Prasanna04

Slide1: 

Use of Crystal Engineering Aspect for understanding TPP and its analogues: Amorphous Polymorphs (TPP:Triphenylphosphite)

Triphenyl Phosphite (TPP): A Candidate for Conformational Polyamorphism: 

Triphenyl Phosphite (TPP): A Candidate for Conformational Polyamorphism Ab initio calculations have shown that it can exists in at least 2 conformations Modeled Cs to C3v geometry transition to determine energy barriers for TPP and TTP Gausian98 program Hartree Fock Method Basis Set 6-31g (dashed line) 6-31g(d,p) (solid line) Liquid at RT Mp = 29C

Two Possible Conformational Conformer: 

Two Possible Conformational Conformer In case, of TPP, surprisingly Cs conformer is debated for the CH-O hydrogen bonding. Thus, theory predicts 2 conformers, what about Experiments?

Experimental Proof for the Behavior of TPP: DSC: 

Experimental Proof for the Behavior of TPP: DSC Sample isothermally held for: 120 min (a), 25 min (b) 10 min (c) glass transition two crystalization transition incomplete formation of glacial phase Sample scanned at different rates Scan a (heating at 10 K/min) three transitions glass, crystalization and melting DHcrys = DHfus Scan b (heating at 1 K/min) four transitions glass, 2 crystallizations and melting DHcrys(2peaks) = Dhfus This is an experimental proof for the presence of two possible amorphous conformations, which is in accordance with NMR, dielectric measurement, density, viscosity and Neutron data.

Problem!!: 

Problem!! Are the 2 peaks observed in DSC to do with Conformational changes, predicted by theory? Or is it something else is happening!!! If something else then what it is?…..

Two ways to study this problem: 

Two ways to study this problem Understand the behavior of the compound thoroughly, by using various techniques 2. Synthesize similar compounds to understand the underline principle…this might end up in NOVEL phenomenona We are taking 2nd route

Structure of TPP: Closer Look: 

Structure of TPP: Closer Look Single Molecule Nearest Neighbors Unit Cell

Experimental Aim: Designing from Understanding: 

Experimental Aim: Designing from Understanding It is evident from the experimental (X-ray, Neutron and DSC) and theoretical data, that TPP crystallizes/precipitate in Cs symmetry and possibly in C3 symmetry due to 1. Steric hindrance of 3 aryl groups around the phosphorous 2. Weak hydrogen bonding 3. Weak van der Waals interaction Thus, to understand the behavior of TPP, following experiments were investigated: Substitution of Sulphur and Selenium instead of Oxygen Introduction of –methyl groups to phenyl ring 3. Introduction of –methoxy group to phenyl ring

TPP Analogues: 

TPP Analogues Substituting Oxygen in TPP to Sulphur and Selenium, results in white colored crystalline compounds. These compounds crystallize in C3 symmetric structures and have melting points in the range from 340 - 370K. On the basis of DSC, both compound, didn’t show any structural change. There structures are analogues to tri(meta-methoxyphenyl) phosphite. By introduction of methyl groups, -ortho, -meta, and/or -para gave a colourless liquid. These compounds show increase in glass transition as compared to TPP, in the order of -meta, -para and -ortho methyl phenyl phosphites. But like TPP, these liquids didn’t show any obvious phase transition in calorimetric analysis.

Zusammen: Hydrogen and Steric Interactions: 

Zusammen: Hydrogen and Steric Interactions Tris(ortho-Methoxy phenyl) phosphite: White Solid Tris(meta-methoxy phenyl) phosphite: yellow sticky solid Tris(para-methoxy phenyl)phosphite: colourless sticky solid

Slide11: 

Synthesis Strategies General Method of synthesis of Phosphites/TPP PCl3 + 3 Phenol P(Phenol)3 + 3HCl New Method of Synthesis….. Methoxy-phenol OºC nBuLi PCl3 P(Ome-Phenol)3 High yield Less biproduct/clean synthesis Time

Crystal Structure of Phosphite:1: 

Crystal Structure of Phosphite:1 In this process we were the first to solve the Single crystal structure of simple aryl phosphites at Room Temperature. It is a rare example of a triaryl phosphite, which is solid at ambient temperature. Crystals suitable for X-ray crystallography were readily grown from toluene. The molecule has 3-fold rotational symmetry and crystallizes in the cubic, non-centro symmetric space group P213.

