CH510 - Structure of d-metal coordination entities

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

Identify the relationship between the two Cl^- ligands

Answer 2

Cis

Question 3

Identify the relationship between the two Cl^- ligands

Answer 3

Trans

Question 4

What is a ligand?

Answer 4

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 5

What is a coordinate compound?

Answer 5

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 6

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

Answer 6

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

Thus complex stability is also affected by HSAB theory.

Question 7

What is a donor atom in coordination entities?

Answer 7

The atom on ligands (lewis bases) which bonds to the central metal atoms.

e.g. N atom on NH₃

Question 8

What is an acceptor atom in coordination entities?

Answer 8

The central metal atom\ion which acts as a lewis acid.

Question 9

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

Answer 9

any one of the
d-block transition metals

Question 10

What is an inner sphere complex?

Answer 10

A coordination entity in which ligands are bonded directly to the central metal atom\ion.

e.g. [Mn(OH₂)₅SO₄]

Question 11

What is an outer sphere complex?

Answer 11

A compound formed by weak electrostatic interaction between a cataionic coordination entity and solvent molecules or anionic ligand molecules.

e.g. {[Mn(OH₂)₆]^{2+ (SO₄)2-}}

Question 12

What is the primary coordination sphere?

Answer 12

The “sphere” formed by inner-sphere ligands.

e.g. the octahedral structure around Mn^{2+ [Mn(OH₂)₆]2+}

Question 13

What is a coordination number?

Answer 13

The number of ligands which form the primary coordination sphere.

e.g. [Mn(OH₂)₆]^{2+ has C.N=6.}

Question 14

Define the term:

Monodentate ligands

Answer 14

Ligands which bond to a single site of attachment while donating one pair of electrons.

Question 15

Define the term:

Polydentate ligands

Answer 15

Ligands which bond to more than one site of attachment.

Bidentate, tridentate ligands are specific cases of polydentate ligands.

Question 16

Define the term:

Ambidentate ligands

Answer 16

Ligands with more than one different potential donor atom.

e.g. NO₂^-, NCS^-

Question 17

Define the term:

Chelate

Answer 17

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

Question 18

Chelates are formed by ________ ligands.

Answer 18

Polydentate

e.g. (en), (ox) ligands

Question 19

Normal chelating ligands will attach to the metal only at two ________ coordination sites, in a ________ fashion.

Answer 19

adjacent
cis

Question 20

A chelate formed from a chain of tetrahedral structures on an octahedral complex, creates a ________ membered ring since it preserves the ________ structure on the ligand and a ________ bite angle.

Td structures - as in a chain of methylene groups.

Answer 20

Five
Tetrahedral
90 degrees

Bite angle - the L-M-L angle

Question 21

Bonds within the coordination sphere are usually ________.

(more stable, less stable)

Answer 21

More stable

Question 22

Bonds within the coordination sphere usually require ________ heat or ________ time to break .

Answer 22

additional heat
additional time

They are stabler than outer-sphere bonds.

Question 23

Changes within the ________ sphere of a coordination entity can change the color of its solution.

As the color of an aqueous solution of a coordination entity.

Answer 23

inner

Question 24

Define the term:

Linkage Isomerism

Answer 24

Isomers formed when the same ligand links through
different atoms.

A complex with Nitrito-κO ligands vs a complex with Nitrito-κN ligands

Question 25

# Define the term: Ionization Isomers

Answer 25

Isomers formed when when a ligand and a counterion in one compound exchange places. e.g. [PtBr₂(NH₃)₄]Cl₂ vs [PtCl₂(NH₃)₄]Br₂

Question 26

# Define the term: Hydrate Isomers

Answer 26

Isomers formed when when water ligands within\without the coordination sphere switch places with other ligands without\within the coordination sphere. e.g. The same general formula CrCl₃(6H₂O) can form the hydrate isomers: [Cr(OH₂)₆]Cl₃, [CrCl(OH₂)₅]Cl₂⋅H₂O, [CrCl₂(OH₂)₄]Cl⋅2H₂O

Question 27

# Define the term: Coordination Isomers

Answer 27

Isomers formed when when several coordination entities can be created using the same general formula. e.g. [Co(NH₃)₆][Cr(CN)₆] and [Cr(NH₃)₆][Co(CN)₆] have the same general formula.

Question 28

# Define the term: Stereoisomerism

Answer 28

Form of isomerism in which molecules have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space ## Footnote Linkage, Ionization, Hydrate and Coordinate isomers are **structural** isomers.

