unit 3 transition metal complexes

what is a transition element

element with partially filled d or f valence shells. groups 3-11.

d_yz orbital

d_xy orbital

d_xz orbital

d_z² orbital

d_x²-y² orbital

d-electron filling for transition metalls

(n+1)s orbital is filled before nd (eg 4s before 3d)

exceptions to d-electron filling for first row

Cr and Cu are anomalous due to extra stability gained from half/fully filled subshells meaning an electron is bumped from 4s to 3d

d-orbital filling for a metal in a compound

filling order reverts to 3d before 4s

d-orbitals on ionisation

any s electrons are removed before the d electrons

trend in IE for d-block

general trend is for IE to increase across a period due to increasing Z_eff. some IEs are anomalously low:

• for IE₁, Cr and Cu

• for IE₂, Mn and Zn are low

• for IE₃, Fe is low

what is a transition metal complex

has a central metal atom or ion surrounded by a set of molecules or ions termed ligands that bind to the metal through electron donation to form dative covalent bonds

coordination complex

none of the ligands bind through a carbon atom

organometallic complex

at least one ligand binds through a carbon atom

coordination number and symbol

CN

number of bonds between the metal and surrounding ligands

how are complexes written/drawn

complex and any counterions are distinguished by placing only the complex inside square brackets. charge for the complex is giving outside the square brackets.

coordinating atom is distinguished when drawn or ambiguous

optionally, the oxidation state for the metal is given next to the metal

simplest idea of metal-ligand bonding

the ligand donates an electron pair to the metal. lone pairs are a good source.

the metal-ligand bond is often dative covalent. the metal accepts electrons so it is a good lewis acid, the ligand donates electrons so it is a lewis base.

good bases are generally also good ligands as they have an available electron pair. transition metals can readily form such complexes as they have energetically available empty d-orbitals.

octahedral complexes:

• diagram

• CN

• adjacent and opposite angles

CN = 6

adjacent angles = 90

opposite angles = 180

tetrahedral complexes:

• diagram

• CN

• adjacent angles

CN = 4

adjacent angles = 109.5

square planar complexes:

• diagram

• CN

• adjacent and opposite angles

CN = 4

adjacent angles = 90

opposite angles = 180

dentate prefixes

mono, bi, tri, tetra, penta, hexa, hepta and octa

water ligands: formula and name of coordinated ligand

H₂O

aquo

ammonia ligands: formula and name of coordinated ligand

NH₃

ammine

fluoride ligands: formula and name of coordinated ligand

F^-

fluorido

chloride ligands: formula and name of coordinated ligand

Cl^-

chlorido

bromide ligands: formula and name of coordinated ligandBr^-

Br^-

bromido

hydroxide ligands: formula and name of coordinated ligand

OH^-

hydroxido

methoxide ligands: formula and name of coordinated ligand

OMe^-

methoxo

cyanide ligands: formula and name of coordinated ligand

CN^-

cyanido

carbon monoxide ligands: formula and name of coordinated ligand

CO

carbonyl

thiocyanide ligands: formula and name of coordinated ligand

SCN^- or NCS^-

thiocyanato or isothiocyanato

trimethylphosphine ligands: formula and name of coordinated ligand

PMe₃

trimethylphosphine

chelate rings

formed by polydentate ligands where two or more donor atoms coordinate to a single metal

constitutional/linkage isomers

same formula, different atom-to-atom connectivity. ligands that can coordinate to a metal through different atoms

eg NO₂: M-NO₂ or M-ONO

geometrical isomers

ligands are arranged differently in space

geometrical isomers in tetrahedral complexes

none

geometrical isomers in square planar complexes

occurs if two ligands are the same. if there are more than 2 types of atom, it is only the 2 same atoms that are important

geometrical isomers in octahedral complexes

occur when two or three ligands are the same.

for three the same:

• three identical forming a face = fac

• three in a plane = mer

optical isomerism

occurs where two isomers are non-superimposable mirror images of each other

the objects are termed chiral and the isomer pair are enantiomers.

optical isomerism in tetrahedral complexes

occurs only if all four ligands are different

optical isomerism in square planar complexes

no optical isomers, mirror images can be superimposed

optical isomerism in octahedral complexes

does not occur with monodentate ligands. can occur when there are two or three bidentate chelating ligands.

order of naming transition metal complexes

• in complex, ligands first, alphabetically, then metal

• in compound, cation first, anion last

• oxidation state for metal is indicated by roman numerals in brackets. this is important as the number of counterions is not stated.

• if the complex is anionic, the metal ends in ate.

prefixes to state number of ligand (and name to use if ligand’s name already uses one of these)

di (bis)

tri (tris)

tetra (tetrakis)

penta (pentakis)

hex (hexakis)