MORPHOLOGY AND GROWTH OF THE NMDA IN THE DIFFERENT SOLVENTS. Li Wang, Chaoguo Wang, Beijing Institute of Technology, Beijing, 100081, China

In actual practice a crystal growth method can not give suitable for different organic crystals. Crystal growth methods are according to the crystal chemistry and properties of the particular compound. Several examples from our recent research work serve to illustrate this point.

The n,n'-bis(4-nitrophenyl)methanediamines (NMDA) crystal is monoclinic system, space group C2, with a=1.6795 b=0.5233, c=0.9802(nm), and [[beta]] =120.6deg.. In this crystal, a type molecules stack along one direction, which means all the molecular dipoles align along the crystal axis[1]. In this structure show the line structure and strongly bond in the line axis. It has stronger SHG effect. One of the most challenging crystal growth problems we have encountered this crystal. The DSC study show it is with many phase transformations, with different SHG effect. Solutions offer the most suitable means to crystal production. Habits of crystallization are growing along needle-like crystals. We have been using more than thirty organic solvents to growing this monocrystal. The influence of crystal growth are assumed to be different morphologies in the dipole moments between the crystallizing component and the solvent. At a solvent providing poor solubility needle crystals can be expected to growing in the solution. For three month period at a small difference in dipole moments from crystallizing substances and solvent is we were able to grow planer and prismatic, which can performed phase matched in perpendicular to the plane or prismatic.

The organic NLO materials have usually hyperpolar molecule, but most typical organic solvents are a dipole moment less than about 3 Debye. The nonpolar solvents tend to form lowly dimensional crystal, and a polar solvents favors formation of bulk crystals.

1 Yamamoto Hironoba, et al., Nippon Kagaku Katshi 1990,(1) 789-96.