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Rings and Cages by Dr. B.W. Tattershall

Rotatable Models of Molecules

Jmol models of some non-metal ring molecules, based on Crystallographic or Ab initio Studies

To view a model, click on the button in the right hand column of a table below

Mouse Control of Models

Left mouse drag rotate; Shift Left drag resize; Shift Right drag z-rotate;
Right click for menu

Scope

The course aimed to explore ideas of synthesis, structure, symmetry and chirality in non-metal ring and cage chemistry.  The molecules chosen for inclusion in this document are not a representative coverage of the course.  They are chosen because their structures were readily found in databases etc. and it was deemed that manipulating their 3D models would be instructive.  Thus, e.g., planar aromatic rings are not included at all, even though they formed an important part of the course. 

Only two of the molecules are of great commercial significance: most of the rest are of academic interest, though some have a long history of investigation.

Symmetry

Almost all of the molecules chosen have more than C1 symmetry in their free states, though, for some for which data have been taken from crystallographic studies, this symmetry is only approximated to.
You should rotate the models on the screen and identify all symmetry elements.  Try to name the point group, then look up the character table in a textbook, and see if you are right (i.e. if all of the symmetry elements are present in the molecule). 

Sulfur rings

 
S8 with VdW radii.  'Crooked Squares'  What kind of axis are you looking down?
   
S12 with VdW radii.  'Triangle on Top'  How many different bond angles?
   
Cp2TiS5  What is the symmetry of the ring?  Why does each Cp show only one proton NMR signal?
   
S7  'Dentist's Chair'  How many different bond lengths?
   

Saturated Cyclic Sulfur Imides

 
S7NH  Is the N planar?
   
1,3-S6(NH)2  Is it chiral?
   
1,4-S6(NH)2  What symmetry operation does it have?  Is it chiral?
   
1,4-S6(NH)2, two isomers in the unit cell  What symmetry operation interconverts these isomers?  What kind of isomers are they?
   

Unsaturated Sulfur Nitrides

 
S4N4  with covalent radii.  Is there a bond between the sulfur atoms?  Try Spacefill.
   
N3S3Cl3  Is the ring planar?  Why are chlorines syn-axial?  Orient the molecule so that you are looking down the ring axis, then Spacefill.
   

Phosphorus Sulfur Cages

 
P4S10  Try looking down a three-fold axis.
   
P4S3
   
β-P4S3I2    What symmetry operation does it have?  Is it chiral?
   
α-P4S3I2    What are related by a C2 axis?
   
α-P4S4
   
β-P4S4
   
α-P4S5
   
P4S7  What common molecule has the same symmetry as this one?  What is the point group symbol?
   
β-P4S5  A minor relative of P4S7 , why?
   

Phosphorus Selenium Cages

 
P3Se4I  Which phosphorus and sulfur containing molecules does this molecule resemble in structure?
   
P2Se5  The simplest binary phosphorus selenide. 
   

Phosphorus Silicon or Phosphorus Tin Molecules

 
P7(SiMe3)3  In the rotatable model, carbon is shown with its covalent radius, to give an idea of steric size of the SiMe3 groups, and the rest of the molecule as sticks, so that you can see into it.  Rotate the model so that you can see up from beneath.  What symmetry do you see?  How is this different from P7H3 ?  What will the other enantiomer of P7(SiMe3)3 look like?
   
spiro-(ButPPBut)2Si (more stable isomer)   with covalent radius for carbon in the rotatable model.  To find the closest approach of But groups between upper and lower rings, turn the model so that the top ring is shown fully open, then Spacefill. 
   
spiro-(ButPPBut)2Si (less stable isomer)  What symmetry elements can you find?  Look at the interaction between top and bottom But groups, as for the more stable isomer above.
   
dispiro-(ButPPBut)8Si2  with covalent radius for silicon in the rotatable model.  Rotate the model to convince yourself that all four phosphorus atoms in the five-membered ring are chemically non-equivalent to each other.  You may like to hide the Hydrogens.
   
ClSn(ButPPBut)3SnCl  with covalent radii for tin and chlorine in the rotatable model.  How many twofold axes does this molecule have?
   
ClSn(ButPPBut)3SnCl, two enantiomers in unit cell  Look down a C2 axis of each molecule to see the difference in chirality.