Coordination Chemistry

Y2

Transiton Element

metal atoms or ions with incomplete d subshell

Oxidation State

The charge left on the metal after all the ligands have been removed

Coordination Complex

A chemical species consisting of a central metal atom/ ion bonded to surrounding molecules or ions

Ligand

molecule or ion that binds to cental metal atom/ ion to from a coordinaton complex

Lewis Acid

e pair acceptor (metal )

Lewis Base

e pair donor (ligand)

monodentate

ligand w two or more donor atoms

ambidentate

ligand with two donor atoms but only one can attach to a metal atom/ion

chelate

bidentate ligand bound to single metal atom/ion

coordination number

number of ligands bonded to a central metal atom/ ion

coordnative/ dative bond

the link formed when a ligand donates bonding e to the metal

Alfred Werner

established coordnation chemistry, has a nice stache

Isomer

compounds that have the same # and type of chemical bonds but differ in their spatial arrangement

structuralisomerism

compounds with the same molecular formula and sequence of bonds but differ only in the 3D orientations of their atoms in space

cis

on this side

trans

across

fac

facial

mer

meridonial

Barycentre

location of d orbitals

Pairing Energy

energy required to flip electron to pair with a spin up electron in the same orbital

CN

Coordination Number

CN Octahedron

6

CN Tetrahedron

4

CN Square Planar

4

which orbitals are destabilsed in an octahedral crystal field

d_x²-y² and d_z²

why are d_x²-y² and d_z² destabilised in an octahedral field?

because they point AT the ligands

what orbitals are stablised in an octahedral crystal field?

d_xy, d_xz, d_yz

e₂

doubly degenerate - oct. complex (higher E)

t₂g

triply degenerate- oct. complex (lower E)

CFSE

Crystal Field Stabilsition Energy

CSFE oct. complex

CFSE=mx(+3/5Δ_o)+ n(-2/5Δ_o)

Energy Gap between eg and t2g

Δ octahedral (abr. o)

electronic configuration for oct. crystal filed

(t_2g)ⁿ(e_g)^m

weak field (high-spin)

Δ_o< pairing energy, small Δ_o = one e- per orbital (t2g and eg) added b4 second e- is added

why do weak filed e- fill up each orbital?

because Δ_o is smaller than the pairing E, it takes more E to flip the electron than to put it into the eg orbital, thus both t2g and eg have an e- added before any e- flipping occurs

strong field (low-spin)

Δ_o> pairing energy. large Δ_o = e- are paired in t2g till full; e- then added to eg orbital

why do strong field e- fill up the t2g orbital first

Δ_o is larger than the pairing energy, thus it takes less e- to flip an e- than to move it to the eg orbital.

Magnitute of octahedral crystal field splitting ( Δ_o ) due to:

identity + ox state of the metal and the nature of the ligands

HONC

Halides, Oxygen, Nitrogen, Carbon

What do we use the acyronym HONC for

from left to right increasing Δ_o ; to remeber spectrochemical series

d-d transition

excitation of an electron by visible light energyfrom a lower-energy d orbital to a higher-energy d orbital

general Δ_o for many ligand fields

12,000 to 27,000 cm^-1

Δ_o increases

with increasing ox. state ( larger pos. charge= ligands r closer to metal ion; increased e-e repulsion, greater field splitting

Δ_o increases

down a group ( larger d orbitals extend out further towards ligands, increases e-e repulsion)

Colourless transition metal complexes

filled or half filled d subshell OR vv strong ligand fild = large Δ_o and lambda_max <380 nm

tetrahedral complex

four ligands approach between x,y, z axes

what orbitals are destabilised in a tetrahedral complex?

d_xy,d_xz,d_yz

why are d_xy,d_xz, and d_yz orbitals destabilised in a tetrahedron?

sort of point AT the ligands

what orbitals are stabilised in a tetrahedron ?

d_x²-y² and d_z²

energy gap between t₂ and e

Δ_T

Δ_T VS Δ_o

Δ_T ≈ 4/9 Δ_o

why is Δ_T ≈ 4/9 Δ_o?

b/c tetrahedrons have 4 ligands as opposed to 6 and less ligand-ligand repulsion = smaller splitting

CFSE tetrahedral complex

CFSE= m(+2/5 Δ_T )+ n(-3/5 Δ_T )

Square Planar Complexes

Ligands approach along the x and y axes

very destabilsed SP orbital

d_x²-y² (points at ligands)

slightly destabilised SP orbital

d_xy (points between four ligands)

slightly stablised SP orbital

d_xz and d_yz (point between two ligands)

very stabilised SP orbital

d_z² (points at NONE of the ligands)

Δ_SP v.s. Δ_o

Δ_SP ≈ 1.3 Δ_o

SP geometry is ubiquitous for

4d⁸ and 5d⁸ metal ions ( Rh(I), Ir (I), Pd(II), Au (III)

3d metal in SP complex

needs a strong field ligand to favour SP over tetrahedral (eg CN-)

linear complexes

approach along z axis

very destabilised linear complex

dz2 (directly @ligands)

slightly destabilised linear complex orbitals

dxz,dyz ( direction of ligands)

very stabilsed linear complex orbitals

dxy, dx2-y2 ( point away from ligands)