transition metal complexes part 1 Flashcards
what are ligands?
Lewis Base
Electron donors
what are metal centers?
Lewis Acids
Electron acceptors
Adduct
the product of a Lewis acid-base reaction
coordination number
number of ligand binding sites on metal center
coordination sphere
central metal and ligands that are closely attached to it are enclosed in a square bracket
most transition metal complexes are either # or # coordinate
CN= #
4 or 6
CN=2
multi-dentate ligands
dentate - greek for ?
ligands that can bind through multiple donor atoms
greek for tooth
ligands that stabilize low oxidation state
CO, CN-, [Fe(CO)5]
ligands that stabilize normal oxidation states
water, ammonia, halides, [Fe(H2O)6]2+, Fe(H2O)6]3+
ligands that stabilize high oxidation state
fluoride, oxide [CoF6]2-, [FeO4]2-
ligands can stabilize low oxidation metal centers, but it is not possible with…
stable compound with iron(0):
? compounds cannot be formed:
not possible with main group metals
Fe(CO)5
Ca(0)… Ca(CO)5
interesting magnetic properties
NiCl4 2-
Ni(CN)4 2-
paramagnetic Ni2+ complex
diamagnetic Ni2+ complex
interesting optical properties
cis-Co(NH3)4Cl2
trans-Co(NH3)4Cl2
green
violet
interesting electrical properties
cannot conduct electricity
conducts electricity
NiO2
TiO2
Valence bond theory:
hybridization of orbitals
each covalent bond is formed by…
the individual orbital identity is…
the bond strength is…
an overlap of atomic orbitals from each atom
retained
proportional to the amount of orbital overlap
Bonding in coordination compounds
Valence bond theory
filled orbital on ligand
empty orbital on metal cation
the original atomic orbitals are mixed together and transformed into a new set of ? that match the ? for bonding
hybrid orbitals
directional requirements
a drawback of the valence bond theory
VB theory can ‘t explain color and magnetism of coordination compound
crystal field theory
the d-orbitals are degenerate in free atoms
all orbitals have the same energy
upon entering a repulsion field, the d-orbitals…
lose their degeneracy
incoming ligands ? electrons in orbitals
repel
the closer the proximity of the ligands…
the more repulsion
ligands directed between orbitals have
low energy
orbitals facing incoming ligands
high energy
incoming ligands generate an ? on the ?
“electronic repulsion field” on the transition metal orbitals
octahedral field
six ligand donor atoms approach in an Oh symmetry
four ligand donor atoms approach in an Td symmetry
tetrahedral field
dxy, dxz, dyz face between …
incoming ligands and relative energy decreases
dx2-y2 and dz2 face directly at …
incoming ligands and relative energy increases
eg
dx2-y2 and dz2 orbitals
t2g
dxy, dxz, and dyz orbitals
factors that affect crystal field splitting
the identity of the transition metal
oxidation state of metal
number of ligands, more ligands, more splitting
nature of the ligands
I- < Br- < Cl- < F- < OH- < OH2 < NH3 <en < CN- < CO
spectrochemical series
weak field/high spin to strong field/ low spin
strong field case
weak field case
the splitting energy is large
the splitting energy is small
low spin complexes tend to be ? while high spin complexes tend to be ?
diamagnetic
paramagnetic
d5 metal in gas phase
d5 metal in weak field
d5 metal in strong field
5-fold degeneracy
weak field: high spin
strong field: low spin
electron pairing energy more than splitting energy
electron pairing energy less than splitting energy
high spin
low spin
d1-d3 and d8-d10
the number of unpaired electrons are the same for strong and weak fields
the number unpaired electrons are not equivalent between strong and weak fields
d4-d7
d0 and d10
the transition metal acts like a main-group metal
crystal field stabilization energy: the lower energy orbitals are more stable than the …
electrons in t2g orbitals
the net change in orbital energies after splitting is
higher energy orbitals
impart extra stability
zero
what is Dq?
differential quanta which comes from quantum mechanics
each electron in t2g decreases energy by
each electron in eg increases energy by
4/10
6/10
tetrahedral complexes
t2g orbitals are ? by incoming ligands
eg orbitals are ? by incoming ligands
repelled
not repelled
tetrahedral ligand field splitting is … octahedral ligand field splitting
always ? field
opposite
always weak field
electrons in the incompletely filled d orbitals can be …
excited from lower occupied to higher unoccupied orbitals
delta = hc/wavelength
the frequency of the absorption is proportional to the crystal field splitting
when the excited state relaxes to the ground, ?
light is emitted
what are the drawbacks of crystal field theory?
-considers only the metal ion d orbitals and give no consideration at all to other metal orbitals like s,p
-unable to account for the relative strength of ligands
-bond between metal and ligands purely ionic. it gives no account to partial covalent nature of the metal-ligand bond
