Week 12 (Intro to Coordination Chem)

Question 1

Coordination Complex (Complex Ion)

Answer 1

-central metal ion surrounded by a certain number of ligands
-the product of a Lewis acid-base reaction in which neutral molecules or anions (called ligands) bond to a central metal atom (or ion) by coordinate covalent bond
-a central metal ion has empty orbitals that can accept electron pairs
-a ligand contains at least one atom capable of donating a pair of electrons
-can be positive, negative, or neutral

Question 1

Coordinate covalent bond (Dative bond)

Answer 1

• a covalent bond (a shared pair of electrons) in which both electrons come from the same atom

Question 2

Ligand

Answer 2

-a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex
-The bonding with the metal generally involves formal donation of one or more of the ligand’s electron pairs, often through Lewis bases
-Lewis Base (electron pair donor)

Question 3

Complex compound

Answer 3

-a compound containing at least 1 complex ion
-example: complex cation + simple anion, simple cation + complex anion, complex cation + complex anion, complex neutral molecule
-when coordination compounds dissolve in water, the complex ions usually remain intact (ionic bonds are soluble in water, while covalent bonds are not soluble in water (complex ions are held together by covalent bonds))

Question 4

Coordination Number

Answer 4

-the number of ligand sites around the central atom
-the CN of a complex ion depends on the nature of both the central metal ion and the ligands (ex. CN of Fe³⁺ is always 6, CN of Co²⁺ can be 4 or 6)
-complexes of different CN can take different geometries

Question 5

Geometries of different complexes

Answer 5

-CN=2 : linear
-CN=4 : tetrahedral/square-planar
-CN=6: octahedral

Question 6

common monodentate ligands

Answer 6

-H₂O
-CN⁻
-CO
-NH₃
-Cl⁻
-O₂

Question 7

Monodentate

Answer 7

-ligands that occupy only one metal binding site (using one pair of lone electrons)

Question 8

Polydentate

Answer 8

-occupy multiple metal binding sites

Question 9

common polydentate ligands

Answer 9

-ethylendiamine (en) (bidentate)
-oxalate (C₂O₄²⁻) (bidentate)
-ethylendiaminetetraacetate (EDTA⁴⁻) (hexadentate)

Question 10

Chelating agent

Answer 10

-compound capable of binding metal ions to form complex ring-like structure “chelates”
-another name for polydentate ligand

Question 11

chelate

Answer 11

compound containing a ligand bonded to a central metal atom at 2 or more points

Question 12

d-orbitals and coordination complexes

Answer 12

-ligands interact with d-orbitals on central metal
-presence of ligands causes the d-orbitals to split in energy
-d-orbitals contain 5 orbitals that fill with electrons
-metals often have empty orbitals
-when surrounded by ligands, orbitals change in energy
-splitting of d-orbitals of central metal allows a complex to absorb the electro-magnetic wave within the visible spectrum (thus, many complexes have color)

Question 13

Colors and d-orbitals

Answer 13

-when d-orbitals split, difference between orbital’s energy levels correlates to color of complex
-energy change of octahedral complexes are greater than energy change of tetrahedral complexes

Question 14

Central metal

Answer 14

-Lewis acid (electron pair acceptor)

Question 15

Counter ion

Answer 15

-an ion with an opposite charge to another ion in a solution, and is present to maintain an ionic species’ electric neutrality
-ex. in [Co(NH3)6]Cl3, Cl3 is the counter ion, whereas Co(NH3)6 would have charge of +3

Question 16

Labile

Answer 16

undergoes ligand substitution rapidly

Question 17

Inert

Answer 17

undergoes ligand substitution slowly or not at all

Question 18

What does lability/inert depend on?

Answer 18

-ligands (some ligands detach from metal ions more easily than other ligands)
-central metal (some metal ions form labile complexes while some form inert (stable) complexes)

Question 19

Ligand substitution

Answer 19

-a chemical reaction that occurs when one ligand in a complex is replaced by another
-occurs in steps, can be stopped in the intermediate steps by controlling the concentration of incoming ligands/sped up by catalyst (determines primary product)

Question 20

Steps of Ligand Substitution

Answer 20

-ML₆ + Y = ML₅Y + L
-ML₅Y + Y = ML₄Y₂ + L
-ML₄Y₂ + Y = ML₃Y₃ + L
etc.

Question 21

catalyst

Answer 21

-a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change
-a molecule or ion that facilitates the exchange of one ligand for another on a central metal atom by lowering the activation energy of the reaction, essentially speeding up the process without being consumed itself

Question 22

Fe(III) complex

Answer 22

-6 C.N. (octahedral geometry)
-FeCl₄⁻ has tetrahedral geometry due to high Cl concentration
-in absence/low concentration of ligands, Fe(III) salts dissolve in water to form the complex ion Fe(H₂O)₆³⁺
-Fe(III) has great affinity for ligands that coordinate by oxygen (PO₄, C₂O₄, EDTA)
-Fe with SCN form red complex

Question 23

Fe(III) and Co(II) in presence of halide ions (Cl, F, Br)

Answer 23

-tetrahedral arrangement

Question 24

Cu(II) complex

Answer 24

-6 C.N. (octahedral geometry)
-CuCl₄⁻ has tetrahedral geometry due to high halide concentration
-in absence/low concentration of ligands, Cu(II) salts dissolve in water to form the complex ion Cu(H₂O)₆²⁺
-addition of other ligands to aqueous solution leads to successive displacement of 4 water ligands, as the fifth and sixth water ligands on elongated octahedral axis are not usually displaced unless there is a surplus of incoming ligands
-With NH₃, (Cu[(NH)₃]₄(H₂O)₂)²⁺ usually forms unless liquid ammonia is used

Question 25

Co(II) complex

Answer 25

-forms both C.N.=6 (octahedral) and C.N.=4 (tetrahedral) complexes
-octahedral forms with neutral complexes
-tetrahedral forms with monodentate negative ligands (Cl, Br, I, SCN, OH)
-octahedral=pink
-tetrahedral=blue
-very labile, undergo ligand substitution rapidly

Question 26

Co(III) complex

Answer 26

-very inert, do not undergo ligand substitution readily
-forms 6 C.N. complex

Question 27

Naming Coordination Compound

Answer 27

-name cation before anion
-name ligands first in alphabetical order, then name central metal
-anionic (negative) ligands end in “o”
-for neutral ligands, common name is used
-greek prefixes are used to designate number of each type of ligand in complex ion
-if ligand is polydentate, prefixes bis- and tris- are used
-if complex ion is cation, metal is named as element
-if complex ion is anion, metal ends with “-ate” (some latin names are used)
-oxidation state of metal is given in roman numerals after metal

Question 28

how splitting of d-orbital relates to wavelength

Answer 28

-distance between split d-orbitals= E
-E= hv or hc/wavelength
-larger distance=smaller wavelength

Question 29

latin names of metals in anionic complexes

Answer 29

-iron= ferrate
-copper= cuprate
-lead= plumbate
-silver= argentate
-gold= aurate
-tin= stannate

Question 30

Co(NH