crystal field theory

Question 1

does crystal field theory assume that bonding in TM complexes are ionic or covalent?

Answer 1

ionic (no covalent character)
electrostatic interactions (point charge interactions between the metal and the ligand)

Question 2

which d orbitals lie on the axis and which ones lie inbetween for octahedral

Answer 2

on: dx^2-y^2 and dz^2
between: dxy, dxz, dyz

Question 3

what is the natural state of the d orbitals in free metal ions?

Answer 3

all 5 d orbitals are degenerate

Question 4

what happens to degenerate orbitals when placed in a ligand field?

Answer 4

the ligands are negatively charged or have lone pairs of electrons which repel the electrons found in the d orbitals therefore energy of the d orbitals increase BUT this assumes a negative charge field

-> change of POV by assuming ligands as negative point charges

Question 5

how are the d orbitals distributed in an octahedral ligand?

Answer 5

dx^2-y^2 and dz^2 directly interact with the concentrated negative point charge of the ligands (repulsion) thus become destabilized and go higher in energy

dxy, dxz, dyz are between the axis thus are electronically relived as they do not point directly towards the ligand (stabilized and energy is lowered)

• these are relative to if the ligands created a sphere of negative charge where all orbitals experience the same amount of repulsion

Question 6

what are the higher energy and lower energy orbitals called in octahedral complexes?

Answer 6

higher: eg (equal)
lower t2g (triplet)

Question 7

what is the barycenter

Answer 7

energy of a spherical ligand field, energy is raised or lowered relative to this value

Question 8

what is CFSE? what represents a more stable value

Answer 8

the stabilisation of the particular arrangement of ligands in a specific geometry with respect to the spherical ligand field

the more negative the value the more stable the complex

Question 9

what is the general CFSE equation for oct and tet?

Answer 9

CFSE(oct) = (-2/5 x no. of electrons in t2g + 3/5 x no. of electrons in eg) x doct + zP

CFSE(tet) = (-3/5 x no. of electrons in t2 + 2/5 x no. of electrons in e) x dtet + zP

zP is the number of extra paired electrons COMPARED TO the barycenter form

Question 10

what is the CFSE of a barycenter geometry of any metal complex?

Answer 10

0

Question 11

what is high spin and low spin

Answer 11

high spin: more unpaired electrons (promoted to HIGHER energy level)
-> all electrons pointing in the same direction therefore higher net spin

low spin: less unpaired electrons (electrons are paired up in lower energy orbital)
-> not all electrons spinning in the same direction therefore lower net spin

Question 12

what determines the size of P

Answer 12

metal + oxidation state

Question 13

what determines the size of doct

Answer 13

metal, oxidation state, ligand

Question 14

what is the range of d values that have high/low spin state for octahedral?

Answer 14

d4-d7

Question 15

which 2 states have no net benefit compared to barycentre?

Answer 15

high spin of d5 and d10

Question 16

what is the relationship between oxidation state and the size of delta oct?

Answer 16

increase oxidation state means higher effective nuclear charge experienced by the ligands thus are pulled closer to the metal ion. this results in a larger electrostatic repulsion between the ligands and the metal ion causing a greater delta oct

Question 17

how does delta oct change down the group?

Answer 17

d orbitals get bigger -> better contact with ligands -> more interactions with ligands -> more destabilizing -> increase in delta oct

another effect: P becomes smaller as there is more space for the electrons to pair up

Question 18

are 2nd and 3rd row TM complexes high spin or low spin and why?

Answer 18

ALL 2nd and 3rd row elements are low spin bc low energy penalty of pairing electrons and greater delta oct

Question 19

what is the effect of field strength of a ligand on delta oct?

Answer 19

weaker field strength -> less interaction with metal ion -> less d orbital splitting (high spin)

vice versa

Question 20

how does electronegativity and sigma donating ability effect the field strength of a ligand?

Answer 20

lower electronegativity means that the electrons are held on less tightly therefore more able to donate -> more interactions with metal ion thus more destabilization

halide < O < N < C

Question 21

which is a stronger field ligand, flourine or chlorine and why?

Answer 21

flourine is stronger because it is smaller thus less distance between the metal and ligand thus more interactions

more electronegative also means that more withdrawing ability thus more interactions d orbital electrons again and more splitting (but at the same time not willing to give up its electrons so less interaction compared to carbon)

Question 22

what is the relationship between pi donor/acceptor and delta oct?

Answer 22

pi donors are weak field ligands thus smaller delta oct

pi acceptors are strong field ligands thus larger delta oct

Question 23

why is P a stronger field ligand than N

Answer 23

P has low lying d orbitals that can accept electron density from the metal ion

Question 24

is water high spin or low spin complex?

Answer 24

high spin complex because it is considered a weaker field ligand

Question 25

what is the degeneracy of d orbitals in a tetrahedral ligand field?

Answer 25

tetrahedral is occupying alternate corners of a cube on: dxy, dxz, dyz between: dx^2-y^2 and dz^2

Question 26

what are the higher energy and lower energy orbitals called in tetrahedral complexes?

Answer 26

higher: t2 lower: e no g because tetrahedral is not an inversion centre

Question 27

compare the size of deltaoct and deltatet

Answer 27

deltatet is much smaller because the ligands are sitting above and below the plane thus do not point directly towards the d orbitals in the metal ion meaning less destabilizing than ligands in octahedral complex which have them pointing directly towards the d orbitals in the metal ion (greater interaction)

Question 28

are tetrahedral complexes high spin or low spin and why?

Answer 28

high spin because the energy penalty of promoting an electron is small (regardless of metal, oxidation state and ligand)

Question 29

draw out the d orbital diagram for square planar complex derived from an octahedral complex

Answer 29

L13 check

Question 30

why would a complex want to be square planar over tetrahedral?

Answer 30

at d8 configuration and large delta, there can be more electrons below the barycenter thus electronic stabilization of the TM complex

Question 31

what are the conditions for forming square planar complexes

Answer 31

d8, coordinate no. 4 3d8 needs strong field ligand for more splitting 4d8 and 5d8 with any ligand (more splitting naturally with larger orbitals)

Question 32

what is a conditions where square planar is adopted but not d8?

Answer 32

if the ligand is bulky it can force a certain geometry (eg. for macrocyclic molecules)

Question 33

are square planar TM complexes high spin or low spin and why?

Answer 33

always low spin due to very large delta

Question 34

what is the jahn-teller effect?

Answer 34

non linear molecules in a degenerate electronic state will undergo distortion to form a system of lower energy and symmetry which removes degeneracy (electrons placement ambiguity is removed to create a consistent but distorted structure through movement of the ligands)

Question 35

what causes distortions in metal complexes?

Answer 35

electrons can be placed in either of the higher spin orbitals, this results in strong and weaker bonding depending on which orbital the electron is placed in, and weaker and stronger bonds lead to different bond lengths and thus distortions in the overall geometry of the TM complex

Question 36

where does the jahn-teller effect most observed

Answer 36

odd number of electrons in eg orbitals (high spin d4, low spin d7) OBSERVATION NOT PREDICTION