
Increasing
e.g. Mg2+, Al3+, Si4+
softness
e.g. Mg2+, Ca2+, Sr2+, Ba2+
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Acids
H+, Li+, Na+, K+
Be2+, Mg2+, Ca2+, Sr2+, Mn2+
Hard
Sc3+, La3+, Co3+, Cr3+, Fe3+, Al3+, Ga3+, As3+
Ti4+, Zr4+, Th4+, U4+, Pu4+
BF3, BCl3, AlCl3, SO3
Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Sn2+, Pb2+
Borderline
Rh3+, Ir3+, Bi3+
SO2
Pd2+, Pt2+, Pt4+
Soft
Cu+, Ag+, Au+, Cd2+, Hg2+, CH3Hg+, Tl+
Br2, Br+, I2, I+
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Bases
NH3, RNH2, N2H4
Hard
H2O, OH-, O2-, ROH, RO-, R2O
CH3COO-, CO32-, NO3-, PO43-, SO42-, ClO4F-, (Cl-)
Borderline
Soft
C6H5NH2, N3-, NO2-, SO32-, BrH-, R-, C2H4, C6H6, CO
SCN-, R3P, R2S, RSH, RS-, S2O32-, I-
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Absolute hardness, 
(I – A)
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I = Ionization energy
A = Electron affinity
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Plot of charge/radius ratio against the ionization energy
(M to M2+) for some divalent metal ions
Biologically
relevant AE
elements
Biologically
relevant TMs
toxic
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Biologically relevant ligands (bases)
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pKa Values of Coordinating Ligands
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Thermodynamics of Metal Ion Complexation
Formation
(stability)
constants
Overall
stability
constants
n = K1 x K2 x … Kn)
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Chelate effect
Chelation refers to coordination of two or more donor atoms from a
single ligand to a central metal ion
The resulting complex is characterized by an unusual thermodynamic
stability
The gain in stability upon chelation is usually ascribed to a significant
gain in entropy (however: this is not always the reason as enthalpy can
be the determining factor)
Example: [Co(H2O)6]3+ + EDTA
[Co(edta)]- + 6 H2O
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Examples of biologically relevant chelating ligands/chelates
The most advanced
chelates are proteins!
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Structure of valinomycin (K+-specific ionophore)
Monensin
Cyclic polyether
Antibiotic with
specificity for Na+
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Kinetic Considerations
Terminology:
Thermodynamic terms: STABLE and UNSTABLE
Kinetic terms:
INERT and LABILE
Definition of labile (Taube):
Reaction half-life (i.e. the time of disappearance of half of the initial compound)
of 1 minute or less
All of the following cyano-complexes are extremely stable! (Dissociation
constant for the hydrolysis of [Ni(CN)4]2- to [Ni(H2O)6]2+ is 10-22 M-2)
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Water Exchange Rates
Diffusion controlled rates of water exchange for alkali metal ions
Calcium has the highest rate constant for abundant non-alkali metal ions
(Role as second messenger)
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