SSI - isomerism

Question 1

what types of elements can form coordination complexes?

Answer 1

metals, mostly d-block

Question 2

do d-block metals form cations or anions?

Answer 2

at metals, they readily lose d-block electrons to become cations

Question 3

what does the cationic charge of a d-block metal also represent?

Answer 3

the oxidation state - expressed by roman numerals
many d-block metals can form ions in a range of oxidation states

Question 4

do d-block metals follow the octet rule?

Answer 4

no

Question 5

coordination complex definition

Answer 5

molecules in which a metal atom/ion is bound to ligands via coordinate bonds

Question 6

ligands definition

Answer 6

molecules/atoms/ions that bind to a central metal ion via coordinate bonds, involving the donation of a lone pair

Question 7

describe a ligand in terms of lewis basicity/acidity

Answer 7

ligands are lewis basic - lone pair donators

Question 8

describe a central metal ion in terms of lewis basicity/acidity

Answer 8

metal ions are lewis acids - lone pair acceptors

Question 9

what property is necessary for a molecule to act as a ligand?

Answer 9

a lone pair

Question 10

coordination number definition

Answer 10

the total number of ligand donor atoms coordinated to the central metal atom/ion

Question 11

coordination geometry definition

Answer 11

the molecular shape formed when considering only the metal atom/ion and its ligand donor atoms (aka the coordination sphere)

Question 12

what are the 3 most common coordination geometries?

Answer 12

octahedral, tetrahedral, square planar

Question 13

homoleptic complex definition

Answer 13

a complex where all the ligands are identical

Question 14

why are charged ligands usually negatively charged, rather than positively?

Answer 14

ligands must have a lone pair, most cations have no lone pairs

Question 15

how do cations interact with metal complex ions?

Answer 15

usually as charge balancing cations outside of the coordination sphere [-]

Question 16

can homoleptic complexes have isomers?

Answer 16

no, only heteroleptic complexes

Question 17

heteroleptic definition

Answer 17

complexes with at least 2 different ligands

Question 18

what isomers does an octahedral complex with a 5:1 A:B ligand ratio form?

Answer 18

no isomers, at all positions of B the complex is identical

Question 19

what isomers does an octahedral complex with a 4:2 A:B ligand ratio form?

Answer 19

a cis isomer - B ligands on one axial and one equatorial position, angle between them = 90 (can be drawn in 2 ways)
a trans isomer - both B ligands in axial positions, angle between them = 180

Question 20

what isomers does an octahedral complex with a 3:3 A:B ligand ratio form?

Answer 20

a fac isomer - B ligands all next to each other on adjacent positions or alternating
a mer isomer - 2 B ligands adjacent and 1 opposite

Question 21

fac definition

Answer 21

stands for face - means positions of ligands complete a face on an octahedron

Question 22

mer definition

Answer 22

stands for meridian - means positions of ligands complete a meridian on an octahedron (from one end to the other)

Question 23

what isomers does a square planar complex with a 3:1 A:B ligand ratio form?

Answer 23

no isomers - all positions of ligand B are identical

Question 24

what isomers does a square planar complex with a 2:2 A:B ligand ratio form?

Answer 24

a cis isomer - like ligands are adjacent, angle between them = 90 (2 ways to draw)
a trans isomer - like ligands are opposite, angle between them = 180

Question 25

what isomers does a tetrahedral complex with a 3:1 A:B ligand ratio form?

Answer 25

no isomers - all positions of ligand B are identical

Question 26

what isomers does a tetrahedral complex with a 2:2 A:B ligand ratio form?

Answer 26

no isomers - all positions of ligands are identical

Question 27

why is isomerism important?

Answer 27

isomerism can affect chemical properties - seen very often in drugs

Question 28

denticity definition

Answer 28

number of donor atoms that a ligand coordinates to the metal with

Question 29

monodentate definition

Answer 29

a ligand with 1 donor atoms (so denticity = 1)

Question 30

what do you call a ligand with 2 donor atoms (so denticity = 2)?

Answer 30

bidentate ligand

Question 31

what do you call a ligand with 3 donor atoms (so denticity = 3)?

Answer 31

tridentate

Question 32

what do you call a ligand with 4 donor atoms (so denticity = 4)?

Answer 32

tetradentate

Question 33

what isomers does an octahedral complex with a 1:4 bi : mono ligand ratio form?

Answer 33

no isomers - all positions of ligands are equal

Question 34

what isomers does an octahedral complex with a 2:2 bi : mono ligand ratio form?

Answer 34

a trans isomer - both ligands in opposite positions to each other 2 cis isomers - both ligands are adjacent to each other, and an optical isomer/enantiomer of this (so would be called Λ/Δ-cis-isomers)

Question 35

what are the 2 types of enantiomers?

Answer 35

lambda Λ and delta Δ

Question 36

what is a lambda Λ isomer?

Answer 36

when tracing the path from the front to back of each bidentate ligand, the path goes anticlockwise/left

Question 37

what is a delta Δ isomer?

Answer 37

when tracing the path from the front to back of each bidentate ligand, the path goes clockwise/right

Question 38

what isomers does an octahedral complex with a 3:0 bi : mono ligand ratio form?

Answer 38

a lambda Λ isomer and a delta Δ isomer

Question 39

what isomers does a square planar complex with a 1:2 bi : mono ligand ratio form?

Answer 39

only the cis conformation is possible (trans is possible too but only with very specific ligands)

Question 40

what isomers does a square planar complex with a 2:0 bi : mono ligand ratio form?

Answer 40

no isomers

Question 41

what isomers does a tetrahedral complex with a 1:2 bi : mono ligand ratio form?

Answer 41

no isomers - all positions of ligands are identical

Question 42

what isomers does a tetrahedral complex with a 2:0 bi : mono ligand ratio form?

Answer 42

no isomers - all positions of ligands are identical

Question 43

chelating ligands definition

Answer 43

all polydentate ligands are chelating ligands because they form chelate rings with metal when coordinated

Question 44

chelate definition

Answer 44

any complex with a chelating ligand

Question 45

what is the chelate effect?

Answer 45

the phenomenon that complexes containing chelating ligands are much more stable than those with purely monodentate ligands

Question 46

how is complex stability quantified?

Answer 46

by formation constant kf - higher kf = more stable complex

Question 47

how can kf be calculated?

Answer 47

through studying ligand exchange reactions on [M(H2O)6] complexes kf = [products]/[reactants]

Question 48

what does it mean if kf > 1?

Answer 48

means numerator is bigger than denominator so equilibrium dominated by products so products are more stable

Question 49

what does it mean if kf < 1?

Answer 49

means denominator is bigger than numerator so equilibrium is dominated by reactants so reactants are more stable

Question 50

what affects the stability of chelate rings?

Answer 50

number of members e.g. 4-membered ring, 5-membered ring, etc

Question 51

which chelate rings are most stable and why?

Answer 51

5-membered chelate rings are most stable below 5 the bond angles within the ring are unfavorably small/tight above 5 the distance between 2 donor atoms is too large so probability of formation decreases