Halogen Bonding: Fundamentals and Applications

On November 7th, 2014, I attended a seminar presented by Dr. Bill Pennington, a professor of inorganic chemistry at Clemson University, and a director of the Molecular Structure Center. He came to UNCG to discuss his research on halogen bonding.  Halogen bonding is a really old interacting process and was recognized as early as 1863, but it did not receive its actual name until the late 90s. Halogen bonding is any noncovalent interaction involving halogens as acceptors of electron density. Dr. Pennington discussed how halogen bonding has a general scheme, of D--X-Y. The "X" stands for the halogen, which is a lewis acid , XB -donor. The "D" stands for any electron donor, which is a Lewis base, XB - acceptor that interacts with a halogen bonded to something else, and it is also a halogen bonding acceptor. The "Y" represents a carbon, nitrogen, halogen, etc.

With my knowledge from general chemistry and some from organic chemistry about hydrogen bonding, I was able to understand some parts about halogen bonding from what Dr. Pennington was talking about. He mentioned that halogen bonding strength tends to decrease as you go up group 7A in the periodic table starting from iodine, to bromine, to chlorine, and all the way up to fluorine. Dr. Pennington outlined his seminar into several topics, which were halogen bonding, X-bonding periodic table, polyiodides and metapolyiodides, and applications. His main focus in his seminar was about the crystal chemistry of materials involving halogen bonding through Lewis acid - Lewis base interactions. He also discussed about how halogen bonding applies to living organisms, like humans. He said that if we did not have halogen bonding, we humans still might be here, but we will not have enough energy to move very fast. This fact really fascinated me, and it made me curious to know more about the process of halogen bonding as it relates to humans. Overall, this was a very interesting seminar, and even though I did not fully grasp the concept, it is something that I would like to do further research on.

Sources:

http://www.clemson.edu/ces/departments/chemistry/people/faculty/pennington.html

Pictures:

http://onlinelibrary.wiley.com/store/10.1002/ejoc.201201512/asset/image_m/mfig000.jpg?v=1&s=9e5f611c0c58c6a5c1e8c1cee19bc5de63e01e3b

http://www.halogenbonding.eu/img/fig1.jpg