NEW CRYSTAL FORM OF AN ORGANIC NONLINEAR-OPTICAL MATERIAL, -(4'-ACETYLPHENYL)-1,4-DIOXA-8-AZASPIRO[4.5]DECANE (APDA)

A new crystal form of an organic nonlinear optical material, -(4'-acet ylphenyl)-1,4-dioxa-8-azaspiro[4.5]decane (APDA) was found in the crys tal growth by plate sublimation. This new crystal structure belongs to the noncentrosymmetric class, orthorhombic P2(1)2(1)2(1), and the uni t-cell dimensions are a = 8.428 (8) Angstrom, b = 28.349 (3) Angstrom, c = 5.634 (2) Angstrom, V = 1346.0 (6) Angstrom(3), Z = 4, which are different from previously reported, orthorhombic Pna2(1). The molecule in the P2(1)2(1)2(1) crystal has less twisting and more bending in th e structure than in Pna2(1). The APDA molecules are coupled in an anti parallel system in the P2(1)2(1)2(1) crystal as if to compensate for t he repulsion arising from dipole-dipole interactions. This is in contr ast to the molecular alignment of the Pna2(1) crystal in which the mol ecules are arranged in the same direction. The molecular hyperpolariza bilities (beta) and a coefficients of the new crystal form were invest igated theoretically by semiempirical CNDO/S-CI.