LAB01 - Background

Question 1

What is a complex?

Answer 1

A structure composed of a central metal ion\atom (M), surrounded by a group of ligands (L).

Question 2

What is a ligand?

Answer 2

An ion or a molecule that can exist on its own. In coordination chemistry, it bonds to a central metal ion\atom through a coordinative covalent bond.

Question 3

What is a coordinate compound?

Answer 3

A neutral complex or an ionic compound in which at least one of the ions (cation or anion) are a complex (a coordination entity).

e.g [Ni(CO)₄], [Co(NH₃)₆]Cl₃

Question 4

How are coordination entities (complex) related to lewis acid\bases?

Answer 4

The metal ion\atom is a lewis acid while the ligands are lewis bases.

Thus complex stability is also affected by HSAB theory.

Question 5

What is a coordination number?

Answer 5

The number of ligands which form the primary coordination sphere.

e.g. [Mn(OH₂)₆]^{2+ has C.N=6.}

Question 6

True or false:

Number of ligands is always equal to the number of M-L bonds.

Answer 6

False

Polydentate ligands such as EDTA^4- are a good counterexample.

Question 7

Define the term:

Chelate

Answer 7

A coordination entity in which
a ligand binds to more than one site and forms a ring that includes the metal atom

Question 8

The geometry of a complex is determined by the ______ number of the central metal atom.

Answer 8

Coordination

Note that there are other determining factors such as period of central metal atom or d electron configuration (as in square planar compounds).

Question 9

Geometries of coordination entities are mostly ______.

Answer 9

Polyhedrons

Question 10

Coordination compounds can be formed from ________ metal groups in the periodic table of elements, but are mostly formed from ________.

Answer 10

any one of the
d-block transition metals

Question 11

Define the term:

Transition metals

Answer 11

Metal elements with valence electrons in d or f orbitals.

Question 12

Coordination bonds in coordination compounds are formed when ______ orbitals on M overlap with ______ orbitals on L.

Answer 12

d or f
free (not involved in other bonds)

Question 13

True or false:

The crystal field theory provides an accurate description of all interactions within a coordination compound.

Answer 13

False

It is a simplified model based on electrostatic interactions between M and L which is used for predictive purposes only.

Question 14

In a spherical field, all 5 d orbitals are ______ degenerate and ______ equivalent.

Answer 14

Energetically degenerate
Spatially equivalent

Question 15

2 assumptions of crystal field theory:

1. metal d-orbitals are electrostatically repelled by neutral ligands (as well as negatively charged ones) because they are ________.
2. Ligands are ________ symmetric and therefore can be modeled as ________.

Answer 15

1. Lewis acids (d-orbitals are repelled by lone pairs on L).
2. spatially symmetric, negative point charges.

Question 16

In an octahedral complex, electrons in e_g orbitals are more likely to be found ______ the (x, y, z) axes.

Answer 16

along

Question 17

In an octahedral complex, electrons in t_2g orbitals are more likely to be found ______ the (x, y, z) axes.

Answer 17

between

They are less likely to be found along the (x, y, z) axes.

Question 18

In an octahedral complex, electrons in e_g orbitals are ______ to the negative charges on L than electrons in t_2g orbitals and therefore are ______ stable.

Answer 18

closer
less stable (higher in energy)

Both orbital sets are electrostatically repelled from L, but eg orbitals are repelled more strongly due to an increased proximity to the lignads.

Question 19

In an octahedral field, the 5 d orbitals on M are no longer ______.

Answer 19

Energetically degenerate

Question 20

dz² orbitals are a linear combination of the ______ and ______ orbitals.

Answer 20

dz²-x² and dz²-y² orbitals

However, the dz²-x² and dz²-y² orbitals cannot exist on their own.

Question 21

Describe splitting of d-orbital in Octahedral field.

Answer 21

Question 22

In an O_h crystal field, the eg orbitals are destabilized.

What is the value of A?