Crystal Structure of Phosphite:2: 

Crystal Structure of Phosphite:2 Single Molecule Nearest Neighbor Unit Cell

Characterization : NMR: 

Characterization : NMR All the aryl phosphites show a single peak in 31P NMR , around 120 ppm. NMR spectra shows all the possible peaks. Interestingly 13C NMR and 1H NMR shows metaH or meta-C in the ring is more deshielded than ortho and para

Fluorescent Molecular Glasses: 

Fluorescent Molecular Glasses

Chiral Molecular Glasses!: 

Chiral Molecular Glasses! The chirality of the compound was assigned on the basis of an  refinement The compound is of course a racemic mixture as prepared, the crystal studied contains a single enatiomeric conformer, of the form R, assigned because the methoxy groups are oriented in a clockwise fashion. Circular Dichroism experiments do not show any chirality.

onclusion: 

onclusion Theory predicts, TPP can possibly crystallize in at least two conformers, CS being the more stable one than C3 conformer. Steric factors in C3 conformation is ruled out, because its analogues, crystallize in C3 conformer only. This means in TPP hydrogen bonding might be a driving force for the stable CS conformer. More efforts are required to understand this phenomenon, in less anisotropic small molecules. We were the first solve the Crystal Structure of simple Aryl Phosphite, at Room Temperature Synthesis might help in developing NOVEL molecular glasses, like chiral, or luminescent.

Acknowledgement: 

Acknowledgement Prof. Jeff Yarger All Yarger group members for healthy interactions Prof. Anderson and his group for patience!! RAM RAM

Concept of Polyamorphism…by Physicists: 

Concept of Polyamorphism…by Physicists When Viscous liquids are supercooled, then sometimes transform into metastable phases that are different from the liquid, the glass and the normal crystal. These phases are “apparently amorphous” in the sense that their X-ray or Neutron scattering patterns do not show Bragg Peaks, and the phenomenon is often referred to as POLYAMORPHISM. Most of the examples of polyamorphism concern tetrahedrally bonded systems such as water, silica and the change is usually obtained by applying a high pressure.

Concept of Polyamorphism…by Chemists: 

Concept of Polyamorphism…by Chemists Similar to well known Polymorphism The phenomenon that a system can exists in at least two liquid or amorphous phases having the same chemical composition but distinct physical behavior like, density, structure has been coined POLYAMORPHISM. Commonly observed for molecules with LARGE ANISOTROPY like liquid crystals, biomolecules, or polymers. USE? It looks like TPP shows similar behavior!!!

NMR:HH: 

NMR:HH

NMR: 13C-1H: 

NMR: 13C-1H

Highlights of TPP Crystal Structure: Neutron and X-ray data: 

Highlights of TPP Crystal Structure: Neutron and X-ray data 1. Crystallizes with hexagonal symmetry, in the space group R3. The unit cell contains 18 molecules, with cell volume 7156 Å3. 2. Two phenyl rings of a TPP molecule point in upward direction towards the phosphorous atom, whereas the third phenyl ring is oriented in the opposite direction (Figure 1). The former phenyl rings are twisted by roughly 15 from the ecliptical position. 3. Neighboring molecules are arranged parallel towards each other forming one dimensional infinite rods, which are aligned parallel to the c-axis of the unit cell (Figure 2). The dipole moments of the molecules in one rod are aligned parallel. Thus, each rod has a net dipolar moment. In order to minimize the repulsive forces between neighboring rods in the hexagonal packing, the rods are aligned anti-parallel. Consequently, the 6-fold rotation axis present in the hexagonal rod packing is reduced to 3-fold rotoinversion symmetry. 4. Figure 3 shows part of such a rod containing two molecules. The shortest interatomic distances are in the range of 2.8 - 3.4 Å demonstrating that the dominating attractive interaction between TPP molecules is based on van der Waals forces.

Analogy of crystal structures:: 

Analogy of crystal structures: In contrast TPP, molecule by Neutron data, as well as Powder X-ray data, showed no symmetry. Two OPO angles are with 102.3˚, and 101.4 ˚, larger than 96.6 ˚ found in meta-methoxy phenyl phosphite, whereas the third OPO angle is smaller, 91.4 ˚. The benzyl rings are connected to O2 and O3 are twisted by roughly 15 ˚ against each other, while in case of 2 they are eclipsed.