Download d-block chemistry – general considerations

d-block chemistry – general considerations
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transition metals (d-block elements) groups 3-12 of the periodic table
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3d orbitals are filled up
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but the 4s orbitals already have electrons in them - a higher sublevel filled first.
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all the transition metals have the same arrangement of outer electrons; only the d
orbitals, lower down, are different.
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most transition metals have variable valence, meaning that they have more than
one possible oxidation state.
Colour:
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transition metals – coloured
characteristic of species with ground state electronic configurations other than d0
and d10
colour originates from electronic “d-d” transitions.
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Shapes of Molecules
Linear
AX2
Tetrahedral
AX4
Trigonal Planar
AX3
Square planar
AX4
Trigonal bipyramidal
AX5
Octahedral
AX6
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Complex formation
Coordination compound or complex:
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compound composed of metal atom or ion and one or more ligands
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ligand – atom, ion, molecule
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Ligand contains atom(s) with lone pair of electrons
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ligand formally donates electrons to the metal – coordinate covalent bond is
formed
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Coordinate covalent bonds are identical to other covalent bonds.
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Coordination compounds also called complexes or complex ions.
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d-block metals readily form complexes
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Complex formation often results in change of colour or intensity of colour
History of Coordination Compounds
Many coordination compounds have been used as pigments in ancient times.
Prussian blue, aureolin yellow, alizarin red dye.
tetraamminecopper(II) ion – royal blue colour – known in prehistoric times
Empirical Formulas of coordination compounds became known in late nineteenth century
Next step: theory describing the structure and bonding
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Organic bonding theory and ideas of ionic charges – inadequate.
New ideas were required !!!!
Example: hexaamminecobalt(III) chloride
[Co(NH3)6)Cl3
Early bonding theories:
only three other atoms can attach to Co – valence of 3.
Similar to FeCl3 these should be Cl- - have CoCl3
six ammonia molecules???
One theory – C.W. Blomstrand and S.M. Jorgensen:
Nitrogens could form chains like carbon – valency of 5
Chlorides attached directly to cobalt bonded more strongly than those bonded to nitrogen.
Blomstrand – dissociation of Cl attached to
ammonium, but not of Cl attached to Co
Another theory – Werner:
Proposed that all six ammonias could bond directly to Co ion
Looser bonding of the chloride ions – now consider as independent
ions
Werner proposed an octahedral structure
Argument between Jorgensen and Werner continued for
years!!!!!
Werner prepared and characterised two isomers of [Co(H2NC2H4NH2)2Cl2]+.
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Claimed – had chlorides arranged trans (opposite each other) and cis (adjacent to each
other) in an octahedral geometry.
Jorgenson offered alternative structures
– conceded defeat in 1907 when Werner synthesised green trans and violet cis isomers of
[Co(NH3)4Cl2]+
- no counterparts in chain theory.
Werner’s Theory – 2 types of bonds:
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molecules or ions (ligands) are attached directly to transition metal ion
positive charge of central metal ion is balanced by negative ions
Coordination sphere:
Complex ion or coordination sphere – formula - in brackets
Made up of metal atom or ion and ligands bonded to the metal.
Coordination sphere acts as a unit.
Ions outside brackets balance charge – free ions in solution
Metal can have from one up to 16 ligands attached to it
4 and 6 most common
Additional water molecules may be added to coordination sphere when compounds are
dissolved in water.
Coordination Number of Metal:
Number of covalent bonds that the metal cation forms with electron donors (ligands).
Nomenclature
Rules to name coordination compounds:
Organic and some inorganic ligands – often older trivial names rather than IUPAC
Naming coordination compounds:
1. Positive ion, cation comes first. Followed by negative ion (anion).
Example: [Ag(NH3)2]Cl – diamminesilver(I) chloride
Example: K3 [Fe(CN)6] – potassium hexacyanoferrate(III)
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2. Inner coordination sphere – square brackets
In coordination sphere: ligands are named before metal but in formulae the metal
ion is written first.
Example: [Cu(NH3)4]SO4 – tetraamminecopper(II) sulfate
Example: [Co(NH3)6]Cl3 – hexaamminecobalt(II) chloride
3. Number of ligands of one kind given by a prefix.
If ligand name include prefix or is complicated use parentheses and second set of
prefixes.
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di
bis
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tri
tris
4
tetra
tetrakis
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penta
pentakis
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hexa
hexakis
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hepta
heptakis
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octa
octakis
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nona
nonakis
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deca
decakis
Example: [Co(NH2CH2CH2NH2)2Cl2]+
dichlorobis(ethylenediamine)cobalt(III)
Example: [Fe(C5H4N-C5H4N)3]2+
tris(bipyridine)iron(II)
4. Ligands are named in alphabetical order.
Use ligand name, not prefixes
Example: [Co(NH3)4Cl2]+
amine first – starts with an a, even though we use tetraammine
chloro second – starts with c, even though we use dichloro
Thus: tetraamminedichlorocobalt(III)
Example: Pt(NH3)BrCl(CH3NH2)
amminebromochloromethylamineplatinum(II)
5. Anionic ligands are given o as suffix.
Neutral ligands – retain name
Water – aqua
Examples:
ClBrSO42H2O
CH3NH2
chloro
bromo
sulfato
aqua
methylamine
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NH3
ammine (double m!!)
6. Two systems for showing charge or oxidation number
(a) Stock system – calculated oxidation number of metal Roman
numeral in parentheses after name of coordination sphere. More
common convention.
(b) Ewing-Basset – charge on coordination sphere in parenthesis
after name of coordination sphere.
If the charge is negative: add suffix –ate to name of coordination sphere.
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Example: [Pt(NH3)4]2+
tetraammineplatinum(II)
tetraammineplatinum(2+)
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Example: [PtCl4]2tetrachloroplatinate(II)
tetrachloroplatinate(2-)
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Example: [PtCl6]2hexachloroplatinate(IV)
hexachloroplatinate(2-)
7. The prefixes cis- and trans- designate adjacent and opposite geometric locations.
[PtCl2(NH3)2]
cis- and trans- diamminedichloroplatinum(II),
[CoCl2(NH3)4]+
cis- and trans-tetraamminedichlorocobalt(III)
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8. Bridging ligands between two metal ion have the prefix µ-
[Co(Co(NH3)4(OH2)3]6+
9. When the complex is negatively charged, use the following metal names
Fe
iron
ferrate
Ag
silver
argentate
Pb
lead
plumbate
Sn
tin
stannate
Sb
antimony
stibate
Au
gold
aurate
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