Answer 22

6

Question 23

In an O_h crystal field, the t_2g orbitals are stabilized.

What is the value of B?

Answer 23

-4

Question 24

What is the splitting energy of the d-orbitals in an octehedral crystal field?

Size of energy gap between t2g and eg MOs

Answer 24

10D_q or Δ_o

Question 25

# Explain splitting pattern of d orbitals in Oh ligand field: Why are the e_g orbitals 3/5 Δ_O above and t_2g orbitals 2/5 Δ_O below their energy in a spherical field?

Answer 25

* There are 2 e_g orbitals and 3 t_2g orbitals. * The transition from a spherical field to an Oh one only changes charge distribution, not the total charge so energy is conserved. * From conservation of energy: (2 e_g orbitals)*3/5 Δ_O + (3 t_2g orbitals)*(-2/5 Δ_O)=0

Question 26

Answer 26

Question 27

## Footnote Give 2 reasons.

Answer 27

Reason #2: Δ_T < Δ_o due to reduced number of ligands (4 in Td vs 6 in Oh).

Question 28

Tetrahedral complexes are always HS, because \_\_\_\_ is smaller than \_\_\_\_. The small value of Δ_T is attributed to \_\_\_\_.

Answer 28

Δ_T P Greater distance between d-orbitals and ligands. ## Footnote P - Pairing energy

Question 29

Answer 29

Question 30

In a Td crystal field, the \_\_\_\_\_\_ orbitals are closer to the ligands than the \_\_\_\_\_\_ orbitals.

Answer 30

d_xy,d_yz,d_xz (t2 orbitals) d_z²,d_x²-y² (e orbitals)

Question 31

In a Td crystal field, the \_\_\_\_\_\_ orbitals are less stable than the \_\_\_\_\_\_ orbitals.

Answer 31

d_xy,d_yz,d_xz (t2 orbitals) d_z²,d_x²-y² (e orbitals) ## Footnote Due to increased proximity of e orbitals to ligands.

Question 32

Describe d orbital splitting in Td crystal field:

Answer 32

Question 33

# What is the value of A? Δ_T=A⋅Δ_O ## Footnote Δ_T - field splitting in Td field Δ_O - field splitting in Oh field

Answer 33

4/9

Question 34

When P<Δ, the number of unpaired electrons is \_\_\_\_\_\_\_ and a \_\_\_\_\_\_\_-spin complex with a \_\_\_\_\_\_\_ splitting field is formed.

Answer 34

minimal low strong

Question 35

When P>Δ, the number of unpaired electrons is \_\_\_\_\_\_\_ and a \_\_\_\_\_\_\_-spin complex with a \_\_\_\_\_\_\_ splitting field is formed.

Answer 35

maximal high weak

Question 36

In a diamagnetic material, all electrons are \_\_\_\_. A diamagnetic material is \_\_\_\_ by an external magnetic field.

Answer 36

Paired Slightly repelled

Question 37

A paramagnetic material has \_\_\_\_. Paramagnetic materials are \_\_\_\_ an external magnetic field.

Answer 37

Unpaired electrons Drawn toward

Question 38

3 factors which determine field strength in an Octahedral field?

Answer 38

1. Oxidation State of M ion - a greater oxidation state leads to stronger interaction with ligands and stronger field. 2. Size of M ion - a larger radii leads to stronger interaction with ligands and stronger field (4d and 5d metals always form a strong-field, low-spin compound). 3. Strength of ligand - ligands which appear higher up in the spectrochemical series form stronger fields.

Question 39

Ligand field theory relies on \_\_\_\_\_\_\_\_ theory to account for the electronic structure of coordination compounds. This theory is more accurate since it adresses the interaction between \_\_\_\_\_\_\_\_ orbitals and \_\_\_\_\_\_\_\_ orbitals.

