New crystal form of an organic nonlinear optical material, 8-(4'-acetylphenyl)-1,4-dioxa-8-azaspiro[4.5]decane (APDA)

A new crystal form of an organic nonlinear optical material, 8-(4‘-acetylphenyl)-1,4-dioxa-8-azaspiro[4.5]decane (APDA) was found in the crystal growth by plate sublimation. This new crystal structure belongs to the noncentrosymmetric class, orthorhombic P212121, and the unit-cell dimensions are a = 8.428 (8) A, b = 28.349 (3) A, c = 5.634 (2) A, V = 1346.0 (6) A3, Z = 4, which are different from previously reported, orthorhombic Pna21. The molecule in the P212121 crystal has less twisting and more bending in the structure than in Pna21. The APDA molecules are coupled in an antiparallel system in the P212121 crystal as if to compensate for the repulsion arising from dipole−dipole interactions. This is in contrast to the molecular alignment of the Pna21 crystal in which the molecules are arranged in the same direction. The molecular hyperpolarizabilities (β) and d coefficients of the new crystal form were investigated theoretically by semiempirical CNDO/S-CI.