Workshop on Dispersion Interactions and DFT

August 1-3, 2012

Dr. James ParkerProgram Manager, Molecular Structure and DynamicsChemical Sciences DivisionU.S. Army Research OfficeResearch Triangle Park, North Carolina

Workshop Goal

To identify new, innovative methods to include quantitative dispersion interactions (predictive)in DFT calculations without compromising cost or accuracy

Molecular Co-Crystal Design

Physical and Chemical Properties of Molecular Crystals are Governed by Structure: Polymorphism

white, red, and black phosphorus

Form white red black

Symmetry bcc amorphousortho-rhombic

Reactivitypyro-phoric

stable; used in matches

low

Density 1.828 2.34 2.69

Bandgap 2.1 0.34

Ref. Index 1.8244 2.4

Properties of Phosphorus

Recrystallization (homomeric) or co-crystallization (heteromeric)

Recrystallization vs. Co-crystallization

Molecular Co-Crystal Design

Molecular Co-Crystal Design

Molecular Co-Crystals

Offers potential to design molecular solid state structures with desired physical and chemical properties

Relies on understanding of molecular interactions in the context of crystal packing

Research Barriers

Synthesis: lack of quantitative predictive ability for developing reliable, effective, and versatile synthetic methods (synthons) for the directed assembly of heteromeric co-crystals

Theory: historically, cannot predict accurate crystal structures from a molecular structure.

Prismatic habits of TNT:CL-20 co-crystal. Scale bar is 500 μm.

Scientific Opportunity: TNT:CL-20 co-crystals are formed in the laboratory

(Matzger) Angew. Chem. 2011, 123, 9122-5.

New energetic co-crystal with 81% energydensity of CL-20 with only 66% Cl-20 by mass

Density of co-crystal is 1.91; compare to TNTdensity of 1.70 and CL-20 density of 2.08

Impact sensitivity of the co-crystal is a factorof 2 less than CL-20 (drop test method)

combines stability of TNT with density and power of CL-20 in one homogeneous material

Molecular Co-Crystal Design

TNT CL-20

Interactions between TNT and CL-20 in the co-crystal.

Scientific Opportunity: New efficient computational chemistry method, SAPT(DFT), can quantitatively predict molecular crystal structures

(Szalewicz) Phys. Chem. Chem. Phys. 2011, 13, 16629-36.

The predicted FOX-7 unit cell configuration superimposed onto the experimental structure

Molecular Co-Crystal Design

a

b

c

Comparison of experimental and predictedcrystallographic parameters

Differences are less than 1 percent!

Scientific Opportunities

Co-crystal formation of TNT:CL-20 has been directed in the laboratory. Predictive computational tools are available for molecular crystal design.

Impact Areas

molecular crystal properties novel energetic materials supramolecular chemistry crystal engineering materials science

Molecular Co-Crystal Design

Intermolecular interactions within the TNT:CL-20 co-crystal