Answer 39

Molecular Orbital Metal Ligand

Question 40

According to ligand field theory, "split d-orbitals" are molecular orbitals formed by overlap of \_\_\_\_\_\_\_\_ with \_\_\_\_\_\_\_\_ that can form \_\_\_\_\_\_\_\_ with them.

Answer 40

According to ligand field theory, "split d-orbitals" are molecular orbitals formed by overlap of **s, p and d orbitals (of eg symmetry)** with **linear combinations of ligand orbitals** that can form **sigma bonds** with them.

Question 41

According to MO theory, each overlap between a metal and a ligand orbital will form a \_\_\_\_\_\_\_\_ and an \_\_\_\_\_\_\_\_ molecular orbital. An orbital that does not overlap with any other orbital will form a \_\_\_\_\_\_\_\_ molecular orbital.

Answer 41

bonding antibonding nonbonding ## Footnote Note: the frontier orbitals (E_gap=Δ) obtained by MO (ligand field) theory are the same as those obtained through crystal field theory.

Question 42

Answer 42

Question 43

Unlike in the crystal field theory, eg orbitals in the ligand field theory are a \_\_\_\_\_\_\_\_ of \_\_\_\_\_\_\_\_ orbitals and \_\_\_\_\_\_\_\_ orbitals.

Answer 43

a combination metal ligand ## Footnote Because they are molecular orbitals, not pure d-metal orbitals as in crystal field theory.

Question 44

According to the ligand-field theory, d-orbitals of a \_\_\_\_\_\_\_\_ symmetry cannot overlap with any of the ligands in an Oh field. Therefore, they form \_\_\_\_\_\_\_\_ molecular orbitals when ineteracting with Oh field ligands. ## Footnote First gap: Mulliken name for a representation of a symmetry point group.

Answer 44

t2g nonbonding

Question 45

π bonds are formed above and below the \_\_\_\_\_\_, in a plane \_\_\_\_\_\_\_\_ to the bond direction.

Answer 45

M-L σ bond running parallel

Question 46

In an octahedral complex, π bonds are formed between \_\_\_\_\_\_\_\_ orbitals on M and ligand \_\_\_\_\_\_\_\_ or \_\_\_\_\_\_\_\_ ligand \_\_\_\_\_\_\_\_ orbitals in the M-L bond plane.

Answer 46

In an octahedral complex, π bonds are formed between **nonbonding t2g** orbitals on M and ligand **π orbitals** (such as π^{*<\sup>orbital in CO) or **unhybridized** ligand **p** orbitals in the M-L bond plane (such as the _y orbitals in RO-<\sup> ligands).}

Question 47

# True or false: π bonds between M and L can be formed without an existing M-L σ bond.

Answer 47

False ## Footnote They are formed in addition to an existing M-L σ bond.

Question 48

**Mixing ligand** π **charater (**π-**donor) into the t_2g set of orbitals in an O_h ligand field results in the t_2g set becoming more \_\_\_\_\_\_\_\_\_.** ***Bonding or Antibonding***

Answer 48

**Antibonding** (Ligand π orbitals are lower in energy than the t_2g set and therefore any mixing results in HOMO frontier orbitals being of antibonding character)

Question 49

**Mixing ligand** π **charater (**π-**acceptor) into the t_2g set of orbitals in an O_h ligand field results in the t_2g set becoming more \_\_\_\_\_\_\_\_\_.** ***Bonding or Antibonding***

Answer 49

**Bonding** (Ligand π* orbitals are higher in energy than the t_2g set and therefore any mixing results in HOMO frontier orbitals being of bonding character)

Question 50

**π-Donors\_\_\_\_\_∆_oh** ***Increase or Decrease***

Answer 50

**Decrease**

Question 51

**π-Acceptors\_\_\_\_\_∆_oh** ***Increases or Decrease***

Answer 51

**Increase** ## Footnote ∆_oh (and complex stability) increases with the ligand's tendancy to accept electrons to it's empty orbitals.

