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In the title compound, (NH(4))(2)[Fe(C(10)H(12)N(2)O(8))(H(2)O)]·3H(2)O, the Fe(II) center is in a distorted penta-gonal-bipyramidal geometry. Two carboxyl-ate O and two N atoms from the ethyl-enediaminetetra-acetate (EDTA) ion and one O atom from coordinated water comprise the equatorial plane. Two other carboxyl-ate O atoms from the EDTA ion occupy the apical sites. Both ammonium cations and all water mol-ecules function as hydrogen-bond donors, and ten N-H⋯O and nine O-H⋯O hydrogen bonds form a three-dimensional network between the complex anions, cations and the water mol-ecules.

We study the forward-dominant output of second-harmonic generation (SHG) in single-defect and dual-localized photonic crystals within the saturation limit. We propose that an asymmetric structure can be used to improve the performance of the enhanced SHG. We get two empirical expressions for the total saturation SHG efficiency and the forward factor and provide a reasonable explanation. The theoretical results predict a nearly 100% conversion efficiency and a nearly 100% forward output. Our work is very valuable for designing nonlinear photonic devices. As a test, a practical asymmetrical structure is presented.