Question 29

Two types of stereoisomers are \_\_\_\_\_\_\_\_ isomers and \_\_\_\_\_\_\_\_ isomers.

Answer 29

Optical Geometrical ## Footnote Geometrical Isomers - Diastereomers (cis\trans forms, non-enantiomer optical isomers etc.) Optical Isomers - Enantiomers

Question 30

# Define the term: Optical Isomers

Answer 30

Optical isomers are stereoisomers that are non-superimposable mirror images of each other (enantiomers).

Question 31

# Isomers formed by: [MA₂B₂] | Square planar complex

Answer 31

Cis and Trans only

Question 32

# Isomers formed by: [MA₂BC] | Square planar complex

Answer 32

Cis and Trans only | Determined by location of A atoms.

Question 33

# Isomers formed by: [MABCD] | Square planar complex

Answer 33

3 stereoisomers | 3 permutations of ABCD atoms around M

Question 34

# Isomers formed by: [M(AB)₂] | Square planar complex (AB) - bidentate ligands

Answer 34

Cis and Trans | Determined by location of A and B atoms.

Question 35

# Isomers formed by: [M(AB)₂] | **Tetrahedral** geometry (AB) - bidentate ligands

Answer 35

2 enentiomers | (optical isomers only)

Question 36

# Isomers formed by: [MABCD] | **Tetrahedral** geometry

Answer 36

2 enentiomers | (optical isomers only)

Question 37

The 2 spatial geometries of 5-coordinate coordination entities are:

Answer 37

Trigonal bipyramidal Hexagonal planar ## Footnote 5-coordinate complexes switch between the 2 spacial arrangements in a process called Berry Pseudorotation.

Question 38

# Isomers formed by: [MA₆] or [MA₅B] | **Octahedral** geometry

Answer 38

No isomers

Question 39

# Isomers formed by: [MA₄B₂] | **Octahedral** geometry

Answer 39

Cis or Trans | By location of B atoms.

Question 40

# Isomers formed by: [MA₃B₃] | **Octahedral** geometry

Answer 40

Fac or Mer | By location of either A or B

Question 41

# **Optical** isomer formed by: [MA₂B₂C₂] | **Octahedral** geometry

Answer 41

All-Cis form | A, B, C pairs in cis form

Question 42

# **Geometrical** isomers formed by: [MA₂B₂C₂] | **Octahedral** geometry

Answer 42

1. One pair in trans configuration, the rest in cis. 2. All pairs in trans configuration. | **4** different isomers

Question 43

# **Optical** isomers formed by: [MA₃B₂C] | **Octahedral** geometry

Answer 43

Fac isomer | By location of A ## Footnote It is optical, since it has no plane of reflection.

Question 44

# **Geometrical** isomers formed by: [MA₃B₂C] | **Octahedral** geometry

Answer 44

A - Mer, B-trans A - Mer, B-cis | 2 geometrical isomers

Question 45

# Isomers formed by: [ML₃] | **Octahedral** geometry

Answer 45

2 enantiomers | 2 optical isomers, no geometrical isomers. ## Footnote L - bidentate ligands with identical atoms at each end.

Question 46

# Optical isomers formed by: [ML₂A₂] | **Octahedral** geometry

Answer 46

All-cis form has 2 enantiomers | 2 optical isomers ## Footnote L - bidentate ligands with identical atoms at each end.

Question 47

# **Geometrical** isomers formed by: [ML₂A₂] | **Octahedral** geometry

Answer 47

Trans by A | 1 geometrical isomer ## Footnote L - bidentate ligands with identical atoms at each end.

Question 48

Number of stereoisomers formed by [MA₄L]? | **Octahedral** geometry

Answer 48

1 | No additional stereoisomers. ## Footnote L - bidentate ligands with identical atoms at each end.

Question 49

Number of optical isomers formed by [MA₃BL]? | **Octahedral** geometry

Answer 49

0 (This formula has no optical isomers since L creates reflection plane in both fac and mer forms.) ## Footnote L - bidentate ligands with identical atoms at each end.

Question 50

Geometrical isomers formed by [MA₃BL]? | **Octahedral** geometry

Answer 50

Fac isomer Mer isomer | Geometrical isomers by A ligands. ## Footnote L - bidentate ligands with identical atoms at each end.

Question 51

Geometrical isomers can only form in complexes with \_\_\_\_\_\_\_\_ or \_\_\_\_\_\_\_\_ geometries.

Answer 51

Square planar Octahedral ## Footnote cis\trans or fac\mer forms are not defined for tetrahedral complexes.