Question 52

When π acceptor ligands interact with t2g orbitals of the metal atom, the energy of the resulting (t2g + π\*) orbitals is \_\_\_\_\_\_\_\_ than the original t2g orbitals and the energy of the resulting (t2g + π\*)\* orbitals is \_\_\_\_\_\_\_\_ than the eg* orbitals formed by the σ bond.

Answer 52

lower higher ## Footnote The HOMO orbital (populated by d-metal atom electrons) is lower in energy and therefore stabilized.

Question 53

When π **donor** ligands interact with t2g orbitals of the metal atom, the energy of the resulting (t2g + π)\* orbitals is \_\_\_\_\_\_\_\_ than the original t2g orbitals and the energy of the resulting (t2g + π) orbitals is \_\_\_\_\_\_\_\_ than the original t2g orbitals.

Answer 53

higher lower ## Footnote The HOMO orbital (populated by d-metal atom electrons) is an antibonding orbital. It is higher in energy and therefore Δ shrinks.

Question 54

When bonding with π acceptor ligands, electrons are donated from the \_\_\_\_\_\_\_\_ to the \_\_\_\_\_\_\_\_. This effect is called \_\_\_\_\_\_\_\_ .

Answer 54

metal atom empty orbitals on the ligand back bonding

Question 55

An M-L bond formed with a π acceptor ligand is \_\_\_\_\_\_\_\_.

Answer 55

Synergetic ## Footnote In a M-L bond with a pi- acceptor, electrons are donated from M to L. The bond is synergetic because it is formed in addition to a sigma bond, where electrons are donated from L to M.

Question 56

When π **donor** ligands interact with t2g orbitals of the metal atom, the resulting (t2g + π) orbitals are filled with \_\_\_\_\_\_\_\_ electrons, whereas the resulting (t2g + π)\* orbitals are filled with \_\_\_\_\_\_\_\_ electrons. Therefore, the HOMO orbitals are of \_\_\_\_\_\_\_\_ character. | Last gap: bonding\antibonding

Answer 56

Ligand Metal Antibonding

Question 57

Wavelengths of visible spectrum?

Answer 57

400 < λ < 800nm

Question 58

Given a coordination entity with field-splitting of Δ_O, what is the frequency of light absorbed by this entity?

Answer 58

ν=Δ_O/h ## Footnote h - Planck's constant

Question 59

From the wavelength of an absorption band on a spectrum of a given complex, we can deduce the magnitude of \_\_\_\_\_\_ for that complex.

Answer 59

Δ_O<\sub>

Question 60

Relation between c, ν and λ?

Answer 60

ν=c/λ

Question 61

If a d orbital of a given complex is populated by more than 1 electron, its absorption spectrum will display \_\_\_\_\_\_ absorption bands.

Answer 61

multiple ## Footnote Number of bands will depend on the number of d electrons and complex symmetry, factors which affect term energies in complex.

Question 62

Δ_O for complexes with double-valence ions of 3d metals (like Cu²⁺)? | In cm^-1

Answer 62

7500-12000 cm^-1

Question 63

Δ_O for complexes with triple-valence ions of 3d metals (such as Fe³⁺)? | In cm^-1

Answer 63

14000-25000 cm^-1

Question 64

For analogous complexes of d-block metals from the same group with the same ion charge (2+, 3+), Δ_O increases by \_\_\_\_\_ with the increase in \_\_\_\_\_ of the metallic element.

Answer 64

30-50% period ## Footnote e.g. Δ_O increases by 30-50% when Co(III) is replaced by Rh(III) (3d atom replaced by 4d atom) and again by 30-50% when Rh(III) is replaced by Ir(III).

Question 65

For analogous complexes (same M and L, same oxidation state on M), Δ will \_\_\_\_ by \_\_\_\_% when complex geometry changes from octahedral to tetrahedral.

Answer 65

decrease 40-50% ## Footnote Δ_T will be 50%-60% of Δ_O in analogous complex.

