transition metals in complexes complex with ligands based on what
based on the number of valence orbitals they need to utilise
a d7 needs how many e- from other studd
d7 needs 11 e- from other things
- ligands
- charge
- metal metal bonds
why is 18e- the best
bc u use all the 3d, 4s and 4p orbitals to give 18 e-
20e- means ur filling unfavourable orbitals // energy levels
16e- means u may have a unstable // reactive complex as theres an orbital available for attacking
why do u sometimes have [M(CO)4] or [M(CO)5] or [M(CO)6]
it all depends on the metal d electron count
if u have a d10 metal,, u only need 8e- to form the 18e- complex,, so having 4CO fits as a CO gives u 2e-
whats the natural method for calculating valence e- count
- find the group of the metal to find its valence e- count
- look at the type of ligands u have,, either 1e- or 2e-, 3, or 4, or 5
- then look at charge of the complex
- look if theres a metal metal bond
- and see if there are any bridging ligands
1e- ligand donor examples
CH3
H-
Cl
Br
I
sigma bonded
name some 2e- ligand donors
NR3, Pyridine, H2O, or pi acceptor ligands like O or PPh3
aka ligands with lone pairs
if we have ligands with a long n ,, aka an alkene with n2 or a ring with n5 or n6 or n4 how do we know how many e- these give
long n ^n
where the n in the power is the electron count we have
an anionic complex what do we do
we add an e-
a cationic complex,, whhat do we do
we take away an e-
metal metal bond e- count
2e- total in the bond
but we give each metal an e-
electron count of a bridging ligand
they give 1e- to each metal
why do we use the 18e- rule
- helps us predict metal metal bonding,, aka will this compound have a metal metal bond or no
- predicts if a ligand substitution is associative or dissociative (we want 18e- or 16e- ,, not 20)
what can even d electron metal counts do
metals with an even number of d electrons,, if we have a CO ligand or a 2e- donor ligand,, we can make a simple mononuclear compound
if a metal has an odd d electron count and theres CO ligands,, what can happen
the 18e- count cannot be made with a mononuclear compound
the simplest compound we can make is a dimer with a metal metal bond
if we have a metal - CO complex that decomposes easily at room temp,, why could this be
bc of backbonding
not bc of the 18e- rule
litch just be of bb
predict the structure of [Mn2 Fe (CO) 14 ) using 18 e- rule
do 18 x 3 bc theres 3 metals to give 54e- complex and then go from here
Mn = d7 aka odd
Fe = d8 aka even
odd metals may need some MM 1e- to make then even so they can form 18e- complexes.
anyways 54-22 from metals = 32e-
14x2 = 28
32-28 = 4 e-
MM bond = 2e-
so we need 2 MM bonds
Mn-Fe-Mn
Fe is even so adding 2e- from the MM is fine
Mn is odd so needs just 1e-.
then add the Co to fulfill the 18e- count.
how do we know if we should use bridging ligands or not when we have. ametal
see if the radius of the metal is small,, aka this trend follows electronegativity.
Mn = LHS of periodic table so bridging is low, u wouldnt rlly see bridging.
exceptions to the 18e- rule
stable 16e- complexes sometimes give a square planar complexxxx
higher oxidation states // early tm cmplexes (Zr)
complexes with extrememly bulky ligands bc u cant fit anymore in to form 18e- ( PtBu3)2
what electron config // groups give stable 16e- square planar
d8 complexes of groups 9 and 10
what orbital is empty in square planar complexes
the dx2-y2 orbital is empty bc its so high in energy bc its facing the ligands directly
associative ligand subs
u add the ligand u wanna add and then remove the other ligand
u have 16 –> 18 –> 16
whats dissociative ligand subs
u remove a ligand then add the one u want
18 –> 16 –> 18
whats associative and dissociate ligand subs used for
its used in catalysis
