New pyridinium–metal iodide complexes toward nonlinear optical materials

Abstract

New pyridinium–metal iodide complexes were synthesized. The 4-substituted pyridinium iodides X–C 5H 4N +–CH 3I −, where X=methyl, amino, cyano, methoxycarbonyl, carbamoyl, or dimethylamino group, were found to form 2:1 crystalline complexes with ZnI 2, except for the carbamoyl derivative, and 1:1 complexes with PbI 2. Three SHG active complexes were found from the lead complexes. Among the complexes prepared, the crystal structures of bis(4-cyano-1-methylpyridinium) tetraiodozincate (CNP/ZnI 4), bis(4-dimethylamino-1-methylpyridinium) tetraiodozincate (DAP/ZnI 4), and 1-methyl-4-carbamoylpyridinium triiodoplumbate (CP/PbI 3) were investigated. It was found that DAP/ZnI 4 and CNP/ZnI 4 crystallized in centrosymmetric monoclinic C2/c space group, while the structure of CP/PbI 3 was refined in noncentrosymmetric orthorhombic P2 12 12 1 space group. It was also established that the inorganic parts of both DAP/ZnI 4 and CNP/ZnI 4 crystals were composed of [ZnI 4] 2− anions with tetrahedral structure, and the inorganic moieties of CP/PbI 3 consisted of one-dimensional face-sharing lead iodide octahedra. CP/PbI 3 was assessed to have approximately one-fourth of the nonlinear optical coefficient ( d) of 3-methyl-4-nitropyridine-1-oxide (POM).