Question 66

## Footnote **Electronic transitions between states with different spin multiplicities.**

Answer 66

**Spin F****orbidden**

Question 67

## Footnote **In O_h and D_4h , all d orbitals are gerade and so too are the states arising from their d configurations. Thus, their electronic transitions between them are\_\_\_\_\_\_\_\_.**

Answer 67

**Laporte Forbidden​**

Question 68

## Footnote **If a system is centrosymmetric, electronic transitions between states with the same inversion symmetry (g --\> g, u --\> u) are forbidden, but transitions between states of different inversion symmetry** **(g --\> u, u --\>g) are allowed.**

Answer 68

**Laporte's Rule​**

Question 69

Intensity (ϵ) for spin-allowed and Laporte allowed transitions?

Answer 69

10⁴ < ϵ < 10⁵

Question 70

Answer 70

Question 71

Answer 71

Question 72

Answer 72

Question 73

Answer 73

Question 74

Answer 74

Question 75

Answer 75

Question 76

Answer 76

Question 77

Answer 77

Question 78

Answer 78

Question 79

Answer 79

Question 80

Intensity (ϵ) for spin-forbidden and Laporte forbidden transitions?

Answer 80

10^-3 < ϵ < 1

Question 81

The color corresponding to the wavelength absorbed by an object is the \_\_\_\_\_\_ color to the color of the object.

Answer 81

complementary

Question 82

Definition for T (transmittance) of light through substance?

Answer 82

T=I_t/I₀ ## Footnote I_t - Intensity of transmitted light I₀ - Intensity of absorbed light

Question 83

The 3 factors which affect transmittance of light (T) through a medium material are?

Answer 83

1. Length of path travelled by light through the medium. 2. Density of matter in medium (or concentration of liquid solution). 3. Molar absorption coefficient (ϵ) - depends on type of material which makes up the medium and wavelength.

Question 84

What is the meaning of Absorption (A)?

Answer 84

A is the probability of a photon being absorbed by a colliding molecule.

Question 85

Relation between absorbance (A) and transmittance (T)?

Answer 85

A=-log(T)

Question 86

What is the Beer-lambert law for absorbance?

Answer 86

A=ϵcl ## Footnote ϵ - molar absorption coefficient c - concentration of solution l - length of optical path through medium

Question 87

Conditions for Beer-lambert law?

Answer 87

Light is passed through dilute, transluscent solutions.

Question 88

To determine solution concentration using spectroscopic methods, one must first create a \_\_\_\_\_\_\_\_ at the wavelength of \_\_\_\_\_\_\_\_ for this specific solution.

Answer 88

calibration curve maximum absorption

Question 89

# Method of measuring multiple wavelengths using a UV-Vis spectrometer: Light is first passed through \_\_\_\_\_\_\_\_ and then through an \_\_\_\_\_\_\_\_ to the \_\_\_\_\_\_\_\_ and then to the sensor.

Answer 89

the sample entrance slit dispersion device

Question 90

# Method of measuring a single wavelength using a UV-Vis spectrometer: Light is first passed through an \_\_\_\_\_\_\_\_ to the \_\_\_\_\_\_\_\_ and then through an \_\_\_\_\_\_\_\_ to the \_\_\_\_\_\_\_\_ and then to the detector.

Answer 90

entrance slit dispersion device exit slit sample

Question 91

Absorption in the vis spectrum is measured using \_\_\_\_\_\_\_\_ or \_\_\_\_\_\_\_\_ cuvettes, while absorption in the UV spectrum is measured using \_\_\_\_\_\_\_\_ cuvettes.

Answer 91

plastic or glass quartz

Question 92

Before conducting any other measurements using a UV-Vis spectrometer, one must first measure the absorption of a \_\_\_\_\_\_\_\_ solution.

Answer 92

blank

Question 93

What is a blank solution?

Answer 93

A solution containing only the matrix, without the compounds we wish to measure.

