2.2,Expert Experimentalist Rating:,The Single-Crystal Shakedown”
Overview,
X-Ray diffraction is an important and powerful tool for determining the solid state
structure of compounds,Modern advances have made data collection and structure solution
almost routine for many small molecules,To use this technique,however,good quality
single crystals are still needed,In this exercise,you will experiment with the art of growing
single crystals,
Techniques Checklist,
Manipulation of milligram quantities of material ?
Syringe use ?
Crystallization techniques for growing good quality single crystals?
Pre-Lab Discussion,
Use of different recrystallization techniques,vapor diffusion,solvent layering,
temperature variation
Goal,
Synthesize Cr(acac)
3
,
2
then perform several slow recrystallizations to obtain a single
crystal of satisfactory quality,
Equipment,
Me
Magnetic stir plate
Heating mantle and Variac
Cr
O
O O
O
O
O
Me
Me
50-mL Round-bottomed flask
2-mL Glass syringe
Me
Condenser
Me
Stir bar
Me
Glass frit (D)
Chromium Acetylacetonate
Cr(acac)
3
250-mL Filter flask and rubber filter adaptor
3 Large vials (white cap)
4 Small vials (black cap)
2 Glass jars
2
Adapted from Szafran,Z.; Pike,R,M.; Sing,M,M,Microscale Inorganic Chemistry,A Comprehensive
Laboratory Experience; Wiley,New York,1991;,Synthesis of Metal Acetylacetonates” p,224-229,
21
WARNING NOTICE,The experiments described in these materials are potentially hazardous and require a high level
ofsafety training,special facilities and equipment,and supervision by appropriate individuals,You bear the sole
responsibility,liability,and risk for the implementation of such safety procedures and measures,MIT shall have no
responsibility,liability,or risk for the content or implementation of any of the material presented,Legal Notices
Experiment Outline,
Before coming to the lab,perform the necessary calculations to fill in the
following table,
O O O
Me Me H
2
N NH
2
2,4-Pentanedione Urea
Reagent Source F.W,Density Mass or
Volume
mmols Equiv
CrCl
3
·6H
2
O 1.00 mmol 1
Urea 17
2,4-Pentanedione 8
Cr(acac)
3
Product
Dissolve CrCl
3
·6H
2
O in 2 mL of distilled water in a
50-mL round-bottomed flask,equipped with a stir bar.
Add the urea in one portion to the flask,and stir until
completely dissolved.
Add the 2,4-pentanedione dropwise via syringe.
Attach the condenser to the flask,and heat the
mixture to vigorous reflux (this is important!),with
stirring,for about 1 hour.
Cool the reaction flask to room temperature,and
collect the product by vacuum filtration on a size D
glass frit funnel,washing the product with cold water.
H
2
H
2
Heat & Stir
O (in)
O (out)
Reaction Setup
Dry the product in your desiccator overnight,and
obtain a yield.
Set up multiple recrystallizations to grow X-ray qualitysingle crystals - see
Growing a Single Crystal Guide,
Note,
Urea slowly hydrolyzes under the reaction conditions,liberating ammonia (NH
3
),
which controls the pH of the reaction,As more NH
3
is generated,the solution becomes
more basic,making it easier to remove the proton from the acetylacetonate (acac),also
known as 2,4-pentanedione,It is the anion of the acetylacetonate that coordinates to the
22
metal to form the desired Cr(acac)
3
complex,What is the limiting reagent? Calculate your
percent yield,
H
2
N NH
2
O
H
2
N OH
O
H
2
O
NH
3
(hydrolysis)
O O O O
NH
3
NH
4
(deprotonation)
Me Me Me Me
Helpful Hints,
When using a saturated solution to grow crystals,it is important that you filter the
solution through a plug of glass wool in a pipet before setting up the crystallization,
Results,
To obtain your "EE Rating," you must obtain ≥ 50% yield of Cr(acac)
3,
and you
must produce at least one single crystal that is suitable for X-ray analysis,
23
Overview,
X-Ray diffraction is an important and powerful tool for determining the solid state
structure of compounds,Modern advances have made data collection and structure solution
almost routine for many small molecules,To use this technique,however,good quality
single crystals are still needed,In this exercise,you will experiment with the art of growing
single crystals,
Techniques Checklist,
Manipulation of milligram quantities of material ?
