Tetra(4-methoxyphenyl)phosphonium iodide: A twinned crystal built up with three-dimensional octupolar nonlinear optical chromophores

The tetra(4-methoxyphenyl)phosphonium iodide C28H28O4PI (MOPPI) is a crysta l built up with quasi octupolar tetrahedral chromophores having quadratic n onlinear optical (NLO) properties. The calculated values of the highest ten sor component beta(xyz) for the hyperpolarizable chromophore, in its most s table S-4 geometry, vary from 4.23 to 9.23 x 10(-30) esu, depending on the methods of calculation. Given the linear absorption maximum at 255 nm, this reveals a good hyperpolarizability-transparency tradeoff, The crystal is t winned by merohedry. The crystal structure was solved until a reliability f actor R = 0.048 using 2189 untwinned reflections. The material crystallizes in the noncentrosymmetric orthorhombic space group P2(1)2(1)2(1) With Z = 4 and the unit cell parameters a = b = 10.131(3) Angstrom, c = 25.682(6) An gstrom. The cation-anion arrangement corresponds to a NaCl-type model weakl y distorted. Signal of second harmonic of a crystalline powder at 1.06 mu m is nearly equivalent to that of urea.