Question 94

Much like alkali metals, Cu valence electrons have a ns¹ configuration. However, its first ionization energy is higher, while its second and third energies are lower than that of alkali metals. Explain why?

Answer 94

The electron configuration of Cu is [Ar]3d¹⁰4s¹. The electron configuration for the alkali metal K is [Ar]4s¹. A full 3d shell is not equivalent to the noble gas configuration obtained when alkali metals loose an electron.

Question 95

The oxidation states of Cu in common compounds are?

Answer 95

Cu⁺, Cu²⁺, Cu³⁺

Question 96

Coordination compounds of Cu⁺ are usually colorless and \_\_\_\_\_\_\_\_ while coordination compounds of Cu²⁺ are usually \_\_\_\_\_\_\_\_. | Paramagnetic\Diamagnetic

Answer 96

Diamagnetic (full 3d shell) Paramagnetic (1 electron missing from 3d shell) ## Footnote The electron configuration of Cu is [Ar]3d¹⁰4s¹

Question 97

Cu²⁺ compounds with amine ligands usually have a \_\_\_\_\_\_\_\_ color.

Answer 97

blue

Question 98

Answer 98

## Footnote Note: Jahn-Teller effect can also occur, albeit to a **lesser degree**, because of non-uniform electron configurations in degenerated nonbonding orbitals (e.g a high-spin d⁷ configuration in an octahedral field).

Question 99

Explain the Jahn-Teller Effect.

Answer 99

If the ground electronic configuration of a nonlinear complex (T_d or O_h) is orbitally degenerate, and asymmetrically filled, then the complex distorts so as to remove the degeneracy and achieve a lower energy.

Question 100

Manifestation of Jahn-Teller effect in Octahedral complexes?

Answer 100

In an O_h complex, this effect manifests as a tetragonal distortion (elongation\compression along mutually perpendicular axes).

Question 101

compared to \_\_\_\_\_\_\_\_, \_\_\_\_\_\_\_\_ is a more common form of tetragonal distortion since \_\_\_\_ instead of \_\_\_\_ bonds are weakened.

Answer 101

Equatorial Elongation Axial Elongation 2 4

Question 102

Cu²⁺ spectrae are characterized by a single \_\_\_\_\_\_\_\_-shaped absorption band. The reason for this is \_\_\_\_\_\_\_\_.

Answer 102

assymetrically the Jahn-Teller effect ## Footnote When orbital degeneracies are removed as a result of the JT effect, additional t_2g->e_g transitions become available. These correspond to absorption frequencies which are close enough to form a single, assymetrical absorption band.

Question 103

Most Cu²⁺ salts dissolve easily in \_\_\_\_\_\_\_\_, creating \_\_\_\_\_\_\_\_ compounds.

Answer 103

Water, Hydrated ([Cu(OH₂)]²⁺)

Question 104

The number of H2O ligands in a hydrated compound which are substituted by other ligands depends on \_\_\_\_\_\_\_\_ of the other ligands in the solutions.

Answer 104

the amount

Question 105

[Cu(NH₃ )₅ (H₂O)]²⁺ compounds can be formed in an aqueous solution, but [Cu(NH₃ )₆ ]²⁺ can only be formed in liquid ammonia. Why?

Answer 105

[Cu(NH₃ )₅ (H₂O)]²⁺ is geometrically assymetrical and therefore has less energetic degeneracy in its split d-orbitals than the perfectly symmetrical [Cu(NH₃ )₆ ]²⁺. The removal of energetic degeneracy is preferred since it allows additional stabillization (as in the JT effect). ## Footnote Same goes for a substitution reaction of a hydrated Cu(II) atom with (en) ligands.

Question 106

Separation process of Cu(II) compounds from aqueous solutions?

Answer 106

Add ligands which create neutral coordination entities with a low to negligent solubility in H2O. Extract sediment from aqueous solution using an organic solvent.