Syringe use ?
Crystallization techniques for growing good quality single crystals?
Pre-Lab Discussion,
Use of different recrystallization techniques,vapor diffusion,solvent layering,
temperature variation
Goal,
Synthesize Cr(acac)
3
,
2
then perform several slow recrystallizations to obtain a single
crystal of satisfactory quality,
Equipment,
Me
Magnetic stir plate
Heating mantle and Variac
Cr
O
O O
O
O
O
Me
Me
50-mL Round-bottomed flask
2-mL Glass syringe
Me
Condenser
Me
Stir bar
Me
Glass frit (D)
Chromium Acetylacetonate
Cr(acac)
3
250-mL Filter flask and rubber filter adaptor
3 Large vials (white cap)
4 Small vials (black cap)
2 Glass jars
2
Adapted from Szafran,Z.; Pike,R,M.; Sing,M,M,Microscale Inorganic Chemistry,A Comprehensive
Laboratory Experience; Wiley,New York,1991;,Synthesis of Metal Acetylacetonates” p,224-229,
21
WARNING NOTICE,The experiments described in these materials are potentially hazardous and require a high level
ofsafety training,special facilities and equipment,and supervision by appropriate individuals,You bear the sole
responsibility,liability,and risk for the implementation of such safety procedures and measures,MIT shall have no
responsibility,liability,or risk for the content or implementation of any of the material presented,Legal Notices
Experiment Outline,
Before coming to the lab,perform the necessary calculations to fill in the
following table,
O O O
Me Me H
2
N NH
2
2,4-Pentanedione Urea
Reagent Source F.W,Density Mass or
Volume
mmols Equiv
CrCl
3
·6H
2
O 1.00 mmol 1
Urea 17
2,4-Pentanedione 8
Cr(acac)
3
Product
Dissolve CrCl
3
·6H
2
O in 2 mL of distilled water in a
50-mL round-bottomed flask,equipped with a stir bar.
Add the urea in one portion to the flask,and stir until
completely dissolved.
Add the 2,4-pentanedione dropwise via syringe.
Attach the condenser to the flask,and heat the
mixture to vigorous reflux (this is important!),with
stirring,for about 1 hour.
Cool the reaction flask to room temperature,and
collect the product by vacuum filtration on a size D
glass frit funnel,washing the product with cold water.
H
2
H
2
Heat & Stir
O (in)
O (out)
Reaction Setup
Dry the product in your desiccator overnight,and
obtain a yield.
Set up multiple recrystallizations to grow X-ray qualitysingle crystals - see
Growing a Single Crystal Guide,
Note,
Urea slowly hydrolyzes under the reaction conditions,liberating ammonia (NH
3
),
which controls the pH of the reaction,As more NH
3
is generated,the solution becomes
more basic,making it easier to remove the proton from the acetylacetonate (acac),also
known as 2,4-pentanedione,It is the anion of the acetylacetonate that coordinates to the
22
metal to form the desired Cr(acac)
3
complex,What is the limiting reagent? Calculate your
percent yield,
H
2
N NH
2
O
H
2
N OH
O
H
2
O
NH
3
(hydrolysis)
O O O O
NH
3
NH
4
(deprotonation)
Me Me Me Me
Helpful Hints,
When using a saturated solution to grow crystals,it is important that you filter the
solution through a plug of glass wool in a pipet before setting up the crystallization,
Results,
To obtain your "EE Rating," you must obtain ≥ 50% yield of Cr(acac)
3,
and you
must produce at least one single crystal that is suitable for X-ray analysis,
23
